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.
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.
Commandeur
J N
JN
Department of Pharmacochemistry, Free University, Amsterdam, The Netherlands.
De Kanter
F J
FJ
Vermeulen
N P
NP
D000105:Acetyl Coenzyme A / Q000378:metabolism*; D000111:Acetylcysteine / Q000378:metabolism*; D000215:Acylation; D000818:Animals; D001711:Biotransformation; D013437:Carbon-Sulfur Lyases; D003545:Cysteine / Q000378:metabolism*; D005466:Fluorocarbons / Q000378:metabolism*; D008401:Gas Chromatography-Mass Spectrometry; D007668:Kidney / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008190:Lyases / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D013347:Subcellular Fractions / Q000378:metabolism; D013997:Time Factors
D005466:Fluorocarbons; D000105:Acetyl Coenzyme A; D008190:Lyases; D013437:Carbon-Sulfur Lyases; C019969:S-alkylcysteine lyase; D003545:Cysteine; C015531:tetrafluoroethylene; D000111:Acetylcysteine