Bioactivation of the cysteine-S-conjugate and mercapturic acid of tetrafluoroethylene to acylating reactive intermediates in the rat: dependence of activation and deactivation activities on acetyl coenzyme A availability

JN Commandeur, FJ De Kanter and NP Vermeulen

Department of Pharmacochemistry, Free University, Amsterdam, The Netherlands.

The beta-lyase-dependent bioactivation of S-conjugates of tetrafluoroethylene by subcellular fractions from rat liver and rat kidney was studied. Incubation of both hepatic and renal cytosol with S- (1,2,2,2-tetrafluoroethyl)-l-cysteine (TFE-Cys) resulted in the formation of previously unidentified difluorothionamides, indicating difluorothionoacyl fluoride as the main reactive intermediate derived from the beta-lyase-dependent bioactivation of TFE-Cys. The presence of N-difluorothionoacetyl-S-(1,1,2,2-tetrafluoroethyl)-l-cystei ne (TFE- PMS) and difluoroacetic acid in urine of rats treated with N-acetyl-S- (1,1,2,2-tetrafluoroethyl)-l-cysteine (TFE-NAC) points to a similar mechanism of bioactivation in vivo. When TFE-NAC was incubated with 11,000 X g supernatants of rat kidney and liver in the absence of exogenous acetyl coenzyme A (acetyl-CoA), N-deacetylation and subsequent beta-lyase-dependent activation to difluorothionoacyl fluoride could be observed. Both the N-deacetylation of TFE-NAC and the beta-lyase-dependent activation of TFE-Cys were much faster in rat kidney then in rat liver. When TFE-Cys was incubated with 11,000 X g supernatants of rat kidney and rat liver, formation of TFE-NAC could only be observed in the presence of 2 mM exogenous acetyl-CoA; the initial rate of N-acetylation was 5-fold higher in renal then in hepatic fractions. Under these conditions, formation of TFE-PMS was very low. The low urinary excretion of unchanged TFE-NAC (3-5% of dose) upon administration of TFE-NAC points to a high N-deacetylation/N- acetylation ratio in vivo. Due to a very high turn-over of TFE-NAC/TFE- Cys, the availability of the cofactor for N-acetylation, acetyl-CoA, might be rate limiting in the kidney, resulting in accumulation of TFE- Cys followed by increasing beta-lyase-dependent bioactivation of TFE- Cys to reactive intermediates.

Volume 36, Issue 4, pp. 654-663, 10/01/1989
Copyright © 1989 by American Society for Pharmacology and Experimental Therapeutics

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