The pregnane X receptor locus is associated with susceptibility to inflammatory bowel disease

Pregnane X receptor alleviates sepsis-induced liver injury through activation of yes-associated protein in mice

The severity of sepsis is attributed to excessive inflammatory responses leading to liver injury. Pregnane X receptor (PXR), a nuclear receptor that controls xenobiotic and endobiotic metabolism, has been implicated in regulating inflammation and liver regeneration. This study aimed to investigate the role of PXR in sepsis-induced liver injury and the underlying mechanisms. Sepsis models were established in mice, the mice were administered the typical mouse PXR agonist PCN (100 mg·kg-1·d-1, i.p.) for 3 consecutive days in advance, then subjected to CLP operation or LPS administration 1 h after the last administration of PCN. The results showed that PCN pretreatment significantly increased the survival rate of septic mice, while the survival rate was reduced after the knockout of Pxr. In addition, PCN pretreatment effectively alleviated sepsis-induced liver injury. In Pxr knockout mice, liver injury was more severe, whereas the protective effects of PCN pretreatment were abolished. Mechanistically, PCN pretreatment significantly upregulated the expression of yes-associated protein (YAP) and its downstream targets and decreased the level of phosphorylated nuclear factor-κB (NF-κB). Moreover, liver-specific knockdown of Yap blocked the protective effects of PCN pretreatment against sepsis-induced liver injury and downregulated the phosphorylation level of NF-κB. In summary, this study demonstrated that PXR activation protects against sepsis-induced liver injury through activation of the YAP signaling pathway, providing a new strategy for the diagnosis and treatment of sepsis-induced liver injury.

Artemisinins: Promising drug candidates for the treatment of autoimmune diseases

Autoimmune diseases are characterized by the immune system's attack on one's own tissues which are highly diverse and diseases differ in severity, causing damage in virtually all human systems including connective tissue (e.g., rheumatoid arthritis), neurological system (e.g., multiple sclerosis) and digestive system (e.g., inflammatory bowel disease). Historically, treatments normally include pain-killing medication, anti-inflammatory drugs, corticosteroids, and immunosuppressant drugs. However, given the above characteristics, treatment of autoimmune diseases has always been a challenge. Artemisinin is a natural sesquiterpene lactone initially extracted and separated from Chinese medicine Artemisia annua L., which has a long history of curing malaria. Artemisinin's derivatives such as artesunate, dihydroartemisinin, artemether, artemisitene, and so forth, are a family of artemisinins with antimalarial activity. Over the past decades, accumulating evidence have indicated the promising therapeutic potential of artemisinins in autoimmune diseases. Herein, we systematically summarized the research regarding the immunoregulatory properties of artemisinins including artemisinin and its derivatives, discussing their potential therapeutic viability toward major autoimmune diseases and the underlying mechanisms. This review will provide new directions for basic research and clinical translational medicine of artemisinins.

Regulation of PXR in drug metabolism: chemical and structural perspectives

INTRODUCTION

Pregnane X receptor (PXR) is a master xenobiotic sensor that transcriptionally controls drug metabolism and disposition pathways. PXR activation by pharmaceutical drugs, natural products, environmental toxins, etc. may decrease drug efficacy and increase drug-drug interactions and drug toxicity, indicating a therapeutic value for PXR antagonists. However, PXR's functions in physiological events, such as intestinal inflammation, indicate that PXR activators may be useful in certain disease contexts.

AREAS COVERED

We review the reported roles of PXR in various physiological and pathological processes including drug metabolism, cancer, inflammation, energy metabolism, and endobiotic homeostasis. We then highlight specific cellular and chemical routes that modulate PXR activity and discuss the functional consequences. Databases searched and inclusive dates: PubMed, 1 January 1980 to 10 January 2024.

EXPERT OPINION

Knowledge of PXR's drug metabolism function has helped drug developers produce small molecules without PXR-mediated metabolic liabilities, and further understanding of PXR's cellular functions may offer drug development opportunities in multiple disease settings.

Microbial metabolites are involved in tumorigenesis and development by regulating immune responses

The human microbiota is symbiotic with the host and can create a variety of metabolites. Under normal conditions, microbial metabolites can regulate host immune function and eliminate abnormal cells in a timely manner. However, when metabolite production is abnormal, the host immune system might be unable to identify and get rid of tumor cells at the early stage of carcinogenesis, which results in tumor development. The mechanisms by which intestinal microbial metabolites, including short-chain fatty acids (SCFAs), microbial tryptophan catabolites (MTCs), polyamines (PAs), hydrogen sulfide, and secondary bile acids, are involved in tumorigenesis and development by regulating immune responses are summarized in this review. SCFAs and MTCs can prevent cancer by altering the expression of enzymes and epigenetic modifications in both immune cells and intestinal epithelial cells. MTCs can also stimulate immune cell receptors to inhibit the growth and metastasis of the host cancer. SCFAs, MTCs, bacterial hydrogen sulfide and secondary bile acids can control mucosal immunity to influence the occurrence and growth of tumors. Additionally, SCFAs, MTCs, PAs and bacterial hydrogen sulfide can also affect the anti-tumor immune response in tumor therapy by regulating the function of immune cells. Microbial metabolites have a good application prospect in the clinical diagnosis and treatment of tumors, and our review provides a good basis for related research.

Aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) play both distinct and common roles in the regulation of colon homeostasis and intestinal carcinogenesis

Both aryl hydrocarbon receptor (AhR) and pregnane X receptor (PXR) belong among key regulators of xenobiotic metabolism in the intestinal tissue. AhR in particular is activated by a wide range of environmental and dietary carcinogens. The data accumulated over the last two decades suggest that both of these transcriptional regulators play a much wider role in the maintenance of gut homeostasis, and that both transcription factors may affect processes linked with intestinal tumorigenesis. Intestinal epithelium is continuously exposed to a wide range of AhR, PXR and dual AhR/PXR ligands formed by intestinal microbiota or originating from diet. Current evidence suggests that specific ligands of both AhR and PXR can protect intestinal epithelium against inflammation and assist in the maintenance of epithelial barrier integrity. AhR, and to a lesser extent also PXR, have been shown to play a protective role against inflammation-induced colon cancer, or, in mouse models employing overactivation of Wnt/β-catenin signaling. In contrast, other evidence suggests that both receptors may contribute to modulation of transformed colon cell behavior, with a potential to promote cancer progression and/or chemoresistance. The review focuses on both overlapping and separate roles of the two receptors in these processes, and on possible implications of their activity within the context of intestinal tissue.

Effects of polymorphisms in pregnane X receptor and ABC transporters on afatinib in Japanese patients with non-small cell lung cancer: pharmacogenomic-pharmacokinetic and exposure-response analysis

PURPOSE

Because of the large interindividual variability of afatinib pharmacokinetics and adverse events, we evaluated the effects of polymorphisms in pregnane X receptor (NR1I2) and ABC transporters (ABCB1, ABCG2, and ABCC2) on the pharmacokinetics of afatinib.

METHODS

The steady-state area under the concentration-time curve (AUC)0-24 of afatinib was analyzed using blood sampling just prior to and at 1, 2, 4, 6, 8, 12, and 24 h on day 15 after administration.

