Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UMLS:C0406810 (NAME)
 13,345 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The nuclear receptor CAR (constitutive active receptor) mediates the induction of transcription of cytochrome P450 (CYP) genes by phenobarbital (PB) and PB-type inducers. A recent study using CAR-null mice has shown that CAR regulates not only the CYP genes but also other genes encoding various drug/steroid-metabolizing enzymes. In addition to coordinating these enzymes, CAR plays other roles in hepatic gene expression: CAR represses various genes including carnitine palmitoyltransferase 1a and phosphoenolpyruvate carboxykinase 1 in response to PB, and the receptor regulates the constitutive expression of genes such as squalene epoxidase. On the other hand, induction of certain genes such as amino levulinate synthase 1 by PB is not regulated by CAR. Here we describe diverse roles of CAR in hepatic gene expression with a particular focus on endogenous substances such as cholesterol, bilirubin, and steroid hormones.
 ...
PMID:The role of the nuclear receptor CAR as a coordinate regulator of hepatic gene expression in defense against chemical toxicity. 1246 60

The drug metabolizing enzyme cytochrome P450 3A4 (CYP3A4) is thought to be involved in the metabolism of nearly 50% of all the drugs currently prescribed. Alteration in the activity or expression of this enzyme seems to be a key predictor of drug responsiveness and toxicity. Currently available studies indicate that the ligand-activated nuclear receptors pregnane X receptor (PXR; NR1I2) and constitutive androstane receptor (CAR; NR1I3) regulate CYP3A4 expression. However, in cell-based reporter assays, CYP3A4 promoter activity was most pronounced in liver-derived cells and minimal or modest in non-hepatic cells, indicating that a liver-specific factor is required for physiological transcriptional response. Here we show that the orphan nuclear receptor hepatocyte nuclear factor-4alpha (HNF4alpha; HNF4A) is critically involved in the PXR- and CAR-mediated transcriptional activation of CYP3A4. We identified a specific cis-acting element in the CYP3A4 gene enhancer that confers HNF4alpha binding and thereby permits PXR- and CAR-mediated gene activation. Fetal mice with conditional deletion of Hnf4alpha had reduced or absent expression of CYP3A. Furthermore, adult mice with conditional hepatic deletion of Hnf4alpha had reduced basal and inducible expression of CYP3A. These data identify HNF4alpha as an important regulator of coordinate nuclear-receptor-mediated response to xenobiotics.
 ...
PMID:The orphan nuclear receptor HNF4alpha determines PXR- and CAR-mediated xenobiotic induction of CYP3A4. 1251 43

Phenobarbital (PB) increases hepatic drug/steroid-metabolic capability by coordinately activating transcription of the genes encoding various metabolizing enzymes. The nuclear receptor CAR was first implicated as a transcription factor that activates the cytochrome P450 Cyp2b10 gene. In response to PB, CAR forms a heterodimer with the retinoid X receptor (RXR), binds to a PB response element (typified by DR-4 motif), and activates transcription of the gene. In the CAR-null mouse, PB does not only induce the Cyp2b10 gene, but also induces genes encoding various metabolizing enzymes. Thus, CAR is a general nuclear receptor that is essential for PB induction of drug/steroid metabolizing enzymes. PB also induces amino levulinate synthase 1 (ALAS-1), the rate-limiting enzyme in heme biosynthesis, to increase heme supply. However, PB induction of the synthase occurs in CAR-null mice, suggesting that CAR does not coordinate the heme synthesis for the induction of drug/steroid metabolism.
 ...
PMID:Phenobarbital induction of drug/steroid-metabolizing enzymes and nuclear receptor CAR. 1257 83

CYP3A4 is the most abundant cytochrome P450 in human liver, comprising approximately 30% of the total liver P450 content. This enzyme has an important role in endogenous processes, most notably steroid catabolism, and also plays a fundamental role in the metabolism of more than half of the clinically used drugs currently prescribed. The majority of CYP3A substrates are also capable of upregulating CYP3A activity, mainly through transcriptional activation. The molecular mechanisms that underlie the transcriptional activation of CYP3A4 are complex, with many steroid hormone nuclear receptors, including GR, PXR, VDR and CAR, playing a role in these mechanisms. However, the net result of transcriptional activation is an increase in the metabolism of the inducing compounds and, therefore, increased clearance. An important side effect of this transcriptional activation is that co-administered chemicals metabolized by CYP3A may also have their pharmacokinetics altered. Such changes can result in reduced clinical efficacy of drugs, resulting in poor patient response, or the development of an adverse drug response. This review will examine examples of established interactions caused through transcriptional activation of CYP3A4, and speculate on whether such effects are clinically important and should be considered during the design of treatment regimes or, alternatively, are relatively minor and cause little physiological effects.
 ...
PMID:Evaluation of the toxicological relevance of CYP3A4 induction. 1261 76

