Inhibitory effect of etodolac, a selective cyclooxygenase-2 inhibitor, on stomach carcinogenesis in Helicobacter pylori-infected Mongolian gerbils

A comprehensive evaluation of an animal model for Helicobacter pylori-associated stomach cancer: Fact and controversy

Even though Helicobacter pylori infection was the most causative factor of gastric cancer, numerous in vivo studies failed to induce gastric cancer using H. pylori infection only. The utilization of established animal studies in cancer research is crucial as they aim to investigate the coincidental association between suspected oncogenes and pathogenesis as well as generate models for the development and testing of potential treatments. The methods to establish gastric cancer using infected animal models remain limited, diverse in methods, and showed different results. This study investigates the differences in animal models, which highlight different pathological results in gaster by literature research. Electronic databases searched were performed in PubMed, Science Direct, and Cochrane, without a period filter. A total of 135 articles were used in this study after a full-text assessment was conducted. The most frequent animal models used for gastric cancer were Mice, while Mongolian gerbils and Transgenic mice were the most susceptible model for gastric cancer associated with H. pylori infection. Additionally, transgenic mice showed that the susceptibility to gastric cancer progression was due to genetic and epigenetic factors. These studies showed that in Mongolian gerbil models, H. pylori could function as a single agent to trigger stomach cancer. However, most gastric cancer susceptibilities were not solely relying on H. pylori infection, and numerous factors are involved in cancer progression. Further study using Mongolian gerbils and Transgenic mice is crucial to conduct and establish the best models for gastric cancer associated H. pylori.

A comparative study: the prospective influence of nanovectors in leveraging the chemopreventive potential of COX-2 inhibitors against skin cancer

Introduction

This study was conducted to elucidate the chemopreventive potential, cytotoxic, and suppression of cellular metastatic activity of etodolac (ETD)-loaded nanocarriers.

Methods

To esteem the effect of charge and composition of the nanovectors on their performance, four types of vectors namely, negative lipid nanovesicles; phosalosomes (N-Phsoms), positive phosalosomes (P-Phsoms), nanostructured lipid carriers (NLCs) and polymeric alginate polymer (AlgNPs) were prepared and compared. ETD was used as a model cyclo-oxygenase-2 (COX-2) inhibitor to evaluate the potency of these nanovectors to increase ETD permeation and retention through human skin and cytotoxicity against squamous cell carcinoma cell line (SCC). Moreover, the chemopreventive activity of ETD nanovector on mice skin cancer model was evaluated.

Results

Among the utilized nanovectors, ETD-loaded N-Phsoms depicted spherical vesicles with the smallest particle size (202.96±2.37 nm) and a high zeta potential of −24.8±4.16 mV. N-Phsoms exhibited 1.5, and 3.6 folds increase in the ETD amount deposited in stratum corneum, epidermis and dermis. Moreover, cytotoxicity studies revealed a significant cytotoxic potential of such nanovector with IC₅₀=181.76 compared to free ETD (IC₅₀=982.75), correlated to enhanced cellular internalization. Its efficacy extended to a reduction in the relative tumor weight with 1.70 and 1.51-fold compared to positive control and free ETD, that manifested by a 1.72-fold reduction in both COX-2 and proliferating cell nuclear antigen mRNA (PCNA-mRNA) levels and 2.63-fold elevation in caspase-3 level in skin tumors relative to the positive control group with no hepato-and nephrotoxicity.

Conclusion

Encapsulation of ETD in nanovector enhances its in-vitro and in-vivo anti-tumor activity and opens the door for encapsulation of more relevant drugs.

