Cyclic 1,N2-propanodeoxyguanosine adducts of acrolein (Acr-dG) and trans-4-hydroxy-2-nonenal (HNE-dG) derived from lipid peroxidation have been detected as endogenous DNA lesions in rodent and human tissues. However, their roles in carcinogenesis are still not clearly understood. Recent in vitro studies in cultured human cells and in DNA fragments containing the human p53 gene have shown that Acr and HNE can bind to the p53 gene preferentially at guanines in a sequence-selective manner and that the binding patterns are similar to p53 mutation hotspots observed in certain human cancers, suggesting the possible roles of Acr-dG and HNE-dG in carcinogenesis. However, no in vivo studies have been conducted to directly examine cyclic adducts in tissues where tumors develop in a relevant animal tumorigenesis model. These studies are important because they provide strong evidence directly linking adducts with mutations and tumor formation in the target tissue. In this application, we propose to use genetically defected Long Evans Cinnamon (LEC) rats and transgenic XPA-deficient (XPA-/-) mice, both of which are highly prone to spontaneous liver cancer without carcinogen treatment, to investigate the roles of Acr-dG and HNE-dG as endogenous DNA lesions in carcinogenesis. LEC rats are inflicted with heightened lipid peroxidation in the liver as a result of abnormal copper accumulation, whereas XPA(-/-) mice are deficient in nucleotide excision repair (NER) which is important for removing Acr- and HNE-dG adducts. Our hypothesis is that the formation of the cyclic adducts will be increased and these adducts will accumulate in the liver DNA of these animals compared with the wild-type Long Evans (LE) rats and XPA(+/+) mice and that the increased formation of these adducts underlies the mechanisms for liver carcinogenesis. We will carry out the following aims to examine this hypothesis.
In Aim 1, we will conduct tumor bioassays in LEC rats and XPA(-/-) mice and their normal strains and study throughout their lives the relationships of cyclic adducts in the liver DNA with liver carcinogenesis at different stages;
In Aim 2, we will map Acr and HNE adduct binding sites in the p53 gene of the liver DNA from LEC rats and XPA (-/-) mice during the tumor bioassays and compare their binding sites with the p53 mutational spectra of the liver tumors harvested at the termination of bioassays.
In Aim 3, we will investigate the effects of antioxidants on the formation of cyclic adducts in the liver DNA and on the development of spontaneous liver cancers in these animals. The data generated from these studies will help us to understand the roles of endogenous cyclic Acr-dG and HNE-dG adducts from lipid peroxidation in hepatocarcinogenesis.
In this proposal, our goal is to investigate the specific biological roles of one class of DNA damage formed by oxidation of polyunsaturated fatty acids called cyclic adducts in causing liver cancer. Incidences of liver cancer are on the rise in the U.S., and evidence indicates that obesity and fatty livers are potential risk factors. Therefore, our long-term goal is to generate information in order to shed light on possible mechanisms of obesity in liver cancer.
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