Long term infection of the gastric mucosa with Helicobacter species does induce atrophic gastritis in an animal model of Helicobacter pylori infection

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.

Immune and microRNA responses to Helicobacter muridarum infection and indole-3-carbinol during colitis

BACKGROUND

Indole-3-carbinol (I3C) and other aryl hydrocarbon receptor agonists are known to modulate the immune system and ameliorate various inflammatory and autoimmune diseases in animal models, including colitis induced by dextran sulfate sodium (DSS). MicroRNAs (miRNAs) are also gaining traction as potential therapeutic agents or diagnostic elements. Enterohepatic Helicobacter (EHH) species are associated with an increased risk of inflammatory bowel disease, but little is known about how these species affect the immune system or response to treatment.

AIM

To determine whether infection with an EHH species alters the response to I3C and how the immune and miRNA responses of an EHH species compare with responses to DSS and inflammatory bowel disease.

METHODS

We infected C57BL/6 mice with Helicobacter muridarum (H. muridarum), with and without DSS and I3C treatment. Pathological responses were evaluated by histological examination, symptom scores, and cytokine responses. MiRNAs analysis was performed on mesenteric lymph nodes to further evaluate the regional immune response.

RESULTS

H. muridarum infection alone caused colonic inflammation and upregulated proinflammatory, macrophage-associated cytokines in the colon similar to changes seen in DSS-treated mice. Further upregulation occurred upon treatment with DSS. H. muridarum infection caused broad changes in mesenteric lymph node miRNA expression, but colitis-associated miRNAs were regulated similarly in H. muridarum-infected and uninfected, DSS-treated mice. In spite of causing colitis exacerbation, H. muridarum infection did not prevent disease amelioration by I3C. I3C normalized both macrophage- and T cell-associated cytokines.

CONCLUSION

Thus, I3C may be useful for inflammatory bowel disease patients regardless of EHH infection. The miRNA changes associated with I3C treatment are likely the result of, rather than the cause of immune response changes.

Intervention effects of lotus leaf flavonoids on gastric mucosal lesions in mice infected with Helicobacter pylori

Helicobacter pylori (H. pylori) is one of the main factors that cause gastric lesions. The lotus leaf is an edible plant used in traditional Eastern medicine. This study evaluates the intervention effects of lotus leaf flavonoids (LLF) on gastric mucosal lesions in mice infected with H. pylori and explores their mechanism of action. High-performance liquid chromatography analysis reveals that LLF contain kaempferitrin (kaempferol-3,7-dirhamnoside), hypericin, astragalin (kaempferol-3-glucoside), phlorizin, and quercetin. LLF can reduce the number of gastric mucosal lesions and tissue lesions in mice with H. pylori-induced gastric lesions. LLF can increase the levels of somatostatin and vasoactive intestinal peptide in the serum of mice with gastric lesions and decrease the levels of substance P and endothelin-1 to inhibit gastric lesions. LLF can also reduce the levels of interleukin (IL)-6, IL-12, tumor necrosis factor (TNF)-α, and interferon-gamma cytokines in the serum of mice with gastric lesions. Using a quantitative polymerase chain reaction assay it can be seen that LLF can downregulate mRNA expressions of TNF-α, IL-1β, myeloperoxidase, keratin (KRT) 16, KRT6b, and transglutaminase 3 epidermal in the gastric tissues of mice with gastric lesions. Western blot analysis indicates that LLF can downregulate the protein expressions of caspase-1, Nod-like receptor protein 3, IL-1β, TNF-α, and Toll-like receptor 4 in the gastric tissues of mice with gastric lesions. LLF have beneficial effects on gastric lesions induced by H. pylori. Meanwhile LLF is more active in competition with ranitidine. LLF represent an active substance that can inhibit H. pylori-induced gastric lesions. The flavones of LLF may enhance the inhibition of gastric mucosal lesions by promoting the interaction between the compounds.

Mouse models for gastric cancer: Matching models to biological questions

Gastric cancer is the third leading cause of cancer-related mortality worldwide. This is in part due to the asymptomatic nature of the disease, which often results in late-stage diagnosis, at which point there are limited treatment options. Even when treated successfully, gastric cancer patients have a high risk of tumor recurrence and acquired drug resistance. It is vital to gain a better understanding of the molecular mechanisms underlying gastric cancer pathogenesis to facilitate the design of new-targeted therapies that may improve patient survival. A number of chemically and genetically engineered mouse models of gastric cancer have provided significant insight into the contribution of genetic and environmental factors to disease onset and progression. This review outlines the strengths and limitations of current mouse models of gastric cancer and their relevance to the pre-clinical development of new therapeutics.

Recapitulating Human Gastric Cancer Pathogenesis: Experimental Models of Gastric Cancer

This review focuses on the various experimental models to study gastric cancer pathogenesis, with the role of genetically engineered mouse models (GEMMs) used as the major examples. We review differences in human stomach anatomy compared to the stomachs of the experimental models, including the mouse and invertebrate models such as Drosophila and C. elegans. The contribution of major signaling pathways, e.g., Notch, Hedgehog, AKT/PI3K is discussed in the context of their potential contribution to foregut tumorigenesis. We critically examine the rationale behind specific GEMMs, chemical carcinogens, dietary promoters, Helicobacter infection, and direct mutagenesis of relevant oncogenes and tumor suppressor that have been developed to study gastric cancer pathogenesis. Despite species differences, more efficient and effective models to test specific genes and pathways disrupted in human gastric carcinogenesis have yet to emerge. As we better understand these species differences, "humanized" versions of mouse models will more closely approximate human gastric cancer pathogenesis. Towards that end, epigenetic marks on chromatin, the gut microbiota, and ways of manipulating the immune system will likely move center stage, permitting greater overlap between rodent and human cancer phenotypes thus providing a unified progression model.

