pregnane X receptor and constitutive androstane receptor modulate differently CYp3A-mediated metabolism in earlyand late-stage cholestasis

AIM To ascertain whether cholestasis affects the expression of two CYP3 A isoforms(CYP3 A1 and CYP3 A2) and of pregnane X receptor(PXR) and constitutive androstane receptor(CAR).METHODS Cholestasis was induced by bile duct ligation in 16 male Wistar rats; whereas 8 sham-operated rats were used as controls. Severity of cholestasis was assessed on histological examination of liver sections, and serum concentrations of albumin, AST, ALT, GGT, ALPK and bilirubin. Gene and protein expressions of PXR, CAR, CYP3 A1 and CYP3 A2 were assessed by means of q RT-PCR and Western blot, respectively. Alterations in CYP3 A activity were measured by calculating the kinetic parameters of 4-OH and 1'-OH-midazolam hydroxylation, marker reactions for CYP3 A enzymes.RESULTS The m RNA and protein expression of CYP3 A1 increased significantly in mild cholestasis(P < 0.01). At variance, m RNA and protein expression of CYP3 A2 didn't change in mild cholestasis, whereas the expression and activity of both CYP3 A1 and CYP3 A2 decreased dramatically when cholestasis became severe. Consistently with these observations, the nuclear expression of both PXR and CAR, which was measured because they both translocate into the cell nucleus after their activation, virtually disappeared in the late stage of cholestatic injury, after an initial increase. These results indicate that early-and late-stage cholestasis affects CYP3 Amediated drug metabolism differently, probably as consequence of the different activation of PXR and CAR.CONCLUSION Early-and late-stage cholestasis affects CYP3 Amediated drug metabolism differently. PXR and CAR might be targeted therapeutically to promote CYP3 Amediated liver detoxification.

Role of pregnane X-receptor in regulating bacterial translocation in chronic liver diseases

Bacterial translocation(BT) has been impeccably implicated as a driving factor in the pathogenesis of a spectrum of chronic liver diseases(CLD). Scientific evidence accumulated over the last four decades has implied that the disease pathologies in CLD and BT are connected as a loop in the gut-liver axis and exacerbate each other. Pregnane X receptor(PXR) is a ligandactivated transcription factor and nuclear receptor that is expressed ubiquitously along the gut-liver-axis. PXR has been intricately associated with the regulation of various mechanisms attributed in causing BT. The importance of PXR as the mechanistic linker molecule in the gutliver axis and its role in regulating bacterial interactions with the host in CLD has not been explored. Pub Med was used to perform an extensive literature search using the keywords PXR and bacterial translocation, PXR and chronic liver disease including cirrhosis. In an adequate expression state, PXR acts as a sensor for bile acid dysregulation and bacterial derived metabolites, and in response shapes the immune profile beneficial to the host. Activation of PXR could be therapeutic in CLD as it counter-regulates endotoxin mediated inflammation and maintains the integrity of intestinal epithelium. This review mainly focuses PXR function and its regulation in BT in the context of chronic liver diseases.

Steroidal and pregnane glycosides from Ypsilandra thibetica

The whole plants of Ypsilandra thibetica have been analyzed as part of a systematic study on saponin constituents of medicinal plants.This has resulted in the isolation of two new bisdesmosidic furostanol saponins,named ypsilandroside P(1)and ypsilandroside Q(2),and one new pregnane glycoside,named ypsilandroside R(3),together with nine known steroidal glycosides.Their structures were elucidated on the basis of extensive spectroscopic analysis,including that of 2D NMR data,and the results of acidic hydrolysis.Ypsilandroside P(1)was cytotoxicity against two human tumor cell lines.

Purification of full-length human Pregnane and Xenobiotic Receptor:polyclonal antibody preparation for immunological characterization

