Gene/Protein Disease Symptom Drug Enzyme Compound
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Query: UNIPROT:P01275 (glucagon)
 26,492 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

The hepatic cytochrome P450 system, with numerous different P450 enzymes, is characterized by its inducibility by a variety of endogenous and exogenous compounds. Specific forms of P450, exhibiting distinct but partially overlapping substrate specificities, are increased in response to a given chemical. Consequently, the rate of elimination of the inducing compound is often enhanced and the system is in this respect adaptive to changes in the environment. Transcriptional activation mechanisms for the endo- or xenobiotically controlled P450 synthesis are well documented. Here we describe a mechanism for posttranslational ligand-dependent stabilization of ethanol-inducible P450IIE1 in hepatocyte cultures. Glucagon or 8-bromoadenosine 3',5'-cyclic monophosphate causes an enhanced rate of P450IIE1 degradation in the hepatocytes as well as phosphorylation on Ser-129, a reaction which denatures the protein under in vitro conditions. Substrates for the enzyme, such as ethanol and imidazole, protect the enzyme from phosphorylation and degradation in hepatocytes but do not influence phosphorylation or degradation of phenobarbital-inducible P450IIB1. Our proposed mechanism, which remains to be shown under in vivo conditions, describes the P450 molecules as receptors for the compounds in question and might provide a way by which endo- and xenobiotics regulate their own rate of metabolism.
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PMID:Substrate-, hormone-, and cAMP-regulated cytochrome P450 degradation. 232 79

Rats given a dose of carbon tetrachloride (CCl4) immediately received injections of glucagon and insulin every 4 h. They frequently died after 4 h and showed a significantly higher mortality between 8 h and 28 h as compared to the control rats where such deaths occurred 16 h later. At 8 h, the derangements of SGPT values and prothrombin time were significantly greater in the hormone-treated rats than in the control rats. In these CCl4-intoxicated rats, hepatic reduced glutathione content at 4 h was significantly reduced after hormone treatment. The treatment significantly enhanced CCl4 metabolism, conversion of 14CCl4 into 14CO2 in vitro, by microsomes isolated from the liver, whereas it did not affect the microsomal cytochrome P450 content. These results suggest that glucagon and insulin treatment increased CCl4 hepatotoxicity in rats through activating the cytochrome P450-dependent mono-oxygenase system. This would merit consideration for the clinical application of this treatment.
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PMID:Enhancement of carbon tetrachloride-induced liver injury by glucagon and insulin treatment. 328 Nov 98

Monolayer cultures were prepared from hepatocytes of 15 d chick embryos and maintained at high cell density in a chemically defined medium. In the absence of growth stimulatory conditions DNA synthesis was observed only during the first 10 to 16 h of culture. Thus, after a 12 h exposure to [3H]thymidine ([3H]dThd, 4 to 16 h) 9.1 +/- 1% (mean +/- SD, n = 4) of the hepatocyte nuclei were labeled. Labeled mitotic nuclei, up to late telophase, were regularly observed in these cultures. Beyond 16 h less than 2% labeled nuclei were found (12 h of [3H]dThd), which indicates that the hepatocytes entered proliferative quiescence. DNA synthesis of "resting" hepatocytes was stimulated by insulin and, only slightly, by hydrocortisone, glucagon, or fetal bovine serum. Triiodothyronine (T3), or the nucleoside inosine (i) did not stimulate. Combination of insulin (I) with hydrocortisone (H), T3 (T), or glucagon (G) resulted in a more than additive effect. Nearly maximal stimulation occurred with the combinations IHT and ITG. Labeling increased at 10 ng/ml of each component and was maximal at 1 to 10 micrograms/ml. A lag period of 8 to 10 h after hormone administration (IHiTG, 10 micrograms/ml) was observed before nuclear labeling increased. Within the subsequent 10 h a considerable proportion of the hepatocytes (up to 30% or more) entered DNA synthesis. Mitotic activity (with nuclei in prophase up to late telophase) also was stimulated. An increase of both total DNA and protein content was measured in several experiments. Hormonal stimulation of hepatocyte DNA synthesis and mitotic activity was associated with decreased beta-naphthoflavone-mediated induction of cytochrome P450. A causal relationship between these two phenomena remains to be established. It is suggested that chick embryo hepatocyte cultures are a useful tool for studies on hepatocyte proliferation and differentiation.
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PMID:Stimulation of DNA synthesis and mitotic activity of chick embryo hepatocytes in primary culture. Effect on induction of polysubstrate monooxygenase activity. 637 Aug 35

