Perfluorooctane sulfonate (PFOS) is a stable environmental contaminant that can activate peroxisome proliferator-activated receptor alpha (PPARα). In the present work, the specific role of mouse and ...human PPARα in mediating the hepatic effects of PFOS was examined in short-term studies using wild type, Ppara-null and PPARA-humanized mice. Mice fed 0.006 % PFOS for seven days (∼10 mg/kg/day), or 0.003 % PFOS for twenty-eight days (∼5 mg/kg/day), exhibited higher liver and serum PFOS concentrations compared to controls. Relative liver weights were also higher following exposure to dietary PFOS in all three genotypes as compared vehicle fed control groups. Histopathological examination of liver sections from mice treated for twenty-eight days with 0.003 % PFOS revealed a phenotype consistent with peroxisome proliferation, in wild-type and PPARA-humanized mice that was not observed in Ppara-null mice. With both exposures, expression of the PPARα target genes, Acox1, Cyp4a10, was significantly increased in wild type mice but not in Ppara-null or PPARA-humanized mice. By contrast, expression of the constitutive androstane receptor (CAR) target gene, Cyp2b10, and the pregnane X receptor (PXR) target gene, Cyp3a11, were higher in response to PFOS administration in all three genotypes compared to controls for both exposure periods. These results indicate that mouse PPARα can be activated in the liver by PFOS causing increased expression of Acox1, Cyp4a10 and histopathological changes in the liver. While histopathological analyses indicated the presence of mouse PPARα-dependent hepatic peroxisome proliferation in wild-type (a response associated with activation of PPARα) and a similar phenotype in PPARA-humanized mice, the lack of increased Acox1 and Cyp4a10 mRNA by PFOS in PPARA-humanized mice indicates that the human PPARα was not as responsive to PFOS as mouse PPARα with this dose regimen. Moreover, results indicate that hepatomegaly caused by PFOS does not require mouse or human PPARα and could be due to effects induced by activation of CAR and/or PXR.
•Non-dioxin-like polychlorinated biphenyls suppress apoptosis in rat hepatocytes.•Suppression was less pronounced when the receptors CAR and/or PXR were knocked-out.•Knocking-out both receptors led ...to a full reconstitution of apoptosis.•Suppression of apoptosis by phenobarbital or dexamethasone were receptor-specific.•Induction and suppression of apoptosis were paralleled by changed caspase activities.
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.
Eight nonaromatic acylphloroglucinol-terpenoid adducts including 7 new compounds were isolated from H. japonicum. Among them, compounds 1–4 showed significant PXR agonistic activity.
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...•Seven novel nonaromatic acylphloroglucinol-terpenoid adducts were isolated.•Compounds 1 − 4 showed significant PXR agonistic activity in dual-luciferase reporter gene model.•Compounds 1 − 4 can upregulate the expression of PXR-targeted gene in mice primary hepatocyte model.•Compounds 1 − 4 efficiently promoted PXR nuclear translocation at 10 μM.•The binding models of active compounds and PXR were elucidated.
Pregnane X receptor (PXR) has been considered as a promising therapeutic target for cholestasis due to its crucial regulation in bile acid biosynthesis and metabolism. To search promising natural PXR agonists, the PXR agonistic activities of five traditional Chinese medicines (TCMs) with hepatoprotective efficacy were assayed, and Hypericum japonicum as the most active one was selected for subsequent phytochemical investigation, which led to the isolation of eight nonaromatic acylphloroglucinol-terpenoid adducts including seven new compounds (1 − 4, 5a, 5b and 6). Their structures including absolute configurations were determined by comprehensive spectroscopic, computational and X-ray diffraction analysis. Meanwhile, the PXR agonistic activities of aplenty compounds were evaluated via dual-luciferase reporter assay, RT-qPCR and immunofluorescence. Among them, compounds 1 − 4 showed more potent activity than the positive drug rifampicin. Furthermore, the molecular docking revealed that 1 − 4 were docked well on the PXR ligand binding domain and formed hydrogen bonds with amino acid residues Gln285, Ser247 and His409. This investigation revealed that H. japonicum may serve as a rich source of natural PXR agonists.
