vitamin-k-semiquinone-radical and 4-acetylaminostilbene

Isolated perfused livers from male Wistar rats were used to study acute and chronic toxic effects of carcinogenic aromatic amines. We investigated the hypothesis that aromatic amines can generate reactive oxygen species as part of their metabolism. Concentrations of 200-400 microM of 2-acetylaminofluorene (AAF), N-hydroxy-AAF, trans-4-acetylaminostilbene (AAS), N-hydroxy-AAS, and N-hydroxy-2-acetylaminophenanthrene in the recirculating perfusate were not toxic in a 2-hr exposure time as assessed by LDH efflux into the perfusate, glutathione excretion into bile, and changes of the beta-hydroxybutyrate/acetoacetate ratio in the perfusate. N-Acetoxy-AAF, however, was severely toxic. Menadione served as a positive control. It is concluded that exposures likely to occur in carcinogenicity studies with these aromatic amines will not be acutely toxic. In additional experiments the isolated perfused liver system was used to demonstrate chronic effects generated by feeding the carcinogenic dose of 0.02% AAF for up to 12 weeks. The following alterations were observed in livers from AAF-fed animals. excretion of glutathione into bile is drastically reduced after 5 or more weeks, increasingly less glucose is released into the perfusate, and oxygen consumption is constantly increased by 20% after 3 and more weeks of AAF feeding. Whereas the total glutathione level increased with time in homogenates of such livers, it decreased in the mitochondrial fraction. The results are interpreted as adaptive responses to chronic toxic effects of AAF which may be related to the promoting properties of this carcinogen.

Topics: 2-Acetylaminofluorene; Amines; Animals; Carcinogens; Glutathione; Hemostatics; Hydroxyacetylaminofluorene; Isotope Labeling; Liver; Male; Mitochondria, Liver; Oxygen Consumption; Perfusion; Phenanthrenes; Rats; Rats, Wistar; Reactive Oxygen Species; Stilbenes; Vitamin K

A possible role of oxidative stress in producing acute toxicity in rat liver by aromatic amines and nitroarenes was tested. Oxidative stress was assessed by measuring the excretion of oxidized glutathione (GSSG) into the bile in isolated perfused livers and in female Wistar rats with cannulated bile ducts. The liver perfusion system was calibrated with t-butylhydroperoxide (t-BH) and menadione. The minimal concentration in the perfusate of t-BH necessary to observe a significant effect was 18 microM for 5 min. It was calculated that rat liver is able to cope with an extra production of about 70 nmol GSSG per min and g liver before GSSG is excreted into bile. No effect was observed when 2-aminofluorene, 2-acetylaminofluorene (AAF), trans-4-aminostilbene, and trans-4-acetylaminostilbene were added to the perfusate at 50 microM for 20 min. Moreover, 2-aminofluorene, trans-4-aminostilbene, 2-nitrofluorene and trans-4-nitrostilbene did not increase GSSG excretion when administered simultaneously with effective concentrations of t-BH. AAF was not acutely toxic, blood transaminases and lipid peroxidation were not increased with AAF doses as high as 1 mmol/kg. Since the dose rate of aromatic amines, like AAF, in feeding studies for tumor formation is about 100 times below that examined in the isolated perfused livers, it is highly unlikely that oxidative stress is generated by metabolites able to undergo redox cycling and that reactive oxygen contributes to acute toxic effects.

Topics: 2-Acetylaminofluorene; Amines; Animals; Bile; Cell Death; Female; Fluorenes; Glutathione; Liver; Oxidative Stress; Perfusion; Peroxides; Rats; Rats, Wistar; Stilbenes; tert-Butylhydroperoxide; Vitamin K