CYTOTOXICITY OF MITOMYCIN-C AND ADRIAMYCIN IN FRESHLY ISOLATED RAT HEPATOCYTES - THE ROLE OF CYTOCHROME-P450

The role of cytochrome P450 (P450) in the cytotoxicity of mitomycin C (MMC) and Adriamycin (ADR) was investigated in freshly isolated hepato cytes from phenobarbital-induced rats. The Loss of cell viability mea sured as lactate dehydrogenase (LDH) leakage upon MMC exposure was ac companied by a rapid and extensive intracellular glutathione (GSH) dep letion and followed by minor lipid peroxidation (LPO). Coincubation of the hepatocytes with the P450 inhibitors, metyrapone and SK&F 525-A, strongly protected against MMC-induced LDH leakage, GSH depletion, and LPO. Inasmuch as the depletion of intracellular GSH by MMC, which is considered as a critical event in the development of MMC cytotoxicity, was not accompanied by a stoichiometric oxidation to oxidized GSH (GS SG), the formation of a MMC-GSH conjugate after one-electron reductive bioactivation of MMC by P450 was anticipated. In contrast to MMC, ADR was only cytotoxic to the hepatocytes upon prior depletion of intrace llular GSH with diethylmaleate. Addition of metyrapone and SK&F 525-A completely protected the hepatocytes against ADR-induced LDH leakage a nd LPO. Moreover, the ADR-induced LDH leakage and LPO were strongly in hibited by dimethyl sulfoxide and ethanol, indicating that hydroxyl ra dicals were involved in the cytotoxicity of ADR. In conclusion, the pr esent investigations indicate that P450 plays a major role in the cyto toxicity of both MMC and ADR in freshly isolated hepatocytes from phen obarbital-induced rats. The present findings lead to a better understa nding of the mechanism of the cytotoxic actions of both MMC and ADR.