Higher methylation levels in gastric mucosae significantly correlate with higher risk of gastric cancers

Background: Helicobacter pylori infection potently induces methylation of CpG islands in gastric mucosae, which is considered to decrease to a certain level after active H. pylori infection discontinues. Noncancerous gastric mucosae of H. pylori-negative cases with a gastric cancer had higher methylation levels than those of H. pylori-negative healthy individuals. Here, using cases with multiple gastric cancers, we analyzed whether the higher methylation levels correlated with the higher risk of gastric cancers. Methods: Twenty-six healthy volunteers (HV), 30 cases with a single well-differentiated gastric cancer (S cases), and 32 cases with multiple well-differentiated gastric cancers (M cases) were recruited. H. pylori infection status was analyzed by the culture method. Methylation levels were quantified by real-time methylation-specific PCR of seven CpG islands. Results: In H. pylori-negative individuals, significant increasing trends were present in the order of HV, S cases, and M cases for FLNc and HAND1 methylation levels (P < 0.01, Spearman's rank-order test). Furthermore, the FLNc methylation level of M cases was significantly higher than that of S cases (P < 0.01, t test). Even adjusted by the extent of gastric atrophy, the FLNc methylation level retained a significant increasing trend (P = 0.03). In contrast, methylation levels in H. pylori -positive individuals were increased to various degrees in all the three groups. Conclusions: In H. pylori-negative individuals, methylation levels in gastric mucosae significantly increased in cases with a single gastric cancer and more in cases with multiple gastric cancers. Quantitative analysis of methylation levels is a promising risk marker for gastric cancers.