To cite this article: Rulcova A, Prokopova I, Krausova L, Bitman M, Vrzal R, Dvorak Z, Blahos J, Pavek P. Stereoselective interactions of warfarin enantiomers with pregnane X nuclear receptor in gene regulation of major drug-metabolizing cytochrome P450 enzymes. J Thromb Haemost 2010; 8: 2708-17.See also Miller GP. Warfarin therapy: how the less interesting half just got interesting. This issue, pp 2705-7.Summary. 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 Senantiomer has three to five times greater anticoagulation potency than its optical congener. Recently, vitamin K 2 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 upregulate 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. Conclusion: 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 coadministered drugs. The results warrant reconsideration of racemic warfarin usage in clinics.

We can conclude that GR-induced expression of HNF4α may contribute to indirect OCT1 gene up-regulation by dexamethasone in primary human hepatocytes, but not in hepatocyte-derived tumor cell lines.

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Antenatal glucocorticoid administration is used in cases of fetuses at risk to be born prematurely to enhancefetal pulmonary surfactant production and prevent infant respiratory distress syndrome. The CYP1A1 isthe most important xenobiotic-metabolizing cytochrome P450 enzyme in the human placenta. Importantly,CYP1A1 generates reactive species and its placental activity is elevated in smoking women. CYP1A1expression is mainly controlled by aryl hydrocarbon receptor (AHR) ligands. Glucocorticoid co-regulationof CYP1A1 has been described in various cell types but has not been systematically examined in the humanplacental trophoblast.We studied the effects of the glucocorticoids dexamethasone and betamethasone on inducibility ofCYP1A1 and other AHR target genes CYP1A2, CYP1B1, UGT1A1 (UDP-glucuronosyltransferase 1A1) andBCRP (Breast cancer resistance protein) by prototype AHR ligand 3-methylcholanthrene (3MC) in isolatedhuman placental trophoblast culture.We show that glucocorticoids alone had no effect on activity and protein/mRNA expression of CYP1A1and little effect on mRNA expression of other AHR target genes. However, glucocorticoids significantlystimulated CYP1A1 mRNA, but not CYP1A2, CYP1B1, UGT1A1 and BCRP mRNAs, induction mediatedby the AHR ligand. Consistently, glucocorticoids significantly augmented 7-ethoxyresorufin-O-deethylation(EROD) enzymatic activity in primary human placental trophoblast. Dexamethasone did not influence AHRand ARNT (Aryl hydrocarbon receptor nuclear translocator) mRNAs, suggesting that this phenomenon isnot due to AHR or ARNT up-regulation by glucocorticoids in human trophoblast.In conclusion, our data suggest that glucocorticoids have no effect on AHR target genes expression perse, but they may potentiate CYP1A1 induction in human term placental trophoblast