Background: Epigenomic damage induced by Helicobacter pylori infection is accumulated in gastric mucosae before the development of malignancy. In individuals without current H. pylori infection, DNA methylation levels of specific CpG islands (CGIs) are associated with gastric cancer risk. Because risk estimation in individuals with past infection is clinically important, we here aimed to identify the risk markers that reflect epigenomic damage induced by H. pylori infection, and that are informative in these individuals.
Methods: Gastric mucosae were obtained from 55 gastric cancer patients (GC-Pt) (21 with current infection and 34 with past infection) and 55 healthy volunteers (HV) (7 never-infected, 21 with current infection, and 27 with past infection). Hypermethylated CGIs were searched for by methylated DNA immunoprecipitation-CGI microarray, and methylation levels were analyzed by quantitative methylation-specific polymerase chain reaction (PCR).
Results: By microarray analysis of a pool of three samples from GC-Pt with past infection and another pool of samples from HV with past infection, 15 hypermethylated CGIs in the former pool were isolated. Seven of them had significantly higher methylation levels in GC-Pt with past infection (n = 10) than in HV with past infection (n = 10) (P < 0.001). In a validation cohort (21 GC-Pt with past infection and 14 HV with past infection), the seven new markers had large areas under the receiver-operating characteristic curves (0.78-0.84) and high odds ratios (12.7-36.0) compared with two currently available markers (0.60-0.65, 5.0-5.7).
Conclusions: We identified seven novel gastric cancer risk markers that are highly informative in individuals with past infection.