Regulation of CAR and PXR Expression in Health and Disease

Rifampicin and its derivatives: stability, disposition, and affinity towards pregnane X receptor employing 2D and 3D primary human hepatocytes

Rifampicin is a model ligand of the pregnane X receptor (PXR), the nuclear receptor involved in the regulation of cytochrome P450 3A4 (CYP3A4). Rifampicin forms several degradation products and metabolites of which 25-desacetylrifampicin is the most abundant in vivo. Here, we aimed to study both the stability and metabolism of rifampicin in media and 2D and 3D primary human hepatocytes (PHHs). Additionally, we analyzed interactions of rifampicin derivatives with PXR. We described that rifampicin gradually degrades by more than 50 % in the medium partly into quinone over 72 h. We observed 25-desacetylrifampicin in 2D PHHs but not in 3D PHHs. Contrary, rifampicin was converted into quinone in a one-direction process in media of 3D PHHs. The potency of rifampicin and its derivatives to activate human PXR was arranged as follows: 3-formylrifamycin SV > rifampicin quinone > rifampicin > rifampicin N-oxide > 25-desacetylrifampicin, respectively, but none activates mouse and rat PXR. The binding differences between rifampicin and 25-desacetylrifampicin were modeled in silico. Finally, we showed that overexpressed uptake organic anion transporting polypeptide 1B1 (OATP1B1) potentiated activation of PXR by rifampicin and rifampicin quinone, but overexpressed efflux multidrug resistance protein 1 (MDR1) decreased PXR activation by all derivatives.

Isotschimgine promotes lifespan, healthspan and neuroprotection of Caenorhabditis elegans via the activation of nuclear hormone receptors

Isotschimgine (ITG) is a bornane-type monoterpenoid derivative naturally occurring in genus Ferula plants and propolis. Its effects on aging and the underlying mechanisms are not yet well understood. This study employed Caenorhabditis elegans (C. elegans) as a model organism to evaluate the potential of ITG in extending lifespan, enhancing healthspan, and promoting neuroprotection, while exploring the underlying mechanisms involved. The results showed that ITG extended the lifespan and healthspan of C. elegans, significantly enhanced stress resistance and detoxification functions. Studies on mutants and qPCR data indicated that ITG-mediated lifespan extension was modulated by the insulin/IGF-1 signaling pathway and nuclear hormone receptors. Furthermore, ITG markedly increased stress-responsive genes, including daf-16 and its downstream genes sod-3 and hsp-16.2, as well as NHR downstream detoxification-related genes cyp35a1, cyp35b3, cyp35c1, gst-4, pgp-3 and pgp-13. Additionally, ITG alleviated β-amyloid-induced paralysis and behavioral dysfunction in transgenic C. elegans strains. The neuroprotective efficacy of ITG was weakened by RNAi knockdown of nuclear hormone receptors daf-12 and nhr-8. Overall, our study identifies ITG as a potential compound for promoting longevity and neuroprotection, mediated through nuclear hormone receptors.

Hepatic Nuclear Receptors in Cholestasis-to-Cholangiocarcinoma Pathology

Cholestasis, characterized by impaired bile flow, is associated with an increased risk of cholangiocarcinoma (CCA), a malignancy originating from the biliary epithelium and hepatocytes. Hepatic nuclear receptors (NRs) are pivotal in regulating bile acid and metabolic homeostasis, and their dysregulation is implicated in cholestatic liver diseases and the progression of liver cancer. This review elucidates the role of various hepatic NRs in the pathogenesis of cholestasis-to-CCA progression. We explore their impact on bile acid metabolism as well as their interactions with other signaling pathways implicated in CCA development. Additionally, we introduce available murine models of cholestasis/primary sclerosing cholangitis leading to CCA and discuss the clinical potential of targeting hepatic NRs as a promising approach for the prevention and treatment of cholestatic liver diseases and CCA. Understanding the complex interplay between hepatic NRs and cholestasis-to-CCA pathology holds promise for the development of novel preventive and therapeutic strategies for this devastating disease.

Moldable Plastics (Polycaprolactone) can be Acutely Toxic to Developing Zebrafish and Activate Nuclear Receptors in Mammalian Cells

Popularized on social media, hand-moldable plastics are formed by consumers into tools, trinkets, and dental prosthetics. Despite the anticipated dermal and oral contact, manufacturers share little information with consumers about these materials, which are typically sold as microplastic-sized resin pellets. Inherent to their function, moldable plastics pose a risk of dermal and oral exposure to unknown leachable substances. We analyzed 12 moldable plastics advertised for modeling and dental applications and determined them to be polycaprolactone (PCL) or thermoplastic polyurethane (TPU). The bioactivities of the most popular brands advertised for modeling applications of each type of polymer were evaluated using a zebrafish embryo bioassay. While water-borne exposure to the TPU pellets did not affect the targeted developmental end points at any concentration tested, the PCL pellets were acutely toxic above 1 pellet/mL. The aqueous leachates of the PCL pellets demonstrated similar toxicity. Methanolic extracts from the PCL pellets were assayed for their bioactivity using the Attagene FACTORIAL platform. Of the 69 measured end points, the extracts activated nuclear receptors and transcription factors for xenobiotic metabolism (pregnane X receptor, PXR), lipid metabolism (peroxisome proliferator-activated receptor γ, PPARγ), and oxidative stress (nuclear factor erythroid 2-related factor 2, NRF2). By nontargeted high-resolution comprehensive two-dimensional gas chromatography (GC × GC-HRT), we tentatively identified several compounds in the methanolic extracts, including PCL oligomers, a phenolic antioxidant, and residues of suspected antihydrolysis and cross-linking additives. In a follow-up zebrafish embryo bioassay, because of its stated high purity, biomedical grade PCL was tested to mitigate any confounding effects due to chemical additives in the PCL pellets; it elicited comparable acute toxicity. From these orthogonal and complementary experiments, we suggest that the toxicity was due to oligomers and nanoplastics released from the PCL rather than chemical additives. These results challenge the perceived and assumed inertness of plastics and highlight their multiple sources of toxicity.

Adverse outcome pathway for pregnane X receptor-induced hypercholesterolemia

Pharmaceuticals and environmental contaminants contribute to hypercholesterolemia. Several chemicals known to cause hypercholesterolemia, activate pregnane X receptor (PXR). PXR is a nuclear receptor, classically identified as a sensor of chemical environment and regulator of detoxification processes. Later, PXR activation has been shown to disrupt metabolic functions such as lipid metabolism and recent findings have shown PXR activation to promote hypercholesterolemia through multiple mechanisms. Hypercholesterolemia is a major causative risk factor for atherosclerosis and greatly promotes global health burden. Metabolic disruption by PXR activating chemicals leading to hypercholesterolemia represents a novel toxicity pathway of concern and requires further attention. Therefore, we constructed an adverse outcome pathway (AOP) by collecting the available knowledge considering the molecular mechanisms for PXR-mediated hypercholesterolemia. AOPs are tools of modern toxicology for systematizing mechanistic knowledge to assist health risk assessment of chemicals. AOPs are formalized and structured linear concepts describing a link between molecular initiating event (MIE) and adverse outcome (AO). MIE and AO are connected via key events (KE) through key event relationships (KER). We present a plausible route of how PXR activation (MIE) leads to hypercholesterolemia (AO) through direct regulation of cholesterol synthesis and via activation of sterol regulatory element binding protein 2-pathway.

