The pregnane X receptor (PXR) is a drug/xenobiotic-activated transcription factor of crucial importance for major cytochrome P450 xenobiotic-metabolizing enzymes (CYP) expression and regulation in the liver and the intestine. One of the major target genes regulated by PXR is the cytochrome P450 enzyme (CYP3A4), which is the most important human drug-metabolizing enzyme. In addition, PXR is supposed to be involved both in basal and/or inducible expression of many other CYPs, such as CYP2B6, CYP2C8, 2C9 and 2C19, CYP3A5, CYP3A7, and CYP2A6. Interestingly, the dynamics of PXR-mediated target genes regulation has not been systematically studied and we have only a few mechanistic mathematical and biologically based models describing gene expression dynamics after PXR activation in cellular models. Furthermore, few indirect mathematical PKPD models for prediction of CYP3A metabolic activity in vivo have been built based on compartmental models with respect to drug⁻drug interactions or hormonal crosstalk. Importantly, several negative feedback loops have been described in PXR regulation. Although current mathematical models propose these adaptive mechanisms, a comprehensive mathematical model based on sufficient experimental data is still missing. In the current review, we summarize and compare these models and address some issues that should be considered for the improvement of PXR-mediated gene regulation modelling as well as for our better understanding of the quantitative and spatial dynamics of CYPs expression.

• Keywords
• Pregnane X receptor, gene regulation, mathematical models, simulation,
• MeSH
• Gene Regulatory Networks * MeSH
• Humans MeSH
• Pregnane X Receptor MeSH
• Receptors, Steroid genetics   metabolism   MeSH
• Cytochrome P-450 Enzyme System genetics   metabolism   MeSH
• Models, Theoretical * MeSH
• Feedback, Physiological MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Review MeSH
• Names of Substances
• Pregnane X Receptor MeSH
• Receptors, Steroid MeSH
• Cytochrome P-450 Enzyme System MeSH

Pregnane X receptor is a ligand-activated nuclear receptor (NR) that mainly controls inducible expression of xenobiotics handling genes including biotransformation enzymes and drug transporters. Nowadays it is clear that PXR is also involved in regulation of intermediate metabolism through trans-activation and trans-repression of genes controlling glucose, lipid, cholesterol, bile acid, and bilirubin homeostasis. In these processes PXR cross-talks with other NRs. Accumulating evidence suggests that the cross-talk is often mediated by competing for common coactivators or by disruption of coactivation and activity of other transcription factors by the ligand-activated PXR. In this respect mainly PXR-CAR and PXR-HNF4α interference have been reported and several cytochrome P450 enzymes (such as CYP7A1 and CYP8B1), phase II enzymes (SULT1E1, Gsta2, Ugt1a1), drug and endobiotic transporters (OCT1, Mrp2, Mrp3, Oatp1a, and Oatp4) as well as intermediate metabolism enzymes (PEPCK1 and G6Pase) have been shown as down-regulated genes after PXR activation. In this review, I summarize our current knowledge of PXR-mediated repression and coactivation interference in PXR-controlled gene expression regulation.

• Keywords
• PXR, cross-talk, gene regulation, metabolism, nuclear receptor,
• Publication type
• Journal Article MeSH
• Review MeSH

Benzimidazole drugs lansoprazole and omeprazole are used for treatment of various gastrointestinal pathologies. Both compounds cause drug-drug interactions because they activate aryl hydrocarbon receptor and induce CYP1A genes. In the current paper, we examined the effects of lansoprazole and omeprazole enantiomers on the expression of key drug-metabolizing enzyme CYP3A4 in human hepatocytes and human cancer cell lines. Lansoprazole enantiomers, but not omeprazole, were equipotent inducers of CYP3A4 mRNA in HepG2 cells. All forms (S-, R-, rac-) of lansoprazole and omeprazole induced CYP3A4 mRNA and protein in human hepatocytes. The quantitative profiles of CYP3A4 induction by individual forms of lansoprazole and omeprazole exerted enantiospecific patterns. Lansoprazole dose-dependently activated pregnane X receptor PXR in gene reporter assays, and slightly modulated rifampicin-inducible PXR activity, with similar potency for each enantiomer. Omeprazole dose-dependently activated PXR and inhibited rifampicin-inducible PXR activity. The effects of S-omeprazole were much stronger as compared to those of R-omeprazole. All forms of lansoprazole, but not omeprazole, slightly activated glucocorticoid receptor and augmented dexamethasone-induced GR transcriptional activity. Omeprazole and lansoprazole influenced basal and ligand inducible expression of tyrosine aminotransferase, a GR-target gene, in HepG2 cells and human hepatocytes. Overall, we demonstrate here that omeprazole and lansoprazole enantiomers induce CYP3A4 in HepG2 cells and human hepatocytes. The induction comprises differential interactions of omeprazole and lansoprazole with transcriptional regulators PXR and GR, and some of the effects were enantiospecific. The data presented here might be of toxicological and clinical importance, since the effects occurred in therapeutically relevant concentrations.

