Modulation of Cocaine Metabolism in Primary Rat Hepatocyte Cultures: Effects on Irreversible Binding and Protein Biosynthesis

To study mechanisms of cocaine-induced hepatotoxicity, short-term-cultured rat hepatocytes were exposed to cocaine or norcocaine at 10(-6) to 10(-4) M. Induction in vivo (with Aroclor 1254) or inhibition in vitro (with SKF-525A) of cytochrome P450 modulated the rate of oxidative biotransformation of cocaine to norcocaine and to other metabolites in vitro. The quantitative changes in the metabolic conversion of cocaine were paralleled by the amount of radiolabeled cocaine equivalents irreversibly bound to hepatocellular protein. Furthermore, induction of cytochrome P450-mediated cocaine or norcocaine metabolism was associated with inhibition of protein biosynthesis in cultured hepatocytes, whereas this effect was restored to normal when the oxidative metabolism was blocked by SKF-525A. Glutathione depletion with buthionine sulfoximine both increased the covalent binding of cocaine to hepatic macromolecules and augmented the inhibitory effect on protein biosynthesis. The integrity of the hepatocellular plasma membrane was not affected (no effect on lactate dehydrogenase leakage). The results indicate that in rat hepatocytes (a) a high proportion of intracellular cocaine is converted to a reactive metabolite which irreversibly binds to protein, and (b) irreversible binding of cocaine to hepatic protein is associated with impairment of hepatocellular function and could play a role in cocaine-mediated hepatotoxicity.