RESULTS

The median oral clearance (CL/F) of afatinib in patients with the NR1I2 7635A allele was significantly lower than those in patients with the 7635G/G genotype (42.0 and 60.0 L/h, respectively, P = 0.025). There were no significant differences in afatinib CL/F between genotypes for NR1I2 8055C > T, -25385C > T, ABCB1, ABCG2, and ABCC2 polymorphisms. Based on the area under the receiver-operating characteristic curve, the threshold afatinib AUC0-24 value for prediction of dose reduction or withdrawal was 689 ng·h/mL at the best sensitivity (81.0%) and specificity (72.7%). In multivariate logistic regression analysis, an afatinib AUC0-24 above 689 ng·h/mL was independently associated with increased risk of dose reduction or withdrawal (OR: 11.66, P = 0.012).

CONCLUSIONS

The NR1I2 7635A allele was related to a lower afatinib CL/F. Based on the AUC of 689 ng h/mL and CL/F, the optimal doses for patients with the NR1I2 7635G/G genotype and 7635A allele were recommended to be set at 40 and 30 mg/day, respectively, and subsequent adjustment of the maintenance dose based on the plasma concentrations of afatinib may be necessary to avoid afatinib-related adverse events.

Effects of NR1I2 and ABCB1 Genetic Polymorphisms on Everolimus Pharmacokinetics in Japanese Renal Transplant Patients

The purpose of this study was to evaluate the effects of NR1I2 (7635G>A and 8055C>T) and ABCB1 (1236C>T, 2677G>T/A, and 3435C>T) genetic polymorphisms on everolimus pharmacokinetics in 98 Japanese renal transplant patients. On day 15 after everolimus administration, blood samples were collected just prior to and 1, 2, 3, 4, 6, 9, and 12 h after administration. The dose-adjusted area under the blood concentration−time curve (AUC0-12) of everolimus was significantly lower in patients with the NR1I2 8055C/C genotype than in those with other genotypes (p = 0.022) and was significantly higher in male patients than female patients (p = 0.045). Significant correlations between the dose-adjusted AUC0-12 of everolimus and age (p = 0.001), aspartate transaminase (p = 0.001), and alanine transaminase (p = 0.005) were found. In multivariate analysis, aging (p = 0.008) and higher alanine transaminase levels (p = 0.032) were independently predictive of a higher dose-adjusted everolimus AUC0-12. Aging and hepatic dysfunction in patients may need to be considered when evaluating dose reductions in everolimus. In renal transplant patients, management using everolimus blood concentrations after administration may be more important than analysis of NR1I2 8055C>T polymorphism before administration.

Xenobiotic receptors and the regulation of intestinal homeostasis: harnessing the chemical output of the intestinal microbiota

The commensal bacteria that reside in the gastrointestinal tract exist in a symbiotic relationship with the host, driving the development of the immune system and maintaining metabolic and tissue homeostasis in the local environment. The intestinal microbiota has the capacity to generate a wide array of chemical metabolites to which the cells of the intestinal mucosa are exposed. Host cells express xenobiotic receptors, such as the aryl hydrocarbon receptor (AhR) and the pregnane X receptor (PXR), that can sense and respond to chemicals that are generated by nonhost pathways. In this review, we outline the physiological and immunological processes within the intestinal environment that are regulated by microbial metabolites through the activation of the AhR and the PXR, with a focus on ligands generated by the stepwise catabolism of tryptophan.

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.

Bile Acids, Their Receptors, and the Gut Microbiota

Bile acids (BAs) are a family of hydroxylated steroids secreted by the liver that aid in the breakdown and absorption of dietary fats. BAs also function as nutrient and inflammatory signaling molecules, acting through cognate receptors, to coordinate host metabolism. Commensal bacteria in the gastrointestinal tract are functional modifiers of the BA pool, affecting composition and abundance. Deconjugation of host BAs creates a molecular network that inextricably links gut microtia with their host. In this review we highlight the roles of BAs in mediating this mutualistic relationship with a focus on those events that impact host physiology and metabolism.

Critical roles of bile acids in regulating intestinal mucosal immune responses

Bile acids are a class of cholesterol derivatives that have been known for a long time for their critical roles in facilitating the digestion and absorption of lipid from the daily diet. The transformation of primary bile acids produced by the liver to secondary bile acids appears under the action of microbiota in the intestine, greatly expanding the molecular diversity of the intestinal environment. With the discovery of several new receptors of bile acids and signaling pathways, bile acids are considered as a family of important metabolites that play pleiotropic roles in regulating many aspects of human overall health, especially in the maintenance of the microbiota homeostasis and the balance of the mucosal immune system in the intestine. Accordingly, disruption of the process involved in the metabolism or circulation of bile acids is implicated in many disorders that mainly affect the intestine, such as inflammatory bowel disease and colon cancer. In this review, we discuss the different metabolism profiles in diseases associated with the intestinal mucosa and the diverse roles of bile acids in regulating the intestinal immune system. Furthermore, we also summarize recent advances in the field of new drugs that target bile acid signaling and highlight the importance of bile acids as a new target for disease intervention.

Bioinformatis analysis reveals possible molecular mechanism of PXR on regulating ulcerative colitis

Inflammatory bowel disease (IBD) is a chronic, recurrent inflammatory disease of the gastrointestinal (GI) tract. Ulcerative colitis (UC) is a type of IBD. Pregnane X Receptor (PXR) is a member of the nuclear receptor superfamily. In order to deepen understanding and exploration of the molecular mechanism of regulation roles of PXR on UC, biological informatics analysis was performed. First, 878 overlapping differentially expressed genes (DEGs) between UC and normal samples were obtained from the Gene Expression Omnibus (GEO) database (GSE59071 and GSE38713) by using the "limma" R language package. Then WGCNA analysis was performed by 878 DEGs to obtain co-expression modules that were positively and negatively correlated with clinical traits. GSEA analysis of PXR results obtained the signal pathways enriched in the PXR high and low expression group and the active genes of each signal pathway. Then the association of PXR with genes that are both active in high expression group and negatively related to diseases (gene set 1), or both active in low expression group and negatively related to diseases (gene set 2) was analyzed by String database. Finally, carboxylesterase 2 (CES2), ATP binding cassette subfamily G member 2 (ABCG2), phosphoenolpyruvate carboxykinase (PCK1), PPARG coactivator 1 alpha (PPARGC1A), cytochrome P450 family 2 subfamily B member 6 (CYP2B6) from gene set 1 and C-X-C motif chemokine ligand 8 (CXCL8) from gene set 2 were screened out. After the above analysis and reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) verification, we speculated that PXR may exert a protective role on UC by promoting CES2, ABCG2, PCK1, PPARGC1A, CYP2B6 expression and inhibiting CXCL8 expression in their corresponding signal pathway in intestinal tissue.