Association Between C-Reactive Protein and Albumin Ratios and Risk of Mortality in Patients with Chronic Obstructive Pulmonary Disease

Purpose

This study was to evaluate the association between C-reactive protein (CRP) to albumin (ALB) ratio (CAR) and the risk of mortality in patients with chronic obstructive pulmonary disease (COPD).

Methods

In this retrospective cohort study, clinical data were extracted from the National Institutes of Health National Health and Nutrition Examination Survey (NHANES) database between 2007 and 2010. Cox proportional hazard regressions were performed to assess the association between CAR and 5-year mortality in COPD patients. Subgroup analyses were applied to identify the consistency of the association based on the severity of COPD, gender, body mass index (BMI), smoking status, cardiovascular disease (CVD), and chronic kidney disease (CKD), and diabetes. The area under the curve (AUC) of the receiver operator characteristic (ROC) curve analysis was used to evaluate the predictive performance of CAR.

Results

A total of 1210 COPD patients were included, of which 110 COPD patients (9.09%) had 5-year mortality. The mean follow-up was 57.76 (0.33) months. A higher CAR was associated with an increased risk of 5-year mortality in COPD patients [hazard ratio (HR): 1.94, 95% confidence interval (CI): 1.07 to 3.50, P =0.029)]. Subgroup analysis showed that the association between CAR and mortality was especially suitable for COPD patients with mild COPD, in COPD patients who were still smoking, in COPD patients with BMI <=29.9 kg/m2, in COPD patients who were without CVD, in COPD patients who were without diabetes, and COPD patients who were without CKD. The AUCs of CAR for predicting 1-year, 3-year, and 5-year mortality in COPD patients were 0.735, 0.615, and 0.608, respectively.

Conclusion

CAR is strongly correlated with mortality in patients with COPD and CAR could be served as a prognostic biomarker for patients with COPD. This study may provide a promising prognostic biomarker for risk stratification and clinical management of patients with COPD.

Panaxytriol upregulates CYP3A4 expression through the interaction between nuclear regulators and DNA response elements

ETHNOPHARMACOLOGICAL RELEVANCE

Cytochrome P3A4 (CYP3A4) is a crucial drug-metabolizing enzyme, and its expression is regulated by the pregnane X receptor (PXR), constitutive androstane receptor (CAR), steroid receptor coactivator 1 (SRC-1), and acetyltransferase P300. Panaxytriol is a naturally derived active substance extracted from the roots of Panax ginseng C. A. Mey. which is widely used clinically. Our previous studies have shown that panaxytriol induces CYP3A4 expression through PXR activation, which is antagonized by high CAR expression. However, the underlying mechanism remains unclear.

AIM OF THE STUDY

This study aimed to investigate the mechanism of panaxytriol in inducing CYP3A4 expression via interactions between nuclear regulators and DNA response elements.

MATERIALS AND METHODS

Immunoprecipitation technique was used to assess the binding levels of PXR and CAR with the coactivators SRC-1 and P300 in HepG2 and Huh-7 cells. Furthermore, chromatin immunoprecipitation assay was used to investigate the PXR and CAR interaction with the CYP3A4 promoter response element ER-6/DR-3.

RESULTS

The binding of PXR to SRC-1, P300, and the response elements ER-6 and DR-3 was improved with an increase in panaxytriol concentration (10-80 μM), and the binding affinity was further enhanced upon CAR silencing. The binding of CAR to SRC-1 and the response elements ER-6 and DR-3 was significantly higher at 80 μM panaxytriol, whereas no significant binding was observed between CAR and P300.

CONCLUSION

Panaxytriol promoted the recruitment of PXR to SRC-1 and P300, binding to ER-6 and DR-3, and upregulating CYP3A4 expression. Furthermore, an interactive dialogue regulatory mechanism between PXR and CAR was observed.

Network-Based Prediction of Side Effects of Repurposed Antihypertensive Sartans against COVID-19 via Proteome and Drug-Target Interactomes

The potential of targeting the Renin-Angiotensin-Aldosterone System (RAAS) as a treatment for the coronavirus disease 2019 (COVID-19) is currently under investigation. One way to combat this disease involves the repurposing of angiotensin receptor blockers (ARBs), which are antihypertensive drugs, because they bind to angiotensin-converting enzyme 2 (ACE2), which in turn interacts with the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. However, there has been no in silico analysis of the potential toxicity risks associated with the use of these drugs for the treatment of COVID-19. To address this, a network-based bioinformatics methodology was used to investigate the potential side effects of known Food and Drug Administration (FDA)-approved antihypertensive drugs, Sartans. This involved identifying the human proteins targeted by these drugs, their first neighbors, and any drugs that bind to them using publicly available experimentally supported data, and subsequently constructing proteomes and protein-drug interactomes. This methodology was also applied to Pfizer's Paxlovid, an antiviral drug approved by the FDA for emergency use in mild-to-moderate COVID-19 treatment. The study compares the results for both drug categories and examines the potential for off-target effects, undesirable involvement in various biological processes and diseases, possible drug interactions, and the potential reduction in drug efficiency resulting from proteoform identification.

Effects of aqueous extract from Baiyedancong-Oolong tea on cytochrome P450 enzymes activities, P-gp and OATs transport abilities and transcription levels in mice

Introduction

Recent studies have been conducted on its influence on drug metabolism and its potential mechanisms, among which the most studies have been focused on CYP3A enzymes.

Methods

In this study, Baiyedancong Oolong tea (BOT) was processed by freeze- and hot air-drying techniques separately to obtain the aqueous extracts of freeze-and hot-dried BOT (FBOT and HBOT, respectively). High and low doses of FBOT (1463.7 and 292.74 mg/kg/d, respectively) and HBOT (1454.46 mg/kg/d, 290.89, respectively) were administered to mice for 7 days.

Results

Aqueous extracts from BOT simultaneously improved liver CYP3A, CYP2E1, and CYP2C37 activities and weakened the transport ability of P-gp and OATs in a dose-dependent manner, thus affecting multiple links of oral drug metabolism in liver, intestinal absorption and metabolism, and renal excretion. Moreover, aqueous extracts from BOT significantly increased the mRNA expressions of liver CYP3A11 and CYP2C37 as well as intestinal CYP3A11. Decreased transcription levels of MDR1 encoding P-gp in small intestine and renal OAT1 and OAT3, which was in the same direction as the regulation of the above enzyme activities and transport capacities. Besides, the transcription level of liver CYP2E1 was weakened, which was inconsistent with its corresponding enzyme activity, suggesting that the increased CYP2E1 activity may be caused by other mechanisms.

Conclusion

Daily consumption or high dose administration of BOT and its related products may affect drug absorption, metabolisms, and excretion.

