Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts:   Target Concepts:
Query: UNIPROT:P06889 (Mol)
 630,302 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Infection of mice with Leishmania donovani resulted in decreased activities of several liver enzymes involved in the metabolism of xenobiotics. Microsomal membranes from infected livers contained reduced amounts of cytochromes P450 and b5 and NADPH-cytochrome P450 reductase. Several cytochrome P450 isoenzymes (P450-PB1, P450-PB3, P450-PCN and P450-UT1) and P450-mediated reactions (aminopyrine demethylase, aniline hydroxylase, benzphentamine demethylase and ethoxycoumarin deethylase) were affected similarly. The metabolism of two carcinogens (nitrosodimethylamine and 7,12-dimethylbenz[a]anthracene) by liver microsomal membrane preparations was also reduced. Leishmania infection caused an increase of cytosolic epoxide hydrolase and microsomal epoxide hydrolase and NADH-cytochrome b5 reductase were unaffected. The results suggest that Leishmania-infected animals are likely to have altered responses to exogenous toxins compared to uninfected animals.
Mol Biochem Parasitol 1990 Jun
PMID:Changes in hepatic xenobiotic-metabolising enzymes in mouse liver following infection with Leishmania donovani. 211 55

The levels of hepatic mRNAs for several enzymes involved in drug metabolism were measured following administration to rats of either phenobarbitone or 2-allyl-2-isopropylacetamide. There was a substantial elevation in the mRNA levels for cytochromes P450 IIB1, IIB2, and IIIA1, epoxide hydrolase, glutathione-S-transferase Ya/Yc subunit, UDP-glucuronosyltransferase isoenzyme (UDPGTr-2), NADPH-cytochrome P450 oxidoreductase, and 5-aminolevulinate synthase. When rats were treated with hemin, together with inducing drug, there was a marked reduction in the induced levels of these mRNAs, with decreases in the range of 55-95%. Basal levels of these mRNAs in the noninduced rat liver were also lowered by hemin administration. Nuclear run-on transcriptional experiments showed that hemin administration substantially lowered both the basal and drug-induced transcriptional activities of the genes for cytochrome P450IIB1/IIB2 and 5-aminolevulinate synthase. In contrast, the mRNA for heme oxygenase was elevated by hemin treatment, whereas the mRNA levels of beta-actin, albumin, and ornithine transcarbamylase, used as controls, were not affected. Treatment of rats with clofibrate resulted in increased levels of mRNA for cytochrome IVA1 and, in addition, those for cytochromes P450IIB1 and P450IIB2. Hemin administration repressed the induction of mRNA levels for cytochromes P450IIB1 and IIB2 but not that for cytochrome P450 IVA1. Additionally, the induction of P450IAI by beta-naphthoflavone was not affected by hemin. The results suggest that heme may negatively control the induction of cytochromes P450IIB1 and IIB2 and other hepatic enzymes by phenobarbitone and phenobarbitone-like drugs and perhaps play a role in regulating drug metabolism. There is, however, no evidence at present as to whether heme has a direct role in such a mechanism or whether injected hemin promotes a secondary response.
Mol Pharmacol 1990 Oct
PMID:Hemin administration to rats reduces levels of hepatic mRNAs for phenobarbitone-inducible enzymes. 223 90

The K-region 5,6-epoxide and non-K-region 1,2- and 3,4-epoxides of chrysene were isolated by normal phase high performance liquid chromatography (HPLC) from a mixture of products formed in the metabolism of chrysene by liver microsomes from untreated (control), phenobarbital-treated, or 3-methylcholanthrene-treated rats in the presence of an epoxide hydrolase inhibitor, 3,3,3-trichloropropylene 1,2-oxide. Epoxides were characterized by ultraviolet, mass, and circular dichroism spectral and chiral stationary phase HPLC analyses. Each of the metabolically formed epoxides was hydrated by rat liver microsomal epoxide hydrolase to a trans-dihydrodiol. The metabolically formed chrysene 5,6-epoxides were determined by chiral stationary phase HPLC and were found to contain (5S,6R):(5R,6S) enantiomer ratios of 68:32 (control), 71:29 (phenobarbital), and 5:95 (3-methylcholanthrene), respectively. The enantiomers of chrysene 1,2-epoxide and 3,4-epoxide were also resolved by chiral stationary phase HPLC. However, the enantiomeric compositions of the metabolically formed chrysene 1,2- and 3,4-epoxides, which racemized rapidly at room temperature, could not be directly determined. By using molecular oxygen-18 in the in vitro incubation of chrysene and by mass spectral analyses of the resulting oxygen-18-containing dihydrodiol metabolites and their acid-catalyzed dehydration (phenolic) products, both 1,2-epoxide and 3,4-epoxide were found to be converted by microsomal epoxide hydrolase-catalyzed water attack at predominantly (greater than or equal to 97%) the allylic carbons.
Mol Pharmacol 1987 Jul
PMID:Stereoselective formations of K-region and non-K-region epoxides in the metabolism of chrysene by rat liver microsomal cytochrome P-450 isozymes. 303 4