Lipidomic profiling reveals triacylglycerol accumulation in the liver during pregnane X receptor activation-induced hepatomegaly

Pregnane X receptor (PXR) is highly expressed in the liver and plays an integral role in the control of xenobiotic and endobiotic metabolism to maintain homeostasis. We previously reported that activation of PXR significantly induced liver enlargement. But the lipid profiling during PXR-induced hepatomegaly remains unclear. This study aimed to characterize the effect of PXR activation on hepatic lipid homeostasis by lipidomics analysis. Mice were intraperitoneally administered with the typical mPXR agonist, pregnenolone 16α-carbonitrile (PCN, 100 mg/kg/d), for 5 days. Liver and serum were collected for further analysis. The results confirmed that PXR activation can significantly induce liver enlargement. An obvious hepatic lipid accumulation was observed in PCN-treated mice, as determined by H&E and Oil Red O staining. Ultra-high performance liquid chromatography-Q Exactive Orbitrap high-resolution mass spectrometer (UHPLC-Q Exactive Orbitrap HRMS)-based lipidomics was performed to characterize the change in lipid species. A total of 20 potential lipid biomarkers were significantly perturbed. The most significant change was found in the triacylglycerol (TG), which constituted with the lower number of carbon atoms and double bonds. Moreover, the mRNA expression levels showed that PCN-induced PXR activation significantly regulated the expression of genes involved in the uptake, synthesis and metabolism of TG, which was consistent with increased TG levels. Collectively, these findings demonstrated that lipids such as TG were significantly accumulated during PXR-induced hepatomegaly.

Distinct Effects of Inflammation on Cytochrome P450 Regulation and Drug Metabolism: Lessons from Experimental Models and a Potential Role for Pharmacogenetics

Personalized medicine strives to optimize drug treatment for the individual patient by taking into account both genetic and non-genetic factors for drug response. Inflammation is one of the non-genetic factors that has been shown to greatly affect the metabolism of drugs—primarily through inhibition of cytochrome P450 (CYP450) drug-metabolizing enzymes—and hence contribute to the mismatch between the genotype predicted drug response and the actual phenotype, a phenomenon called phenoconversion. This review focuses on inflammation-induced drug metabolism alterations. In particular, we discuss the evidence assembled through human in-vitro models on the effect of inflammatory mediators on clinically relevant CYP450 isoform levels and their metabolizing capacity. We also present an overview of the current understanding of the mechanistic pathways via which inflammation in hepatocytes may modulate hepatic functions that are critical for drug metabolism. Furthermore, since large inter-individual variability in response to inflammation is observed in human in-vitro models and clinical studies, we evaluate the potential role of pharmacogenetic variability in the inflammatory signaling cascade and how this can modulate the outcome of inflammation on drug metabolism and response.

Associations between Pregnane X Receptor and Breast Cancer Growth and Progression

Pregnane X receptor (PXR, NR1I2) is a member of the ligand-activated nuclear receptor superfamily. This receptor is promiscuous in its activation profile and is responsive to a broad array of both endobiotic and xenobiotic ligands. PXR is involved in pivotal cellular detoxification processes to include the regulation of genes that encode key drug-metabolizing cytochrome-P450 enzymes, oxidative stress response, as well as enzymes that drive steroid and bile acid metabolism. While PXR clearly has important regulatory roles in the liver and gastrointestinal tract, this nuclear receptor also has biological functions in breast tissue. In this review, we highlight current knowledge of PXR’s role in mammary tumor carcinogenesis. The elevated level of PXR expression in cancerous breast tissue suggests a likely interface between aberrant cell division and xeno-protection in cancer cells. Moreover, PXR itself exerts positive effect on the cell cycle, thereby predisposing tumor cells to unchecked proliferation. Activation of PXR also plays a key role in regulating apoptosis, as well as in acquired resistance to chemotherapeutic agents. The repressive role of PXR in regulating inflammatory mediators along with the existence of genetic polymorphisms within the sequence of the PXR gene may predispose individuals to developing breast cancer. Further investigations into the role that PXR plays in driving tumorigenesis are needed.

Genetic variation in the farnesoid X-receptor predicts Crohn's disease severity in female patients

The farnesoid X receptor (FXR) is implicated in Crohn's disease (CD) pathogenesis. It is unclear how genetic variation in FXR impacts CD severity versus genetic variation in nuclear receptors such as pregnane X receptor (PXR) and the multi-drug resistance protein 1 (MDR1, ABCB1). To evaluate FXR-1G > T as a genomic biomarker of severity in CD and propose a plausible molecular mechanism. A retrospective study (n = 542) was conducted in a Canadian cohort of CD patients. Genotypic analysis (FXR-1G > T, MDR1 3435C > T and PXR -25385C > T) as well as determination of the FXR downstream product, fibroblast growth factor (FGF) 19 was performed. Primary outcomes included risk and time to first CD-related surgery. The effect of estrogen on wild type and variant FXR activity was assessed in HepG2 cells. The FXR-1GT genotype was associated with the risk of (odds ratio, OR = 3.34, 95% CI = 1.58–7.05, p = 0.002) and earlier progression to surgery (hazard ratio, HR = 3.00, 95% CI = 1.86–4.83, p < 0.0001) in CD. Female carriers of the FXR-1GT genotype had the greatest risk of surgery (OR = 14.87 95% CI = 4.22–52.38, p < 0.0001) and early progression to surgery (HR = 6.28, 95% CI = 3.62–10.90, p < 0.0001). Women carriers of FXR-1GT polymorphism had a three-fold lower FGF19 plasma concentration versus women with FXR-1GG genotype (p < 0.0001). In HepG2 cells cotransfected with estrogen receptor (ER) and FXR, presence of estradiol further attenuated variant FXR activity. MDR1 and PXR genotypes were not associated with surgical risk. Unlike MDR1 and PXR, FXR-1GT genetic variation is associated with earlier and more frequent surgery in women with CD. This may be through ER-mediated attenuation of FXR activation.

Activation of PXR by Alpinetin Contributes to Abrogate Chemically Induced Inflammatory Bowel Disease

Alpinetin is a naturally occurring flavonoid from the ginger plants. We previously reported the identification of alpinetin as a ligand of human pregnane X receptor (hPXR). The current study investigated the role of alpinetin as a putative PXR activator in ameliorating chemically induced inflammatory bowel disease (IBD). We found that oral administration of alpinetin significantly alleviated the severity of dextran sulfate sodium (DSS)-induced colitis in mice by decreasing the inflammatory infiltration, the levels of the pro-inflammatory mediators, and the PXR target genes in the colon. In vitro, alpinetin blocked the nuclear translocation of p-p65 in lipopolysaccharide (LPS)-stimulated RAW264.7 macrophages. Further, alpinetin significantly upregulated PXR target genes and inhibited TNF-α-induced NF-κB-luciferase activity in LS174T colorectal cells; however, this regulatory effects were lost when cellular PXR gene was knocked down. In PXR transactivation assays, alpinetin increased both mouse and human PXR transactivation in a dose-dependent manner. Ligand occluding mutants, S247W/C284W and S247W/C284W/S208W, in hPXR-reporter assays, abrogated alpinetin-induced hPXR transactivation. Finally, alpinetin bound to the hPXR-ligand-binding domain (LBD) was confirmed by competitive ligand binding assay. The current study significantly extends prior observations by validating a PXR/NF-κB regulatory mechanism governing alpinetin's anti-inflammatory effects in a murine model of IBD.

