High Levels of Aberrant DNA Methylation in Helicobacter pylori–Infected Gastric Mucosae and its Possible Association with Gastric Cancer Risk

Abstract

Introduction: Risk prediction of gastric cancers is important to implement appropriate screening procedures. Although aberrant DNA methylation is deeply involved in gastric carcinogenesis, its induction by Helicobacter pylori, a strong gastric carcinogen, is unclear. Here, we analyzed the effect of H. pylori infection on the quantity of methylated DNA molecules in noncancerous gastric mucosae and examined its association with gastric cancer risk. Experimental Design: Gastric mucosae were collected from 154 healthy volunteers (56 H. pylori negative and 98 H. pylori positive) and 72 cases with differentiated-type gastric cancers (29 H. pylori negative and 43 H. pylori positive) by endoscopy. The numbers of DNA molecules methylated and unmethylated for eight regions of seven CpG islands (CGI) were quantified by quantitative PCR after bisulfite modification, and fractions of methylated molecules (methylation levels) were calculated. Results: Among healthy volunteers, methylation levels of all the eight regions were 5.4-to 303-fold higher in H. pylori positives than in H. pylori negatives (P < 0.0001). Methylation levels of the LOX, HAND1, andTHBD promoter CGIs and p41ARC exonic CGI were as high as 7.4% or more in H. pylori^positive individuals. Among H. pylori^negative individuals, methylation levels of all the eight regions were 2.2-to 32-fold higher in gastric cancer cases than in age-matched healthy volunteers (P V 0.01). Among H. pylori^positive individuals, methylation levels were highly variable, and that of only HAND1 was significantly increased in gastric cancer cases (1.4-fold, P = 0.02). Conclusions: It was indicated that H. pylori infection potently induces methylation of CGIs to various degrees. Methylation levels of specific CGIs seemed to reflect gastric cancer risk in H. pylori^negative individuals.Gastric cancer is one of the most common malignancies worldwide and remains a leading cause of cancer death in Asia and some European countries (1). To reduce its mortality, early detection by endoscopy and curative resection are important (2). However, considering the potential risk and costs of early detection by endoscopic examination, implementation reflecting an individual's risk for developing a gastric cancer would be ideal. Also, endoscopic mucosal resection, which conserves the noncancerous gastric mucosae, is becoming popular, and the problem of metachronous gastric cancer recurrence is being recognized (3). Again, if the future risk of developing metachronous cancers in a specific case can be estimated, the information will be useful in the decision on either surgical resection or endoscopic mucosal resection for the case.The major etiologic risk factor for gastric cancers is Helicobacter pylori infection, which increases gastric cancer risk 2.2-to 21-fold (4 -6). In an animal model with Mongolian gerbil chronic infection with H. pylori rarely induces gastric cancers by itself, but markedly enhances their incidences after initiation with a mutagen, such as N-methyl-N-nitrosourea (7). Thi...

Alteration in Methylation Pattern of Retinoblastoma 1 Gene Promotor Region in Intestinal Metaplasia with or without Helicobacter pylori and Gastric Cancer Patients

“…Moreover, inflammatory processes repress the expression of a number of genes and methylation is known to be promoted by the decrease in gene expression [25]. Similar results to those found in our study were also reported by Lui et al In their study, Lui et al…”

“…Abnormal methylations in promoter regions of several genes are induced by H. pylori in gastric mucosa including cell growth-related genes p16(INK4a), p14(ARF), and APC; DNArepair genes, hMLH1, BRCA1, and MGMT; the cell adherence gene E-cadherin; as well as LOX, FLNC, HRASLS, HAND1, THBD, and p41ARC, which are known to be methylated in GC patients [22][23][24]. Individuals with H. pylori infection have increased level of gene methylations, which decrease in the absence of the bacteria, consistent with the notion that methylations are induced by the bacterial infection [4,22,24,25].…”

DNA methylation profiles of gastric carcinoma characterized by quantitative DNA methylation analysis

“…This result is consistent with those of previous studies that have demonstrated the close association of HP infection with aberrant CpG island hypermethylation. [25][26][27] We found that HP infection was a confounding factor in the comparison of methylation between CG and GCN and the analysis restricted to HP-positive cases did not show any difference in the number of methylated genes between CG and GCN. This was in contrast to the previous study of Waki et al, 28 who demonstrated higher number of methylated CpG island loci in GCN than in CG using MSP.…”

“…Recent studies exhibited a marked difference of methylation levels between CG and GCN in HP-negative cases but no difference between them in HP-positive cases. 27,29 The CpG island locus of CACNA1G corresponds to MINT31, which was used as one of the reference CpG island loci to determine CpG island methylator phenotype of GCs or colorectal carcinomas. 20,30,31 According to Toyota et al's 30 study using COBRA, MINT31 was never methylated in GC-associated normal stomach samples.…”

Morphologic Characterization of Residual DNA Methylation in the Gastric Mucosa after Helicobacter Pylori Eradication

“…Helicobacter pylori (H. pylori) infection plays an important role in gastric cancer development [3][4][5]. H. pylori-infected gastric mucosa is characterized as chronic inflammation and atrophy [5], leading to epigenetic changes characterized by the promoter methylation of multiple genes [6,7]. This phenomenon can be explained by the concept of an "epigenetic-field-defect" which is linked to gastric cancer predisposition.…”