Selective inactivation of mouse liver cytochrome P-450IIIA by cannabidiol.
Cannabidiol (CBD) inhibits hepatic drug metabolism in mice, particularly those activities known to be catalyzed by the cytochrome P-450IIIA (P-450IIIA) subfamily. CBD treatment (120 mg/kg) inhibited more than 75% of hepatic 6 beta-testosterone hydroxylase and erythromycin N-demethylase activities (functional markers of P-450IIIA) after 2 hr. An isozyme of the P-450IIIA subfamily (Mr 49,960) was purified to apparent homogeneity from hepatic microsomes of untreated mice and was found to catalyze testosterone hydroxylation at the 2 beta-, 6 beta-, and 15 beta-positions exclusively. Incubation of this isozyme with CBD in a reconstituted system resulted in a time- and concentration-dependent inactivation, with almost complete loss of P-450 chromophore and corresponding increase in P-420 content. NH2-terminal sequence analysis of the isozyme revealed an 86% similarity to the corresponding sequence of rat P-450IIIA2, a constitutive P-450 isozyme in the male rat liver. Pretreatment of mice with dexamethasone markedly (6-fold) increased the steroid-inducible P-450IIIA-dependent activities 6 beta-testosterone hydroxylation and erythromycin N-demethylation. CBD treatment of dexamethasone-pretreated animals failed to inhibit these activities, indicating that the steroid-inducible P-450IIIA was refractory to CBD-mediated inactivation. 3-Methylcholanthrene-inducible P-450IA and phenobarbital-inducible P-450IIB also appear to be refractory to CBD-mediated inactivation. On the other hand, erythromycin N-demethylase activity increased 4-fold after phenobarbital pretreatment and, as in untreated animals, was comparably inhibited by CBD, demonstrating its susceptibility to this drug. Thus, CBD appears to inactivate the P-450IIIA isozymes that are constitutively present in hepatic microsomes of untreated mice and/or inducible by phenobarbital pretreatment but not those that are steroid inducible.
Department of Pharmacology, University of California, San Francisco 94143.
L M
LM
Bornheim
M A
MA
Correia
D000595:Amino Acid Sequence; D000818:Animals; D002185:Cannabidiol / Q000378:metabolism / Q000494:pharmacology*; D002186:Cannabinoids / Q000494:pharmacology*; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000032:analysis / Q000302:isolation & purification; D004790:Enzyme Induction; D007527:Isoenzymes / Q000037:antagonists & inhibitors*; D008099:Liver / Q000201:enzymology*; D008297:Male; D008565:Membrane Proteins; D051379:Mice; D008969:Molecular Sequence Data; D012737:Sex Factors
D002186:Cannabinoids; D065607:Cytochrome P-450 Enzyme Inhibitors; D007527:Isoenzymes; D008565:Membrane Proteins; D002185:Cannabidiol; D003577:Cytochrome P-450 Enzyme System; C496508:Cyp3a11 protein, mouse; D051544:Cytochrome P-450 CYP3A