Dose-dependent effects of 2-acetylaminofluorene on hepatic foci development and cell proliferation in rats

Abstract

Dose-dependent development of pre-neoplastic liver cell foci induced by 2-acetylaminofluorene (2-AAF) was investigated in relation to cell-proliferative activity. Male F344 rats were initially given a single i.p. injection of diethylnitrosamine (DEN, 200 mg/kg) and starting 2 weeks later received diets containing 2-AAF at dose levels of 150, 100, 60, 45, 35 or 30 p.p.m., 500 p.p.m. phenobarbital (PB) or basal diet as a control for 6 weeks. Two-thirds partial hepatectomy (PH) was performed at week 3. The rats were sequentially killed from weeks 0 to 16 and liver sections were analysed by double staining for both BrdU incorporation and glutathione S-transferase placental form (GST-P) expression. 2-AAF increased numbers and areas of GST-P positive (GST-P+) foci in a dose-dependent manner, especially after PH. Proliferation of hepatocytes, as indicated by BrdU labelling indices (LI), was higher in GST-P+ foci than in surrounding hepatocytes in all 2-AAF-treated groups, even after cessation of carcinogen administration. Proliferative response of hepatocytes to PH was delayed in rats treated with the highest dose of 2-AAF in both foci and in surrounding areas possibly due to the 2-AAF toxicity. In the PB treated group, the results were similar to those for the lower dose 2-AAF-treated groups. It is concluded that the development of GST-P+ foci and cell proliferation in GST-P+ foci are directly related to 2-AAF treatment in a dose-dependent manner and the present assay system is reliable for detection of carcinogenicity of chemicals even at low doses.

Review Article: A Medium-Term Rat Liver Bioassay as a Rapid In Vivo Test for Carcinogenic Potential: A Historical Review of Model Development and Summary of Results from 291 Tests

“…Using 3 hepatocarcinogens, 2-AAF, 3'-Me-DAB, and DL-ethionine, at 3 dose levels, it was clearly indicated that the degree of induction of GST-P-positive foci and nodules in the medium-term bioassay system corresponds with the incidences of hepatocellular carcinomas as revealed by longterm carcinogen exposure (35). A precise dose-response study was also performed using 2-AAF as a model compound to compare the results with the EDO, mega-mouse study of hepatocarcinogenicity (44), and the reliability of our system was again confirmed (51 4 carcinogenic peroxisome proliferators, and tamoxifen did not enhance development of GST-P-positive foci development. With regard to the carcinogenicity of nonmutagenic peroxisome proliferators, it is important to remember that they depress GST-P expression, and the lesions associated with their hepato- (Table III).…”

Evidence of a Threshold Dose for Promotion of Hepatocarcinogenesis by Hexachlorobenzene in a Rat Medium-Term Liver Bioassay

“…Furthermore, this bioassay was recommended as an acceptable alternative to the long-term rodent carcinogenicity test at the Fourth International Conference on Harmonization 16 . Since the required time is relatively short and the quantitative measurement of GST-P positive foci is very sensitive, it is relatively easy to conduct studies with many different doses of chemical to assess dose-dependence of carcinogenic potency 18,19 . In particular, a Japanese research group has been approaching this very important issue using this assay system 20 .…”

Evaluation of Flutamide Genotoxicity in Rats and in Primary Human Hepatocytes

“…With the liver foci assay, false negative results are estimated to occur for about 10% of hepatocarcinogenic agents (Tiwawech et al 1991). As a consequence, the missing significant increase in the number and size of g-glutamyltranspeptidase-positive foci in the liver of rats given 100 and 500 mg/kg/week flutamide for 6 successive weeks indicates that this drug is most likely not capable of acting as initiator of liver tumours.…”