Prevention of Gastric Cancer: Eradication of Helicobacter Pylori and Beyond

Although its prevalence is declining, gastric cancer remains a significant public health issue. The bacterium Helicobacter pylori is known to colonize the human stomach and induce chronic atrophic gastritis, intestinal metaplasia, and gastric cancer. Results using a Mongolian gerbil model revealed that H. pylori infection increased the incidence of carcinogen-induced adenocarcinoma, whereas curative treatment of H. pylori significantly lowered cancer incidence. Furthermore, some epidemiological studies have shown that eradication of H. pylori reduces the development of metachronous cancer in humans. However, other reports have warned that human cases of atrophic metaplastic gastritis are already at risk for gastric cancer development, even after eradication of these bacteria. In this article, we discuss the effectiveness of H. pylori eradication and the morphological changes that occur in gastric dysplasia/cancer lesions. We further assess the control of gastric cancer using various chemopreventive agents.

Helicobacter pylori infection, gastrin and cyclooxygenase-2 in gastric carcinogenesis

Gastric cancer is one of the most frequent neoplasms and a main cause of death worldwide, especially in China and Japan. Numerous epidemiological, animal and experimental studies support a positive association between chronic Helicobacter pylori (H. pylori) infection and the development of gastric cancer. However, the exact mechanism whereby H. pylori causes gastric carcinogenesis remains unclear. It has been demonstrated that expression of cyclooxygenase-2 (COX-2) is elevated in gastric carcinomas and in their precursor lesions. In this review, we present the latest clinical and experimental evidence showing the role of gastrin and COX-2 in H. pylori-infected patients and their possible association with gastric cancer risk.

Role of Helicobacter pylori in Gastric Neoplasia

Helicobacter pylori infection is one of the most important factors in gastric carcinogenesis in humans. Epidemiological studies have revealed that H. pylori-infected patients develop significantly more gastric cancers than uninfected individuals. In rodent models, H. pylori inoculation causes strong promoting effects in carcinogen-treated animals, whereas the bacterial infection alone causes only hyperplasic, atrophic, and/or metaplastic lesions. In both human and rodent models, eradication of H. pylori helps inhibit gastric carcinogenesis, especially when there is only mild gastric inflammation and no evidence of severe atrophy or intestinal metaplasia. Chemoprevention studies in humans have been reported and have shown the effectiveness of several medications including a cyclooxygenase-2 inhibitor. Candidate chemicals used in rodent models could hopefully be used in humans in the future.

Apigenin has anti-atrophic gastritis and anti-gastric cancer progression effects in Helicobacter pylori-infected Mongolian gerbils

ETHNOPHARMACOLOGICAL RELEVANCE

Apigenin, one of the most common flavonoids, is abundant in celery, parsley, chamomile, passionflower, and other vegetables and fruits. Celery is recognized as a medicinal vegetable in Oriental countries to traditionally treat inflammation, swelling, blood pressure, serum lipid, and toothache. In this study, we investigated apigenin treatment effects on Helicobacter pylori-induced atrophic gastritis and gastric cancer progression in Mongolian gerbils.

MATERIALS AND METHODS

Five to eight-week-old Mongolian gerbils were inoculated with Helicobacter pylori for four weeks without (atrophic gastritis group) or with N'-methyl-N'-nitro-N-nitroso-guanidine (MNNG) (gastric cancer group) in drinking water, and were then rested for two weeks. During the 7th-32th (atrophic gastritis group) or the 7th-52th (gastric cancer group) weeks, they were given various doses (0-60 mg/kgbw/day) of apigenin. At the end of the 32th (atrophic gastritis group) or the 52th (atrophic gastritis group) week, all Mongolian gerbils were sacrificed using the CO2 asphyxia method. The histological changes of Helicobacter pylori colonization, neutrophil and monocyte infiltrations, and atrophic gastritis in both atrophic gastritis and gastric cancer Mongolian gerbils were examined using immunohistochemistry stain and Sydney System scoring.

RESULTS

Apigenin treatments (30-60 mg/kgbw/day) effectively decreased atrophic gastritis (atrophic gastritis group) and dysplasia/gastric cancer (gastric cancer group) rates in Mongolian gerbils. Apigenin treatment (60 mg/kgbw/day) significantly decreased Helicobacter pylori colonization and Helicobacter pylori-induced histological changes of neutrophil and monocyte infiltrations and atrophic gastritis in both atrophic gastritis and gastric cancer Mongolian gerbils.

