Pregnane X receptor and constitutive androstane receptor at the crossroads of drug metabolism and energy metabolism

Discovery of Highly Potent Solute Carrier 13 Member 5 (SLC13A5) Inhibitors for the Treatment of Hyperlipidemia

In the face of escalating metabolic disease prevalence, largely driven by modern lifestyle factors, this study addresses the critical need for novel therapeutic approaches. We have identified the sodium-coupled citrate transporter (NaCT or SLC13A5) as a target for intervention. Utilizing rational drug design, we developed a new class of SLC13A5 inhibitors, anchored by the hydroxysuccinic acid scaffold, refining the structure of PF-06649298. Among these, LBA-3 emerged as a standout compound, exhibiting remarkable potency with an IC50 value of 67 nM, significantly improving upon PF-06649298. In vitro assays demonstrated LBA-3's efficacy in reducing triglyceride levels in OPA-induced HepG2 cells. Moreover, LBA-3 displayed superior pharmacokinetic properties and effectively lowered triglyceride and total cholesterol levels in diverse mouse models (PCN-stimulated and starvation-induced), without detectable toxicity. These findings not only spotlight LBA-3 as a promising candidate for hyperlipidemia treatment but also exemplify the potential of targeted molecular design in advancing metabolic disorder therapeutics.

Effects of intermittent fasting on the histology and mRNA expression of major drug-metabolizing cyp450s in the liver of diabetic mice

Introduction:There is a variation in drug response among patients who practice intermittent fasting. Alteration in the expression of drug-metabolizing enzymes (DMEs) can affect the pharmacokinetics and drug response.Aims: This research aimed to determine the effect of intermittent fasting on the mRNA expression of major drug-metabolizing cyp450s in the liver of diabetic mice.Methods: Thirty-two male Balb/c mice were divided into four groups; control, nonfasting diabetic, non-diabetic fasting, and diabetic fasting mice. Insulin-dependent diabetes was induced in mice by a single high-dose (250 mg/kg) streptozocin. Mice of non-diabetic and diabetic fasting groups were subjected to 10-day intermittent fasting for 17 hours daily. Then, the mRNA expression of mouse phase I DMEs cyp1a1, cyp2c29, cyp2d9, and cyp3a11 was analyzed using real-time polymerase chain reaction. In addition, the liver of mice in all groups was examined for pathohistological alterations.Results: Diabetes downregulated the mRNA expression of hepatic drug-metabolizing cyp450s in diabetic mice, while intermittent fasting significantly (P < 0.05) increased it. Also, cyp2d9 and cyp3a11 were upregulated in the liver of diabetic fasting mice. These alterations in the gene expression were correlated with the pathohistological alterations, where livers of diabetic mice showed dilatation in the blood sinusoids and inflammatory cells leukocyte infiltrations. Whereas livers of diabetic fasting mice showed almost comparable histological findings to control mice.Conclusions: Intermittent fasting can protect the liver against diabetes-induced hepatotoxicity and the down-regulation of DME genes in the diabetic liver. These results can explain, at least partly, the inter-individual variation in the drug response during practicing fasting.

Bempedoic Acid Unveils Therapeutic Potential in Non-Alcoholic Fatty Liver Disease: Suppression of the Hepatic PXR-SLC13A5/ACLY Signaling Axis

The hepatic SLC13A5/SLC25A1-ATP-dependent citrate lyase (ACLY) signaling pathway, responsible for maintaining the citrate homeostasis, plays a crucial role in the pathogenesis of non-alcoholic fatty liver disease (NAFLD). Bempedoic acid (BA), an ACLY inhibitor commonly used for managing hypercholesterolemia, has shown promising results in addressing hepatic steatosis. This study aimed to elucidate the intricate relationships in processes of hepatic lipogenesis among SLC13A5, SLC25A1, and ACLY and to examine the therapeutic potential of BA in NAFLD, providing insights into its underlying mechanism. In murine primary hepatocytes and HepG2 cells, the silencing or pharmacological inhibition of SLC25A1/ACLY resulted in significant upregulation of SLC13A5 transcription and activity. This increase in SLC13A5 activity subsequently led to enhanced lipogenesis, indicating a compensatory role of SLC13A5 when the SLC25A1/ACLY pathway was inhibited. However, BA effectively counteracted this upregulation, reduced lipid accumulation, and ameliorated various biomarkers of NAFLD. The disease-modifying effects of BA were further confirmed in NAFLD mice. Mechanistic investigations revealed that BA could reverse the elevated transcription levels of SLC13A5 and ACLY, and the subsequent lipogenesis induced by PXR activation in vitro and in vivo. Importantly, this effect was diminished when PXR was knocked down, suggesting the involvement of the hepatic PXR-SLC13A5/ACLY signaling axis in the mechanism of BA action. In conclusion, SLC13A5-mediated extracellular citrate influx emerges as an alternative pathway to SLC25A1/ACLY in the regulation of lipogenesis in hepatocytes, BA exhibits therapeutic potential in NAFLD by suppressing the hepatic PXR-SLC13A5/ACLY signaling axis, while PXR, a key regulator in drug metabolism may be involved in the pathogenesis of NAFLD. SIGNIFICANCE STATEMENT: This work describes that bempedoic acid, an ATP-dependent citrate lyase (ACLY) inhibitor, ameliorates hepatic lipid accumulation and various hallmarks of non-alcoholic fatty liver disease. Suppression of hepatic SLC25A1-ACLY pathway upregulates SLC13A5 transcription, which in turn activates extracellular citrate influx and the subsequent DNL. Whereas in hepatocytes or the liver tissue challenged with high energy intake, bempedoic acid reverses compensatory activation of SLC13A5 via modulating the hepatic PXR-SLC13A5/ACLY axis, thereby simultaneously downregulating SLC13A5 and ACLY.

Estrogenic and non-estrogenic effects of bisphenol A and its action mechanism in the zebrafish model: An overview of the past two decades of work

Bisphenol A (BPA) is the most simple and predominant component of the Bisphenol family. BPA is widely present in the environment and the human body as a result of its extensive usage in the plastic and epoxy resins of consumer goods like water bottles, food containers, and tableware. Since the 1930s, when BPA's estrogenic activity was first observed, and it was labeled as a "mimic hormone of E2", studies on the endocrine-disrupting effects of BPA then have been widely conducted. As a top vertebrate model for genetic and developmental studies, the zebrafish has caught tremendous attention in the past two decades. By using the zebrafish, the negative effects of BPA either through estrogenic signaling pathways or non-estrogenic signaling pathways were largely found. In this review, we tried to draw a full picture of the current state of knowledge on the estrogenic and non-estrogenic effects of BPA with their mechanisms of action through the zebrafish model of the past two decades, which may help to fully understand the endocrine-disrupting effects of BPA and its action mechanism, and give a direction for the future studies.

Xenobiotic Receptors, a Journey of Rewards

The xenobiotic nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) were discovered or characterized in 1998. PXR and CAR have since been defined as master regulators of xenobiotic responses through their transcriptional regulation of drug-metabolizing enzymes and transporters. This article aims to provide an overview on the discovery of PXR and CAR as xenobiotic receptors.

Mixture effects of co-formulants and two plant protection products in a liver cell line

Plant protection products (PPPs) consist of one or more active substances and several co-formulants. Active substances provide the functionality of the PPP and are consequently evaluated according to standard test methods set by legal data requirements before approval, whereas co-formulants' toxicity is not as comprehensively assessed. However, in some cases mixture effects of active substances and co-formulants might result in increased or different forms of toxicity. In a proof-of-concept study we hence built on previously published results of Zahn et al. (2018[38]) on the mixture toxicity of Priori Xtra^® and Adexar^® to specifically investigate the influence of co-formulants on the toxicity of these commonly used fungicides. Products, their respective active substances in combination as well as some co-formulants were applied to human hepatoma cell line (HepaRG) in several dilutions. Cell viability analysis, mRNA expression, abundance of xenobiotic metabolizing enzymes and intracellular concentrations of active substances determined by LC-MS/MS analyses demonstrated that the toxicity of the PPPs is influenced by the presence of co-formulants in vitro. PPPs were more cytotoxic than the mix of their active substances. Gene expression profiles of cells treated with the PPPs were similar to those treated with their respective mixture combinations with marked differences. Co-formulants can cause gene expression changes on their own. LC-MS/MS analyses revealed higher intracellular concentrations of active substances in cells treated with PPPs compared to those treated with the respective active substances' mix. Proteomic data showed co-formulants can induce ABC transporters and CYP enzymes. Co-formulants can contribute to the observed increased toxicity of PPPs compared to their active substances in combination due to kinetic interactions, necessitating a more comprehensive evaluation approach.

