Development of a mouse model of Helicobacter pylori infection that mimics human disease

Long-term infection with Helicobacter felis and inactivation of the tumour suppressor gene p53 cumulatively enhance the gastric mutation frequency in Big Blue transgenic mice

The aims of this study were to determine whether colonization with Helicobacter felis resulted in the accumulation of mutations within murine gastric tissue and whether the degree of genetic damage was increased by p53 deficiency. Female C57BL/6 mice carrying either the lambda/lacI transgene (Big Blue transgenic mice) or the lambda/lacI transgene and deficient in one allele of the p53 tumour suppressor gene (TSG-p53/Big Blue) were inoculated with H felis. Seven months after inoculation, mutations in the target lacI gene were assessed using the Big Blue transgenic mutagenesis assay system in these animals and in controls. There was an approximately two-fold increase in lacI mutations in gastric mucosa harvested from mice infected with H felis and also from non-infected mice heterozygous for the p53 allele relative to wild-type mice. The mutation frequency in mice infected with H felis and deficient in one allele of p53 was increased approximately three-fold. Active gastric inflammation was significantly greater in H felis-infected p53 hemizygous mice compared with H felis p53 wild-type mice. Gastric epithelial proliferation was similarly increased with infection in both of these latter groups of mice. In infected mice, there was a significant correlation between the mutation frequency and the degree of active gastric inflammation. These data suggest a synergistic action between infection with H felis and p53 deficiency in the accumulation of mutations within gastric tissue. Active neutrophil infiltration in gastric Helicobacter infection may contribute to the increased levels of mutation observed.

Helicobacter pylori toxin VacA is transferred to host cells via a novel contact-dependent mechanism

Helicobacter pylori is the causative agent of peptic ulcer disease. A major virulence factor of H. pylori is VacA, a toxin that causes massive vacuolization of epithelial cell lines in vitro and gastric epithelial erosion in vivo. Although VacA is exported over the outer membrane and is released from the bacteria, a portion of the toxin remains associated with the bacterial surface. We have found surface-associated toxin to be biologically active and spatially organized into distinct toxin-rich domains on the bacterial surface. Upon bacterial contact with host cells, toxin clusters are transferred directly from the bacterial surface to the host cell surface at the bacteria-cell interface, followed by uptake and intoxication. This contact-dependent transfer of VacA represents a cost-efficient route for delivery of VacA and potentially other bacterial effector molecules to target cells.

Effect of heparin binding on Helicobacter pylori resistance to serum

The objective of this study was to evaluate the effect of heparin binding to Helicobacter pylori cells on their survival in the presence of fresh rabbit serum with or without active complement components. Three H. pylori strains were compared and the amounts of heparin added reflected the physiological concentrations that can be found in animal tissues. No growth of H. pylori was noted in the presence of serum. Serum with or without active complement produced a reduction in c.f.u. for strains SPM 326, CCUG 17874(T) and SS1. However, addition of heparin resulted in increased survival of bacterial cells in serum with or without active complement. It appears that heparin binding to H. pylori can prevent bacterial cell death due to the alternative complement system. Heparin binding could also protect from heated serum (complement-inactivated), indicating protection from other serum components besides complement. In vivo, the process of heparin binding could possibly result in facilitated colonization due to a higher survival rate.

Cellular vacuolation and mitochondrial cytochrome c release are independent outcomes of Helicobacter pylori vacuolating cytotoxin activity that are each dependent on membrane channel formation

Helicobacter pylori vacuolating toxin (VacA) is a secreted toxin that is reported to produce multiple effects on mammalian cells. In this study, we explored the relationship between VacA-induced cellular vacuolation and VacA-induced cytochrome c release from mitochondria. Within intoxicated cells, vacuolation precedes cytochrome c release and occurs at lower VacA concentrations, indicating that cellular vacuolation is not a downstream consequence of cytochrome c release. Conversely, bafilomycin A1 blocks VacA-induced vacuolation but not VacA-induced cytochrome c release, which indicates that cytochrome c release is not a downstream consequence of cellular vacuolation. Acid activation of purified VacA is required for entry of VacA into cells, and correspondingly, acid activation of the toxin is required for both vacuolation and cytochrome c release, which suggests that VacA must enter cells to produce these two effects. Single amino acid substitutions (P9A and G14A) that ablate vacuolating activity and membrane channel-forming activity render VacA unable to induce cytochrome c release. Channel blockers known to inhibit cellular vacuolation and VacA membrane channel activity also inhibit cytochrome c release. These data indicate that cellular vacuolation and mitochondrial cytochrome c release are two independent outcomes of VacA intoxication and that both effects are dependent on the formation of anion-selective membrane channels.

Helicobacter pylori VacA activates the p38/activating transcription factor 2-mediated signal pathway in AZ-521 cells

Persistent Helicobacter pylori colonization in the stomach induces gastritis and peptic ulcer and interferes with ulcer healing. Most strains of H. pylori produce a cytotoxin, VacA, that induces cytoplasmic vacuolation in epithelial cells with structural and functional changes, leading to gastric injury. VacA is known to cause cell death by mitochondrial damage. We hypothesized that VacA might disrupt other signaling pathways; to that end, we examined the effects of VacA on MAPKs to elucidate their role in the abnormalities seen in VacA-treated cells. VacA stimulated phosphorylation of p38 and Erk1/2, but not JNK, in AZ-521 cells. Both phosphorylation and kinase activation of p38 were maximal 10-30 min after addition of VacA and declined thereafter. Treatment with anti-VacA antibody or the p38 inhibitor SB203580 blocked p38 phosphorylation caused by VacA and inhibited VacA-induced phosphorylation of activating transcription factor 2 (ATF-2), which is implicated in transcriptional control of stress-responsive genes. These data indicate that VacA stimulates a p38/ATF-2-mediated signal pathway. However, 10 microM SB203580, which is sufficient to decrease p38 phosphorylation, did not inhibit VacA-induced cellular vacuolation, decrease in mitochondrial membrane potential, or cytochrome c release from mitochondria. These results suggest that VacA-induced activation of p38/ATF-2-mediated signal pathway is independent of cellular vacuolation, decrease in mitochondrial membrane potential, or cytochrome c release from mitochondria caused by VacA. The cytotoxin may thus act independently on several cellular targets, leading to disruption of signaling, regulatory, and metabolic pathways.