Evaluating the Role of the Steroid and Xenobiotic Receptor (SXR/PXR) in PCB-153 Metabolism and Protection against Associated Adverse Effects during Perinatal and Chronic Exposure in Mice

BACKGROUND

Polychlorinated biphenyls (PCBs) are environmental toxicants; PCB exposure has been associated with adverse effects on wildlife and humans. However, the mechanisms underlying these adverse effects are not fully understood. The steroid and xenobiotic receptor [SXR; also known as the pregnane X receptor (PXR) and formally known as NR1I2] is a nuclear hormone receptor that regulates inducible metabolism of drugs and xenobiotics and is activated or inhibited by various PCB congeners.

OBJECTIVES

The aim of this study was to investigate the effects of exposure to PCB-153, the most prevalent PCB congener in human tissues, on SXR knockout mice (SXRKO) and to elucidate the role of SXR in PCB-153 metabolism and promotion of its harmful effects.

METHODS

Wild-type (WT) and SXRKO mice were chronically or perinatally exposed to a low dose (54μg/kg/d) of PCB-153. Blood, livers, and spleens were analyzed using transcriptome sequencing (RNA-seq) and molecular techniques to investigate the impacts of exposure on metabolism, oxidative stress, and hematological parameters.

RESULTS

SXRKO mice perinatally exposed to PCB-153 displayed elevated oxidative stress, symptoms of hemolytic anemia, and premature death. Transcriptomal analysis revealed that expression of genes involved in metabolic processes was altered in SXRKO mice. Elevated levels of the PCB-153 metabolite, 3-OH-PCB-153, were found in exposed SXRKO mice compared to exposed WT mice. Blood hemoglobin (HGB) levels were lower throughout the lifespan, and the occurrence of intestinal tumors was larger in SXRKO mice chronically exposed to PCB-153 compared to vehicle and WT controls.

DISCUSSION

Our results suggest that altered metabolism induced by SXR loss of function resulted in the accumulation of hydroxylated metabolites upon exposure to PCB-153, leading to oxidative stress, hemolytic anemia, and tumor development in a mouse model. These results support a major role for SXR/PXR in protection against xenobiotic-induced oxidative stress by maintaining proper metabolism in response to PCB-153 exposure. This role of SXR could be generally applicable to other environmental toxicants as well as pharmaceutical drugs. https://doi.org/10.1289/EHP6262.

Patchouli alcohol activates PXR and suppresses the NF-κB-mediated intestinal inflammatory

ETHNOPHARMACOLOGICAL RELEVANCE

The pregnane-X-receptor (PXR) is involved in inflammatory bowel disease (IBD). Patchouli alcohol (PA) has anti-inflammatory effects; however, the effect of PA on IBD pathogenesis remains largely unknown.

AIM OF THE STUDY

The aim of the present study was to investigate the anti-inflammatory effect of PA, primarily focused on crosstalk between PA-mediated PXR activation and NF-κB inhibition.

MATERIALS AND METHODS

We evaluated the anti-inflammatory effect of PA with respect to PXR/NF-κB signalling using in vitro and in vivo models. In vitro, PA, identified as a PXR agonist, was evaluated by hPXR transactivation assays and through assessing for CYP3A4 expression and activity. NF-κB inhibition was analysed based on NF-κB luciferase assays, NF-κB-mediated pro-inflammatory gene expression, and NF-κB nuclear translocation after activation of PXR by PA. In vivo, colonic mPXR and NF-κB signalling were analysed to assess PA-mediated the protective effect against dextran sulphate sodium (DSS)-induced colitis. Furthermore, pharmacological inhibition of PXR was further evaluated by examining PA protection against DSS-induced colitis.

RESULTS

PA induced CYP3A4 expression and activity via an hPXR-dependent mechanism. PA-mediated PXR activation attenuated inflammation by inhibiting NF-κB activity and nuclear translocation. The anti-inflammatory effect of PA on NF-κB was abolished by PXR knockdown. PA prevented DSS-induced inflammation by regulating PXR/NF-κB signalling, whereas pharmacological PXR inhibition abated PA-mediated suppressive effects on NF-κB inflammation signalling.

CONCLUSIONS

PA activates PXR signalling and suppresses NF-κB signalling, consequently causing amelioration of inflammation. Our results highlight the importance of PXR-NF-κB crosstalk in colitis and suggest a novel therapeutic reagent.

Role of Nuclear Receptors PXR and CAR in Xenobiotic-Induced Hepatocyte Proliferation and Chemical Carcinogenesis

Nuclear receptors pregnane X receptor (PXR) and constitutive active/androstane receptor (CAR) are xenobiotic-responsible transcriptional factors that belong to the same subfamily and are expressed abundantly in the liver. They play crucial roles in various liver functions including xenobiotic disposition and energy metabolism. CAR is also involved in xenobiotic-induced hepatocyte proliferation and hepatocarcinogenesis in rodents. However, there are some open questions on the association between chemical carcinogenesis and these nuclear receptors. These include the molecular mechanism for CAR-mediated hepatocyte proliferation and hepatocarcinogenesis. Another important question is whether PXR is associated with hepatocyte proliferation. We have recently reported a novel and unique function of PXR associated with murine hepatocyte proliferation: PXR activation alone does not induce hepatocyte proliferation but accelerates hepatocyte proliferation induced by various types of stimuli including CAR- or peroxisome proliferator-activated receptor alpha activating compounds, liver injury, and growth factors. We have also reported a role of yes-associated protein (YAP), a transcriptional cofactor controlling organ size and cell growth under the Hippo pathway, in CAR-mediated hepatocyte proliferation in mice. In this review, I will introduce our recent results as well as related studies on the roles of PXR and CAR in xenobiotic-induced hepatocyte proliferation and their molecular mechanisms.

Pregnane X receptor activation constrains mucosal NF-κB activity in active inflammatory bowel disease

Background

The Pregnane X Receptor (PXR) is a principal signal transducer in mucosal responses to xenobiotic stress. It is well-recognized that inflammatory bowel disease is accompanied by xenobiotic stress, but the importance of the PXR in limiting inflammatory responses in inflammatory bowel disease remains obscure at best.

Methods

We stimulate a total of 106 colonic biopsies from 19 Crohn’s disease patients with active disease, 36 colonic biopsies from 8 control patients, colonic organoids and various cell culture models (either proficient or genetically deficient with respect to PXR) in vitro with the PXR ligand rifampicin or vehicle. Effects on NF-κB activity are assessed by measuring interleukin-8 (IL-8) and interleukin-1ß (IL-1ß) mRNA levels by qPCR and in cell culture models by NF-κB reporter-driven luciferase activity and Western blot for signal transduction elements.

Results

We observe a strict inverse correlation between colonic epithelial PXR levels and NF-κB target gene expression in colonic biopsies from Crohn’s disease patients. PXR, activated by rifampicin, is rate-limiting for mucosal NF-κB activation in IBD. The correlation between colonic epithelial PXR levels and NF-κB target gene expression was also observed in intestinal organoids system. Furthermore, in preclinical in vitro models of intestinal inflammation, including intestinal organoids, genetic inactivation of PXR unleashes NF-κB-dependent signal transduction whereas conversely NF-κB signaling reduces levels of PXR expression.

Conclusions

Our data indicate that the PXR is a major and clinically relevant antagonist of NF-κB activity in the intestinal epithelial compartment during inflammatory bowel disease.