The effects of elevated intracellular cyclic adenosine monophosphate (cAMP) in regulating phenobarbital (PB)-inducible gene expression in primary rat hepatocyte cultures were investigated. Cells were exposed to various concentrations (0.1-100 microM) of cAMP analogs and/or activators of intracellular cAMP-dependent pathways. Effects of these treatments were assessed either using a 1-h pulse prior to PB (100 microM) exposure or in conjunction with PB during a 24-h exposure period. PB-inducible responses were measured in hepatocytes by hybridization to cytochrome P450 (CYP) CYP2B1, CYP2B2, and CYP3A1 mRNAs. The cAMP analogs, 8-bromo-cAMP, 8-(4-chlorophenylthio)-cAMP, dibutyryl cAMP, and (Sp)-5,6-DCl-cBiMPS ((Sp)-5,6-dichloro-1-beta-D-ribofuranosylbenzimidazole-3', 5'-monophosphorothioate), and the activators of adenylate cyclase, forskolin and glucagon, dramatically inhibited PB-mediated induction of CYP2B1 and CYP2B2 in a concentration-dependent manner. A similar inhibition of PB-induced CYP3A1 mRNA levels was effected by the cAMP analogs and glucagon. The phosphodiesterase inhibitors isobutylmethylxanthine and RO 201724 potentiated the cAMP responses. Increasing the concentration of PB (0.05-1.00 mM) did not alleviate the cAMP-mediated repression. A requirement for protein kinase A (PKA) was demonstrated by the use of (Sp)-cAMPS, a highly specific activator of PKA, whereas the inactive diastereoisomer, (Rp)-cAMPS, was ineffective in modulating PB induction. The response to cAMP was specific since elevated intracellular cAMP levels did not perturb beta-naphtholflavone-mediated induction of CYP1A1, CYP1A2, microsomal epoxide hydrolase, or dexamethasone-mediated induction of CYP3A1 gene expression. Nor did elevated intracellular cAMP modulate the liver-selective albumin gene expression levels. The results of the present study demonstrated striking inhibition of PB-mediated CYP gene induction by cAMP and PKA activators, indicating a negative regulatory role for the cAMP signal transduction pathway on PB gene induction.
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PMID:cAMP-associated inhibition of phenobarbital-inducible cytochrome P450 gene expression in primary rat hepatocyte cultures. 775 30

The major rat glucocorticoid-inducible cytochrome P450 (CYP3A1) is known to be regulated at a transcriptional level by glucocorticoids and at a post-translational level by substrate-dependent stabilization. We have investigated mechanisms of substrate/ligand stabilization using primary hepatocytes, isolated liver microsomes from dexamethasone-treated rats, and purified enzymes. Treatment of hepatocytes with glucagon caused a 3-fold increase in CYP3A1 phosphorylation as well as an enhanced degradation rate of the enzyme. Specific CYP3A1 substrates or ligands, such as erythromycin, triacetyloleandomycin, and clotrimazole (CTZ) protected the enzyme from degradation in hepatocytes and inhibited in a concomitant manner (r = 0.99) glucagon-induced phosphorylation of the enzyme. In vitro experiments with purified CYP3A1 and isolated liver microsomes revealed one major site (Ser393) phosphorylated by the catalytic subunit of cAMP-dependent kinase, a reaction inhibited by ligands. Experiments in microsomes showed the presence of an endogenous cAMP-dependent kinase active on CYP3A1. Addition of exogenous cAMP-dependent kinase increased the rate of microsomal CYP3A1 phosphorylation, a reaction further stimulated by NADPH, but inhibited by CTZ. The microsomal phosphorylation caused a pronounced denaturation of cytochrome P450, as revealed spectrophotometrically, whereas CTZ protected from this reaction. Similar effects were noted when the CYP3A1-dependent 6 beta-hydroxylation of testosterone was monitored. It is suggested that the cellular CYP3A1 level is regulated to a significant extent posttranslationally by substrate-regulated cAMP-dependent phosphorylation on Ser393, followed by denaturation and degradation in the endoplasmic reticulum.
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PMID:Substrate-regulated, cAMP-dependent phosphorylation, denaturation, and degradation of glucocorticoid-inducible rat liver cytochrome P450 3A1. 803 84