Spontaneaous linear gastric tears in a cat

An 11-year-old female cat presented for chronic vomiting. Endoscopy revealed an altered gastric mucosa and spontaneous formation of linear gastric tears during normal organ insufflations. The histopathological diagnosis was atrophic gastritis with Helicobacter pylori infection. Medical treatment permitted a complete resolution of clinical signs. The linear tears observed resembled gastric lesions rarely reported in humans, called "Mallory-Weiss syndrome". To the authors' knowledge this is the first report of spontaneous linear gastric tears in animals.

Helicobacter heilmannii sensu lato: An overview of the infection in humans

Helicobacter heilmannii sensu lato (H. heilmannii s.l.) is a group of gastric non-Helicobacter pylori Helicobacter species that are morphologically indistinguishable from each other. H. heilmannii s.l. infect the stomach of several animals and may have zoonotic potential. Although the prevalence of these infections in humans is low, they are associated with gastric pathology, including mucosa-associated lymphoid tissue lymphoma, making them a significant health issue. Here, the taxonomy, epidemiology, microbiology, diagnosis, and treatment of these infections will be reviewed. The gastric pathology associated with H. heilmannii s.l. infections in humans will also be addressed. Finally, the features of the complete bacterial genomes available and studies on species-specific pathogenesis will be reviewed. The understanding of the mechanisms that underlie gastric disease development mediated by the different bacterial species that constitute H. heilmannii s.l. is essential for developing strategies for prevention and treatment of these infections.

Mouse models of gastric carcinogenesis

Gastric cancer is one of the most common cancers in the world. Animal models have been used to elucidate the details of the molecular mechanisms of various cancers. However, most inbred strains of mice have resistance to gastric carcinogenesis. Helicobacter infection and carcinogen treatment have been used to establish mouse models that exhibit phenotypes similar to those of human gastric cancer. A large number of transgenic and knockout mouse models of gastric cancer have been developed using genetic engineering. A combination of carcinogens and gene manipulation has been applied to facilitate development of advanced gastric cancer; however, it is rare for mouse models of gastric cancer to show aggressive, metastatic phenotypes required for preclinical studies. Here, we review current mouse models of gastric carcinogenesis and provide our perspectives on future developments in this field.

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.

Coinfection with Enterohepatic Helicobacter species can ameliorate or promote Helicobacter pylori-induced gastric pathology in C57BL/6 mice

To investigate how different enterohepatic Helicobacter species (EHS) influence Helicobacter pylori gastric pathology, C57BL/6 mice were infected with Helicobacter hepaticus or Helicobacter muridarum, followed by H. pylori infection 2 weeks later. Compared to H. pylori-infected mice, mice infected with H. muridarum and H. pylori (HmHp mice) developed significantly lower histopathologic activity index (HAI) scores (P < 0.0001) at 6 and 11 months postinoculation (MPI). However, mice infected with H. hepaticus and H. pylori (HhHp mice) developed more severe gastric pathology at 6 MPI (P = 0.01), with a HAI at 11 MPI (P = 0.8) similar to that of H. pylori-infected mice. H. muridarum-mediated attenuation of gastritis in coinfected mice was associated with significant downregulation of proinflammatory Th1 (interlukin-1beta [Il-1β], gamma interferon [Ifn-γ], and tumor necrosis factor-alpha [Tnf-α]) cytokines at both time points and Th17 (Il-17A) cytokine mRNA levels at 6 MPI in murine stomachs compared to those of H. pylori-infected mice (P < 0.01). Coinfection with H. hepaticus also suppressed H. pylori-induced elevation of gastric Th1 cytokines Ifn-γ and Tnf-α (P < 0.0001) but increased Th17 cytokine mRNA levels (P = 0.028) at 6 MPI. Furthermore, mRNA levels of Il-17A were positively correlated with the severity of helicobacter-induced gastric pathology (HhHp>H. pylori>HmHp) (at 6 MPI, r² = 0.92, P < 0.0001; at 11 MPI, r² = 0.82, P < 0.002). Despite disparate effects on gastritis, colonization levels of gastric H. pylori were increased in HhHp mice (at 6 MPI) and HmHp mice (at both time points) compared to those in mono-H. pylori-infected mice. These data suggest that despite consistent downregulation of Th1 responses, EHS coinfection either attenuated or promoted the severity of H. pylori-induced gastric pathology in C57BL/6 mice. This modulation was related to the variable effects of EHS on gastric interleukin 17 (IL-17) responses to H. pylori infection.