• MeSH
• Hep G2 Cells MeSH
• Cytochrome P-450 CYP3A genetics   metabolism   MeSH
• Hepatocytes drug effects   metabolism   MeSH
• Cells, Cultured MeSH
• Lansoprazole adverse effects   pharmacology   MeSH
• Humans MeSH
• Omeprazole adverse effects   pharmacology   MeSH
• Pregnane X Receptor MeSH
• Anti-Ulcer Agents adverse effects   pharmacology   MeSH
• Receptors, Glucocorticoid metabolism   MeSH
• Receptors, Steroid metabolism   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• CYP3A4 protein, human MeSH Browser
• Cytochrome P-450 CYP3A MeSH
• Lansoprazole MeSH
• Omeprazole MeSH
• Pregnane X Receptor MeSH
• Anti-Ulcer Agents MeSH
• Receptors, Glucocorticoid MeSH
• Receptors, Steroid MeSH

Pregnane X receptor (PXR) is a member of the nuclear receptor (NR) superfamily of ligand-activated transcription factors and is activated by a huge variety of endobiotics and xenobiotics, including many clinical drugs. PXR plays key roles not only as a xenosensor in the regulation of both major phase I and II drug metabolism and transporters but also as a physiological sensor in the modulation of bile acid and cholesterol metabolism, glucose and lipid metabolism, and bone and endocrine homeostasis. Post-translational modifications such as phosphorylation have been shown to modulate the activity of many NRs, including PXR, and constitute an important mechanism for crosstalk between signaling pathways and regulation of genes involved in both xenobiotic and endobiotic metabolism. In addition, microRNAs have recently been shown to constitute another level of PXR activity regulation. The objective of this review is to comprehensively summarize current understanding of post-transcriptional and post-translational modifications of PXR in regulation of xenobiotic-metabolizing cytochrome P450 (CYP) genes, mainly in hepatic tissue. We also discuss the importance of PXR in crosstalk with cell signaling pathways, which at the level of transcription modify expression of genes associated with some physiological and pathological stages in the organs. Finally, we indicate that these PXR modifications may have important impacts on CYP-mediated biotransformation of some clinically used drugs.

• MeSH
• Biotransformation MeSH
• Enzyme Induction drug effects   MeSH
• Protein Interaction Domains and Motifs MeSH
• Liver drug effects   enzymology   metabolism   MeSH
• Humans MeSH
• RNA, Messenger metabolism   MeSH
• RNA Processing, Post-Transcriptional * drug effects   MeSH
• Protein Processing, Post-Translational * drug effects   MeSH
• Pregnane X Receptor MeSH
• Receptors, Steroid chemistry   genetics   metabolism   MeSH
• Cytochrome P-450 Enzyme System genetics   metabolism   MeSH
• Xenobiotics metabolism   pharmacokinetics   toxicity   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Review MeSH
• Names of Substances
• RNA, Messenger MeSH
• Pregnane X Receptor MeSH
• Receptors, Steroid MeSH
• Cytochrome P-450 Enzyme System MeSH
• Xenobiotics MeSH

Khellin and visnagin are two furanochromones that can be frequently found in ethnomedical formulations in Asia and the Middle East. Both compounds possess anti-inflammatory and analgesic properties, therefore modern medicine uses these compounds or structurally related derivatives for treatment of vitiligo, bronchial asthma and renal colics. Despite their frequent usage, the potential toxic properties of visnagin and khellin are not well characterized up-to-now. Many natural compounds modulate the expression and activity of cytochrome P450 1A1 (CYP1A1), which is well-known to bioactivate pro-carcinogens. The expression of this enzyme is controlled by the aryl hydrocarbon receptor (AHR), a ligand-activated transcription factor and regulator of drug metabolism. Here, we investigated the influence of both furanochromones on AHR signaling in human HepG2 hepatocarcinoma cells and primary human hepatocytes. Both compounds transactivated xenobiotic response element (XRE)-driven reporter gene activity in a dose-dependent manner and induced CYP1A1 transcription in HepG2 cells and primary hepatocytes. The latter was abolished in presence of a specific AHR antagonist. CYP1A enzyme activity assays done in HepG2 cells and primary hepatocytes revealed an inhibition of enzyme activity by both furanochromones, which may become relevant regarding the metabolism of xenobiotics and co-administered therapeutic drugs. The observed induction of several other members of the AHR gene battery, whose gene products are involved in regulation of cell growth, differentiation and migration, indicates that a further toxicological characterization of visnagin and khelllin is urgently required in order to minimize potential drug-drug interactions and other toxic side-effects that may occur during therapeutic usage of these furanochromones.

