Frequencies and Spectra of Aflatoxin B-induced Mutations in Liver Genomes of NEIL1-deficient Mice As Revealed by Duplex Sequencing

Increased risk for the development of hepatocellular carcinoma (HCC) is driven by a number of etiological factors including hepatitis viral infection and dietary exposures to foods contaminated with aflatoxin-producing molds. Intracellular metabolic activation of aflatoxin B (AFB) to a reactive epoxide generates highly mutagenic AFB-Fapy-dG adducts. Previously, we demonstrated that repair of AFB-Fapy-dG adducts can be initiated by the DNA glycosylase NEIL1 and that male mice were significantly more susceptible to AFB-induced HCC relative to wild-type mice. To investigate the mechanisms underlying this enhanced carcinogenesis, WT and mice were challenged with a single, 4 mg/kg dose of AFB and frequencies and spectra of mutations were analyzed in liver DNAs 2.5 months post-injection using duplex sequencing. The analyses of DNAs from AFB-challenged mice revealed highly elevated mutation frequencies in the nuclear genomes of both males and females, but not the mitochondrial genomes. In both WT and mice, mutation spectra were highly similar to the AFB-specific COSMIC signature SBS24. Relative to wild-type, the NEIL1 deficiency increased AFB-induced mutagenesis with concomitant elevated HCCs in male mice. Our data establish a critical role of NEIL1 in limiting AFB-induced mutagenesis and ultimately carcinogenesis.