Gastric carcinoma: failed adaptation to Helicobacter pylori

Helicobacter pylori

Helicobacter pylori infection causes peptic ulcer disease, gastric adenocarcinoma, gastric lymphoma, and probably nonulcer dyspepsia. Although the prevalence of infection is declining over time, the organism still infects approximately one half of the world's population. Only a minority will ever suffer serious consequences from their infection. This article reviews current knowledge about H. pylori and presents some of the dilemmas surrounding clinical and public health approaches to this widespread pathogen.

How does Helicobacter pylori cause mucosal damage? Its effect on acid and gastrin physiology

Helicobacter pylori infection increases gastric acid secretion in patients with duodenal ulcers but diminishes acid output in patients with gastric cancer and their relatives. Investigation of the basic mechanisms may show how H. pylori causes different diseases in different persons. Infection of the gastric antrum increases gastrin release. Certain cytokines released in H. pylori gastritis, such as tumor necrosis factor alpha and specific products of H. pylori, such as ammonia, release gastrin from G cells and might be responsible. The infection also diminishes mucosal expression of somatostatin. Exposure of canine D cells to tumor necrosis factor alpha in vitro reproduces this effect. These changes in gastrin and somatostatin increase acid secretion and lead to duodenal ulceration. But the acid response depends on the state of the gastric corpus mucosa. The net effect of corpus gastritis is to decrease acid secretion. Specific products of H. pylori inhibit parietal cells. Also, interleukin 1 beta, which is overexpressed in H. pylori gastritis, inhibits both parietal cells and histamine release from enterochromaffin-like cells. H. pylori also promotes gastric atrophy, leading to loss of parietal cells. Factors such as a high-salt diet and a lack of dietary antioxidants, which also increase corpus gastritis and atrophy, may protect against duodenal ulcers by decreasing acid output. However, the resulting increase of intragastric pH may predispose to gastric cancer by allowing other bacteria to persist and produce carcinogens in the stomach.

Helicobacter pylori may cause "reflux" gastritis after gastrectomy

Patients with "reflux" gastritis after gastrectomy suffer from a variety of symptoms, and this type of gastritis may sometimes compromise the quality of life of these patients. Since Helicobacter pylori is considered to be one of the most important pathogenetic factors in gastritis, the association between H. pylori and reflux gastritis was investigated in this study. A total of 145 patients with gastrectomy were entered into the study. Five biopsy specimens from the gastric remnant were taken at upper gastrointestinal endoscopy. One specimen was examined pathohistologically, and the remaining four were examined for H. pylori infection. Fifty-two patients (36%) demonstrated H. pylori infection. The prevalence of H. pylori was significantly higher in patients who had a partial gastrectomy, and it was significantly lower in patients who had undergone gastrectomy more than 4 years previously. The histologic gastritis score in patients with H. pylori infection was significantly higher. Furthermore, H. pylori was eradicated in patients with some symptoms of gastritis and no bile reflux to the residual stomach at endoscopy; in these patients the symptoms were relieved and the histologic gastritis score decreased significantly. In conclusion, possible involvement of H. pylori is suspected in the pathogenesis of "nonreflux" gastritis after gastrectomy.

Country-specific constancy by age in cagA+ proportion of Helicobacter pylori infections

Helicobacter pylori strains may be either cagA+ or cagA-, and in logitudinal studies, infection with a cagA+ strain has been associated with increased risk for the development of atrophic gastritis and cancer of the distal stomach. We sought to determine the relative proportion of strains producing CagA in different geographic locales, and the extent to which CagA seroprevalence varied in countries with different gastric and esophageal cancer rates. Using an enzyme-linked immunosorbent assay (ELISA) to detect serum IgG to CagA, we examined sera from 468 asymptomatic H. pylori-infected adults from Canada, Peru, China, Thailand, The Netherlands and 3 different ethnic groups in New Zealand. The CagA seroprevalence in Peru and Thailand (82.2% and 78.8%, respectively) were each substantially higher than for the Chinese (37.9%), Canadian (41.9%), Dutch (39.0%) and New Zealand (28.2%) subjects, but within each population, rates were relatively constant across gender and age groups. Reported gastric but not esophageal cancer rates for the 8 studied populations were significantly associated with H. pylori seroprevalence. Variation in CagA positivity rates was not significantly associated with variation in either gastric or esophageal cancer rates. Our data suggest that CagA seroprevalence is not the major factor influencing gastric cancer rates.