Comparative whole genome sequence analysis of the carcinogenic bacterial model pathogen Helicobacter felis

The gram-negative bacterium Helicobacter felis naturally colonizes the gastric mucosa of dogs and cats. Due to its ability to persistently infect laboratory mice, H. felis has been used extensively to experimentally model gastric disorders induced in humans by H. pylori. We determined the 1.67 Mb genome sequence of H. felis using combined Solexa and 454 pyrosequencing, annotated the genome, and compared it with multiple previously published Helicobacter genomes. About 1,063 (63.6%) of the 1,671 genes identified in the H. felis genome have orthologues in H. pylori, its closest relative among the fully sequenced Helicobacter species. Many H. pylori virulence factors are shared by H. felis: these include the gamma-glutamyl transpeptidase GGT, the immunomodulator NapA, and the secreted enzymes collagenase and HtrA. Helicobacter felis lacks a Cag pathogenicity island and the vacuolating cytotoxin VacA but possesses a complete comB system conferring natural competence. Remarkable features of the H. felis genome include its paucity of transcriptional regulators and an extraordinary abundance of chemotaxis sensors and restriction/modification systems. Helicobacter felis possesses an episomally replicating 6.7-kb plasmid and harbors three chromosomal regions with deviating GC content. These putative horizontally acquired regions show homology and synteny with the recently isolated H. pylori plasmid pHPPC4 and homology to Campylobacter bacteriophage genes (transposases, structural, and lytic genes), respectively. In summary, the H. felis genome harbors a variety of putative mobile elements that are unique among Helicobacter species and may contribute to this pathogen’s carcinogenic properties.

Inhibition of ADP ribosylation prevents and cures helicobacter-induced gastric preneoplasia

Gastric adenocarcinoma develops as a consequence of chronic inflammation of the stomach lining that is caused by persistent infection with the bacterium Helicobacter pylori. Gastric carcinogenesis progresses through a sequence of preneoplastic lesions that manifest histologically as atrophic gastritis, intestinal metaplasia, and dysplasia. We show here in several preclinical models of Helicobacter-induced atrophic gastritis, epithelial hyperplasia, and metaplasia that the inhibition of ADP ribosylation by the small-molecule inhibitor PJ34 not only prevents the formation of gastric cancer precursor lesions, but also efficiently reverses preexisting lesions. PJ34 exerts its chemopreventive and therapeutic effects by impairing Helicobacter-specific T-cell priming and T(H)1 polarization in the gut-draining mesenteric lymph nodes. The subsequent infiltration of pathogenic T cells into the gastric mucosa and the ensuing gastric T cell-driven immunopathology are prevented efficiently by PJ34. Our data indicate that PJ34 directly suppresses T-cell effector functions by blocking the IFN-gamma production of mesenteric lymph node T cells ex vivo. Upon exposure to PJ34, purified T cells failed to synthesize ADP-ribose polymers and to activate the transcription of genes encoding IFN-gamma, interleukin 2, and the interleukin 2 receptor alpha chain in response to stimuli such as CD3/CD28 cross-linking or phorbol 12-myristate 13-acetate/ionomycin. The immunosuppressive and chemoprotective effects of PJ34 therefore result from impaired T-cell activation and T(H)1 polarization, and lead to the protection from preneoplastic gastric immunopathology. In conclusion, ADP-ribosylating enzymes constitute novel targets for the treatment of Helicobacter-associated gastric lesions predisposing infected individuals to gastric cancer and may also hold promise for the treatment of other T cell-driven chronic inflammatory conditions and autoimmune pathologies.

A commensal Helicobacter sp. of the rodent intestinal flora activates TLR2 and NOD1 responses in epithelial cells

Helicobacter spp. represent a proportionately small but significant component of the normal intestinal microflora of animal hosts. Several of these intestinal Helicobacter spp. are known to induce colitis in mouse models, yet the mechanisms by which these bacteria induce intestinal inflammation are poorly understood. To address this question, we performed in vitro co-culture experiments with mouse and human epithelial cell lines stimulated with a selection of Helicobacter spp., including known pathogenic species as well as ones for which the pathogenic potential is less clear. Strikingly, a member of the normal microflora of rodents, Helicobacter muridarum, was found to be a particularly strong inducer of CXC chemokine (Cxcl1/KC, Cxcl2/MIP-2) responses in a murine intestinal epithelial cell line. Time-course studies revealed a biphasic pattern of chemokine responses in these cells, with H. muridarum lipopolysaccharide (LPS) mediating early (24–48 h) responses and live bacteria seeming to provoke later (48–72 h) responses. H. muridarum LPS per se was shown to induce CXC chemokine production in HEK293 cells stably expressing Toll-like receptor 2 (TLR2), but not in those expressing TLR4. In contrast, live H. muridarum bacteria were able to induce NF-κB reporter activity and CXC chemokine responses in TLR2–deficient HEK293 and in AGS epithelial cells. These responses were attenuated by transient transfection with a dominant negative construct to NOD1, and by stable expression of NOD1 siRNA, respectively. Thus, the data suggest that both TLR2 and NOD1 may be involved in innate immune sensing of H. muridarum by epithelial cells. This work identifies H. muridarum as a commensal bacterium with pathogenic potential and underscores the potential roles of ill-defined members of the normal flora in the initiation of inflammation in animal hosts. We suggest that H. muridarum may act as a confounding factor in colitis model studies in rodents.