Short-Term High-Fat Diet Alters Acetaminophen Metabolism in Healthy Individuals

BACKGROUND

Acetaminophen is metabolized through a nontoxic sulfation and glucuronidation pathway and toxic oxidation pathway (via CYP2E1 and CYP1A2). A short-term high-fat diet induces alterations in the steatotic liver and may alter hepatic drug enzyme activity. In the case of acetaminophen, these alterations may result in an increased risk of hepatotoxicity. Therefore, this study was conducted to assess the effect of a 3-day hypercaloric high-fat diet on the plasma levels of acetaminophen metabolites.

METHODS

Nine healthy subjects participated in this randomized, crossover intervention study. The subjects consumed a regular diet or a regular diet supplemented with 500 mL of cream (1700 kcal) for 3 days and then fasted overnight. After ingesting 1000-mg acetaminophen, the plasma concentration of acetaminophen (APAP) and its metabolites [acetaminophen glucuronide, acetaminophen sulfate, 3-cysteinyl-acetaminophen, and 3-(N-acetyl-L-cystein-S-yl)-acetaminophen, and 3-methoxy-acetaminophen] were measured.

RESULTS

The 3-day high-fat diet increased the extrapolated area under the concentration-time curve from 0 to infinity (area under the curve 0-inf ) of APAP-Cys by approximately 20% ( P = 0.02) and that from 0 to 8 hours (area under the curve 0-8 ) of APAP-Cys-NAC by approximately 39% ( P = 0.01). The 3-day high-fat diet did not alter the pharmacokinetic parameters of the parent compound acetaminophen and other metabolites.

CONCLUSIONS

A short-term, hypercaloric, high-fat diet increases the plasma levels of the APAP metabolites formed by the oxidation pathway, which may increase the risk of hepatotoxicity.

Role of nuclear receptor PXR in immune cells and inflammatory diseases

Pregnane X receptor (PXR, NR1I2), a prototypical member of the nuclear receptor superfamily, has been implicated in various processes including metabolism, immune response, and inflammation. The immune system is made up of many interdependent parts, including lymphoid organs, cells, and cytokines, which play important roles in identifying, repelling, and eliminating pathogens and other foreign chemicals. An impaired immune system could contribute to various physical dysfunction, including severe infections, allergic diseases, autoimmune disorders, and other inflammatory diseases. Recent studies revealed the involvement of PXR in the pathogenesis of immune disorders and inflammatory responses. Thus, the aim of this work is to review and discuss the advances in research associated with PXR on immunity and inflammatory diseases and to provide insights into the development of therapeutic interventions of immune disorders and inflammatory diseases by targeting PXR.

Gestational Diabetes Sensitizes Mice to Future Metabolic Syndrome That Can Be Relieved by Activating CAR

Diabetes and related metabolic syndrome are common metabolic disorders. Gestational diabetes mellitus (GDM) is rather prevalent in the clinic. Although most GDM resolves after therapeutic intervention and/or after delivery, the long-term health effect of GDM remains to be better understood. The constitutive androstane receptor (CAR), initially characterized as a xenobiotic receptor, was more recently proposed to be a therapeutic target for obesity and type 2 diabetes mellitus (T2DM). In this study, high-fat diet (HFD) feeding was used to induce GDM. Upon delivery, GDM mice were returned to chow diet until the metabolic parameters were normalized. Parous non-GDM control females or metabolically normalized GDM females were then subjected to HFD feeding to induce nongestational obesity and T2DM. Our results showed that GDM sensitized mice to metabolic abnormalities induced by a second hit of HFD. Treatment with the CAR agonist 1,4-bis [2-(3,5 dichloropyridyloxy)] benzene efficiently attenuated GDM-sensitized and HFD-induced obesity and T2DM, including decreased body weight, improved insulin sensitivity, inhibition of hyperglycemia and hepatic steatosis, increased oxygen consumption, and decreased adipocyte hypertrophy. In conclusion, our results have established GDM as a key risk factor for the future development of metabolic disease. We also propose that CAR is a therapeutic target for the management of metabolic disease sensitized by GDM.

Role of Bile Acids and Nuclear Receptors in Acupuncture in Improving Crohn's Disease

Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the transcription of target genes. Bile acids (BAs) can be used as effector molecules to regulate physiological processes in the gut, and NRs are important receptors for bile acid signaling. Relevant studies have shown that NRs are closely related to the occurrence of Crohn's disease (CD). Although the mechanism of NRs in CD has not been clarified completely, growing evidence shows that NRs play an important role in regulating intestinal immunity, mucosal barrier, and intestinal flora. NRs can participate in the progress of CD by mediating inflammation, immunity, and autophagy. As the important parts of traditional Chinese medicine (TCM) therapy, acupuncture and moxibustion in the treatment of CD curative mechanism can get a lot of research support. At the same time, acupuncture and moxibustion can regulate the changes of related NRs. Therefore, to explore whether acupuncture can regulate BA circulation and NRs expression and then participate in the disease progression of CD, a new theoretical basis for acupuncture treatment of CD is provided.

Implication of Intestinal Barrier Dysfunction in Gut Dysbiosis and Diseases

The intestinal mucosal barrier, also referred to as intestinal barrier, is widely recognized as a critical player in gut homeostasis maintenance as it ensures the complex crosstalk between gut microbes (both commensals and pathogens) and the host immune system. Highly specialized epithelial cells constantly cope with several protective and harmful agents to maintain the multiple physiological functions of the barrier as well as its integrity. However, both genetic defects and environmental factors can break such equilibrium, thus promoting gut dysbiosis, dysregulated immune-inflammatory responses, and even the development of chronic pathological conditions. Here, we review and discuss the molecular and cellular pathways underlying intestinal barrier structural and functional homeostasis, focusing on potential alterations that may undermine this fine balance.

Pharmacogenomics of statins: lipid response and other outcomes in Brazilian cohorts

Statins are inhibitors of 3-hydroxy-3-methylglutaryl-CoA reductase, a key enzyme in cholesterol biosynthesis, that are highly effective in reducing plasma low-density lipoprotein (LDL) cholesterol and decreasing the risk of cardiovascular events. In recent years, a multitude of variants in genes involved in pharmacokinetics (PK) and pharmacodynamics (PD) have been suggested to influence the cholesterol-lowering response. However, the vast majority of studies have analyzed the pharmacogenetic associations in populations in Europe and the USA, whereas data in other populations, including Brazil, are mostly lacking. This narrative review provides an update of clinical studies on statin pharmacogenomics in Brazilian cohorts exploring lipid-lowering response, adverse events and pleiotropic effects. We find that variants in drug transporter genes (SLCO1B1 and ABCB1) positively impacted atorvastatin and simvastatin response, whereas variants in genes of drug metabolizing enzymes (CYP3A5) decreased response. Furthermore, multiple associations of variants in PD genes (HMGCR, LDLR and APOB) with statin response were identified. Few studies have explored statin-related adverse events, and only ABCB1 but not SLCO1B1 variants were robustly associated with increased risk in Brazil. Statin-related pleiotropic effects were shown to be influenced by variants in PD (LDLR, NR1H2) and antioxidant enzyme (NOS3, SOD2, MTHFR, SELENOP) genes. The findings of these studies indicate that statin pharmacogenomic associations are distinctly different in Brazil compared to other populations. This review also discusses the clinical implications of pharmacogenetic studies and the rising importance of investigating rare variants to explore their association with statin response.