Integrated transcriptomic analysis of liver and kidney after 28 days of thioacetamide treatment in rats

Thioacetamide (TAA) was developed as a pesticide; however, it was soon found to cause hepatic and renal toxicity. To evaluate target organ interactions during hepatotoxicity, we compared gene expression profiles in the liver and kidney after TAA treatment. Sprague-Dawley rats were treated daily with oral TAA and then sacrificed, and their tissues were evaluated for acute toxicity (30 and 100 mg/kg bw/day), 7-day (15 and 50 mg/kg bw/day), and 4-week repeated-dose toxicity (10 and 30 mg/kg). After the 4-week repeated toxicity study, total RNA was extracted from the liver and kidneys, and microarray analysis was performed. Differentially expressed genes were selected based on fold change and significance, and gene functions were analyzed using ingenuity pathway analysis. Microarray analysis showed that significantly regulated genes were involved in liver hyperplasia, renal tubule injury, and kidney failure in the TAA-treated group. Commonly regulated genes in the liver or kidney were associated with xenobiotic metabolism, lipid metabolism, and oxidative stress. We revealed changes in the molecular pathways of the target organs in response to TAA and provided information on candidate genes that can indicate TAA-induced toxicity. These results may help elucidate the underlying mechanisms of target organ interactions during TAA-induced hepatotoxicity.

Supplementary Information

The online version contains supplementary material available at 10.1007/s43188-022-00156-y.

PPARα Induces the Expression of CAR That Works as a Negative Regulator of PPARα Functions in Mouse Livers

The nuclear receptor peroxisome proliferator-activated receptor α (PPARα) is a transcription factor that controls the transcription of genes responsible for fatty acid metabolism. We have recently reported a possible drug-drug interaction mechanism via the interaction of PPARα with the xenobiotic nuclear receptor constitutive androstane receptor (CAR). Drug-activated CAR competes with the transcriptional coactivator against PPARα and prevents PPARα-mediated lipid metabolism. In this study, to elucidate the crosstalk between CAR and PPARα, we focused on the influence of PPARα activation on CAR's gene expression and activation. Male C57BL/6N mice (8-12 weeks old, n = 4) were treated with PPARα and CAR activators (fenofibrate and phenobarbital, respectively), and hepatic mRNA levels were determined using quantitative reverse transcription PCR. Reporter assays using the mouse Car promoter were performed in HepG2 cells to determine the PPARα-dependent induction of CAR. CAR KO mice were treated with fenofibrate, and the hepatic mRNA levels of PPARα target genes were determined. Treatment of mice with a PPARα activator increased Car mRNA levels as well as genes related to fatty acid metabolism. In reporter assays, PPARα induced the promoter activity of the Car gene. Mutation of the putative PPARα-binding motif prevented PPARα-dependent induction of reporter activity. In electrophoresis mobility shift assay, PPARα bound to the DR1 motif of the Car promoter. Since CAR has been reported to attenuate PPARα-dependent transcription, CAR was considered a negative feedback protein for PPARα activation. Treatment with fenofibrate induced the mRNA levels of PPARα target genes in Car-null mice more than those in wild-type mice, suggesting that CAR functions as a negative feedback factor for PPARα.

The Function of Xenobiotic Receptors in Metabolic Diseases

Metabolic diseases are a series of metabolic disorders that include obesity, diabetes, insulin resistance, hypertension, and hyperlipidemia. The increased prevalence of metabolic diseases has resulted in higher mortality and mobility rates over the past decades, and this has led to extensive research focusing on the underlying mechanisms. Xenobiotic receptors (XRs) are a series of xenobiotic-sensing nuclear receptors that regulate their downstream target genes expression, thus defending the body from xenobiotic and endotoxin attacks. XR activation is associated with the development of a number of metabolic diseases such as obesity, nonalcoholic fatty liver disease, type 2 diabetes, and cardiovascular diseases, thus suggesting an important role for XRs in modulating metabolic diseases. However, the regulatory mechanism of XRs in the context of metabolic disorders under different nutrient conditions is complex and remains controversial. This review summarizes the effects of XRs on different metabolic components (cholesterol, lipids, glucose, and bile acids) in different tissues during metabolic diseases. As chronic inflammation plays a critical role in the initiation and progression of metabolic diseases, we also discuss the impact of XRs on inflammation to comprehensively recognize the role of XRs in metabolic diseases. This will provide new ideas for treating metabolic diseases by targeting XRs. SIGNIFICANCE STATEMENT: This review outlines the current understanding of xenobiotic receptors on nutrient metabolism and inflammation during metabolic diseases. This work also highlights the gaps in this field, which can be used to direct the future investigations on metabolic diseases treatment by targeting xenobiotic receptors.

The effects of hexabromocyclododecane on the transcriptome and hepatic enzyme activity in three human HepaRG-based models

The disruption of thyroid hormone homeostasis by hexabromocyclododecane (HBCD) in rodents is hypothesized to be due to HBCD increasing the hepatic clearance of thyroxine (T4). The extent to which these effects are relevant to humans is unclear. To evaluate HBCD effects on humans, the activation of key hepatic nuclear receptors and the consequent disruption of thyroid hormone homeostasis were studied in different human hepatic cell models. The hepatoma cell line, HepaRG, cultured as two-dimensional (2D), sandwich (SW) and spheroid (3D) cultures, and primary human hepatocytes (PHH) cultured as sandwich were exposed to 1 and 10 µM HBCD and characterized for their transcriptome changes. Pathway enrichment analysis showed that 3D models, followed by SW, had a stronger transcriptome response to HBCD, which is explained by the higher expression of hepatic nuclear receptors but also greater accumulation of HBCD measured inside cells in these models. The Pregnane X receptor pathway is one of the pathways most upregulated across the three hepatic models, followed by the constitutive androstane receptor and general hepatic nuclear receptors pathways. Lipid metabolism pathways had a downregulation tendency in all exposures and in both PHH and the three cultivation modes of HepaRG. The activity of enzymes related to PXR/CAR induction and T4 metabolism were evaluated in the three different types of HepaRG cultures exposed to HBCD for 48 h. Reference inducers, rifampicin and PCB-153 did affect 2D and SW HepaRG cultures' enzymatic activity but not 3D. HBCD did not induce the activity of any of the studied enzymes in any of the cell models and culture methods. This study illustrates that for nuclear receptor-mediated T4 disruption, transcriptome changes might not be indicative of an actual adverse effect. Clarification of the reasons for the lack of translation is essential to evaluate new chemicals' potential to be thyroid hormone disruptors by altering thyroid hormone metabolism.

