No abstract

Helicobacter pylori infection has been considered as a risk factor for gastric carcinoma. Strong evidence exists that reactive oxygen species (ROS) play an important role in carcinogenesis, and in vivo investigations have shown increased synthesis of ROS in the gastric mucosa of H.pylori-infected patients. In the present study the direct effects of H.pylori on ROS and DNA synthesis, induction of apoptosis and DNA repair were investigated in the gastric epithelial cell lines AGS and HM02. Incubation of gastric cells with H.pylori extract induced the synthesis of ROS, diminished the levels of reduced glutathione (GSH), induced DNA fragmentation and increased DNA synthesis in gastric cells. Poly(ADP-ribose) formation was increased in gastric cells exposed to H.pylori extract. FACS analysis of gastric cells exposed to H.pylori extract did not reveal any change in the percentage of cells in the G(2)/M phase of the cell cycle. The radical scavengers MnTBAP (a cell permeable superoxide dismutase mimic), ebselen (a GSH peroxidase mimic) and high doses of catalase completely blocked H.pylori extract-induced elevation in DNA synthesis. Our results indicate that H.pylori extract directly induces the synthesis of ROS in gastric epithelial cells and causes DNA damage.

The effect of food intake and gut bacterial flora on gastrointestinal lesions caused by oral indometacin (IND) was studied in rats. A dose of 10 mg/kg IND caused no intestinal lesions when the animals were starved before and after treatment; it produced moderate lesions when the animals were continuously fed and maximal lesions when the animals were fed in the postdrug period after starvation in the predrug period. Under germ-free conditions, 15 mg/kg IND induced significantly less intestinal lesions than under specific pathogen-free conditions. The differences in the magnitude of intestinal lesions under the varying feeding and maintenance conditions were not associated with different IND concentrations in the jejunal mucosa. The dose of 10 mg/kg IND produced most gastric lesions when the animals were previously starved for 24 h and subsequently fed, medium lesions in continuously starved animals and only a few lesions in animals fed before and after IND. The disposition of IND from the gastric mucosa did not differ under the different feeding conditions. As the dose of IND is high enough to inhibit prostaglandin synthesis, it was concluded that additional factors are important for the development of gastrointestinal lesions caused by IND. Secondary bile acids in conjunction with IND are important for the development of intestinal lesions, while gastric acid influences the intensity of gastric lesions.

Heat stability was determined by heating the H.pylori cytosolic extract to 95°C for 30 min. For digestion of protein, the bacterial extract was incubated with 0.1 µg/ml trypsin for 2 h at 37°C. The reaction was stopped with soy bean trypsin inhibitor. For preliminary sizing of the protein, the cytosolic