The effect of gender on Helicobacter felis-mediated gastritis, epithelial cell proliferation, and apoptosis in the mouse model

The murine Helicobacter felis model has been extensively used to investigate the importance of host factors in the development of chronic gastritis. The effect of gender in this murine model is unknown. Male and female C57BL/6J mice were infected with H felis for up to 1 year. At 4, 8, 19, 36, and 52 weeks post-infection, gastric histopathology, epithelial cell proliferation, and apoptosis were examined and compared with age- and gender-matched controls. In female mice, infection with H felis resulted in an earlier onset of chronic gastric inflammation, epithelial hyperplasia, and oxyntic cell loss than males. In females, there was a trend towards increased gastric pathology compared with males, with long-term-infected female mice having significantly greater (p < 0.05) chronic inflammation than male mice. The histopathological differences in male and female mice did not relate to the density of H felis infection. Female mice infected with H felis had significantly increased gastric epithelial cell proliferation in the cardia and corpus at both 8 and 52 weeks post-infection (p < 0.05). Epithelial cell apoptosis in the glandular mucosa of the corpus at 36 and 52 weeks post-infection was significantly increased (p < 0.05) in female mice compared with uninfected gender controls. In contrast, there was no significant increase in epithelial cell proliferation or apoptosis in any area of the stomach at any time point after H felis infection in male mice. These results demonstrate that there are gender differences in the gastric inflammatory and epithelial response to H felis in the murine model. The functional importance of gender should be considered in future murine studies on H felis- and H pylori-induced chronic gastritis.

Protective immunity against Helicobacter is characterized by a unique transcriptional signature

Immunization with a whole-cell sonicate vaccine of Helicobacter felis in conjunction with cholera toxin as a mucosal adjuvant induces long-term protective immunity in a majority of laboratory mice. We have combined gene expression profiling and immunohistochemical analysis on a set of immunized animals to better understand the mechanism of protection. The stomachs of protected animals exhibited a strikingly different transcriptional profile compared with those of nonprotected or control mice, indicating that vaccination targets the appropriate site and leaves a molecular signature. Among the genes whose up-regulation is significantly correlated with protection are a number of adipocyte-specific factors. These include the fat-cell-specific cytokines adipsin, resistin, and adiponectin and the adipocyte surface marker CD36. Interestingly, potentially protective T and B lymphocytes can be found embedded in the adipose tissue surrounding protected stomachs but never in control or unprotected stomachs. Adipsin-specific immunohistochemical staining of protected stomach sections further revealed molecular cross-talk between adjacent lymphoid and adipose cell populations. We propose a mechanism of protection that involves the effector responses of either or both lymphocyte subclasses as well as the previously unappreciated paracrine functions of adipose tissue surrounding the resident lymphocytes.

Helicobacter pylori induces cyclooxygenase-1 and cyclooxygenase-2 expression in vascular endothelial cells

BACKGROUND

Helicobacter pylori induces cyclooxygenase activity in the stomach, although the COX isoform and cellular source are unclear. A potential source is the vascular endothelial cell, which plays a role in regulating mucosal blood flow and inflammatory cell infiltration.

METHODS

We examined the effect of four strains (toxigenic and non-toxigenic) of H. pylori on COX isoform expression in vascular endothelial cells. Prostaglandin synthesis was measured by enzyme immunoassay and COX isozyme expression determined by Western blot and RT-PCR. Gene induction was examined using 5' deletion constructs of the COX-1 and COX-2 promoters coupled with luciferase.

RESULTS

All H. pylori strains induced prostaglandin generation and expression of both COX-1 and COX-2 in HUVEC, although this was most pronounced with the highly toxigenic strain H. pylori 60190. Treatment of the cells with selective COX inhibitors demonstrated that COX-1 was predominantly responsible for the enhanced generation of prostacyclin induced by H. pylori 60190. Similar results were seen with H. pylori broth culture filtrates, suggesting that a secreted product was responsible. Induction of COX-2 reflected both enhanced gene expression and stabilization of the mRNA.

CONCLUSIONS

H. pylori increased both COX-1 and COX-2 activity in vascular endothelial cells. This increased generation of endothelial cell prostacyclin may play a role in modulating mucosal blood flow, platelet function and inflammatory cell infiltration in response to H. pylori infection. The regulation of COX-1 at the transcriptional level by H. pylori described in this study is a novel finding and calls into question the traditional description of COX-1 as a purely constitutive, housekeeping gene.

Enhanced mucosal and systemic immune responses to Helicobacter pylori antigens through mucosal priming followed by systemic boosting immunizations

It is estimated that Helicobacter pylori infects the stomachs of over 50% of the world's population and if not treated may cause chronic gastritis, peptic ulcer disease, gastric adenocarcinoma and gastric B-cell lymphoma. The aim of this study was to enhance the mucosal and systemic immune responses against the H. pylori antigens cytotoxin-associated gene A (CagA) and neutrophil-activating protein (NAP), through combinations of mucosal and systemic immunizations in female BALB/c mice. We found that oral or intranasal (i.n.) followed by i.m. immunizations induced significantly higher serum titres against NAP and CagA compared to i.n. alone, oral alone, i.m. alone, i.m. followed by i.n. or i.m. followed by oral immunizations. However, only oral followed by i.m. immunizations induced anti-NAP antibody-secreting cells in the stomach. Moreover, mucosal immunizations alone or in combination with i.m., but not i.m. immunizations alone, induced mucosal immunoglobulin A (IgA) responses in faeces. Any single route or combination of immunization routes with NAP and CagA preferentially induced antigen-specific splenic interleukin-4-secreting cells and far fewer interferon-gamma-secreting cells in the spleen. Moreover, i.n. immunizations alone or in combination with i.m. immunizations induced predominantly serum IgG1 and far less serum IgG2a. Importantly, we found that while both i.n. and i.m. recall immunizations induced similar levels of serum antibody responses, mucosal IgA responses in faeces were only achieved through i.n. recall immunization. Collectively, our data show that mucosal followed by systemic immunization significantly enhanced local and systemic immune responses and that i.n. recall immunization is required to induce both mucosal and systemic memory type responses.

