Atrazine-induced environmental nephrosis was mitigated by lycopene via modulating nuclear xenobiotic receptors-mediated response.

The burden and morbidity of environmental nephrosis is increasing globally. Atrazine (ATR) and degradation products in the environment are considered key determinants of nephrosis. However, the lack of highly effective treatments for environmental nephrosis creates an urgent need to better understand the preventive strategies and mechanisms. This study aimed to highlight the mechanism of ATR-induced environmental nephrosis and the chemoprotective potential of lycopene (LYC) against the renal injury and nephrosis. Male mice were treated with LYC (5 mg/kg) and/or ATR (50 mg/kg or 200 mg/kg) by gavage administration for 21 days. Histopathological changes and biochemical function, cytochrome P450 enzymes system (CYP450s), nuclear xenobiotic receptors (NXRs) response and the transcription of CYP isoforms (CYPs) were detected. ATR exposure caused the changes of the histopathological and biochemical function, activated the NXR response and disturbed the CYP450s homeostasis. Supplementary LYC significantly prevented ATR-induced nephrotoxicity and alleviated the alternation of histopathological and biochemical function via modulating the CYP450s homeostasis and the NXR response. The results demonstrated AHR, CAR, PXR, PPAR (α, γ), CYP1, CYP2, CYP3 and CYP4 superfamily play a vital role in LYC-ATR interaction. Our findings provide new evidence that ATR exposure can cause the environmental nephrosis via inducing the kidney injury. Supplementary LYC showed significant chemoprotective potential against ATR-induced renal injury and environmental nephrosis via regulating the NXR response and the CYP450s homeostasis.

Modulation of Cytochrome P450, P-glycoprotein and Pregnane X Receptor by Selected Antimalarial Herbs-Implication for Herb-Drug Interaction.

Seven medicinal plants popularly used for treating malaria in West Africa were selected to assess herb-drug interaction potential through a series of in vitro methods. Fluorescent cytochrome P450 (CYP) assays were conducted using the recombinant CYP enzymes for CYP1A2, CYP2A6, CYP2B6, CYP2C9, CYP2C19, CYP2D6 and CYP3A4 to assess the effect of the methanolic extracts on the metabolic activity of CYPs. Secondly, the inhibitory effect of the extracts was evaluated on P-glycoproteins (P-gp) using calcein-AM, a fluorescent substrate, in MDCK-II and hMDR1-MDCK-II cells. The inhibition of P-gp activity was determined as a reflection of increase in calcein-AM uptake. Additionally, the enzyme induction potential of the extracts was assessed through the modulation of PXR activity in HepG2 cells transiently transfected with pSG5-PXR and PCR5 plasmid DNA. Significant inhibition of CYP activity (IC50 < 10 µg/mL) was observed with the following herbs: A. muricata [CYP2C9, 3A4 and CYP2D6]; M. indica [CYP2C9]; M. charantia [CYP2C9 and CYP2C19]; P. amarus [CYP2C19, CYP2C9 and CYP3A4]; T. diversifolia [CYP2C19 and CYP3A4]. Extracts of four herbs (P. amarus, M. charantia, T. diversifolia and A. muricata) exhibited significant inhibition of P-gp with IC50 values (µg/mL) of 17 ± 1, 16 ± 0.4, 26 ± 1, and 24 ± 1, respectively. In addition, four herbs (A. mexicana, M. charantia, P. amarus and T. diversifolia) showed a >two-fold increase in induction in PXR activity. These findings suggest that these herbs may be capable of eliciting herb-drug interactions if consumed in high quantities with concomitant use of conventional therapies.

[Pharmacology research on PXR as a potential target in screening bioactive components of Chinese material medica].

Pregnane X receptor (PXR) is key transcription factors which mainly regulate the expression of CYP3A genes. At the molecular level, PXR has been revealed the protection mechanism of the body against xenochemicals and a major mode of the drug-drug interactions. Besides playing an important role in drug metabolism and interactions, PXR and its target genes also play an important role in maintaining normal physiological function and homeostasis. Therefore, it is necessary to study the regulation of PXR and its related pharmacological effects of TCM and natural products, and to provide new clues for the new pharmacological pathway.

Treatment of cardiovascular disease by traditional Chinese medicine against pregnane X receptor.

