Effects of cyclooxygenase-2 inhibitor on gastric acid secretion in Helicobacter pylori-infected C57BL/6 mice

A human mode of intestinal type gastric carcinoma

Gastric cancer is a malignant tumor originating from the gastric mucosa epithelium. Intestinal type gastric cancer is frequently taken on elderly men, and there are many high incidence areas around the world. Intestinal type gastric cancer often is accompanied by gastric mucosal atrophy, intestinal metaplasia. The clinical manifestation involves hypergastrinemia, low stomach acid, PG I/II progressive decreasing, anemia, and protein energy malnutrition. The neck cells of gastric glands act as tissue stem cells to regenerate the gastric glands. In addition to secreting gastric acid and intrinsic factor, the parietal cells also have the function of inducing differentiation of themselves and gastric epithelial cells. When the function of parietal cells is normal, the neck cells differentiate into mature cells, and the glands regenerate intact. When the function of parietal cells is defective, the neck cells maybe differentiate into mature intestinal cells, and the gastric glands will regenerate in form of the intestinal metaplasia. When the function of parietal cells is lost, the neck cells can not differentiate into mature cells successfully, and the accumulation of immature cells in gastric mucosal tissue forms atypical hyperplasia of different degrees and cancers of various differentiation grades. Any factors that can reduce the function of parietal cell could result in intestinal type gastric carcinogenesis. Adrenal cortical hypofunction can make the parietal cell hypofunction, hypohematopoiesis, protein synthesis rates reducing and protein degradation rates increasing. The patients develop gastric cancer, and come with lack of gastric acid and intrinsic factor, anemia, protein energy malnutrition. Autoimmune gastritis can produce parietal cell antibodies to damage parietal cells. Patients with autoimmune gastritis gastric exhibit hypergastrinemia, lack of gastric acid and internal factor, higher incidence of gastric cancer. H. pylori can damage gastric parietal cells directly and indirectly. When declining in quantity of parietal cells, the patients exhibit hypergastrinemia, low gastric acid, mucosa atrophy, intestinal metaplasia and gastric cancer. Medicine that inhibits the function of parietal cells also could increase the risk of gastric cancer development. The distribution of mucosa atrophy, intestinal metaplasia and intestinal type gastric cancer is opposite with the distribution of parietal cells in stomach. With age the quantity of parietal cells decreases, the atrophy area of gastric mucosa extends upward from antrum to body and downward from cardia to body along lesser curvature, and the location of distal gastric cancer moves upward and the gastric cardiac cancer increase.

Mouse models of gastric cancer

Animal models have greatly enriched our understanding of the molecular mechanisms of numerous types of cancers. Gastric cancer is one of the most common cancers worldwide, with a poor prognosis and high incidence of drug-resistance. However, most inbred strains of mice have proven resistant to gastric carcinogenesis. To establish useful models which mimic human gastric cancer phenotypes, investigators have utilized animals infected with Helicobacter species and treated with carcinogens. In addition, by exploiting genetic engineering, a variety of transgenic and knockout mouse models of gastric cancer have emerged, such as INS-GAS mice and TFF1 knockout mice. Investigators have used the combination of carcinogens and gene alteration to accelerate gastric cancer development, but rarely do mouse models show an aggressive and metastatic gastric cancer phenotype that could be relevant to preclinical studies, which may require more specific targeting of gastric progenitor cells. Here, we review current gastric carcinogenesis mouse models and provide our future perspectives on this field.

Interaction of Helicobacter pylori infection and nonsteroidal anti-inflammatory drugs in gastric and duodenal ulcers

BACKGROUND

Gastric (GU) and duodenal ulcers (DU) are in most instances either induced by Helicobacter pylori infection or by nonsteroidal anti-inflammatory drugs (NSAIDs). Whether eradication of H. pylori is beneficial in NSAID users for preventing NSAID induced GU and DU has been the focus of different studies.

MATERIALS AND METHODS

Mechanisms shared by both H. pylori and NSAIDs for the induction of GU and DU were reviewed and randomized controlled trials on H. pylori eradication for prevention and healing of GU and DU in patients requiring NSAID therapy were identified by a PubMed search.

RESULTS

Key factors in the induction of GU and DU for both H. pylori and NSAIDs are a decrease in pH, imbalance between apoptosis and proliferation, reduction in mucosal blood flow, and recruitment of polymorphonucleates in distinct compartments. For primary ulcer prevention, H. pylori eradication before starting an NSAID therapy reduces the risk of NSAID induced GU and virtually abolishes the risk of DU. H. pylori eradication alone is not sufficient for secondary prevention of NSAID induced GU and DU. H. pylori infection appears to further increase the protective effects of proton-pump inhibitors (PPI) to reduce the risk of ulcer relapse. H. pylori eradication does not influence the healing of both GU and DU if NSAID intake is discontinued.

CONCLUSIONS

Duodenal ulcer is more closely related to H. pylori infection than GU in NSAID users. H. pylori eradication is recommended for primary prevention of GU and DU in patients requiring NSAID therapy. PPI therapy is mandatory for secondary prevention of gastroduodenal ulcers, and appears to further reduce the risk of ulcer relapse in the presence of H. pylori.

Gastric acidity in patients with follicular gastritis is significantly reduced, but can be normalized after eradication for Helicobacter pylori

BACKGROUND

Follicular gastritis is thought to be caused by Helicobacter pylori infection. However, the pathophysiology of it remains unclear.