CONCLUSIONS

Apigenin has the remarkable ability to inhibit Helicobacter pylori-induced atrophic gastritis and gastric cancer progression as well as possessing potent anti-gastric cancer activity.

Cancer development based on chronic active gastritis and resulting gastric atrophy as assessed by serum levels of pepsinogen and Helicobacter pylori antibody titer

Our study investigated the relationship between gastric cancer development and activity of Helicobacter pylori-associated chronic gastritis or the resulting chronic atrophic gastritis (CAG). A cohort of 4,655 healthy asymptomatic subjects, in whom serum pepsinogen (PG) and H. pylori antibody titer had been measured to assess the activity and stage of H. pylori-associated chronic gastritis, was followed for up to 16 years, and cancer development was investigated. In subjects with a serologically diagnosed healthy stomach (H. pylori-negative/CAG-negative), cancer incidence rate was low, at 16/100,000 person-years. With the establishment of H. pylori infection and progression of chronic gastritis, significant stepwise cancer risk elevations were seen from CAG-free subjects (H. pylori-positive/CAG-negative) [hazard ratio (HR) = 8.9, 95% confidence interval (CI) = 2.7-54.7] to subjects with CAG (H. pylori-positive/CAG-positive) (HR = 17.7, 95% CI = 5.4-108.6) and finally to subjects with metaplastic gastritis (H. pylori-negative/CAG-positive) (HR = 69.7, 95% CI = 13.6-502.9). In H. pylori-infected CAG-free subjects, significantly elevated cancer risk was observed in the subgroup with active inflammation-based high PG II level or potent immune response-based high H. pylori antibody titer; the former was associated with a particularly high risk of diffuse-type cancer, and both subgroups showed high cancer incidence rates of around 250/100,000 person-years, comparable to that in subjects with CAG. No such risk elevation was observed in H. pylori-infected subjects with CAG. These results clearly indicate that gastric cancer develops mainly from the gastritis-atrophy-metaplasia-cancer sequence and partly from active inflammation-based direct carcinogenesis, and that serum levels of PG and H. pylori antibody titer provide indices of cancer development in H. pylori-infected subjects.

Endoscopic diagnosis of gastric intestinal metaplasia: a prospective multicenter study

BACKGROUND

Intestinal metaplasia (IM) of the gastric mucosa has long attracted attention as a premalignant lesion involved in gastric carcinogenesis. However, endoscopic diagnosis of IM has remained unclear for a long time. In recent years, the methylene blue staining technique and narrow-band imaging (NBI) magnifying endoscopy have facilitated clinical diagnosis of IM, although these methods have some problems due to their complexity. Simple methods for diagnosis of IM using conventional endoscopy and the indigo carmine contrast (IC) method are necessary.

PATIENTS AND METHODS

This study was a multicenter, prospective, randomized, comparative study involving 10 facilities. The appearance of IM was examined using conventional and IC methods with an electronic endoscope.

RESULTS

Subjects included 163 patients, of whom 87 and 76 underwent conventional and IC methods, respectively. Sensitivity, specificity, and receiver operating characteristic/area under thecurve (ROC/AUC) of conventional and IC methods for the detection of IM in the gastric antrum showed that diagnostic performance of the conventional method was higher, but not significantly, than that of the IC method. Sensitivity, specificity and ROC/AUC of conventional and IC methods for the detection of IM in the gastric body showed that the IC method yielded better (but not significantly better) results than the conventional method.

CONCLUSION

The diagnostic performance of the conventional method did not significantly differ from that of the IC method. A villous appearance, whitish mucosa, and rough mucosal surface, as observed by both methods, and areae gastricae pattern, as observed by the IC method, were useful indicators for endoscopic diagnosis of IM.