The role of oxygen tension, insulin, and glucagon on the preservation and induction of cytochrome P450 isoenzyme activities and contents was investigated in rat hepatocytes cultured for 4 days on crude liver membrane fractions at 4 or 13% O2. At 13% O2, three out of six immunochemically analyzed P450 isoenzymes were significantly higher than in 4% O2. Exposure to phenobarbital (PB) from Days 1 to 4 dose dependently increased the protein content and decreased the albumin secretion in 13% O2 cultures only. The maximal induction of P450 isoenzymes CYP2B1/2B2 (20- to 25-fold) and CYP2C6 (6-fold) were found at 0.75 mM PB at both oxygen tensions. In contrast, the highest induction of CYP1A1/1A2 (3-fold), of CYP3A (2-fold), and EROD activity were found with 3 mM PB in 4% O2 cultures. CYP2B-dependent testosterone hydroxylation at positions 16 alpha/beta was elevated to a greater extent in 13% O2 cultures (96-fold at 0.75 mM PB) compared to 4% O2 cultures (42-fold). This activity was affected by the insulin concentrations and the insulin:glucagon ratio. With decreasing insulin concentration (100 to 1 nM) or with increasing insulin:glucagon ratios (1:100-1:0.1), the enzyme activity increased preferentially in 4% O2 cultures. The results of these investigations demonstrate that different tissue oxygen tension modulates the responsiveness of the cultured hepatocytes to the glucoregulatory hormones insulin and glucagon and this modulation results in a altered activity of cytochrome P450 isoforms.
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PMID:Oxygen tension, insulin, and glucagon affect the preservation and induction of cytochrome P450 isoforms in cultured rat hepatocytes. 820 90

Previously, we demonstrated that elevated levels of cyclic AMP (cAMP) repressed phenobarbital (PB)-inducible cytochrome P450 (CYP)2B gene expression in primary rat hepatocyte cultures. Although CYP3A1 induction by PB was similarly repressed by most of the cAMP-enhancing strategies, forskolin additions in particular resulted in marked stimulation of CYP3A1 expression. Here we examined whether this effect was due to forskolin's ability to activate adenylate cyclase. By using a specific ELISA for assessment of intracellular cAMP levels, we determined that forskolin and a water-soluble analog (L858051; 7 beta-desacetyl-7 beta-(N-methylpiperazine)) were equipotent in stimulating adenylate cyclase activity. However, only forskolin and its inactive 1,9-dideoxy analog were active as inducers of CYP3A1. In comparative studies, both dexamethasone and PB were ineffective in stimulating production of intracellular cAMP. Furthermore, treatment of hepatocytes with glucagon, dibutyryl-cAMP, or N6O2'-dibutyryl-cyclic GMP, resulted in no detectable enhancement of CYP3A1 gene expression. These results demonstrated that CYP3A1 induction by forskolin is independent of cAMP, and instead is likely to involve a direct chemical effect of forskolin on the CYP3A1 activation pathway.
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PMID:Forskolin-mediated induction of CYP3A1 mRNA expression in primary rat hepatocytes is independent of elevated intracellular cyclic AMP. 855 37

Our laboratory recently described a new human cytochrome P450 arachidonic acid epoxygenase (CYP2J2) and the corresponding rat homolog (CYP2J3). Immunoblotting studies using a polyclonal antibody raised against recombinant human CYP2J2 confirmed CYP2J protein expression in human and rat pancreatic tissues. Immunohistochemical staining of formalin-fixed paraffin-embedded rat and human pancreas using the anti-CYP2J2 IgG and avidin-biotin-peroxidase detection revealed that CYP2J2 protein expression was highly localized to cells in the islets of Langerhans, with minimal staining in pancreatic exocrine cells. Colocalization studies using antibodies to the glucagon, insulin, somatostatin, and pancreatic polypeptide as markers for alpha-, beta-, delta-, and PP cells, respectively, showed that CYP2J protein expression was abundantly present in all four cell types, but was highest in the glucagon-producing alpha-cells. Direct evidence for the epoxidation of arachidonic acid by pancreatic cytochrome P450 was provided by documenting, for the first time, the presence of epoxyeicosatrienoic acids in vivo in human and rat pancreas by gas chromatography/mass spectrometry. Importantly, the levels of immunoreactive CYP2J2 in different human pancreatic tissues were highly correlated with endogenous epoxyeicosatrienoic acid concentrations. We conclude that human and rat pancreas contain an arachidonic acid epoxygenase belonging to the CYP2J subfamily that is highly localized to islet cells. These data together with previous work showing effects of epoxyeicosatrienoic acids in stimulating insulin and glucagon secretion from isolated rat pancreatic islets support the hypothesis that epoxygenase products may be involved in stimulus-secretion coupling in the pancreas.
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PMID:Predominant expression of an arachidonate epoxygenase in islets of Langerhans cells in human and rat pancreas. 904 44