Determinants of non-toxicity in the gastric pathogen Helicobacter pylori

The Helicobacter pylori vacuolating cytotoxin gene, vacA, is naturally polymorphic, the two most diverse regions being the signal region (which can be type s1 or s2) and the mid region (m1 or m2). Previous work has shown which features of vacA make peptic ulcer and gastric cancer-associated type s1/m1 and s1/m2 strains toxic. vacA s2/m2 strains are associated with lower peptic ulcer and gastric cancer risk and are non-toxic. We now define the features of vacA that determine the non-toxicity of these strains. To do this, we deleted parts of vacA and constructed isogenic hybrid strains in which regions of vacA were exchanged between toxigenic and non-toxigenic strains. We showed that a naturally occurring 12-amino acid hydrophilic N-terminal extension found on s2 VacA blocks vacuolating activity as its removal (to make the strain s1-like) confers activity. The mid region of s2/m2 vacA does not cause the non-vacuolating phenotype, but if VacA is unblocked, it confers cell line specificity of vacuolation as in natural s1/m2 strains. Chromosomal replacement of vacA in a non-toxigenic strain with vacA from a toxigenic strain confers full vacuolating activity proving that this activity is entirely controlled by elements within vacA. This work defines why H. pylori strains with different vacA allelic structures have differing toxicity and provides a rational basis for vacA typing schemes.

Animal models of Helicobacter pylori infection and disease

The acceptance of Helicobacter pylori as a major human pathogen has necessitated the development of animal models to help elucidate the pathogenic mechanisms of this bacterium and aid in the development of improved strategies for the treatment of gastric disease. Appropriate models, utilising a range of animal species, have been developed to examine factors such as the influence of host responses and bacterial factors in disease development and the success of new therapeutic regimens, including vaccination, to cure infection.

Effect of total secondary carotenoids extracts from Chlorococcum sp on Helicobacter pylori-infected BALB/c mice

Helicobacter pylori is a human pathogen associated with type B gastritis, peptic ulcer disease and gastric cancer. A high intake of carotenoids has been suggested to prevent development of gastric malignancies. Microalgae Chlorococcum sp. could accumulate secondary carotenoids under stress conditions. The aim of the present study was to investigate whether dietary cell extract of Chlorococcum sp. could affect the bacterial load of H. pylori infected BALB/c mice and whether it could induce modulation of cytokine production. BALB/c mice were infected with H. pylori three times at 2-day intervals. Two weeks later, they were orally fed with cell extract of Chlorococcum sp. for the following 2 weeks. Animals were killed at the end of the experiments. Stomachs were removed and paraffin sections were stained for histology examination. Splenocytes were obtained and cultured in vitro with H. pylori sonicate to evaluate induction of interferon gamma (IFN-gamma) and interleukin 4 (IL-4) secretion. Mice treated with carotenoids-rich algal meal showed significantly reduced bacterial load and gastric inflammation. These changes were associated with a shift of the T-lymphocytes response from a predominant T helper type 1 (Th1) response dominated by IFN-gamma to a Th1/Th2 response with IFN-gamma and IL-4.

Functional and morphological aspects of Helicobacter pylori-induced gastric cancer in Mongolian gerbils

BACKGROUND

Helicobacter pylori infection of Mongolian gerbils is an established model of gastric carcinogenesis, but gastric secretory aspects of this carcinogenesis have not been studied.

METHODS

The effects of single intragastric inoculation of gerbils with H. pylori strain (cagA+ vacA+, 5 x 10(6) CFU/ml) or vehicle (saline) were examined at 1, 2, 4, 6, 9, 12 and 30 weeks from inoculation. Gastric morphology, the presence of H. pylori using the rapid urease test, the density of H. pylori and 16S rRNA and the plasma gastrin and somatostatin were determined.

RESULTS

H. pylori was detected in gastric mucosa in all infected animals. Basal gastric acid in gerbils was reduced by about 50% after H. pylori inoculation. Early lesions seen at 4 weeks after H. pylori inoculation consisted of chronic gastritis with thickened mucosal folds, oedema, congestion and mucosal lymphocytic infiltration. Adenomatous hyperplasia with cellular atypia with increased mitotic activity and the formation of apoptotic bodies and visible erosions and ulcerations were observed at 12-30 weeks after inoculation. The atypical gastric glands were situated 'back-to-back', suggesting gastric pre-cancer. The gastric blood flow in H. pylori-infected gerbils was significantly lower than that in the controls. Six- to seven-fold increase in plasma gastrin levels combined with significant fall in gastric somatostatin contents and the intraepithelial neoplasia were noticed in gerbils at all tested periods.

CONCLUSION

H. pylori-infection in gerbils resulted in gastric pre-cancer associated with functional changes, such as suppression of gastric secretion and impairment of both gastric mucosal microcirculation and the gastrin-somatostatin link.

Five month persistence of Helicobacter pylori infection in guinea pigs

Seven Dunkin-Hartley guinea pigs were infected with the Sydney strain of H. pylori (SS1). Gastric histopathology was evaluated and serum antibody response to H. pylori cell-surface proteins was analysed by enzyme immunoassay (EIA) and immunoblot. Tissue and faecal samples from five control animals were analysed for the presence of naturally occurring Helicobacter spp. infection by culture and Helicobacter genus-specific PCR. The H. pylori infection persisted for 5 months, in most animals accompanied by a histologically severe antral gastritis, exhibiting focal degeneration and necrosis of gastric crypt epithelium. Increased numbers of mitotic figures were observed in the gastric epithelium, indicating a regenerative process. Infected animals displayed specific antibodies towards H. pylori cell-surface proteins in immunoblot, whereas EIA was of dubious value creating false-positive results. Serum complement C3 and cholesterol levels appeared to be elevated in infected animals. Helicobacter spp. infection was not detected in the control animals. The persistent infection, accompanied by severe gastritis and a prominent serum antibody response, and the apparent absence of a natural Helicobacter spp. infection makes the guinea pig model useful in H. pylori research.

Orogastric vaccination of guinea pigs with Helicobacter pylori sonicate and a high dose of cholera toxin lowers the burden of infection

Guinea pigs were vaccinated orogastrically with Helicobacter pylori cell sonicate (CS) and 10 microg or 100 microg cholera toxin (CT) or CT only. Nai;ve animals were used as a control. In both experiments, vaccination primed the local IgG and IgA response, irrespective of the CT dose. After challenge, only the group of animals immunised with CS and 100 microg CT had a significantly lower number of H. pylori in the antral region of the stomach, but vaccination did not prevent H. pylori infection. This protective effect was not associated with a switch in IgG subclass, which remained predominantly IgG2. The levels of specific antibodies in serum and the gastric mucosa which were similar to naive unprotected animals. In conclusion, the ability of mucosal adjuvants such as CT to induce a protective immune response may be host dependent and findings in the Helicobacter-mouse model should be interpreted with caution.

