Search results for "hydroxylation"
showing 10 items of 102 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…
The inhibition by flavonoids of 2-amino-3-methylimidazo[4,5-f]quinoline metabolic activation to a mutagen: a structure-activity relationship study.
1997
The mutagenicity of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) in Salmonella typhimurium TA98 is inhibited by flavonoids with distinct structure-antimutagenicity relationships (Edenharder, R., I. von Petersdorff I. and R. Rauscher (1993). Antimutagenic effects of flavonoids, chalcones and structurally related compounds on the activity of 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) and other heterocyclic amine mutagens from cooked food, Mutation Res., 287, 261-274). With respect to the mechanism(s) of antimutagenicity, the following results were obtained here. (1) 7-Methoxy- and 7-ethoxyresorufin-O-dealkylase activities in rat liver microsomes, linked to cytochrome P-450-dependent 1A1 and…
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…
Oxidation of tienilic acid by human yeast-expressed cytochromes P-450 2C8, 2C9, 2C18 and 2C19. Evidence that this drug is a mechanism-based inhibitor…
1996
Oxidation of tienilic acid by human cytochromes P-450 (CYP) 2C9, 2C18, 2C8 and 2C19 was studied using recombinant enzymes expressed in yeast. CYP 2C9 was the best catalyst for 5-hydroxylation of tienilic acid (K(m) = 5 +/- 1 microM, kcat = 1.7 +/- 0.2 min-1), 30-fold more potent in terms of kcat/K(m) than CYP 2C18 (K(m) = 150 +/- 15 microM, kcat = 1.8 +/- 0.2 min-1) and 300-fold more potent than CYP 2C8 (K(m) = 145 +/- 15 microM, kcat = 0.2 +/- 0.1 min-1). CYP 2C19 was unable to catalyze this hydroxylation under our experimental conditions. During this study, a marked effect of the ionic strength on the activities (hydroxylations of tienilic acid and tolbutamide) of these cytochromes P-450 …
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…
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…
Heterogeneity of osteogenesis imperfecta. Biochemical and morphological findings in a case of type III according to Sillence.
1986
A male infant with pale-blue sclerae, who died at the age of 6 weeks through the aspiration of food, presented multiple fractures and deformation of the long tubular bones. The clinical and radiological findings and the course indicated osteogenesis imperfecta, type III, according to Sillence's classification. The family history was unremarkable. Light and electron microscopic studies of iliac crest bone obtained postmortem, showed an abrupt interruption of endochondral ossification, with an active periosteal ossification. In the region of the fractures, a mixed desmochondral callus was seen. The endoplasmic reticulum of the osteoblasts was markedly dilated, the mitochondria were swollen. T…
Kinetics of tienilic acid bioactivation and functional generation of drug–protein adducts in intact rat hepatocytes
2005
13 pages; Drug-induced autoimmune hepatitis is among the most severe hepatic idiosyncratic adverse drug reactions. Considered multifactorial, the disease combines immunological and metabolic aspects, the latter being to date much better known. As for many other model drugs, studies on tienilic acid (TA)-induced hepatitis have evidenced the existence of bioactivation during the hepatic oxidation of the drug, allowing the identification of the neoantigen of anti-LKM2 autoantibodies and the pathway responsible for its formation. However, most of these results are based on the use of microsomal fractions whose relevance to the liver in vivo still needs to be established. In the more complex int…
Differential stabilization of cytochrome P-450 isoenzymes in primary cultures of adult rat liver parenchymal cells.
1991
Cytochrome P-450 dependent hydroxylation of testosterone was measured in 7-day-old cultures of primary rat liver parenchymal cells. Determinations were carried out in monocultures of parenchymal cells and co-cultures of parenchymal cells with rat liver nonparenchymal epithelial cells, or mouse embryo fibroblasts. In the monoculture system, testosterone metabolism was drastically reduced and hardly measurable after 7 days in culture. In the co-culture systems, individual P-450 isoenzymes were stabilized on different levels. P-450s p and presumably c were well preserved, P-450 a was reduced but clearly measurable, P-450 h was totally lost whereas P-450s b and e were not measurable after 7 day…
Non-competitive inhibition of clomipramineN-demethylation by fluvoxamine
1995
The selective serotonin reuptake inhibitor fluvoxamine interferes with the metabolism of tricyclic antidepressants. The present investigation was set out to characterize these interactions in vitro using rat liver microsomes and in vivo by analysing levels of clomipramine and metabolites in sera of depressed patients treated concomitantly with fluvoxamine and clomipramine. Clomipramine was N-demethylated and hydroxylated in vitro by microsomes to N-desmethyl-clomipramine, 8-hydroxyclomipramine, and 10-hydroxyclomipramine. Kinetic analyses revealed Km values of 6.2 microM for N-demethylation and 1.2 microM for 8-hydroxylation. Fluvoxamine was a non-competitive inhibitor for N-demethylation w…