Gene expression analysis of a Helicobacter pylori-infected and high-salt diet-treated mouse gastric tumor model: identification of CD177 as a novel prognostic factor in patients with gastric cancer

BACKGROUND

Helicobacter pylori (H. pylori) infection and excessive salt intake are known as important risk factors for stomach cancer in humans. However, interactions of these two factors with gene expression profiles during gastric carcinogenesis remain unclear. In the present study, we investigated the global gene expression associated with stomach carcinogenesis and prognosis of human gastric cancer using a mouse model.

METHODS

To find candidate genes involved in stomach carcinogenesis, we firstly constructed a carcinogen-induced mouse gastric tumor model combined with H. pylori infection and high-salt diet. C57BL/6J mice were given N-methyl-N-nitrosourea in their drinking water and sacrificed after 40 weeks. Animals of a combination group were inoculated with H. pylori and fed a high-salt diet. Gene expression profiles in glandular stomach of the mice were investigated by oligonucleotide microarray. Second, we examined an availability of the candidate gene as prognostic factor for human patients. Immunohistochemical analysis of CD177, one of the up-regulated genes, was performed in human advanced gastric cancer specimens to evaluate the association with prognosis.

RESULTS

The multiplicity of gastric tumor in carcinogen-treated mice was significantly increased by combination of H. pylori infection and high-salt diet. In the microarray analysis, 35 and 31 more than two-fold up-regulated and down-regulated genes, respectively, were detected in the H. pylori-infection and high-salt diet combined group compared with the other groups. Quantitative RT-PCR confirmed significant over-expression of two candidate genes including Cd177 and Reg3g. On immunohistochemical analysis of CD177 in human advanced gastric cancer specimens, over-expression was evident in 33 (60.0%) of 55 cases, significantly correlating with a favorable prognosis (P = 0.0294). Multivariate analysis including clinicopathological factors as covariates revealed high expression of CD177 to be an independent prognostic factor for overall survival.

CONCLUSIONS

These results suggest that our mouse model combined with H. pylori infection and high-salt diet is useful for gene expression profiling in gastric carcinogenesis, providing evidence that CD177 is a novel prognostic factor for stomach cancer. This is the first report showing a prognostic correlation between CD177 expression and solid tumor behavior.

Helicobacter pylori infection and gastric carcinogenesis in rodent models

Helicobacter pylori infection is an important factor for gastric carcinogenesis in human. In carcinogen-treated Mongolian gerbils, H. pylori infection enhances stomach carcinogenesis, while infection alone induced severe hyperplasia called heterotopic proliferative glands. A high-salt diet or early acquisition of the bacteria exacerbates inflammation and carcinogenesis. Oxygen radical scavengers or anti-inflammatory chemicals as well as eradication of H. pylori are effective to prevent carcinogenesis. H. pylori-associated inflammation induces intestinal metaplasia and intestinalization of stomach cancers independently. It is necessary to control cancer development not only in H. pylori-positive cases but also in H. pylori-negative metaplastic gastritis.

Animal models of gastric cancer

Gastric cancer is the second most common cause of cancer-related mortality (9.7% of the total) worldwide. Gastric carcinogenesis is a multiple-step process that involves multiple factors, such as bacteria, immune response and host factors. Animal models play a crucial role in the research of the biological behavior, diagnosis and treatment of gastric cancer. In this article we will review current advances in the development of animal models of gastric cancer in terms of microorganism-induced models, chemical carcinogen-induced models, tumor cell implantation, genetically modified models and in silico models.