Effects of Isosakuranetin on Pharmacokinetic Changes of Tofacitinib in Rats with N-Dimethylnitrosamine-Induced Liver Cirrhosis

Tofacitinib, a Janus kinase 1 and 3 inhibitor, is used to treat rheumatoid arthritis. It is mainly metabolized by the cytochromes p450 (CYP) 3A1/2 and CYP2C11 in the liver. Chronic inflammation eventually leads to cirrhosis in patients with rheumatoid arthritis. Isosakuranetin (ISN), a component of Citrus aurantium L., has hepatoprotective effects in rats. This study was performed to determine the effects of ISN on the pharmacokinetics of tofacitinib in rats with N-dimethylnitrosamine-induced liver cirrhosis (LC). After intravenous administration of 10 mg/kg tofacitinib to control (CON), LC, and LC treated with ISN (LC-ISN) rats, the total area under the plasma concentration-time curves (AUC) from time zero to infinity increased by 158% in LC rats compared to those in CON rats; however, the AUC of LC-ISN rats decreased by 35.1% compared to that of LC rat. Similar patterns of AUC changes were observed in the LC and LC-ISN rats after oral administration of 20 mg/kg tofacitinib. These results can be attributed to decreased non-renal clearance (CL_NR) and intestinal intrinsic clearance (CL_int) in the LC rats and increased intestinal and hepatic CL_int in the LC-ISN rats. Our findings imply that ISN treatment in LC rats restored the decrease in either CL_NR or CL_int, or both, through increased hepatic and intestinal expression of CYP3A1/2 and CYP2C11, which is regulated by the induction of pregnane X receptor (PXR) and constitutive androstane receptor (CAR).

Effects of Dextran Sulfate Sodium-Induced Ulcerative Colitis on the Disposition of Tofacitinib in Rats

Tofacitinib, a Janus kinase 1 and 3 inhibitor, is mainly metabolized by CYP3A1/2 and CYP2C11 in the liver. The drug has been approved for the chronic treatment of severe ulcerative colitis, a chronic inflammatory bowel disease. This study investigated the pharmacokinetics of tofacitinib in rats with dextran sulfate sodium (DSS)-induced ulcerative colitis. After 1-min of intravenous infusion of tofacitinib (10 mg/kg), the area under the plasma concentration-time curves from time zero to time infinity (AUC) of tofacitinib significantly increased by 92.3%. The time-averaged total body clearance decreased significantly by 47.7% in DSS rats compared with control rats. After the oral administration of tofacitinib (20 mg/kg), the AUC increased by 85.5% in DSS rats. These results could be due to decreased intrinsic clearance of the drug caused by the reduction of CYP3A1/2 and CYP2C11 in the liver and intestine of DSS rats. In conclusion, ulcerative colitis inhibited CYP3A1/2 and CYP2C11 in the liver and intestines of DSS rats and slowed the metabolism of tofacitinib, resulting in increased plasma concentrations of tofacitinib in DSS rats.

Chicken xenobiotic receptor upregulates the BCRP/ABCG2 transporter

The transporter breast cancer resistance protein (BCRP, encoded by ABCG2) influences the bioavailability and elimination of numerous substrate drugs during clinical therapy. The xenobiotic-sensing nuclear receptors pregnane X receptor (PXR) and constitutive androstane receptor (CAR) reportedly regulate functional expression of BCRP in mammalian species. However, it is unknown whether chicken xenobiotic receptor (CXR) regulates the expression and activity of BCRP. This study aimed to investigate the role of CXR in regulation of BCRP in chicken using in vitro and in vivo models. CXR was expressed in the main drug-metabolizing tissues of chickens, and its expression correlated well with that of the prototypical target genes CYP2H1 and ABCG2. BCRP expression was upregulated, and transporter activity was increased, in chicken primary hepatocytes exposed to the CXR agonist metyrapone. Using RNA interference and ectopic expression techniques to manipulate the cellular CXR status, we confirmed that ABCG2 gene regulation depended on CXR. In vivo experiments showed that metyrapone induced BCRP in the liver, kidney, duodenum, and jejunum of chickens. Coadministration of metyrapone significantly changed the pharmacokinetic behavior of orally administered florfenicol (substrate of chicken BCRP), with a lower C_max (4.62 vs. 7.35 µg/mL, P < 0.01) and AUC_0-t (15.83 vs. 24.18 h·mg/L, P < 0.01) as well as a higher T_max (0.96 vs. 0.79 h, P < 0.05) and Cl/F (0.13 vs. 0.08 L/h/kg, P < 0.05). Together, our data suggest that CXR is involved in regulation of BCRP, and consequently, coadministration of a CXR agonist can affect the pharmacokinetic behavior of an orally administered BCRP substrate.

Circadian clock-mediated nuclear receptors in cancer

Circadian system coordinates the daily periodicity of physiological and biochemical functions to adapt to environmental changes. Circadian disruption has been identified to increase the risk of cancer and promote cancer progression, but the underlying mechanism remains unclear. And further mechanistic understanding of the crosstalk between clock components and cancer is urgent to achieve clinical anticancer benefits from chronochemotherapy. Recent studies discover that several nuclear receptors regulating circadian clock, also play crucial roles in mediating multiple cancer processes. In this review, we aim to summarize the latest developments of clock-related nuclear receptors in cancer biology and dissect mechanistic insights into how nuclear receptors coordinate with circadian clock to regulate tumorigenesis and cancer treatment. A better understanding of circadian clock-related nuclear receptors in cancer could help prevent tumorigenesis and improve anticancer efficacy.

Effect of DSS-Induced Ulcerative Colitis and Butyrate on the Cytochrome P450 2A5: Contribution of the Microbiome

Several studies have indicated the beneficial anti-inflammatory effect of butyrate in inflammatory bowel disease (IBD) therapy implying attempts to increase butyrate production in the gut through orally administered dietary supplementation. Through the gut-liver axis, however, butyrate may reach directly the liver and influence the drug-metabolizing ability of hepatic enzymes, and, indirectly, also the outcome of applied pharmacotherapy. The focus of our study was on the liver microsomal cytochrome P450 (CYP) 2A5, which is a mouse orthologue of human CYP2A6 responsible for metabolism of metronidazole, an antibiotic used to treat IBD. Our findings revealed that specific pathogen-free (SPF) and germ-free (GF) mice with dextran sulfate sodium (DSS)-induced colitis varied markedly in enzyme activity of CYP2A and responded differently to butyrate pre-treatment. A significant decrease (to 50%) of the CYP2A activity was observed in SPF mice with colitis; however, an administration of butyrate prior to DSS reversed this inhibition effect. This phenomenon was not observed in GF mice. The results highlight an important role of gut microbiota in the regulation of CYP2A under inflammatory conditions. Due to the role of CYP2A in metronidazole metabolism, this phenomenon may have an impact on the IBD therapy. Butyrate administration, hence, brings promising therapeutic potential for improving symptoms of gut inflammation; however, possible interactions with drug metabolism need to be further studied.