Infection of Mongolian gerbils with Chinese Helicobacter pylori strains

To date only a few Helicobacter pylori strains have been demonstrated to colonise Mongolian gerbils successfully. The aim of this study was to establish stable colonisation of Chinese strains of H. pylori in gerbils. Fresh clinical isolates from Chinese patients were inoculated into gerbils. At 4-6 weeks post inoculation, infection status was evaluated by culture, biopsy urease test and pathology. Sequencing of glmM and random amplified polymorphic DNA (RAPD) fingerprinting of DNA from cultured H. pylori were used to evaluate the genetic identity of pre-inoculated and post-inoculated strains. The ability of pre- and post-inoculated strains to stimulate interleukin-8 transcription in L5F11 gastric epithelial cells was analysed. Three of five clinical isolates colonised gerbils. The three pre- and post-inoculation strains had identical glmM sequences and RAPD profiles, and stimulated luciferase secretion from L5F11 epithelial cells. The strain that caused severe pathological changes was selected for repeat infection to prove reproducible and stable colonisation. The cagA+ strain 42GX gave stable colonisation in the gerbil and induced severe gastritis.

Protein-tyrosine phosphatase alpha, RPTP alpha, is a Helicobacter pylori VacA receptor

Helicobacter pylori vacuolating cytotoxin, VacA, induces vacuolation, mitochondrial damage, cytochrome c release, and apoptosis of gastric epithelial cells. To detect gastric proteins that serve as VacA receptors, we used VacA co-immunoprecipitation techniques following biotinylation of the cell surface and identified p250, a receptor-like protein-tyrosine phosphatase beta (RPTP beta) as a VacA-binding protein (Yahiro, K., Niidome, T., Kimura, M., Hatakeyama, T., Aoyagi, H., Kurazono, H., Imagawa, K., Wada, A., Moss, J., and Hirayama, T. (1999) J. Biol. Chem. 274, 36693-36699). VacA causes vacuolation of G401 cells, a human kidney tumor cell line, although they do not express RPTP beta. By co-immunoprecipitation with VacA, we identified p140 as a potential receptor in those cells. p140 purified by chromatography on a peanut agglutinin affinity matrix contained internal amino acid sequences of RGEENTDYVNASFIDGYRQK and AEGILDVFQTVK, which are identical to those in RPTP alpha. The peptide mass fingerprinting of p140 by time of flight-MS analysis also supported this identification. Treatment of G401 cells with RPTP alpha-morpholino antisense oligonucleotide before exposure to toxin inhibited vacuolation. These data suggest that RPTP alpha acts as a receptor for VacA in G401 cells. Thus, two receptor tyrosine phosphatases, RPTP alpha and RPTP beta, serve as VacA receptors.

Binding and internalization of Helicobacter pylori VacA via cellular lipid rafts in epithelial cells

In this study we investigated the roles of lipid rafts and glycosylphosphatidylinositol-anchored proteins (GPI-APs) in the process of VacA binding and internalization into epithelial cells. Vacuolating activity analysis in AGS, CHO cells, and a CHO-derived line that highly expresses GPI-linked fasI proteins indicated the significance of cholesterol and GPI-APs for VacA activity. Flow cytometric analysis along with VacA-cholesterol co-extraction experiments showed a cholesterol-dependent manner for VacA cell-binding activity, while GPI-APs were not related to it. Differential detergent extraction and fractionation in sucrose density gradient showed co-association of VacA and fasI with rafts on cell membranes. Subcellular distribution of fasI visualized by confocal microscope suggested that fasI trafficked via a newly defined endocytic pathway for GPI-APs in the derived line. Upon VacA intoxication, VacA was visualized to co-migrate along with fasI and finally induced vacuolation coupled with dramatic redistribution of fasI molecules. These results suggest that VacA exploits rafts for docking and entering the cell via the endocytic pathway of GPI-APs.

Profiling and identification of eubacteria in the stomach of Mongolian gerbils with and without Helicobacter pylori infection

BACKGROUND

Mongolian gerbils are frequently used to study Helicobacter pylori-induced gastritis and its consequences. The presence of an indigenous bacterial flora with suppressive effect on H. pylori may cause difficulties with establishing this experimental model.

AIM

The aim of the present study was to determine bacterial profiles in the stomach of Mongolian gerbils with and without (controls) H. pylori infection.

METHODS

Gastric tissue from H. pylori ATCC 43504 and CCUG 17874 infected and control animals were subjected to microbial culturing and histology. In addition, gastric mucosal samples from H. pylori ATCC 43504 infected and control animals were analyzed for bacterial profiling by temporal temperature gradient gel electrophoresis (TTGE), cloning and pyrosequencing of 16S rDNA variable V3 region derived PCR amplicons.

RESULTS

Oral administration of H. pylori ATCC 43504, but not CCUG 17874, induced colonization and gastric inflammation in the stomach of Mongolian gerbils. Temporal temperature gradient gel electrophoresis (TTGE) and partial 16S rDNA pyrosequencing revealed the presence of DNA representing a mixed bacterial flora in the stomach of both H. pylori ATCC 43504 infected and control animals. In both cases, lactobacilli appeared to be dominant.

CONCLUSION

These findings suggest that indigenous bacteria, particularly lactobacilli, may have an impact on the colonization and growth of H. pylori strains in the stomach of Mongolian gerbils.

Gastric mucosal blood flow changes in Helicobacter pylori infection and NSAID-induced gastric injury

BACKGROUND

The impact of H. pylori infection on gastric mucosal blood flow and NSAID-induced gastric damage is unclear.

AIM

To study the effects of H. pylori infection on gastric mucosal blood flow, both at basal conditions and after NSAID exposure, and its relation with mucosal damage and nitric oxide production.

METHODS

Gastric mucosal blood flow, nitric oxide production and gastric damage were assessed in time after H. pylori SS1 or E. coli inoculation in mice. Experiments were conducted in basal conditions or after oral exposure to indomethacin (20 mg/kg).

RESULTS

H. pylori infected mice exhibited a significant increase in gastric blood flow and gastric nitric oxide production 1 week after infection, but those parameters returned to basal levels by 4 weeks. NSAID challenge elicited a similar reduction in gastric blood flow [25-35%] in H. pylori-infected and control animals. However, only 1 week H. pylori-infected mice, which exhibited a significant baseline hyperemia, were able to maintain gastric blood flow values within the normal range after NSAID exposure. NSAID-induced gastric damage was increased in H. pylori-infected mice by 4 weeks, but not 1 week after infection.

CONCLUSIONS

Underlying H. pylori infection aggravates acute NSAID-induced gastric damage. However, at early phases, gastric hyperemia associated with increased nitric oxide production may exert some protective role.