This review summarizes recent findings indicating that members of the orphan nuclear receptor superfamily regulate the synthesis of their CYP genes which code CYP enzymes involved in metabolism of endogenous and exogenous compounds. The foreign compounds metabolism and the role played by individual cytochrome P450 (CYP) enzymes in the activation and detoxification of xenochemicals prevalent in the environment are important areas of molecular pharmacology and toxicology. The advances in our understanding of the mechanisms through which foreign chemicals impact on these CYP-dependent metabolic processes have been made during the past years. Role for three "orphan" nuclear receptor superfamily members, designated CAR (constitutive androstane receptor), PXR/SXR (pregnelone X receptor) and PPAR (peroxisome proliferator activated receptor), in respectively mediating the induction of hepatic CYPs belonging to families CYP2, CYP3, and CYP4 has now been established. The CYP gene products such as CYP3A, CYP2B and PPAR are essential for metabolism of endogenous steroid hormones, fatty acids and various xenobiotics including drugs. Unexpectedly, it has been shown that SXR, which regulates CYP3A, can also regulate CYP2B via recognition of the phenobarbital response element (PBRE). In a type of functionally symmetry, orphan receptor CAR was found to activate CYP3A through SXR/PXR response element. Indeed, SXR/PXR binds to inverted (IR-6) and direct (DR-4) response element localized to regulatory DNA regions of human CYP3A4 and rat CYP3A23 genes, respectively. These observations provide a rational explanation for the activation of multiple CYP gene classes by certain xenobiotics as well as the propensity for drug-drug interactions. In addition, both endogenous and exogenous ligands which act as activators of nuclear receptors can result in disruption of cellular homeostasis.
 ...
PMID:[The role of nuclear receptors in cytochrome P-450 induction by xenochemicals]. 1266 59

The aim of this study was to investigate the effect of nitric oxide on renal Na+,K(+)-ATPase and ouabain-sensitive H+,K(+)-ATPase activities. The study was performed in male Wistar rats. The investigated substances were infused under general anaesthesia into abdominal aorta proximally to the renal arteries. The activity of ATPases was assayed in isolated microsomal fraction. NO donor, S-nitroso-N-acetylpenicillamine (SNAP), infused at doses of 10(-7) and 10(-6)mol/kg/min decreased medullary Na+,K(+)-ATPase activity by 29.4% and 45.2%, respectively. Another NO donor, spermine NONOate, administered at the same doses reduced Na+,K(+)-ATPase activity in the renal medulla by 31.7% and 46.5%, respectively. Neither of NO releasers had any effect on Na+,K(+)-ATPase in the renal cortex and on either cortical or medullary ouabain-sensitive H+,K(+)-ATPase. Infusion of NO precursor, L-arginine (100 micromol/kg/min), decreased medullary Na+,K(+)-ATPase activity by 32.2%, whereas inhibitor of nitric oxide synthase, L-NAME (10 nmol/kg/min), increased this activity by 20.7%. The effect of synthetic NO donors was mimicked by 8-bromo-cGMP and blocked by inhibitors of soluble guanylate cyclase, ODQ or methylene blue, as well as by specific inhibitor of protein kinase G, KT5823. In addition, inhibitory effect of either SNAP or 8-bromo-cGMP on medullary Na+,K(+)-ATPase was abolished by 17-octadecynoic acid (17-ODYA), which inhibits cytochrome P450-dependent metabolism of arachidonic acid. These data suggest that NO decreases Na+,K(+)-ATPase activity in the renal medulla through the mechanism involving cGMP, protein kinase G, and cytochrome P450-dependent arachidonate metabolites. In contrast, NO has no effect on Na+,K(+)-ATPase in the renal cortex and on either cortical or medullary ouabain-sensitive H+,K(+)-ATPase.
 ...
PMID:Nitric oxide decreases renal medullary Na+, K+-ATPase activity through cyclic GMP-protein kinase G dependent mechanism. 1283 21

The mechanisms of fenretinide-induced cell death of neuroblastoma cells are complex, involving signaling pathways mediated by free radicals or reactive oxygen species (ROS). The aim of this study was to identify mechanisms generating ROS and apoptosis of neuroblastoma cells in response to fenretinide. Fenretinide-induced ROS or apoptosis of SH-SY5Y or HTLA 230 neuroblastoma cells were not blocked by Nitro l-argenine methyl ester (l-NAME), an inhibitor of nitric oxide synthase. Flavoprotein-dependent superoxide-producing enzymes such as NADPH oxidase were also not involved in fenretinide-induced apoptosis or ROS generation. Similarly, ketoconazole, a cytochrome P450 inhibitor, and inhibitors of cyclooxygenase (COX) were also ineffective. In contrast, inhibition of phospholipase A(2) or lipoxygenases (LOX) blocked the induction of ROS and apoptosis in response to fenretinide. Using specific inhibitors of LOX, blocking 12-LOX but not 5- or 15-LOX inhibited both fenretinide-induced ROS and apoptosis. The effects of eicosatriynoic acid, a specific 12-LOX inhibitor, were reversed by the addition of the 12-LOX products, 12 (S)-hydroperoxyeicosatetraenoic acid and 12 (S)-hydroxyeicosatetraenoic acid. The targeting of 12-LOX in neuroblastoma cells may thus be a novel pathway for the development of drugs inducing apoptosis of neuroblastoma with improved tumor specificity.
 ...
PMID:Mechanisms of free-radical induction in relation to fenretinide-induced apoptosis of neuroblastoma. 1285 36

