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.

Effect of Oxygen on the Dehalogenation of 1,2-Dibromo-3-chloropropane by Cytochrome P450cam (CYP101)

“…Biodehalogenation reactions catalyzed by the cytochrome P450 family of enzymes are important conversions in the clearance of inhalation anesthetics and xenobiotics in human tissues (2, 3) and in environmental detoxification of halocarbons by microorganisms (4, 5). Products of these reactions are poorly characterized but have profound effects as to whether the conversions are beneficial or detrimental to the organ or environment in which they occur (3, 6, 7). For example, in the conversion of the soil fumigant 1,2‐dibromo‐3‐chloropropane, either tissue‐damaging free radicals are formed under reducing conditions, or nucleic acid‐alkylating intermediates are formed under oxidation conditions (8, 9).…”

Dual negative precursor ion scan approach for rapid detection of glutathione conjugates using liquid chromatography/tandem mass spectrometry

“…Electrophilic species are capable of forming adducts with various endogenous nucleophiles in the body including DNA, proteins and cellular glutathione (GSH), where toxicity results through covalent adduct formation which can alter essential cellular machinery 3–5. Similarly, toxicological events mediated by free‐radical formation have also been reported for various xenobiotics 6, 7. While a body of circumstantial evidence correlating idiosyncratic adverse drug reactions and reactive metabolites exists, a direct link has yet to be established 8–10.…”