Significance of Helicobacter pylori infection as a risk factor in gastric cancer: serological and histological studies

We conducted a case-control study to examine the association of Helicobacter pylori infection as a risk factor in gastric cancer in the Japanese population. Serum IgG antibodies for Helicobacter pylori were determined in 55 consecutive patients with gastric cancer and in 75 age- and sex-matched mass survey subjects and 57 age- and sex-matched cancer-free patients with conditions considered at a high risk for development of gastric cancer (precancerous condition). We examined the histology in all subjects and particular focus was placed on the extent of Helicobacter pylori-associated gastritis. The seroprevalence of Helicobacter pylori in gastric cancer patients (82%) and those with a precancerous condition (89%) was significantly higher (P < 0.005) than that in the mass survey subjects (60%). Positive relative risk associations were found for patients with gastric cancer (odds ratio, 3, with 95% confidence intervals of 1.69-5.33) and those with a precancerous condition (odds ratio, 5.66, with 95% confidence intervals 2.66-12.03). Significant differences were found when comparisons were made among the case-control groups who were H. pylori-positive and had inflammatory cell infiltration (P = 0.0127). The characteristics of Helicobacter pylori in histologically examined gastric mucosa showed differences between Helicobacter pylori-infected and uninfected persons in all groups. However, for none of these groups was there a significant differences between background mucosa for Helicobacter pylori-infected persons with or without gastric cancer. Helicobacter pylori seroprevalence is strongly associated with an increased risk of gastric cancer and with a precancerous condition; histological investigation did not define additional factors that might be associated with increased cancer risk.

Pathophysiology of Helicobacter pylori-induced gastritis and peptic ulcer disease

Helicobacter pylori causes persistent infection and inflammation in the human stomach, yet only a small fraction of persons harboring this organism develop peptic ulcer disease. An important question is why this variation in infection outcome exists. Recent studies have demonstrated that H pylori isolates possess substantial phenotypic and genotypic diversity that may engender differential host inflammatory responses that influence clinical outcome. Further investigation in this field may help to define which H pylori-infected persons bear the highest risk for subsequent development of peptic ulcer disease, and thus enable physicians to focus eradication therapy.

Synchronous adenocarcinoma and low grade B-cell lymphoma of mucosa associated lymphoid tissue (MALT) of the stomach

We describe nine cases of gastric adenocarcinoma (six intestinal and three diffuse type) occurring in the stomach synchronously with primary low grade B-cell lymphoma of mucosa associated lymphoid tissue. In four cases the two neoplasms were admixed to form collision tumours. Where collision was present between lymphoma and adenocarcinoma of intestinal type no lymphoepithelial lesions were seen involving neoplastic glands. Helicobacter pylori-like organisms were seen in seven cases (78%) which is consistent with an aetiological role for this organism in both tumours in the stomach.

The somatostatin-gastrin link of Helicobacter pylori infection

Helicobacter pylori is the new-found cause of duodenal ulcers (DU), but acid secretion remains necessary and is elevated in DU patients. My group and others have asked whether H. pylori itself alters gastric physiology. This infection has been found to decrease local expression of the inhibitory peptide somatostatin, and to increase release of the acid-stimulating hormone gastrin. H. pylori infection can alter acid secretion in both directions. Acid disappears temporarily on first infection, and may dwindle later if H. pylori causes gastric atrophy. DU patients have approximately twice the normal parietal cell mass, which increases their maximal secretory capacity, but it is not clear whether or not this is due to H. pylori. However, the infection certainly does change physiological control of acid secretion, as expected from the endocrine changes. Acid secretion is elevated during fasting, during stimulation with an acidic meal and during infusions of gastrin-releasing peptide. The balance between these opposing effects of H. pylori on acid may be crucial in determining the clinical outcome of H. pylori infection. High-acid secretion leads to DUs whilst low acid secretion is found in patients with gastric ulcers and gastric cancer. Inflammatory cytokines released in H. pylori gastritis may cause some of these changes in gastric physiology.