Allosteric Antagonism of the Pregnane X Receptor (PXR): Current-State-of-the-Art and Prediction of Novel Allosteric Sites

The pregnane X receptor (PXR, NR1I2) is a xenobiotic-activated transcription factor with high levels of expression in the liver. It not only plays a key role in drug metabolism and elimination, but also promotes tumor growth, drug resistance, and metabolic diseases. It has been proposed as a therapeutic target for type II diabetes, metabolic syndrome, and inflammatory bowel disease, and PXR antagonists have recently been considered as a therapy for colon cancer. There are currently no PXR antagonists that can be used in a clinical setting. Nevertheless, due to the large and complex ligand-binding pocket (LBP) of the PXR, it is challenging to discover PXR antagonists at the orthosteric site. Alternative ligand binding sites of the PXR have also been proposed and are currently being studied. Recently, the AF-2 allosteric binding site of the PXR has been identified, with several compounds modulating the site discovered. Herein, we aimed to summarize our current knowledge of allosteric modulation of the PXR as well as our attempt to unlock novel allosteric sites. We describe the novel binding function 3 (BF-3) site of PXR, which is also common for other nuclear receptors. In addition, we also mention a novel allosteric site III based on in silico prediction. The identified allosteric sites of the PXR provide new insights into the development of safe and efficient allosteric modulators of the PXR receptor. We therefore propose that novel PXR allosteric sites might be promising targets for treating chronic metabolic diseases and some cancers.

Potential Pharmacokinetic Effect of Chicken Xenobiotic Receptor Activator on Sulfadiazine: Involvement of P-glycoprotein Induction

Studies on pharmacokinetic drug−drug interactions have highlighted the importance of P-glycoprotein (P-gp) because of its involvement in substrate drug transport. This study aimed to investigate the role of chicken xenobiotic receptor (CXR) in the regulation of P-gp and its influences on pharmacokinetics of P-gp substrate sulfadiazine. ALAS1 and CYP2C45, the prototypical target genes of CXR, were used as a positive indicator for CXR activation in this study. Results show that ABCB1 gene expression was upregulated, and transporter activity was increased when exposed to the CXR activator metyrapone. Using ectopic expression techniques and RNA interference to manipulate the cellular CXR status, we confirmed that ABCB1 gene regulation depends on CXR. In vivo experiments showed that metyrapone induced ABCB1 in the liver, kidney, duodenum, jejunum and ileum of chickens. In addition, metyrapone significantly changed the pharmacokinetic behavior of orally administered sulfadiazine, with a Cmax (8.01 vs. 9.61 μg/mL, p < 0.05) and AUC0-t (31.46 vs. 45.59 h·mg/L, p < 0.01), as well as a higher T1/2λ (2.42 vs.1.67 h, p < 0.05), Cl/F (0.62 vs. 0.43 L/h/kg, p < 0.01) and Vz/F (2.16 vs.1.03 L/kg, p < 0.01). Together, our data suggest that CXR is involved in the regulation of P-gp, and, consequently, the CXR activator can affect, at least in part, the pharmacokinetic behavior of orally administered sulfadiazine.

Panaxytriol upregulates CYP3A4 expression based on the interaction of PXR, CAR, HSP90α, and RXRα

BACKGROUND

Cytochrome P450 3A4 (CYP3A4) is one of the most important drug-metabolizing enzymes in the human body, mainly existing in the liver, small intestine, and kidney. Panaxytriol is one of the key active components in red ginseng and Shenmai injection. Our previous study demonstrated that panaxytriol regulates CYP3A4 expression mainly by activating pregnancy X receptor (PXR). At a high concentration of panaxytriol (80 μM), the constitutive androstane receptor (CAR) is also involved in the upregulation of CYP3A4.

PURPOSE

This study investigated how the cofactors heat shock protein 90 alpha (HSP90α) and retinoid X receptor alpha (RXRα) interact with PXR and CAR to participate in the regulation of CYP3A4 by panaxytriol from the perspective of the PXR and CAR interaction.

METHODS

The mRNA and protein expressions of PXR, CAR, CYP3A4, RXRα, and HSP90α in HepG2 cells and Huh-7 cells were detected by quantitative PCR and western blot analysis, respectively. The binding levels of PXR and CAR to RXRα and HSP90α were determined by co-immunoprecipitation analysis. The nuclear translocation of PXR and RXRα into HepG2 cells and human (hCAR)-silenced HepG2 cells were measured by immunofluorescence.

RESULTS

In HepG2 cells and Huh-7 cells, panaxytriol (10-80 μM) upregulated CYP3A4 expression in a concentration-dependent manner by decreasing PXR binding to HSP90α and increasing PXR binding to RXRα. When hCAR was silenced, panaxytriol further enhanced CYP3A4 expression by strengthening PXR binding to RXRα, but it had no significant effect on the binding level of PXR and HSP90α. Additionally, at the high concentration of 80 μM panaxytriol, CAR binding to HSP90α was weakened while binding to RXRα was enhanced.

CONCLUSION

Panaxytriol can upregulate CYP3A4 expression by promoting PXR dissociation from HSP90α and enhancing PXR binding to RXRα in HepG2 cells and Huh-7 cells. At high concentrations of panaxytriol, CAR also participates in the induction of CYP3A4 through a similar mechanism. However, in general, CAR antagonizes PXR binding to RXRα, thereby attenuating the upregulation of CYP3A4 by panaxytriol.

The Role of Bile Acids in the Human Body and in the Development of Diseases

Bile acids are specific and quantitatively important organic components of bile, which are synthesized by hepatocytes from cholesterol and are involved in the osmotic process that ensures the outflow of bile. Bile acids include many varieties of amphipathic acid steroids. These are molecules that play a major role in the digestion of fats and the intestinal absorption of hydrophobic compounds and are also involved in the regulation of many functions of the liver, cholangiocytes, and extrahepatic tissues, acting essentially as hormones. The biological effects are realized through variable membrane or nuclear receptors. Hepatic synthesis, intestinal modifications, intestinal peristalsis and permeability, and receptor activity can affect the quantitative and qualitative bile acids composition significantly leading to extrahepatic pathologies. The complexity of bile acids receptors and the effects of cross-activations makes interpretation of the results of the studies rather difficult. In spite, this is a very perspective direction for pharmacology.

Prenatal glucocorticoid administration enhances bilirubin metabolic capacity and increases Ugt1a and Abcc2 gene expression via glucocorticoid receptor and PXR in rat fetal liver

AIM

Jaundice is especially common in premature infant born before 35 weeks. Because the premature infant liver is not fully developed at birth it may be incomplete the bilirubin metabolism. The purpose was to evaluate the metabolism and the excretion of bilirubin in the premature infant rat liver following prenatal glucocorticoid (GC) administration.

METHODS

Dexamethasone (DEX) was administered subcutaneously to pregnant Wistar rats for two consecutive days on gestational days 17 and 19. The fetus were delivered by cesarean section in gestational days 19 and 21. The mRNA levels and protein levels of bilirubin-metabolic enzymes and transporters in the fetal liver tissues were analyzed using RT-PCR immunohistochemistry staining and ELISA, respectively. We evaluated that the effect of bilirubin-metabolic enzymes in the primary fetal rat hepatocytes treated with DEX after pretreated with glucocorticoid receptor (GR, Nr3c1) and Pxr (Nr1i2) siRNA.

