Immunohistochemical localization of DNA adducts in rat liver tissue and phenotypically altered foci during oral administration of 2-acetylaminofluorene.

Histological studies using paired immunofluorescence staining and peroxidase-anti-peroxidase staining were performed on sections of rat livers with an antiserum specific for the 2-acetylaminofluorene (AAF)-DNA adduct N-deoxyguanosin-(8-yl)-aminofluorene (dG-8-AF). This is the predominant adduct in rat liver DNA at 5 (80%) and 28 (100%) days of AAF feeding. Nuclear staining was observed in livers of male Fischer rats fed 0.02% AAF for these time periods, and was not present in livers of animals fed control diet or detected when specific antiserum, first absorbed with the immunogen adduct, was utilized. In addition, nuclear staining was unchanged after incubation with RNase and abolished after incubation with DNase. Adducts were not readily detectable when whole-liver adduct concentrations were less than an average of 10(5) adducts per cell (30-50 fmol/micrograms DNA). The overall pattern of adduct distribution in livers of AAF-fed animals was distinctly non-uniform. A predominance of nuclear staining was found in the periportal areas by both immunofluorescence and immunoperoxidase procedures. In contrast, staining was very weak in the centrilobular areas. When animals were fed AAF for 28 days and control diet subsequently for 7, 14, 21 or 28 days, the overall intensity of the immunohistochemical staining decreased with time on control diet. However, the pattern of localization remained the same as in livers of rats fed AAF for 28 days, with the predominance of adducts being in the periportal areas. In male rats fed 0.02% AAF for 8 weeks, foci positive for gamma-glutamyltranspeptidase (GGT) became apparent, and the nuclei in these areas showed no immunofluorescence, indicating the absence of detectable levels of the dG-8-AF adduct. Twenty adduct-negative areas in the median lobes of three rat livers were positive for GGT, which suggests that loss of ability to form adducts in these regions occurs concomitantly with early phenotypic changes.