Exposure to various benzene derivatives differently induces cytochromes P450 2B1 and P450 2E1 in rat liver

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Abstract
Benzene (B), toluene (T), ethylbenzene (EB), styrene (S) and xylene isomers (oX, mX, pX) are important environmental pollutants and B is a proved human carcinogen. Their inhalation by male Wistar rats (4 mg/1,20 h/day, 4 days) caused cytochrome P450 (P450) induction. The degree of P450 2B1 induction increased and that of 2E1 decreased in the series B, T, EB, S, oX, mX and pX, as estimated by Western blots, while neither solvent was as effective for 2B1 induction as phenobarbital and B was more effective for 2E1 than ethanol. The levels of several other P450s decreased after exposure to these solvents, B being most effective. Exposure to these solvents increased in vitro hepatic microsomal oxidation of B and aniline (AN) (2E1 substrates) 3 to 6-fold, indicating induction of this P450. T oxidation was increased 2 to 4-fold and chlorobenzene (ClB) oxidation 3-fold. Sodium phenobarbital (PB, 80 mg/kg/day, 4 days, i.p.) did not increase ethylmorphine (EM) and benzphetamine (BZP) demethylation (2B1 substrates), neither of the B derivatives did so, and oX decreased it; however, pentoxyresorufin O-dealkylation was well related to the immunochemically detected 2B1 levels in control, PB and B microsomes. PB did not increase B, but increased T and C1B oxidation 2–4 and 3-fold, respectively, indicating possible 2B1 role in their oxidation. B oxidation after various inducers was related to immunochemical 2E1 levels, T and C1B oxidation to both 2B1 and 2E1 and AN oxidation to 2E1 and 1A2 levels. Very efficient B oxidation by 2E1 at low B levels indicates that induction of 2E1 may contribute to B myelotoxicity in vivo more than any other P450 enzyme tested, especially considering the fact that B is the most efficient inducer of its metabolism.