Aflatoxin B1-DNA Adduct Formation and Mutagenicity in Livers of Neonatal Male and Female B6C3F1 Mice

Leslie L Woo,Roongtiwa Wattanawaraporn,Patricia A Egner,John M Essigmann,Gerald N Wogan,Robert G Croy,John D Groopman,Crystal L Belanger,Laura J Trudel

doi:10.1093/toxsci/kfr087

Leslie L Woo, Roongtiwa Wattanawaraporn + Show 7 more

Open Access

https://doi.org/10.1093/toxsci/kfr087

Copy DOI

Abstract

Exposure to genotoxic chemicals at a young age increases cancer incidence later in life. Aflatoxin B(1) (AFB(1)) is a potent genotoxin that induces hepatocellular carcinoma (HCC) in many animal species and in humans. Whereas adult mice are insensitive to aflatoxin-induced carcinogenesis, mice treated with AFB(1) shortly after birth develop a high incidence of HCC in adulthood. Furthermore, the incidence of HCC in adult male mice treated as infants is much greater than in females, reasons for which are unclear. In this study, treatment with AFB(1) produced similar levels of DNA damage and mutations in the liver of newborn male and female gpt delta B6C3F1 mice. Twenty-four hours after dosing with AFB(1) (6 mg/kg), the highly mutagenic AFB(1)-FAPY adduct was present at twice the level of AFB(1)-N(7)-guanine in liver DNA of males and females. A multiple dose regimen (3 × 2 mg/kg), while delivering the same total dose, resulted in lower AFB(1) adduct levels. Mutation frequencies in the gpt transgene in liver were increased by 20- to 30-fold. The most prominent mutations in AFB(1)-treated mice were G:C to T:A transversions and G:C to A:T transitions. At this 21-day time point, no significant differences were found in mutation frequency or types of mutations between males and females. These results show that infant male and female B6C3F1 mice experience similar amounts of DNA damage and mutation from AFB(1) that may initiate the neoplastic process. The gender difference in the subsequent development of HCC highlights the importance of elucidating additional factors that modulate HCC development.

Highlights

Animals treated with chemical carcinogens during the perinatal period typically experience higher tumor incidence and shorter latency of tumor emergence (Anderson et al, 2000; Rice, 1981)
This study examined relationships among levels of liver aflatoxin B1 (AFB1)-DNA adducts and mutagenesis in liver cells of newborn transgenic gpt delta B6C3F1
We found that dosing with AFB1 created very similar levels of adducts in liver DNA of both sexes and induced nearly identical mutation frequencies and types of mutations in the gpt transgene in liver cells

Summary

Introduction

Animals treated with chemical carcinogens during the perinatal period typically experience higher tumor incidence and shorter latency of tumor emergence (Anderson et al, 2000; Rice, 1981). Brief exposures to large doses of aflatoxin during the neonatal period result in a high incidence of HCC in adulthood, whereas adult mice exposed to the same doses fail to develop HCC at any age (Vesselinovitch et al, 1972). The overall objectives of our study were to quantify aflatoxin adduct levels, characterize the frequency and spectrum of mutations induced in the liver of male and female gpt delta B6C3F1 mice, and assess relationships of these parameters to the known sensitivity of this strain of mice to AFB1-induced HCC. A prior study with similar objectives carried out in Big Blue lacI transgenic mice showed that AFB1 is a potent liver mutagen in neonatal animals, but much less potent in the adult (Chen et al, 2010), in which fewer AFB1DNA adducts were previously found (Shupe and Sell, 2004). This work is an early stage of a continuing effort to define biochemical markers related to age, gender, and strain capable of identifying key biochemical processes that underlie sensitivity and resistance to carcinogens

Objectives

Methods

Results

Conclusion