Lack of association of Helicobacter pylori seroprevalence and gastric cancer in a population with low gastric cancer incidence

BACKGROUND

Previous studies have suggested that infection with Helicobacter pylori is associated with an increased risk of gastric adenocarcinoma.

METHODS

We examined the sera of 111 Caucasian patients with histologically confirmed gastric cancer (36 with cancer of the cardia, 70 with cancer of the body or antrum, and 5 with stump carcinomas after Billroth-II procedures) and 111 age-matched controls with colorectal carcinomas for the presence of H. pylori IgG antibodies by enzyme-linked immunoassay.

RESULTS

The overall prevalence of H. pylori infection was 58.6% (65 of 111) in gastric cancer patients as compared with 50.5% (56 of 111) in matched control subjects (odds ratio, 1.39; 95% confidence interval, 0.82 to 2.36). Carcinomas of the cardia were not linked to H. pylori infection (odds ratio, 1.25; 95% confidence interval, 0.65 to 2.46), nor diffuse or intestinal-type carcinomas (odds ratios, 1.79 and 1.0; 95% confidence intervals, 0.69 to 4.67 and 0.34 to 2.91, respectively). Age, sex, and height of the IgG immune response did not affect risk.

CONCLUSIONS

In contrast to previous results, these data do not provide evidence that the contribution of H. pylori infection to the carcinogenesis of gastric cancer is of major significance in a population with low gastric cancer rates and with high socioeconomic status.

Pathogenic mechanisms

Research is asking how H. pylori causes diseases, and also why the same bacteria produces different conditions in different persons. The process involves bacterial factors and the host's response. Some bacterial factors such as urease are produced by all strains of H. pylori. This enzyme may damage the gastric epithelium by practically releasing ammonia. Other bacterial factors such as vacuolating toxin are only produced by some strains, and these strains are more likely to cause ulcers or cancer. The host's response has been studied by physiologists, immunologists, and histologists, but the separation of systems is artificial. For example, physiologists find that H. pylori stops gastric D-cells from expressing somatostatin normally, which impairs reflex inhibition of acid secretion, but the D-cell malfunction is probably due to inflammatory factors. In H. pylori gastritis, the gastric epithelial cells behave like immunocytes and express class II molecules and cytokines such as interleukin-8. The patient's histological response to H. pylori is quite closely related to the disease outcome. Patients who respond by developing gastric atrophy are more likely to get gastric ulcers or stomach cancer, but patients whose gastric corpus remains healthy tend to secrete more acid and develop duodenal ulcers, particularly if they have gastric metaplasia in their duodenum. Studies of disease mechanisms provide a valuable insight into the development of these common diseases, and may enable us to identify at-risk groups who particularly merit eradication therapy.

Helicobacter pylori infection increases following cholecystectomy

Cholecystectomy is frequently linked with duodenogastric reflux and gastritis but its effect on Helicobacter Pylori (H pylori) infection has not been examined. In a prospective study, twenty two patients with documented cholelithiasis underwent upper gastrointestinal endoscopy and biopsy and 24hr dual channel pH monitoring prior to cholecystectomy and again at 3-6 months post-operatively. The antral biopsies were histologically assessed for H pylori and gastritis and awarded an alkaline reflux score. The number of patients with H pylori infection increased from 7 (32%) preoperatively to 15 (68%) post-cholecystectomy (p < 0.05). Cholecystectomy was also associated with an increase in the incidence of gastritis from 7 to 15 (p < 0.05). The increase in H pylori infection rate occurred in association with an increase in the percentage time gastric pH > 4 in the supine position, from 9.6 (2.2) to 22.2 (4.8) percent, (p < 0.01). The median chemical gastritis score, however, did not change significantly following surgery [8(3-11) vs 7(3-11)]. Seven patients remained symptomatic following cholecystectomy all of whom were H pylori positive and had gastritis. H pylori can survive in the alkaline environment which follows cholecystectomy and may contribute to the post-cholecystectomy syndrome.

