rifampin and hyperforin

The organic cation transporter 1 (OCT1) transports cationic drugs into hepatocytes. The high hepatic expression of OCT1 is controlled by the HNF4α and USF transcription factors. Pregnane X receptor (PXR) mediates induction of the principal xenobiotic metabolizing enzymes and transporters in the liver. Here, we have assessed the down-regulation of OCT1 expression by PXR activation.. We used primary human hepatocytes and related cell lines to measure OCT1 expression and activity, by assaying MPP(+) accumulation. Western blotting, qRT-PCR, the OCT1 promoter gene reporter constructs and chromatin immunoprecipitation assays were also used.. OCT1 mRNA in human hepatocytes was down-regulated along with reduced [(3) H]MPP(+) accumulation in differentiated HepaRG cells after treatment with rifampicin. Rifampicin and hyperforin as well as the constitutively active PXR mutant T248D suppressed activity of the 1.8 kb OCT1 promoter construct in gene reporter assays. Silencing of both PXR and HNF4α in HepaRG cells blocked the PXR ligand-mediated down-regulation of OCT1 expression. The mutation of HNF4α and USF1 (E-box) responsive elements reversed the PXR-mediated inhibition in gene reporter assays. Chromatin immunoprecipitation assays indicated that PXR activation sequestrates the SRC-1 coactivator from the HNF4α response element and E-box of the OCT1 promoter. Consistent with these findings, exogenous overexpression of the SRC-1, but not the PGC1α coactivator, relieved the PXR-mediated repression of OCT1 transactivation.. PXR ligands reduced the HNF4α-mediated and USF-mediated transactivation of OCT1 gene expression by competing for SRC-1 and decreased delivery of a model OCT1 substrate into hepatocytes.

Topics: Dose-Response Relationship, Drug; Down-Regulation; Hep G2 Cells; Hepatocytes; Humans; Nuclear Receptor Coactivator 1; Octamer Transcription Factor-1; Phloroglucinol; Pregnane X Receptor; Receptors, Steroid; Rifampin; Structure-Activity Relationship; Terpenes; Tumor Cells, Cultured

ATP-driven efflux transporters are important, selective elements of the blood-brain barrier. Abcg2 (also brain multidrug resistance protein) and Abcb1 (P-glycoprotein) belong to the best known ABC-transporters which limit the access of therapeutic drugs to the brain and impair pharmacotherapy of central nervous system (CNS) disorders. To investigate the question how ATP-binding cassette (ABC)-transporters are regulated, we analyzed the influence of the nuclear receptor, pregnane X receptor (PXR) on transporter expression. PXR is a xenobiotic-activated transcription factor that is highly expressed in barrier tissue. Xenobiotics like rifampicin and hyperforin activate PXR and induce Abcb1 expression. ABC-transporter up-regulation could have potential effects on pharmacokinetics of different drugs. To study the influence of PXR on the two most prominent efflux transporters we used a primary culture of porcine brain capillary endothelial cells (PBCEC) due to higher homologies to the human form of PXR. For activation of the pregnane X receptor the ligands hyperforin and rifampicin were used. We investigated the effects on the transporters on RNA level (quantitative real time PCR), protein level (Western blotting) and transport level (uptake assay, active transport). The stimulation of the PBCEC with rifampicin or hyperforin showed a significant up-regulation of both ABC-transporters on RNA level after 6h, whereas an increased protein expression was strongest after 12h. Also the transport activity intensified after a period of 12h for Abcg2 and Abcb1. In conclusion our data prove PXR activation by rifampicin and hyperforin lead to an increased ABC-transporter expression and transport activity.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B; ATP Binding Cassette Transporter, Subfamily B, Member 1; Benzimidazoles; Blood-Brain Barrier; Blotting, Western; Capillaries; Cells, Cultured; Electric Stimulation; Endothelial Cells; Fluorescent Dyes; Phloroglucinol; Pregnane X Receptor; Real-Time Polymerase Chain Reaction; Receptors, Steroid; Rifampin; RNA; Stimulation, Chemical; Swine; Terpenes; Up-Regulation

