Monoclonal antibody-directed characterization of cytochrome P450 isozymes responsible for toluene metabolism in rat liver.
Monoclonal antibodies (MAbs) were used to study the contribution of cytochromes P450IA1/IA2, P450IIB1/IIB2, P450IIC11/IIC6 and P450IIE1 to toluene side-chain (benzyl alcohol, BA, formation) and ring (o- and p-cresol formation) oxidation in liver microsomes from fed, one-day fasted, and phenobarbital (PB)-, 3-methylcholanthrene (MC)- and ethanol-treated rats. All rats were fed synthetic liquid diets. MAb 1-7-1 against P450IA1/IA2 inhibited markedly o-cresol formation and slightly p-cresol formation but not BA formation only in microsomes from MC-treated rats. MAbs 2-66-3, 4-7-1 and 4-29-5 against P450IIB1/IIB2 strongly inhibited BA, o-cresol and p-cresol formation only in PB-induced microsomes. MAb 1-68-11 against P450IIC11/IIC6 inhibited BA formation at high toluene concentration in the following order: fed greater than fasted greater than ethanol = MC greater than PB, and ethanol greater than or equal to fed = fasted greater than MC greater than PB on the basis of the percentage and net amount inhibition, respectively. MAb 1-91-3 against P450IIE1 inhibited BA formation at low toluene concentration, but not at high concentration, in the following order: ethanol greater than fasted = fed greater than MC, and ethanol greater than fasted greater than fed greater than MC on the basis of percentage and net inhibition, respectively. MAbs 1-68-11 and 1-91-3 also inhibited p-cresol formation at high and low toluene concentrations, respectively. These results indicate that (i) both P450IIE1 and P450IIC11/IIC6 are constitutive isozymes mainly responsible for the formation of BA and p-cresol from toluene as low- and high-Km isozymes, respectively; (ii) P450IIE1, but not P450IIC11/IIC6, is induced by one-day fasting and ethanol treatment; (iii) both P450IIE1 and P450IIC11/IIC6 are decreased by PB and MC treatments; (iv) P450IIE1 is inhibited by high concentration of toluene; (v) P450IIB1/IIB2 can contribute to the formation of BA, o- and p-cresol from toluene, while P450IAI/IA2 preferentially contributes to the formation of o-cresol.
Nakajima
T
T
Department of Hygiene, Shinshu University School of Medicine, Matsumoto, Japan.
Wang
R S
RS
Elovaara
E
E
Park
S S
SS
Gelboin
H V
HV
Hietanen
E
E
Vainio
H
H
D000818:Animals; D000911:Antibodies, Monoclonal / Q000276:immunology / Q000494:pharmacology*; D019905:Benzyl Alcohol; D001592:Benzyl Alcohols / Q000378:metabolism; D003408:Cresols / Q000378:metabolism; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000276:immunology; D000431:Ethanol; D007527:Isoenzymes / Q000037:antagonists & inhibitors* / Q000276:immunology; D007700:Kinetics; D008748:Methylcholanthrene; D008862:Microsomes, Liver / Q000201:enzymology*; D010634:Phenobarbital; D051381:Rats; D014050:Toluene / Q000378:metabolism*
D000911:Antibodies, Monoclonal; D001592:Benzyl Alcohols; D003408:Cresols; D065607:Cytochrome P-450 Enzyme Inhibitors; D007527:Isoenzymes; C032538:4-cresol; D014050:Toluene; D000431:Ethanol; D008748:Methylcholanthrene; D003577:Cytochrome P-450 Enzyme System; D019905:Benzyl Alcohol; D010634:Phenobarbital