In vitro biotransformation of 2-methylpropene (isobutene): epoxide formation in mice liver.
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.
Cornet
M
M
Department of Toxicology, Vrije Universiteit Brussel, Belgium.
Sonck
W
W
Callaerts
A
A
Csanády
G
G
Vercruysse
A
A
Laib
R J
RJ
Rogiers
V
V
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
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