Coumarin Derivatives in Inflammatory Bowel Disease

Inflammatory bowel disease (IBD) is a non-communicable disease characterized by a chronic inflammatory process of the gut and categorized into Crohn’s disease and ulcerative colitis, both currently without definitive pharmacological treatment and cure. The unclear etiology of IBD is a limiting factor for the development of new drugs and explains the high frequency of refractory patients to current drugs, which are also related to various adverse effects, mainly after long-term use. Dissatisfaction with current therapies has promoted an increased interest in new pharmacological approaches using natural products. Coumarins comprise a large class of natural phenolic compounds found in fungi, bacteria, and plants. Coumarin and its derivatives have been reported as antioxidant and anti-inflammatory compounds, potentially useful as complementary therapy of the IBD. These compounds produce protective effects in intestinal inflammation through different mechanisms and signaling pathways, mainly modulating immune and inflammatory responses, and protecting against oxidative stress, a central factor for IBD development. In this review, we described the main coumarin derivatives reported as intestinal anti-inflammatory products and its available pharmacodynamic data that support the protective effects of these products in the acute and subchronic phase of intestinal inflammation.

PXR-ABC drug transporters/CYP-mediated ursolic acid transport and metabolism in vitro and vivo

The transporting kinetics and metabolic kinetics of ursolic acid were studied in transgenic cell models. Then, the pharmacokinetics features of ursolic acid and the expression of ATP-binding cassette transporters (ABC transporter) and cytochrome P450 (CYP) enzymes in tissues after pregnane X receptor (PXR) activation by 5-pregnen-3β-ol-20-one-16α-carbonitrile (PCN) were investigated in rats. After silencing of PXR in Caco2-siRNA-PXR cells, there was a decrease in the protein abundance of P-glycoprotein, breast cancer-resistant protein, multidrug resistance-associated protein 2 (MRP2), and CYP2C9. The apparent permeability (PDR) values of 10, 20, and 50 µM ursolic acid in Caco2 cells were 2.19 ± 0.44, 1.40 ± 0.17, and 1.25 ± 0.07, respectively, whereas in Caco2-siRNA-PXR cells, they were 1.85 ± 0.36, 1.24 ± 0.11, and 1.19 ± 0.04, respectively. PXR-RXRα would significantly activate ABC transporter expression in Caco2 cells. Compared with Caco2 cells, when the concentrations of ursolic acid were 10, 20, and 50 µM, the PDR values increased in Caco2-PXR-RXRα cells after PXR activation: 1.60 ± 0.31 versus 1.97 ± 0.21, 1.46 ± 0.08 versus 2.01 ± 0.19, and 1.32 ± 0.26 versus 2.09 ± 0.22, respectively. Simultaneously, PXR-RXRα would activate the expression of CYP2C9; metabolic kinetics of ursolic acid in CYP metabolizing enzyme lysate of Caco2 cells and Caco2-PXR-RXR cells was studied and it was found that the Km values were 81.99 ± 44.32 and 60.05 ± 29.62 µg/ml, and Vmax values were 3.77 ± 0.86 and 3.41 ± 0.96 µg · ml-1  · min-1 , respectively. However, in human CYP metabolizing recombinase, we found that both CYP2C9 and CYP34A were involved in the metabolism of ursolic acid. Vm and Km values for CYP3A4 and CYP2C9 were 3.57 ± 1.12 µg · ml-1  · min-1 and 81.71 ± 18.38 µg/ml, 3.85 ± 1.46 µg · ml-1  · min-1 and 62.18 ± 14.56 µg/ml, respectively. As a strong agonist for mouse pxr, PCN could significantly affect pharmacokinetics of ursolic acid in rats, and it showed discrepant effects on messenger RNA expression of cyp and transporters in tissues.

Influence of Single Nucleotide Polymorphisms on Rifampin Pharmacokinetics in Tuberculosis Patients

Rifampin (RF) is metabolized in the liver into an active metabolite 25-desacetylrifampin and excreted almost equally via biliary and renal routes. Various influx and efflux transporters influence RF disposition during hepatic uptake and biliary excretion. Evidence has also shown that Vitamin D deficiency (VDD) and Vitamin D receptor (VDR) polymorphisms are associated with tuberculosis (TB). Hence, genetic polymorphisms of metabolizing enzymes, drug transporters and/or their transcriptional regulators and VDR and its pathway regulators may affect the pharmacokinetics of RF. In this narrative review, we aim to identify literature that has explored the influence of single nucleotide polymorphisms (SNPs) of genes encoding drug transporters and their transcriptional regulators (SLCO1B1, ABCB1, PXR and CAR), metabolizing enzymes (CES1, CES2 and AADAC) and VDR and its pathway regulators (VDR, CYP27B1 and CYP24A1) on plasma RF concentrations in TB patients on antitubercular therapy. Available reports to date have shown that there is a lack of any association of ABCB1, PXR, CAR, CES1 and AADAC genetic variants with plasma concentrations of RF. Further evidence is required from a more comprehensive exploration of the association of SLCO1B1, CES2 and Vitamin D pathway gene variants with RF pharmacokinetics in distinct ethnic groups and a larger population to reach conclusive information.

Phase 0 of the Xenobiotic Response: Nuclear Receptors and Other Transcription Factors as a First Step in Protection from Xenobiotics

This mini-review examines the crucial importance of transcription factors as a first line of defense in the detoxication of xenobiotics. Key transcription factors that recognize xenobiotics or xenobiotic-induced stress such as reactive oxygen species (ROS), include AhR, PXR, CAR, MTF, Nrf2, NF-κB, and AP-1. These transcription factors constitute a significant portion of the pathways induced by toxicants as they regulate phase I-III detoxication enzymes and transporters as well as other protective proteins such as heat shock proteins, chaperones, and anti-oxidants. Because they are often the first line of defense and induce phase I-III metabolism, could these transcription factors be considered the phase 0 of xenobiotic response?

Transcriptomic responses of hypothalamus to acute exercise in type 2 diabetic Goto-Kakizaki rats

The hypothalamus has an integral role in energy homeostasis regulation, and its dysfunctions lead to the development of type 2 diabetes (T2D). Physical activity positively affects the prevention and treatment of T2D. However, there is not much information on the adaptive mechanisms of the hypothalamus. In this study, RNA sequencing was used to determine how acute exercise affects hypothalamic transcriptome from both type 2 diabetic Goto-Kakizaki (GK) and control Wistar rats with or without a single session of running (15 m/min for 60 min). Through pairwise comparisons, we identified 957 differentially expressed genes (DEGs), of which 726, 197, and 98 genes were found between GK and Wistar, exercised GK and GK, and exercised Wistar and Wistar, respectively. The results of Gene Ontology and Kyoto Encyclopedia of Genes and Genomes pathway enrichment revealed that lipid metabolism-related terms and pathways were enriched in GK and exercised GK rats, and nervous system related terms and pathways were enriched in exercised GK and Wistar rats. Furthermore, 45 DEGs were associated with T2D and related phenotypes according to the annotations in the Rat Genome Database. Among these 45 DEGs, several genes (Plin2, Cd36, Lpl, Wfs1, Cck) related to lipid metabolism or the nervous system are associated with the exercise-induced benefits in the hypothalamus of GK rats. Our findings might assist in identifying potential therapeutic targets for T2D prevention and treatment.

Sex Hormone-Binding Globulin Expression Correlates With Acetyl-Coenzyme A Carboxylase and Triglyceride Content in Human Liver

CONTEXT

There is emerging evidence that SHBG is substantially reduced in chronic metabolic diseases, including obesity and nonalcoholic fatty liver disease (NAFLD). We have recently reported, through use of in vitro (HepG2 cells) and in vivo (SHBG-C57BL/ksJ-db/db mice) models, that SHBG could play a role in arresting the progression of NAFLD by downregulating lipogenesis.

