Oxygen free radical production mediated by cocaine and its ethanol-derived metabolite, cocaethylene, in rat hepatocytes

Abstract

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.

Cocaine mutagenicity and hepatocarcinogenicity evaluations in rodents

“…route is one of the main routes used by human cocaine addicts. Having a high degree of solubility and a low ionization rate, cocaine is easily absorbed and, once in the circulation, is quickly metabolized by the liver, producing metabolites and reactive oxygen species that are responsible for its toxicity [7,21]. The present results indicate that cocaine does not induce increased frequencies of PCEMN in bone marrow cells of this mouse strain and therefore should not be assumed to have a mutagenic potential under these bioassay conditions.…”

“…In humans, the liver morphological and biochemical effects induced by cocaine are quite similar to mice [26,27]. The oxidative stress, which seems to be one of the mechanisms associated with cocaine toxicity [7], could play a role in the liver carcinogenesis process, similar to that exerted by peroxisome proliferators [32]. It is interesting that the peroxisome proliferator and non-genotoxic hepatocarcinogen di-(2-ethyllhexyl)phthalate shares a common structure biophore with cocaine [9].…”

“…However, among the possible mechanisms by which cocaine exerts its cytotoxic effects, direct oxidative damage by reactive oxygen species seems most important [7]. Thus, possible mutagenic and carcinogenic potentials could be hypothesized.…”

Cocaine Toxicity and Hepatic Oxidative Stress

“…First, it has been suggested that the nitrosonium ion, generated during the oxidation of norcocaine, or other as yet unidentified reactive metabolites, bind covalently to cellular macromolecules. However, the same authors, investigating mechanisms of cocaine toxicity in hepatocyte cultures, proved the key role of ROS but suggested that their generation occurred through nonperoxidative mechanisms [38,39]. The litera-ture studies investigating the role of ROS that lead to oxidative stress are contradictory.…”

“…Alcohol appeared to potentiate cocaine hepatotoxicity in both humans and mice [64]. [39] suggested that the increased amount of ROS, generated during the interaction of cocaine and cocaethylene with cytochrome P 450 is responsible for intensified cocaine liver injury. The hepatotoxic implications of cocaethylene in humans have not been fully described.…”