Recently, cardiovascular disease, also known as loop circulatory system diseases or disorders, is one of the serious diseases including heart disease, stroke, atherosclerosis, myocardial infarction, hypertension, hypotension, and thrombosis. Human pregnane X receptor, PXR, plays a crucial role in exogenous and endobiotic metabolism for rabbit, rat, mouse, and human. The PXR activation can protect the blood vessels from damage of hazardous substances. In this study we aim to investigate the potent lead compounds as PXR receptor agonist against cardiovascular disease. To improve drug development of TCM compounds, we aim to investigate the potent lead compounds as PXR agonists from the TCM compounds in TCM Database@Taiwan. The top three TCM compounds, bis(4-hydroxybenzyl) ether mono-ß-D-glucopyranoside (BEMG), ixerisoside, and tangshenoside II, have displayed higher potent binding affinities than the positive control, PNU-142721, in the docking simulation. After MD simulations, which can optimize the result of docking simulation and validate the stability of H-bonds between each ligand and PXR protein under dynamic conditions, top TCM compounds, BEMG and tangshenoside II, maintain most of interactions with PXR protein, which keep the ligand binding stable in the binding domain. Hence, we propose BEMG and tangshenoside II as potential lead compounds for further study in drug development process with the PXR protein.

Pregnane X receptor (PXR)--a contributor to the diabetes epidemic?

Pregnane X receptor (PXR), a ligand-activated nuclear receptor, was originally identified as a regulator of drug and bile acid metabolism. Studies in experimental animals and humans within the last decade have revealed PXR as a regulator of energy metabolism repressing gluconeogenesis and hepatic lipid oxidation. The most recent in vivo studies demonstrate that PXR activation has a detrimental role in the regulation of glucose metabolism. The prevalence of many PXR agonists in low concentrations in our environments as well as the PXR-activating properties of numerous commonly used medications and herbal remedies may have unanticipated health effects. It could be speculated that, due to its dual role as a xenosensor and a regulator of energy metabolism, PXR, in concert with a mixture of PXR agonists in the environment, contributes to the present-day type 2 diabetes epidemic. With this hypothesis in mind, we review the current literature on PXR as a regulator of glucose and hepatic lipid metabolism and the association of exposure to PXR agonists with diabetes susceptibility.

Milk thistle's active components silybin and isosilybin: novel inhibitors of PXR-mediated CYP3A4 induction.

Because cancer is often treated with combination therapy, unexpected pharmacological effects can occur because of drug-drug interactions. Several drugs are able to cause upregulation or downregulation of drug transporters or cytochrome P450 enzymes, particularly CYP3A4. Induction of CYP3A4 may result in decreased plasma levels and therapeutic efficacy of anticancer drugs. Since the pregnane X receptor (PXR) is one of the major transcriptional regulators of CYP3A4, PXR antagonists can possibly prevent CYP3A4 induction. Currently, a limited number of PXR antagonists are available. Some of these antagonists, such as sulphoraphane and coumestrol, belong to the so-called complementary and alternative medicines (CAM). Therefore, the aim was to determine the potential of selected CAM (ß-carotene, Echinacea purpurea, garlic, Ginkgo biloba, ginseng, grape seed, green tea, milk thistle, saw palmetto, valerian, St. John's Wort, and vitamins B6, B12, and C) to inhibit PXR-mediated CYP3A4 induction at the transcriptional level, using a reporter gene assay and a real-time polymerase chain reaction assay in LS180 colon adenocarcinoma cells. Furthermore, computational molecular docking and a LanthaScreen time-resolved fluorescence resonance energy transfer (TR-FRET) PXR competitive binding assay were performed to explore whether the inhibiting CAM components interact with PXR. The results demonstrated that milk thistle is a strong inhibitor of PXR-mediated CYP3A4 induction. The components of milk thistle responsible for this effect were identified as silybin and isosilybin. Furthermore, computational molecular docking revealed a strong interaction between both silybin and isosilybin and PXR, which was confirmed in the TR-FRET PXR assay. In conclusion, silybin and isosilybin might be suitable candidates to design potent PXR antagonists to prevent drug-drug interactions via CYP3A4 in cancer patients.

Sulforaphane is not an effective antagonist of the human pregnane X-receptor in vivo.