Modification in the ppk gene of Helicobacter pylori during single and multiple experimental murine infections

The bacterial pathogen Helicobacter pylori is highly adapted to the human stomach, and a high level of polymorphism is observed among clinical isolates. This polymorphism may be the consequence of adaptive changes during colonization, making a strain better able to survive, to evade the immune system, and to provoke a chronic infection. To investigate the mechanisms involved in the acquisition of diversity in H. pylori, mouse models of single infections, coinfections, and superinfections were developed. These experimental infections were conducted with strain SS1, well known to be mouse adapted, and with two strains freshly isolated from infected patients: Hp141 and Hp145. Genetic modifications occurring in these strains were studied over time by comparing randomly selected colonies of the emerging strains to those of the infecting strains by using randomly amplified polymorphic DNA fingerprinting with six different primers and by using PCR to amplify the vacA and cagA genes. We showed that, regardless of the number of infecting strains, only one emerged from the animals and that the establishment of a first strain thwarted the implantation of a second strain. During both a single infection and a coinfection with SS1, Hp141 was replaced by a genetic variant (Hp141v) that overcame SS1 in coinfection experiments. Hp141v exhibited a deletion of a 102-bp repeated sequence within the ppk gene, which encodes polyphosphate kinase (PPK), an enzyme involved in the physiological adaptation of the microbial cell to nutritional and environmental stresses. The deletion led to higher enzymatic activity of PPK, and the variant exhibited a better capacity to colonize mice. Considering that the modified gene is known to be involved in adaptation to a new environment, our results are consistent with an adaptive change in strain Hp141 and suggest that PPK is an important virulence factor in H. pylori.

Helicobacter pylori virulence factors and the host immune response: implications for therapeutic vaccination

Helicobacter pylori colonizes the human gastric mucosa and is associated with specific gastric disease. Virulence factors, such as urease, the vacuolating toxin (VacA), the cytotoxin-associated antigen CagA or blood-group-antigen-binding adhesin (BabA), an adherence factor, might account for the development of different diseases. Vaccination trials exploiting the antigenic properties of some of these proteins have not been successful in preventing infection in humans. A more in-depth understanding of the immune response to H. pylori infection as well as additional information on suitable epitopes and adjuvants will be required before a successful vaccine can be developed.

Recombinant HpaA purified from Escherichia coli has biological properties similar to those of native Helicobacter pylori HpaA

The aim of this study was to recombinantly produce and purify Helicobacter pylori adhesin A (HpaA) from Escherichia coli and compare it to purified native H. pylori HpaA, for potential use as a vaccine antigen. The hpaA gene was cloned from H. pylori, transferred to two different expression vectors, and transformed into E. coli. Expression of rHpaA was analysed by immunoblot, inhibition ELISA, and semi-quantitative dot-blot. Using affinity chromatography, rHpaA was purified from E. coli and native HpaA from H. pylori. The binding of both purified proteins to sialic acid was analysed and antibody titres to native and rHpaA were compared after intraperitoneal immunisation of C57/Bl mice. The rHpaA protein was highly expressed in E. coli from both vectors. Purified recombinant and native HpaA bound similarly to fetuin but also to the non-sialylated asialofetuin. Both native HpaA and rHpaA induced comparable amounts of specific antibodies in serum after immunisation and they were identical in double immunodiffusion. In conclusion, rHpaA was successfully produced in E. coli. Purified rHpaA showed biological properties similar to those of native HpaA isolated from H. pylori and may therefore be further used as an antigen in the development of a vaccine against H. pylori infection.

Deleterious effect of Helicobacter pylori infection on the course of acute pancreatitis in rats

BACKGROUND

Helicobacter pylori (Hp) infection is involved in various gastroduodenal pathologies. Also, the potential role of Hp infection has been proposed in several extragastroduodenal disorders, such as cardiovascular, skin or immunological diseases. The role of Hp infection in acute pancreatitis has not been tested. The aim of this study was to determine the influence of Hp infection on the course of acute ischemia/reperfusion-induced pancreatitis in rats.

METHODS

Inoculation with CagA- and VacA-positive Hp or administration of vehicle were performed after visceral ischemia. Visceral ischemia was evoked by clamping of the celiac artery for 30 min. Four weeks later, after full recovery from primary ischemia-induced damage, acute pancreatitis was evoked by limitation of pancreatic blood flow (PBF) in the splenic artery for 30 min using microvascular clips. Rats were sacrificed 1 h or 1, 3, 5, 10, and 21 days after removal of the vascular clips. Hp infection was assessed by the urease test and gastric histology.

RESULTS

In Hp-negative rats ischemia followed by reperfusion caused acute pancreatitis as manifested by a reduction in PBF and pancreatic DNA synthesis, as well as by increases in plasma amylase, lipase, interleukin-1beta (IL-1beta) and interleukin-10 (IL-10). The morphological features of pancreatic tissue showed necrosis, strongly pronounced edema, hemorrhages and leukocyte infiltration. The maximal intensity of pancreatic damage was observed between the 1st and 3rd day of reperfusion, then pancreatic tissue underwent regeneration. Hp infection resulted in a significant reduction in PBF and an aggravation of pancreatic ischemia 1 h and 3 and 5 days after reperfusion. Plasma amylase in Hp-infected rats was significantly higher than in Hp-negative animals 1 h and 1 and 3 days after ischemia, whereas in lipase this significant difference was observed between the 1st and 3rd day. DNA synthesis in Hp-positive rats was additionally reduced 1 h and 3 and 5 days after ischemia. Also ischemia evoked an increase in serum IL-1beta and IL-10, and morphological manifestations of pancreatitis were additionally enhanced by Hp infection.

CONCLUSIONS

(1) Hp infection increases the severity of ischemia-induced pancreatitis; (2) Hp infection increases production of pro-inflammatory IL-1beta, and (3) Hp infection aggravates disturbances in pancreatic microcirculation in acute pancreatitis.

Generation of Helicobacter pylori ghosts by PhiX protein E-mediated inactivation and their evaluation as vaccine candidates

Bacterial ghosts are empty cell envelopes, which may be generated by the controlled expression of the PhiX174 lysis gene E in gram-negative bacteria to obtain vaccine candidates. We describe here the application of this technology to Helicobacter pylori. The lysis gene cassette was cloned into an Escherichia coli-Helicobacter pylori shuttle vector and introduced into an H. pylori recipient strain by bacterial conjugation. Temperature induction of the lysis gene cassette revealed a quantitative killing of the H. pylori culture without induction of lysis-resistant bacteria. Biochemical and transmission electron microscopic studies identified structurally intact H. pylori. Prophylactic oral vaccination experiments using these H. pylori ghosts in the BALB/c mouse model showed a significant reduction of the bacterial load in the ghost group, as measured by a quantitative bacterial reisolation procedure. Ten of 10 and 5 of 10 mice were protected, respectively, without the use of a mucosal adjuvant. Coadministration of ghosts with cholera toxin as mucosal adjuvant resulted in a complete protection of 10 of 10 and 8 of 8 mice against H. pylori challenge, with three animals showing a sterile immunity.