Differential regulation of urease activity in Helicobacter hepaticus and Helicobacter pylori

Helicobacter hepaticus is a pathogen of rodents, which causes diverse enteric and hepatic inflammatory diseases and malignancies. The urease enzyme is an important colonization factor of gastric Helicobacter species like Helicobacter pylori, but little is known about the role and regulation of urease in enterohepatic Helicobacter species. Here it is reported that urease activity of H. hepaticus does not contribute to acid resistance, and that it is nickel-responsive at the post-translational level. H. hepaticus strain ATCC 51449 did not grow or survive at pH 3·0, and supplementation with urea or NiCl2 did not abrogate this acid sensitivity. Furthermore, urease enzyme activity of H. hepaticus was acid-independent, which contrasts with the acid-induced urease system of H. pylori. Nickel supplementation of Brucella medium resulted in a tenfold increase in urease activity in both H. hepaticus and H. pylori, but the maximum level of urease activity in H. hepaticus was still three- to fivefold lower when compared to H. pylori in the same conditions. The increase in urease activity of H. hepaticus was not associated with elevation of urease mRNA or protein levels. Inhibition of protein synthesis by chloramphenicol did not affect nickel-responsive induction of urease activity in H. hepaticus, and confirmed that nickel induction occurs at the post-translational level, probably by activation of preformed apo-enzyme. In conclusion, both the role of the urease enzyme and the regulation of urease activity differ between the enterohepatic pathogen H. hepaticus and the gastric pathogen H. pylori.

The role of antigenic drive and tumor-infiltrating accessory cells in the pathogenesis of helicobacter-induced mucosa-associated lymphoid tissue lymphoma

Gastric B-cell lymphoma of mucosa-associated lymphoid tissue type is closely linked to chronic Helicobacter pylori infection. Most clinical and histopathological features of the tumor can be reproduced by prolonged Helicobacter infection of BALB/c mice. In this study, we have addressed the role of antigenic stimulation in the pathogenesis of the lymphoma by experimental infection with Helicobacter felis, followed by antibiotic eradication therapy and subsequent re-infection. Antimicrobial therapy was successful in 75% of mice and led to complete histological but not "molecular" tumor remission. Although lympho-epithelial lesions disappeared and most gastric lymphoid aggregates resolved, transcriptional profiling revealed the long-term mucosal persistence of residual B cells. Experimental re-introduction of Helicobacter led to very rapid recurrence of the lymphomas, which differed from the original lesions by higher proliferative indices and more aggressive behavior. Immunophenotyping of tumor cells revealed massive infiltration of lesions by CD4(+) T cells, which express CD 28, CD 69, and interleukin-4 but not interferon-gamma, suggesting that tumor B-cell proliferation was driven by Th 2-polarized, immunocompetent, and activated T cells. Tumors were also densely colonized by follicular dendritic cells, whose numbers were closely associated with and predictive of treatment outcome.

Chronic gastritis rat model and role of inducing factors

AIM: To establish an experimental animal model of chronic gastritis in a short term and to investigate the effects of several potential inflammation-inducing factors on rat gastric mucosa.

METHODS: Twenty-four healthy, male SD rats were treated with intragastric administration of 600 mL/L alcohol, 20 mmol/L sodium deoxycholate and 0.5 g/L ammonia (factor A), forage containing low levels of vitamins (factor B), and/or indomethacin (factor C), according to an L₈(2⁷) orthogonal design. After 12 wk, gastric antral and body mucosae were pathologically examined.

RESULTS: Chronic gastritis model was successfully induced in rats treated with factor A for 12 wk. After the treatment of animals, the gastric mucosal inflammation was significantly different from that in controls, and the number of pyloric glands at antrum and parietal cells at body were obviously reduced (P < 0.01). Indomethacin induced gastritis but without atrophy, and short-term vitamin deficiency failed to induce chronic gastritis and gastric atrophy. In addition, indomethacin and vitamin deficiency had no synergistic effect in inducing gastritis with the factor A. No atypical hyperplasia and intestinal metaplasia in the gastric antrum and body were observed in all rats studied.

CONCLUSION: Combined intragastric administration of 600 mL/L alcohol, 20 mmol/L sodium deoxycholate and 0.5 g/L ammonia induces chronic gastritis and gastric atrophy in rats. Indomethacin induces chronic gastritis only. The long-term roles of these factors in gastric inflammation and carcinogenesis need to be further elucidated.

Gastric B-cell mucosa-associated lymphoid tissue (MALT) lymphoma in an animal model of 'Helicobacter heilmannii' infection

While Helicobacter pylori is accepted as the dominant human gastric bacterial pathogen, a small percentage of human infections have been associated with another organism, commonly referred to as 'Helicobacter heilmannii', which is more prevalent in a range of animal species. This latter bacterium has been seen in association with the full spectrum of human gastric diseases including gastritis, peptic ulceration, and gastric carcinomas, including gastric B-cell mucosa-associated lymphoid tissue (MALT) lymphoma. This study describes an analysis of the pathogenic potential of a number of 'H heilmannii' isolates in an animal model of gastric MALT lymphoma. BALB/c mice were infected with ten different 'H heilmannii' isolates originating from both human and animal hosts. The animals were examined at various time points for up to 28 months after infection. The infected animals initially developed a chronic inflammatory response within 6 months. This histological response increased in severity with the length of infection, with the development of overt lymphoma in some animals 18 months after infection. MALT lymphomas were detected in up to 25% of the infected animals. The prevalence of lymphoma was dependent on the length of infection and the origin of the infecting isolates. A range of other histological features accompanied the lymphocytic infiltration, including invaginations of the gastric epithelium and associated hyperplastic tissue, mucus metaplasia, and a small number of diffuse large B-cell lymphomas. The ability to manipulate experientially the presence of the bacterium in the animal model will allow further studies examining the role of antigen drive in the development of Helicobacter-associated MALT lymphoma.