Mouse models of gastric tumors: Wnt activation and PGE2 induction

Accumulating evidence has suggested that cooperation of oncogenic activation and the host responses is important for cancer development. In gastric cancer, activation of Wnt signaling appears to be a major oncogenic pathway that causes tumorigenesis. In the chronic gastritis caused by Helicobacter pylori infection, cyclooxigenase-2 induces prostaglandin E(2) (PGE(2)) biosythesis, which plays an important role in tumorigenesis. We constructed a series of mouse models and investigated the role of each pathway in the gastric tumorigenesis. Wnt activation in gastric epithelial cells suppresses differentiation, and induces development of preneoplastic lesions. On the other hand, induction of the PGE(2) pathway in gastric mucosa induces development of spasmolytic polypeptide-expressing metaplasia (SPEM), which is a possible preneoplastic metaplasia. Importantly, simultaneous activation of Wnt and PGE(2) pathways leads to dysplastic gastric tumor development. Moreover, induction of the PGE(2) pathway also promotes gastric hamartoma development when bone morphogenetic protein (BMP) signaling is suppressed. These results indicate that alteration in the Wnt or BMP signaling impairs epithelial differentiation, and the PGE(2) pathway accelerates tumor formation regardless of the types of oncogenic pathways. We review the phenotypes and gene expression profiles of the respective models, and discuss the cooperation of oncogenic pathways and host responses in gastric tumorigenesis.

Preventive effects of etodolac, a selective cyclooxygenase-2 inhibitor, on cancer development in extensive metaplastic gastritis, a Helicobacter pylori-negative precancerous lesion

The present study investigated the preventive effects of etodolac, a selective cyclo-oxygenase (COX)-2 inhibitor, on metachronous cancer development after endoscopic resection of early gastric cancer. Among 267 early gastric cancer patients who underwent endoscopic resection, 47 patients with extensive metaplastic gastritis were selected based on endoscopic findings and our previously described criteria of serum pepsinogen (PG) test-positive and Helicobacter pylori antibody-negative conditions. Nonrandomized etodolac treatment (300 mg/day) was administered to 26 patients (Group A), while the remaining 21 patients were untreated (Group B). No significant differences in age, sex distribution, lifestyle factors or extent of metaplastic gastritis at baseline were identified between groups. Patients were followed for metachronous cancer development with endoscopy every 6-12 months for up to 5 years. Mean (standard deviation) follow-up period was 4.2 (0.9) years. In Group B, 5 cancers developed (incidence rate = 6,266/100,000 person-years), significantly more than the 1 cancer in Group A (incidence rate = 898/100,000 person-years; p < 0.05). Long-term etodolac treatment did not influence the extent of metaplastic gastritis as revealed by endoscopic findings or by serum PG levels, but effectively reduced metachronous cancer development in patients with extensive metaplastic gastritis. These results strongly suggest that chemoprevention of cancer in the metaplastic stomach is possible by controlling COX-2 expression.

Prostaglandin E2, Wnt, and BMP in gastric tumor mouse models

The development of gastric cancer is closely associated with Helicobacter pylori (H. pylori) infection. The expression of cylooxigenase-2 (COX-2), a rate-limiting enzyme for prostaglandin biosynthesis, is induced in H. pylori-associated chronic gastritis, which thus results in the induction of proinflammatory prostaglandin, PGE(2). The COX-2/PGE(2) pathway plays a key role in gastric tumorigenesis. On the other hand, several oncogenic pathways have been shown to trigger gastric tumorigenesis. The activation of Wnt/beta-catenin signaling is found in 30-50% of gastric cancers, thus suggesting that Wnt signaling plays a causal role in gastric cancer development. Mutations in the bone morphogenetic protein (BMP) signaling pathway are responsible for the subset of juvenile polyposis syndrome (JPS) that develops hamartomas in the gastrointestinal tract. BMP suppression appears to contribute to gastric cancer development because gastric cancer risk is increased in JPS. Wnt signaling is important for the maintenance of gastrointestinal stem cells, while BMP promotes epithelial cell differentiation. Accordingly, it is possible that both Wnt activation and BMP suppression can cause gastric tumorigenesis through enhancement of the undifferentiated status of epithelial cells. Recent mouse model studies have indicated that induction of the PGE(2) pathway is required for the development of both gastric adenocarcinoma and hamartoma in the Wnt-activated and BMP-suppressed gastric mucosa, respectively. This article reviews the involvement of the PGE(2), Wnt, and BMP pathways in the development of gastric cancer, and gastric phenotypes that are found in transgenic mouse models of PGE(2) induction, Wnt activation, BMP suppression, or a combination of these pathways.

