Biomaterial Database

Oxidation of 1,2-epoxy-3-butene to 1,2:3,4-diepoxybutane by cDNA-expressed human cytochromes P450 2E1 and 3A4 and human, mouse and rat liver microsomes. 1995

M J Seaton, and M H Follansbee, and J A Bond

Chemical Industry Institute of Toxicology, Research Triangle Park, NC, USA.

1,3-Butadiene is carcinogenic in B6C3F1 mice and Sprague-Dawley rats, and has been classified as a probable human carcinogen. The genetic basis for butadiene carcinogenicity is likely mediated by its metabolite, 1,2:3,4-diepoxybutane (BDE). Oxidation of butadiene to 1,2-epoxy-3-butene (BMO) and further activation to BDE is catalysed by cytochrome P450 (CYP) isozymes. The production of BMO from butadiene is mediated by CYP2E1 and, at high butadiene concentrations, by CYP2A6. The purpose of the present study was to identify which human CYP isozymes have the ability to oxidize BMO to BDE, and to determine the extent to which this reaction occurs in B6C3F1 mouse, Sprague-Dawley rat, and human liver microsomes. Of the human cDNA-expressed CYP isozymes tested, only CYP2E1 formed detectable concentrations of BDE at 80 microM BMO. CYP2E1 and CYP3A4 were active at 5.0 mM BMO. Interindividual and interspecies variation in the initial rate of oxidation of 80 microM BMO to BDE was determined using 10 samples of human liver microsomes and single pooled samples from rats and mice. Those experiments revealed a 60-fold variation in activity among 10 human liver samples (range: 0.005-0.324 nmol/mg protein/min). Rates of BMO oxidation for mouse and rat liver microsomes were 0.473 and 0.166 nmol/mg protein/min, respectively. Apparent kinetic constants for the oxidation of BMO to BDE by four human microsomal preparations, and pooled samples from mice and rats were estimated from detailed investigations of BMO oxidation at various BMO substrate concentrations. Apparent Km for the human liver samples ranged from 0.304-0.880 mM, and Vmax values ranged from 0.38 to 1.2 nmol/mg protein/min. The apparent values of Km and Vmax for mouse liver microsomes were 0.141 +/- 0.007 mM (mean +/- SE) and 1.303 +/- 0.141 nmol/mg protein/min, respectively. For rat liver microsomes, apparent Km and Vmax were 0.145 +/- 0.036 mM and 0.408 +/- 0.031 nmol/mg protein/min, respectively. Measured rates of BDE formation correlated well with CYP2E1 protein concentrations in the human microsome samples. These results implicate human CYP2E1 as a hepatic isoform responsible for the oxidation of BMO to BDE at low concentrations of BMO. Moreover, our in vitro results reveal that microsomes prepared from human, rat and mouse liver possess the ability to form BDE from BMO. Previous in vitro results suggest that following exposure to butadiene more BMO would probably be present in mice than in rats or humans. Thus, in mice more BMO would be available for activation to BDE.(ABSTRACT TRUNCATED AT 400 WORDS)

