The essential role of microsomal deacetylase activity in the metabolic activation, DNA-(deoxyguanosin-8-yl)-2-aminofluorene adduct formation and initiation of liver tumors by N-hydroxy-2-acetylaminofluorene in the livers of infant male B6C3F1 mice

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Abstract
Deacetylation of N-hydroxy-2-acetylaminofluorene. (N-hydroxy- AAF) to N-hydroxy-2-aminofluorene (N-hydroxy-AF) has been proposed as one of the critical metabolic steps in the formation of hepatic DNA adducts and the initiation of liver tumors in 12-day-old male B6C3F1 mice. In this study, the importance of the microsomal deacetylase activity for N-hydroxy-AAF in the initiation of hepatocarcinogenesis in these mice was demonstrated by using a carboxylesterase and amidase inhibitor, bis(p-nitrophenyl)phosphate (BNPP), that is much less toxic in vivo than is paraoxon. Pre-incubation of liver microsomes from 12-day-old male B6C3F1 mice with 10−3 M BNPP reduced the deacetylase activity by 80% while paraoxon inhibited the deacetylase activity completely at a concentration of 10−4 M. Pretreatment of 12-day-old male B6C3F1 mice with 4 × 75 μg doses of BNPP/g body weight before the administration of n-hydroxy-AAF reduced the hepatic N-(dGuo-8-yl)-AF adduct levels to 1.09 and 0.68 pmol/mg DNA compared with 2.87 and 1.64 pmol/mg DNA for mice treated once with 0.06 or 0.03 μmol of N-hydroxy-AAF/g body weight respectively. However, BNPP pretreatments did not affect the levels of the acetylated DNA adducts, N-(dGuo-8-yl)-AAF and 3-(dGuo-N2-yl)-AAF, formed by these doses of N-hydroxy-AAF. The initiation of liver tumors by n-hydroxy-AAF was also inhibited by BNPP pretreatment. Thus, for mice that received single doses of 0.12, 0.06 and 0.03 μmol of N-hydroxy-AAF/g body weight, the multiplicities of liver tumors at 10 months were reduced by BNPP pretreatments to 5.6, 1.0 and 0.3 compared with multiplicities of 11.8, 4.8 and 1.7 without pretreatment respectively. On the other hand, BNPP pretreatments had no significant inhibitory effects on the levels of the hepatic DNA-N-dGuo-8-yl)-AF adduct or on the liver tumor multiplicities induced by comparable doses of N-hydroxy-AF. It is concluded that deacetylation of n-hydroxy-AAF to N-hydroxy-AF is essential for the metabolic activation, DNA-N-(dGuo-8-yl)-AF adduct formation and liver tumor initiation in infant male B6C3F1 mice by N-hydroxy-AAF.