Emerging roles of bile acids in mucosal immunity and inflammation

Bile acids are cholesterol-derived surfactants that circulate actively between the liver and ileum and that are classically recognized for emulsifying dietary lipids to facilitate absorption. More recent studies, however, have revealed new functions of bile acids; as pleotropic signaling metabolites that regulate diverse metabolic and inflammatory pathways in multiple cell types and tissues through dynamic interactions with both germline-encoded host receptors and the microbiota. Accordingly, perturbed bile acid circulation and/or metabolism is now implicated in the pathogenesis of cholestatic liver diseases, metabolic syndrome, colon cancer, and inflammatory bowel diseases (IBDs). Here, we discuss the three-dimensional interplay between bile acids, the microbiota, and the mucosal immune system, focusing on the mechanisms that regulate intestinal homeostasis and inflammation. Although the functions of bile acids in mucosal immune regulation are only beginning to be appreciated, targeting bile acids and their cellular receptors has already proven an important area of new drug discovery.

Constitutive androstane receptor and pregnane X receptor cooperatively ameliorate DSS-induced colitis

BACKGROUND

Nuclear receptor pregnane X receptor (PXR) was shown to be protective in case of dextran sulfate sodium (DSS)-induced colitis. Constitutive androstane receptor (CAR) belongs to the same nuclear receptor subfamily with PXR. The roles of both receptors in DSS-induced colitis were evaluated.

METHODS

Wild-type, Car-null, Pxr-null, and Car/Pxr-null mice were treated with a CAR/PXR agonist or vehicle and administered 2.5% DSS in the drinking water. The typical clinical symptoms, histological scoring, proinflammatory cytokine, and apoptosis were analyzed.

RESULTS

Mice treated with the PXR agonist pregnenolone-16α-carbonitrile (PCN) were protected from DSS-induced colitis, as in a previous study. Mice treated with the CAR agonist, 4-bis[2-(3,5-dichloropyridyloxy)]benzene (TCPOBOP) were also protected from DSS-induced colitis. Interestingly, the protective effects of PCN in the Car-null mice and those of TCPOBOP in the Pxr-null mice both decreased. PCN or TCPOBOP pretreatment significantly decreased the macrophage and monocyte infiltration in DSS-induced colitis. PXR and CAR agonists reduced the mRNA expression of several proinflammatory cytokines in a PXR- and CAR-dependent manner, respectively. CAR inhibited apoptosis by inducing Gadd45b. PXR inhibited TNF-α and IL-1b and CAR induced Gadd45b in in vitro cell analyses.

CONCLUSIONS

We showed that CAR and PXR cooperatively ameliorate DSS-induced colitis. PXR and CAR protected against DSS-induced colitis by inhibiting proinflammatory cytokines and apoptosis, respectively.

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.

Pregnane X Receptor Regulates Liver Size and Liver Cell Fate by Yes-Associated Protein Activation in Mice

Activation of pregnane X receptor (PXR), a nuclear receptor that controls xenobiotic and endobiotic metabolism, is known to induce liver enlargement, but the molecular signals and cell types responding to PXR-induced hepatomegaly remain unknown. In this study, the effect of PXR activation on liver enlargement and cell change was evaluated in several strains of genetically modified mice and animal models. Lineage labeling using AAV-Tbg-Cre-treated Rosa26^EYFP mice or Sox9-Cre^ERT , Rosa26^EYFP mice was performed and Pxr-null mice or AAV Yap short hairpin RNA (shRNA)-treated mice were used to confirm the role of PXR or yes-associated protein (YAP). Treatment with selective PXR activators induced liver enlargement and accelerated regeneration in wild-type (WT) and PXR-humanized mice, but not in Pxr-null mice, by increase of cell size, induction of a regenerative hybrid hepatocyte (HybHP) reprogramming, and promotion of hepatocyte and HybHP proliferation. Mechanistically, PXR interacted with YAP and PXR activation induced nuclear translocation of YAP. Blockade of YAP abolished PXR-induced liver enlargement in mice. Conclusion: These findings revealed a function of PXR in enlarging liver size and changing liver cell fate by activation of the YAP signaling pathway. These results have implications for understanding the physiological functions of PXR and suggest the potential for manipulation of liver size and liver cell fate.

Activating the pregnane X receptor by imperatorin attenuates dextran sulphate sodium-induced colitis in mice

BACKGROUND AND PURPOSE

Activation of the human pregnane X receptor (PXR; NR1I2) has potential therapeutic uses for inflammatory bowel disease (IBD). Imperatorin (IMP), a naturally occurring coumarin, is the main bioactive ingredient of Angelica dahurica Radix, which is regularly used to treat the common cold and intestinal disorders. However, there are no data on the protective effects of IMP against IBD.

EXPERIMENTAL APPROACH

The effects of IMP on PXR-modulated cytochrome P450 3A4 (CYP3A4) expression were assessed using a PXR transactivation assay, a mammalian two-hybrid assay, a competitive ligand-binding assay, analysis of CYP3A4 mRNA and protein expression levels and measurement of CYP3A4 activity using a cell-based reporter gene assay and in vitro model. The inhibitory effects of IMP on NF-κB activity were evaluated by a reporter assay and NF-κB p65 nuclear translocation. The anti-IBD effects of IMP were investigated in a dextran sulphate sodium (DSS)-induced colitis mouse model. Colon inflammatory cytokines were assessed by elisa.

KEY RESULTS

IMP activated CYP3A4 promoter activity, recruited steroid receptor coactivator 1 to the ligand-binding domain of PXR and increased the expression and activity of CYP3A4. PXR knockdown substantially reduced IMP-induced increase in CYP3A4 expression. Furthermore, IMP-mediated PXR activation suppressed the nuclear translocation of NF-κB and down-regulated LPS-induced expression of pro-inflammatory genes. Nevertheless, PXR knockdown partially reduced the IMP-mediated inhibition of NF-κB. IMP ameliorated DSS-induced colitis by PXR/NF-κB signalling.

CONCLUSIONS AND IMPLICATIONS

IMP acts as a PXR agonist to attenuate DSS-induced colitis by suppression of the NF-κB-mediated pro-inflammatory response in a PXR/NF-κB-dependent manner.

Enteric Microbiota⁻Gut⁻Brain Axis from the Perspective of Nuclear Receptors

Nuclear receptors (NRs) play a key role in regulating virtually all body functions, thus maintaining a healthy operating body with all its complex systems. Recently, gut microbiota emerged as major factor contributing to the health of the whole organism. Enteric bacteria have multiple ways to influence their host and several of them involve communication with the brain. Mounting evidence of cooperation between gut flora and NRs is already available. However, the full potential of the microbiota interconnection with NRs remains to be uncovered. Herewith, we present the current state of knowledge on the multifaceted roles of NRs in the enteric microbiota–gut–brain axis.