Sulforaphane (SFN), is an effective in vitro antagonist of ligand activation of the human pregnane and xenobiotic receptor (PXR). PXR mediated CYP3A4 up-regulation is implicated in adverse drug-drug interactions making identification of small molecule antagonists a desirable therapeutic goal. SFN is not an antagonist to mouse or rat PXR in vitro; thus, normal rodent species are not suitable as in vivo models for human response. To evaluate whether SFN can effectively antagonize ligand activation of human PXR in vivo, a three-armed, randomized, crossover trial was conducted with 24 healthy adults. The potent PXR ligand - rifampicin (300mg/d) was given alone for 7days in arm 1, or in daily combination with 450µmol SFN (Broccoli Sprout extract) in arm 2; SFN was given alone in arm 3. Midazolam as an in vivo phenotype marker of CYP3A was administered before and after each treatment arm. Rifampicin alone decreased midazolam AUC by 70%, indicative of the expected increase in CYP3A4 activity. Co-treatment with SFN did not reduce CYP3A4 induction. Treatment with SFN alone also did not affect CYP3A4 activity in the cohort as a whole, although in the subset with the highest basal CYP3A4 activity there was a statistically significant increase in midazolam AUC (i.e., decrease in CYP3A4 activity). A parallel study in humanized PXR mice yielded similar results. The parallel effects of SFN between humanized PXR mice and human subjects demonstrate the predictive value of humanized mouse models in situations where species differences in ligand-receptor interactions preclude the use of a native mouse model for studying human ligand-receptor pharmacology.

Ligand- and structure-based pregnane X receptor models.

The human pregnane X receptor (PXR) is a ligand dependent transcription factor that can be activated by structurally diverse agonists including steroid hormones, bile acids, herbal drugs, and prescription medications. PXR regulates the transcription of several genes involved in xenobiotic detoxification and apoptosis. Activation of PXR has the potential to initiate adverse effects by altering drug pharmacokinetics or perturbing physiological processes. Hence, more reliable prediction of PXR activators would be valuable for pharmaceutical drug discovery to avoid potential toxic effects. Ligand- and protein structure-based computational models for PXR activation have been developed in several studies. There has been limited success with structure-based modeling approaches to predict human PXR activators, which can be attributed to the large and promiscuous site of this protein. Slightly better success has been achieved with ligand-based modeling methods including quantitative structure-activity relationship (QSAR) analysis, pharmacophore modeling and machine learning that use appropriate descriptors to account for the diversity of the ligand classes that bind to PXR. These combined computational approaches using molecular shape information may assist scientists to more confidently identify PXR activators. This chapter reviews the various ligand and structure based methods undertaken to date and their results.

Analysis of tanshinone IIA induced cellular apoptosis in leukemia cells by genome-wide expression profiling.

BACKGROUND: Tanshinone IIA (Tan IIA) is a diterpene quinone extracted from the root of Salvia miltiorrhiza, a Chinese traditional herb. Although previous studies have reported the anti-tumor effects of Tan IIA on various human cancer cells, the underlying mechanisms are not clear. The current study was undertaken to investigate the molecular mechanisms of Tan IIA's apoptotic effects on leukemia cells in vitro. METHODS: The cytotoxicity of Tan IIA on different types of leukemia cell lines was evaluated by the 3-[4,5-dimethylthiazol-2,5]-diphenyl tetrazolium bromide (MTT) assay on cells treated without or with Tan IIA at different concentrations for different time periods. Cellular apoptosis progression with and without Tan IIA treatment was analyzed by Annexin V and Caspase 3 assays. Gene expression profiling was used to identify the genes regulated after Tan IIA treatment and those differentially expressed among the five cell lines. Confirmation of these expression regulations was carried out using real-time quantitative PCR and ELISA. The antagonizing effect of a PXR inhibitor L-SFN on Tan IIA treatment was tested using Colony Forming Unit Assay. RESULTS: Our results revealed that Tan IIA had different cytotoxic activities on five types of leukemia cells, with the highest toxicity on U-937 cells. Tan IIA inhibited the growth of U-937 cells in a time- and dose-dependent manner. Annexin V and Caspase-3 assays showed that Tan IIA induced apoptosis in U-937 cells. Using gene expression profiling, 366 genes were found to be significantly regulated after Tan IIA treatment and differentially expressed among the five cell lines. Among these genes, CCL2 was highly expressed in untreated U-937 cells and down-regulated significantly after Tan IIA treatment in a dose-dependent manner. RT-qPCR analyses validated the expression regulation of 80% of genes. Addition of L-sulforaphane (L-SFN), an inhibitor of Pregnane×receptor (PXR) significantly attenuated Tan IIA's effects using colony forming assays. CONCLUSIONS: Tan IIA has significant growth inhibition effects on U-937 cells through the induction of apoptosis. And Tan IIA-induced apoptosis might result from the activation of PXR, which suppresses the activity of NF-κB and lead to the down-regulation of CCL2 expression.

Glucocorticoids are critical regulators of dendritic spine development and plasticity in vivo.

