Formation, characterization, and immunoreactivity of lysine thioamide adducts from fluorinated nephrotoxic cysteine conjugates in vitro and in vivo.

Fluorinated nephrotoxic cysteine conjugates undergo bioactivation via the beta-lyase pathway to thionoacetyl fluorides (TAF), the putative reactive intermediates. The TAF derived from S-(1,1,2,2,-tetrafluoroethyl)-L-cysteine (TFEC) difluorothionoacetylates amine nucleophiles found in proteins and lipids. A specific antisera, raised against (trifluoroacetamido)lysine adducts formed in vivo after halothane treatment, has previously been used to localize TFEC-derived protein adducts immunohistochemically, and a good correlation between adduction and toxicity was demonstrated. Interestingly, thioamide formation is facilitated by acyl-transfer catalysts such as imidazoles and phenols. However, although putative lysine adducts have been reported to be formed from the related TAF derived from S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFC), protein adducts derived from CTFC metabolism have not been completely characterized. In the present investigation we characterize (chlorofluorothionacetamido)lysine (CFTAL) adduct formation during S-(2-chloro-1,1,2-trifluoroethyl)-L-cysteine (CTFC) metabolism, both in vitro and in vivo. Our data indicate that formation of CTFC-derived lysine thioamides was not as dependent on nucleophilic catalysis as observed for TFEC, and this appears to be due to an apparent greater reactivity of the TAF resulting in a higher trapping efficiency in the absence of catalyst. Also, qualitative and quantitative differences in the structures and time course of CTFC versus TFEC adduct breakdown were observed. Antibodies raised against the halothane metabolite protein adduct (trifluoroacetamido)lysine cross-react with specific mitochondrial proteins from the kidneys of TFEC-treated rats. Using this antibody, we have found that the pattern of adducted proteins from TFEC- and CTFC-treated Fischer rats was similar, but the intensity was considerably lower after treatment with equimolar concentrations of CTFC in vivo.