Nitric oxide and cytochrome P450 arachidonic acid metabolites participate in blood pressure regulation. The synthesis of these autacoids leads to arterial hypertension. However, it is not known whether there is an interaction between them. Therefore, we studied the modulatory effect of nitric oxide and cytochrome P450-arachidonic acid metabolites, their interaction on blood pressure, and the renal content of cytochrome P450. Male Wistar rats were divided: 1) control, 2) L-NAME (100 mg/kg/d p.o.), 3) L-NAME + SnCl2 (10 mg/kg/d i.p.), and 4) L-NAME + dexamethasone (1 mg/kg/d s.c.). We measured blood pressure and collected urine and blood for nitric oxide measurement. NO2 was quantified by HPLC. Blood pressure was: control, 97 +/- 7 mmHg; L-NAME, 151 +/- 4.6 mmHg; L-NAME + SnCl2, 133 +/- 3 mmHg, and L-NAME + dexamethasone 152 +/- 4.5 mmHg. Urine nitrite concentration was: 1) 1.832 +/- 0.32, 2) 1.031 +/- 0.23, 3) 1.616 +/- 0.33, and 4) 1.244 +/- 0.33 mumol/mL, while the concentration in blood was: 1) 0.293 +/- 0.06, 2) 0.150 +/- 0.05, 3) 0.373 +/- 0.13, and 4) 0.373 +/- 0.07 mumol/mL. L-NAME + SnCl2 decreased cytochrome P450 renal content, and L-NAME + dexamethasone showed a similar response. In conclusion, both, nitric oxide and CYP-arachidonic acid metabolites play a role in the regulation of blood pressure. Nitric oxide also partially regulates renal cytochrome P450 content.
 ...
PMID:[Participation of nitric oxide and arachidonic acid metabolites via cytochrome - P450 in the regulation of arterial blood pressure]. 1289 86

The present study evaluated the potential mechanism involved in the hypotensive effect induced by ET-1 in rats treated with the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in the drinking water during 7 days. Hypertension developed in the L-NAME-treated rats (164+/-3 versus 112+/-1 mm Hg in untreated control rats), and the hypotensive effect of ET-1 (100 pmol/kg IV) was significantly enhanced compared with control rats (32+/-2% versus 20+/-1% fall in mean arterial pressure). The enhanced ET-1 hypotensive effect in L-NAME-treated rats was abolished by the ETB receptor antagonist BQ-788 but was unaltered by the cyclooxygenase inhibitor diclofenac, the cytochrome P450 inhibitor fluconazole, or the potassium channel blockers apamin, glibenclamide, tetraethylammonium, and 4-aminopyridine. Pretreatment with the cannabinoid CB1 receptor antagonist SR141716A significantly reduced the hypotensive response to ET-1 in L-NAME-treated rats (20+/-1%), although it did not modify the response in untreated control rats (17+/-1%). These findings indicate that in rats under chronic NOS inhibition, the hypotensive effect of ET-1 is unexpectedly enhanced and appears to be mediated by a non-NO/non-prostanoid mechanism and involves an SR141716A-sensitive mechanism triggered by ETB receptor activation.
 ...
PMID:SR141716A-sensitive enhancement of ET-1 hypotensive effect by chronic NOS inhibition. 1291 62

Nitric oxide (NO) is responsible for cytochrome P450 (CYP450) loss during isolation and cytokine treatment of primary rat hepatocytes. As P450s mediate the metabolism of toxic chemicals, their inhibition could compromise the cells competence to eliminate toxins, a condition potentially relevant in neurological diseases involving constitutive activation of nitric oxide synthase (NOS) and NO over-production. Here, we have investigated the correlation between NO accumulation and CYP1A2 down-regulation during maturation of mouse cerebellar granule cells (CGC). As neurons matured in culture, the inducible levels of CYP1A2 protein and catalytic activity decreased to almost undetectable values. In parallel, a significant increase in NO concentration was observed. Neuronal NOS remained constitutively active during maturation, thus contributing to NO accumulation. The NOS inhibitor l-NAME, restored CYP1A2 catalytic activity up to 9 days in vitro, supporting a role for NO in the inhibition process. Maturation was also followed by increased NMDA receptor activity and intracellular Ca2+ concentration. We suggest that maintained NOS activity during CGC maturation could lead to NO accumulation and to decreased CYP1A2 inducibility. Increased NMDA receptor activity and Ca2+ entry could contribute to this process. Thus, neurodegeneration could diminish the induction of specific P450s and impair the metabolism of foreign and/or endogenous chemicals in the CNS.
 ...
PMID:Down-regulation of CYP1A2 induction during the maturation of mouse cerebellar granule cells in culture: role of nitric oxide accumulation. 1462 87


<< Previous 1 2 3 4 5 6 7 8 9 10 Next >>