Stimulation of adhesion molecule expression by Helicobacter pylori and increased neutrophil adhesion to human umbilical vein endothelial cells

Helicobacter pylori upregulates endothelial adhesion molecules but the pattern is unclear. Human umbilical vein endothelial cells (HUVEC) were exposed to control medium or H. pylori 60190. Binding of monoclonal antibodies against P-selectin, E-selectin, vascular adhesion molecule-1 (VCAM-1) and intercellular adhesion molecule-1 (ICAM-1) was determined using enzyme-linked immunosorbent assay. Binding of polymorphonuclear leukocytes to HUVEC was determined on cells exposed as above. After 6 h exposure to H. pylori, there were 30%, 124%, 167% and 100% increases in P-selectin, E-selectin, VCAM-1 and ICAM-1 levels and a 400% increase in polymorphonuclear leukocyte adhesion in HUVEC exposed to H. pylori. Effects of incubation for other intervals between 0 and 18 h are also described. H. pylori exerts some of its effects on gastric mucosa via gastric vasculature. This study gives insight into the pattern of H. pylori-associated endothelial adhesion molecule upregulation.

Experimental colonization of mice by fresh clinical isolates of Helicobacter pylori is not influenced by the cagA status and the vacA genotype

Developing murine models of infection by Helicobacter pylori is quite useful but not all the strains are able to colonize the mouse. In order to study the influence of the two main virulence factors, CagA and VacA, on the establishment of H. pylori in mice, we have inoculated C57BL/6 mice with 15 strains randomly chosen among clinical strains freshly isolated from biopsy specimens of infected patients and five reference strains. Only six of the clinical strains and two of the reference strains could infect the animals regardless of the cagA status and the vacA genotype. We concluded that 40% of the H. pylori strains are able to infect mice and that the capacity of colonization is not influenced by the cagA status and the vacA genotype. These factors cannot be used to predict the success of an experimental infection.

Multiparameter selection of Helicobacter pylori antigens identifies two novel antigens with high protective efficacy

A multiparameter selection of Helicobacter pylori antigens for vaccine development identified 15 candidates, 6 of which are known protective antigens. Two novel antigens with low homology to other organisms (HP0231 and HP0410) were overexpressed and purified with high yields. Both confer protective immunity in the mouse Helicobacter infection model.

Real-time quantitative PCR for detection of Helicobacter pylori

Helicobacter pylori is one of the most common chronic infections in humans, in whom it is a key etiological factor in peptic ulcer disease, gastric mucosa-associated lymphoid tissue lymphoma, and gastric adenocarcinoma. Humans are the bacterium's only host. Here we report the development of a real-time quantitative (Q) PCR-based assay to measure ureC gene copy number to detect H. pylori, based on the fact that there is only one copy of the ureC gene per bacterium. Upon optimization of LightCycler Q-PCR conditions, we obtained a standard curve with a linear range (correlation coefficient = 1) across six logs of DNA concentration. We were able to accurately quantify as few as 1,000 bacteria in our assay. Analysis of variance on 15 randomly selected clinical samples showed good reproducibility of this assay. Comparison of Q-PCR results with bacterial culture and histopathological results from an additional 85 clinical biopsy samples showed a significant difference for the presence of H. pylori. Many samples that were negative for H. pylori by culture and histopathology were positive by Q-PCR. Contamination of PCR by H. pylori or H. pylori genetic material could not be ruled out. In summary, we developed a rapid, sensitive, and real-time Q-PCR method for detecting H. pylori. This technique offers a significant improvement over other available methods for detecting H. pylori in clinical and research samples.

Two predicted chemoreceptors of Helicobacter pylori promote stomach infection

Helicobacter pylori must be motile or display chemotaxis to be able to fully infect mammals, but it is not known how this chemotaxis is directed. We disrupted two genes encoding predicted chemoreceptors, tlpA and tlpC. H. pylori mutants lacking either of these genes are fully motile and chemotactic in vitro and are as able as the wild type to infect mice when they are the sole infecting strains. In contrast, when mice are coinfected with the H. pylori SS1 tlpA or tlpC mutant and the wild type, we find more wild type than mutant after 2 weeks of colonization. Neither strain has an in vitro growth defect. These results suggest that the tlpA- and tlpC-encoded proteins assist colonization of the stomach environment.

Plasma membrane cholesterol modulates cellular vacuolation induced by the Helicobacter pylori vacuolating cytotoxin

The Helicobacter pylori vacuolating cytotoxin (VacA) induces the degenerative vacuolation of mammalian cells both in vitro and in vivo. Here, we demonstrate that plasma membrane cholesterol is essential for vacuolation of mammalian cells by VacA. Vacuole biogenesis in multiple cell lines was completely blocked when cholesterol was extracted selectively from the plasma membrane by using beta-cyclodextrins. Moreover, increasing plasma membrane cholesterol levels strongly potentiated VacA-induced vacuolation. In contrast, inhibiting de novo biosynthesis of cholesterol with lovastatin or compactin had no detectable effect on vacuolation. While depletion of plasma membrane cholesterol has been shown to interfere with both clathrin-mediated endocytosis and caveola-dependent endocytosis, neither of these two internalization pathways was found to be essential for vacuolation of cells by VacA. Depleting plasma membrane cholesterol attenuated the entry of VacA into HeLa cells. In addition, beta-cyclodextrin reagents blocked vacuolation of cells that were either preloaded with VacA or had VacA directly expressed within the cytosol. Collectively, our results suggest that plasma membrane cholesterol is important for both the intoxication mechanism of VacA and subsequent vacuole biogenesis.

New strategies for the prevention and treatment of Helicobacter pylori infection

Helicobacter pylori infects the stomach of > 50% of the human population worldwide, with higher prevalence in the developing countries. A strict correlation between H. pylori infection and gastroduodenal diseases has been demonstrated, including gastritis, peptic ulcer and gastric cancer. Current therapies against H. pylori consist of an antisecretory plus antibiotics. These therapies are effective in 80 - 90% of the cases; presently, no alternative therapies have been shown to give comparable or better results. There are two main reasons for therapy failure: poor compliance, which results in cure discontinuation, and antibiotic resistance. To overcome the drawbacks inherent to any antibiotic therapy, a prophylactic vaccine seems to be the most reasonable approach. Vaccines have been developed based on data obtained in animal models, a number of which are currently in Phase I clinical trials, in some cases giving encouraging data for safety and immunogenicity. In the absence of any immunological correlate of protection against H. pylori, it will be possible to evaluate the efficacy of these vaccines only in large Phase III clinical trials.

