Abstract
Exposure to methyltertiary-butyl ether (MTBE), a commonly used octane booster in gasoline, has previously been shown to alter various muscle, kidney, and liver metabolic activities. In the present study, the metabolism of MTBE by liver microsomes from acetoneor phenobarbital-treated Sprague-Dawley rats was studied at concentrations of up to 5 mM MTBE. Equimolar amounts oftertiary-butanol, as measured by head-space gas chromatography, and formaldehyde were formed. TheV max for the demethylation increased by 4-fold and 5.5-fold after acetone and phenobarbital treatments, respectively. The apparentK m value of 0.70 mM using control microsomes was decreased slightly after acetone treatment, but was increased by 2-fold after phenobarbital treatment. The metabolism of MTBE (1 mM) was inhibited by 35% by monoclonal antibodies against P450IIE1, the acetone/ethanol inducible form of cytochrome P450, suggesting a partial contribution by this isozyme. A single 18-h pretreatment of rats with 1 or 5 ml/kg MTBE (i. p.) resulted in a 50-fold induction of liver microsomal pentoxyresorufin dealkylase activity but no change inN-nitrosodimethylamine demethylase activity. These trends in activity agreed with immunoblot analysis which showed an elevation in P450IIB1 but no change in P450IIE1 levels.
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Abbreviations
- MTBE:
-
methyltertiary-butyl ether
- P450:
-
cytochrome P450
References
Arcos JC, Bryant GM, Venkatesan N, Argus MF (1975) Repression of dimethylnitrosamine-demethylase by typical inducers of microsomal mixed-function oxidases. Biochem Pharmacol 24: 1544–1547
Baker RC, Sorenson SM, Eby SR, Deitrich RA (1979) Acetone excretion followingt-butanol treatment in rats. Alc Clin Exp Res 3: 271
Brady JF, Lee MJ, Li M, Ishizaki H, Yang CS (1988) Diethyl ether as a substrate for acetone/ethanol-inducible cytochrome P-450 and as an inducer for cytochrome(s) P-450. Mol Pharmacol 33: 148–154
Cederbaum AI, Cohen G (1980) Oxidative demethylation oft-butyl alcohol by rat liver microsomes. Biochem Biophys Res Commun 97: 730–736
Dong Z, Hong J, Ma Q, Li D, Bullock J, Gonzalez FJ, Park SS, Gelboin HV, Yang CS (1988) Mechanism of induction of cytochrome P-450ac (P-450j) in chemically induced and spontaneously diabetic rats. Arch Biochem Biophys 263: 29–35
Eisenthal R, Cornish-Bowden A (1974) The direct linear plot. A new graphical procedure for estimating enzyme kinetic parameters. Biochem J 139: 715–720
Eliasson E, Johansson I, Ingelman-Sundberg M (1988) Ligand-dependent maintenance of ethanol-inducible cytochrome P-450 in primary rat hepatocyte cell cultures. Biochem Biophys Res Commun 150: 436–443
Johansson I, Ingelman-Sundberg M (1985) Carbon tetrachloride-induced lipid peroxidation dependent on an ethanol-inducible form of rabbit liver microsomal cytochrome P-450. FEBS Lett 183: 265–269
Johansson I, Ingelman-Sundberg M (1988) Benzene metabolism by ethanol-, acetone-, and benzene-inducible cytochrome P-450 (IIE1) in rat and rabbit liver microsomes. Cancer Res 48: 5387–5390
Johansson I, Ekström G, Scholte B, Puzycki D, Jörnvall H, Ingelman-Sundberg M (1988) Ethanol-, fasting-, and acetone-inducible cytochromes P-450 in rat liver: regulation and characteristics of enzymes belonging to the IIB and IIE gene subfamilies. Biochemistry 27: 1925–1934
Kalf GF, Post GB, Snyder R (1987) Solvent toxicology: recent advances in the toxicity of benzene, the glycol ethers, and carbon tetrachloride. Ann Rev Pharmacol Toxicol 27: 399–427
Nebert DW, Adesnik M, Coon MJ, Estabrook RW, Gonzalez FJ, Guengerich FP, Gunsalus IC, Johnson EF, Kemper B, Levin W, Phillips IR, Sato R, Waterman MR (1987) The P450 gene superfamily: recommended nomenclature. DNA 6: 1–11
Park SS, Ko I-Y, Patten C, Yang CS, Gelboin HV (1986) Monoclonal antibodies to ethanol-induced cytochrome P-450 that inhibit aniline and nitrosamine metabolism. Biochem Pharmacol 35: 2855–2858
Savolainen H, Pfaffli P, Elovaara E (1985) Biochemical effects of methyl tertiary-butyl ether in extended vapour exposure of rats. Arch Toxicol 57: 285–288
Song BJ, Veech RL, Park SS, Gelboin HV, Gonzalez FJ (1989) Induction of rat hepaticN-nitrosodimethylamine demethylase by acetone is due to protein stabilization. J Biol Chem 264: 3568–3572
Terelius Y, Ingelman-Sundberg M (1986) Metabolism ofn-pentane by ethanol-inducible cytochrome P-450 in liver microsomes and reconstituted membranes. Eur J Biochem 161: 303–308
Woodside WF, Heimberg M (1976) Effects of anti-insulin serum, insulin, and glucose on output of triglycerides and on ketogenesis by the prefused rat liver. J Biol Chem 251: 13–23
Wrighton SA, Thomas PE, Molowa DT, Haniu M, Shively JE, Maines SL, Watkins PB, Parker G, Mendez-Picon G, Levin W, Guzelian P (1986) Characterization of ethanol inducible human liverN-nitrosodimethylamine demethylase. Biochemistry 25: 6731–6735
Yoo JSH, Cheung RJ, Patten CJ, Wade D, Yang CS (1987) Nature ofN-nitrosodiemthylamine demethylase and its inhibitors. Cancer Res 47: 3378–3383
Yoo JSH, Guengerich FP, Yang CS (1988) Metabolism ofN-nitrosodialkylamines in human liver microsomes. Cancer Res 48: 1499–1504
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The nomenclature for the P450 isozymes follows the convention described by Nebert et al. (1987).
Supported by Grant ES-03938 from the National Institutes of Health and Grant 88B18 from the American Institute for Cancer Research
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Brady, J.F., Xiao, F., Ning, S.M. et al. Metabolism of methyltertiary-butyl ether by rat hepatic microsomes. Arch Toxicol 64, 157–160 (1990). https://doi.org/10.1007/BF01974403
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DOI: https://doi.org/10.1007/BF01974403