Liver X receptor α (LXRα) controls important biological and pathophysiological processes such as lipid homeostasis. Inhibiting LXRα transactivation may beneficial in the treatment of nonalcoholic ...fatty liver disease (NAFLD), which is one of the main causes of liver diseases and hyperlipidemia. Oleanolic acid (OA) is a naturally occurring triterpenoid found in many plants. It has several beneficial effects on biological pathways; however, the mechanisms underlying its effects on LXRα are unclear. Therefore, we evaluated the effects of OA on T0901317-induced LXRα activation and explored whether OA can attenuate hepatic lipogenesis. The results showed that OA significantly decreased the promoter activities of LXR response element and sterol regulatory element binding protein-1c (SREBP-1c). It also decreased the mRNA and protein expression of LXRα target genes. These resulted in reduced hepatocellular lipid content. Our results also revealed that the overall binding pose of OA is similar to the X-ray pose of T0901317. Furthermore, OA stimulated AMP-activated protein kinase phosphorylation in hepatic cells. Additionally, it increased small heterodimer partner-interacting leucine zipper protein (SMILE) but decreased steroid receptor coactivator-1 (SRC-1) recruitment to the SREBP-1c promoter region. OA also enhanced LXRα-mediated induction of reverse cholesterol transport (RCT)-related gene, ATP-binding cassette transporter (ABC) A1, and ABCG1 expression in intestinal cells. It was found that OA increased the binding of SRC-1 but decreased SMILE recruitment to the ABCG1 gene promoter region. Furthermore, it reduced valproate- and rifampin-induced LXRα- and pregnane X receptor-mediated lipogenesis, respectively, which indicates its potential benefit in treating drug-induced hepatic steatosis. The results also show that OA is liver-specific and can be selectively repressed of lipogenesis. Moreover, it preserves and enhances LXRα-induced RCT stimulation. The results show that OA may be a promising treatment for NAFLD. Additionally, it can be used in the development of LXRα agonists to prevent atherosclerosis.
Xiaoaiping injection, a traditional Chinese medical injection extracted from root of Marsdenia tenacissima (Roxb.) Moon, has been exclusively used on curing malignant tumor in China and as adjuvant ...therapeutic agent for chemotherapeutics, including paclitaxel.
The goal of this study was to investigate the synergistic inhibitory efficacy of Xiaoaiping injection and paclitaxel on ovarian cancer. The mechanism may be associated with nuclear receptor pregnane X receptor (PXR) regulating its downstream molecules.
In vitro, MTT assay, flow cytometry and Hoechst dyeing were used to evaluate the SK-OV-3 cell proliferation, apoptosis and cell cycle respectively. The mRNA and protein expression of PXR and its downstream CYP450 enzymes, transporters and Bcl-2 families were measured by qRT-PCR and Western blot. Rhodamine 123 efflux experiment was conducted to detect the P-gp efflux ability. PXR plasmid and PXR siRNA were transiently transfected into SK-OV-3 cells respectively to establish PXR-overexpressed or PXR-interfered cells. In vivo, xenograft tumor mice model was established by SK-OV-3 cells to estimate the antitumor effect of Xiaoaiping injection combined with paclitaxel. The expressions of PXR and its downstream molecules in tumor tissues were determined to further clarify the potential mechanism.
Xiaoaiping injection significantly enhanced the anti-proliferation, pro-apoptosis effect of paclitaxel on SK-OV-3 cells. The synergetic effect was displayed by Xiaoaiping injection inhibiting paclitaxel-induced PXR and CAR expression, which subsequently inhibited CYP450 enzymes CYP2C8 and CYP3A4, transporter P-gp and anti-apoptotic proteins Bcl-2 and Bcl-xl in SK-OV-3 cells. In PXR-overexpressed cells, Xiaoaiping injection down-regulated the expression of PXR and its downstream molecules. The result of xenograft tumor model showed that Xiaoaiping injection combined with paclitaxel enhanced anti-tumor effect on ovarian cancer in vivo.
Xiaoaiping injection enhances anti-tumor effect of paclitaxel by inhibiting cell proliferation, inducing apoptosis process. The mechanism may be associated with Xiaoaiping injection inhibiting PXR and its downstream metabolic enzymes CYP2C8, CYP3A4, transporter P-gp and anti-apoptosis protein Bcl-2.
