Mucosa-related bacteria in the stomach

Helicobacter pylori CagA: From Pathogenic Mechanisms to Its Use as an Anti-Cancer Vaccine

Helicobacter pylori colonizes the gastric mucosa of more than 50% of the human population, causing chronic inflammation, which however is largely asymptomatic. Nevertheless, H. pylori-infected subjects can develop chronic gastritis, peptic ulcer, gastric mucosa-associated lymphoid tissue lymphoma, and gastric cancer. Chronic exposure to the pathogen and its ability to induce epithelial to mesenchymal transition (EMT) through the injection of cytotoxin-associated gene A into gastric epithelial cells may be key triggers of carcinogenesis. By deregulating cell-cell and cell-matrix interactions as well as DNA methylation, histone modifications, expression of micro RNAs, and resistance to apoptosis, EMT can actively contribute to early stages of the cancer formation. Host response to the infection significantly contributes to disease development and the concomitance of particular genotypes of both pathogen and host may turn into the most severe outcomes. T regulatory cells (Treg) have been recently demonstrated to play an important role in H. pylori-related disease development and at the same time the Treg-induced tolerance has been proposed as a possible mechanism that leads to less severe disease. Efficacy of antibiotic therapies of H. pylori infection has significantly dropped. Unfortunately, no vaccine against H. pylori is currently licensed, and protective immunity mechanisms against H. pylori are only partially understood. In spite of promising results obtained in animal models of infection with a number of vaccine candidates, few clinical trials have been conducted so far and with no satisfactory outcomes. However, prophylactic vaccination may be the only means to efficiently prevent H. pylori-associated cancers.

Profiling of microdissected gastric epithelial cells reveals a cell type-specific response to Helicobacter pylori infection

BACKGROUND AND AIMS

Helicobacter pylori colonizes the epithelial lining of the human stomach and is associated with disorders ranging from chronic gastritis to peptic ulcers and gastric cancer. We have explored the transcriptional response of the epithelium globally by applying a whole-genome approach to a murine model of infection.

METHODS

The 3 major epithelial lineages of the stomach-the parietal, mucus-producing, and chief cells-were harvested from cryosections of infected and uninfected murine stomachs by laser microdissection and subjected to gene expression profiling. The localization and quantity of selected transcripts were verified by in situ hybridization and quantitative real-time reverse-transcription polymerase chain reaction.

RESULTS

Each cell type is characterized by a transcriptional signature profile. The parietal cell profile is highly enriched for factors involved in mitochondrial energy generation, whereas the chief cell predominantly expresses digestive enzymes and glycosylation-associated proteins. In contrast, the mucus cell signature is distinguished by an abundance of cell-surface receptors, signaling molecules, and factors involved in antigen presentation. All of these indicate a role in sampling, sensing, and responding to environmental stimuli. In line with this biological function, we measured a strong transcriptional response to Helicobacter pylori infection only in this cell type. The genes that are differentially expressed upon infection are implicated in a proinflammatory and mucosal defense response as well as modulation of angiogenesis, iron availability, and tumor suppression.

CONCLUSIONS

Laser microdissection-assisted transcriptional profiling is a useful tool to explore the biology of specific cell populations and is sensitive enough to measure the transcriptional response to bacterial infection in vivo.

Duodenal ulcer, Helicobacter pylori, and gastric secretion

Patients with chronic dyspepsia were categorised by macroscopic appearance at oesophagogastroduodenoscopy as having duodenal ulceration (DU), other diagnosed lesions such as reflux oesophagitis, carcinoma of stomach, etc, or no organic lesion (non-ulcer dyspepsia, NUD). Material was collected to identify gastric infection with Helicobacter pylori (H pylori) by CP urease test, culture, and histological examination and to make the microscopic diagnosis of active chronic gastritis. Each patient in the DU and NUD categories was then invited to volunteer for a gastric secretion study in which maximal gastric secretion in response to histamine was measured. Sixty two gastric secretion tests were performed (31 DU, 31 NUD). The presence of H pylori was associated with active chronic gastritis (100%). DU patients secreted more acid than the NUD patients. H pylori positivity was associated with decreased maximal gastric secretion in both groups. There was a positive correlation between smoking and maximal acid output shown only in H pylori negative but not in H pylori positive patients. These findings were clear cut when all corrections of maximal gastric secretion were made for pyloric loss, duodenogastric reflux, and stature. This study failed to show any aetiological link between H pylori and DU by increased maximal gastric secretion.

Does the stomach adapt to Helicobacter pylori?

To shed some light on the question of gastric adaptation to Helicobacter pylori infection, an overview is given of the various histopathological and clinical consequences of H. pylori infection in man. H. pylori infection can be considered as a chronic bacterial infection. For many individuals there is a balance between a low degree of infection and a low degree of inflammation. The microbial or host factors in adaptation of this balance are largely unknown. If and how 'downregulation' of the inflammatory/immune response does occur need further study.

Helicobacter pylori and gastric acid output in peptic ulcer disease

Helicobacter pylori is associated with peptic ulcer, and a causal relationship has been postulated. We investigated the association between Helicobacter pylori and gastric acid output. Two hundred forty-one patients were studied: 173 with duodenal ulcer, 51 with gastric ulcer (41 corpus, 10 prepyloric), and 17 with combined gastric and duodenal ulcer. In 194 patients (80%), Helicobacter pylori could be demonstrated histologically from gastric antral biopsies. The presence or absence of Helicobacter pylori was not influenced by age, sex, or use of tobacco or analgesics. Patients with duodenal ulcer or combined gastric and duodenal ulcer had similar gastric acid outputs irrespective of the presence or absence of Helicobacter pylori. However, gastric ulcer patients with Helicobacter had higher basal and maximal acid outputs when compared to patients without Helicobacter (mean basal output: 4.1 mmol/hr vs 2.4, P less than 0.05; mean maximal output 19.5 mmol/hr vs. 14.4, P less than 0.05). Although Helicobacter pylori is associated with both gastric ulcer and duodenal ulcer, its significance may be different in the two diseases.