OBJECTIVE

The main aim of this study was to investigate the mechanisms by which SHBG prevents hepatic lipogenesis by examining the relationship between SHBG and a key lipogenic enzyme, such as acetyl-coenzyme A carboxylase (ACC) in the liver of obese persons.

PARTICIPANTS AND METHODS

SHBG and ACC mRNA levels, as well as triglyceride content, were analyzed in 41 liver samples from nondiabetic obese patients with NAFLD who had undergone bariatric surgery. We also studied the effect of SHBG overexpression in HepG2 cells cultured under high-glucose conditions.

RESULTS

SHBG mRNA and protein levels were lower in patients with metabolic syndrome than in those without metabolic syndrome; however, these differences were significant only for mRNA level. SHBG mRNA levels correlated positively with SHBG protein levels and hepatic triglyceride content. In addition, SHBG mRNA and protein levels correlated negatively with ACC mRNA levels and triglyceride content. Furthermore, SHBG overexpression abrogated the increase in ACC expression induced by high-glucose treatment in HepG2 cells.

CONCLUSIONS

Our findings suggest that SHBG plays a role in regulating hepatic lipogenesis by reducing ACC levels. These results suggest a strategy for the treatment of NAFLD.

Regulation of Hepatic Long Noncoding RNAs by Pregnane X Receptor and Constitutive Androstane Receptor Agonists in Mouse Liver

Altered expression of long noncoding RNAs (lncRNAs) by environmental chemicals modulates the expression of xenobiotic biotransformation-related genes and may serve as therapeutic targets and novel biomarkers of exposure. The pregnane X receptor (PXR/NR1I2) is a critical xenobiotic-sensing nuclear receptor that regulates the expression of many drug-processing genes, and it has similar target-gene profiles and DNA-binding motifs with another xenobiotic-sensing nuclear receptor, namely, constitutive andronstrane receptor (CAR/Nr1i3). To test our hypothesis that lncRNAs are regulated by PXR in concert with protein-coding genes (PCGs) and to compare the PXR-targeted lncRNAs with CAR-targeted lncRNAs, RNA-Seq was performed from livers of adult male C57BL/6 mice treated with corn oil, the PXR agonist PCN, or the CAR agonist 1, 4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP). Among 125,680 known lncRNAs, 3843 were expressed in liver, and 193 were differentially regulated by PXR (among which 40% were also regulated by CAR). Most PXR- or CAR-regulated lncRNAs were mapped to the introns and 3'-untranslated regions (UTRs) of PCGs, as well as intergenic regions. Combining the RNA-Seq data with a published PXR chromatin immunoprecipitation coupled with high-throughput sequencing; cytochrome P450 (P450; ChIP-Seq) data set, we identified 774 expressed lncRNAs with direct PXR-DNA binding sites, and 26.8% of differentially expressed lncRNAs had changes in PXR-DNA binding after PCN exposure. De novo motif analysis identified colocalization of PXR with liver receptor homolog (LRH-1), which regulates bile acid synthesis after PCN exposure. There was limited overlap of PXR binding with an epigenetic mark for transcriptional activation (histone-H3K4-di-methylation, H3K4me2) but no overlap with epigenetic marks for transcriptional silencing [H3 lysine 27 tri-methylation (H3K27me3) and DNA methylation]. Among differentially expressed lncRNAs, 264 were in proximity of PCGs, and the lncRNA-PCG pairs displayed a high coregulatory pattern by PXR and CAR activation. This study was among the first to demonstrate that lncRNAs are regulated by PXR and CAR activation and that they may be important regulators of PCGs involved in xenobiotic metabolism.

Nuclear Receptors in the Pathogenesis and Management of Inflammatory Bowel Disease

Nuclear receptors (NRs) are ligand-dependent transcription factors that regulate the transcription of target genes. Previous epidemiological and genetic studies have documented the association of NRs with the risk of inflammatory bowel disease (IBD). Although the mechanisms of action of NRs in IBD have not been fully established, accumulating evidence has demonstrated that NRs play complicated roles in regulating intestinal immunity, mucosal barriers, and intestinal flora. As one of the first-line medications for the treatment of IBD, 5-aminosalicylic acid (5-ASA) activates peroxisome proliferator-activated receptor gamma (PPARγ) to attenuate colitis. The protective roles of rifaximin and rifampicin partly depend on promoting pregnane X receptor (PXR) expression. The aims of this review are to discuss the roles of several important NRs, such as PPARγ, PXR, vitamin D receptor (VDR), farnesoid X receptor (FXR), and RAR-related orphan receptor gammat (RORγt), in the pathogenesis of IBD and management strategies based on targeting these receptors.

(-)-Epigallocatechin-3-gallate (EGCG) inhibits starch digestion and improves glucose homeostasis through direct or indirect activation of PXR/CAR-mediated phase II metabolism in diabetic mice

As a major component of green tea, (-)-epigallocatechin-3-gallate (EGCG) has attracted interest from scientists owing to its potential to combat a variety of human diseases including abnormal glucose metabolism in obesity and diabetes. This study aims to (1) evaluate the molecular mechanism of EGCG in starch digestion before EGCG absorption; (2) investigate the link between PXR/CAR-mediated phase II metabolism and glucose homeostasis after EGCG is transported to small intestine and liver. EGCG suppressed starch hydrolysis both in vitro and in vivo. Molecular simulation results demonstrated that EGCG could bind to the active site of α-amylase and α-glucosidase, acting as an inhibitor. In addition, the anti-diabetic action of EGCG was investigated in high fat diet and STZ-induced type 2 diabetes. EGCG improved glucose homeostasis and inhibited the process of gluconeogenesis (PEPCK and G-6-Pase) and lipogenesis (SREBP-1C, FAS and ACC1) in the liver. Meanwhile, EGCG treatment activated PXR/CAR, accompanied by upgrading PXR/CAR-mediated phase II drug metabolism enzyme expression in small intestine and liver, involving SULT1A1, UGT1A1 and SULT2B1b. Dietary polyphenol EGCG could serve as a promising PXR/CAR activator and therapeutic intervention in diabetes.

Identification of Modulators That Activate the Constitutive Androstane Receptor From the Tox21 10K Compound Library

The constitutive androstane receptor (CAR; NR1I3) is a nuclear receptor involved in all phases of drug metabolism and disposition. However, recently it's been implicated in energy metabolism, tumor progression, and cancer therapy as well. It is, therefore, important to identify compounds that induce human CAR (hCAR) activation to predict drug-drug interactions and potential therapeutic usage. In this study, we screen the Tox21 10,000 compound collection to characterize hCAR activators. A potential novel structural cluster of compounds was identified, which included nitazoxanide and tenonitrozole, whereas known structural clusters, such as flavones and prazoles, were also detected. Four compounds, neticonazole, diphenamid, phenothrin, and rimcazole, have been identified as novel hCAR activators, one of which, rimcazole, shows potential selectivity toward hCAR over its sister receptor, the pregnane X receptor (PXR). All 4 compounds translocated hCAR from the cytoplasm into the nucleus demonstrating the first step to CAR activation. Profiling these compounds as hCAR activators would enable an estimation of drug-drug interactions, as well as identify prospective therapeutically beneficial drugs.

Metabolomic Approaches Reveal the Role of CAR in Energy Metabolism

The constitutive androstane receptor (CAR; NR1I3) contributes important regulatory roles in biotransformation, xenobiotic transport function, energy metabolism and lipid homeostasis. In this investigation, global serum and liver tissue metabolomes were assessed analytically in wild type and CAR-null transgenic mice using NMR, GC–MS and UPLC–MS/MS-based metabolomics. Significantly, CAR activation increased serum levels of fatty acids, lactate, ketone bodies and tricarboxylic acid cycle products, whereas levels of phosphatidylcholine, sphingomyelin, amino acids and liver glucose were decreased following short-term activation of CAR. Mechanistically, quantitative mRNA analysis demonstrated significantly decreased expression of key gluconeogenic pathways, and increased expression of glucose utilization pathways, changes likely resulting from down-regulation of the hepatic glucose sensor and bidirectional transporter, Glut2. Short-term CAR activation also resulted in enhanced fatty acid synthesis and impaired β-oxidation. In summary, CAR contributes an expansive role regulating energy metabolism, significantly impacting glucose and monocarboxylic acid utilization, fatty acid metabolism and lipid homeostasis, through receptor-mediated regulation of several genes in multiple associated pathways.