Pregnane and Xenobiotic Receptor (PXR; or Steroid and Xenobiotic Receptor, SXR), a new member of the nuclear receptor superfamily, is thought to modulate a network of genes that are involved in xenobiotic metabolism and elimination. To further explore the role of PXR in body’s homeostatic mechanisms, we for the first time, report successful prokary- otic expression and purification of full-length PXR and preparation of polyclonal antibody against the whole protein. The full-length cDNA encoding a 434 amino acids protein was sub-cloned into prokaryotic expression vector, pET-30b and transformed into E. coli BL21(DE3) cells for efficient over expression. The inclusion body fraction, containing the expressed recombinant protein, was purified first by solubilizing in sarcosine extraction buffer and then by affinity column chromatography using Ni-NTA His-Bind matrix. The efficacy of anti-PXR antibody was confirmed by immunocytology, Western blot analysis, EMSA and immunohistochemistry. The antibody obtained was capable of detecting human and mouse PXR with high specificity and sensitivity. Immunofluorescence staining of COS-1 cells transfected with human or mouse PXR showed a clear nuclear localization. Results from immunohistochemistry showed that level of PXR in liver sections is immunologically detectable in the nuclei. Similar to exogenously transfected PXR, Western blot analysis of cell extract from HepG2 and COLO320DM cells revealed a major protein band for endogenous PXR having the expected molecular weight of 50 kDa. Relevance of other immunodetectable bands with reference to PXR isoforms and current testimony are evaluated. Advantages of antibody raised against full-length PXR protein for functional characterization of receptor is discussed and its application for clinical purposes is envisaged.

A Novel Pregnane Glycoside from Biondia chinensis

A novel pregnane glycoside, biondianoside E, was isolated from the roots of Biondia chinensis. By the spectroscopic and chemical methods, this structure was elucidated as 3B, 5B, 14B, 205, 21-pentahydroxypregnane 3-O-B-D-glucopyranosyl-(1-4)-B-D-cymaropyranoside .

A New Pregnane Glycoside from Fermented Leaves of Agave americana

A new minor pregnane glycoside was isolated from the fermented leaves of Agave americana. Its structure was elucidated as (20S)-5a-pregnane-3? 20-diol 20-O--D-glucopyrano- side (1) by spectral methods.

Advances in drug resistance of triple negative breast cancer caused by pregnane X receptor

Breast cancer is the most common malignancy in women worldwide.Triplenegative breast cancer(TNBC),refers breast cancer negative for estrogen receptor,progesterone receptor and human epidermal growth factor receptor 2,characterized by high drug resistance,high metastasis and high recurrence,treatment of which is a difficult problem in the clinical treatment of breast cancer.In order to better treat TNBC clinically,it is a very urgent task to explore the mechanism of TNBC resistance in basic breast cancer research.Pregnane X receptor(PXR)is a nuclear receptor whose main biological function is to participate in the metabolism,transport and clearance of allobiological agents in PXR.PXR plays an important role in drug metabolism and clearance,and PXR is highly expressed in tumor tissues of TNBC patients,which is related to the prognosis of breast cancer patients.This reviews synthesized the important role of PXR in the process of high drug resistance to TNBC chemotherapeutic drugs and related research progress.

Microcantilever-based Nanomechanical Studies of the Orphan Nuclear Receptor Pregnane X Receptor-Ligand Interactions

Human pregnane X receptor (PXR) is of vital importance in pharmaceutical and exogenous compound metabolism within the body. This provides strong motivation for investigating this orphan receptor’s activation by various pharmaceuticals, xenobiotics, and endocrine disrupting chemicals (EDCs). A nanomechanical transducer is developed to study xenobiotic and EDC interactions with the bioreceptor PXR’s ligand binding domain (LBD). The combination of immobilized LBD PXR with a nanostructured microcantilever (MC) platform allows for the sensitive, label-free study of ligand interaction with the receptor. PXR shows real-time, reversible responses when exposed to a specific pharmaceutical, EDCs, and xenobiotic ligands. Three EDCs binding interactions are tested, which include phthalic acid, nonylphenol, and bisphenol A, with PXR. PXR LBD was exposed to rifampicin, a potent PXR activator, with various injection and recovery times to study their interaction. A two protein array of PXR and estrogen receptor ? (ER-?) directly compares the nanomechanical responses of these receptors with rifampicin on a single platform.

Activation of pregnane X receptor sensitizes alcoholic steatohepatitis by transactivating fatty acid binding protein 4

