4‐Aminobiphenyl induces liver DNA adducts in both neonatal and adult mice but induces liver mutations only in neonatal mice

Abstract

The mechanisms underlying the susceptibility of neonatal mice to genotoxic carcinogens were investigated by analyzing the DNA adducts and mutations induced in the livers of neonatal and adult Big Blue transgenic mice by 4-aminobiphenyl (4-ABP), a potent human and rodent carcinogen. Neonatal and adult mice were treated with a regimen of 4-ABP known to induce tumors in neonatal mice. Animals were sacrificed 1 day after the last treatment for DNA adduct analysis and 8 weeks after the last treatment for analysis of lacI and cII mutant frequency (MF). N-(Deoxyguanosin-8-yl)-4-ABP was the major DNA adduct identified in the livers of the 4-ABP-treated mice and levels of this adduct were significantly higher in treated animals than in the controls for both the neonates and adults. Adduct levels for adult females (44.0 6 4.8 adducts/10 6 nucleotides) were higher than in neonatal females (25.9 6 2.2 adducts/10 6 nucleotides), while adduct levels in adult males (13.5 6 2.0 adducts/10 6 nucleotides) were lower than in neonatal males (33.8 6 4.1 adducts/10 6 nucleotides). 4-ABP treatment significantly increased the liver cII MFs in both sexes of neonatal mice but not in adult mice. Sequence analysis of cII mutant DNA revealed that 4-ABP induced a unique spectrum of mutations in neonatal mice, characterized by a high frequency of G:CfiT:A transversion, while the mutation spectrum in 4-ABP-treated adults was similar to that of control mice. Our results indicate that DNA adduct formation by 4-ABP depends as much on sex as it does on age, whereas the conversion of DNA adducts into mutations differed with animal age. These observations suggest that neonates are more sensitive than adults to genotoxic carcinogens because the relatively high levels of cell division in the developing animal facilitate the conversion of DNA damage into mutation. Supplementary material for this article can be found on the International Journal of Cancer website at

Influence of arylamine n‐acetyltransferase, sex, and age on 4‐aminobiphenyl‐induced in vivo mutant frequencies and spectra in mouse liver

“…However, the absolute mutant frequencies tended to be lower in adults than in neonates, especially at lower ABP doses, despite much greater total ABP exposures (20,000-40,000 nmol vs. 600-1,200 nmol). This confirms previous findings that neonatally exposed animals are much more sensitive to the mutagenic effects of ABP, presumably because the increased rate of cell proliferation in developing liver enhances the likelihood of fixation of mutations instead of damage repair [Chen et al, 2005]. Unlike in neonates where no sex differences were observed, adult females demonstrated significantly higher levels of ABPinduced mutant frequencies than males, which correlates with the C8-dG-ABP data we generated using adult mice [Sugamori et al, 2012].…”

“…As with the mutant frequencies, the ABP-induced mutation spectra in adults were distinct from those in neonates, with the most prominent difference being a lack of increase in G-T transversions in all groups of adult mice. Although the relatively small number of mutants analyzed in our study precludes any firm conclusions, our results are consistent with the findings of Chen et al [2005], and highlight the potential importance of age-related factors in determining the genotoxic actions of ABP.…”

“…An increase in G-T transversions following ABP exposure has been reported previously, and was attributed to the formation of C8-dG-ABP [Chen et al, 2005;Yoon et al, 2012]. We also observed a significant increase in the proportion of G-T transversions in wild-type mice dosed using the neonatal ABP exposure protocol.…”

“…Both in vitro and in vivo studies have shown that ABP generates a high frequency of G-T transversions that are suggested to be critical in tumor initiation [Lasko et al, 1988;Verghis et al, 1997;Fletcher et al, 1998;Zayas-Rivera et al, 2001;Besaratinia et al, 2002;Heddle et al, 2003;Chen et al, 2005]. Furthermore, the ability of ABP to generate G-T transversions in mouse liver has been taken as evidence for the importance of C8-dG-ABP adducts, which produce mainly G-T transversions in vitro, in tumor initiation [Chen et al, 2005]. The purpose of the current study was to use the transgenic Muta TM Mouse in vivo mutation model [Gossen et al, 1989] to determine whether sex and strain differences in ABP-induced mutant frequencies and/or mutation spectra could explain the differences we observed in liver tumor incidence following ABP exposure.…”

Organ Specificity of the Bladder Carcinogen 4-Aminobiphenyl in Inducing DNA Damage and Mutation in Mice

“…In confirmation, Poirier and colleagues (36) and Flammang and colleagues (37) have reported higher levels of 4-ABP-DNA adducts in bladder tissues than liver tissues of male mice fed with 4-ABP via drinking water for 28 days (a reverse pattern of DNA adduction was found in the respective tissues in female mice). The organ-and gender-specific differences in 4-ABP-DNA adduction and tumorigenesis in mice may relate to tissue-and sex-specific metabolic activation of 4-ABP (e.g., O-conjugation) and hormonal status (e.g., promoting effects of testosterone), respectively (38). We note that due to low yield of DNA from mouse bladder, we only had limited amount of DNA available for simultaneous analysis of DNA adducts and mutations in this organ.…”