Cocaine Toxicity in Cultured Chicken Hepatocytes: Role of Cytochrome P450

Abstract

Cocaine (COC) causes liver damage in several species, including man. Chicken embryo hepatocyte cultures were evaluated as a model system to investigate the mechanism of cocaine-mediated hepatotoxicity. Parameters used to assess toxicity were: (1) release of lactate dehydrogenase (LDH); (2) decreased induction of 5-aminolevulinic acid synthase (ALAS), measured as porphyrin accumulation; and (3) decreased protein synthesis. Exposure of untreated cultures to COC or norcocaine (NOR) caused dose-dependent increases in LDH release, decreased protein synthesis, and eventual cell death. Pretreatment with 2-propyl-2-isopropylacetamide (PIA), a phenobarbital-like inducer of cytochrome P450, accelerated toxicity and lowered the threshold dose at which toxicity occurred. PIA pretreatment also increased rates of elimination of both COC and NOR and increased rates of formation of NOR from COC. The toxicity of COC and NOR could also be detected as decreased porphyrin accumulation. Addition of the P450 inhibitor SKF-525A concurrently with COC or NOR decreased their rates of elimination. SKF-525A also prevented the increase in LDH release as well as the decrease in protein synthesis caused by treatment with COC or N-hydroxynorcocaine (N-OH). Addition of SKF-525A up to 3 hr after COC resulted in partial prevention of the LDH increase. Exposure of the cultures to COC induced cytochrome P450 2H protein. We conclude that this hepatocyte culture system is highly sensitive to COC toxicity and that constitutive as well as induced cytochrome P450 isoforms are involved in the production of liver damage from COC.