Effects of polymorphisms in NR1I2, CYP3A4, and ABC transporters on the steady-state plasma trough concentrations of bosutinib in Japanese patient with chronic myeloid leukemia

We investigated the effects of polymorphisms in NR1I2 (7635A>G, 8055C>T), CYP3A4 (20230G>A), ABCB1 (1199G>A, 1236C>T, 2677G>T/A, 3435C>T), and ABCG2 (421C>A) on the mean plasma trough concentrations (C₀) of bosutinib at the steady-state in 30 Japanese patients with chronic myeloid leukemia. Bosutinib C₀ values were monitored using high-performance liquid chromatography. The median coefficient of variation (CV) value of the bosutinib C₀ for one patient (intrapatient) during bosutinib therapy was 25.9% (range: 7.66-44.24%). During bosutinib therapy, 17 of 30 patients received 300 mg/day bosutinib. The interpatient CV value for the bosutinib C₀ after administration of 300 mg/day was 45.0%. There were no significant differences in the bosutinib C₀ between genotypes for ABCB1, ABCG2, and CYP3A4 polymorphisms. However, the bosutinib C₀ in patients with the NR1I2 7635G/G or 8055T/T genotype was significantly lower than those in patients with the 7635A allele or 8055C allele, respectively (P = 0.050 and 0.022, respectively). In addition, the bosutinib C₀ in patients with both NR1I2 7635G/G and 8055T/T genotypes was significantly lower than those in patients with other genotypes (P = 0.022). Because patients with the NR1I2 7635G/G or 8055T/T genotype may have increased activity of pregnane X receptor-regulated genes and thereafter higher intestinal expression of CYP3A4 and ABC efflux drug transporters, these patients may have a lower bosutinib C₀. Therefore, information on the NR1I2 genotype may be useful for achieving optimal systemic exposure of bosutinib.

Targeting the PXR-TLR4 signaling pathway to reduce intestinal inflammation in an experimental model of necrotizing enterocolitis

BackgroundThere is substantial evidence that signaling through Toll-like receptor 4 (TLR4) contributes to the pathogenesis of necrotizing enterocolitis (NEC). Pregnane X receptor (PXR), a xenobiotic sensor and signaling intermediate for certain host-bacterial metabolites, has been shown to negatively regulate TLR4 signaling. Here we investigated the relationship between PXR and TLR4 in the developing murine intestine and explored the capacity of PXR to modulate inflammatory pathways involved in experimental NEC.MethodsWild-type and PXR^-/- mice were studied at various time points of development in an experimental model of NEC. In addition, we studied the ability of the secondary bile acid lithocholic acid (LCA), a known PXR agonist in liver, to activate intestinal PXR and reduce NEC-related intestinal inflammation.ResultsWe found a reciprocal relationship between the developmental expression of PXR and TLR4 in wild-type murine intestine, with PXR acting to reduce TLR4 expression by decreasing TLR4 mRNA stability. In addition, PXR^-/- mice exhibited a remarkably heightened severity of disease in experimental NEC. Moreover, LCA attenuated intestinal proinflammatory responses in the early stages of experimental NEC.ConclusionThese findings provide proactive insights into the regulation of TLR4 in the developing intestine. Targeting PXR may be a novel approach for NEC prevention.

Update on Bile Acid Malabsorption: Finally Ready for Prime Time?

PURPOSE OF REVIEW

To provide an update on the prevalence, pathophysiology, disease associations, and treatment options for bile acid malabsorption (BAM).

RECENT FINDINGS

•Molecular mechanisms-BAs prevent water reabsorption and increase water secretion by intracellular mediators, increasing aquaporin channels and intracellular permeability. •Inflammatory bowel disease-new molecular mechanisms of BAM are identified in patients without ileal disease, including changes in expression of ileal BA transporter and nuclear receptors involved in BA homeostasis. •Microscopic colitis-BAM is one of the mechanisms leading to microscopic colitis. •Diagnostic testing-new diagnostic tests have been launched in the USA (serum C4 and fecal 48-h BA excretion); stimulated FGF19 has higher detection of BAM compared to fasting sample alone. •Treatment-investigational FXR agonists may provide a daily, oral option for treatment of BAM instead of BA sequestrants. There is a greater appreciation of the biological role of bile acids across multiple fields of medicine, including gastrointestinal indications.

Advancements in drug development for diarrhea-predominant irritable bowel syndrome

INTRODUCTION

Diarrhea-predominant irritable bowel syndrome (IBS-D) is a common disorder characterized by a complex pathophysiology hampering optimal targeted drug development. Recent advances in our understanding of key underlying mechanisms prompted novel therapeutics including novel pharmacological approaches.

AREAS COVERED

This review summarizes the latest advancements in the pipeline of IBS-D drugs focusing on new pharmacological targets, efficacy and safety of medicinal products considering the recent harmonization of regulatory requirements by the FDA and the EMA.

EXPERT OPINION

The new 5-HT3 receptor antagonist ramosetron appears a promising therapeutic approach devoid of significant adverse events, although it is presently unavailable in Western countries, most likely because of the precautionary approach taken by regulatory agencies with this drug class. New pharmacological concepts on full agonists/antagonists, mixed-receptor activity and novel drug targets may streamline the present drug pipeline along with the adherence on new regulatory guidelines on outcome measures. Eluxadoline can be taken as an example of this paradigm shift. It has now been granted marketing authorization for IBS-D on both sides of the Atlantic, but it is still considered as a second-line agent by the NICE. There is still much work to be done to fully cover clinical needs of patients with IBS-D.

Rifaximin decreases virulence of Crohn's disease-associated Escherichia coli and epithelial inflammatory responses

Escherichia coli with an adherent and invasive pathotype (AIEC) is implicated in the pathogenesis of Crohn's disease (CD). Rifaximin improves symptoms in mild-to-moderate CD. It is unclear if this outcome is due to its effects on bacteria or intestinal epithelial inflammatory responses. We examined the effects of rifaximin on the growth and virulence of CD-associated E. coli and intestinal epithelial inflammatory responses. Seven well-characterized CD-associated E. coli strains (six AIEC, one non-AIEC; four rifaximin-resistant, three sensitive) were evaluated. We assessed the effects of rifaximin on CD-associated E. coli growth, adhesion to, and invasion of epithelial cells, virulence gene expression, motility, and survival in macrophages. Additionally, we determined the effects of rifaximin on intestinal epithelial inflammatory responses. In vitro rifaximin exerted a dose-dependent effect on the growth of sensitive strains but did not affect the growth of resistant strains. Rifaximin reduced adhesion, invasion, virulence gene expression and motility of CD-associated E. coli in a manner that was independent of its antimicrobial effect. Furthermore, rifaximin reduced IL-8 secretion from pregnane X receptor-expressing T84 colonic epithelial cells. The effect of rifaximin on adhesion was largely attributable to its action on bacteria, whereas decreases in invasion and cytokine secretion were due to its effect on the epithelium. In conclusion, our results show that rifaximin interferes with multiple steps implicated in host-AIEC interactions related to CD, including adhesion to, and invasion of epithelial cells, virulence gene expression, motility, and pro-inflammatory cytokine secretion. Further study is required to determine the relationship of these effects to clinical responses in CD patients.

PXR: More Than Just a Master Xenobiotic Receptor

Pregnane X receptor (PXR) is a nuclear receptor considered to be a master xenobiotic receptor that coordinately regulates the expression of genes encoding drug-metabolizing enzymes and drug transporters to essentially detoxify and eliminate xenobiotics and endotoxins from the body. In the past several years, the function of PXR in the regulation of xenobiotic metabolism has been extensively studied, and the role of PXR as a xenobiotic sensor has been well established. It is now clear, however, that PXR plays many other roles in addition to its xenobiotic-sensing function. For instance, recent studies have discovered previously unidentified roles of PXR in inflammatory response, cell proliferation, and cell migration. PXR also contributes to the dysregulation of these processes in diseases states. These recent discoveries of the role of PXR in the physiologic and pathophysiologic conditions of other cellular processes provides the possibility of novel targets for drug discovery. This review highlights areas of PXR regulation that require further clarification and summarizes the recent progress in our understanding of the nonxenobiotic functions of PXR that can be explored for relevant therapeutic applications.