High prevalence of Helicobacter Species detected in laboratory mouse strains by multiplex PCR-denaturing gradient gel electrophoresis and pyrosequencing

Rodent models have been developed to study the pathogenesis of diseases caused by Helicobacter pylori, as well as by other gastric and intestinal Helicobacter spp., but some murine enteric Helicobacter spp. cause hepatobiliary and intestinal tract diseases in specific inbred strains of laboratory mice. To identify these murine Helicobacter spp., we developed an assay based on PCR-denaturing gradient gel electrophoresis and pyrosequencing. Nine strains of mice, maintained in four conventional laboratory animal houses, were assessed for Helicobacter sp. carriage. Tissue samples from the liver, stomach, and small intestine, as well as feces and blood, were collected; and all specimens (n = 210) were screened by a Helicobacter genus-specific PCR. Positive samples were identified to the species level by multiplex denaturing gradient gel electrophoresis, pyrosequencing, and a H. ganmani-specific PCR assay. Histologic examination of 30 tissue samples from 18 animals was performed. All mice of eight of the nine strains tested were Helicobacter genus positive; H. bilis, H. hepaticus, H. typhlonius, H. ganmani, H. rodentium, and a Helicobacter sp. flexispira-like organism were identified. Helicobacter DNA was common in fecal (86%) and gastric tissue (55%) specimens, whereas samples of liver tissue (21%), small intestine tissue (17%), and blood (14%) were less commonly positive. Several mouse strains were colonized with more than one Helicobacter spp. Most tissue specimens analyzed showed no signs of inflammation; however, in one strain of mice, hepatitis was diagnosed in livers positive for H. hepaticus, and in another strain, gastric colonization by H. typhlonius was associated with gastritis. The diagnostic setup developed was efficient at identifying most murine Helicobacter spp.

Establishment of mouse models with long-term infection of H. pylori

AIM: To develop a mouse model with long-term infection of H. pylori.

METHODS: Each mouse was inoculated with H. pylori Sydney strain 1 (SS1). Noninfected control mice and infected mice were killed at 4, 12 and 24 wk after H. pylori infection. A piece of gastric mucosa obtained from the posterior wall of the antrum of each mouse was used for culture of H. pylori, rapid urease testing and histopathological detection. Serum was obtained to measure the IgG antibody level to H. pylori.

RESULTS: After 4 wk of infection, the H. pylori was cultured from 6 of 7 infected Babl/c mice and 5 of 7 the H. pylori-infected C57BL/6 mice. After 12 and 24 wk of infection, all of 7 infected Babl/c and 6 of 7 the H. pylori-infected C57BL/6 mice showed the positive results. At the different wk, the rapid urease test results were consistent with the H. pylori culture test. At 12 wk after inoculation, chronic inflammation was observed in the pyloric mucosa by histopathological examination. At 24 wk after inoculation, lymphoid follicles were especially conspicuous in the submucosa, and they were also found in the deep portion of the mucosa.

CONCLUSION: H. pylori SS1 can colonize easily in the glandular stomach mucosa of mouse, and the histopathological changes are similar to those of humans with H. pylori infection.

Presence of active aliphatic amidases in Helicobacter species able to colonize the stomach

Ammonia production is of great importance for the gastric pathogen Helicobacter pylori as a nitrogen source, as a compound protecting against gastric acidity, and as a cytotoxic molecule. In addition to urease, H. pylori possesses two aliphatic amidases responsible for ammonia production: AmiE, a classical amidase, and AmiF, a new type of formamidase. Both enzymes are part of a regulatory network consisting of nitrogen metabolism enzymes, including urease and arginase. We examined the role of the H. pylori amidases in vivo by testing the gastric colonization of mice with H. pylori SS1 strains carrying mutations in amiE and/or amiF and in coinfection experiments with wild-type and double mutant strains. A new cassette conferring resistance to gentamicin was used in addition to the kanamycin cassette to construct the double mutation in strain SS1. Our data indicate that the amidases are not essential for colonization of mice. The search for amiE and amiF genes in 53 H. pylori strains from different geographic origins indicated the presence of both genes in all these genomes. We tested for the presence of the amiE and amiF genes and for amidase and formamidase activities in eleven Helicobacter species. Among the gastric species, H. acinonychis possessed both amiE and amiF, H. felis carried only amiF, and H. mustelae was devoid of amidases. H. muridarum, which can colonize both mouse intestine and stomach, was the only enterohepatic species to contain amiE. Phylogenetic trees based upon the sequences of H. pylori amiE and amiF genes and their respective homologs from other organisms as well as the amidase gene distribution among Helicobacter species are strongly suggestive of amidase acquisition by horizontal gene transfer. Since amidases are found only in Helicobacter species able to colonize the stomach, their acquisition might be related to selective pressure in this particular gastric environment.

Long-term evaluation of mice model infected with Helicobacter pylori: focus on gastric pathology including gastric cancer

BACKGROUND

Long-term evaluation of gastric pathology after H. pylori infection is very important in order to reveal its clinical implications, since debate still exists on the gastric carcinogenesis provoked by H. pylori infection in animal models.