Inappropriate hypergastrinaemia in asymptomatic healthy subjects infected with Helicobacter pylori

An ELISA test determined serologically that eight of 95 apparently healthy men (aged 19-26 years) had an asymptomatic infection with Helicobacter pylori at the time of simultaneous measurement of 24 hour intragastric acidity and 24 hour plasma gastrin concentration. There was no significant difference in the median integrated 24 hour intragastric acidity between the H. pylori positive and H. pylori negative subjects (688 and 842 mmol/h/l; p = 0.271, respectively), whereas the median integrated 24 hour plasma gastrin concentration was significantly higher in the H pylori positive than in the H pylori negative subjects (389 and 198 pmol/h/l; p less than 0.001). Longterm hypergastrinaemia, associated with persistent H pylori infection, could be a cause of the increased parietal cell mass that is considered characteristic of duodenal ulcer patients.

Nitrofurans in the treatment of gastritis associated with Campylobacter pylori. The Gastrointestinal Physiology Working Group of Cayetano Heredia and The Johns Hopkins Universities

We conducted a double-blind, placebo-controlled, randomized treatment study in Peruvian adults with antral gastritis associated with Campylobacter pylori. Patients received either 400 mg of furazolidone (n = 14), 400 mg of nitrofurantoin (n = 24), or a placebo (n = 31) for 14 days. Endoscopy was carried out at baseline, 1 day after ceasing therapy, and 6 wk after the end of treatment to verify colonization by C. pylori and determine the extent of gastric inflammation. Treatment with nitrofurantoin or furazolidone markedly reduced or, in some cases, cleared C. pylori from the antrum (p less than 0.0005 compared with placebo). Resolution of acute gastric inflammation, as evidenced by decreased polymorphonuclear leukocyte infiltration and regeneration of the mucus layer, paralleled the reduction in bacterial colonization (p less than 0.005 compared with placebo). A high percentage of patients experienced relapse (recolonization by C. pylori and return to pretreatment levels of gastritis) within 6 wk after cessation of treatment. Significant relief of dyspeptic symptoms was not evident during the study.

Acid secretion and serum gastrin levels in individuals with Campylobacter pylori

Campylobacter pylori may cause gastritis and has been proposed as an etiologic factor in the development of peptic ulcer. However, it may be an acid-sensitive microbe and before it can be implicated in the pathogenesis of peptic ulcer, it should be consistently found in ulcer patients with normal acid secretion. Thirty-six patients with C. pylori by Warthin-Starry stain underwent gastric analysis; 25 were normochlorhydric and 11 hypochlorhydric. Ulcers were present in 19 normochlorhydric patients (10, gastric; 9, duodenal) and 2 hypochlorhydric patients (gastric). Median basal acid output was higher for those with duodenal ulcer (38 mmol/h) than gastric ulcer (28 mmol/h) or miscellaneous endoscopic features (33 mmol/h). The hypergastrinemia seen in 12 patients with negative secretin provocation tests was believed to be due to various nongastrinoma conditions. Campylobacter pylori was found in 6 normogastrinemic patients with elevated acid output and in 1 gastrinoma patient with marked acid hypersecretion. Histologic chronic gastritis was present in all subjects and 29 had active chronic gastritis. Twenty-three patients were taking H2-receptor antagonists at the time of diagnosis which did not seem to interfere with culture results. Using standard acid secretory tests, we conclude that C. pylori can survive in a wide range of acid conditions.

Campylobacter like organisms in duodenal and antral endoscopic biopsies: relationship to inflammation

In 66 endoscopic duodenal biopsies studied retrospectively and in 84 paired duodenal and antral biopsies assessed prospectively campylobacter like organisms were seen in 22 (33%) of the retrospectively examined duodenal biopsies and in 61 (73%) examined prospectively, and in 70 (83%) of antral biopsies. In the duodenum the organisms were mostly confined to the surface epithelium in areas showing gastric metaplasia, while in the antrum they were also found within superficial glands. A strong association was shown between the presence of campylobacter like organisms and histological active duodenal inflammation.

Clinical importance of Campylobacter pyloridis and associated serum IgG and IgA antibody responses in patients undergoing upper gastrointestinal endoscopy

Campylobacter pyloridis was isolated from 77% of 220 (35%) unselected adults undergoing gastroscopy. Isolation was significantly associated with histological gastritis (p less than 0.0001), duodenal ulcer (p less than 0.0001), and to a much lesser extent, with gastric ulcer (p less than 0.05). The relation between the isolation of C pyloridis and peptic ulcer seemed to be independent of coexisting gastritis. In those with no endoscopic or histological evidence of disease there was no relation between isolation and increasing age. Antibody responses to a whole cell sonicate of a strain of C pyloridis were measured by means of an enzyme linked immunosorbent assay (ELISA). Increased IgA (p less than 0.0001) and IgG (p less than 0.0001) antibody titres were found in patients with C pyloridis. Peptic ulceration or gastritis were present in 78% and 100% of patients with a high concentration of IgG and IgA, respectively, but in only 9% and 18% of those with low titres. These results provide further evidence for a possible pathogenic role of these organisms in gastric disease and suggest that immunological markers of their presence might be useful non-invasive indicators of disease.