title: Stereoselective interactions of warfarin enantiomers with the pregnane X nuclear receptor in gene regulation of major drug-metabolizing cytochrome P450 enzymes.
abstract: BACKGROUND
  Warfarin, an antagonist of vitamin K, is an oral coumarin anticoagulant widely used to control and prevent thromboembolic disorders. Warfarin is clinically available as a racemic mixture of R- and S-warfarin. The S-enantiomer has three to five times greater anticoagulation potency than its optical congener. Recently, vitamin K₂ function has been proposed via the pregnane X receptor (PXR) in osteocytes. PXR acts as a xenobiotic sensor that controls expression of many genes involved in drug/xenobiotic metabolic clearance.
  
  
  OBJECTIVE
  The aim was to examine whether enantiomers of warfarin stereoselectively interact with PXR to up-regulate main drug/xenobiotic-metabolizing enzymes of the cytochrome P450 superfamily.
  
  
  METHODS
  Interactions of warfarin enantiomers with PXR were tested by gene reporter assays and time-resolved fluorescence resonance energy transfer technology (TR-FRET) ligand binding assay. Up-regulation of PXR-target gene mRNAs by warfarin enantiomers was studied using semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) in primary human hepatocytes.
  
  
  RESULTS
  We found that R-warfarin interacts with the PXR nuclear receptor. Consistently, R-warfarin significantly induced CYP3A4 and CYP2C9 mRNAs in cultures of primary human hepatocytes or in LS174T intestinal cells. On the other hand, S-warfarin is a less potent inducer of PXR-target genes in human hepatocytes and activates PXR only at supraphysiological concentrations. In addition, we showed that racemic 10- and 4'-hydroxywarfarins are also highly potent PXR ligands and inducers of CYP3A4 and CYP2C9 mRNA in human hepatocytes.
  
  
  CONCLUSIONS
  We showed that R-warfarin can significantly up-regulate major drug-metabolizing enzymes CYP3A4 and CYP2C9 in the liver and thus may cause drug-drug interactions (DDI) with co-administered drugs. The results warrant reconsideration of racemic warfarin usage in clinics.
authors.affiliation: Department of Pharmacology and Toxicology, Faculty of Pharmacy in Hradec Kralove, Charles University in Prague, Heyrovskeho, Hradec Kralove, Czech Republic.
authors.forename: A
authors.initials: A
authors.lastname: Rulcova
authors.forename: I
authors.initials: I
authors.lastname: Prokopova
authors.forename: L
authors.initials: L
authors.lastname: Krausova
authors.forename: M
authors.initials: M
authors.lastname: Bitman
authors.forename: R
authors.initials: R
authors.lastname: Vrzal
authors.forename: Z
authors.initials: Z
authors.lastname: Dvorak
authors.forename: J
authors.initials: J
authors.lastname: Blahos
authors.forename: P
authors.initials: P
authors.lastname: Pavek
mesh_terms: D000925:Anticoagulants / Q000737:chemistry / Q000494:pharmacology*; D045744:Cell Line, Tumor; D003577:Cytochrome P-450 Enzyme System / Q000235:genetics*; D031541:Fluorescence Resonance Energy Transfer; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D017930:Genes, Reporter; D006801:Humans; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid / Q000187:drug effects*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013237:Stereoisomerism; D015533:Transcriptional Activation; D020798:Two-Hybrid System Techniques; D015854:Up-Regulation / Q000187:drug effects; D014859:Warfarin / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D000925:Anticoagulants; D000077297:Pregnane X Receptor; D011987:Receptors, Steroid; D014859:Warfarin; D003577:Cytochrome P-450 Enzyme System