MATERIALS AND METHODS

We assessed gastric acidity in 15 patients with follicular gastritis, aged 20-37 years, using a 24-hour intragastric pH-metry, as well as by histologic and serologic evaluations; and compared it with that in other age-matched groups: 18 cases of H. pylori-positive antrum-predominant gastritis, 12 of pangastritis, and 24 H. pylori-negative normals. In eight cases with follicular gastritis, it was re-assessed 6 months after the eradication therapy for H. pylori.

RESULTS

During nighttime, the percentage of time with intragastric pH above 3.0 in follicular gastritis was significantly higher than that in normals (p<.0001), and in antrum-predominant gastritis (p<.001), but was comparable with that in pangastritis. In the daytime period, this parameter in follicular gastritis was significantly higher than that in normal (p<.001), in antrum-predominant gastritis (p<.001), and in pangastritis (p<.05). Marked mononuclear cell and neutrophil infiltration but no apparent glandular atrophy were observed in both the antrum and corpus. Serum pepsinogen I/II ratio was significantly lower in follicular gastritis than that in normals (p<.0001) and in antrum-predominant gastritis (p<.001), whereas serum gastrin was significantly higher than that in normals (p<.0001), in antrum-predominant gastritis (p<.01) and in pangastritis (p<.05). After eradication for H. pylori, all of the parameters in follicular gastritis were altered to the same ranges as those in normals.

CONCLUSIONS

In follicular gastritis, gastric acidity is significantly reduced, but can be normalized by eradication of H. pylori. It can thus be speculated that inflammatory cytokines or H. pylori-infection-induced prostaglandins might strongly inhibit gastric acid secretion in follicular gastritis.

COX-2-selective inhibitor, etodolac, suppresses choroidal neovascularization in a mice model

Cyclooxygenases (COXs) are involved in choroidal neovascularization (CNV). However, the relative contribution of COX-1 and -2 to CNV has not been determined. In this study, the expression of COX-2 was investigated in CNVs in a murine laser-induced model. Subsequently, we found that experimental CNV expressed COX-2, most remarkably around the highly vascularized lesions. To examine the effect of COX-2 inhibition on CNV, etodolac, a non-steroidal anti-inflammatory drug with a high COX-2 selectivity, was tested on murine CNV model. The results demonstrated that the intensity of fluorescein leakage from the photocoagulated lesions decreased significantly compared to the control eyes following etodolac administration. The area of CNV lesions, as examined using histological sections and choroidal flatmounts at day 7, demonstrated that the average size of the CNV lesions was significantly reduced in the etodolac-treated eyes compared to the control eyes. Together, our results demonstrated that selective COX-2 inhibition suppresses CNV.

Chronic Helicobacter pylori infection results in gastric hypoacidity and hypergastrinemia in wild-type mice but vagally induced hypersecretion in gastrin-deficient mice

Helicobacter pylori infection is a causal factor of gastric cancer (which is associated with low gastric acid secretion) or duodenal ulcer (high acid secretion). Parietal cells and ECL cells in the stomach are controlled by gastrin, which plays a crucial role in the regulation of acid secretion. The present study was undertaken to identify a possible role of gastrin in determining the different responses of the parietal cells and ECL cells to chronic H. pylori infection. Wild-type (C57BL/6J) gastrin(+/+) mice and gastrin(-/-) knockout mice, generated through targeted gene disruption and backcrossed eight times to C57BL/6J, were infected with H. pylori for 9 months. The acid output was measured 4 h after pylorus ligation (known to cause vagal excitation). The gastric mucosa was examined by immunocytochemistry with antisera to alpha-subunit of H+/K(+)-ATPase for the parietal cells, and to histamine and vesicle monoamine transporter-2 for the ECL cells, and by quantitative electron microscopy. In infected gastrin(+/+) mice, the acid output and the percentage of secreting parietal cells (freely fed state) were 20-30% of the values in uninfected controls, while the density and ultrastructure of parietal cells were normal. The infected mice had hypergastrinemia and displayed hypertrophy and hyperplasia of ECL cells. Although uninfected gastrin(-/-) mice had lower the acid output than uninfected gastrin(+/+) mice, there was a higher acid output (approximately 3 times) in infected gastrin(-/-) mice than their uninfected homologues. The numbers of parietal cells and ECL cells remained unchanged in infected gastrin(-/-) mice. In conclusion, chronic H. pylori infection results to impaired parietal-cell function (acid hyposecretion), hypergastrinemia and hyperplasia of ECL cells in wild-type mice but leads to vagally induced hypersecretion in gastrin-deficient mice.

Review article: How useful are the rodent animal models of gastric adenocarcinoma?

Gastric cancer is the second most common cause of cancer-related mortality world-wide. In most cases, it develops via the pre-malignant stages of atrophic gastritis, intestinal metaplasia and dysplasia, following Helicobacter pylori infection of susceptible individuals. A number of rodent models have recently provided valuable insights into the host, bacterial and environmental factors involved in gastric carcinogenesis. Wild-type rodents do not develop gastric adenocarcinoma, but early studies showed that the disease could be induced in several rodent species by chemical carcinogens. More recently, it has been demonstrated that gastric adenocarcinoma can be induced in Mongolian gerbils by H. pylori infection and in C57BL/6 mice by long-term H. felis infection. These models have allowed the importance of Helicobacter virulence genes, host factors, such as gender, strain and immune response, and environmental factors, such as dietary salt, to be explored. A number of transgenic mice with alterations in various pathways, including the immune response, gastrin biosynthesis, parietal cell development, growth factors and tumour suppressors, have also provided models of various stages of gastric carcinogenesis. One model that has proved to be particularly valuable is the hypergastrinaemic INS-GAS mouse, in which gastric carcinoma develops spontaneously in old animals, but the process is greatly accelerated by Helicobacter infection.