Several studies have suggested the efflux transporter P-glycoprotein (P-gp) to play a role in the etiology of Alzheimer's disease through the clearance of amyloid beta (Aβ) from the brain. In this study, we aimed to investigate the possibility of P-gp as a potential therapeutic target for Alzheimer's disease by examining the impact of P-gp up-regulation on the clearance of Aβ, a neuropathological hallmark of Alzheimer's disease.. Uptake studies for ¹²⁵I-radiolabelled Aβ₁₋₄₀, and fluorescent immunostaining technique for P-gp and fluorescent imaging of Aβ₁₋₄₀ were carried out in LS-180 cells following treatment with drugs known to induce P-gp expression.. Approximately 10-35% decrease in ¹²⁵I-Aβ₁₋₄₀ intracellular accumulation was observed in cells treated with rifampicin, dexamethasone, caffeine, verapamil, hyperforin, β-estradiol and pentylenetetrazole compared with control. Also, fluorescent micrographs showed an inverse relationship between levels of P-gp expression and 5-carboxyfluorescein labelled Aβ (FAM-Aβ₁₋₄₀) intracellular accumulation. Quantitative analysis of the micrographs revealed that the results were consistent with those of the uptake studies using ¹²⁵I-Aβ₁₋₄₀.. The investigated drugs were able to improve the efflux of Aβ₁₋₄₀ from the cells via P-gp up-regulation compared with control. Our results elucidate the importance of targeting Aβ clearance via P-gp up-regulation, which will be effective in slowing or halting the progression of Alzheimer's disease.

Topics: Alzheimer Disease; Amyloid beta-Peptides; ATP Binding Cassette Transporter, Subfamily B, Member 1; Caffeine; Cell Line; Central Nervous System Agents; Dexamethasone; Estradiol; Humans; Pentylenetetrazole; Phloroglucinol; Rifampin; Staining and Labeling; Terpenes; Up-Regulation; Verapamil

Drug transporters are increasingly recognized as important determinants of variability in drug disposition and therapeutic response, both in pre-clinical and clinical stages of drug development process. The role P-glycoprotein (P-gp) plays in drug interactions via its inhibition is well established. However, much less knowledge is available about drugs effect on P-gp up-regulation. The objective of this work was to in vitro investigate and rank commonly used drugs according to their potencies to up-regulate P-gp activity utilizing the same experimental conditions.. The in vitro potencies of several drugs of diverse physicochemical and therapeutic properties including rifampicin, dexamethasone, caffeine, verapamil, pentylenetetrazole, hyperforin, and β-estradiol over broad concentration range to up-regulate P-gp expression and activity were examined. For dose-response studies, LS-180 cells were treated with different concentrations of the selected drugs followed by P-gp protein and gene expressions analyses. P-gp functionality was determined by uptake studies with rhodamine 123 as a P-gp substrate, followed by Emax/EC50 evaluation.. The results demonstrated a dose-dependent increase in P-gp expression and activity following treatments. At 50 uM concentration (hyperforin, 0.1 uM), examined drugs increased P-gp protein and gene expressions by up to 5.5 and 6.2-fold, respectively, while enhanced P-gp activity by 1.8-4-fold. The rank order of these drugs potencies to up-regulate P-gp activity was as following: hyperforin >>> dexamethasone ~ beta-estradiol > caffeine > rifampicin ~ pentylenetetrazole > verapamil.. These drugs have the potential to be involved in drug interactions when administered with other drugs that are P-gp substrates. Further studies are needed to in vivo evaluate these drugs and verify the consequences of such induction on P-gp activity for in vitro-in vivo correlation purposes.

Topics: ATP Binding Cassette Transporter, Subfamily B, Member 1; Caffeine; Cell Line, Tumor; Dexamethasone; Dose-Response Relationship, Drug; Drug Interactions; Estradiol; Gene Expression; Humans; Pentylenetetrazole; Pharmaceutical Preparations; Phloroglucinol; Rhodamine 123; Rifampin; Stimulation, Chemical; Terpenes; Up-Regulation; Verapamil

Monkeys have been proposed as an animal model to predict the magnitude of human clinical drug-drug interactions caused by CYP3A4 enzyme induction. To evaluate whether the cynomolgus monkey can be an effective in vivo model, human CYP3A4 inducers were evaluated both in vitro and in vivo. First, a full-length pregnane X receptor (PXR) was cloned from the cynomolgus monkey, and the sequence was compared with those of rhesus monkey and human PXR. Cynomolgus and rhesus monkey PXR differed by only one amino acid (A68V), and both were highly homologous to human PXR (approximately 96%). When the transactivation profiles of 30 compounds, including known inducers of CYP3A4, were compared between cynomolgus and human PXR, a high degree of correlation with EC(50) values was observed. These results suggest that cynomolgus and human PXR respond in a similar fashion to these ligands. Second, two known human CYP3A4 inducers, rifampicin and hyperforin, were tested in monkey and human primary hepatocytes for induction of CYP3A enzymes. Both monkey and human hepatocytes responded similarly to the inducers and resulted in increased RNA and enzyme activity changes of CYP3A8 and CYP3A4, respectively. Lastly, in vivo induction of CYP3A8 by rifampicin and hyperforin was shown by significant reductions of midazolam exposure that were comparable with those in humans. These results show that the cynomolgus monkey can be a predictive in vivo animal model of PXR-mediated induction of human CYP3A4 and can provide a useful assessment of the resulting pharmacokinetic changes of affected drugs.

