Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UMLS:C0028754 (obesity)
 124,988 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The X-ray crystal structure of the human constitutive androstane receptor (CAR, NR1I3)/retinoid X receptor alpha (RXRalpha, NR2B1) heterodimer sheds light on the mechanism of ligand-independent activation of transcription by nuclear receptors. CAR contains a single-turn Helix X that restricts the conformational freedom of the C-terminal AF2 helix, favoring the active state of the receptor. Helix X and AF2 sit atop four amino acids that shield the CAR ligand binding pocket. A fatty acid ligand was identified in the RXRalpha binding pocket. The endogenous RXRalpha ligand, combined with stabilizing interactions from the heterodimer interface, served to hold RXRalpha in an active conformation. The structure suggests that upon translocation, CAR/RXRalpha heterodimers are preorganized in an active conformation in cells such that they can regulate transcription of target genes. Insights into the molecular basis of CAR constitutive activity can be exploited in the design of inverse agonists as drugs for treatment of obesity.
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PMID:A structural basis for constitutive activity in the human CAR/RXRalpha heterodimer. 1561 Jul 35

Guggulsterone is the active ingredient in gugulipid, an organic extract of the Commiphora mukul plant. Gugulipid has been used for nearly 3000 years in Ayurvedic medicine, mainly as a treatment for arthritis. Herbal practitioners currently use gugulipid therapy in conditions as diverse as rheumatism, coronary artery disease, arthritis, hyperlipidemia, acne, and obesity. The active ingredient in gugulipid is guggulsterone, a plant sterol compound recently identified as a pregnane X receptor (PXR; NR1I2) ligand. We show herein that guggulsterone treatment represses the expression of cytochrome P450 2b10 (Cyp2b10) gene expression by inhibiting constitutive androstane receptor (CAR; NR1I3) activity in hepatocytes lacking functional PXR (PXR-knockout). We also show that PXR-CAR cross-talk determines the net activity of guggulsterone treatment toward Cyp2b10 gene expression. Using mammalian two-hybrid assays, we show that treatment with guggulsterone differentially affects protein cofactor recruitment to these two nuclear receptors. These data identify guggulsterone as an inverse agonist of the nuclear receptor CAR. When viewed together with the data showing that PXR and CAR expression is highly variable in different ethnic populations and that CAR expression is under the control of a circadian rhythm, our data provide important insight into the molecular mechanism of interindividual variability of drug metabolism. These data, together with the recent resolution of the crystal structures of PXR and CAR, will likely aid in the rational design of more specific CAR inverse agonists that are currently viewed as potential antiobesity drugs.
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PMID:The ratio of constitutive androstane receptor to pregnane X receptor determines the activity of guggulsterone against the Cyp2b10 promoter. 1583 98

Lipids are essential components of biological membranes, fuel molecules and metabolic regulators that control cellular functions, metabolism and homeostasis. The liver plays a central role in regulating lipid metabolism and whole body lipid homeostasis. Sterols, bile acids and fatty acids are the endogenous ligands of the liver orphan receptor, farnesoid X receptor, peroxisome proliferator-activated receptor, vitamin D receptor, constitutive androstane receptor and pregnane X receptor. These metabolic receptors coordinately regulate lipid, glucose, energy and drug metabolism. Alteration of lipid homeostasis causes dyslipidemia, which is a major risk factor contributing to atherosclerotic cardiovascular diseases, diabetes, obesity and liver diseases. Advances in the understanding of the mechanisms of nuclear receptor regulation of lipid homeostasis have provided an opportunity to investigate potential therapeutic drugs targeted to nuclear receptors. This could be useful for the treatment of diabetes, and cardiovascular and chronic liver diseases.
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PMID:Nuclear receptor regulation of lipid metabolism: potential therapeutics for dyslipidemia, diabetes, and chronic heart and liver diseases. 1625 20

The nuclear receptor constitutive androstane receptor (CAR), a key transcription factor for the expression of cytochrome P450 (CYP) 2B genes, resides in the cytoplasm under untreated conditions and translocates into the nucleus upon xenobiotic exposure. CAR forms a multiprotein complex including heat shock protein 90 in the cytoplasm as the glucocorticoid receptor, and it is likely that protein phosphatase 2A plays a critical role in the first step of CAR nuclear translocation. In addition to the xenobiotic induction of CYP2Bs, our recent studies have indicated that CAR is important for sex and strain differences and obesity/diabetes-associated changes in the expression of CYP2B genes. These results have raised the hypothesis that the expression of nuclear receptors varies depending on the physiologic condition, leading to the dysregulation of CYP expression. In obese mice fed a high-fat diet, however, hepatic CYP3A levels are drastically decreased without any significant changes in the expression of nuclear receptors including the pregnane X receptor and hepatocyte nuclear factor-4, which are known to be key transcription factors in the expression of CYP3A genes. These results indicate that it is important to investigate the mechanism of the transcriptional regulation of nuclear receptor genes as well as the activation of nuclear receptors to understand the CYP expression system fully.
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PMID:[Roles of nuclear receptors in the gene expression of drug-metabolizing enzymes under various physiological conditions]. 1667 42