Many toxic effects are not caused by the administered compound itself, but are due to metabolites. All cell types express some xenobiotic-metabolizing enzymes, but levels and patterns are very variable. Critical metabolic steps may occur within the target cell and/or at other sites. This complex situation is difficult to mimic in vitro. The further problem is that cells that are taken into culture tend to rapidly cease the expression of important xenobiotic-metabolizing enzymes. Part of the problem may be solved by the addition of exogenous metabolizing systems, for example, in the form of freshly isolated hepatocytes, crude subcellular preparations, or purified enzymes. In these systems, the plasma membrane of the target cell may act as a barrier for the active metabolite and thereby lead to false negative results. The alternative is the use of metabolically active target cells. We therefore screened 18 cell lines for monooxygenase, cytochrome P-450 reductase, epoxide hydrolase, glutathione transferase, and UDP-glucuronosyl transferase activities. In further studies, IEC-17, IEC-18, and HuFoe-15 cells showed their capabilities of activating a broad spectrum of structurally heterogenous promutagens, as indicated by the induction of micronuclei. These cells, however, were not suited for the study of a more relevant genetic end point, the induction of hereditary functional changes (gene mutations), implying that a compromise had to be made on the level of the toxicodynamics. In the second approach, cDNAs encoding the rat cytochromes P-450IA1 and P-450IIB1, set under the control of a constitutive promoter, were transfected into V79 Chinese hamster cells, which do not express cytochromes P-450 but are ideal target cells for gene mutation assays. The resulting substrains (XEM1, XEM2, XEM3; SD1) stably expressed cytochromes P-450IA1 and P-450IIB1, respectively, and showed the corresponding monooxygenase activities. Aflatoxin B1, cyclophosphamide, dibutylnitrosamine, and benzo[a]pyrene mutated SD1 and/or XEM1 and XEM2 cells, but were inactive in parental V79 cells. The mutagenicity of benzo[a]pyrene 7,8-trans-dihydrodiol was about 1000 times more potent in XEM1 and XEM2 cells than in SD1 and V79 cells. Other promutagens were inactive in V79 as well as in the genetically engineered daughter lines. This system therefore is not yet optimal in general screening for the detection of new mutagens, but appears ideal in the identification of critical xenobiotic-metabolizing enzymes for a given mutagen.
Mol Toxicol
PMID:Search for cell culture systems with diverse xenobiotic-metabolizing activities and their use in toxicological studies. 315

To characterize the distribution and inducibility of drug metabolizing enzymes within different hepatic cell populations, the activities of aminopyrine N-demethylase, ethoxyresorufin O-deethylase, microsomal epoxide hydrolase and cytosolic glutathione transferase were measured in liver parenchymal, Kupffer, and endothelial cells isolated from untreated rats or rats pretreated with phenobarbital, 3-methylcholanthrene, or Aroclor 1254. Enzyme activities, measurable in all cases, were 2.3- to 5.7-fold higher in parenchymal cells than in Kupffer and endothelial cells. Phenobarbital increased aminopyrine N-demethylase, microsomal epoxide hydrolase, and cytosolic glutathione transferase activities, whereas 3-methylcholanthrene enhanced ethoxyresorufin O-deethylase, epoxide hydrolase, and glutathione transferase activities in the three cell populations. Aroclor 1254 consistently induced each of the enzyme activities in parenchymal, Kupffer, and endothelial cells. Western blot analyses revealed clear differences in the expression of proteins immunologically related to cytochrome P-450 PB-1, and glutathione transferases B and X in parenchymal cells compared with the corresponding Kupffer and endothelial cells. In contrast, only minor differences between the cell types were apparent in the expression of cytochromes P-450 PB-4, P-450 MC1a, P-450 MC1b and microsomal epoxide hydrolase. These studies establish that oxidative and postoxidative drug metabolizing enzymes are not restricted to parenchymal cells: similar but distinguishable complements of these enzymes are also found in Kupffer and endothelial cells.
Mol Pharmacol 1987 Oct
PMID:Xenobiotic metabolizing enzymes are not restricted to parenchymal cells in rat liver. 367 Feb 81