Chemoprevention of glandular stomach carcinogenesis through duodenogastric reflux in rats by a COX-2 inhibitor

Duodenogastric reflux (DGR) causes glandular stomach carcinogenesis in rats without carcinogens. We aimed to investigate how this carcinogenesis might be prevented by a selective COX-2 inhibitor, meloxicam. A series of 188 Fisher 344 rats underwent a surgical DGR procedure and were divided into 2 groups. One group was given commercial chow (control group), and the other an experimental chow containing meloxicam [0.3 mg/kg bw/day] (meloxicam group). The animals were sequentially sacrificed at weeks 20, 30, 40, 50 and 60 after surgery. The stomachs were removed and examined for the presence of carcinoma, incidence of reflux-induced morphologic changes, COX-2 expression and its activity. Adenocarcinoma in the glandular stomach developed in 7 of 21 animals (33%) in the control group at week 60, but none of 20 (0%) in the meloxicam group (p < 0.01). Moreover, reflux-induced gastritis was definitely alleviated in the meloxicam group compared with the control group. COX-2 immunoreactivity was predominantly detected in stromal cells such as macrophages and fibroblasts. Compared with nonsurgical rats, RNA expression of COX-2 in the mucosa increased, reaching peak at an early phase of week 20 in both groups (p < 0.005). Expression of microsomal prostaglandin E synthase-1 was lower in the meloxicam group than in the control group. PGE(2) production was significantly suppressed throughout the experiment in the meloxicam group compared with the control group (p < 0.01). Gastric carcinogenesis via duodenal reflux was mediated by the COX-2 pathway in rats. Administration of meloxicam prevented this carcinogenesis by suppressing the inflammatory process.

Translational research in gastric malignancy

This article discusses recent advances in gastric cancer research that have improved treatment and outcomes of gastric malignancy, or have the potential to do so. The significance of Helicobacter pylori infection and eradication, immunology, host genetics, proto-oncogenes, and epigenetic alterations in gastric cancer are discussed. Abnormal signaling through growth factor pathways (tyrosine kinases and gastrointestinal peptides) presents ample opportunities for therapeutic intervention that are currently being tested in clinical trials. Drugs targeting abnormal epigenetic changes, such as DNA hypermethylation and histone deacetylation, are also on the horizon, although most of this research is still in the preclinical phase. The potential prognostic implications of genetics and immunology in gastric cancer prognosis are also reviewed.

4-Vinyl-2,6-dimethoxyphenol (canolol) suppresses oxidative stress and gastric carcinogenesis in Helicobacter pylori-infected carcinogen-treated Mongolian gerbils

Oxidative stress is linked to gastric carcinogenesis because of its ability to damage DNA. Here we examined antioxidative and anti-inflammatory effects of 4-vinyl-2,6-dimethoxyphenol (canolol), a recently identified potent antioxidative compound obtained from crude canola oil, on Helicobacter (H.) pylori-induced gastritis and gastric carcinogenesis using a Mongolian gerbil model. The animals were allocated to H. pylori-infection alone (12 weeks) or H.pylori + N-methyl-N-nitrosourea (MNU) administration (52 weeks). After oral inoculation of H. pylori, they were fed for 10 and 44 weeks with or without 0.1% canolol. H. pylori-induced gastritis, 5'-bromo-2'-deoxyuridine (BrdU) labeling and scores for cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) immunohistochemistry were attenuated in the canolol-treated groups. Expression of interleukin-1 beta (IL-1 beta), tumor necrosis factor-alpha (TNF-alpha), COX-2 and iNOS mRNA in the gastric mucosa, and serum 8-hydroxy-2'-deoxyguanosine (8-OHdG), anti-H. pylori IgG and gastrin levels were also significantly lower in canolol-treated groups. Furthermore, the incidence of gastric adenocarcinomas was markedly reduced in the H. pylori + MNU + canolol-treated group [15.0% (6/40)] compared to the control group [39.4% (13/33)] (p < 0.05). These data indicate canolol to be effective for suppressing inflammation, gastric epithelial cell proliferation and gastric carcinogenesis in H. pylori-infected Mongolian gerbils. Interestingly, the viable H. pylori count was not changed by the canolol containing diet. Thus, the data point to the level of inflammation because of H. pylori rather than the existence of the bacteria as the determining factor. Importantly, canolol appears to suppress induction of mRNAs for inflammatory cytokines.