RESULTS

Ugt1a1 and Bsep (Abcb11) mRNA levels were significantly increased in the fetuses by prenatal GC administration. The mRNA levels of nuclear transcription factors Nr1i2, Car (Nr1i3), and Rxrα (Nr2b1) were also significantly increased in the fetuses by prenatal GC administration. In addition, DEX increased Nr1i2, Ugt1a1, and Abcc2 (Mrp2) mRNA levels in the primary fetal hepatocytes. The Nr3c1 or Nr1i2 siRNA-mediated knockdown suppressed the increases of Ugt1a1, and Abcc2 mRNA levels induced by DEX, indicating that DEX are mediated by GC receptor and PXR in primary fetal hepatocytes.

CONCLUSIONS

These results suggest that prenatal GC administration increases bilirubin-metabolic ability, in the premature liver, which may prevent jaundice in neonates.

Pregnane X Receptor and the Gut-Liver Axis: A Recent Update

It is well-known that the pregnane X receptor (PXR)/Nr1i2 is a critical xenobiotic-sensing nuclear receptor enriched in liver and intestine and is responsible for drug-drug interactions, due to its versatile ligand binding domain (LBD) and target genes involved in xenobiotic biotransformation. PXR can be modulated by various xenobiotics including pharmaceuticals, nutraceuticals, dietary factors, and environmental chemicals. Microbial metabolites such as certain secondary bile acids (BAs) and the tryptophan metabolite indole-3-propionic acid (IPA) are endogenous PXR activators. Gut microbiome is increasingly recognized as an important regulator for host xenobiotic biotransformation and intermediary metabolism. PXR regulates and is regulated by the gut-liver axis. This review summarizes recent research advancements leveraging pharmaco- and toxico-metagenomic approaches that have redefined the previous understanding of PXR. Key topics covered in this review include: (1) genome-wide investigations on novel PXR-target genes, novel PXR-DNA interaction patterns, and novel PXR-targeted intestinal bacteria; (2) key PXR-modulating activators and suppressors of exogenous and endogenous sources; (3) novel bidirectional interactions between PXR and gut microbiome under physiologic, pathophysiological, pharmacological, and toxicological conditions; and (4) modifying factors of PXR-signaling including species and sex differences and time (age, critical windows of exposure, and circadian rhythm). The review also discusses critical knowledge gaps and important future research topics centering around PXR. SIGNIFICANCE STATEMENT: This review summarizes recent research advancements leveraging O'mics approaches that have redefined the previous understanding of the xenobiotic-sensing nuclear receptor pregnane X receptor (PXR). Key topics include: (1) genome-wide investigations on novel PXR-targeted host genes and intestinal bacteria as well as novel PXR-DNA interaction patterns; (2) key PXR modulators including microbial metabolites under physiological, pathophysiological, pharmacological, and toxicological conditions; and (3) modifying factors including species, sex, and time.

Time-dependent regulation of hepatic Cytochrome P450 mRNA in male liver-specific PGC-1α knockout mice

The circadian rhythm has profound effect on the body, exerting effects on diverse events like sleep-wake patterns, eating behavior and hepatic detoxification. The cytochrome p450 s (Cyps) is the main group of enzymes responsible for detoxification. However, the underlying mechanisms behind circadian regulation of the Cyps are currently not fully clarified. Therefore, the aim of the present study was to investigate the requirement of hepatic peroxisome proliferator-activated receptor gamma coactivator-1α (PGC-1α) for the circadian regulation of the hepatic expression of Cyp1-4 using liver-specific PGC-1α knockout (LKO) mice and littermate controls. The circadian regulator genes Bmal1 and Clock displayed decreased mRNA content at zietgeber time (ZT) 12, compared to ZT-2 and the mRNA content of Cyp2a4 and Cyp2e1 was higher at ZT-12 than at ZT-2. Moreover, the increase in Cyp2e1 mRNA content was not observed in the PGC-1α LKO mice and hepatic PGC-1α deficiency tended to blunt the rhythmic expression of Clock and Bmal1. However, no circadian regulation was evident at the protein level for the investigated Cyps except for a change in Cyp2e1 protein content in the LKO mice. Of the measured transcription factors, only, the mRNA content of peroxisome proliferator-activated receptor α, showed rhythmic expression. To further analyze the difference between the control and LKO mice, principal component analyses were executed on the mRNA data. This demonstrated a clear separation of the experimental groups with respect to ZT and genotype. Our finding provides novel insight into the role of hepatic PGC-1α for basic and circadian expression of Cyps in mouse liver. This is important for our understanding of the molecular events behind circadian Cyp regulation and hence circadian regulation of hepatic detoxification capacity.

The Nuclear Receptor PXR in Chronic Liver Disease

Pregnane X receptor (PXR), a nuclear receptor known for modulating the transcription of drug metabolizing enzymes and transporters (DMETs), such as cytochrome P450 3A4 and P-glycoprotein, is functionally involved in chronic liver diseases of different etiologies. Furthermore, PXR activity relates to that of other NRs, such as constitutive androstane receptor (CAR), through a crosstalk that in turn orchestrates a complex network of responses. Thus, besides regulating DMETs, PXR signaling is involved in both liver damage progression and repair and in the neoplastic transition to hepatocellular carcinoma. We here summarize the present knowledge about PXR expression and function in chronic liver diseases characterized by different etiologies and clinical outcome, focusing on the molecular pathways involved in PXR activity. Although many molecular details of these finely tuned networks still need to be fully understood, we conclude that PXR and its modulation could represent a promising pharmacological target for the identification of novel therapeutical approaches to chronic liver diseases.

New Insights Into Gut-Bacteria-Derived Indole and Its Derivatives in Intestinal and Liver Diseases

The interaction between host and microorganism widely affects the immune and metabolic status. Indole and its derivatives are metabolites produced by the metabolism of tryptophan catalyzed by intestinal microorganisms. By activating nuclear receptors, regulating intestinal hormones, and affecting the biological effects of bacteria as signaling molecules, indole and its derivatives maintain intestinal homeostasis and impact liver metabolism and the immune response, which shows good therapeutic prospects. We reviewed recent studies on indole and its derivatives, including related metabolism, the influence of diets and intestinal commensal bacteria, and the targets and mechanisms in pathological conditions, especially progress in therapeutic strategies. New research insights into indoles will facilitate a better understanding of their druggability and application in intestinal and liver diseases.

Phenobarbital Induces SLC13A5 Expression through Activation of PXR but Not CAR in Human Primary Hepatocytes

Phenobarbital (PB), a widely used antiepileptic drug, is known to upregulate the expression of numerous drug-metabolizing enzymes and transporters in the liver primarily via activation of the constitutive androstane receptor (CAR, NR1I3). The solute carrier family 13 member 5 (SLC13A5), a sodium-coupled citrate transporter, plays an important role in intracellular citrate homeostasis that is associated with a number of metabolic syndromes and neurological disorders. Here, we show that PB markedly elevates the expression of SLC13A5 through a pregnane X receptor (PXR)-dependent but CAR-independent signaling pathway. In human primary hepatocytes, the mRNA and protein expression of SLC13A5 was robustly induced by PB treatment, while genetic knockdown or pharmacological inhibition of PXR significantly attenuated this induction. Utilizing genetically modified HepaRG cells, we found that PB induces SLC13A5 expression in both wild type and CAR-knockout HepaRG cells, whereas such induction was fully abolished in the PXR-knockout HepaRG cells. Mechanistically, we identified and functionally characterized three enhancer modules located upstream from the transcription start site or introns of the SLC13A5 gene that are associated with the regulation of PXR-mediated SLC13A5 induction. Moreover, metformin, a deactivator of PXR, dramatically suppressed PB-mediated induction of hepatic SLC13A5 as well as its activation of the SLC13A5 luciferase reporter activity via PXR. Collectively, these data reveal PB as a potent inducer of SLC13A5 through the activation of PXR but not CAR in human primary hepatocytes.