• MeSH
• Enzyme Activation drug effects   MeSH
• Aryl Hydrocarbon Hydroxylases metabolism   MeSH
• Cell Line MeSH
• Cytochrome P-450 CYP1A1 genetics   metabolism   MeSH
• Gene Expression MeSH
• Hepatocytes drug effects   metabolism   MeSH
• Khellin pharmacology   MeSH
• Humans MeSH
• Receptors, Aryl Hydrocarbon metabolism   MeSH
• Gene Expression Regulation drug effects   MeSH
• Genes, Reporter MeSH
• Signal Transduction drug effects   MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Names of Substances
• Aryl Hydrocarbon Hydroxylases MeSH
• Cytochrome P-450 CYP1A1 MeSH
• Khellin MeSH
• Receptors, Aryl Hydrocarbon MeSH
• visnagin MeSH Browser

We examined the effects of anthocyanidins (cyanidin, delphinidin, malvidin, peonidin, petunidin, pelargonidin) on the aryl hydrocarbon receptor (AhR)-CYP1A1 signaling pathway in human hepatocytes, hepatic HepG2 and intestinal LS174T cancer cells. AhR-dependent reporter gene expression in transfected HepG2 cells was increased by pelargonidin in a concentration-dependent manner at 24h. Similarly, pelargonidin induced the expression of CYP1A1 mRNA up to 5-fold in HepG2 and LS174T cells relative to the induction by 5 nM 2,3,7,8-tetrachlorodibenzodioxin (TCDD), the most potent activator of AhR. CYP1A1 and CYP1A2 mRNAs were also increased by pelargonidin in three primary human hepatocytes cultures (approximately 5% of TCDD potency) and the increase in CYP1A1 protein in HepG2 and LS174T cells was comparable to the increase in catalytic activity of CYP1A1 enzyme. Ligand binding analysis demonstrated that pelargonidin was a weak ligand of AhR. Enzyme kinetic analyses using human liver microsomes revealed inhibition of CYP1A1 activity by delphinidin (IC50 78 μM) and pelargonidin (IC50 33 μM). Overall, although most anthocyanidins had no effects on AhR-CYP1A1 signaling, pelargonidin can bind to and activate the AhR and AhR-dependent gene expression, and pelargonidin and delphinidin inhibit the CYP1A1 catalytic activity.

• MeSH
• Transcriptional Activation drug effects   MeSH
• Anthocyanins pharmacology   MeSH
• Hep G2 Cells MeSH
• Cytochrome P-450 CYP1A1 biosynthesis   MeSH
• Enzyme Induction MeSH
• Hepatocytes drug effects   enzymology   MeSH
• Microsomes, Liver enzymology   MeSH
• Kinetics MeSH
• Humans MeSH
• Ligands MeSH
• RNA, Messenger biosynthesis   MeSH
• Liver Neoplasms enzymology   MeSH
• Polychlorinated Dibenzodioxins pharmacology   MeSH
• Primary Cell Culture MeSH
• Promoter Regions, Genetic drug effects   MeSH
• Receptors, Aryl Hydrocarbon drug effects   metabolism   MeSH
• Signal Transduction drug effects   MeSH
• Intestinal Neoplasms enzymology   MeSH
• Transfection MeSH
• Basic Helix-Loop-Helix Transcription Factors drug effects   metabolism   MeSH
• Dose-Response Relationship, Drug MeSH
• Check Tag
• Humans MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• AHR protein, human MeSH Browser
• Anthocyanins MeSH
• CYP1A1 protein, human MeSH Browser
• Cytochrome P-450 CYP1A1 MeSH
• Ligands MeSH
• RNA, Messenger MeSH
• pelargonidin MeSH Browser
• Polychlorinated Dibenzodioxins MeSH
• Receptors, Aryl Hydrocarbon MeSH
• Basic Helix-Loop-Helix Transcription Factors MeSH