Effects of aspirin on the development of Helicobacter pylori-induced gastric inflammation and heterotopic proliferative glands in Mongolian gerbils

BACKGROUND

Helicobacter pylori infection is a major cause of gastritis and gastric carcinoma. Aspirin has anti-inflammatory and antineoplastic activity. The aim of the present study was to determine the effects of aspirin on H. pylori-induced gastritis and the development of heterotopic proliferative glands.

METHODS

H. pylori strain SS1 was inoculated into the stomachs of Mongolian gerbils. Two weeks after inoculation, the animals were fed with the powder diets containing 0 p.p.m. (n = 10), 150 p.p.m. (n = 10), or 500 p.p.m. (n = 10) aspirin. Mongolian gerbils were killed after 36 weeks of infection. Uninfected Mongolian gerbils (n = 10) were used as controls. Histologic changes, epithelial cell proliferation and apoptosis, and prostaglandin E(2) (PGE(2)) levels of gastric tissue were determined.

RESULTS

H. pylori infection induced gastric inflammation. Administration of aspirin did not change H. pylori-induced gastritis, but alleviated H. pylori-induced hyperplasia and the development of heterotopic proliferative glands. Administration of aspirin accelerated H. pylori-associated apoptosis but decreased H. pylori-associated cell proliferation. In addition, the increased gastric PGE(2) levels due to H. pylori infection were suppressed by treatment with aspirin, especially at the dose of 500 p.p.m.

CONCLUSIONS

Aspirin alleviates H. pylori-induced hyperplasia and the development of heterotopic proliferative glands. Moreover, aspirin increases H. pylori-induced apoptosis. We demonstrated the antineoplastic activities of aspirin in H. pylori-related gastric carcinogenesis.

Animal models of stomach carcinogenesis

Although incidences of stomach cancer have decreased over the past several decades, the disease remains an important public health problem. To identify pathological and molecular biochemical mechanisms, various experimental animal models have been established in rats and mice with chemical carcinogens including N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) and N-methyl-N-nitrosourea (MNU). Helicobacter pylori(H. pylori) is one of the most important factors for human stomach disorders, including neoplasia, and the H. pylori-infected and carcinogen-treated Mongolian gerbil (MG) has proven very useful for analyses of underlying processes. The findings with this model support the hypothesis that intestinal metaplasia is important not as a precancerous lesion but rather as a paracancerous condition and that intestinalization of stomach cancer progresses with chronic inflammation. Furthermore, dose-dependent enhancing effects of salt on stomach carcinogenesis could be demonstrated in MGs treated with MNU and H. pylori modifying surface mucous gel layer. H. pylori itself only causes chronic inflammation and acts as a promoter of stomach carcinogenesis in experimental models. Based on the precise pathological diagnosis of stomach lesions such as noncancerous heterotopic proliferative glands (HPG) and adenocarcinomas, a basis for understanding mechanisms of carcinogenesis has been established on which chemoprevention can be modeled.

