Accumulation of 8-Hydroxy-2’- Deoxyguanosine Adducts in HBx Recombinant HepG2 Cells and HBx Transgenic Mice

Background/Aims: Transgenic mice overexpressing hepatitis B x protein (HBx) show an increased susceptibility to mutations if exposed to mutagens. Also involved in HBx signalling, reactive oxygen intermediates (ROI) can induce DNA adducts such as 8-hydroxy-2′-deoxyguanosine that can in turn lead to G/T transversion mutations. Therefore, we investigated whether HBx expression increases the level of the mutational precursor 8-hydroxy-2′-deoxyguanosine in hepatocellular DNA. Methods: 8-hydroxy-2′-deoxyguanosine concentrations of DNA hydrolysates of HBx protein expressing HepG2 cells and livers of HBx transgenic mouse lines were determined electrochemically after HPLC fractionation. Results: 8-hydroxy-2′-deoxyguanosine concentrations in genomic DNA of HBx protein expressing cell lines correlated with the factor of transactivation. The 8-hydroxy-2′-deoxyguanosine levels were reduced after incubation of HBx recombinant cell lines with 0.1 or 1 mM of the antioxidant N-acetylcysteine. Hepatic 8-hydroxy-2′-deoxyguanosine concentrations in DNA of old transgenic mice were significantly, i.e. twofold, (p < 0.01) increased as compared to those of old nontransgenic or young transgenic controls and of control mice expressing a second HBV transactivator (MHBst76). Conclusion: HBx expression results in elevated DNA adduct levels. This could reflect a direct inhibitory interaction of HBx with cellular repair mechanisms. Alternatively, this may be an effect of an increased generation of reactive oxygen intermediates through HBx.