Biomechanisms of cocaine-induced hepatocyte injury mediated by the formation of reactive metabolites

Abstract

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.

In Vitro Models to Study Hepatotoxicity

“…Liver-slice models have been used in investigational pathology to assess a number of hepatotoxic effects and a variety of substances have been studied such as halogenated hydrocarbons (41), paracetamol (70), a atoxin B1 (102), endotoxin (80), paraquat (97), cocaine (15), or metals such as zinc (107). Although the main advantages are represented by the preservation of lobular structures in contrast to cell cultures and the possible application of biochemical and molecular biological methods in contrast to organ perfusions, the main disadvantages are based on the short viability and the missing bile collection.…”

Covalent Protein Adduction by Drugs of Abuse

“…However, data collected from the current study are not consistent with any proposed mechanism of covalent cocaine adduction that exists in the literature. In contrast, Investigation of adduction products arising from nitrogen oxidation as well as methyl ester activation as reported in the literature 23,[95][96][97][98][99] were performed in the current study; however, the in vitro systems utilized were unable to confirm these previously proposed mechanisms. Other research has employed immunogenic detection using antibodies raised against tropane nitrogen haptenized cocaine as evidentiary support for adduct formation via tropane nitrogen oxidation.…”

“…The hydrolysis of the methyl ester to yield benzoylecgonine is the predominant pathway for ex vivo degradation of cocaine (however, human liver carboxylesterase 1 (hCE-1) promotes the hydrolytic cleavage in vivo). 23,24 In the body, enzymatic cleavage of the benzoyl ester to form ecgonine methyl ester is catalyzed by plasma pseudocholinesterase and human liver carboxylesterase 2 (hCE-2). 20,23,24 Coadministration of cocaine with ethanol results in the production of cocaethylene via transesterification by hCE-1 and fatty acid ethyl synthase (FAES).…”

“…23,24 In the body, enzymatic cleavage of the benzoyl ester to form ecgonine methyl ester is catalyzed by plasma pseudocholinesterase and human liver carboxylesterase 2 (hCE-2). 20,23,24 Coadministration of cocaine with ethanol results in the production of cocaethylene via transesterification by hCE-1 and fatty acid ethyl synthase (FAES). 20,24 If cocaine is smoked, the pyrolysis products of cocaine, anhydroecgonine methyl ester and associated metabolites (e.g., anhydroecgonine), can be detected in the blood.…”

“…20 In addition to Phase I metabolism, research has suggested that products of cocaine biotransformation are amenable to Phase II modification (e.g., methylation, sulfation, glucuronidation) at the sites of Phase I hydroxylation (i.e., aromatic hydroxyl(s), N-hydroxyl), although identification of such conjugation products has yet to be reported in the literature. 23,25 While the majority of these metabolites are pharmacologically deactivated by Phase I and II biotransformation, the transesterification product cocaethylene has been shown to maintain similar physiochemical properties to cocaine. 20 Methamphetamine (Figure 7, 2) is a sympathomimetic amine with CNS stimulant properties whose pharmacological action is a result of dopamine release from storage vesicles.…”