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 ligand-activated 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 gut-liver axis and its role in regulating bacterial interactions with the host in CLD has not been explored. PubMed 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.

Pregnane X receptor promotes ethanol-induced hepatosteatosis in mice

The pregnane X receptor (PXR, NR1I2) is a xenobiotic-sensing nuclear receptor that modulates the metabolic response to drugs and toxic agents. Both PXR activation and deficiency promote hepatic triglyceride accumulation, a hallmark feature of alcoholic liver disease. However, the molecular mechanism of PXR-mediated activation of ethanol (EtOH)-induced steatosis is unclear. Here, using male wildtype (WT) and Pxr-null mice, we examined PXR-mediated regulation of chronic EtOH-induced hepatic lipid accumulation and hepatotoxicity. EtOH ingestion for 8 weeks significantly (1.8-fold) up-regulated Pxr mRNA levels in WT mice. The EtOH exposure also increased mRNAs encoding hepatic constitutive androstane receptor (3-fold) and its target, Cyp2b10 (220-fold), in a PXR-dependent manner. Furthermore, WT mice had higher serum EtOH levels and developed hepatic steatosis characterized by micro- and macrovesicular lipid accumulation. Consistent with the development of steatosis, lipogenic gene induction was significantly increased in WT mice, including sterol regulatory element-binding protein 1c target gene fatty-acid synthase (3.0-fold), early growth response-1 (3.2-fold), and TNFα (3.0-fold), whereas the expression of peroxisome proliferator-activated receptor α target genes was suppressed. Of note, PXR deficiency suppressed these changes and steatosis. Protein levels, but not mRNAs levels, of EtOH-metabolizing enzymes, including alcohol dehydrogenase 1, aldehyde dehydrogenase 1A1, and catalase, as well as the microsomal triglyceride transfer protein, involved in regulating lipid output were higher in Pxr-null than in WT mice. These findings establish that PXR signaling contributes to ALD development and suggest that PXR antagonists may provide a new approach for ALD therapy.

Rifaximin and diverticular disease: Position paper of the Italian Society of Gastroenterology (SIGE)

Management of diverticular disease has significantly improved in the last decade. Antibiotic treatment is used for symptom relief and prevention of complications. In Italy, the non-absorbable antibiotic rifaximin is one of the most frequently used drugs, and it is perceived as the reference drug to treat symptomatic diverticular disease. Its non-systemic absorption and high faecal concentrations have oriented rifaximin use to the gastrointestinal tract, where rifaximin exerts eubiotic effects representing an additional value to its antibiotic activity. This position paper was commissioned by the Italian Society of Gastroenterology governing board for a panel of experts (RC, GB, BA) to highlight the indications for treatment of diverticular disease. There is a lack of rationale for drug use for the primary prevention of diverticulitis in patients with diverticulosis; thus, rifaximin use should be avoided. The cyclic use of rifaximin, in association with high-fibre intake, is safe and useful for the treatment of symptomatic uncomplicated diverticular disease, even if the cost-efficacy of long-term treatment remains to be determined. The use of rifaximin in the prevention of diverticulitis recurrence is promising, but the low therapeutic advantage needs to be verified. No evidence is available on the efficacy of rifaximin treatment on acute uncomplicated diverticulitis.

Tauroursodeoxycholic acid protects bile acid homeostasis under inflammatory conditions and dampens Crohn's disease-like ileitis

Bile acids regulate the expression of intestinal bile acid transporters and are natural ligands for nuclear receptors controlling inflammation. Accumulating evidence suggests that signaling through these receptors is impaired in inflammatory bowel disease. We investigated whether tauroursodeoxycholic acid (TUDCA), a secondary bile acid with cytoprotective properties, regulates ileal nuclear receptor and bile acid transporter expression and assessed its therapeutic potential in an experimental model of Crohn's disease (CD). Gene expression of the nuclear receptors farnesoid X receptor, pregnane X receptor and vitamin D receptor and the bile acid transporters apical sodium-dependent bile acid transporter and organic solute transporter α and β was analyzed in Caco-2 cell monolayers exposed to tumor necrosis factor (TNF)α, in ileal tissue of TNF^ΔARE/WT mice and in inflamed ileal biopsies from CD patients by quantitative real-time polymerase chain reaction. TNF^ΔARE/WT mice and wild-type littermates were treated with TUDCA or placebo for 11 weeks and ileal histopathology and expression of the aforementioned genes were determined. Exposing Caco-2 cell monolayers to TNFα impaired the mRNA expression of nuclear receptors and bile acid transporters, whereas co-incubation with TUDCA antagonized their downregulation. TNF^ΔARE/WT mice displayed altered ileal bile acid homeostasis that mimicked the situation in human CD ileitis. Administration of TUDCA attenuated ileitis and alleviated the downregulation of nuclear receptors and bile acid transporters in these mice. These results show that TUDCA protects bile acid homeostasis under inflammatory conditions and suppresses CD-like ileitis. Together with previous observations showing similar efficacy in experimental colitis, we conclude that TUDCA could be a promising therapeutic agent for inflammatory bowel disease, warranting a clinical trial.

Constitutive androstane receptor regulates the intestinal mucosal response to injury

BACKGROUND AND PURPOSE

The pathogenesis of the inflammatory bowel diseases (IBD), comprising Crohn's disease (CD) and ulcerative colitis (UC), involves aberrant interactions between a genetically susceptible individual, their microbiota and environmental factors. Alterations in xenobiotic receptor expression and function are associated with increased risk for IBD. Here, we have assessed the role of the constitutive androstane receptor (CAR), a xenobiotic receptor closely related to the pregnane X receptor, in the regulation of intestinal mucosal homeostasis.

EXPERIMENTAL APPROACH

CAR expression was assessed in intestinal mucosal biopsies obtained from CD and UC patients, and in C57/Bl6 mice exposed to dextran sulphate sodium (DSS; 3.5% w/v in drinking water) to evoke intestinal inflammation and tissue damage. CAR-deficient mice were exposed to DSS and mucosal healing assessed. Modulation of wound healing by CAR was assessed in vitro. The therapeutic potential of CAR activation was evaluated, using 3,3',5,5'-tetrachloro-1,4-bis(pyridyloxy)benzene (TCPOBOP), a selective rodent CAR agonist.

KEY RESULTS

CAR expression was reduced in CD and UC samples, compared with expression in healthy controls. This was reproduced in our DSS studies, where CAR expression was reduced in colitic mice. CAR-deficient mice exhibited reduced healing following DSS exposure. In vitro, CAR activation accelerated intestinal epithelial wound healing by enhancing cell migration. Lastly, treating mice with TCPOBOP, following induction of colitis, enhanced mucosal healing.

CONCLUSION AND IMPLICATIONS

Our results support the notion that xenobiotic sensing is altered during intestinal inflammation, and suggest that CAR activation may prove effective in enhancing mucosal healing in patients with IBD.

