Search results for "phenobarbital."
showing 10 items of 61 documents
Cultures with cryopreserved hepatocytes: applicability for studies of enzyme induction
2000
The use of hepatocyte cultures is well established for the study of drug-drug interactions. However, the major hindrance for the use of human hepatocyte cultures is that human hepatocytes are only occasionally available. This problem could be overcome by cryopreservation. Although cryopreserved hepatocytes have been recommended for short term applications in suspension, studies on induction of enzyme activity, requiring a more prolonged maintenance of cryopreserved hepatocytes in culture, represent a new field of research. In the present study, we established a technique that allows preparation of rat hepatocyte co-cultures, using cryopreserved hepatocytes. After incubation with phenobarbit…
Distribution and induction of cytochrome P-450 and two cytochrome P-450-dependent monooxygenase activities in rat liver parenchymal cell subpopulatio…
1989
Liver parenchymal cells from the periportal and centrilobular zones differ in their morphological, biochemical and functional characteristics. In an effort to obtain fractions enriched in either periportal or centrilobular cells, isolated rat liver parenchymal cells were separated into five subpopulations by centrifugal elutriation. The mean diameters of the cells present in fractions I-V were 19.6, 21.1, 21.8, 22.7 and 23.5 micron, respectively. The content of cytochrome P-450 as well as benzphetamine N-demethylase and 7-ethoxyresorufin O-deethylase activities were higher in the larger parenchymal cells than in the smaller ones. After administration of phenobarbital the content of cytochro…
Regio- and stereoselective regulation of monooxygenase activities by isoenzyme-selective phosphorylation of cytochrome P450.
1989
The phosphorylation of the two major phenobarbital-inducible cytochrome P450 isoenzymes IIB1 and IIB2 was increased in hepatocytes by the action of the membrane permeating cAMP derivatives N6-dibutyryl-cAMP and 8-thiomethyl-cAMP. Under these conditions the dealkylation of 7-pentoxyresorufin, a selective substrate of cytochrome P450IIB1 and P450IIB2 was markedly reduced. 16 beta-Hydroxylation of testosterone which is catalyzed specifically only by cytochrome P450IIB1 and IIB2 was strongly reduced; for 16 alpha-hydroxylation which is also catalyzed by cytochrome P450IIB1 and IIB2 but additionally by 3 further cytochrome P450 isoenzymes, this reduction was less pronounced; for the oxidation of…
Ethoxyquin as an inducer and inhibitor of phenobarbital-type cytochrome P-450 in rat liver microsomes.
1977
Abstract The effect of ethoxyquin in vivo and in vitro on drug metabolism in rat liver microsomes was studied. In feeding experiments, a threshold dose of induction was found at 0.05% ethoxyquin for 14 days. At 0.5% ethoxyquin, relative liver weight, cytochrome P-450 content, cytochrome b5 content, ethylmorphine demethylation, and ethoxycoumarin deethylation were increased by a factor of 1.5 to 2. Aryl hydrocarbon hydroxylase activity was, however, not induced but even decreased by 0.5% ethoxyquin in food. Induction of epoxide hydratase was marked, amounting to 400% of control after 0.5% ethoxyquin. The induced enzyme was similar to the phenobarbital-inducible cytochrome P-450 in its CO spe…
Enzymic control of irreversible binding of metabolically activated benzo(a)pyrene in perfused rat liver by monooxygenase activity.
1977
Addition of [3H]-benzo(a)pyrene to the perfusion medium of isolated rat livers results in irreversible binding of radioactivity to DNA, RNA and protein. Binding to DNA accounted for about 0.1% of the total radioactivity which was bound in livers from animals treated with oil or saline and was increased by a factor of 3–5 after pretreatment of the animals with β-naphthoflavone or with phenobarbital. When the inhibitiors of monooygenase activity, α-naphthoflavone or metyrapone, were present in the perfusion medium, irreversible binding was reduced in livers from both β-naphthoflavone- and phenobarbital-pretreated animals, irrespective of the inhibitor used.
