title: Bioactivation to free radicals and cytotoxicity of 1,1-dichloro-1-fluoroethane (HCFC-141b).
abstract: 1. The in vitro bioactivation by rat liver microsomes and the cytotoxicity in rat hepatocytes of 1,1-dichloro-1-fluoroethane (HCFC-141b), a replacement for some ozone depleting chlorofluorocarbons (CFC), have been investigated. 2. Anaerobic incubations of liver microsomes from pyridine-induced rats with HCFC-141b in the presence of the spin-trapping agent N-t-butyl-alpha-phenylnitrone (PBN) resulted in the formation of a typical ESR radical signal. 3. In the presence of HCFC-141b, a dose-dependent formation of conjugated dienes was observed that was partially inhibited by PBN, glutathione (GSH) and vitamin C. Moreover, HCFC-141b increased the release of lactate dehydrogenase (LDH) and the depletion of cellular glutathione in isolated rat hepatocytes under both normoxic and hypoxic conditions. 4. HCFC-141b-dependent cytotoxicity was completely prevented by PBN under both conditions and it was partially prevented under normoxic conditions by the broad-spectrum P450 inhibitor metyrapone, the P4502E1 specific inhibitor 4-methylpyrazole and the P4503A-specific inhibitor troleandomycin. Interestingly, HCFC-141b-dependent glutathione depletion was not prevented by PBN, metyrapone, 4-methylpyrazole or troleandomycin, whereas two glutathione depletors, 2,6-dimethyl-2,5-heptadien-4-one (phorone) and diethylmaleate, partially prevented LDH release. 5. The present results indicate that HCFC-141b is reductively metabolized in vitro to free radical intermediates by P450, in particular by the CYP2E1 and, to a lower extent, CYP3A isoforms, leading to peroxidative membrane damage and glutathione-independent cytotoxicity.
authors.affiliation: Department of Environmental Medicine & Public Health, University of Padua Medical School, Italy.
authors.forename: A
authors.initials: A
authors.lastname: Zanovello
authors.forename: R
authors.initials: R
authors.lastname: Tolando
authors.forename: R
authors.initials: R
authors.lastname: Ferrara
authors.forename: S
authors.initials: S
authors.lastname: Bortolato
authors.forename: M
authors.initials: M
authors.lastname: Manno
mesh_terms: D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D017402:Chlorofluorocarbons / Q000633:toxicity*; D064227:Chlorofluorocarbons, Ethane; D019392:Cytochrome P-450 CYP2E1 / Q000378:metabolism; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D051544:Cytochrome P-450 CYP3A; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000187:drug effects / Q000378:metabolism; D004578:Electron Spin Resonance Spectroscopy; D004791:Enzyme Inhibitors / Q000494:pharmacology; D000077604:Fomepizole; D005609:Free Radicals / Q000378:metabolism*; D005978:Glutathione / Q000378:metabolism; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D007527:Isoenzymes / Q000378:metabolism; D007770:L-Lactate Dehydrogenase / Q000187:drug effects / Q000378:metabolism; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D008797:Metyrapone / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000378:metabolism*; D010089:Oxidoreductases, N-Demethylating; D011720:Pyrazoles / Q000494:pharmacology; D011725:Pyridines / Q000494:pharmacology; D051381:Rats; D017208:Rats, Wistar; D014217:Troleandomycin / Q000494:pharmacology
chemical_list: D017402:Chlorofluorocarbons; D064227:Chlorofluorocarbons, Ethane; D065691:Cytochrome P-450 CYP2E1 Inhibitors; D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D005609:Free Radicals; D007527:Isoenzymes; D011720:Pyrazoles; D011725:Pyridines; D000077604:Fomepizole; D003577:Cytochrome P-450 Enzyme System; D014217:Troleandomycin; D007770:L-Lactate Dehydrogenase; D019392:Cytochrome P-450 CYP2E1; D001189:Aryl Hydrocarbon Hydroxylases; D051544:Cytochrome P-450 CYP3A; D010089:Oxidoreductases, N-Demethylating; D005978:Glutathione; C023666:pyridine; C068320:1,1-dichloro-1-fluoroethane; D008797:Metyrapone