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•Xiaoaiping injection enhances antitumor efficacy of paclitaxel on ovarian cancer.•Overexpression of PXR resulted in significant increasing of CYP2C8, CYP3A4, P-gp and Bcl-2.•The level of PXR, CYP450 enzymes, P-gp and Bcl-2 were reduced by Xiaoaiping injection.
Parabens are widely used as preservatives in personal care products, medicines and foods, resulting in substantial human exposures, even though some harmful effects, such as endocrine-disrupting ...activity, have been reported. Pregnane X receptor (PXR), constitutive androstane receptor (CAR) and peroxisome proliferator-activated receptor α (PPARα), which are members of the nuclear receptor superfamily, regulate the metabolism of endogenous substrates including hormones. Therefore, we hypothesized that parabens may alter hormone-metabolizing activities by acting on these receptors, and such changes could contribute to the endocrine-disrupting activity. To test this idea, we systematically examined the effects of 17 parabens on these receptors using reporter gene assays. Nine parabens significantly activated human and rat PXR. Parabens with C2–C5 (linear and branched) side chains were most active. Butylparaben and isobutylparaben also significantly activated rat CAR. We found that long-side-chain (C7–C12) parabens showed up to 2-fold activation of PPARα at 10 μM. Furthermore, pentylparaben and hexylparaben showed rat PXR antagonistic activity and rat CAR inverse agonistic activity. The activity of butylparaben towards PXR and CAR was lost after carboxylesterase-mediated metabolism. These findings confirm that parabens influence the activities of PXR, CAR and PPARα, and thus have the potential to contribute to endocrine disruption by altering hormone metabolism.
•Assays of 17 parabens showed different patterns of h/rPXR, rCAR and rPPARα activation.•Pentylparaben, hexylparaben and heptylparaben showed rPXR antagonistic activity.•Pentylparaben and hexylparaben showed rCAR inverse agonistic activity.•Parabens with long side chains (C7–C12) showed potent PPARα activation.•Butylparaben activities on PXR and CAR were lost upon metabolism by carboxylesterase.
Pregnane X receptor (PXR) plays an important role in the regulation of metabolic homeostasis. Yes-associated protein (YAP) is a critical regulator of liver size and liver regeneration. Recently, we ...reported that PXR-induced liver enlargement and regeneration depend on YAP signalling, but the underlying mechanisms remain unclear. This study aimed to reveal how PXR regulates or interacts with YAP signalling during PXR-induced hepatomegaly and liver regeneration. Immunoprecipitation (IP), Co-IP and GST pull-down assays were performed in vitro to reveal the regulatory mechanisms involved in the PXR-YAP interaction. The roles of YAP-TEAD binding and Sirt2-driven deacetylation and polyubiquitination of YAP were further investigated in vitro and in vivo. The results showed that the ligand-binding domain (LBD) of PXR and the WW domain of YAP were critical for the PXR-YAP interaction. Furthermore, disruption of the YAP-TEAD interaction using the binding inhibitor verteporfin significantly decreased PXR-induced liver enlargement and regeneration after 70 % partial hepatectomy (PHx). Mechanistically, PXR activation significantly decreased YAP acetylation, which was interrupted by the sirtuin inhibitor nicotinamide (NAM). In addition, p300-induced YAP acetylation contributed to K48-linked YAP ubiquitination. Interestingly, PXR activation remarkably inhibited K48-linked YAP ubiquitination while inducing K63-linked YAP polyubiquitination. Sirt2 interference abolished the deacetylation and K63-linked polyubiquitination of YAP, suggesting that the PXR-induced deacetylation and polyubiquitination of YAP are Sirt2 dependent. Taken together, this study demonstrates that PXR induce liver enlargement and regeneration via the regulation of YAP acetylation and ubiquitination and YAP-TEAD binding, providing evidences for using PXR as potential target to promote hepatic development and liver repair.