Inhibitory effect of nordihydroguaiaretic acid, a plant lignan, on Helicobacter pylori-associated gastric carcinogenesis in Mongolian gerbils

Recent epidemiological studies have demonstrated that consumption of certain natural products can lower cancer risk in humans. For example, plant-derived lignans have been shown to exert chemopreventive effects against cancer in vitro and in vivo. In the present study, the effects of three such lignans, termed arctiin, arctigenin, and nordihydroguaiaretic acid (NDGA), on the proliferation of Helicobacter pylori and the prevention of H. pylori-associated gastric cancer were investigated in Mongolian gerbils. To examine the effects of arctigenin and NDGA on stomach carcinogenesis, specific pathogen-free male, 5-week-old gerbils were infected with H. pylori, administered 10 p.p.m. N-methyl-N-nitrosourea in their drinking water and fed diets containing various concentrations of lignans until they were killed after 52 weeks. At a dietary level of 0.25%, NDGA significantly decreased the incidence of gastric adenocarcinomas. Arctigenin, in contrast, failed to attenuate neoplasia at a level of 0.1%. Both NDGA and arctigenin significantly reduced serum 8-hydroxy-2'-deoxyguanosine levels at doses of 0.25 and 0.05% (NDGA), and 0.1% (arctigenin). Administration of 0.25% NDGA significantly suppressed the formation of intestinal metaplasia both in the antrum and the corpus. Although all three lignans dose-dependently inhibited the in vitro proliferation of H. pylori, there were no differences in the titers of anti-H. pylori antibodies or the amount of the H. pylori-specific urease A gene among all H. pylori-infected groups. These results suggest that NDGA might be effective for prevention of gastric carcinogenesis. The possible mechanisms appear to be related to inhibitory effects on progression of gastritis and antioxidative activity rather than direct antimicrobial influence.

Citrus Auraptene Reduces Helicobacter pylori Colonization of Glandular Stomach Lesions in Mongolian Gerbils

We examined the efficacy of auraptene (AUR), an antioxidant agent of a citrus coumarin derivative, for suppressing gastric inflammation introduced by Helicobacter pylori (Hp) infection in Mongolian gerbils (MGs). Hp-infected MGs were placed on diets containing 100 or 500 ppm AUR for 7 weeks. Real-time PCR was used to estimate the Hp population in glandular stomach lesions, and a histological assessment of inflammation was performed. At a dose of 500 ppm, AUR reduced the Hp population to 21.9+/-12.0% of the control group (p<0.05). However, no apparent differences were seen in hematoxylin and eosin sections between AUR-administered and control groups. We conclude that dietary supplementation with 500 ppm of AUR suppresses Hp colonization, but does not reduce gastric inflammation.

Helicobacter pylori and gastric cancer

PURPOSE OF REVIEW

Although chronic Helicobacter pylori infection is the strongest known risk factor for development of gastric adenocarcinoma, only a small proportion of infected individuals will ever develop tumours. This article discusses various bacterial, host and environmental factors which may influence an individual's susceptibility.

RECENT FINDINGS

Recent research on bacterial virulence factors has focussed upon the cag pathogenicity island, particularly its roles in regulating epithelial growth and adhesion. Studies of host genetic factors have included several analyses of polymorphisms in inflammatory cytokines in human cohorts. Animal studies have recently clarified the roles of dysregulated epithelial apoptosis, proliferation and differentiation pathways during gastric carcinogenesis, and novel experiments involving H. felis infection of bone marrow transplanted irradiated mice have suggested that gastric cancer may originate from bone marrow-derived stem cells. Important roles for signalling between epithelial and mesenchymal cells, particularly myofibroblasts, are also emerging. Recent research on the importance of environmental factors has demonstrated how helminth coinfection may protect against atrophic gastritis and T helper type 1 responses.

SUMMARY

Complex interactions between several bacterial, host genetic and environmental factors determine whether H. pylori infected individuals develop gastric carcinoma. The importance of bone marrow stem cell engraftment during human gastric neoplasia is an area requiring urgent investigation.