Alcoholic steatohepatitis (ASH) is a liver disease characterized by steatosis, inflammation, and necrosis of the liver tissue as a result of excessive alcohol consumption. Pregnane X receptor (PXR) is a xenobiotic nuclear receptor best known for its function in the transcriptional regulation of drug metabolism and disposition. Clinical reports suggested that the antibiotic rifampicin, a potent human PXR activator, is a contraindication in alcoholics, but the mechanism was unclear. In this study, we showed that the hepatic expression of fatty acid binding protein 4 (FABP4) was uniquely elevated in ASH patients and a mouse model of ASH. Pharmacological inhibiting FABP4 attenuated ASH in mice. Furthermore, treatment of mice with the mouse PXR agonist pregnenolon-16α-carbonitrile (PCN) induced the hepatic and circulating levels of FABP4 and exacerbated ASH in a PXR-dependent manner. Our mechanism study established FABP4 as a transcriptional target of PXR. Treatment with andrographolide, a natural compound and dual inhibitor of PXR and FABP4, alleviated mice from ASH. In summary, our results showed that the PXR-FABP4 gene regulatory axis plays an important role in the progression of ASH, which may have accounted for the contraindication of rifampicin in patients of alcoholic liver disease. Pharmacological inhibition of PXR and/or FABP4 may have its promise in the clinical management of ASH.

A New Pregnane from Munronia delavayi Franc （Meliaceae）

To search for pharmacologically active constituents of folk medicine, a new pregnane, 2α,3α,15β-trihydroxy-20（S）-tigloyl-pregnane （compound 1）, and nine known compounds, geranylgeraniol （compound 2）, β-daucosterol （compound 3）, 6-hydroxystigmast-4oen-3-one （compound 4）, sitoindoside Ⅰ （compound 5）, sitoindoside Ⅱ （compound 6）, β-sitosterol （compound 7）, kaempferol （compound 8）, quercetin （compound 9）, and rutin （compound 10）, were isolated from the ethanol extract of whole plants of Munronia delavayi Franch using chromatographic methods. The structures of compounds 1-10 were elucidated on the basis of spectral data.

Pregnane Glycosides from Stems of Marsdenia tenacissima

Objective To study the chemical constituents from the stems of Marsdenia tenacissima.Methods The chemical constituents were isolated by various column chromatography and their structures were identified by spectral and chemical analysis.Results Two pregnane glycosides were isolated from the stems of M.tenacissima and identified as 3-O-β-D-glucopyranosyl-(1→4)-6-deoxy-3-O-methyl-β-D-allopyranosyl-(1→4)-β-D-oleandropyranosyl-11α-O- tigloyltenacigenin B,named as tenacigenoside I(1)and 3-O-β-D-glucopyranosyl-(1→4)-6-deoxy-3-O-methyl-β-D- allopyranosyl-(1→4)-β-D-oleandropyranosyl-11α,12β-di-O-acetyltenacigenin B,named as tenacigenoside K(2).Conclusion Compound 1 is a new compound,1H-NMR and 13C-NMR data of compound 2 are reported for the first time.

The 3’-untranslated region contributes to the pregnane X receptor(PXR) expression downregulation by PXR ligands and up-regulation by glucocorticoids

Pregnane X receptor(PXR)is the major regulator of xenobiotic metabolism.PXR itself is controlled by various signaling molecules including glucocorticoids.Moreover,negative feed-back regulation has been proposed at the transcriptional level.We examined the involvement of the 3’-untranslated region(3’-UTR)of NR1I2 mRNA and microRNAs in PXR-and glucocorticoid receptor(GR)-mediated regulation of NR1I2 gene expression.PXR ligands were found to significantly downregulate NR1I2 mRNA expression in a set of 14 human hepatocyte cultures.Similarly,PXR was downregulated by PCN in the C57/BL6 mice liver.In mechanistic studies with the full-length 3’-UTR cloned into luciferase reporter or expression vectors,we showed that the 3’-UTR reduces PXR expression.From the miRNAs tested,miR-18a-5p inhibited both NR 112 expression and CYP3A4 gene induction.Importantly,we observed significant upregulation of miR-18a-5p expression 6 h after treatment with the PXR ligand rifampicin,which indicates a putative mechanism underlying NR1I2 negative feed-back regulation in hepatic cells.Additionally,glucocorticoids upregulated NR1I2 expression not only through the promoter region but also via 3’-UTR regulation,which likely involves downregulation of miR-18a-5p.We conclude that miR-18a-5p is involved in the down-regulation of NR1I2expression by its ligands and in the upregulation of NR1I2 mRNA expression by glucocorticoids in hepatic cells.

Pregnane X receptor： a double-edged sword

During the last decade, much progress has been made in exploring the mechanisms of alterations elicited by foreign compounds in xeno- and endobiotic metabolism regulated by the human nuclear pregnane X receptor （PXR）. PXR, identified as a human nuclear receptor in 1998 and generally regarded as a sensor activated by exogenous and endogenous chemicals, regulates a large number of enzymes and transporters involved in the response of mammals to their chemical environment.