AIM

Either to evaluate the long-term outcome of H. pylori infection or to determine how H. pylori could provoke gastric cancer in the mice model.

METHODS

Four-week-old specific pathogen free C57BL/6 mice (n = 115) were infected with SS1, the mouse-adapted H. pylori strain. After 4, 8, 16, 24, 36, 50 and 80 weeks of bacterial infection, the H. pylori-infected mice were sacrificed.

RESULTS

After 80 weeks of infection, almost all the H. pylori-infected mice developed hyperplastic gastritis, but did not show any evidence of gastric adenoma, dysplasia or carcinoma. PCNA positive cells were most abundant after 50 weeks and tended to decrease thereafter up to 80 weeks, whereas apoptosis began to be noted 8 weeks after H. pylori infection, showing 7-8 apoptotic cells/high power field, and tending to increase as time passed. Normally observed neutral mucin decreased during the experiment, showing the most marked decrease 50 weeks after H. pylori infection. In contrast, acidic mucin was noted from 50 weeks after infection.

CONCLUSION

The SS1-infected mouse seems to be a suitable animal model for H. pylori-related research, and H. pylori itself does not induce gastric cancer in normal wild-type mouse model following long-term exposure, which could be explained by the balance that exists between cell proliferation and apoptosis.

Emergence of diverse Helicobacter species in the pathogenesis of gastric and enterohepatic diseases

Since Helicobacter pylori was first cultivated from human gastric biopsy specimens in 1982, it has become apparent that many related species can often be found colonizing the mucosal surfaces of humans and other animals. These other Helicobacter species can be broadly grouped according to whether they colonize the gastric or enterohepatic niche. Gastric Helicobacter species are widely distributed in mammalian hosts and are often nearly universally prevalent. In many cases they cause an inflammatory response resembling that seen with H. pylori in humans. Although usually not pathogenic in their natural host, these organisms serve as models of human disease. Enterohepatic Helicobacter species are an equally diverse group of organisms that have been identified in the intestinal tract and the liver of humans, other mammals, and birds. In many cases they have been linked with inflammation or malignant transformation in immunocompetent hosts and with more severe clinical disease in immunocompromised humans and animals. The purpose of this review is to describe these other Helicobacter species, characterize their role in the pathogenesis of gastrointestinal and enterohepatic disease, and discuss their implications for our understanding of H. pylori infection in humans.

Outbred mice with long-term Helicobacter felis infection develop both gastric lymphoid tissue and glandular hyperplastic lesions

Experimental infection of mice with Helicobacter felis reproduces many aspects of the gastritis observed in Helicobacter pylori-infected humans. The development of gastric inflammatory lesions in chronically infected inbred mice is host-dependent; in BALB/c mice, gastric B-cell MALT lymphomas were observed, whilst other murine hosts (e.g. C57BL/6) developed severe glandular hyperplasia. The aims of this investigation were to characterize and immunophenotype Helicobacter-induced inflammatory lesions in mice with an outbred genetic background. Swiss mice (n=10 per group) were either inoculated with a suspension of H. felis or left untreated. H. felis-inoculated mice and age-matched control animals were killed 13 months later. The severity of gastric inflammatory lesions in the animals was graded and the number and distribution of B (CD45R(+)) and T (CD3(+)) lymphocytes in lymphoid tissues was determined by immunohistochemistry. Compared with control mice, animals with long-term H. felis infection developed severe hyperplastic gastritis (0.80+/-0.63 vs. 2.7+/-0.68), with epithelial dedifferentiation (0. 40+/-0.52 vs. 2.3+/-0.82) and lengthening of the pits and glands (0. 46+/-0.05 vs. 0.8+/-0.19). Gastric CD45R(+) and CD3(+) lymphocyte scores were significantly elevated (r=0.803) in infected animals, while lymphoepithelial lesions and polymorphonuclear leucocyte infiltrates were absent. Although prominent lymphoid follicles were present in the tissues of all infected animals, and in one control animal, only a proportion (55%) of the mucosal follicles had a dominant B-cell phenotype (defined as > or =75% CD45R(+) labelling), and all were poorly labelled with anti-mouse immunoglobulin antibodies. It was concluded that the lesions in outbred Swiss mice differed from B-cell MALT lymphomas. In contrast to inbred mice, outbred animals developed both glandular and lymphoid tissue lesions to chronic H. felis infection. It is suggested that the default T-helper phenotype of the host influences glandular lesion formation or B-cell lymphomagenesis in this model of infection.

Molecular epidemiology, pathogenesis and prevention of gastric cancer

Cancer of the stomach is one of the most commonly diagnosed malignancies and remains an important cause of mortality world wide. This type of cancer is not uniformly distributed among populations but shows a marked variation in both incidence and mortality. Although gastric cancer is declining in many parts of the world, the reasons for this decline are not well understood and its etiology remains unclear. Several factors are suspected to play a role in gastric carcinogenesis, including the effects of diet, exogenous chemicals, intragastric synthesis of carcinogens, genetic factors, infectious agents and pathological conditions in the stomach (such as gastritis). A new look at the results of epidemiological and experimental studies is important for the establishment of strategies for control. Since cancer of the stomach has a very poor prognosis in its more advanced stages, such a control program must have its main focus on primary prevention. This review describes our knowledge about cancer of the stomach regarding epidemiology, pathogenesis and prevention.