Animal studies reveal that fasting and caloric restriction produce increased activity of specific metabolic pathways involved in resistance to weight loss in liver. Evidence suggests that this phenomenon may in part occur through the action of the constitutive androstane receptor (CAR, NR1I3). Currently, the precise molecular mechanisms that activate CAR during fasting are unknown. We show that fasting coordinately induces expression of genes encoding peroxisome proliferator-activated receptor gamma coactivator-1alpha (PGC-1alpha), CAR, cytochrome P-450 2b10 (Cyp2b10), UDP-glucuronosyltransferase 1a1 (Ugt1a1), sulfotransferase 2a1 (Sult2a1), and organic anion-transporting polypeptide 2 (Oatp2) in liver in mice. Treatments that elevate intracellular cAMP levels also produce increased expression of these genes in cultured hepatocytes. Our data show that PGC-1alpha interaction with hepatocyte nuclear factor 4alpha (HNF4alpha, NR2A1) directly regulates CAR gene expression through a novel and evolutionarily conserved HNF4-response element (HNF4-RE) located in its proximal promoter. Expression of PGC-1alpha in cells increases CAR expression and ligand-independent CAR activity. Genetic studies reveal that hepatic expression of HNF4alpha is required to produce fasting-inducible CAR expression and activity. Taken together, our data show that fasting produces increased expression of genes encoding key metabolic enzymes and an uptake transporter protein through a network of interactions involving cAMP, PGC-1alpha, HNF4alpha, CAR, and CAR target genes in liver. Given the recent finding that mice lacking CAR exhibit a profound decrease in resistance to weight loss during extended periods of caloric restriction, our findings have important implications in the development of drugs for the treatment of obesity and related diseases.
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PMID:Regulation of constitutive androstane receptor and its target genes by fasting, cAMP, hepatocyte nuclear factor alpha, and the coactivator peroxisome proliferator-activated receptor gamma coactivator-1alpha. 1682 89

Physiological and pathophysiological conditions often affect the expression of drug metabolizing enzymes such as cytochromes P450 (P450s). Diabetes is one such factor and it is of great interest to understand its effects on drug metabolism, since diabetic patients generally have increased need for pharmacotherapy. We have recently reported the coordinated reduction of CYP2B1/2 and their transcriptional regulator constitutive androstane receptor (CAR), a member of the nuclear receptor superfamily, in the liver of genetically obese/diabetic Zucker fatty rats (Xiong, H., Yoshinari, K., et al., Drug Metab. Dispos., 30, 918-923, 2002). In this study, we investigated the expression of P450s and liver-enriched nuclear receptors in the liver of genetically diabetic db/db mice. Surprisingly, both CYP2B10 and CAR levels were increased in db/db mice. CYP4A expression was also increased at both mRNA and protein levels in db/db mice, while those of peroxisome proliferator-activated receptor alpha, a key regulator for the transcriptional activation of CYP4As, were comparable to those in age-matched C57BL/6 mice. Our results demonstrate that db/db mice and Zucker fatty rats exhibit different expression profiles of P450s and nuclear receptors despite their similar characteristics for obesity and diabetes resulting from a defect in the leptin signaling pathway.
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PMID:Changes in the expression of cytochromes P450 and nuclear receptors in the liver of genetically diabetic db/db mice. 1688 Jun 18

Dehydroepiandrosterone (DHEA), the major precursor of androgens and estrogens, has several beneficial effects on the immune system, on memory function, and in modulating the effects of diabetes, obesity, and chemical carcinogenesis. Treatment of rats with DHEA influences expression of cytochrome P450 (P450) genes, including peroxisome proliferator-activated receptor alpha (PPAR alpha)- and pregnane X receptor (PXR)-mediated induction of CYP4As and CYP3A23, and suppression of CYP2C11. DHEA treatment elevated the expression and activities of CYP3A4, CYP2C9, CYP2C19, and CYP2B6 in primary cultures of human hepatocytes. Induction of CYP3A4 in human hepatocytes was consistent with studies in rats, but induction of CYP2Cs was unexpected. The role of PXR in this response was studied in transient transfection assays. DHEA activated hPXR in a concentration-dependent manner. Because CYP2B6 induction by DHEA in human hepatocytes might involve either PXR or constitutive androstane receptor (CAR) activation, we performed experiments in primary hepatocytes from CAR knockout mice and observed that CAR was required for maximal induction of Cyp2b10 by DHEA. Furthermore, CAR-mediated Cyp2b10 induction by DHEA was inhibited by the inverse agonist of CAR, androstanol (5 alpha-androstan-3 alpha-ol). Further evidence for CAR activation was provided by cytoplasmic/nuclear transfer of CAR upon DHEA treatment. Elucidation of CAR activation and subsequent induction of CYP2B6 by DHEA presented an additional mechanism by which the sterol can modify the expression of P450s. The effect of DHEA on the activation of the xenosensors PPAR alpha, PXR, and CAR, and the consequent potential for adverse drug/toxicant interactions should be considered in humans treated with this nutriceutical agent.
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PMID:Dehydroepiandrosterone induces human CYP2B6 through the constitutive androstane receptor. 1759 76

