Aflatoxin-Guanine DNA Adducts and Oxidatively Induced DNA Damage in Aflatoxin-Treated Mice in Vivo as Measured by Liquid Chromatography-Tandem Mass Spectrometry with Isotope Dilution

Dietary exposure to aflatoxin B ₁ (AFB ₁ ) is a significant contributor to the incidence of hepatocellular carcinomas globally. AFB ₁ exposure leads to the formation of AFB ₁ -N ⁷ -guanine (AFB ₁ -N ⁷ -Gua) and two diastereomers of the imidazole ring-opened 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxyaflatoxin B ₁ (AFB ₁ -FapyGua) in DNA. These adducts lead to G → T transversion mutations with the ring-opened adduct being more mutagenic than the cationic species. Accurate measurement of these three adducts as biomarkers in DNA and urine will help identify dietary exposure to AFB ₁ as a risk factor in the development of hepatocellular carcinoma worldwide. Herein, we report an improved methodology for the measurement of AFB ₁ -N ⁷ -Gua and the two diastereomers of AFB ₁ -FapyGua using liquid chromatography-tandem mass spectrometry with isotope dilution. We measured the levels of these compounds in liver DNA of six control mice and six AFB ₁ -treated mice. Levels varying from 1.5 to 45 lesions/10 ⁶ DNA bases in AFB ₁ -treated mice were detected depending on the compound and animal. No background levels of these adducts were detected in control mice. We also tested whether the AFB ₁ treatment caused oxidatively induced DNA base damage using gas chromatography-tandem mass spectrometry with isotope dilution. Although background levels of several pyrimidine- and purine-derived lesions were detected, no increases in these levels were found upon AFB ₁ treatment of mice. On the other hand, significantly increased levels of (5′R)- and (5′S)-8,5′-cyclo-2′-deoxyadenosines were observed in liver DNA of AFB ₁ -treated mice. The impact of this work is expected to achieve the accurate measurement of three AFB ₁ -DNA adducts and oxidatively induced DNA lesions as biomarkers of AFB ₁ exposure as germane to investigations designed for the prevention of aflatoxin-related hepatocellular carcinomas and for determining the effects of genetic deficiencies in human populations.