A novel haemoprotein induced by isosafrole pretreatment in the rat
1978
Abstract Sodium dodecyl sulphate-polyacrylamide gel electrophoresis has been used to demonstrate that pretreatment of rats with isosafrole results in the formation of a novel species of cytochrome P-450 (mol. wt. 54,000) quite distinct from that induced by phenobarbitone pretreatment (mol. wt. 50,000) or 3-methylcholanthrene (mol. wt. 58,000).
Isolation of a high spin form of cytochrome P-450 induced in rat liver by 3-methylcholanthrene.
1983
Abstract A form of cytochrome P-450 (P-450 MC1) has been isolated from the livers of 3-methylcholanthrene-treated rats. The molecular weight is 54,500 and the heme iron is in the high spin configuration which clearly differenciates this form from the other major cytochrome induced by 3-methylcholanthrene (P-450 MC2). Whilst MC2 actively dealkylated 7-ethoxycoumarin and 7-ethoxyresorufin, MC1 was only active with 7-ethoxyresorufin. Ouchterlony immunodiffusion analysis and ELISA showed that anti MC1 and anti MC2 reacted with both MC1 and MC2 but preferentially with the homologous antigen. Both anti MC1 and MC2 cross-reacted strongly with microsomes from 3-methylcholanthrene, Aroclor 1254 and …
Studies on the Biosynthesis of Microsomal Membrane Proteins. Site of Synthesis and Mode of Insertion of Cytochrome b5, Cytochrome b5 Reductase, Cytoc…
1982
The site of synthesis and mechanism of insertion into membranes of several microsomal polypeptides was studied using translation system programmed in vitro with polysomes or with mRNA extracted from free and membrane-bound rat liver polysomes. Primary translation products of cytochrome b5, NADH: cytochrome b5 oxidoreductase, NADPH: cytochrome P-450 oxidoreductase and epoxide hydrolase were isolated by specific immunoprecipitation and compared with the mature proteins. The following observations were made: 1 While cytochrome b5 and NADH: cytochrome b5 oxidoreductase are synthesized in free polysomes, NADPH: cytochrome P-450 oxidoreductase and epoxide hydrolase are made in membrane-bound poly…
Hepatocytes cultured in alginate microspheres: an optimized technique to study enzyme induction.
2004
An important application of hepatocyte cultures is identification of drugs acting as inducers of biotransformation enzymes that alter metabolic clearance of other therapeutic agents. In the present study we optimized an in vitro system with hepatocytes cultured in alginate microspheres that allow studies of enzyme induction with excellent sensitivity. Induction factors obtained with standard inducers, such as 3-methylcholanthrene or phenobarbital, were higher compared to those with conventional hepatocyte co-cultures on collagen coated dishes. This is illustrated by activities of 7-ethoxyresorufin-O-deethylase (EROD) after incubation with 5 microM 3-methylcholanthrene (3-MC), a standard ind…
The cytotoxicity of mitomycin C and Adriamycin in genetically engineered V79 cell lines and freshly isolated rat hepatocytes
1995
The objective of the present study was to investigate the cytotoxicity of Adriamycin (ADR) and mitomycin C (MMC) in tumor and non-tumor cells with respect to the role of cytochrome P450 (P450). Therefore, genetically engineered V79 Chinese hamster fibroblasts expressing only single enzymes of P450 were used. SD1 and XEM2 cells expressed rat P450IIB1 and P450IA1, respectively, whereas the V79 parental cells contained no detectable P450 levels. The cytotoxicity of ADR and MMC in the V79 cell system was compared with that in freshly isolated hepatocytes from phenobarbital (PB-hepatocytes)- and beta-naphthoflavone (beta NF-hepatocytes)-induced rats. Following 24 h of exposure to ADR equal cytot…