Lack of salidroside impact on selected cytochromes encoding genes transcription in the liver of ethanol induced rats

Introduction: The molecular basis of in vivo metabolism of selected representatives of phenylethanoids in the presence of ethanol has not been fully elucidated.

Objective: The aim was to estimate a salidroside (Sal) metabolism in the liver tissue in rats with induced alcohol tolerance by assessing changes in the transcription of genes encoding cytochromes: CYP1A2, 2D2, 3A1, 2C23.

Methods: cDNA was synthesized from total RNA isolated from rat liver samples. mRNA level changes were evaluated using real-time PCR (qRT-PCR) technique.

Results: Ethanol caused a significant induction of the CYP1A2 and CYP2C23 genes transcription, and a decrease in the CYP3A1 mRNA level, predominantly without statistical significance. A statistically significant increase of the CYP1A2 mRNA level was observed in the group receiving only Sal (4.5 mg/kg b.w.; p.o.) (p<0.01).

Conclusions: There was no unequivocal effect of salidroside on the transcription of investigated cytochrome genes in the liver of rats with induced alcohol tolerance.

Regulation of PXR Function by Coactivator and Corepressor Proteins: Ligand Binding Is Just the Beginning

The pregnane X receptor (PXR, NR1I2) is a nuclear receptor which exerts its regulatory function by heterodimerization with the retinoid-X-receptor α (RXRα, NR2B1) and binding to the promoter and enhancer regions of diverse target genes. PXR is involved in the regulation of drug metabolism and excretion, metabolic and immunological functions and cancer pathogenesis. PXR activity is strongly regulated by the association with coactivator and corepressor proteins. Coactivator proteins exhibit histone acetyltransferase or histone methyltransferase activity or associate with proteins having one of these activities, thus promoting chromatin decondensation and activation of the gene expression. On the contrary, corepressor proteins promote histone deacetylation and therefore favor chromatin condensation and repression of the gene expression. Several studies pointed to clear cell- and ligand-specific differences in the activation of PXR. In this article, we will review the critical role of coactivator and corepressor proteins as molecular determinants of the specificity of PXR-mediated effects. As already known for other nuclear receptors, understanding the complex mechanism of PXR activation in each cell type and under particular physiological and pathophysiological conditions may lead to the development of selective modulators with therapeutic potential.

Suppression of apoptotic signaling in rat hepatocytes by non-dioxin-like polychlorinated biphenyls depends on the receptors CAR and PXR

Non-dioxin-like polychlorinated biphenyls (NDL-PCBs) represent a sub-group of persistent organic pollutants found in food, environmental samples and human and animal tissues. Promotion of pre-neoplastic lesions in rodent liver has been suggested as an indicator for a possible increased risk of liver cancer in humans exposed to NDL-PCBs. In rodent hepatocytes, suppression of DNA damage-triggered apoptosis is a typical mode of action of liver tumor promoters. Here, we report that NDL-PCBs suppress apoptosis in rat hepatocytes treated in culture with an apoptogenic dose of UV light. Suppression became less pronounced when the constitutive androstane receptor (CAR) and/or the pregnane-X-receptor (PXR) where knocked-out using siRNAs, while knocking-out both receptors led to a full reconstitution of apoptosis. In contrast, suppression of apoptosis by the CAR or PXR activators phenobarbital or dexamethasone were CAR- or PXR-specific. Induction and suppression of apoptosis were paralleled by changes in caspase 3/7, 8 and 9 activities. Our findings indicate that NDL-PCBs can suppress UV-induced apoptosis in rat hepatocytes by activating CAR and PXR. It needs further investigation if these mechanisms of action are also of relevance for human liver.

[Functioning of pregnan X receptor under conditions of nitrosative stress]

Pregnan X receptor (PXR) is a nuclear receptor that plays an important role in the regulation of the expression of biotransformation and metabolic enzymes. The functioning and possible mechanisms of PXR regulation under conditions of nitrosative stress have not been studied, which served as the purpose of this study. The work was performed on Caco-2 cells. Nitrosative stress (NS) was modeled using S-nitrosoglutathione (GSNO) at concentrations of 1 μM, 10 μM, 50 μM, 100 μM, and 500 μM and incubation during of 3 h, 24 h, and 72 h. The amount of PXR was assessed byWestern blotting. Incubation of Caco-2 cells with all concentrations GSNO for 3 h led to a decrease in the amount of PXR. Incubation with GSNO (1-50 μM) for 24 h was accompanied by an increase in the amount of PXR, while at a concentration of 100 μM this indicator did not significantly differ from the control, at a concentration of 500 μM it was lower. Prolonged incubation (72 h) enhanced NS and led to a normalization (1 μM GSNO) or a decrease of the PXR level (10-500 μM GSNO). The induction of PXR by GSNO was mediated by the effect of the nitrosative stress product bityrosine on the transcription factor. It was shown that bityrosine at concentrations of 0,4 mM and 1 mM increased the amount of PXR.

An optimized protocol with a stepwise approach to identify specific nuclear receptor ligands from cultured mammalian cells

Here, we describe an optimized protocol to identify specific nuclear receptor ligands. First, to rule out any compound interference with luciferase activity per se, we describe an in vitro assay assessing potential inhibition or activation of luciferase enzymatic activity. Second, to comply with EMA and FDA guidelines to mitigate drug-drug interactions, we detail assays assessing constitutive androstane receptor (CAR) and pregnane X receptor (PXR) activation ability. Finally, to minimize off-target detection effects, we describe the use of mammalian one- (or two-) hybrid systems. For complete details on the use and execution of this protocol, please refer to Hering et al. (2018).

Activation of the Constitutive Androstane Receptor Inhibits Leukocyte Adhesiveness to Dysfunctional Endothelium

Leukocyte cell recruitment into the vascular subendothelium constitutes an early event in the atherogenic process. As the effect of the constitutive androstane receptor (CAR) on leukocyte recruitment and endothelial dysfunction is poorly understood, this study investigated whether the role of CAR activation can affect this response and the underlying mechanisms involved. Under physiological flow conditions, TNFα-induced endothelial adhesion of human leukocyte cells was concentration-dependently inhibited by preincubation of human umbilical arterial endothelial cells with the selective human CAR ligand CITCO. CAR agonism also prevented TNFα induced VCAM-1 expression, as well as MCP-1/CCL-2 and RANTES/CCL-5 release in endothelial cells. Suppression of CAR expression with a small interfering RNA abrogated the inhibitory effects of CITCO on these responses. Furthermore, CITCO increased interaction of CAR with Retinoid X Receptor (RXR) and reduced TNFα-induced p38-MAPK/NF-κB activation. In vivo, using intravital microscopy in the mouse cremasteric microcirculation treatment with the selective mouse CAR ligand TCPOBOP inhibited TNFα-induced leukocyte rolling flux, adhesion, and emigration and decreased VCAM-1 in endothelium. These results reveal that CAR agonists can inhibit the initial inflammatory response that precedes the atherogenic process by targeting different steps in the leukocyte recruitment cascade. Therefore, CAR agonists may constitute a new therapeutic tool in controlling cardiovascular disease-associated inflammatory processes.