Glucocorticoids are a family of hormones that coordinate diverse physiological processes in responding to stress. Prolonged glucocorticoid exposure over weeks has been linked to dendritic atrophy and spine loss in fixed tissue studies of adult brains, but it is unclear how glucocorticoids may affect the dynamic processes of dendritic spine formation and elimination in vivo. Furthermore, relatively few studies have examined the effects of stress and glucocorticoids on spines during the postnatal and adolescent period, which is characterized by rapid synaptogenesis followed by protracted synaptic pruning. To determine whether and to what extent glucocorticoids regulate dendritic spine development and plasticity, we used transcranial two-photon microscopy to track the formation and elimination of dendritic spines in vivo after treatment with glucocorticoids in developing and adult mice. Corticosterone, the principal murine glucocorticoid, had potent dose-dependent effects on dendritic spine dynamics, increasing spine turnover within several hours in the developing barrel cortex. The adult barrel cortex exhibited diminished baseline spine turnover rates, but these rates were also enhanced by corticosterone. Similar changes occurred in multiple cortical areas, suggesting a generalized effect. However, reducing endogenous glucocorticoid activity by dexamethasone suppression or corticosteroid receptor antagonists caused a substantial reduction in spine turnover rates, and the former was reversed by corticosterone replacement. Notably, we found that chronic glucocorticoid excess led to an abnormal loss of stable spines that were established early in life. Together, these findings establish a critical role for glucocorticoids in the development and maintenance of dendritic spines in the living cortex.

Pregnane X receptor- and CYP3A4-humanized mouse models and their applications.

Pregnane X receptor (PXR) is a pivotal nuclear receptor modulating xenobiotic metabolism primarily through its regulation of CYP3A4, the most important enzyme involved in drug metabolism in humans. Due to the marked species differences in ligand recognition by PXR, PXR-humanized (hPXR) mice, and mice expressing human PXR and CYP3A4 (Tg3A4/hPXR) were established. hPXR and Tg3A4/hPXR mice are valuable models for investigating the role of PXR in xenobiotic metabolism and toxicity, in lipid, bile acid and steroid hormone homeostasis, and in the control of inflammation.

Nuclear receptor drug discovery.

Nuclear receptors (NR) are ligand-activated transcription factors that regulate the activation of a variety of important target genes. There are 48 genes that encode NRs in the human genome, and these receptors now represent one of the most important targets for therapeutic drug development. Successful identification of selective NR modulators has transformed the NR drug discovery strategy from the designing of synthetic compounds that mimic the full function of cognate ligands to developing compounds that selectively modulate the functional activity of an NR in a manner that is distinct from the cognate ligands. Current efforts regarding NR drug development continue to focus on improving the function and tissue selectivity of drug candidates to reduce undesirable side effects. This review focuses on modulators of the glucocorticoid receptor (GR), androgen receptor (AR), and pregnane X receptor (PXR).

Machine learning methods and docking for predicting human pregnane X receptor activation.

The pregnane X receptor (PXR) regulates the expression of genes involved in xenobiotic metabolism and transport. In vitro methods to screen for PXR agonists are used widely. In the current study, computational models for human PXR activators and PXR nonactivators were developed using recursive partitioning (RP), random forest (RF), and support vector machine (SVM) algorithms with VolSurf descriptors. Following 10-fold randomization, the models correctly predicted 82.6-98.9% of activators and 62.0-88.6% of nonactivators. The models were validated using separate test sets. The overall ( n = 15) test set prediction accuracy for PXR activators with RP, RF, and SVM PXR models is 80-93.3%, representing an improvement over models previously reported. All models were tested with a second test set ( n = 145), and the prediction accuracy ranged from 63 to 67% overall. These test set molecules were found to cover the same area in a principal component analysis plot as the training set, suggesting that the predictions were within the applicability domain. The FlexX docking method combined with logistic regression performed poorly in classifying this PXR test set as compared with RP, RF, and SVM but may be useful for qualitative interpretion of interactions within the LBD. From this analysis, VolSurf descriptors and machine learning methods had good classification accuracy and made reliable predictions within the model applicability domain. These methods could be used for high throughput virtual screening to assess for PXR activation, prior to in vitro testing to predict potential drug-drug interactions.

The phytoestrogen coumestrol is a naturally occurring antagonist of the human pregnane X receptor.