A selective gut bacterial bile salt hydrolase alters host metabolism

The human gut microbiota impacts host metabolism and has been implicated in the pathophysiology of obesity and metabolic syndromes. However, defining the roles of specific microbial activities and metabolites on host phenotypes has proven challenging due to the complexity of the microbiome-host ecosystem. Here, we identify strains from the abundant gut bacterial phylum Bacteroidetes that display selective bile salt hydrolase (BSH) activity. Using isogenic strains of wild-type and BSH-deleted Bacteroides thetaiotaomicron, we selectively modulated the levels of the bile acid tauro-β-muricholic acid in monocolonized gnotobiotic mice. B. thetaiotaomicron BSH mutant-colonized mice displayed altered metabolism, including reduced weight gain and respiratory exchange ratios, as well as transcriptional changes in metabolic, circadian rhythm, and immune pathways in the gut and liver. Our results demonstrate that metabolites generated by a single microbial gene and enzymatic activity can profoundly alter host metabolism and gene expression at local and organism-level scales.

The Role of PPAR and Its Cross-Talk with CAR and LXR in Obesity and Atherosclerosis

The prevalence of obesity and atherosclerosis has substantially increased worldwide over the past several decades. Peroxisome proliferator-activated receptors (PPARs), as fatty acids sensors, have been therapeutic targets in several human lipid metabolic diseases, such as obesity, atherosclerosis, diabetes, hyperlipidaemia, and non-alcoholic fatty liver disease. Constitutive androstane receptor (CAR) and liver X receptors (LXRs) were also reported as potential therapeutic targets for the treatment of obesity and atherosclerosis, respectively. Further clarification of the internal relationships between these three lipid metabolic nuclear receptors is necessary to enable drug discovery. In this review, we mainly summarized the cross-talk of PPARs-CAR in obesity and PPARs-LXRs in atherosclerosis.

Effects of Microcystis aeruginosa on the expression of nuclear receptor genes in Daphnia similoides sinensis

Nuclear receptor (NR) genes form a conserved superfamily, which is involved in organism metabolism, reproduction, development, homeostasis, and resource allocation. Microcystis aeruginosa can inhibit the growth and reproduction of Daphnia. However, whether M. aeruginosa can affect the expression of Daphnia NR genes is unknown. In total, 18 NRs were identified in this study based on previous Daphnia similoides sinensis transcriptome data. In treatments containing M. aeruginosa, the gene expression of the NR1 subfamily (E75a, E75b, HR3, HR96, NHR-1, HR97a, HR97g, and NHR97) and the NR2 subfamily (RXR, TLL, PNR, and SVP) were down-regulated 59% and 79%, respectively. In treatments containing M. aeruginosa, although the expression of 78% of the genes showed a similar trend in clones 1 and 2, the expression of 42% of the genes in clone 3 showed the opposite trend compared to clones 1 and 2, suggesting that the adaptability and molecular mechanism differ in individuals with different Microcystis tolerance genotypes.

Genetic variations of the xenoreceptors NR1I2 and NR1I3 and their effect on drug disposition and response variability

NR1I2 (PXR) and NR1I3 (CAR) are nuclear receptors that are classified as xenoreceptors. Upon activation by various xenobiotics, including marketed drugs, they regulate the transcription level of major drug-metabolizing enzymes and transporters and facilitate the elimination of xenobiotics from the body. The modulation of the activity of these two xenoreceptors by various ligands is a major source of pharmacokinetic variability of environmental origin. NR1I2 and NR1I3 genetic polymorphisms can affect the pharmacokinetics and therapeutic response to many drugs, such as irinotecan, tacrolimus and atazanavir. This review provides an overview of NR1I2 and NR1I3 pharmacogenetic studies in various therapeutic fields (oncology, immunomodulation and infectiology) and discusses the implementation of NR1I2 and NR1I3 genetic polymorphism testing in the clinical routine.

Impact of fasting followed by short-term exposure to interleukin-6 on cytochrome P450 mRNA in mice

The gene expression of the cytochrome P450 (CYP) enzyme family is regulated by numerous factors. Fasting has been shown to induce increased hepatic CYP mRNA in both humans and animals. However, the coordinated regulation of CYP, CYP-regulating transcription factors, and transcriptional co-factors in the liver linking energy metabolism to detoxification has never been investigated. Interleukin-6 (IL-6) has been suggested to be released during fasting and has been shown to regulate CYP expression. The present study investigated the hepatic mRNA content of selected CYP, AhR, CAR, PXR and PPARα in mice fasted for 18h and subsequently exposed to IL-6. Furthermore, the impact of fasting on PGC-1α, HNF-4α, SIRT1 and SIRT3 mRNA was examined. Fasting induced a marked increase in Cyp2b10, Cyp2e1 and Cyp4a10 mRNA, while CYP1a1, Cyp1a2, Cyp2a4 and Cyp3a11 mRNA levels remained unchanged. In accordance, the mRNA levels of CAR and PPARα were also increased with fasting. The PGC-1α, SIRT1 and SIRT3 mRNA levels were also increased after fasting, while the HNF-4α mRNA levels remained unchanged. In mice subjected to IL-6 injection, the fasting-induced PXR, PPARα and PGC-1α mRNA responses were lower than after saline injection. In conclusion, fasting was demonstrated to be a strong inducer of hepatic CYP mRNA as well as selected transcription factors controlling the expression of the investigated CYP. Moreover, the mRNA levels of transcriptional co-factors acting as energy sensors and co-factors for CYP regulation was also increased in the liver, suggesting crosstalk at the molecular level between regulation of energy metabolism and detoxification.

Modulation of bilirubin neurotoxicity by the Abcb1 transporter in the Ugt1-/- lethal mouse model of neonatal hyperbilirubinemia

Moderate neonatal jaundice is the most common clinical condition during newborn life. However, a combination of factors may result in acute hyperbilirubinemia, placing infants at risk of developing bilirubin encephalopathy and death by kernicterus. While most risk factors are known, the mechanisms acting to reduce susceptibility to bilirubin neurotoxicity remain unclear. The presence of modifier genes modulating the risk of developing bilirubin-induced brain damage is increasingly being recognised. The Abcb1 and Abcc1 members of the ABC family of transporters have been suggested to have an active role in exporting unconjugated bilirubin from the central nervous system into plasma. However, their role in reducing the risk of developing neurological damage and death during neonatal development is still unknown.To this end, we mated Abcb1a/b-/- and Abcc1-/- strains with Ugt1-/- mice, which develop severe neonatal hyperbilirubinemia. While about 60% of Ugt1-/- mice survived after temporary phototherapy, all Abcb1a/b-/-/Ugt1-/- mice died before postnatal day 21, showing higher cerebellar levels of unconjugated bilirubin. Interestingly, Abcc1 role appeared to be less important.In the cerebellum of Ugt1-/- mice, hyperbilirubinemia induced the expression of Car and Pxr nuclear receptors, known regulators of genes involved in the genotoxic response.We demonstrated a critical role of Abcb1 in protecting the cerebellum from bilirubin toxicity during neonatal development, the most clinically relevant phase for human babies, providing further understanding of the mechanisms regulating bilirubin neurotoxicity in vivo. Pharmacological treatments aimed to increase Abcb1 and Abcc1 expression, could represent a therapeutic option to reduce the risk of bilirubin neurotoxicity.