The Effect of Chronic Iloperidone Treatment on Cytochrome P450 Expression and Activity in the Rat Liver: Involvement of Neuroendocrine Mechanisms

In order to achieve a desired therapeutic effect in schizophrenia patients and to maintain their mental wellbeing, pharmacological therapy needs to be continued for a long time, usually from the onset of symptoms and for the rest of the patients' lives. The aim of our present research is to find out the in vivo effect of chronic treatment with atypical neuroleptic iloperidone on the expression and activity of cytochrome P450 (CYP) in rat liver. Male Wistar rats received a once-daily intraperitoneal injection of iloperidone (1 mg/kg) for a period of two weeks. Twenty-four hours after the last dose, livers were excised to study cytochrome P450 expression (mRNA and protein) and activity, pituitaries were isolated to determine growth hormone-releasing hormone (GHRH), and blood was collected for measuring serum concentrations of hormones and interleukin. The results showed a broad spectrum of changes in the expression and activity of liver CYP enzymes, which are important for drug metabolism (CYP1A, CYP2B, CYP2C, and CYP3A) and xenobiotic toxicity (CYP2E1). Iloperidone decreased the expression and activity of CYP1A2, CP2B1/2, CYP2C11, and CYP3A1/2 enzymes but increased that of CYP2E1. The CYP2C6 enzyme remained unchanged. At the same time, the level of GHRH, GH, and corticosterone decreased while that of T₃ increased, with no changes in IL-2 and IL-6. The presented results indicate neuroendocrine regulation of the investigated CYP enzymes during chronic iloperidone treatment and suggest a possibility of pharmacokinetic/metabolic interactions produced by the neuroleptic during prolonged combined treatment with drugs that are substrates of iloperidone-affected CYP enzymes.

Derivation, characterisation and analysis of an adverse outcome pathway network for human hepatotoxicity

Adverse outcome pathways (AOPs) and their networks are important tools for the development of mechanistically based non-animal testing approaches, such as in vitro and/or in silico assays, to assess toxicity induced by chemicals. In the present study, an AOP network connecting 14 linear AOPs related to human hepatotoxicity, currently available in the AOP-Wiki, was derived according to established criteria. The derived AOP network was characterised and analysed with regard to its structure and topological features. In-depth analysis of the AOP network showed that cell injury/death, oxidative stress, mitochondrial dysfunction and accumulation of fatty acids are the most highly connected and central key events. Consequently, these key events may be considered as the rational and mechanistically anchored basis for selecting, developing and/optimising in vitro and/or in silico assays to predict hepatotoxicity induced by chemicals in view of animal-free hazard identification.

Critical evaluation of the human relevance of the mode of action for rodent liver tumor formation by activators of the constitutive androstane receptor (CAR)

Many nongenotoxic chemicals have been shown to produce liver tumors in mice and/or rats by a mode of action (MOA) involving activation of the constitutive androstane receptor (CAR). Studies with phenobarbital (PB) and other compounds have identified the key events for this MOA: CAR activation; increased hepatocellular proliferation; altered foci formation; and ultimately the development of adenomas/carcinomas. In terms of human relevance, the pivotal species difference is that CAR activators are mitogenic agents in mouse and rat hepatocytes, but they do not stimulate increased hepatocellular proliferation in humans. This conclusion is supported by substantial in vitro studies with cultured rodent and human hepatocytes and also by in vivo studies with chimeric mice with human hepatocytes. Examination of the literature reveals many similarities in the hepatic effects and species differences between activators of rodent CAR and the peroxisome proliferator-activated receptor alpha (PPARα), with PPARα activators also not being mitogenic agents in human hepatocytes. Overall, a critical analysis of the available data demonstrates that the established MOA for rodent liver tumor formation by PB and other CAR activators is qualitatively not plausible for humans. This conclusion is supported by data from several human epidemiology studies.

PXR-mediated expression of FABP4 promotes valproate-induced lipid accumulation in HepG2 cells

Valproate (valproic acid, VPA) is widely used in the therapy of epilepsy. However, adverse effect like hepatic steatosis has been reported in patients receiving VPA treatment. But whether nuclear receptor pregnane X receptor (PXR) and fatty acid binding protein 4 (FABP4) are involved in the regulation of VPA-induced steatosis or not is still unknown. In this study, the roles of PXR and FABP4 in VPA-induced lipid accumulation in HepG2 cells were investigated. We found that the expression of PXR and FABP4 were increased by VPA in a dose-dependent manner. Knockdown of PXR not only reduced lipid accumulation but also impaired the induction of FABP4 by VPA. While overexpression of PXR enhanced both lipid accumulation and FABP4 expression. Moreover, exogenous expression of FABP4 increased triglyceride levels and enhanced lipid accumulation caused by VPA. Taken together, these results suggest that PXR-mediated expression of FABP4 is responsible for lipid accumulation caused by VPA.

Nuclear Receptors as Multiple Regulators of NLRP3 Inflammasome Function

Nuclear receptors are important bridges between lipid signaling molecules and transcription responses. Beside their role in several developmental and physiological processes, many of these receptors have been shown to regulate and determine the fate of immune cells, and the outcome of immune responses under physiological and pathological conditions. While NLRP3 inflammasome is assumed as key regulator for innate and adaptive immune responses, and has been associated with various pathological events, the precise impact of the nuclear receptors on the function of inflammasome is hardly investigated. A wide variety of factors and conditions have been identified as modulators of NLRP3 inflammasome activation, and at the same time, many of the nuclear receptors are known to regulate, and interact with these factors, including cellular metabolism and various signaling pathways. Nuclear receptors are in the focus of many researches, as these receptors are easy to manipulate by lipid soluble molecules. Importantly, nuclear receptors mediate regulatory mechanisms at multiple levels: not only at transcription level, but also in the cytosol via non-genomic effects. Their importance is also reflected by the numerous approved drugs that have been developed in the past decade to specifically target nuclear receptors subtypes. Researches aiming to delineate mechanisms that regulate NLRP3 inflammasome activation draw a wide range of attention due to their unquestionable importance in infectious and sterile inflammatory conditions. In this review, we provide an overview of current reports and knowledge about NLRP3 inflammasome regulation from the perspective of nuclear receptors, in order to bring new insight to the potentially therapeutic aspect in targeting NLRP3 inflammasome and NLRP3 inflammasome-associated diseases.