Search results for "epoxide hydrolase"
showing 10 items of 118 documents
Radioactively labelled epoxides. Part VI. tritium-labelled mono- and dimethyl substituted phenyl oxiranes (styrene oxides)
1988
Tritium-labelled (E)- and (Z)-2,3-dimethyl-2-phenyl oxirane 4, (E)- and (Z)-2-methyl-3-phenyl oxirane 7 and 2,2-dimethyl-3-phenyl oxirane 11 have been prepared by reduction of the corresponding bromoketones with sodium borotritide to the corresponding bromohydrins followed by cyclization to the oxiranes. These oxiranes were successfully used as diagnostic substrates to distinguish between different forms of epoxide hydrolase and glutathione transferase.
Genotoxicity characteristics of reverse diol-epoxides of chrysene.
2017
Trans-3,4-dihydroxy-3,4-dihydrochrysene (chrysene-3,4-diol), a major metabolite of chrysene, is further metabolized by rat liver enzymes to products which effectively revert the his- Salmonella typhimurium strain TA98 to histidine prototrophy, but are only weakly mutagenic in strain TA100 and in Chinese hamster V79 cells (acquisition of resistance to 6-thioguanine). The liver enzyme mediated mutagenicity of chrysene-3,4-diol is substantially enhanced in the presence of 1,1,1-trichloropropene 2,3-oxide, an inhibitor of microsomal epoxide hydrolase. The predominant metabolites of chrysene-3,4-diol, namely the anti- and syn-isomers of its 1,2-oxide (termed reverse diol-epoxides), proved to be …
Cryopreserved primary hepatocytes as a constantly available in vitro model for the evaluation of human and animal drug metabolism and enzyme inductio…
2000
The use of primary hepatocytes is now well established for both studies of drug metabolism and enzyme induction. Cryopreservation of primary hepatocytes decreases the need for fresh liver tissue. This is especially important for research with human hepatocytes because availability of human liver tissue is limited. In this review, we summarize our research on optimization and validation of cryopreservation techniques. The critical elements for successful cryopreservation of hepatocytes are (1) the freezing protocol, (2) the concentration of the cryoprotectant [10% dimethyl-sulfoxide (DMSO)], (3) slow addition and removal of DMSO, (4) carbogen equilibration during isolation of hepatocytes and…
Isoenzyme-specific phosphorylation of cytochromes P-450 and other drug metabolizing enzymes.
1987
Abstract A series of fourteen cytochrome P-450 isoenzymes was treated with three different protein kinases and found to devide into isoenzymes phosphorylated (i) by both the cyclic AMP-dependent kinase and the calcium-phospholipid-dependent kinase (P-450 PB 3a and PB 2e), (ii) by none of these kinases (P-450 PB 1b, MC 1b, UT 1, and thromboxane synthase), and (iii) by either the cyclic AMP-dependent kinase (P-450 LM 2, PB 2d, and PB 3b) or the calcium-phospholipid-dependent kinase (P-450 PB 1a, PB 2a, MC 1a, LM 3c, and LM 4). Other components of the monooxygenase system, cytochrome P-450 reductase, cytochrome b5, cytochrome b5 reductase as well as microsomal epoxide hydrolase, were poor subs…
Determination of DNA single strand breaks and selective DNA amplification by N-nitrodimethylamine and analogs, and estimation of the indicator cells'…
1986
N-nitrodimethylamine is metabolized oxidatively to N-nitrohydroxymethylmethylamine, which decomposes to yield formaldehyde and N-nitromethylamine. All four compounds and N-nitromethylamine were tested for their ability to induce DNA single strand breaks in hepatocytes and in SV 40-transformed Chinese hamster embryo cell lines. Only the two monoalkylnitramines were positive. They induced single strand breaks in hepatocytes, but were not effective in the other cells. Formaldehyde and N-nitrohydroxymethylmethylamine were toxic to the cells. None of the compounds tested was able to induce selective DNA amplification in the two transformed cell lines. Enzymes involved in drug metabolism were ass…
An insect juvenile hormone-specific epoxide hydrolase is related to vertebrate microsomal epoxide hydrolases.
1996
Abstract We describe the first cDNA sequence encoding a juvenile hormone-specific epoxide hydrolase from an insect. A full-length cDNA clone revealed a 462-amino-acid open reading frame encoding an amino acid sequence with 44% identity and 64% similarity to human microsomal epoxide hydrolase. All residues in the catalytic triad (residues Asp 227 -His 428 -Asp 350 in the M. sexta protein) were present, as was the conserved Trp 154 corresponding to the oxyanion hole. The surprising similarity of insect juvenile hormone epoxide hydrolase to vertebrate microsomal epoxide hydrolases, coupled with the ancient lineage of the epoxide hydrolases and haloalkane dehalogenases, suggests that this catab…
Analysis of the Effects of Modifying Agents on Six Different Phenotypes in Preneoplastic Foci in the Liver in Medium-Term Bioassay Model in Rats
1988
Recently a great deal of interest has been expressed in characterizing the altered enzyme phenotype of putative preneoplastic rat liver lesions. In particular, attention has been given to the changes in drug metabolizing potential, conferring physiological advantage to initiated cells, and their usefulness as marker lesions for the analysis of the development of neoplasia1–2.
Mechanisms of Toxification and Detoxification which Challenge Drug Candidates and Drugs
2007
Almost all drugs are metabolized in the human organism. In most cases this changes the toxicity, sometimes by toxification, sometimes by detoxification. For obvious ethical reasons, the toxicity cannot be experimentally studied in human beings. In systems available for toxicity studies such as whole animals or human or animal cells in culture, the drug metabolism is substantially different from that in the human organism. Risk assessment for human therefore requires knowledge of drug metabolism, its differences between systems, and the consequences for toxicity. In phase 1 of drug metabolism (oxidoreductions and hydrolyses) drugs are often toxified. This is especially the case if the result…
Drug-metabolizing enzymes in the skin of man, rat, and pig.
2007
The mammalian skin has long been considered to be poor in drug metabolism. However, many reports clearly show that most drug metabolizing enzymes also occur in the mammalian skin albeit at relatively low specific activities. This review summarizes the current state of knowledge on drug metabolizing enzymes in the skin of human, rat, and pig, the latter, because it is often taken as a model for human skin on grounds of anatomical similarities. However only little is known about drug metabolizing enzymes in pig skin. Interestingly, some cytochromes P450 (CYP) have been observed in the rat skin which are not expressed in the rat liver, such as CYP 2B12 and CYP2D4. As far as investigated most d…
Epoxides derived from various polycyclic hydrocarbons as substrates of homogeneous and microsome-bound epoxide hydratase. A general assay and kinetic…
1976
A general assay for epoxide hydratase using epoxides derived from polycyclic aromatic hydrocarbons as substrates is described. Addition of dimethylsulphoxide to the incubation mixture after incubation allowed unreacted epoxide and its phenolic by-product to be extracted into light petroleum whilst the product dihydrodiol remained in the aqueous phase. The product was then extracted into ethyl acetate and estimated radiochemically. This assay gave low extraction blanks (0.8-3.8%) when six K-region epoxides of polycyclic hydrocarbons were used, with high recoveries of the corresponding dihydrodiol in the ethyl acetate phase (65-89%). Radiochromatograms demonstrated that all the radioactivity …