Correlation between clastogenicity and promotion activity in liver carcinogenesis by N-hydroxy-2-acetylaminofluorene, N-hydroxy-4'-fluoro-4-acetylaminobiphenyl and N-hydroxy-4-acetylaminobiphenyl

N-Hydroxy-2-acetylaminofluorene (N-OH-AAF), N-hydroxy-4'-fluoro-4-acetylaminobiphenyl (N-OH-FAABP) and N-hydroxy-4-acetylaminobiphenyl (N-OH-AABP) were compared for their initiation and promotion activity in the rat liver using a modified Solt-Farber system. N-OH-AAF, N-OH-FAABP and N-OH-AABP showed comparable initiation capacity when administered to male Wistar rats at a dose of 30, 120 and 120 mumol/kg respectively, 24 h after a two-thirds partial hepatectomy (PH). In contrast, only N-OH-AAF was very effective as promoter when administered to rats previously initiated with diethylnitrosamine. This was evidenced by a high number of large gamma-glutamyltranspeptidase-positive (GGT+) foci occupying a high percentage (22%) of liver volume. N-OH-FAABP was a much weaker promoter, resulting in smaller foci and lower percentage (4%) of GGT+ liver volume. The incomplete carcinogen N-OH-AABP was totally ineffective as promoter in our model. A similar difference was seen in the clastogenicity of these carcinogens in rat liver in vivo as measured by the formation of micronuclei: N-OH-AAF was far more clastogenic than N-OH-FAABP, which in turn was more clastogenic than N-OH-AABP. We have recently shown that N-acetylated deoxyguanosine adducts are responsible for clastogenicity of N-OH-AAF and may be important for promotion. DNA adduct analysis after injection of 120 mumol/kg of tritium-labeled N-OH-FAABP or N-OH-AABP, 24 h after PH, showed that N-acetylated adducts to C8 of deoxyguanosine are also formed from these structurally related liver carcinogens. However, the formation of these adducts from N-OH-FAABP and N-OH-AABP was approximately 8 and approximately 5% of the formation of dG-C8-AAF after injection of 25 mumol/kg N-OH-AAF. These data show that for the structurally related liver carcinogens N-OH-AAF, N-OH-FAABP and N-OH-AABP, clastogenicity does not predict initiating efficacy but correlates with promotion activity. Possibly, N-acetylated adducts to C8 of deoxyguanosine are involved in both clastogenicity and promotion.

The role of specific DNA adducts in the induction of micronuclei by N-hydroxy-2-acetylaminofluorene in rat liver in vivo

N-Hydroxy-2-acetylaminofluorene (N-OH-AAF) was administered i.p. to male Wistar rats 17 h after partial hepatectomy. Hepatocytes were analyzed for the presence of micronuclei 7 h, 1, 2, 3 and 4 days after injection. N-OH-AAF treatment resulted in a high frequency of micronucleated hepatocytes at days 3 and 4 (19.5% and 19.6% respectively). The frequency of micronucleated hepatocytes was not increased above control values when hepatocytes were isolated as early as 7 h, 1 or 2 days after injection. Pretreatment with the sulfotransferase inhibitor pentachlorophenol (PCP) 45 min before injection of N-OH-AAF almost completely prevented the formation of micronuclei by N-OH-AAF. Parallel biochemical studies indicated that inhibition of sulfation of N-OH-AAF by PCP pretreatment prevented the formation of the N-acetylated DNA adducts N-deoxyguanosin-8-yl-AAF and 3-deoxyguanosin-N2-yl-AAF by approximately 85%. Total adduct formation to DNA was, however, not lowered because of an increase in the formation of the deacetylated adduct, N-deoxyguanosin-8-yl-AAF. The lower frequency of micronucleated hepatocytes observed in the group pretreated with PCP, did not result from less proliferative activity in this group as compared to the group treated with N-OH-AAF alone. Therefore, the decrease in the formation of micronuclei indicates that PCP prevents the clastogenic damage caused by N-OH-AAF. It is concluded that the clastogenicity of N-OH-AAF in rat liver is related to the formation of N-acetylated DNA adducts (i.e. N-deoxyguanosin-8-yl-AAF and/or 3-deoxyguanosin-N2-yl-AAF) and is not related to the formation of the deacetylated DNA adduct N-deoxyguanosin-8-yl-AF.