The transcription factor Maf-S regulates metabolic resistance to insecticides in the malaria vector Anopheles gambiae

Background

Malaria control in Africa is dependent upon the use insecticides but intensive use of a limited number of chemicals has led to resistance in mosquito populations. Increased production of enzymes that detoxify insecticides is one of the most potent resistance mechanisms. Several metabolic enzymes have been implicated in insecticide resistance but the processes controlling their expression have remained largely elusive.

Results

Here, we show that the transcription factor Maf-S regulates expression of multiple detoxification genes, including the key insecticide metabolisers CYP6M2 and GSTD1 in the African malaria vector Anopheles gambiae. Attenuation of this transcription factor through RNAi induced knockdown reduced transcript levels of these effectors and significantly increased mortality after exposure to the pyrethroid insecticides and DDT (permethrin: 9.2% to 19.2% (p = 0.015), deltamethrin: 3.9% to 21.6% (p = 0.036) and DDT: 1% to 11.7% (p = <0.01), whilst dramatically decreasing mortality induced by the organophosphate malathion (79.6% to 8.0% (p = <0.01)). Additional genes regulated by Maf-S were also identified providing new insight into the role of this transcription factor in insects.

Conclusion

Maf-S is a key regulator of detoxification genes in Anopheles mosquitoes. Disrupting this transcription factor has opposing effects on the mosquito’s response to different insecticide classes providing a mechanistic explanation to the negative cross resistance that has been reported between pyrethroids and organophosphates.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4086-7) contains supplementary material, which is available to authorized users.

Functions of pregnane X receptor in self-detoxification

Pregnane X receptor (PXR, NR1I2), a member of the nuclear receptor superfamily, is a crucial regulator of nutrient metabolism and metabolic detoxification such as metabolic syndrome, xenobiotic metabolism, inflammatory responses, glucose, cholesterol and lipid metabolism, and endocrine homeostasis. Notably, much experimental and clinical evidence show that PXR senses xenobiotics and triggers the detoxification response to prevent diseases such as diabetes, obesity, intestinal inflammatory diseases and liver fibrosis. In this review we summarize recent advances on remarkable metabolic and regulatory versatility of PXR, and we emphasizes its role and potential implication as an effective modulator of self-detoxification in animals and humans.

Glucose-dependent regulation of pregnane X receptor is modulated by AMP-activated protein kinase

Pregnane X receptor (PXR) is a xenobiotic receptor that regulates the detoxification and clearance of drugs and foreign compounds from the liver. There has been mounting evidence of crosstalk between the drug metabolism pathway and the energy metabolism pathway, but little is known about this cross-regulation. To further delineate the energy metabolism and drug metabolism crosstalk in this study, we exposed HepG2 cells to varying glucose concentrations. We observed that PXR activity was induced under high-glucose conditions. This finding is consistent with previous clinical reports of increased drug clearance in patients with untreated diabetes. We demonstrated that AMP-activated protein kinase (AMPK) modulates PXR transcriptional activity and that pharmacologically manipulated AMPK activation exhibits an inverse relation to PXR activity. Activation of AMPK was shown to downregulate PXR activity and, consistent with that, potentiate the response of cells to the drug. Taken together, our results delineate a hitherto unreported axis of regulation that involves the energy status of the cell, PXR regulation, and drug sensitivity.

Relationship between NR1I2 polymorphisms and inflammatory bowel disease risk: A systematic review and meta-analysis

BACKGROUND AND OBJECTIVE

Inconsistent results regarding an association between polymorphisms within the Homo sapiens nuclear receptor subfamily 1 group I member 2 (NR1I2) gene and susceptibility to inflammatory bowel disease (IBD) have been reported. A systematic review and meta-analysis was thus undertaken to determine whether NR1I2 gene polymorphisms are associated with an increased risk of IBD.

METHODS

Article retrieval was performed using on-line databases, such as PubMed, Embase, CENTRAL, and WOS. After extracting eligible data, Mantel-Haenszel statistics were applied to calculate the odds radio (OR), 95% confidence interval (95% CI) and P value under a random or fixed-effects model.

RESULTS

A total of seven articles with 4410 IBD subjects and 4028 controls were included. Compared with the control group, no significant increase in IBD susceptibility was observed for the -25385C/T (OR=0.92, 95% CI=0.78∼1.07, P=0.259), -24381A/C (OR=0.96, 95% CI=0.87∼1.06, P=0.378), +8055C/T (OR=1.06, 95% CI=0.97∼1.15, P=0.186), or +7635A/G (OR=0.96, 95% CI=0.87∼1.05, P=0.348) polymorphisms within the NR1I2 gene under the allele model.

CONCLUSIONS

Our meta-analysis failed to demonstrate an association between -25385C/T, -24381A/C, +8055C/T, or +7635A/G polymorphisms within the NR1I2 gene and overall IBD risk. A larger sample size is needed to validate our conclusion.

Ginkgolide B lowers body weight and ameliorates hepatic steatosis in high-fat diet-induced obese mice correlated with pregnane X receptor activation

Ginkgolide B (GB) is a natural occurring terpene lactone and a selective agonistic ligand of hPXR.

Activation of the Constitutive Androstane Receptor by Monophthalates

Humans in industrialized areas are continuously exposed to phthalate plasticizers, prompting concerns of their potential toxicities. Previous studies from our laboratory and others have shown that various phthalates activate several mammalian nuclear receptors, in particular the constitutive androstane receptor (CAR), the pregnane X receptor (PXR), and the peroxisomal proliferator-activated receptors (PPARs), although often at concentration levels of questionable relevance to human exposure. We discovered that di(2-ethylhexyl) phthalate (DEHP) and di-isononyl phthalate (DiNP), two of the highest volume production agents, were potent activators of human CAR2 (hCAR2), a unique human CAR splice variant and, to a lesser degree, human PXR (hPXR). These diphthalates undergo rapid metabolism in mammalian systems, initially to their major monophthalate derivatives MEHP and MiNP. Although MEHP and MiNP are reported activators of the rodent PPARs, with lower affinities for the corresponding human PPARs, it remains unclear whether these monophthalate metabolites activate hCAR2 or hPXR. In this investigation, we assessed the relative activation potential of selected monophthalates and other low molecular weight phthalates against hCAR, the most prominent hCAR splice variants, as well as hPXR and human PPAR. Using transactivation and mammalian two-hybrid protein interaction assays, we demonstrate that these substances indeed activate hCARs and hPXR but to varying degrees. MEHP and MiNP exhibit potent activation of hCAR2 and hPXR with higher affinities for these receptors than for the hPPARs. The rank order potency for MEHP and MiNP was hCAR2 > hPXR > hPPARs. Results from primary hepatocyte experiments also reflect the MEHP and MiNP upregulation of the respective human target genes. We conclude that both di- and monophthalates are potently selective hCAR2 activators and effective hPXR activators. These results implicate these targets as important mediators of selective phthalate effects in humans. The striking differential affinities for these compounds between human and rodent nuclear receptors further implies that biological results obtained from rodent models may be of only limited relevance for interpolating phthalate-mediated effects in humans.

