title: Dose-dependent induction of cytochrome P450 (CYP) 3A4 and activation of pregnane X receptor by topiramate.
abstract: OBJECTIVE
  In clinical studies, topiramate (TPM) was shown to cause a dose-dependent increase in the clearance of ethinyl estradiol. We hypothesized that this interaction results from induction of hepatic cytochrome P450 (CYP) 3A4 by TPM. Accordingly, we investigated whether TPM induces CYP3A4 in primary human hepatocytes and activates the human pregnane X receptor (hPXR), a nuclear receptor that serves as a regulator of CYP3A4 transcription.
  
  
  METHODS
  Human hepatocytes were treated for 72 h with TPM (10, 25, 50, 100, 250, and 500 microM) and known inducers, phenobarbital (PB; 2 mM), and rifampicin (10 microM). The rate of testosterone 6beta-hydroxylation by hepatocytes served as a marker for CYP3A4 activity. The CYP3A4-specific protein and mRNA levels were determined by using Western and Northern blot analyses, respectively. The hPXR activation was assessed with cell-based reporter gene assay.
  
  
  RESULTS
  Compared with controls, TPM (50-500 microM)-treated hepatocytes exhibited a considerable increase in the CYP3A4 activity (1. 6- to 8.2-fold), protein levels (4.6- to 17.3-fold), and mRNA levels (1.9- to 13.3-fold). Comparatively, rifampicin (10 microM) effected 14.5-, 25.3-, and a 20.3-fold increase in CYP3A4 activity, immunoreactive protein levels, and mRNA levels, respectively. TPM (50-500 microM) caused 1.3- to 3-fold activation of the hPXR, whereas rifampicin (10 microM) caused a 6-fold activation.
  
  
  CONCLUSIONS
  The observed induction of CYP3A4 by TPM, especially at the higher concentrations, provides a potential mechanistic explanation of the reported increase in the ethinyl estradiol clearance by TPM. It also is suggestive of other potential interactions when high-dose TPM therapy is used.
authors.affiliation: College of Pharmacy, University of Cincinnati Medical Center, 3223 Eden Avenue, Cincinnati, OH 45267, U.S.A.
authors.forename: Srikanth C
authors.initials: SC
authors.lastname: Nallani
authors.forename: Tracy A
authors.initials: TA
authors.lastname: Glauser
authors.forename: Niresh
authors.initials: N
authors.lastname: Hariparsad
authors.forename: Kenneth
authors.initials: K
authors.lastname: Setchell
authors.forename: Donna J
authors.initials: DJ
authors.lastname: Buckley
authors.forename: Arthur R
authors.initials: AR
authors.lastname: Buckley
authors.forename: Pankaj B
authors.initials: PB
authors.lastname: Desai
mesh_terms: D000818:Animals; D000927:Anticonvulsants / Q000494:pharmacology*; D002460:Cell Line; D002478:Cells, Cultured; D051544:Cytochrome P-450 CYP3A; D003577:Cytochrome P-450 Enzyme System / Q000096:biosynthesis* / Q000235:genetics; D004305:Dose-Response Relationship, Drug; D005347:Fibroblasts / Q000187:drug effects; D005632:Fructose / Q000031:analogs & derivatives* / Q000494:pharmacology*; D022781:Hepatocytes / Q000187:drug effects; D006801:Humans; D010634:Phenobarbital / Q000494:pharmacology; D000077297:Pregnane X Receptor; D012333:RNA, Messenger / Q000235:genetics; D018160:Receptors, Cytoplasmic and Nuclear / Q000187:drug effects* / Q000502:physiology; D011987:Receptors, Steroid / Q000187:drug effects* / Q000502:physiology; D012293:Rifampin / Q000494:pharmacology; D013739:Testosterone / Q000378:metabolism; D000077236:Topiramate; D014158:Transcription, Genetic / Q000187:drug effects; D014162:Transfection
chemical_list: D000927:Anticonvulsants; D000077297:Pregnane X Receptor; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D011987:Receptors, Steroid; D000077236:Topiramate; D005632:Fructose; D013739:Testosterone; D003577:Cytochrome P-450 Enzyme System; C104464:CYP3A protein, human; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human; D012293:Rifampin; D010634:Phenobarbital