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The pregnane X receptor (PXR, NR1I2) belongs to the nuclear receptor family and functions as a xenobiotic and endobiotic sensor by binding to various molecules through its relatively flexible ...ligand-binding domain. In addition to these well-known canonical roles, we previously reported that PXR represses osteoblast differentiation. However, the mechanisms underlying the PXR-mediated repression of osteoblast differentiation remains unknown. In this study, we analyzed the changes in global gene expression profiles induced by PXR in calvarial osteoblasts cultured in standard fetal bovine serum (in which PXR induces repression of differentiation), and in those cultured in charcoal-stripped fetal bovine serum (in which PXR does not induce repression of differentiation). The comparison revealed that PXR attenuated the Hedgehog-mediated signaling in culture conditions that induced PXR-mediated repression of differentiation. Real-time PCR analysis showed that PXR repressed the Hedgehog signaling-induced genes such as Gli1 and Hhip, and conversely induced the Hedgehog signaling-repressed genes such as Cdon, Boc, and Gas1. Activation of Smo-mediated signaling in osteoblasts following treatment with a Smo agonist (SAG) significantly restored Gli-mediated transcriptional activity and osteoblast differentiation. Our results demonstrate the osteoblast-autonomous effects of PXR and identify a novel regulation of Hedgehog signaling by nuclear receptors.
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Nonalcoholic fatty liver disease (NAFLD) is the most prevalent chronic liver disease due to the current epidemics of obesity and diabetes. The pregnane X receptor (PXR) is a ...xenobiotic-sensing nuclear receptor known for trans-activating liver genes involved in drug metabolism and transport, and more recently implicated in energy metabolism. The gut microbiota can modulate the host xenobiotic biotransformation and contribute to the development of obesity. While the male sex confers a higher risk for NAFLD than women before menopause, the mechanism remains unknown. We hypothesized that the presence of PXR promotes obesity by modifying the gut-liver axis in a sex-specific manner. Male and female C57BL/6 (wild-type/WT) and PXR-knockout (PXR-KO) mice were fed control or high-fat diet (HFD) for 16-weeks. Serum parameters, liver histopathology, transcriptomic profiling, 16S-rDNA sequencing, and bile acid (BA) metabolomics were performed. PXR enhanced HFD-induced weight gain, hepatic steatosis and inflammation especially in males, accompanied by PXR-dependent up-regulation in hepatic genes involved in microbial response, inflammation, oxidative stress, and cancer; PXR-dependent increase in intestinal Firmicutes/Bacteroides ratio (hallmark of obesity) and the pro-inflammatory Lactobacillus, as well as a decrease in the anti-obese Allobaculum and the anti-inflammatory Bifidobacterum, with a PXR-dependent reduction of beneficial BAs in liver. The resistance to NAFLD in females may be explained by PXR-dependent decrease in pro-inflammatory bacteria (Ruminococcus gnavus and Peptococcaceae). In conclusion, PXR exacerbates hepatic steatosis and inflammation accompanied by obesity- and inflammation-prone gut microbiome signature, suggesting that gut microbiome may contribute to PXR-mediated exacerbation of NAFLD.
Schisandrol B (SolB) is one of the bioactive components from a traditional Chinese medicine Schisandra chinensis or Schisandra sphenanthera. It has been demonstrated that SolB exerts hepatoprotective ...effects against drug-induced liver injury and promotes liver regeneration. It was found that SolB can induce hepatomegaly but the involved mechanisms remain unknown.
This study aimed to explore the mechanisms involved in SolB-induced hepatomegaly.
Male C57BL/6 mice were injected intraperitoneally with SolB (100 mg/kg) for 5 days. Serum and liver samples were collected for biochemical and histological analyses. The mechanisms of SolB were investigated by qRT-PCR and western blot analyses, luciferase reporter gene assays and immunofluorescence.
SolB significantly increased hepatocyte size and proliferation, and then promoted liver enlargement without liver injury and inflammation. SolB transactivated human PXR, activated PXR in mice and upregulated hepatic expression of its downstream proteins, such as CYP3A11, CYP2B10 and UGT1A1. SolB also significantly enhanced nuclear translocation of PXR and YAP in human cell lines. YAP signal pathway was activated by SolB in mice.
These findings demonstrated that SolB can significantly induce liver enlargement, which is associated with the activation of PXR and YAP pathways.
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