Obesity and type 2 diabetes are related metabolic disorders of high prevalence. The constitutive androstane receptor (CAR) was initially characterized as a xenobiotic receptor regulating the responses of mammals to xenotoxicants. In this study, we have uncovered an unexpected role of CAR in preventing obesity and alleviating type 2 diabetes. Using a high fat diet (HFD)-induced obesity model, we showed that treatment of wild type mice with the CAR agonist 1,4-bis[2-(3,5 dichloropyridyloxy)] benzene (TCPOBOP) efficiently prevented obesity from happening or reversed preinduced obesity. Treatment with TCPOBOP improved insulin sensitivity in both the HFD-induced type 2 diabetic model and the ob/ob mice. In contrast, CAR null mice maintained on a chow diet showed spontaneous insulin insensitivity, which cannot be relieved by TOPOBOP treatment. The hepatic steatosis in HFD-treated mice and ob/ob mice was markedly reduced by the TCPOBOP treatment. The metabolic benefits of CAR activation may have resulted from the combined effect of inhibition of lipogenesis, very low density lipoprotein secretion and export of triglycerides, and gluconeogenesis as well as increases in brown adipose tissue energy expenditure and peripheral fat mobilization. Moreover, the skeletal muscle of CAR-activated mice showed a decreased incomplete oxidation, despite having a lower expression level of peroxisome proliferator-activated receptor alpha and its target genes involved in fatty acid oxidation. In summary, our results have revealed an important metabolic function of CAR and may establish this "xenobiotic receptor" as a novel therapeutic target for the prevention and treatment of obesity and type 2 diabetes.
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PMID:The constitutive androstane receptor is an anti-obesity nuclear receptor that improves insulin sensitivity. 1961 49

The pregnane X receptor (PXR) and the constitutive androstane receptor (CAR) are two closely related and liver-enriched nuclear hormone receptors originally defined as xenobiotic receptors. PXR and CAR regulate the transcription of drug-metabolizing enzymes and transporters, which are essential in protecting our bodies from the accumulation of harmful chemicals. An increasing body of evidence suggests that PXR and CAR also have an endobiotic function that impacts energy homeostasis through the regulation of glucose and lipids metabolism. Of note and in contrast, disruptions of energy homeostasis, such as those observed in obesity and diabetes, also have a major impact on drug metabolism. This review will focus on recent progress in our understanding of the integral role of PXR and CAR in drug metabolism and energy homeostasis.
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PMID:Pregnane X receptor and constitutive androstane receptor at the crossroads of drug metabolism and energy metabolism. 2073 25

Constitutive androstane receptor (CAR) and pregnane X receptor (PXR) are closely related orphan nuclear receptor proteins that share several ligands and target overlapping sets of genes involved in homeostasis and all phases of drug metabolism. CAR and PXR are involved in the development of certain diseases, including diabetes, metabolic syndrome and obesity. Ligand screens for these receptors so far have typically focused on steroid hormone analogs with pharmacophore-based approaches, only to find relatively few new hits. Multiple CAR isoforms have been detected in human liver, with the most abundant being the constitutively active reference, CAR1, and the ligand-dependent isoform CAR3. It has been assumed that any compound that binds CAR1 should also activate CAR3, and so CAR3 can be used as a ligand-activated surrogate for CAR1 studies. The possibility of CAR3-specific ligands has not, so far, been addressed. To investigate the differences between CAR1, CAR3 and PXR, and to look for more CAR ligands that may be of use in quantitative structure-activity relationship (QSAR) studies, we performed a luciferase transactivation assay screen of 60 mostly non-steroid compounds. Known active compounds with different core chemistries were chosen as starting points and structural variants were rationally selected for screening. Distinct differences in agonist versus inverse agonist/antagonist effects were seen in 49 compounds that had some ligand effect on at least one receptor and 18 that had effects on all three receptors; eight were CAR1 ligands only, three were CAR3 only ligands and four affected PXR only. This work provides evidence for new CAR ligands, some of which have CAR3-specific effects, and provides observational data on CAR and PXR ligands with which to inform in silico strategies. Compounds that demonstrated unique activity on any one receptor are potentially valuable diagnostic tools for the investigation of in vivo molecular targets.
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PMID:Rational quantitative structure-activity relationship (RQSAR) screen for PXR and CAR isoform-specific nuclear receptor ligands. 2086 55


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