Chemical basis of pregnane X receptor activators in the herbal supplement Gancao (licorice)

Background and aims:The herbal supplement Gancao,also known as licorice,belongs to the genus Glycyrrhiza and has been used worldwide for its hepatoprotective effect.Recent studies have raised concerns about potential herb-drug interactions associated with Gancao via pregnane X receptor(PXR)-mediated induction of hepatic cytochrome P4503A4(CYP3A4).The current work aimed to determine the phytochemicals in Gancao that activate PXR and induce CYP3A4.Methods:DPX2 cells were used for cell-based PXR reporter assays.The phytochemicals in Gancao extract were identified using a metabolomics approach.The effects of PXR activators identified from in vitro studies were further investigated in PXR-and CYP3A4-humanized mouse models.Results:Gancao was verified to be a PXR-activating herb.Two major phytochemicals in Gancao,gly-cyrrhizin(GZ)and glycyrrhetinic acid(GA),did not activate PXR in the cell-based reporter assays.However,glabridin was shown to activate PXR in a dose-dependent manner.In vivo studies confirmed that GZ is not a PXR activator and glabridin is a weak PXR activator.Although GA did not active PXR in vitro,it induced CYP3A4 expression in a PXR-dependent manner in the PXR-and CYP3A4-humanized mice.

Pregnane X receptor in drug-induced liver injury: Friend or foe?

The pregnane X receptor(PXR)is a ligand activated nuclear receptor that is highly expressed in the liver and regulates many cellular functions including drug metabolism,endobiotic metabolism,oxidative stress response,apoptosis,inflammation,cell proliferation and regeneration.PXR activation promotes drug-induced liver injury(DILI)through its ability to increase the expression of phaseⅠand phaseⅡdrug metabolizing enzymes.The PXR also increases lipid synthesis and fatty acid uptake into the liver,leading to lipid accumulation and steatosis.In recent years,PXR has been explored as an important target in DILI and liver diseases.This review will highlight the roles of PXR in modulating DILI.PXR polymorphisms that have been associated with DILI will also be discussed.

Interaction of Hepatitis B Virus X Protein with the Pregnane X Receptor Enhances the Synergistic Effects of Aflatoxin B1 and Hepatitis B Virus on Promoting Hepatocarcinogenesis

Background and Aims:Hepatitis B virus(HBV)infection has been found to increase hepatocellular sensitivity to carcinogenic xenobiotics,by unknown mechanisms,in the generation of hepatocellular carcinoma.The pregnane X receptor(PXR)is a key regulator of the body’s defense against xenobiotics,including xenobiotic carcinogens and clinical drugs.In this study,we aimed to investigate the molecular mechanisms of HBV X protein(HBx)-PXR signaling in the synergistic effects of chemical carcinogens in HBV-associated hepatocarcinogenesis.Methods:The expression profile of PXR-cytochrome p4503A4(CYP3A4)signaling was determined by PCR,western blotting,and tissue microarray.Cell viability and aflatoxin B1(AFB1)cytotoxicity were measured using the cell counting kit-8 assay.Target gene expression was evaluated using transient transfection and real time-PCR.The genotoxicity of AFB1 was assessed in newborn mice with a single dose of AFB1.Results:HBx enhanced the hepatotoxicity of AFB1 by activating CYP3A4 and reducing glutathione Stransferase Mu 1(GSTM1)in cell lines.Activation of PXR by pregnenolone 16α-carbonitrile increased AFB1-induced liver tumor incidence by up-regulating oncogenic KRAS to enhance interleukin(IL)-11:IL-11 receptor subunit alpha-1(IL11RA-1)-mediated inflammation in an HBx transgenic model.Conclusions:Our finding regarding AFB1 toxicity enhancement by an HBx-PXR-CYP3A4/GSTM1-KRASIL11:IL11RA signaling axis provides a rational explanation for the synergistic effects of chemical carcinogens in HBV infection-associated hepatocarcinogenesis.

