Co-induction of cytochrome P-450 isozymes in rat liver by 2,4,5,2',4',5'-hexachlorobiphenyl or 3-methoxy-4-aminoazobenzene

M Kelley, P Hantelle, S Safe, W Levin and PE Thomas

A multitude of xenobiotics have been demonstrated to co-induce either cytochromes P-450c and P-450d or cytochromes P-450b and P-450e in rat hepatic microsomes. Recently, the compounds 2,4,5,2',4',5'- hexachlorobiphenyl (HCB) and 3-methoxy-4-aminoazobenzene (3-MeO-AAB) have been suggested as selective inducers of cytochrome P-450b (Eur. J. Biochem. 151:67 (1985)) and P-450d (Biochem. Biophys. Res. Commun. 133:1072 (1985)), respectively. Since the identification of inducers with such unique characteristics would have implications with regard to the mechanism of induction of all four isozymes, we have examined the induction of cytochromes P-450b and P-450e by HCB and cytochromes P- 450c and P-450d by 3-MeO-AAB in liver microsomes from adult male rats. Immunoblot analysis with monoclonal antibodies directed against cytochromes P-450b and P-450e indicate that HCB induces both isozymic species at the three dosage levels examined (10, 90, and 180 mg/kg). Similarly, 3-MeO-AAB does not appear to represent a unique inducer. Immunoblots of hepatic microsomes from animals treated with three different dosage regimens of 3-MeO-AAB demonstrate that, even at the lowest dosage level (50 mg/kg), both cytochromes P-450c and P-450d are induced. Moreover, immunoinhibition of 7-ethoxyresorufin O-deethylase (EROD) activity by monospecific antibody against either cytochrome P- 450c or P-450d confirms this result. 3-MeO-AAB increases this enzyme activity 10-fold; approximately one-third of this induced activity is inhibited with monospecific anti-P-450c, while two-thirds is inhibited with monospecific anti-P-450d. This study also demonstrates that hepatic EROD activity is not an accurate estimate of cytochrome P-450c content since the majority of this enzyme activity in control and 3-MeO- AAB-treated rats is inhibited with monospecific anti-P-450d but not with monospecific anti-P-450c.

Volume 32, Issue 1, pp. 206-211, 08/01/1987
Copyright © 1987 by American Society for Pharmacology and Experimental Therapeutics

This article has been cited by other articles:

				M. Levine, E. Y. W. Law, S. M. Bandiera, T. K. H. Chang, and G. D. Bellward In Vivo Cimetidine Inhibits Hepatic CYP2C6 and CYP2C11 but Not CYP1A1 in Adult Male Rats, J. Pharmacol. Exp. Ther., February 1, 1998; 284(2): 493 - 499. [Abstract] [Full Text]

				M. G. Sturgill and G. H. Lambert Xenobiotic-induced hepatotoxicity: mechanisms of liver injury and methods of monitoring hepatic function Clin. Chem., August 1, 1997; 43(8): 1512 - 1526. [Abstract] [Full Text] [PDF]