Cocaine is an intrinsic hepatotoxin in laboratory animals, and there is growing evidence that high doses of cocaine can precipitate hepatic necrosis in humans. The rodent model of cocaine hepatotoxicity is commensurate with the concept that a multistep mainly cytochrome P-450 dependent N-oxidative pathway is responsible for the expression of hepatocellular injury. Among the possible biomechanisms by which cocaine exerts its cytotoxic effects, direct oxidative damage by reactive oxygen species generated by redox cycling during the metabolic cascade seems most important. The role of the ensuing lipid peroxidation and protein thiol oxidation is less clear. Similarly, the functional role of irreversible (covalent) binding of a not yet defined electrophilic cocaine intermediate to hepatocellular proteins remains enigmatic so long as the critical molecular targets have not been identified. Finally, glutathione plays a pivotal protective role against cocaine-induced hepatic injury. Interactions with ethanol or inducers of the expression of the cytochrome P-450IIB subfamily can potentiate cocaine hepatotoxicity. Thus, the net amount of the ultimate reactive species seems to determine the severity of the hepatic lesions and to be responsible for the marked interspecies, interstrain, and sex differences. Recent advances in culture techniques of hepatocytes and precision-cut liver slices from various species including man have made it possible to correlate cocaine biotransformation with cytotoxicity and to selectively study the putative cellular mechanisms. Clearly, more studies are necessary to further illuminate our understanding of the role of the biochemical and molecular events precipitating hepatic necrosis during cocaine-mediated hepatotoxicity.

Cocaine ethyl ester ("cocaethylene") is a cocaine metabolite formed by hepatic carboxylesterases in the presence of ethanol. In the human liver, this pharmacologically active cocaine analog may reach concentrations similar to those of cocaine. To further investigate the intrinsic hepatotoxic potential of cocaethylene and to compare its effects with the known hepatocyte-damaging effects of cocaine, primary short-term cultures of hepatocytes derived from phenobarbital-pretreated rats were exposed to cocaine or cocaethylene (10 to 1000 mumol/L). Both drugs caused time- and concentration-dependent release of lactate dehydrogenase into the extracellular medium in a congruent pattern. Spontaneous hydrolysis of cocaethylene was negligible at pH 7.4, and the rate of 2-diethylaminoethyl-2,2-diphenylvalerate (SKF-525A) and phenylmethylsulfonylfluoride-sensitive enzymatic degradation in hepatocyte cultures was similar to that of cocaine (half-time, approximately 3 hr). Furthermore, both cocaine and cocaethylene induced massive NADPH-dependent reactive oxygen species production in hepatic microsomal suspensions and in homogenates of cultured hepatocytes, as directly demonstrated by superoxide dismutase- and catalase-sensitive luminol chemiluminescence. The integrated photon emission and the maximal slopes of the luminol chemiluminescence displayed similar concentration-response curves for cocaine and cocaethylene. These data suggest that reactive oxygen species, generated during the interaction of cocaine and cocaethylene with cytochrome P-450, may be the common mediators of hepatotoxicity induced by these compounds. Moreover, they indicate that the potential for cocaethylene to induce acute lethal cell injury in hepatocytes through oxidative mechanisms is similar to that of its parent compound, cocaine.

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