Integrative Network-based Analysis of Colonic Detoxification Gene Expression in Ulcerative Colitis According to Smoking Status

BACKGROUNDS AND AIMS

The effect of cigarette smoking [CS] is ambivalent since smoking improves ulcerative colitis [UC] while it worsens Crohn's disease [CD]. Although this clinical relationship between inflammatory bowel disease [IBD] and tobacco is well established, only a few experimental works have investigated the effect of smoking on the colonic barrier homeostasis focusing on xenobiotic detoxification genes.

METHODS

A comprehensive and integrated comparative analysis of the global xenobiotic detoxification capacity of the normal colonic mucosa of healthy smokers [n = 8] and non-smokers [n = 9] versus the non-affected colonic mucosa of UC patients [n = 19] was performed by quantitative real-time polymerase chain reaction [qRT PCR]. The detoxification gene expression profile was analysed in CD patients [n = 18], in smoking UC patients [n = 5], and in biopsies from non-smoking UC patients cultured or not with cigarette smoke extract [n = 8].

RESULTS

Of the 244 detoxification genes investigated, 65 were dysregulated in UC patients in comparison with healthy controls or CD patients. The expression of ≥ 45/65 genes was inversed by CS in biopsies of smoking UC patients in remission and in colonic explants of UC patients exposed to cigarette smoke extract. We devised a network-based data analysis approach for differentially assessing changes in genetic interactions, allowing identification of unexpected regulatory detoxification genes that may play a major role in the beneficial effect of smoking on UC.

CONCLUSIONS

Non-inflamed colonic mucosa in UC is characterised by a specifically altered detoxification gene network, which is partially restored by tobacco. These mucosal signatures could be useful for developing new therapeutic strategies and biomarkers of drug response in UC.

A pharmacogenomic study on the pharmacokinetics of tacrolimus in healthy subjects using the DMETTM Plus platform

Genetic association studies on the pharmacokinetics of tacrolimus have reported conflicting results, except for the role of the CYP3A5*3 polymorphism. The objective of this study was to identify genetic variants affecting the pharmacokinetics of tacrolimus using the DMETTM Plus microarray in 42 healthy males. Aside from CYP3A5*3, the rs3814055 polymorphism in the NR1I2 gene was associated with the tacrolimus pharmacokinetics based on false discovery rate-corrected multiple tests and the least absolute shrinkage and selection operator analysis. The area under the concentration-time curve to the last quantifiable time point (AUClast) was 3.42 times greater in subjects with homozygous mutations in both genes (CYP3A5*3/*3 and NR1I2 T/T) than in wild-type subjects. The two variants explained the 54% variability in the tacrolimus AUClast. An in vitro luciferase reporter assay indicated that downregulation of PXR expression is the likely molecular mechanism responsible for the increased exposure to tacrolimus in subjects carrying the rs3814055 C>T variant.

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.

Pregnenolone 16α-carbonitrile ameliorates concanavalin A-induced liver injury in mice independent of the nuclear receptor PXR activation

The pregnane X receptor (PXR) is well-known as a key regulator of drug/xenobiotic clearance. Upon activation by ligand, PXR transcriptionally upregulates the expression of drug-metabolizing enzymes and drug transporters. Recent studies have revealed that PXR also plays a role in regulating immune/inflammatory responses. Specific PXR activators, including synthetic ligands and phytochemicals, have been shown to ameliorate chemically induced colitis in mice. In this study, we investigated an anti-inflammatory effect of pregnenolone 16α-carbonitrile (PCN), a prototypical activator for rodent PXR, in concanavalin A (Con A)-induced liver injury, a model of immune-mediated liver injury, using wild-type and Pxr^-/- mice. Unexpectedly, pretreatment with PCN significantly ameliorated Con A-induced liver injury in not only wild-type but Pxr^-/- mice as well, accompanied with lowered plasma ALT levels and histological improvements. Pretreatment with PCN was found to significantly repress the induction of Cxcl2 and Ccl2 mRNA expression and neutrophil infiltration into the liver of both wild-type and Pxr^-/- mice at the early time point of Con A-induced liver injury. Our results indicate that PCN has unexpected immunosuppressive activity independent of PXR activation to protect mice from immune-mediated liver injury induced by Con A.

Pregnane X Receptor Activation Attenuates Inflammation-Associated Intestinal Epithelial Barrier Dysfunction by Inhibiting Cytokine-Induced Myosin Light-Chain Kinase Expression and c-Jun N-Terminal Kinase 1/2 Activation

The inflammatory bowel diseases (IBDs) are chronic inflammatory disorders with a complex etiology. IBD is thought to arise in genetically susceptible individuals in the context of aberrant interactions with the intestinal microbiota and other environmental risk factors. Recently, the pregnane X receptor (PXR) was identified as a sensor for microbial metabolites, whose activation can regulate the intestinal epithelial barrier. Mutations in NR1I2, the gene that encodes the PXR, have been linked to IBD, and in animal models, PXR deletion leads to barrier dysfunction. In the current study, we sought to assess the mechanism(s) through which the PXR regulates barrier function during inflammation. In Caco-2 intestinal epithelial cell monolayers, tumor necrosis factor-α/interferon-γ exposure disrupted the barrier and triggered zonula occludens-1 relocalization, increased expression of myosin light-chain kinase (MLCK), and activation of c-Jun N-terminal kinase 1/2 (JNK1/2). Activation of the PXR [rifaximin and [[3,5-Bis(1,1-dimethylethyl)-4-hydroxyphenyl]ethenylidene]bis-phosphonic acid tetraethyl ester (SR12813); 10 μM] protected the barrier, an effect that was associated with attenuated MLCK expression and JNK1/2 activation. In vivo, activation of the PXR [pregnenolone 16α-carbonitrile (PCN)] attenuated barrier disruption induced by toll-like receptor 4 activation in wild-type, but not Pxr-/-, mice. Furthermore, PCN treatment protected the barrier in the dextran-sulfate sodium model of experimental colitis, an effect that was associated with reduced expression of mucosal MLCK and phosphorylated JNK1/2. Together, our data suggest that the PXR regulates the intestinal epithelial barrier during inflammation by modulating cytokine-induced MLCK expression and JNK1/2 activation. Thus, targeting the PXR may prove beneficial for the treatment of inflammation-associated barrier disruption in the context of IBD.

Small-molecule modulators of PXR and CAR

Two nuclear receptors, the pregnane X receptor (PXR) and the constitutive androstane receptor (CAR), participate in the xenobiotic detoxification system by regulating the expression of drug-metabolizing enzymes and transporters in order to degrade and excrete foreign chemicals or endogenous metabolites. This review aims to expand the perceived relevance of PXR and CAR beyond their established role as master xenosensors to disease-oriented areas, emphasizing their modulation by small molecules. Structural studies of these receptors have provided much-needed insight into the nature of their binding promiscuity and the important elements that lead to ligand binding. Reports of species- and isoform-selective activation highlight the need for further scrutiny when extrapolating from animal data to humans, as animal models are at the forefront of early drug discovery. This article is part of a Special Issue entitled: Xenobiotic nuclear receptors: New Tricks for An Old Dog, edited by Dr. Wen Xie.