The small/short heterodimer partner (SHP, NR0B2) is a nuclear receptor corepressor lacking a DNA binding domain. SHP is induced by bile acid-activated farnesoid X receptor (FXR) resulting in CYP7A1 gene suppression. In contrast, Pregnane X receptor (PXR) activation by its ligands was recently suggested to inhibit SHP gene transactivation to maximize the induction of PXR target genes. However, there are also conflicting reports in literature whether PXR or rodent Pxr activation down-regulates SHP/Shp expression. Moreover, the PXR-mediated regulation of the SHP gene has been studied only at the SHP mRNA and transactivation (gene reporter assay) levels. In this study, we studied the effect of rifampicin, a prototype PXR ligand, on SHP mRNA, and protein expression in three primary human hepatocyte cultures. We found that SHP mRNA is not systematically down-regulated in hepatocyte in culture after 24 h treatment with rifampicin. Consistently, we did not observe down-regulation of SHP protein in primary human hepatocytes after 24 and 48 h of incubation with rifampicin. We can conclude that although we observed slight down-regulation of SHP mRNA and protein in several hepatocyte preparations, the phenomenon is unlikely critical for PXR-mediated induction of its target genes.

• Keywords
• CYP3A4, PXR, SHP, cytochrome P450, induction,
• Publication type
• Journal Article MeSH

Metformin is widely used in the treatment of type-2 diabetes. The pleotropic effects of metformin on glucose and lipid metabolism have been proposed to be mediated by the activation of AMP-activated protein kinase (AMPK) and the subsequent up-regulation of small heterodimer partner (SHP). SHP suppresses the functions of several nuclear receptors involved in the regulation of hepatic metabolism, including pregnane X receptor (PXR), which is referred to as a "master regulator" of drug/xenobiotic metabolism. In this study, we hypothesize that metformin suppresses the expression of CYP3A4, a main detoxification enzyme and a target gene of PXR, due to SHP up-regulation. We employed various gene reporter assays in cell lines and qRT-PCR in human hepatocytes and in Pxr(-/-) mice. We show that metformin dramatically suppresses PXR-mediated expression of CYP3A4 in hepatocytes. Consistently, metformin significantly suppressed the up-regulation of Cyp3a11 mRNA in the liver and intestine of wild-type mice, but not in Pxr(-/-) mice. A mechanistic investigation of the phenomenon showed that metformin does not significantly up-regulate SHP in human hepatocytes. We further demonstrate that AMPK activation is not involved in this process. We show that metformin disrupts PXR's interaction with steroid receptor coactivator-1 (SRC1) in a two-hybrid assay independently of the PXR ligand binding pocket. Metformin also inhibited vitamin D receptor-, glucocorticoid receptor- and constitutive androstane receptor (CAR)-mediated induction of CYP3A4 mRNA in human hepatocytes. We show, therefore, a suppressive effect of metformin on PXR and other ligand-activated nuclear receptors in transactivation of the main detoxification enzyme CYP3A4 in human hepatocytes.

• MeSH
• Transcriptional Activation MeSH
• Cytochrome P-450 CYP3A genetics   metabolism   MeSH
• Hepatocytes drug effects   metabolism   MeSH
• Hypoglycemic Agents pharmacology   MeSH
• Nuclear Receptor Coactivators metabolism   MeSH
• Constitutive Androstane Receptor MeSH
• Cells, Cultured MeSH
• Humans MeSH
• Membrane Proteins genetics   metabolism   MeSH
• RNA, Messenger metabolism   MeSH
• Metformin pharmacology   MeSH
• Mice, Inbred C57BL MeSH
• Mice, Knockout MeSH
• Mice MeSH
• Reflex, Righting drug effects   MeSH
• Pregnane X Receptor MeSH
• AMP-Activated Protein Kinases physiology   MeSH
• Receptors, Cytoplasmic and Nuclear metabolism   physiology   MeSH
• Receptors, Glucocorticoid physiology   MeSH
• Receptors, Calcitriol physiology   MeSH
• Genes, Reporter MeSH
• Signal Transduction MeSH
• Receptors, Steroid genetics   physiology   MeSH
• Animals MeSH
• Check Tag
• Humans MeSH
• Mice MeSH
• Animals MeSH
• Publication type
• Journal Article MeSH
• Research Support, Non-U.S. Gov't MeSH
• Research Support, N.I.H., Extramural MeSH
• Names of Substances
• Cyp3a11 protein, mouse MeSH Browser
• Cytochrome P-450 CYP3A MeSH
• Hypoglycemic Agents MeSH
• Nuclear Receptor Coactivators MeSH
• Constitutive Androstane Receptor MeSH
• Membrane Proteins MeSH
• RNA, Messenger MeSH
• Metformin MeSH
• nuclear receptor subfamily 0, group B, member 2 MeSH Browser
• Pregnane X Receptor MeSH
• AMP-Activated Protein Kinases MeSH
• Receptors, Cytoplasmic and Nuclear MeSH
• Receptors, Glucocorticoid MeSH
• Receptors, Calcitriol MeSH
• Receptors, Steroid MeSH