COCAINE N-DEMETHYLATION AND THE METABOLISM-RELATED HEPATOTOXICITY CANBE PREVENTED BY CYTOCHROME-P450 3A INHIBITORS

Cocaine is eliminated and detoxified principally through the metabolis m of nonspecific plasma and tissue esterases. Microsomal oxidative met abolism is of importance in cocaine N-demethylation, this being a prin cipal pathway of cocaine bioactivation and hepatotoxicity. The contrib ution of different cytochrome P450 (CYP) enzymes to cocaine N-demethyl ase activity was studied in vitro with DBA/2 mouse and human liver mic rosomes, and cocaine hepatotoxicity was examined in vivo in DBA/2 male mice. Species dependent enzyme kinetics was observed. Cocaine N-demet hylase displayed two K-m values in murine liver (40-60 mu M and 2-3 mM ), whereas only one K-m value was observed in human liver microsomes ( 2.3-2.7 mM). We suggest that CYP3A plays a prominent role in the N-dem ethylation of cocaine for the following reasons: (i) pregnenolone-16 a lpha-carbonitrile, an inducer of CYP3As increases cocaine N-demethylas e in parallel with testosterone 6 beta-hydroxylase activity and immuno reactive 3A protein in mouse liver; (ii) human and mouse cocaine N-dem ethylase and testosterone 6 beta-hydroxylase activities can be inhibit ed by triacetyloleandomycin, cannabidiol, or gestodene, all selective inhibitors of CYP3A P450s; (iii) antibodies directed against P450s wit hin subfamilies 1A, 2A, 2B, 2C, or 2E inhibited cocaine N-demethylase activity only marginally, and finally, (iv) treatment of mice with tri acetyloleandomycin or cannabidiol in vivo significantly attenuated the cocaine-elicited hepatotoxicity as assessed by the serum alanine amin otransferase activity and liver histology in parallel with decreased c ocaine N-demethylase activity. The present results demonstrate that th e first step of cocaine bioactivation is catalyzed by the CYP3A enzyme (s) in both murine and human liver microsomes and cocaine-induced live r injury in mice may be prevented by the administration of the CYP3A i nhibitors.