Frequencies and spectra of aflatoxin B 1 -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 1 (AFB 1 ) to a reactive epoxide generates highly mutagenic AFB 1 -Fapy-dG adducts. Previously, we demonstrated that repair of AFB 1 -Fapy-dG adducts can be initiated by the DNA glycosylase NEIL1 and that male Neil1 -/- mice were significantly more susceptible to AFB 1 -induced HCC relative to wild-type mice. To investigate the mechanisms underlying this enhanced carcinogenesis, WT and Neil1 -/- mice were challenged with a single, 4 mg/kg dose of AFB 1 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 1 -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 Neil1 -/- mice, mutation spectra were highly similar to the AFB 1 -specific COSMIC signature SBS24. Relative to wild-type, the NEIL1 deficiency increased AFB 1 -induced mutagenesis with concomitant elevated HCCs in male Neil1 -/- mice. Our data establish a critical role of NEIL1 in limiting AFB 1 -induced mutagenesis and ultimately carcinogenesis.