The parenchymal cell fraction was isolated from abattoir adult porcine livers and cultured in Dulbecco's Modified Eagles' medium/Ham's F12 medium (DMEM/F12; 1:1) medium supplemented with 5% foetal calf serum, 10 ng/mL glucagon, 10 microg/mL insulin, 60 ng/mL hydrocortisone and eight other factors (NAIR-1 medium). The fraction contained a number of epithelial cells other than hepatocytes, some of which attached to the culture plates as cell clusters and began to grow after 3 days in culture. These epithelial cells growing as colonies were found to express cytokeratin 18 by immunocytochemistry. After 7-8 days, duct-like structures emerged in the central parts of the colonies. The cells constituting the duct-like structures and some cells located outside the structures were positive for cytokeratin 19 and gamma-glutamyltransferase (GGT). The albumin-positive cells were located in the outer parts of the colonies rather than their central parts. Albumin was also detectable in the cells surrounded by the duct-like structures. Moreover, cytochrome P450 IA1 was induced by 3-methylcholanthrene (3-MC) on day 16. These results suggest that porcine liver epithelial cell clusters may contain stem-like cells which can differentiate into mature hepatocytes or bile duct epithelial cells.
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PMID:Colonial growth and differentiation of epithelial cells derived from abattoir adult porcine livers. 979 36

Insulin resistance in liver and muscle tissue, together with beta-cell secretory defects, leads to overt type 2 diabetes mellitus. In the early stages of this progressive disorder, glycaemic control can be established through diet and exercise alone. Indeed, in some patients, marked weight reduction can lead to normalized fasting blood glucose. As a consequence, pharmacological approaches to weight loss have been investigated as a new option for the management of type 2 diabetes in obese patients. The serotonin- and noradrenaline-reuptake inhibitor sibutramine has emerged as the most promising agent in the treatment of obesity, although it appears to be less effective in diabetic patients than in non-diabetic patients. Other weight-reducing agents of potential benefit include noradrenergic anorexiants, orlistat, leptin, and beta3-agonists. Insulin and insulin secretagogues, the oldest available antidiabetic drugs, have been used to compensate for beta-cell secretory defects in patients with type 2 diabetes. Repaglinide, a new, fast-acting insulin secretagogue with a short duration of action, reduces postprandial hyperglycaemia when taken shortly before meals. Other novel antidiabetic agents are currently under development, including pramlintide (an amylin analogue) and glucagon-like peptide. Pramlintide slows gastric emptying and delays glucose absorption, and glucagon-like peptide is the most potent endogenous stimulator of glucose-induced insulin release. Recent advances in type 2 diabetes therapy have seen the development of the thiazolidinediones (troglitazone, rosiglitazone, and pioglitazone), which improve insulin resistance in patients whose diabetes is poorly controlled by diet and exercise therapy. Thiazolidinediones bind to peroxisome proliferator-activated receptor-gamma (PPAR-gamma) and act through a process involving gene regulation at a transcriptional level. Troglitazone, the first approved drug in the class, has been shown to decrease plasma glucose levels as monotherapy but is more effective in combination with sulphonylureas, metformin, or insulin. However, despite its generally good safety profile, troglitazone has been associated with severe idiosyncratic hepatocellular injury. There have been more than 150 spontaneous reports of serious hepatic events, including at least 25 instances in which patients died or required a liver transplant. Rosiglitazone, the most potent thiazolidinedione, is still in clinical development, as is pioglitazone. To date, rosiglitazone has been shown to have no reported cases of idiosyncratic drug reactions leading to jaundice or liver failure and no clinically significant drug interactions with cytochrome P450 3A4-metabolized drugs such as nifedipine. Although the available data for pioglitazone are limited to the results of short-term studies, it is reported to be safe and well tolerated. Combination therapy is increasingly important in type 2 diabetes management following failure of monotherapy because complementary mechanisms of action of the different classes of oral agents demonstrate synergistic effects when used in combination. Oral agents may also be used as adjuncts to insulin for achieving glycaemic control.
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PMID:Promising new approaches. 1122 Feb 87


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