In this study we are investigating the role and mechanism of formation of Lipid-peroxidation (LPO)-derived DNA adduct formation in obesity-related hepatocarcinogenesis. Obesity has been implicated as a risk factor for many types of cancer, particularly hepatocellular carcinoma (HCC). HCC incidence correlates with the increasing prevalence of non-alcoholic fatty liver disease (NAFLD) and non-alcoholic steatohepatitis (NASH) in the US. The mechanisms underlying this increased risk of liver cancer in the obese population are still unclear. Liver tissue damage from fat accumulation in NAFLD and NASH produce inflammation and increased levels of reactive oxygen species (ROS). ROS induce LPO of polyunsaturated fatty acids (PUFAs) in cell membranes leading to the formation of reactive aldehydes, such as acrolein and 4-hydroxy-2-nonenal (HNE), which react with DNA forming the DNA adducts γ-OHPdG and DHH-ϵdA, respectively. γ-OHPdG is derived from ω-6 and ω-3 PUFAs, while DHH-ϵdA is specifically from ω-6 fatty acids. Previous data has indicated that mutational hotspots targeted by γ-OHPdG and DHH-ϵdA may be within key cancer driver genes, such as p53. Research has shown that B-6 mice fed a high fat diet (HFD) develop fatty liver disease and eventually HCC. The livers of B-6 mice fed a HFD showed an increased ω-6/ω-3 PUFAs ratio. We have detected and quantified γ-OHPdG and DHH-ϵdA by LC-MS/MS in livers from six healthy individuals and six NAFLD patients and found that levels of DHH-ϵdA in the DNA of the fatty liver samples were nearly three-fold higher than that in normal liver samples. Preliminary in vitro data using primary human hepatocytes has indicated that treatment with oleic and palmitic acid promote the formation of γ-OHPdG. Similarly, treatment of these cells with the epoxide of HNE, 2,3-epoxy-4-hydroxynonanal (EH), and the omega-6 fatty acid, arachidonic acid, induce the formation of DHH-ϵdA, supporting the proposed mechanism of adduct formation. In an 80-week tumor bioassay using C57Bl/6J mice on a HFD, we have observed through live-animal MRI imaging and immunohistochemistry, an increase in pro-inflammatory white adipose tissue accumulation, infiltration of fat into the liver and an increase in overall body weight compared to a low fat diet control. In addition, in mice fed a HFD combined with the green-tea derived antioxidant Theaphenon E, we observed through MRI, reduction in body weight gain, white adipose tissue, and lipid accumulation in liver. Theaphenon E has the potential to decrease fat accumulation and inflammation within the liver that lead to decreases in LPO-derived adduct formation and consequently, the mutations critical for HCC development.
Citation Format: Heidi Coia, Hongyi Guan, Ying Fu, Marcin Dyba, Fung-Lung Chung. Lipid peroxidation-derived DNA adduct formation in obesity-related hepatocarcinogenesis. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4051.