Aberrant DNA methylation accumulated in normal tissues, namely methylation burden, is closely associated with risk of carcinogenesis, especially in cancers related to chronic inflammation. Methylation burden is known to be influenced by multiple factors, such as genetic factors and strengths of carcinogens. However, the impact of the duration of exposure to a carcinogen is still unclear. Here, using a Mongolian gerbil model of Helicobacter pylori (H. pylori)-induced chronic gastritis, we aimed to clarify the impact of the duration of exposure on the methylation burden in normal gastric tissues (gastric mucosae). Following infection with H. pylori, DNA methylation levels at four CpG islands, HE6, SA9, SB5, and SD2, increased, depending upon the exposure duration. After eradication of H. pylori, DNA methylation levels decreased, but tended to be higher in gastric mucosae with a longer infection period. DNA molecules with dense DNA methylation, but not those with sparse DNA methylation, increased depending upon the infection period. DNA methylation levels at one of the four CpG islands, SA9, tended to be higher in the gastric mucosae of gerbils infected with H. pylori than in those of non-infected gerbils, even 50 weeks after eradication. These results showed, for the first time, that the methylation burden in normal tissues is influenced by the duration of exposure to a carcinogenic factor.
Citation Format: Harumi Yamada, Hideyuki Takeshima, Tohru Niwa, Takeshi Toyoda, Satoshi Yamashita, Toshikazu Ushijima. The methylation burden is determined by the duration of exposure to carcinogenic factors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5340.