Commandeur J N, De Kanter F J, Vermeulen N P
Department of Pharmacochemistry, Free University, Amsterdam, The Netherlands.
Mol Pharmacol. 1989 Oct;36(4):654-63.
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.
研究了大鼠肝脏和大鼠肾脏亚细胞组分对四氟乙烯S-共轭物的β-裂解酶依赖性生物活化作用。用S-(1,2,2,2-四氟乙基)-L-半胱氨酸（TFE-Cys）孵育肝和肾的胞质溶胶，导致形成了以前未鉴定的二氟硫代酰胺，表明二氟硫代酰氟是TFE-Cys的β-裂解酶依赖性生物活化产生的主要反应性中间体。用N-乙酰-S-(1,1,2,2-四氟乙基)-L-半胱氨酸（TFE-NAC）处理的大鼠尿液中存在N-二氟硫代乙酰基-S-(1,1,2,2-四氟乙基)-L-半胱氨酸（TFE-PMS）和二氟乙酸，这表明体内存在类似的生物活化机制。当TFE-NAC在没有外源性乙酰辅酶A（乙酰-CoA）的情况下与大鼠肾脏和肝脏的11,000×g上清液孵育时，可以观察到N-脱乙酰化以及随后β-裂解酶依赖性激活生成二氟硫代酰氟。TFE-NAC的N-脱乙酰化和TFE-Cys的β-裂解酶依赖性激活在大鼠肾脏中比在大鼠肝脏中快得多。当TFE-Cys与大鼠肾脏和肝脏的11,000×g上清液孵育时，只有在存在2 mM外源性乙酰-CoA的情况下才能观察到TFE-NAC的形成；肾脏组分中N-乙酰化的初始速率比肝脏组分高5倍。在这些条件下，TFE-PMS的形成非常低。给予TFE-NAC后，未改变的TFE-NAC在尿液中的排泄量很低（剂量的3-5%），这表明体内N-脱乙酰化/N-乙酰化比率很高。由于TFE-NAC/TFE-Cys的周转率非常高，肾脏中N-乙酰化的辅因子乙酰-CoA的可用性可能是限速的，导致TFE-Cys积累，随后TFE-Cys的β-裂解酶依赖性生物活化增加，生成反应性中间体。