Topics: Adult; Amino Acid Sequence; Animals; Bridged Bicyclo Compounds; Cell Line; Cell Line, Tumor; Cell Survival; Cloning, Molecular; Cytochrome P-450 CYP3A; Drug Interactions; Enzyme Induction; Female; Gene Expression; Hepatocytes; Humans; Hypericum; Macaca fascicularis; Macaca mulatta; Male; Midazolam; Middle Aged; Models, Animal; Molecular Sequence Data; Phloroglucinol; Plant Extracts; Pregnane X Receptor; Receptors, Steroid; Rifampin; Sequence Homology, Amino Acid; Terpenes; Transcriptional Activation; Transfection; Xenobiotics

Pharmacotherapy of central nervous system (CNS) disorders is impaired by the drug efflux transporter, P-glycoprotein, which limits drug penetration across the blood-brain barrier into the CNS. One strategy to increase brain drug levels is to modulate P-glycoprotein regulation. This approach requires understanding of the mechanisms that control transporter expression and function. One mechanism through which P-glycoprotein is regulated is the nuclear receptor, pregnane X receptor (PXR). Xenobiotics including drugs activate PXR and induce P-glycoprotein, which potentially affects pharmacokinetics/pharmacodynamics of coadministered drugs. Because rodent models are not suitable to predict xenobiotic interactions with human PXR, in a porcine model, we studied functional similarities between pig and human PXR. We used brain capillary endothelial cells from pig to study the effect of PXR activation on P-glycoprotein. To activate PXR, we used the PXR ligands, rifampicin, hyperforin, and pregnenolone-16alpha-carbonitrile (PCN), and measured abcb1 mRNA with quantitative polymerase chain reaction, P-glycoprotein expression with Western blotting, and P-glycoprotein transport activity with a calcein assay. We provide first proof of principle that the human PXR ligands, rifampicin and hyperforin, but not the rodent PXR ligand, PCN, activate pig PXR at the blood-brain barrier and induce mRNA, protein expression, and transport activity of P-glycoprotein. Our data indicate functional similarities between human and pig PXR that suggest the pig model could be useful for predicting xenobiotic-PXR interactions in humans. Because PXR is crucial in controlling drug efflux transporters, our findings will contribute to a better understanding of the regulation of blood-brain barrier function, which could potentially have important clinical implications for the treatment of CNS disorders.

Topics: Animals; ATP Binding Cassette Transporter, Subfamily B, Member 1; Blood-Brain Barrier; Blotting, Western; Bridged Bicyclo Compounds; Cell Separation; Cells, Cultured; Endothelial Cells; Fluoresceins; Humans; Immunohistochemistry; Myocytes, Smooth Muscle; Phloroglucinol; Pregnane X Receptor; Receptors, Steroid; Reverse Transcriptase Polymerase Chain Reaction; Rifampin; RNA, Messenger; Swine; Terpenes; Up-Regulation; Xenobiotics

Continuous use of St. John's wort decreases the bioavailabilities of a variety of drugs. This interaction is attributed to the induction of cytochrome P450 3A4 and/or P-glycoprotein. In this study, we aimed to examine the chronic effects of St. John's wort and its constituents, hyperforin and hypericin, on the expression and function of P-glycoprotein in an intestinal cell line, LS 180. We also examined the acute inhibitory effect of St. John's wort on P-glycoprotein by using LLC-GA5-COL150 cells, which overexpress P-glycoprotein. St. John's wort and hyperforin but not hypericin increased the expression of P-glycoprotein in LS 180 cells. Removal of St. John's wort resulted in a restoration of P-glycoprotein level within 48 h. The content of hyperforin in St. John's wort extract was high enough to induce P-glycoprotein, suggesting that the induction of P-glycoprotein by St. John's wort can be almost attributable to hyperforin. The LS 180 cells chronically exposed to St. John's wort or hyperforin exhibited the increase in the function of P-glycoprotein assessed by the efflux of digoxin, and the activities correlated well with P-glycoprotein level. On the other hand, St. John's wort and its two constituents did not show any acute effect on P-glycoprotein-mediated transport of digoxin. St. John's wort induced P-glycoprotein in vitro that functions as a drug efflux pump. Hyperforin is considered to be a primary cause of the inductive effect of St. John's wort. Long-term administration of St. John's wort may cause clinically significant decrease in the plasma concentrations of P-glycoprotein substrates.

