title: In vitro biotransformation of 2-methylpropene (isobutene): epoxide formation in mice liver.
abstract: Until now, no data are available concerning the biotransformation and toxicity of 2-methylpropene (or isobutene), a gaseous alkene widely used in industry (rubber, fuel additives, plastic polymers, adhesives, antioxidants). In this work, the biotransformation of 2-methylpropene (MP) has been studied, using total liver homogenates of mice, supplemented with a NADPH-generating system. In analogy to other olefins, 2-methylpropene is metabolized to its epoxide 2-methyl-1,2-epoxypropane (MEP), as proved by the identification by gas chromatography coupled with mass spectrometry. The epoxidation is cytochrome P-450 dependent, as shown by experiments in the absence of the NADPH-generating system and in the presence of various concentrations of metyrapone and SKF 525-A, two known inhibitors of the mono-oxygenases. A simple gas chromatographic headspace method has been developed for the quantitative determination of the epoxide formed. The formation of MEP is never linear in function of time and it reaches a maximum after 20 min. Thereafter is decreases continuously to undetectable levels. This observation can be explained by the immediate action of epoxide hydrolase and glutathione S-transferase, converting the epoxide to 2-methyl-1,2-propanediol and to the glutathione conjugate respectively. The involvement of both enzymes has been demonstrated by the addition of 3,3,3-trichloropropene oxide and indomethacin. These inhibitors of, respectively, epoxide hydrolase and glutathione S-transferase increase the epoxide formation in a significant way. The actual concentration of MEP is therefore not only dependent on its formation by cytochrome P-450 dependent mono-oxygenases, but also on its conversion by epoxide hydrolase and glutathione S-transferase, both very active in liver tissue.
authors.affiliation: Department of Toxicology, Vrije Universiteit Brussel, Belgium.
authors.forename: M
authors.initials: M
authors.lastname: Cornet
authors.forename: W
authors.initials: W
authors.lastname: Sonck
authors.forename: A
authors.initials: A
authors.lastname: Callaerts
authors.forename: G
authors.initials: G
authors.lastname: Csanády
authors.forename: A
authors.initials: A
authors.lastname: Vercruysse
authors.forename: R J
authors.initials: RJ
authors.lastname: Laib
authors.forename: V
authors.initials: V
authors.lastname: Rogiers
mesh_terms: D000475:Alkenes / Q000378:metabolism* / Q000633:toxicity; D000818:Animals; D001711:Biotransformation; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism; D004851:Epoxide Hydrolases / Q000378:metabolism; D004852:Epoxy Compounds / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008808:Mice, Inbred CBA; D008815:Mice, Inbred Strains; D010084:Oxidation-Reduction; D013997:Time Factors
chemical_list: D000475:Alkenes; D004852:Epoxy Compounds; C071507:2-methyl-1,2-epoxypropane; D003577:Cytochrome P-450 Enzyme System; D005982:Glutathione Transferase; D004851:Epoxide Hydrolases; C008176:isobutylene