Editor's Highlight: Neonatal Activation of the Xenobiotic-Sensors PXR and CAR Results in Acute and Persistent Down-regulation of PPARα-Signaling in Mouse Liver

Safety concerns have emerged regarding the potential long-lasting effects due to developmental exposure to xenobiotics. The pregnane X receptor (PXR) and constitutive androstane receptor (CAR) are critical xenobiotic-sensing nuclear receptors that are highly expressed in liver. The goal of this study was to test our hypothesis that neonatal exposure to PXR- or CAR-activators not only acutely but also persistently regulates the expression of drug-processing genes (DPGs). A single dose of the PXR-ligand PCN (75 mg/kg), CAR-ligand TCPOBOP (3 mg/kg), or vehicle (corn oil) was administered intraperitoneally to 3-day-old neonatal wild-type mice. Livers were collected 24 h post-dose or from adult mice at 60 days of age, and global gene expression of these mice was determined using Affymetrix Mouse Transcriptome Assay 1.0. In neonatal liver, PCN up-regulated 464 and down-regulated 449 genes, whereas TCPOBOP up-regulated 308 and down-regulated 112 genes. In adult liver, there were 15 persistently up-regulated and 22 persistently down-regulated genes following neonatal exposure to PCN, as well as 130 persistently up-regulated and 18 persistently down-regulated genes following neonatal exposure to TCPOBOP. Neonatal exposure to both PCN and TCPOBOP persistently down-regulated multiple Cyp4a members, which are prototypical-target genes of the lipid-sensor PPARα, and this correlated with decreased PPARα-binding to the Cyp4a gene loci. RT-qPCR, western blotting, and enzyme activity assays in livers of wild-type, PXR-null, and CAR-null mice confirmed that the persistent down-regulation of Cyp4a was PXR and CAR dependent. In conclusion, neonatal exposure to PXR- and CAR-activators both acutely and persistently regulates critical genes involved in xenobiotic and lipid metabolism in liver.

Long-term exposure to abnormal glucose levels alters drug metabolism pathways and insulin sensitivity in primary human hepatocytes

Hyperglycemia in type 2 diabetes mellitus has been linked to non-alcoholic fatty liver disease, which can progress to inflammation, fibrosis/cirrhosis, and hepatocellular carcinoma. Understanding how chronic hyperglycemia affects primary human hepatocytes (PHHs) can facilitate the development of therapeutics for these diseases. Conversely, elucidating the effects of hypoglycemia on PHHs may provide insights into how the liver adapts to fasting, adverse diabetes drug reactions, and cancer. In contrast to declining PHH monocultures, micropatterned co-cultures (MPCCs) of PHHs and 3T3-J2 murine embryonic fibroblasts maintain insulin-sensitive glucose metabolism for several weeks. Here, we exposed MPCCs to hypo-, normo- and hyperglycemic culture media for ~3 weeks. While albumin and urea secretion were not affected by glucose level, hypoglycemic MPCCs upregulated CYP3A4 enzyme activity as compared to other glycemic states. In contrast, hyperglycemic MPCCs displayed significant hepatic lipid accumulation in the presence of insulin, while also showing decreased sensitivity to insulin-mediated inhibition of glucose output relative to a normoglycemic control. In conclusion, we show for the first time that PHHs exposed to hypo- and hyperglycemia can remain highly functional, but display increased CYP3A4 activity and selective insulin resistance, respectively. In the future, MPCCs under glycemic states can aid in novel drug discovery and mechanistic investigations.

Pregnane X Receptor and Cancer: Context-Specificity is Key

Pregnane X receptor (PXR) is an adopted orphan nuclear receptor that is activated by a wide-range of endobiotics and xenobiotics, including chemotherapy drugs. PXR plays a major role in the metabolism and clearance of xenobiotics and endobiotics in liver and intestine via induction of drug-metabolizing enzymes and drug-transporting proteins. However, PXR is expressed in several cancer tissues and the accumulating evidence strongly points to the differential role of PXR in cancer growth and progression as well as in chemotherapy outcome. In cancer cells, besides regulating the gene expression of enzymes and proteins involved in drug metabolism and transport, PXR also regulates other genes involved in proliferation, metastasis, apoptosis, anti-apoptosis, inflammation, and oxidative stress. In this review, we focus on the differential role of PXR in a variety of cancers, including prostate, breast, ovarian, endometrial, and colon. We also discuss the future directions to further understand the differential role of PXR in cancer, and conclude with the need to identify novel selective PXR modulators to target PXR in PXR-expressing cancers.

Activation of the Constitutive Androstane Receptor induces hepatic lipogenesis and regulates Pnpla3 gene expression in a LXR-independent way

The Constitutive Androstane Receptor (CAR, NR1I3) has been newly described as a regulator of energy metabolism. A relevant number of studies using animal models of obesity suggest that CAR activation could be beneficial on the metabolic balance. However, this remains controversial and the underlying mechanisms are still unknown. This work aimed to investigate the effect of CAR activation on hepatic energy metabolism during physiological conditions, i.e. in mouse models not subjected to metabolic/nutritional stress. Gene expression profiling in the liver of CAR knockout and control mice on chow diet and treated with a CAR agonist highlighted CAR-mediated up-regulations of lipogenic genes, concomitant with neutral lipid accumulation. A strong CAR-mediated up-regulation of the patatin-like phospholipase domain-containing protein 3 (Pnpla3) was demonstrated. Pnpla3 is a gene whose polymorphism is associated with the pathogenesis of nonalcoholic fatty liver disease (NAFLD) development. This observation was confirmed in human hepatocytes treated with the antiepileptic drug and CAR activator, phenobarbital and in immortalized human hepatocytes treated with CITCO. Studying the molecular mechanisms controlling Pnpla3 gene expression, we demonstrated that CAR does not act by a direct regulation of Pnpla3 transcription or via the Liver X Receptor but may rather involve the transcription factor Carbohydrate Responsive Element-binding protein. These data provide new insights into the regulation by CAR of glycolytic and lipogenic genes and on pathogenesis of steatosis. This also raises the question concerning the impact of drugs and environmental contaminants in lipid-associated metabolic diseases.

A Molecular Aspect in the Regulation of Drug Metabolism: Does PXR-Induced Enzyme Expression Always Lead to Functional Changes in Drug Metabolism?

Pregnane X receptor (PXR, NR112) is a xenobiotic receptor whose primary function is to regulate the expression of drug-metabolizing enzymes (DMEs) and drug transporters. Drug-induced PXR activation and subsequent enzyme and transporter induction has been proposed to be an important mechanism for the drug-drug interactions. In addition to activating PXR, many pharmaceutical chemicals can also function as reversible or irreversible inhibitors of DMEs, which may also impact the pharmacokinetics and pharmacodynamics (PK/PD) of drugs. Therefore, we cannot simply conclude that the PXR-induced alteration in enzyme expression always reflects functional changes. We should consider both PXR activation and DMEs inhibition to improve drug safety in the clinic.

Bioinformatic analysis of microRNA networks following the activation of the constitutive androstane receptor (CAR) in mouse liver

The constitutive androstane receptor (CAR; NR1I3) is a member of the nuclear receptor superfamily that functions as a xenosensor, serving to regulate xenobiotic detoxification, lipid homeostasis and energy metabolism. CAR activation is also a key contributor to the development of chemical hepatocarcinogenesis in mice. The underlying pathways affected by CAR in these processes are complex and not fully elucidated. MicroRNAs (miRNAs) have emerged as critical modulators of gene expression and appear to impact many cellular pathways, including those involved in chemical detoxification and liver tumor development. In this study, we used deep sequencing approaches with an Illumina HiSeq platform to differentially profile microRNA expression patterns in livers from wild type C57BL/6J mice following CAR activation with the mouse CAR-specific ligand activator, 1,4-bis-[2-(3,5,-dichloropyridyloxy)] benzene (TCPOBOP). Bioinformatic analyses and pathway evaluations were performed leading to the identification of 51 miRNAs whose expression levels were significantly altered by TCPOBOP treatment, including mmu-miR-802-5p and miR-485-3p. Ingenuity Pathway Analysis of the differentially expressed microRNAs revealed altered effector pathways, including those involved in liver cell growth and proliferation. A functional network among CAR targeted genes and the affected microRNAs was constructed to illustrate how CAR modulation of microRNA expression may potentially mediate its biological role in mouse hepatocyte proliferation. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Pharmacokinetic and Metabolic Characteristics of Herb-Derived Khellactone Derivatives, A Class of Anti-HIV and Anti-Hypertensive: A Review

A vast number of structural modifications have been performed for khellactone derivatives (KDs) that have been widely concerned owing to their diverse biological properties, including anti-hypertension, anti-HIV, reversing P-glycoprotein (P-gp) mediated multidrug resistance, and anti-inflammation effects, to find the most active entity. However, extensive metabolism of KDs results in poor oral bioavailability, thus hindering the clinical trial performance of those components. The primary metabolic pathways have been revealed as hydrolysis, oxidation, acyl migration, and glucuronidation, while carboxylesterases and cytochrome P450 3A (CPY3A), as well as UDP-glucuronosyltransferases (UGTs) primarily mediate these metabolic pathways. Attention was mainly paid to the pharmacological features, therapeutic mechanisms and structure-activity relationships of KDs in previous reviews, whereas their pharmacokinetic and metabolic characteristics have seldom been discussed. In the present review, KDs' metabolism and their pharmacokinetic properties are summarized. In addition, the structure-metabolism relationships of KDs and the potential drug-drug interactions (DDIs) induced by KDs were also extensively discussed. The polarity, the acyl groups substituted at C-3' and C-4' positions, the configuration of C-3' and C-4', and the moieties substituted at C-3 and C-4 positions play the determinant roles for the metabolic profiles of KDs. Contributions from CYP3A4, UGT1A1, P-gp, and multidrug resistance-associated protein 2 have been disclosed to be primary for the potential DDIs. The review is expected to provide meaningful information and helpful guidelines for the further development of KDs.