Topics: Adenocarcinoma; Animals; Anthracenes; ATP Binding Cassette Transporter, Subfamily B, Member 1; Biological Transport; Bridged Bicyclo Compounds; Cell Line, Tumor; Colonic Neoplasms; Digoxin; Humans; Hypericum; LLC-PK1 Cells; Perylene; Phloroglucinol; Plant Extracts; Rifampin; Swine; Terpenes; Transfection

St. John's wort is a commonly used herbal medication that increases cytochrome P450 3A (CYP3A) activity. Because docetaxel is inactivated by CYP3A, we studied the effects of the St. John's wort constituent hyperforin on docetaxel metabolism in a human hepatocyte model.. Hepatocytes, isolated from three donor livers, were exposed to hyperforin (0.1, 0.5, or 1.5 micromol/L) or rifampin (10 micromol/L) for 48 hours. After 48 hours, hyperforin- or rifampin-containing medium was replaced with medium containing 100 micromol/L docetaxel. After 1 hour, docetaxel metabolism was characterized by liquid chromatography-tandem mass spectrometry. Subsequent incubations characterized the specific cytochrome P450s that produced the docetaxel metabolites observed in hepatocyte incubations.. Rifampin induced docetaxel metabolism 6.8- to 32-fold above docetaxel metabolism in control cultures. Hyperforin induced docetaxel metabolism in all three hepatocyte preparations. Hyperforin induction was dose-dependent and, at maximum, was 2.6- to 7-fold greater than that in controls. Docetaxel metabolites identified in rifampin- and hyperforin-treated hepatocyte preparations included the previously described tert-butyl-hydroxylated metabolite and two previously unidentified metabolites involving hydroxylation on the baccatin ring. CYP3A4 produced the tert-butyl-hydroxylated metabolite and the two ring-hydroxylated metabolites. CYP2C8 produced one of the newly described ring-hydroxylated metabolites.. Exposure to the St. John's wort constituent hyperforin induces docetaxel metabolism in vitro. This implies that subtherapeutic docetaxel concentrations may result when docetaxel is administered to patients using St. John's wort on a chronic basis. The results also show induction of previously undescribed metabolic pathways for docetaxel, one of which may be analogous to the known 6-alpha-hydroxylation of paclitaxel by CYP2C8.

Topics: Aged; Antineoplastic Agents; Aryl Hydrocarbon Hydroxylases; Bridged Bicyclo Compounds; Chromatography, Liquid; Cytochrome P-450 CYP2C8; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Docetaxel; Drug Synergism; Female; Hepatocytes; Humans; Hypericum; Ions; Liver; Mass Spectrometry; Middle Aged; Models, Chemical; Phloroglucinol; Rifampin; Taxoids; Terpenes; Time Factors

Human CYP2C9 is important in the metabolism of numerous clinically used drugs such as the anticoagulant warfarin, the anticonvulsant phenytoin, antidiabetic drugs such as tolbutamide and glipizide, the hypertensive agent losartan, and numerous nonsteroidal anti-inflammatory drugs. Several studies have reported that certain drugs such as rifampicin and phenobarbital induce CYP2C9, but the molecular basis for this induction remains unknown. In the present study, we demonstrate that the human pregnane X receptor (hPXR) mediates induction of CYP2C9 by the prototype drugs rifampicin, hyperforin (found in St. John's Wart), and phenobarbital. Deletion and mutagenesis studies with luciferase reporter constructs showed that a functional PXR-responsive element located -1839/-1824 base pairs upstream from the translation start site was the primary binding site mediating the rifampicin induction of CYP2C9. This site was previously described as a constitutive androstane receptor-responsive element (CAR-RE). Mutational analysis of 3- and 12-kilobase CYP2C9 promoter fragments indicated that this proximal binding site was essential for rifampicin inducibility, although a cooperative effect could be attributed to a second CAR-RE located at -2899/-2883. In summary, we have demonstrated rifampicin induction of CYP2C9 promoter constructs that is consistent with the magnitude of induction of CYP2C9 protein and mRNA reported in vivo and in primary human hepatocytes, and we have identified the cis-element essential for this response. This is the first report to demonstrate that the nuclear receptor PXR mediates induction of CYP2C9 with rifampicin, phenobarbital, and hyperforin.