Effects of oral vaccination and immunomodulation by cholera toxin on experimental Helicobacter pylori infection, reinfection, and gastritis

Therapeutic vaccination is an attractive strategy to control infection and disease caused by Helicobacter pylori. In mice infected with H. pylori we have studied the protective effect of oral immunization with an H. pylori lysate preparation given together with the mucosal adjuvant cholera toxin (CT), both against the initial infection and against a later reinfection challenge. We have also examined the effects of treatment with the CT adjuvant alone on H. pylori infection and reinfection. Specific immunization with lysate was found to result in a sixfold reduction of the extent (bacterial load) of the primary infection and also to provide similar levels of protection against reinfection. However, these effects were associated with severe postimmunization gastritis. In contrast, oral treatment with CT alone at the time of initial infection, while unable to suppress the initial infection, gave rise to a 20-fold reduction in bacterial load upon reinfection without causing any associated gastric inflammation. Both the infected animals that were specifically immunized and those that were treated with CT only displayed increased in vitro proliferative responses of mononuclear cells to H. pylori antigens. Antibody levels in response to H. pylori were on the other hand only marginally increased after treatment with CT, whereas they were markedly elevated after immunization with lysate plus CT, with a rise in both (Th2-driven) immunoglobulin G1 (IgG1) and, especially, (Th1-driven) IgG2a antibodies. The results illustrate the complex balance between protection and harmful inflammation after postinfection vaccination against H. pylori as studied in a mouse model.

Fluorescence resonance energy transfer microscopy of the Helicobacter pylori vacuolating cytotoxin within mammalian cells

The Helicobacter pylori vacuolating cytotoxin (VacA) binds and enters mammalian cells to induce cellular vacuolation. To investigate the quaternary structure of VacA within the intracellular environment where toxin cytotoxicity is elaborated, we employed fluorescence resonance energy transfer (FRET) microscopy. HeLa cells coexpressing full-length and truncated forms of VacA fused to cyan fluorescent protein (CFP) or yellow fluorescent protein (YFP) were analyzed for FRET to indicate direct associations. These studies revealed that VacA-CFP and VacA-YFP interact within vacuolated cells, supporting the belief that monomer associations at an intracellular site are important for the toxin's vacuolating activity. In addition, the two fragments of proteolytically nicked VacA, p37 and p58, interact when coexpressed within mammalian cells. Because p37 and p58 function in trans when expressed separately within mammalian cells, these data suggest that the mechanism by which these two fragments induce vacuolation requires direct association. FRET microscopy also demonstrated interactions between mutant forms of VacA, as well as wild-type VacA with mutant forms of the toxin within vacuolated cells. Finally, a dominant-negative form of the toxin directly associates with wild-type VacA in cells where vacuolation was not detectable, suggesting that the formation of complexes comprising wild-type and dominant-negative forms of toxin acts to block intracellular toxin function.

Rapid genetic analysis of Helicobacter pylori gastric mucosal colonization in suckling mice

Previously described animal models for Helicobacter pylori infection have been limited by cumbersome host requirements (e.g., germ-free conditions or unusual species) or are applicable to only special subsets of H. pylori strains (e.g., fresh clinical isolates or animal-adapted derivatives). Here, we report that 5- to 6-day-old outbred CD-1 (ICR) suckling mice support 24-h colonization of all H. pylori strains tested (SS1, 26695 SmR-1, 43504 SmR-1, and G27 SmR-1), including lab-passaged strains that cannot be adapted for colonization of adult animals. Total colony-forming units (cfu) recovered from infection with lab-passaged strains did not differ from those with mouse-adapted SS1. We also tested this model's ability to detect colonization defects in strains carrying mutations in known virulence genes by coinfecting with wild-type H. pylori and measuring differential recovery. This competition assay identified colonization defects in several classes of known attenuated mutants, including those defective in acid resistance (ureA), metabolism (frdA), motility (motB), and chemotaxis (cheY). A mutant defective in copA (copper transporting P-type ATPase) is nonattenuated in adult and infant mice. Possibly because of the limited duration of infection, our model did not identify defects in vacuolating cytotoxin (vacA) or gamma-glutamyltranspeptidase (ggt) as attenuating, in contrast to results from other animal models. We also identified a new virulence gene (HP0507) encoding a conserved hypothetical protein, which is important for colonization in our model. The suckling mouse model offers a rapid method to identify colonization defects in any H. pylori strain and may have utility as a new tool for studying immunity to primary infection.

Role of tumor necrosis factor alpha in Helicobacter pylori gastritis in tumor necrosis factor receptor 1-deficient mice

Increased gastric production of interleukin 8 and tumor necrosis factor alpha (TNF-alpha) has been implicated in the pathogenesis of Helicobacter pylori-associated gastroduodenal disease. In the present study we used a mouse model to demonstrate whether loss of the tumor necrosis factor receptor 1 (TNF-R1) function leads to differences in gastric inflammation or the systemic immune response in H. pylori infection. Six different clinical isolates of H. pylori (three cytotoxin-positive and three cytotoxin-negative strains) were adapted to C57BL/6 mice. TNF-R1-deficient (TNF-R1(-/-)) mice (n = 19) and isogenetic controls (n = 24) were infected and sacrificed after 4 weeks of infection. Inflammation of the stomach and the humoral immune response to H. pylori were evaluated by histological, immunohistochemical, and serological methods. There was no detectable difference in the grade or activity of gastritis in TNF-R1(-/-) mice when they were compared with wild-type mice, but the number of lymphoid aggregates was slightly reduced in the gastric mucosa of TNF-R1(-/-) mice. Interestingly, total immunoglobulin G (IgG), as well as IgG1, IgG2b, and IgG3, H. pylori-specific antibody titers were significantly higher in wild-type mice. As revealed by immunoblot analysis, the difference in reactivity against H. pylori antigens was not based on a failure to recognize single H. pylori antigens in TNF-R1(-/-) mice. We therefore suggest that TNF-R1-mediated TNF-alpha signals might support a systemic humoral immune response against H. pylori and that the gastric inflammatory response to H. pylori infection seems to be independent of TNF-R1-mediated signals.

