Immunohistochemical and microfluorometric determination of hepatic DNA adduct removal in rats fed 2-acetylaminofluorene

Induction of O6-alkylguanine-DNA-alkyltransferase in the hepatocytes of rats following treatment with 2-acetylaminofluorene

Molecular and immunohistological techniques have been used to study the induction in rat liver of the DNA repair protein O6-alkylguanine-DNA-alkyltransferase (ATase), following an acute dose (60 mg/kg) of the hepatocarcinogen, 2-acetylaminofluorene (2-AAF). An increase in ATase activity was specific to the liver, with a five- to six-fold induction being observed 72 hr after administration of 2-AAF. A similar temporal increase of both activity and ATase protein (detected by immunoblotting) was observed up to 1 week following treatment, but after 2 weeks the activity had returned to control levels. Although maximal induction of hepatic ATase mRNA was observed as early as 24 hr, the levels remained elevated at least 1 week after 2-AAF treatment. Using a rabbit antiserum raised against purified recombinant rat ATase, ATase-specific staining was observed in the nuclei of both nonhepatocytes and hepatocytes in control liver sections. There was, however, a significant differential staining of hepatocytes across the liver lobule, with ATase staining being most intense in the periportal region. In the livers of 2-AAF-treated rats, an increased intensity of staining was observed in hepatocytes throughout the liver lobule, whereas the nonparenchymal cells showed much less, or no, increase in staining. The increased expression of ATase in hepatocytes and its differential distribution across the lobule were confirmed by image analysis. Thus, ATase induction in response to 2-AAF treatment was an hepatocyte-specific response and not confined to any particular region of the liver lobule.

Genetic toxicity of 2-acetylaminofluorene, 2-aminofluorene and some of their metabolites and model metabolites

2-Acetylaminofluorene and 2-aminofluorene are among the most intensively studied of all chemical mutagens and carcinogens. Fundamental research findings concerning the metabolism of 2-acetylaminofluorene to electrophilic derivatives, the interaction of these derivatives with DNA, and the carcinogenic and mutagenic responses that are associated with the resulting DNA damage have formed the foundation upon which much of genetic toxicity testing is based. The parent compounds and their proximate and ultimate mutagenic and carcinogenic derivatives have been evaluated in a variety of prokaryotic and eukaryotic assays for mutagenesis and DNA damage. The reactive derivatives are active in virtually all systems, while 2-acetylaminofluorene and 2-aminofluorene are active in most systems that provide adequate metabolic activation. Knowledge of the structures of the DNA adducts formed by 2-acetylaminofluorene and 2-aminofluorene, the effects of the adducts on DNA conformation and synthesis, adduct distribution in tissues, cells and DNA, and adduct repair have been used to develop hypotheses to understand the genotoxic and carcinogenic effects of these compounds. Molecular analysis of mutations produced in cell-free, bacterial, in vitro mammalian, and intact animal systems have recently been used to extend these hypotheses.