激活核受体PXR促进小鼠GM-CSF来源的树突状细胞的分化

目的:研究孕烷受体(PXR)激动剂pregnane-16α-carbonitrile(PCN)对小鼠GM-CSF来源树突状细胞(DC)分化的影响。方法:建立小鼠DC体外GM-CSF和IL-4诱导分化体系,并用PCN对体系进行处理。流式细胞术检测CD11c+DC的比例;ELISA和流式细胞术检测DC产生细胞因子IFN-γ、IL-1、IL-2和IL-12的量;实时荧光定量聚合酶链反应(Real-time RT-PCR)检测调控DC分化相关信号通路基因的表达。结果:成功建立小鼠DC体外分化体系;PCN处理能显著促进DC分化,且DC产生的细胞因子IFN-γ和IL-2的量显著增多;Real-time RT-PCR检测结果表明,与对照组相比,PCN处理组中调控DC分化的Notch和Wnt信号通路相关基因HES1、WISP1和WISP2的表达量显著上升。结论:PXR激动剂PCN能显著促进小鼠GM-CSF来源的DC的分化及其IFN-γ和IL-2的产量,并且这种促进作用可能是通过Notch和Wnt信号通路进行调控。

Hepatic drug transporters and nuclear receptors:Regulation by therapeutic agents

The canalicular membrane represents the excretory pole of hepatocytes.Bile is an important route of elimination of potentially toxic endo-and xenobiotics(including drugs and toxins),mediated by the major canalicular transporters:multidrug resistance protein 1(MDR1, ABCB1),also known as P-glycoprotein,multidrug resistance-associated protein 2(MRP2,ABCC2),and the breast cancer resistance protein(BCRP,ABCG2).Their activities depend on regulation of expression and proper localization at the canalicular membrane,as regulated by transcriptional and post-transcriptional events,respectively.At transcriptional level,specific nuclear receptors(NR)s modulated by ligands,co-activators and co-repressors,mediate the physiological requirements of these transporters.This complex system is also responsible for alterations occurring in specific liver pathologies.We briefly describe the major ClassⅡNRs, pregnane X receptor(PXR)and constitutive androstane receptor(CAR),and their role in regulating expression of multidrug resistance proteins.Several therapeutic agents regulate the expression of relevant drug transporters through activation/inactivation of these NRs.We provide some representative examples of the action of therapeutic agents modulating liver drug transporters, which in addition,involve CAR or PXR as mediators.

Lithocholic acid induction of the FGF19 promoter in intestinal cells is mediated by PXR

To study the effect of the toxic secondary bile acid lithocholic acid （LCA） on the expression of fibroblast growth factor 19 （FGF19） in intestinal cells and to characterize the pregnane-X-receptor （PXR） response of the FGF19 promoter region. METHODS： The intestinal cell line LS174T was stimulated with various concentrations of chenodeoxy- cholic acid and lithocholic acid for several time points. FGF19 mRNA levels were determined with quantitative realtime RT-PCR. FGF19 deletion promoter constructs were generated and the LCA response was analzyed in reporter assays. Co-transfections with PXR and RXR were carried out to study FGF19 regulation by these factors, RESULTS： LCA and CDCA strongly up-regulate FGF19 mRNA expression in LS174T cells in a time and dose dependent manner. Using reporter gene assays with several deletion constructs we found that the LCA responsive element in the human FGF19 promoter maps to the proximal regulatory region containing two poten- tial binding sites for PXR. Overexpression of PXR and its dimerization partner retinoid X receptor （RXR） and stimulation with LCA or the potent PXR ligand rifampicin leads to a significant induction of FGF19 promoter activ- ity in intestinal cells. CONCLUSION： LCA induced feedback inhibition of bile acid synthesis in the liver is likely to be regulated by PXR inducing intestinal FGF19 expression.

Effects of flavonoids derived from Taxus yunnanensis on p-glycoprotein and cytochrome P450 3A4

The intestinal uptake of paclitaxel is hampered by trans-membrane efflux transporters such as P-glycoprotein(P-gp),and paclitaxel is mainly metabolized by cytochrome P4503A4(CYP3A4)presented in the liver.Our previous results demonstrated that flavonoids extracted from Taxus yunnanensis could improve the oral absorption of paclitaxel.The current study was purposed to investigate the effects of the flavonoid extracts on P-gp and CYP3A4 in vitro.The expression and activity of P-gp were detected by western blotting and intracellular rhodamine 123 accumulation assay in Caco-2 cells treated with the flavonoids extract.The expression of CYP3A4 was investigated by western blotting in mouse primary hepatocytes and the activity of CYP3A4 was detected by LC-MS/MS method using rat liver microsomes.Our results showed that the flavonoid extracts from T.yunnanensis could inhibit P-gp activity and concurrently decrease the expression and activity of CYP3A4.In conclusion,activity of P-gp and CYP3A4 could be inhibited by flavonoids extracted from T.yunnanensis which might be potential candidates for development of oral formulation of paclitaxel.