Characterization of Helicobacter felis by pulsed-field gel electrophoresis, plasmid profiling and ribotyping

BACKGROUND

Helicobacter felis, an organism naturally infecting both canine and feline gastric mucosa, has been largely used as in animal models to study the ecology and treatment of human Helicobacter pylori infections. H. felis has not yet been studied at the genetic level.

METHODS

The aims of this study were to modify an in situ DNA isolation method suitable for H. felis and, by the use of pulsed-field gel electrophoresis (PFGE), plasmid profiling, and ribotyping, to determine the degree of genetic variation among H. felis strains isolated from cats and dogs from various geographic locations, and to determine the genome size of H. felis. Furthermore, the ability of these new H. felis strains to colonize mice was tested.

RESULTS

Most H. felis strains were distinguishable from each other, and 20 distinct PFGE types were detected. Four pairs of strains within a country and animal species produced identical patterns. All strains tested were found to carry several plasmids and plasmid profiling was equally discriminatory to PFGE. Ribotyping was not able to discriminate all the strains.

CONCLUSIONS

The genome size of H. felis was found to be approximately 1.6 Mb.

The role of gastric Helicobacter and N-methyl-N'-nitro- N-nitrosoguanidine in carcinogenesis of mice

BACKGROUND

The aim of this study was to determine whether gastric epithelial proliferation due to gastric Helicobacter infection in mice represents a preneoplastic lesion.

MATERIALS AND METHODS

Helicobacter heilmannii infected and uninfected mice were treated with 150 microg/ml N-methyl-N'-nitro-N-nitrosoguanidine in drinking water for either 20 or 38 weeks. Mice were killed 12 or 18 months after bacterial inoculation.

RESULTS

All infected mice developed lymphoplasmocytic gastritis and epithelial hyperplasia. Proliferative gastric lesions were characterised by nodular hypertrophy of the glandular mucosa, multifocal epithelial hyperplasia, and elevated BrdU labeling index. Intestinal metaplasia and true atrophy were not present but proliferative glands were poorly differentiated, lined by mucus-type epithelial cells with no parietal, chief or other specialized cell types. Neoplasms developed only in MNNG-treated mice. of the 180 treated mice the following neoplasms developed: 14 squamous cell carcinomas of mouth and forestomach; 37 hemangiosarcomas of the intestinal serosa; and 15 splenic lymphomas. No tumors were present in the glandular gastric mucosa, and infection did not affect tumor incidence. p53 overexpression occurred in 79% of hemangiosarcomas and 71% of squamous cell carcinomas but not in normal or proliferative gastric glandular mucosa.

CONCLUSIONS

Gastric proliferative lesions in Helicobacter-infected mice are not preneoplastic, and the combination of an alkylating agent and non-neoplastic proliferation does not result in gastric carcinogenesis in mice.

What is the role for vaccination in Helicobacter pylori?

Helicobacter pylori has been implicated in the etiology of peptic ulcer disease, chronic gastritis, gastric carcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Although significant progress has been made in treating this infection with combinations of either antimicrobial agents or antimicrobial agents plus proton pump inhibitors, these antimicrobial-based treatments continue to be suboptimal. Over the past few years it has become increasingly recognized that direct mucosal immunization can induce protection from infection at mucosal surfaces. Therefore, prevention of H. pylori infection by oral immunization is an alternative approach for the control of H. pylori disease. Using the Helicobacter felis mouse model or H. pylori mouse model, both prophylactic and therapeutic oral immunizations have been shown to be effective against H. pylori. In addition, several H. pylori proteins have been identified as potential candidate vaccines, and a phase 1 clinical trial has been completed that demonstrates the safety and tolerability of urease as a vaccine antigen. Such antigens in combination with a safe mucosal adjuvant could be used in the form of an oral vaccine administered during childhood before exposure to H. pylori to prevent infection. In addition, therapeutic immunization alone or as an adjunct to antimicrobial therapy may be capable of achieving a cure rate approaching 100%.

Role of the host in pathogenesis of Helicobacter-associated gastritis: H. felis infection of inbred and congenic mouse strains

In humans, Helicobacter pylori establishes a chronic infection which can result in various degrees of gastric inflammation, peptic ulcer disease, and a predisposition to gastric cancer. It has been suggested that bacterial virulence factors such as the vacuolating toxin (VacA) and the cytotoxin-associated gene product (CagA) may play a major role in determining the clinical outcome of Helicobacter infections. The role of host responses in these varied outcomes has received little attention. Helicobacter felis, which does not express CagA or VacA, causes chronic infection and inflammation in a well-characterized mouse model. We have used this model to evaluate the role of host responses in Helicobacter infections. BALB/c, C3H, and C57BL/6 mice were orally infected with a single strain of H. felis, and 2 and 11 weeks after infection, the mice were sacrificed and evaluated histologically for magnitude of H. felis infection. Intensity and extent of inflammation, and cellular composition of the inflammatory infiltrate. All three strains of mice demonstrated comparable levels of infection at 11 weeks, but the pattern and intensity of inflammation varied from minimal in BALB/c mice to severe in C57BL/6 mice. Gastric epithelial erosions were noted in C3H mice, and mucous cell hyperplasia was observed in C3H and C57BL/6 mice. Abundant mucosal mast cells were observed in the gastric tissues of all three mouse strains. Studies using major histocompatibility complex (MHC)-congenic mice revealed probable contributions by both MHC and non-MHC genes to Helicobacter-induced inflammation. Thus, large variations in the severity of disease were observed after infection of different inbred strains and congenic mice with a single isolate of H. felis. These results demonstrate the importance of the host response in disease outcome following gastric Helicobacter infection.

