Spontaneous hydrolysis of 4-trifluoromethylphenol to a quinone methide and subsequent protein alkylation

4-Trifluoromethylphenol (4-TFMP) was cytotoxic to precision-cut rat liver slices as indicated by loss of intracellular potassium. Intracellular glutathione levels decreased and fluoride ion levels increased in a time and concentration-dependent manner. The cytotoxicity of 4-TFMP did not appear to be due to the release of fluoride, however, since equimolar concentrations of sodium fluoride or potassium fluoride were not toxic. The ortho isomer (2-TFMP), which had a threefold slower rate of fluoride release, was much less toxic to liver slices. Ln incubations without slices, 4-TFMP spontaneously hydrolyzed in aqueous buffer at physiological pH to form 4-hydroxybenzoic acid via a quinone methide intermediate. The quinone methide was trapped by the addition of glutathione. Analysis of the glutathione adduct indicated that all of the fluorine atoms were lost during the hydrolysis, yielding a cresol derivative with the glutathione moiety attached to a benzylic carbonyl group. The glutathione conjugate was the primary product formed at low alkylphenol/glutathione ratios; however, at higher 4-TFMP concentrations additional unidentified products were observed. 4-TFMP also inhibited the in vitro enzyme activity of purified glyceraldehyde-3-phosphate dehydrogenase, a sulfhydryl-dependent enzyme, in a time and concentration-dependent manner. Loss of thiol residues closely paralleled the loss in enzyme activity. The coaddition of glutathione prevented 4-TFMP-induced loss of enzyme activity. The cytotoxicity of 4-TFMP therefore appears to be due to spontaneous quinone methide formation and subsequent alkylation of cellular macromolecules. (C) 2000 Elsevier Science Ireland Ltd. All rights reserved.