Helicobacter pylori infection in children with recurrent abdominal pain

Helicobacter pylori was cultured and Helicobacter-like organisms (HLO) were seen in 6 (16%) of 37 children with recurrent abdominal pain. Five children had concomitant histological inflammation, but none had endoscopic changes. All 6 children demonstrated positive serology. Compared with the total group, they were more often from developing countries, larger families and lower social groups. Treatment with phenoxymethyl penicillin and colloidal bismuth subcitrate did not result in side effects or elevated serum levels of serum bismuth. Three children demonstrated metronidazole-resistant strains and the treatment of these children remained an unsolved problem. Among the 31 H. pylori/HLO negative children 8 (26%) demonstrated histological changes, 5 (16%) endoscopic changes and 11 (35%) had positive serology. In conclusion, pathological findings at upper gastrointestinal endoscopy are common in children with recurrent abdominal pain. Because of disconcordance between endoscopy, histology and culture, we recommend that biopsies should always be taken to clarify the diagnosis.

Helicobacter pylori gastritis in dyspeptic children. A long-term follow-up after treatment with colloidal bismuth subcitrate and tinidazole

The connection between dyspeptic symptoms and Helicobacter pylori infection was studied prospectively in 21 children treated for verified H. pylori infection with bismuth subcitrate and tinidazole. Gastroscopy with biopsy was performed before and a mean of 4 months after discontinuation of the treatment. A second post-treatment check with determination of H. pylori antibodies and serum pepsinogen 1 level was made a mean of 1.5 years after cessation of treatment. The therapy given cleared the bacteria in 67% of the patients. No significant difference in symptoms was observed between treatment successes and failures. The histopathologic diagnosis of H. pylori infection was accompanied by positive IgG serology in 15 (75%) of the 20 patients tested, and a decrease in antibody levels was observed in children with successful eradication. Serum pepsinogen 1 seemed to be even a better marker in the follow-up. The healing of acute and also to some extent of chronic gastritis took place closely after successful eradication. Our results suggest that healing of H. pylori-induced gastritis should be confirmed at reendoscopy only, independent of the symptoms.

Gastric cancer--a long-term consequence of Helicobacter pylori infection?

Chronic gastritis and chronic atrophic gastritis in particular are risk factors for gastric cancer. In Western societies, for example Finland, up to 70% of gastric cancer cases are associated with Helicobacter pylori-positive chronic non-atrophic or atrophic gastritis, approximately 15% appear in conjunction with autoimmune chronic corpus-limited H. pylori-negative atrophic gastritis, and 15% develop in individuals with a histologically normal stomach. The role of H. pylori infection in chronic gastritis has led to the hypothesis that this infection could be involved in the pathogenesis of gastric cancer. There are three main factors in support of this hypothesis: (i) H. pylori infection is the single causal aetiological agent in more than 80% of cases with chronic gastritis; (ii) H. pylori-positive chronic gastritis will develop into mucosal atrophy (atrophic gastritis) and intestinal metaplasia in a large proportion of affected individuals; (iii) the risk of gastric cancer is known to be high in people with chronic gastritis, and particularly in those with atrophic gastritis. In addition, there exists some correlation between the rates of H. pylori infection and gastric cancer mortality worldwide, and H. pylori infection relates to socioeconomic conditions known to associate with gastric cancer. Although H. pylori-positive gastritis cannot be considered a single and direct cause of gastric cancer, it is strongly associated with it and may trigger a cascade of events in the gastric mucosa that results in the development of gastric cancer in some patients.