Helicobacter infections in laboratory animals: a model for gastric neoplasias?

Evidence is rapidly accumulating that Helicobacter pylori is a major risk factor for human gastric adenocarcinomas and all low-grade B-cell gastric lymphomas. Given this, there is a need to develop animal models with a view to discovering not only how carcinogenesis is initiated, but also how the process can be prevented. The lack of H. pylori animal models suitable for long-term studies means that alternatives are needed. The most productive models are likely to be the Helicobacter mustelae-infected ferret or the mouse infected with either Helicobacter felis or 'Helicobacter heilmannii'. The first evidence that helicobacter infection induces a chronic inflammation that progresses to gastric atrophy, the precursor lesion to gastric adenocarcinoma in humans, has come from the mouse model. The severity of inflammation is dependent on the type of mouse strain used, highlighting the importance of host factors in the development of gastritis. Carcinogenesis studies should only be done with mouse strains known to cause atrophy. The H. mustaelae-infected ferret appears very susceptible to the development of adenocarcinoma following ingestion of chemical carcinogens. Long-term infection of mice with H. felis results in the development of low-grade B-cell gastric lymphomas indistinguishable to those found in H. pylori-infected humans. Helicobacter-infected animals, rodents in particular are going to provide exciting opportunities to investigate not only important aspects of gastric cancer and lymphoma but also fundamental issues of carcinogenesis in general.

Animal models and vaccine development

Following the demonstration of Helicobacter pylori as a major gastroduodenal pathogen there was a need to develop animal models in order to investigate mechanisms of pathogenesis and to be able to test new treatment strategies. Helicobacter pylori will only colonize a limited number of hosts including non-human primates, germ-free or barrier raised piglets, germ-free dogs and recently laboratory raised cats. Although these models have proved useful there is a need for more convenient small animal models. The ferret infected with its natural gastric organism, Helicobacter mustelae, is the only other animal to show peptic ulceration and has been successfully used to investigate gastritis and antimicrobial agents. The other commonly used animal model is the laboratory mouse or rat infected with either Helicobacter felis or Helicobacter heilmannii, bacteria that normally colonize cat or dog gastric mucosae. Active/chronic gastritis, gastric atrophy, and lymphoma-like lesions have been shown to develop in H. felis infected mice. The most recent and exciting use of an animal model has been the use of the H. felis mouse model in the development of human vaccines against H. pylori. Mice can be protected against infection with large doses of viable H. felis by oral immunization using sonicates of H. felis or H. pylori or recombinant H. pylori urease together with cholera toxin or cholera toxin-B subunit as the mucosal adjuvant. More importantly it has been shown that immunization of already infected animals results in eradication of infection. This raises the intriguing possibility that therapeutic immunization might be a viable option in the management of Helicobacter-associated disease. If immunization as a therapy of peptic ulcers was combined with short-term acid suppression, the possibility of reinfection may also be eliminated. In those countries where H. pylori infection rates are very high and infection occurs at an early age, large scale oral immunization of sections of the community would not only protect the young from the deleterious consequences of long-term H. pylori infection but could also cure existing disease.

Helicobacter-associated gastritis in SCID mice

Immunodeficient (SCID) and immunocompetent mice were infected with Helicobacter felis to address the role of autoimmunity in Helicobacter-associated gastritis. The extents of inflammation were equivalent in the two groups. The numbers of H. felis organisms were marginally increased in the SCID mice but did not achieve statistical significance. These results indicate that autoimmunity is not necessary to induce disease and that the presence of an adaptive immune system does not significantly affect H. felis colonization.

Recombinant antigens prepared from the urease subunits of Helicobacter spp.: evidence of protection in a mouse model of gastric infection

Urease is an important virulence factor for gastric Helicobacter spp. To elucidate the efficacy of individual urease subunits to act as mucosal immunogens, the genes encoding the respective urease subunits (UreA and UreB) of Helicobacter pylori and Helicobacter felis were cloned in an expression vector (pMAL) and expressed in Escherichia coli cells as translational fusion proteins. The recombinant UreA and UreB proteins were purified by affinity and anion-exchange chromatography techniques and had predicted molecular masses of approximately 68 and 103 kDa, respectively. Western blotting (immunoblotting) studies indicated that the urease components of the fusion proteins were strongly immunogenic and were specifically recognized by polyclonal rabbit anti-Helicobacter sp. sera. The fusion proteins (50 micrograms) were used, in combination with a mucosal adjuvant (cholera toxin), to orogastrically immunize mice against H. felis infection. Gastric tissues from H. felis-challenged mice were assessed by the biopsy urease test and by histology. In mice immunized with recombinant H. felis UreB, 60% of animals (n = 7) were histologically negative for H. felis bacteria after challenge at 17 weeks. This compared with 25% (n = 8) for mice immunized with the heterologous H. pylori UreB antigen. Neither the homologous nor the heterologous UreA subunit elicited protective responses against H. felis infection in mice. The study demonstrated that a recombinant subunit antigen could induce an immunoprotective response against gastric Helicobacter infection.