C57BL/6J (C57) and DBA/JBOMf (DBA) mice were used to study the role of adipose tissue as a modifier of tissue distribution, biological effects, and elimination of a lipophilic foreign chemical, 2,4,5,2',4',5'-hexachlorobiphenyl (HCB). As an indication of biological potency of the model compound, the activities of hepatic drug-metabolizing enzymes were determined. DBA mice contained twice as much body fat as C57 mice. Since the highly lipophilic HCB was primarily sequestered by the adipose tissue, DBA mice required greater doses of HCB than did C57 mice to reach similar tissue levels of the chemical. Accordingly, greater HCB doses were required by DBA mice for elevation of drug-metabolizing enzyme activities. Phenobarbital elevated enzyme activities in a similar way in both mouse strains. When the dietary intake of DBA mice was restricted, the body fat content decreased from 15% to 5% of body weight during 1 week. In these animals the tissue accumulation of HCB and enzyme induction resembled the situation in C57 mice fed ad libitum. Highest elevations were seen in the activities of 7-ethoxycoumarin-O-deethylase and arylhydrocarbon hydroxylase (EC 1.14.14.2). In addition, the activity of epoxide hydrolase (EC 3.3.2.3) was increased, whereas glutathione S-transferase as well as UDP-glucuronosyltransferase (EC 2.4.1.17) activities remained unchanged. The abundant adipose tissue content played no role in the nonresponsiveness of DBA mice to 3-methylcholanthrene since, in contrast to C57 mice, no changes in enzyme activities were detected in DBA mice deprived of food, even after large doses of 3-methylcholanthrene. The adipose tissue content also affected the rate of elimination of HCB. DBA mice excreted smaller quantities of HCB than did C57 mice after equal doses. When, however, fasted DBA mice received HCB, they excreted it at rates similar to those of C57 mice fed ad libitum. In C57 mice, concomitant to the elevation of monooxygenase activities, there was an increase in the rate of excretion of HCB. No such elevation could be seen after a dose that was too small to elevate enzyme activities.
Mol Pharmacol 1983 Nov
PMID:Adipose tissue content as a modifier of the tissue distribution, biological effects, and excretion of a hexachlorobiphenyl in C57BL/6J and DBA/JBOMf mice. 641

Two forms of cytochrome P-450 have been purified to electrophoretic homogeneity from hepatic microsomes of rabbits treated with imidazole. Several criteria indicate that the cytochrome of higher electrophoretic mobility is identical with ethanol-inducible isozyme 3a. "Imidazole-3a" and "ethanol-3a" exhibit the same chromatographic characteristics and have identical electrophoretic mobilities upon sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Furthermore, the two protein preparations have the same absorbance maxima and absorption coefficients in the oxidized, reduced, and reduced-CO states. A single immunoprecipitin band exhibiting complete identity was observed upon reaction of imidazole-3a and ethanol-3a with the immunoglobulin G fraction from sheep immunized with the latter protein. The amino acid composition and first 10 residues of the amino terminus of the two protein preparations are indistinguishable, as are the high-performance liquid chromatographic maps of the peptides obtained upon cleavage with trypsin, Staphylococcus aureus V8 protease, or Lys C endoproteinase . Furthermore, these preparations have very similar activities in the oxidation of ethanol to acetaldehyde and the p-hydroxylation of aniline. Evidence was obtained that the cytochrome of lower electrophoretic mobility isolated from imidazole-treated rabbits is probably identical with isozyme 6; the spectral characteristics, amino acid composition, and carboxyl-terminal sequence are described. As an inducer, imidazole has the advantage over ethanol of being less variable in its effects and requiring a shorter period of treatment. From the resulting liver microsomes, one can readily isolate, in addition to P-450 isozymes 3a and 6, isozymes 3c and 4 as well as epoxide hydrolase.
Mol Pharmacol 1984 May
PMID:Purification of liver microsomal cytochrome P-450 isozymes 3a and 6 from imidazole-treated rabbits. Evidence for the identity of isozyme 3a with the form obtained by ethanol treatment. 642 1

Epoxide formation from drugs, chemicals, food additives and environmental pollutants is catalyzed by cytochrome P-450 dependent monooxygenase(s). Epoxides are converted to glycols or dihydrodiols by epoxide hydrolase (EH). These enzymes are known to be present in the microsomes of different mammalian tissues and in the hepatic nuclei from rats and humans. The balance between the epoxide forming (AHH) and metabolizing (EH) enzyme activities may provide information about the "epoxide exposure" of a tissue. We thus investigated AHH and EH in the nuclear and microsomal fractions from six livers, four kidneys, four lungs, and two adrenals from human fetuses (gestational age between 15 and 24 weeks). Tissues were obtained at legal abortion for sociomedical reasons. AHH activity was measured according to van Cantfort et al (Biochem Biophys Res Commun 79: 505, 1977) using beno (a)pyrene as substrate. EH was measured as described by Jerina et al (Mol Pharmacol 13:342, 1977) using both styrene oxide (SO) and benzo(a)pyrene-4,5-oxide (BPO) as substrate. The nuclear fraction was isolated by a multistep procedure including centrifugation in high density sucrose ( Pacifici et al, unpublished). The hepatic AHH activity (pmole/min/mg; mean +/- SEM) was 11.5 +/- 2.2 in the nuclear fraction and 34.7 +/- 1.7 in the microsomes. In adrenals it was 6.0 (nuclei) and 4.4 (microsomes). The nuclear fraction from kidneys and lungs did not catalyze this reaction at a measurable rate, whereas microsomal AHH activity was 1.3 +/- 0.3 and 5.3 +/- 1.1, respectively, in these tissues.(ABSTRACT TRUNCATED AT 250 WORDS)
 ...
PMID:Epoxide hydrolase and aryl hydrocarbon hydroxylase in human fetal tissues: activities in nuclear and microsomal fractions and in isolated hepatocytes. 667 72

