Abstract 1261: Lipid-peroxidation derived DNA damage is prevented in obesity-related hepatocarcinogenesis through CD4+ mediated apoptosis in the livers of mice on a green-tea diet
Authors: Coia Heidi , Ma Ning , Dyba Marcin , Chung Fung-Lung 
Published: July 2017

Using a C57BL/6J bioassay, we assessed whether formation of a lipid-peroxidation (LPO)-derived DNA adduct would induce mutations during the progression of obesity-induced hepatocarcinogenesis and if its formation could be prevented using a diet infused with Theaphenon E, a mixture of polyphenols extracted from green tea. Obesity is now the leading risk factor for the development of hepatocellular carcinoma in the United States. We have conducted a life-time C57BL/6J tumor bioassay to assess the role of obesity in the formation of γ-hydroxy-1,N2-propanodeoxyguanosine (γ-OHPdG), a promutagenic DNA adduct formed endogenously by LPO. Previously, we have shown γ-OHPdG was detected in FFPE liver tissues of patients with different stages of liver disease, demonstrating that its formation is consistent with LPO in the early stages of liver disease and suggesting that it may be a source of endogenous DNA damage in hepatocarcinogenesis. Tea polyphenols, predominately EGCG, are antioxidants that have been shown to prevent obesity and tumorigenesis. For the bioassay, mice were fed either a high fat, low fat, or high fat 2% TE diet starting at 4 weeks of age. Tissue and blood were collected over the course of 80 weeks at 11 separate time points. Health of the mice was assessed using serum concentrations of ALT and AST, gross morphology and immunohistochemistry of TUNEL, Ki67 and CD4+. In contrast to the high-fat and low-fat diet mice, the TE treated mice maintained a healthy body weight, liver to body weight ratio and low levels of AST and ALT enzymes which are elevated in liver disease. Additionally, the health of the liver appears to be maintained through increased CD4+ mediated apoptosis in TE treated mice as demonstrated through decreased Ki67 expression and TUNEL staining showing increased apoptosis in TE treated mice livers in conjunction with increased CD4+ cells. The CD4+ immune response may, therefore, be targeting cells with mutagenic potential. Similar to the trend indicated by the clinical samples, during hepatocarcinogenesis in the high fat diet mice, adduct levels were increased initially and likely fixed into mutation at later time points, where their levels decreased, as quantified by LC-MS/MS. In contrast, in the TE treated mice, the average γ-OHPdG levels remained consistently low. Further studies incorporating whole exome sequencing of the tumors that were formed during the life-time bioassay will indicate whether γ-OHPdG may contribute to the mutations that occured. In conclusion, our study has shown that a robust immune system response mediated by TE may be an underlying mechanism to combat the DNA adduct-induced DNA damage that may lead to HCC.

Citation Format: Heidi Coia, Ning Ma, Marcin Dyba, Fung-Lung Chung. Lipid-peroxidation derived DNA damage is prevented in obesity-related hepatocarcinogenesis through CD4+ mediated apoptosis in the livers of mice on a green-tea diet [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 1261. doi:10.1158/1538-7445.AM2017-1261