Abstract 47: DNA adductome: An ultimate exposome of human tissues.

Abstract

Abstract The formation of DNA adducts and the subsequent generation of mutations in the genome is believed to be a pivotal event in the pathogenesis of cancer, but several obstacles have hampered a concrete demonstration of the molecular species, quantity, and significance of DNA adducts in human tissues. For the last few years, we have attempted to demonstrate the existence of multiple DNA adducts in human tissues using a single experiment involving liquid chromatography tandem mass spectrometry. This procedure discloses a hundred to a few hundred peaks with distinct mass/charge and retention times in each sample. In previous experiments, we validated the presence of some tobacco-related and other DNA adducts in the lungs of a smoker and a non-smoker. Recently, we demonstrated the presence of lipid peroxidation-induced DNA adducts in several autopsy tissues including the lung, liver, pancreas, and spleen. In this presentation, we would like to show an adductome map for two regions of the human stomach in which the prevalence of gastric cancer differs. The DNA samples were obtained under anti-oxidation conditions from the gastric mucosa from regions adjacent to, but distant from, the cancer lesion in 22 patients with gastric cancer (12 cases in China and 10 cases in Japan) who underwent a gastrectomy. We identified 141 peaks in the Japanese sample and 159 peaks in the Chinese sample. Ninety-two of these peaks were present in both the Japanese and Chinese samples. Seven lipid peroxidation-related DNA adducts (1,N6-etheno-2′-deoxyadenosine [ϵdA], butanone-etheno-2′-deoxycytidine [BϵdC], butanone-etheno-2′-deoxy-5-methylcytidine [BϵmedC], butanone-etheno-2′-deoxyadenosine [BϵdA], heptanone-etheno-2′-deoxycytidine [HϵdC], heptanone-etheno-2′-deoxyadenosine [HϵdA], and heptanone-etheno-2′-deoxyguanosine [HϵdG]) were identified in a total of 22 gastric mucosa samples. The levels of these adducts ranged from 0 to 30,000 per 109 bases, and the levels of BedC, BedA, and HedA were higher in the Japanese gastric mucosa samples. Next, the mutation spectrum for p53 in gastric cancer tissues from the same hospital in China was investigated and compared with that of gastric cancer tissues obtained in Japan. The prevalence of a G-to-A transition in a non-GC area was higher in those derived from China; that is, G-to-A transitions in a GC rich area, which has been assumed to be related to endogenous inflammation, were more prevalent in the Japanese gastric cancer specimens. We interpreted these results as indicating that inflammation can mediate carcinogenesis via lipid peroxidation-induced adducts, and the mutation process that may consequently arise may play a greater role in Japanese gastric cancers than in Chinese gastric cancers. To delve into the mechanism of the cellular reactions to these adducts, oligonucleotides containing ϵdA, ϵdC, BϵdC, BϵdG, HϵdC, and HϵdG were synthesized and used as substrates for a gel retardation assay using the recombinant proteins of 8 different base excision repair genes. In contrast to their considerable capacity to repair smaller modified bases, such as ϵdA and ϵdC, the base excision repair gene products seemed to be less capable of repairing the larger modified bases BϵdC, BϵdG, HϵdC, and HϵdG, except for a few combinations. While a comprehensive understanding of the modifications of DNA bases, both endogenous and exogenous, and the corresponding host machineries might seem like a distant goal and an adductome approach is admittedly at a burgeoning stage, combing every un-annotated spot in an adductome map could help to realize a comprehensive understanding of the effects of exposures of various kinds. Citation Format: Haruhiko Sugimura, Hong Tao, Nobuya Kurabe, Masanori Goto, Yoshitaka Matsushima, Hidetaka Yamada, Kazuya Shinmura, Yohei Miyagi, Akira Tsuburaya, Takaki Yoshikawa, Yukari Totsuka, Hitoshi Nakagama, Yaping Wang, Tomonari Matsuda. DNA adductome: An ultimate exposome of human tissues. [abstract]. In: Proceedings of the AACR Special Conference on Post-GWAS Horizons in Molecular Epidemiology: Digging Deeper into the Environment; 2012 Nov 11-14; Hollywood, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2012;21(11 Suppl):Abstract nr 47.