Human liver microsomal epoxide hydrolase was purified to apparent homogeneity as judged by a single protein-staining band in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Sheep antibody to human liver epoxide hydrolase reacted with the enzyme in detergent-solubilized human liver microsomes, giving a single immunoprecipitin band which formed a line of identity with the pure human enzyme. Antibody against the human enzyme reacted well with epoxide hydrolase in detergent-solubilized monkey liver microsomes by the Ouchterlony test but less strongly cross-reacted with the enzyme from rat liver and several other species. The antibody produced against purified human liver epoxide hydrolase precipitated the enzyme but did not inhibit catalytic activity, reminiscent of the relationship of rat liver epoxide hydrolase to its antibody. The absolute level of epoxide hydrolase in liver microsomal samples from 11 human subjects, as measured by a radial immunodiffusion assay, varied 3.4-fold whereas the rate of hydration of octene oxide varied 2.9-fold. The excellent correlation of the amounts of epoxide hydrolase determined catalytically or immunochemically (r = 0.99) indicated that interindividual variation in octene oxide hydration rates by human liver microsomes is a consequence of differences in amount of epoxide hydrolase protein which is present, and not the result of differences in levels of endogenous modulators of catalytic activity.
Mol Pharmacol 1982 Jul
PMID:Human liver microsomal epoxide hydrolase. Correlation of immunochemical quantitation with catalytic activity. 681 57

Parenteral administration of naphthalene produces a dose-dependent and tissue-, species-, and cell-selective lesion of murine Clara cells. The rate and stereoselectivity of naphthalene metabolism by microsomal preparations correlate with tissue and species differences in cytotoxicity. Because earlier studies used microsomes obtained from whole tissue, differences in susceptibility of proximal and distal airways could not be related to differences in the metabolic activation or detoxication of naphthalene. Specific subcompartments of the respiratory system, obtained by microdissection, have been used to study the cytochrome P450-dependent metabolism of naphthalene and the epoxide hydrolase/glutathione transferase-dependent metabolism of naphthalene oxide. The rates of naphthalene metabolism were substantially higher in mouse airways than in comparable airways of hamsters or rats. Rates of metabolism were higher in distal airways than in the trachea of all species studied. Metabolism in mouse airways was highly stereoselective, whereas that in hamster and rat tissues was not. Nonciliated cells at all airway levels in mice were heavily labeled with an antibody to cytochrome P450 2F2; little labeling was observed in any portion of rat and hamster lungs. Postmitochondrial supernatants prepared from mouse and hamster airways metabolized racemic naphthalene oxide to diol and glutathione adducts at substantially higher rates than did comparable preparations from rats. Although glutathione levels varied 2-4-fold at different airway levels in the three species studied, levels at the most susceptible site (mouse distal bronchioles) were as high as or higher than those at other, less susceptible, sites. These studies support the view that the rate and stereoselectivity of naphthalene metabolism to naphthalene 1R,2S-oxide catalyzed by cytochrome P450 2F2 are critical determinants in the species-specific and region-selective cytotoxicity of naphthalene in mice. The lack of major differences in the catalytic activity or enantioselectivity of putative detoxication enzymes (epoxide hydrolase or glutathione transferases) between mouse and hamster tissue, combined with data showing that the differences in the metabolic fate of naphthalene oxide in proximal versus distal airways are not dramatic, suggests that the initial epoxidation of naphthalene is an important factor in site-selective toxicity. These studies support the need to use tissue from defined airway levels for studies on the relationship of biochemical and metabolic factors important in cellular injury by lung toxicants, such as naphthalene, where there are dramatic regional differences in susceptibility to injury within the respiratory system.
Mol Pharmacol 1995 Jan
PMID:Relationship of cytochrome P450 activity to Clara cell cytotoxicity. IV. Metabolism of naphthalene and naphthalene oxide in microdissected airways from mice, rats, and hamsters. 783 35


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