A comprehensive analysis and functional characterization of naturally occurring non-synonymous variants of nuclear receptor PXR

Pregnane & Xenobiotic Receptor (PXR) acts as a xenosensing transcriptional regulator of many drug metabolizing enzymes and transporters of the 'detoxification machinery' that coordinate in elimination of xenobiotics and endobiotics from the cellular milieu. It is an accepted view that some individuals or specific populations display considerable differences in their ability to metabolize different drugs, dietary constituents, herbals etc. In this context we speculated that polymorphisms in PXR gene might contribute to variability in cytochrome P450 (CYP450) metabolizing enzymes of phase I, drug metabolizing components of phase II and efflux components of the detoxification machinery. Therefore, in this study, we have undertaken a comprehensive functional analysis of seventeen naturally occurring non-synonymous variants of human PXR. When compared, we observed that some of the PXR SNP variants exhibit distinct functional and dynamic responses on parameters which included transcriptional function, sub-cellular localization, mitotic chromatin binding, DNA-binding properties and other molecular interactions. One of the unique SNP located within the DNA-binding domain of PXR was found to be functionally null and distinct on other parameters. Similarly, some of the non-synonymous SNPs in PXR imparted reduced transactivation function as compared to wild type PXR. Interestingly, PXR is reported to be a mitotic chromatin binding protein and such an association has been correlated to an emerging concept of 'transcription memory' and altered transcription output. In view of the observations made herein our data suggest that some of the natural PXR variants may have adverse physiological consequences owing to its influence on the expression levels and functional output of drug-metabolizing enzymes and transporters. The present study is expected to explain not only the observed inter-individual responses to different drugs but may also highlight the mechanistic details and importance of PXR in drug clearance, drug-drug interactions and diverse metabolic disorders. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

A SUMO-acetyl switch in PXR biology

Post-translational modification (PTM) of nuclear receptor superfamily members regulates various aspects of their biology to include sub-cellular localization, the repertoire of protein-binding partners, as well as their stability and mode of degradation. The nuclear receptor pregnane X receptor (PXR, NR1I2) is a master-regulator of the drug-inducible gene expression in liver and intestine. The PXR-mediated gene activation program is primarily recognized to increase drug metabolism, drug transport, and drug efflux pathways in these tissues. The activation of PXR also has important implications in significant human diseases including inflammatory bowel disease and cancer. Our recent investigations reveal that PXR is modified by multiple PTMs to include phosphorylation, SUMOylation, and ubiquitination. Using both primary cultures of hepatocytes and cell-based assays, we show here that PXR is modified through acetylation on lysine residues. Further, we show that increased acetylation of PXR stimulates its increased SUMO-modification to support active transcriptional suppression. Pharmacologic inhibition of lysine de-acetylation using trichostatin A (TSA) alters the sub-cellular localization of PXR in cultured hepatocytes, and also has a profound impact upon PXR transactivation capacity. Both the acetylation and SUMOylation status of the PXR protein is affected by its ability to associate with the lysine de-acetylating enzyme histone de-acetylase (HDAC)3 in a complex with silencing mediator of retinoic acid and thyroid hormone receptor (SMRT). Taken together, our data support a model in which a SUMO-acetyl 'switch' occurs such that acetylation of PXR likely stimulates SUMO-modification of PXR to promote the active repression of PXR-target gene expression. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.

Ginkgolide B protects human umbilical vein endothelial cells against xenobiotic injuries via PXR activation

AIM

Pregnane X receptor (PXR) is a nuclear receptor that regulates a number of genes encoding drug metabolism enzymes and transporters and plays a key role in xeno- and endobiotic detoxification. Ginkgolide B has shown to increase the activity of PXR. Here we examined whether ginkgolide B activated PXR and attenuated xenobiotic-induced injuries in endothelial cells.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with ginkgolide B. The expression of PXR, CYP3A4, MDR1, VCAM-1, E-selectin and caspase-3 were quantified with qRT-PCR and Western blot analysis. Cell apoptosis was analyzed with flow cytometry. Fluorescently labeled human acute monocytic leukemia cells (THP-1 cells) were used to examine cell adhesion.

RESULTS

Ginkgolide B (30-300 μmol/L) did not change the mRNA and protein levels of PXR in the cells, but dose-dependently increased nuclear translocation of PXR protein. Ginkgolide B increased the expression of CYP3A4 and MDR1 in the cells, which was partially reversed by pretreatment with the selective PXR signaling antagonist sulforaphane, or transfection with PXR siRNA. Functionally, ginkgolide B dose-dependently attenuated doxorubicin- or staurosporine-induced apoptosis, which was reversed by transfection with PXR siRNA. Moreover, ginkgolide B suppressed TNF-α-induced THP-1 cell adhesion and TNF-α-induced expression of vascular adhesion molecule 1 (VCAM-1) and E-selectin in the cells, which was also reversed by transfection with PXR siRNA.

CONCLUSION

Ginkgolide B exerts anti-apoptotic and anti-inflammatory effects on endothelial cells via PXR activation, suggesting that a PXR-mediated endothelial detoxification program may be important for protecting endothelial cells from xeno- and endobiotic-induced injuries.

Compound- and sex-specific effects on programming of energy and immune homeostasis in adult C57BL/6JxFVB mice after perinatal TCDD and PCB 153

Early life exposure to endocrine disrupting compounds has been linked to chronic diseases later in life, like obesity and related metabolic disorders. We exposed C57BL/6JxFVB hybrid mice to the aryl hydrocarbon receptor agonist 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and the constitutive androstane receptor/pregnane X receptor agonist polychlorinated biphenyl 153 (PCB 153) in an experimental design relevant for human exposure. Exposure occurred during gestation and lactation via maternal feed to a wide dose range (TCDD: 10-10,000 pg/kg body weight/day; PCB 153: 0.09-1406 μg/kg body weight/d). Then exposure was ceased and offspring were followed up to 1 year of age. Metabolic parameters like body weight, fat pad weights, glucose tolerance, endocrine serum profile, and neurobehavioral and immunological parameters were determined. Body weight was transiently affected by both compounds throughout the follow-up. TCDD-exposed males showed decreased fat pad and spleen weights and an increase in IL-4 production of splenic immune cells. In contrast, females showed increased fat pad weights and production of IFNγ. PCB 153-exposed males showed an increase in glucose, whereas females showed an increase in glucagon, a decrease in pancreas weight, and an increase in thymus weight. In conclusion, early life exposure to TCDD appears to affect programming of energy and immune homeostasis in offspring, whereas the effects of perinatal PCB 153 were mainly on programming of glucose homeostasis. Both compounds act sex-specifically. Lowest derived BMDLs (lower bounds of the (two sided) 90%-confidence interval for the benchmark dose) for both compounds are not lower than current tolerable daily intakes.