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Background: Helicobacter pylori gastritis increases gastric cancer risk. Microsatellite instability-type mutations are secondary to deficient DNA mismatch repair. H. pylori gastritis is more frequent in patients with microsatellite instability-positive gastric cancers, and H. pylori organisms independently of inflammation can reduce DNA mismatch repair protein levels, raising the hypothesis that H. pylori organisms might lead to mutagenesis during infection. Materials and Methods: Mutations were detected using a green fluorescent protein reporter vector (pEGFP-CA13). Gastric cancer AGS cells transfected with pEGFP-CA13 were cocultured with H. pylori or Escherichia coli. The numbers of green fluorescent protein (GFP)-positive cells were determined, and GFP, hMSH2, and hMLH1 protein levels were measured by Western blot. The effect of H. pylori on CpG methylation status of hMLH1 was determined by methylation-specific polymerase chain reaction. Results: GFP levels and GFP-positive cell numbers in AGS cells cocultured with H. pylori significantly increased, as the levels of hMLH1 and hMSH2 dropped. H. pylori cocultures induced low-level CpG methylation of the hMLH1 promoter. Sequence analysis of cells cocultured with H. pylori showed an increased number of frameshift mutations and point mutations as compared to cells not cocultured with H. pylori ( p = .03 and p = .001, respectively). Conclusions: This is the first report showing that H. pylori bacteria may lead to accumulation of genomic mutations, independently of underlying inflammation. This is associated with reduced DNA mismatch repair, and is at least in part associated with CpG methylation of the hMLH1 promoter. These data support the notion that H. pylori-induced mutations and epigenetic alterations in gastric epithelial cells during chronic gastritis may contribute to an increased risk of gastric cancer associated with H. pylori infection. [ABSTRACT FROM AUTHOR]

Helicobacer pyloriinfection is a major gastric cancer risk factor. Deficient DNA mismatch repair (MMR) caused byH. pylorimay underlie microsatellite instability (MSI) in the gastric epithelium and may represent a major mechanism of mutation accumulation in the gastric mucosa during the early stages ofH. pylori-associated gastric carcinogenesis. In this study, we examined the expression of DNA MMR protein (hMLH1 and hMSH2) in patients with chronicH. pyloriinfection before and after eradication of the infection.Gastric tissue samples were collected from 60 patients withH. pylorigastritis and peptic ulcer disease before and after eradication of the infection. The DNA MMR protein expression (hMLH1 and hMSH2) was determined by immunohistochemical staining in 60 patients before and afterH. pylorieradication. The percentage of epithelial cell nuclei and intensity of staining were then compared in gastric biopsies before and after eradication.The percentage of hMLH1 (76.60 ± 20.27, 84.82 ± 12.73,p = .01) and hMSH2 (82.36 ± 12.86, 88.11 ± 9.27,p < .05) positive epithelial cells significantly increased in 53 patients who becameH. pylori-negative after eradication therapy. However, the intensity of hMLH1 and hMSH2 staining was not significantly different. In those 7 patients, who did not respond to the eradication therapy and were stillH. pylori-positive, the percent positivity and intensity of hMLH1 and hMSH2 staining did not change.The expression of DNA MMR proteins increased in the gastric mucosa afterH. pylorieradication, indicating thatH. pylorigastritis may be associated with a reduced DNA MMR system during infection. The effect ofH. pyloriinfection on MMR protein expression appears to be at least partially reversible afterH. pylorieradication. These data suggest thatH. pylorigastritis might lead to a deficiency of DNA MMR in gastric epithelium that may increase the risk of mutation accumulation in the gastric mucosa cells during chronicH. pyloriinfection. [ABSTRACT FROM AUTHOR]

Background. The β-lactam group of antibiotics kills bacteria by inhibiting the terminal stages of peptidoglycan metabolism. We have recently identified amoxicillin-resistant Helicobacter pylori, none of which expressed β-lactamase. Penicillin-binding proteins (PBPs) represent a group of target enzymes for the β-lactam antibiotic family, and alterations in PBPs have been described in other penicillin-resistant bacteria. The amoxicillin-resistant phenotype characteristically was lost after freezing but could be restored by consecutive transfers into gradient plates. Materials and Methods. To determine whether amoxicillin resistance in H. pylori was related to alterations in any of the H. pylori PBPs, five H. pylori strains resistant to amoxicillin and three amoxicillin-sensitive strains were tested. PBPs were extracted from bacteria grown to logarithmic phase, labeled in vivo with 3H-benzylpenicillin, and analyzed by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) and fluorography. Four main PBPs were separated from all amoxicillin-sensitive H. pylori strains. Results. Only three of the four main PBPs were found in the amoxicillin-resistant H. pylori strains. The differentially detectable PBP (PBP D) had an apparent molecular weight of 30 to 32 kD. Conclusion. These results suggest that PBP D might play a role in the amoxicillin-resistant phenotype of H. pylori strains lacking β-lactamase activity. [ABSTRACT FROM AUTHOR]