Ethanol-induced enhancement of cocaine bioactivation and irreversible protein binding: evidence against a role of cytochrome P-450IIE1.
Chronic ethanol consumption potentiates cocaine-induced liver injury in rodents. Since cocaine has to be bioactivated by a cytochrome P-450-dependent N-oxidative pathway to exert its hepatotoxic effects, we studied the role of the ethanol-inducible P-450IIE1 for cocaine metabolism. Male Sprague-Dawley rats were pretreated with either a liquid diet containing ethanol (30% of calories) for 4 weeks or injected with pyrazole (200 mg/kg/day, ip, for 3 days). Both agents induced microsomal p-nitrophenol hydroxylation which is a probe for the catalytic activity of P-450IIE1. However, only ethanol, but not pyrazole, increased both microsomal cocaine N-demethylase activity (by 47%) and the extent of irreversible binding of [3H]-cocaine to microsomal proteins (by 100%), which was taken as a quantitative endpoint for the formation of a reactive metabolite. Cocaine N-demethylation and irreversible protein binding of cocaine were not inhibited by P-450IIE1 isozyme-selective substrates, nor was the rate of cocaine metabolism and binding decreased by functionally active polyclonal anti-rat P-450IIE1 antibodies. Furthermore, pyrazole pretreatment sensitized cultured hepatocytes to the glutathione-dependent cytotoxic effects of nontoxic concentrations of cocaine. These results indicate that (a) cocaine is not a major substrate for the ethanol-inducible P-450IIE1, (b) the enhancing effects of ethanol on cocaine bioactivation may be due to induction of other P-450 isoforms, and (c) induction of P-450IIE1 may potentiate cocaine-induced hepatocellular toxicity in vitro independently of cocaine metabolism, e.g., by P-450IIE1-dependent oxidative stress.
Boelsterli
U A
UA
Institute of Toxicology, Swiss Federal Institute of Technology, Schwerzenbach.
Atanasoski
S
S
Göldlin
C
C
D000818:Animals; D001711:Biotransformation / Q000502:physiology; D002478:Cells, Cultured; D003042:Cocaine / Q000493:pharmacokinetics* / Q000633:toxicity; D003577:Cytochrome P-450 Enzyme System / Q000502:physiology*; D000431:Ethanol / Q000494:pharmacology*; D008099:Liver / Q000187:drug effects / Q000201:enzymology; D008297:Male; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D010089:Oxidoreductases, N-Demethylating / Q000502:physiology; D051381:Rats; D011919:Rats, Inbred Strains
D000431:Ethanol; D003577:Cytochrome P-450 Enzyme System; D010089:Oxidoreductases, N-Demethylating; C054553:cocaine N-demethylase; D003042:Cocaine