Bioactivation to free radicals and cytotoxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b)

1. The in vitro bioactivation by rat liver microsomes and the cytotoxicity in rat hepatocytes of 1,1-dichloro-1-fluoroethane (HCFC-141b), a replacemen t for some ozone depleting chlorofluorocarbons (CFC), have been investigate d. 2. Anaerobic incubations of liver microsomes from pyridine-induced rats wit h HCFC-141b in the presence of the spin-trapping agent N-t-butyl-alpha -phe nylnitrone (PBN) resulted in the formation of a typical ESR radical signal. 3. In the presence of HCFC-141b, a dose-dependent formation of conjugated d ienes was observed that was partially inhibited by PBN, glutathione (GSH) a nd vitamin C. Moreover, HCFC-141b increased the release of lactate dehydrog enase (LDH) and the depletion of cellular glutathione in isolated rat hepat ocytes under both normoxic and hypoxic conditions. 4. HCFC-141b-dependent cytotoxicity was completely prevented by PBN under b oth conditions and it was partially prevented under normoxic conditions by the broad-spectrum P450 inhibitor metyrapone, the P4502E1 specific inhibito r 4-methylpyrazole and the P4503A-specific inhibitor troleandomycin. Intere stingly, HCFC-141b-dependent glutathione depletion was not prevented by PBN , metyrapone, 4-methylpyrazole or troleandomycin, whereas two glutathione d epletors, 2,6-dimethyl-2,5-heptadien-4-one (phorone) and diethylmaleate, pa rtially prevented LDH release. 5. The present results indicate that HCFC-141b is reductively metabolized i n vitro to free radical intermediates by P450, in particular by the CYP2E1 and, to a lower extent, CYP3A isoforms, leading to peroxidative membrane da mage and glutathione-independent cytotoxicity.