Antagonizing the action of the human nuclear xenobiotic receptor pregnane X receptor (PXR) may have important clinical implications in preventing drug-drug interactions and improving therapeutic efficacy. We provide evidence that a naturally occurring phytoestrogen, coumestrol, is an antagonist of the nuclear receptor PXR (NR1I2). In transient transfection assays, coumestrol was able to suppress the agonist effects of SR12813 on human PXR activity. PXR activity was assessed and correlated with effects on the metabolism of the anesthetic tribromoethanol and on gene expression in primary human hepatocytes. We found that coumestrol was able to suppress the effects of PXR agonists on the expression of the known PXR target genes, CYP3A4 and CYP2B6, in primary human hepatocytes as well as inhibit metabolism of tribromoethanol in humanized PXR mice. Coumestrol at concentrations above 1.0 microm competed in scintillation proximity assays with a labeled PXR agonist for binding to the ligand-binding cavity. However, mammalian two-hybrid assays and transient transcription data using ligand-binding-cavity mutant forms of PXR show that coumestrol also antagonizes coregulator recruitment. This effect is likely by binding to a surface outside the ligand-binding pocket. Taken together, these data imply that there are antagonist binding site(s) for coumestrol on the surface of PXR. These studies provide the basis for development of novel small molecule inhibitors of PXR with the ultimate goal of clinical applications toward preventing drug-drug interactions.

Lignans, bacteriocides and organochlorine compounds activate the human pregnane X receptor (PXR).

The pregnane X receptor (PXR) mediates the induction of enzymes involved in steroid metabolism and xenobiotic detoxification. The receptor is expressed in liver and intestinal tissues and is activated by a wide range of compounds. The ability of a diverse range of dietary compounds to activate PXR-mediated transcription was assayed in HuH7 cells following transient transfection with human PXR (hPXR). The compounds investigated included phytochemicals such as lignans and phytoestrogens, organochlorine dietary contaminants such as polychlorinated biphenyls (PCBs) and triclosan and selected steroid, drug and herbal compounds. The hPXR activation at the top concentrations tested (10 microM) relative to the positive control 10 microM rifampicin ranged from 1.3% (trans-resveratrol) to 152% (ICI 182780). Hydroxylated compounds were marginally more potent than the parent compounds (tamoxifen activation was 74.6% whereas 4 hydroxytamoxifen activation was 84.2%) or significantly greater (vitamin D3 activation was 1.6%, while hydroxylated vitamin D3 activation was 55.6%). Enterolactone, the metabolite of common dietary lignans, was a medium activator of PXR (35.6%), compared to the lower activation of a parent lignan, secoisolariciresinol (20%). Two non-hydroxylated PCB congeners (PCB 118 and 153), which present a larger fraction of the PCB contamination of fatty foods, activated hPXR by 26.6% and 17%, respectively. The pesticide trans-nonachlor activation was 53.8%, while the widely used bacteriocide triclosan was a medium activator of hPXR at 46.2%. The responsiveness of PXR to activation by lignan metabolites suggests that dietary intake of these compounds may affect the metabolism of drugs that are CYP3A substrates. Additionally, the evidence that organochlorine chemicals, particularly the ubiquitous triclosan, activate hPXR suggests that these environmental chemicals may, in part, exhibit their endocrine disruptor activities by altering PXR-regulated steroid hormone metabolism with potential adverse health effects in exposed individuals.

Cucurbitacins are insect steroid hormone antagonists acting at the ecdysteroid receptor.

Two triterpenoids, cucurbitacins B and D, have been isolated from seeds of Iberis umbellata (Cruciferae) and shown to be responsible for the antagonistic activity of a methanolic extract of this species in preventing the 20-hydroxyecdysone (20E)-induced morphological changes in the Drosophila melanogaster BII permanent cell line. With a 20E concentration of 50 nM, cucurbitacins B and D give 50% responses at 1.5 and 10 microM respectively. Both cucurbitacins are able to displace specifically bound radiolabelled 25-deoxy-20-hydroxyecdysone (ponasterone A) from a cell-free preparation of the BII cells containing ecdysteroid receptors. The Kd values for cucurbitacins B and D (5 and 50 microM respectively) are similar to the concentrations required to antagonize 20E activity with whole cells. Cucurbitacin B (cucB) prevents stimulation by 20E of an ecdysteroid-responsive reporter gene in a transfection assay. CucB also prevents the formation of the Drosophila ecdysteroid receptor/Ultraspiracle/20E complex with the hsp27 ecdysteroid response element as demonstrated by gel-shift assay. This is therefore the first definitive evidence for the existence of antagonists acting at the ecdysteroid receptor. Preliminary structure/activity studies indicate the importance of the Delta23-22-oxo functional grouping in the side chain for antagonistic activity. Hexanorcucurbitacin D, which lacks carbon atoms C-22 to C-27, is found to be a weak agonist rather than an antagonist. Moreover, the side chain analogue 5-methylhex-3-en-2-one possesses weak antagonistic activity.