In vitro biotransformation of 2-methylpropene (isobutene) : epoxide formation in mice liver

• Published in: Archives of toxicology Vol. 65; no. 4; pp. 263 - 267
• Main Authors: CORNET, M, SONCK, W, CALLAERTS, A, CSANADY, G, VERCRUYSSE, A, LAIB, R. J, ROGIERS, V
• Format: Journal Article
• Language: English
• Published: Berlin Springer 1991
• Subjects: Alkenes - metabolism; Alkenes - toxicity; Animals; Biological and medical sciences; Biotransformation; Chemical and industrial products toxicology. Toxic occupational diseases; Cytochrome P-450 Enzyme System - metabolism; Epoxide Hydrolases - metabolism; Epoxy Compounds - metabolism; Gas, fumes; Glutathione Transferase - metabolism; Liver - metabolism; Male; Medical sciences; Mice; Mice, Inbred CBA; Mice, Inbred Strains; Oxidation-Reduction; Time Factors; Toxicology; Gases; Vertebrata; Mammalia; Mouse; Animal; Liver; Rodentia; Metabolism toxicity relation; Epoxidation; In vitro
• DOI: 10.1007/BF01968959
• EISSN: 1432-0738
• ISSN: 0340-5761

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.