Cytotoxicity of chloroquine in isolated rat hepatocytes.

Chloroquine is a synthetic quinoline being used as an antimalaria and antirheumatoid agent. Several cases of hepatotoxicity have been reported with the use of chloroquine. However, the mechanism(s) of its hepatotoxic effect is unknown. The purpose of this study was to investigate the cytotoxic mechanism of chloroquine. Cytotoxicity was studied using freshly isolated rat hepatocytes incubated in Krebs-Henseleit buffer under a flow of 95% O(2) and 5% CO(2). Chloroquine was toxic towards hepatocytes and caused cell death with an ED(50) of about 100 mm in 2 h. The events before cell death were rapid GSH depletion and lipid peroxidation. Cytochrome P-450 inhibitors, troleandromycine, cimetidine and quinidine increased the cytotoxicity of chloroquine. Antioxidants significantly prevented the cytotoxicity of chloroquine. Depleting the hepatocyte GSH beforehand increased the chloroquine cytotoxicity. Preventing chloroquine metabolism by specific P-450 inhibitors increased its toxicity, suggesting that a major part of its toxicity is mediated by chloroquine and not by its metabolites. A depletion of the antioxidant defense system is involved in the mechanism of cytotoxicity.