UI	MeSH Term	Description	Entries
D007700	Kinetics	The rate dynamics in chemical or physical systems.
D008297	Male		Males
D008815	Mice, Inbred Strains	Genetically identical individuals developed from brother and sister matings which have been carried out for twenty or more generations, or by parent x offspring matings carried out with certain restrictions. All animals within an inbred strain trace back to a common ancestor in the twentieth generation.	Inbred Mouse Strains,Inbred Strain of Mice,Inbred Strain of Mouse,Inbred Strains of Mice,Mouse, Inbred Strain,Inbred Mouse Strain,Mouse Inbred Strain,Mouse Inbred Strains,Mouse Strain, Inbred,Mouse Strains, Inbred,Strain, Inbred Mouse,Strains, Inbred Mouse
D008862	Microsomes, Liver	Closed vesicles of fragmented endoplasmic reticulum created when liver cells or tissue are disrupted by homogenization. They may be smooth or rough.	Liver Microsomes,Liver Microsome,Microsome, Liver
D009153	Mutagens	Chemical agents that increase the rate of genetic mutation by interfering with the function of nucleic acids. A clastogen is a specific mutagen that causes breaks in chromosomes.	Clastogen,Clastogens,Genotoxin,Genotoxins,Mutagen
D010084	Oxidation-Reduction	A chemical reaction in which an electron is transferred from one molecule to another. The electron-donating molecule is the reducing agent or reductant; the electron-accepting molecule is the oxidizing agent or oxidant. Reducing and oxidizing agents function as conjugate reductant-oxidant pairs or redox pairs (Lehninger, Principles of Biochemistry, 1982, p471).	Redox,Oxidation Reduction
D010089	Oxidoreductases, N-Demethylating		N-Demethylase,N-Demethylases,Oxidoreductases, N Demethylating,Demethylating Oxidoreductases, N,N Demethylase,N Demethylases,N Demethylating Oxidoreductases,N-Demethylating Oxidoreductases
D011994	Recombinant Proteins	Proteins prepared by recombinant DNA technology.	Biosynthetic Protein,Biosynthetic Proteins,DNA Recombinant Proteins,Recombinant Protein,Proteins, Biosynthetic,Proteins, Recombinant DNA,DNA Proteins, Recombinant,Protein, Biosynthetic,Protein, Recombinant,Proteins, DNA Recombinant,Proteins, Recombinant,Recombinant DNA Proteins,Recombinant Proteins, DNA
D002273	Carcinogens	Substances that increase the risk of NEOPLASMS in humans or animals. Both genotoxic chemicals, which affect DNA directly, and nongenotoxic chemicals, which induce neoplasms by other mechanism, are included.	Carcinogen,Oncogen,Oncogens,Tumor Initiator,Tumor Initiators,Tumor Promoter,Tumor Promoters,Initiator, Tumor,Initiators, Tumor,Promoter, Tumor,Promoters, Tumor
D003577	Cytochrome P-450 Enzyme System	A superfamily of hundreds of closely related HEMEPROTEINS found throughout the phylogenetic spectrum, from animals, plants, fungi, to bacteria. They include numerous complex monooxygenases (MIXED FUNCTION OXYGENASES). In animals, these P-450 enzymes serve two major functions: (1) biosynthesis of steroids, fatty acids, and bile acids; (2) metabolism of endogenous and a wide variety of exogenous substrates, such as toxins and drugs (BIOTRANSFORMATION). They are classified, according to their sequence similarities rather than functions, into CYP gene families (>40% homology) and subfamilies (>59% homology). For example, enzymes from the CYP1, CYP2, and CYP3 gene families are responsible for most drug metabolism.	Cytochrome P-450,Cytochrome P-450 Enzyme,Cytochrome P-450-Dependent Monooxygenase,P-450 Enzyme,P450 Enzyme,CYP450 Family,CYP450 Superfamily,Cytochrome P-450 Enzymes,Cytochrome P-450 Families,Cytochrome P-450 Monooxygenase,Cytochrome P-450 Oxygenase,Cytochrome P-450 Superfamily,Cytochrome P450,Cytochrome P450 Superfamily,Cytochrome p450 Families,P-450 Enzymes,P450 Enzymes,Cytochrome P 450,Cytochrome P 450 Dependent Monooxygenase,Cytochrome P 450 Enzyme,Cytochrome P 450 Enzyme System,Cytochrome P 450 Enzymes,Cytochrome P 450 Families,Cytochrome P 450 Monooxygenase,Cytochrome P 450 Oxygenase,Cytochrome P 450 Superfamily,Enzyme, Cytochrome P-450,Enzyme, P-450,Enzyme, P450,Enzymes, Cytochrome P-450,Enzymes, P-450,Enzymes, P450,Monooxygenase, Cytochrome P-450,Monooxygenase, Cytochrome P-450-Dependent,P 450 Enzyme,P 450 Enzymes,P-450 Enzyme, Cytochrome,P-450 Enzymes, Cytochrome,Superfamily, CYP450,Superfamily, Cytochrome P-450,Superfamily, Cytochrome P450