Topics: Anti-Bacterial Agents; Aryl Hydrocarbon Hydroxylases; Binding Sites; Bridged Bicyclo Compounds; Cytochrome P-450 CYP2C9; Enzyme Induction; Excitatory Amino Acid Antagonists; Gene Expression Regulation, Enzymologic; Humans; Phenobarbital; Phloroglucinol; Pregnane X Receptor; Promoter Regions, Genetic; Receptors, Cytoplasmic and Nuclear; Receptors, Steroid; Rifampin; Terpenes; Transcriptional Activation; Tumor Cells, Cultured

Vitamin K2 is a critical nutrient required for blood clotting that also plays an important role in bone formation. Vitamin K2 supplementation up-regulates the expression of bone markers, increases bone density in vivo, and is used clinically in the management of osteoporosis. The mechanism of vitamin K2 action in bone formation was thought to involve its normal role as an essential cofactor for gamma-carboxylation of bone matrix proteins. However, there is evidence that suggests vitamin K2 also has a transcriptional regulatory function. Vitamin K2 bound to and activated the orphan nuclear receptor SXR and induced expression of the SXR target gene, CYP3A4, identifying it as a bona fide SXR ligand. Vitamin K2 treatment of osteosarcoma cells increased mRNA levels for the osteoblast markers bone alkaline phosphatase, osteoprotegerin, osteopontin, and matrix Gla protein. The known SXR activators rifampicin and hyperforin induced this panel of bone markers to an extent similar to vitamin K2. Vitamin K2 was able to induce bone markers in primary osteocytes isolated from wild-type murine calvaria but not in cells isolated from mice deficient in the SXR ortholog PXR. We infer that vitamin K2 is a transcriptional regulator of bone-specific genes that acts through SXR to favor the expression of osteoblastic markers. Thus, SXR has a novel role as a mediator of bone homeostasis in addition to its role as a xenobiotic sensor. An important implication of this work is that a subset of SXR activators may function as effective therapeutic agents for the management of osteoporosis.

Topics: Alkaline Phosphatase; Animals; Biomarkers; Bone and Bones; Bone Density; Bridged Bicyclo Compounds; COS Cells; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Gene Expression; Glycoproteins; HeLa Cells; Homeostasis; Humans; Mice; Mice, Knockout; Osteoblasts; Osteocalcin; Osteopontin; Osteoprotegerin; Osteosarcoma; Phloroglucinol; Pregnane X Receptor; Receptors, Cytoplasmic and Nuclear; Receptors, Steroid; Receptors, Tumor Necrosis Factor; Recombinant Proteins; Reverse Transcriptase Polymerase Chain Reaction; Rifampin; RNA, Messenger; Sialoglycoproteins; Terpenes; Transfection; Tumor Cells, Cultured; Vitamin K 2

St John's wort (SJW), an extract of the medicinal plant Hypericum perforatum, is widely used as a herbal antidepressant. Recently, this agent has been found to adversely affect the metabolism of various coadministered drugs. Steroid X receptor (SXR), an orphan nuclear receptor, induces hepatic cytochrome P450 gene expression in response to diverse endogenous steroids, xenobiotics and drugs. Here, we report that, when coexpressed with SXR, a reporter construct derived from the cytochrome P450 3A promoter is activated by St John's wort. A GAL4-SXR ligand binding domain (LBD) fusion mediates concentration-dependent transactivation by SJW, whereas a mutant GAL4-SXR fusion, containing substitutions in key residues in a transactivation domain, is inactive. SJW recruits steroid receptor coactivator-1 to SXR in a two-hybrid assay and competes with radiolabelled ligand in binding studies, suggesting it interacts directly with the receptor LBD. Of two constituents of SJW, we find that hyperforin, but not hypericin, mediates both transactivation and coactivator recruitment by SXR. Our observations suggest that SXR activation by St John's wort mediates its adverse interaction with drugs metabolised via the CYP 3A pathway. Future development of SJW derivatives lacking SXR activation, may enable its antidepressant and drug-metabolising properties to be dissociated.

Topics: Animals; Anthracenes; Antidepressive Agents; Aryl Hydrocarbon Hydroxylases; Binding, Competitive; Bridged Bicyclo Compounds; Corticosterone; Cytochrome P-450 CYP3A; Cytochrome P-450 Enzyme System; Dose-Response Relationship, Drug; Histone Acetyltransferases; Humans; Hypericum; Mice; Nuclear Receptor Coactivator 1; Oxidoreductases, N-Demethylating; Perylene; Phloroglucinol; Plants, Medicinal; Pregnane X Receptor; Protein Binding; Receptors, Steroid; Rifampin; Terpenes; Transcription Factors; Transcription, Genetic; Tumor Cells, Cultured