Helicobacter pylori does not require Lewis X or Lewis Y expression to colonize C3H/HeJ mice

Helicobacter pylori strains frequently express Lewis X (Le(x)) and/or Le(y) on their cell surfaces as constituents of the O antigens of their lipopolysaccharide molecules. To assess the effect of Le(x) and Le(y) expression on the ability of H. pylori to colonize the mouse stomach and to adhere to epithelial cells, isogenic mutants were created in which fucT1 alone or fucT1 and fucT2, which encode the fucosyl transferases necessary for Le(x) and Le(y) expression, were deleted. C3H/HeJ mice were experimentally challenged with either wild-type 26695 H. pylori or its isogenic mutants. All strains, whether passaged in the laboratory or recovered after mouse passage, colonized the mice well and without consistent differences. During colonization by the mutants, there was no reversion to wild type. Similarly, adherence to AGS and KatoIII cells was unaffected by the mutations. Together, these findings indicate that Le expression is not necessary for mouse gastric colonization or for H. pylori adherence to epithelial cells.

O6-alkylguanines, dietary N-nitroso compounds, and their precursors in gastric cancer

Several N-nitroso compounds, present in foods and beverages or formed in the stomach from their precursors, act as alkylating agents. By using a highly reliable technique (high-resolution gas chromatography-mass spectrometry with negative-ion chemical ionization and selected ion recording), we measured a series of specific O6-alkylguanines in snap-frozen paired stomach tissue samples (tumor and noninvolved mucosa) obtained at surgery from 24 gastric cancer patients identified in Florence, Italy. Samples of noninvolved mucosa had higher levels of total O6-alkylguanines and more frequently detectable levels (54%) than tumor samples (29.2%). O6-propylguanine and O6-methylguanine were the single adducts most frequently detected in noninvolved mucosa and tumor tissue, respectively. Tumor samples showed higher levels of total O6-alkylguanines in female patients (p = 0.03) and among those with a diffuse histological type (p = 0.06) or seronegative for Helicobacter pylori CagA antibodies (p = 0.06). Mean dietary nitrate intake was significantly higher in patients with detectable levels of adducts in tumor samples (p = 0.03). Estimated intakes of dimethylamine and N-nitrosodimethylamine correlated with total levels of O6-alkylguanines in noninvolved gastric mucosa. These findings, although based on a small series of cases, support a role for N-nitroso compounds from dietary sources in the etiology of gastric cancer.

Effects of metronidazole, tetracycline, and bismuth-metronidazole-tetracycline triple therapy in the Helicobacter pylori SS1 mouse model after 1 day of dosing: development of an H. pylori lead selection model

We evaluated the effect of optimized doses and dosing schedules of metronidazole, tetracycline, and bismuth-metronidazole-tetracycline (BMT) triple therapy with only 1 day of dosing on Helicobacter pylori SS1 titers in a mouse model. A reduction of bacterial titers was observable with 22.5 and 112.5 mg of metronidazole per kg of body weight (as well as BMT) given twice daily and four times daily (QID). Two hundred milligrams of tetracycline per kilogram, given QID, resulted in only a slight reduction of H. pylori titers in the stomach. We argue that optimization of doses based on antimicrobial drug levels in the animal and shortened (1 or 2 days) drug administration can be used to facilitate early evaluation of putative anti-H. pylori drug candidates in lieu of using human doses and extended schedules (7 to 14 days), as can be deduced from the results seen with these antimicrobial agents.

Isogenic mutants of the cag pathogenicity island of Helicobacter pylori in the mouse model of infection: effects on colonization efficiency

Strains of Helicobacter pylori that contain the cag pathogenicity island (cag PAI) are associated with increased virulence and severe clinical outcomes. To evaluate the role of the cag island in infection, isogenic null mutations were generated in two clinical isolates (SS1 and Iris1) with distinct genetic backgrounds. When tested for their ability to establish infection in the stomach of CD1/SPF mice, at the early phase of infection, strains in which cagE, ORF528, ORF527 or ORF525 were inactivated showed a reduced capacity to initiate colonization compared to the wild-type strain. Strains with a mutation in the ORF524 gene were more efficient than the other mutants, but still less efficient than the wild-type strain. Mutation in the effector protein, CagA, which is injected into host cells and tyrosine-phosphorylated, did not change the colonization efficiency. In conclusion, all cag genes analysed, with the exception of the effector protein, CagA, influenced the early phase of colonization in the mouse model of infection. These results suggest that the structure of the H. pylori secretion apparatus itself is involved in this process.

Reduced activation of inflammatory responses in host cells by mouse-adapted Helicobacter pylory isolates

Helicobacter pylori strains that harbour the Cag pathogenicity island (Cag PAI) induce interleukin (IL)-8 secretion in gastric epithelial cells, via the activation of NF- kappa B, and are associated with severe inflammation in humans. To investigate the influence of Cag PAI-mediated inflammatory responses on H. pylori adaptation to mice, a selection of H. pylori clinical isolates (n = 12) was cag PAI genotyped and tested in co-culture assays with AGS gastric epithelial cells, and in mouse colonization studies. Six isolates were shown to harbour a complete cag PAI and to induce NF- kappa B activation and IL-8 secretion in AGS cells. Of the eight isolates that spontaneously colonized mice, six had a cag PAI(-) genotype and did not induce pro-inflammatory responses in these cells. Mouse-to-mouse passage of the two cag PAI(+) -colonizing strains yielded host-adapted variants that infected mice with bacterial loads 100-fold higher than those of the respective parental strains (P= 0.001). These mouse-adapted variants were affected in their capacity to induce pro-inflammatory responses in host cells, yet no changes in cag PAI gene content were detected between the strains by DNA microarray analysis. This work provides evidence for in vivo selection of H. pylori bacteria with a reduced capacity to induce inflammatory responses and suggests that such bacteria are better adapted to colonize mice.

Putative effect of Helicobacter pylori and gastritis on gastric acid secretion in cat

Helicobacter pylori may increase or inhibit gastric acid. We studied acid variations and plasma gastrin in cats harboring Helicobacter felis, harboring H. pylori, or free of gastric pathogens with reference to thioperamide (H(3) receptor antagonist) and SR-27417A (PAF receptor antagonist). In cats harboring H. felis, gastric mucosa were histologically normal. After H. felis eradication, pentagastrin-stimulated acid secretion was increased (40%) compared with the situation before eradication. Thioperamide abolished this inhibitory effect of H. felis, whereas SR-27417A did not. Basal and meal-stimulated plasma gastrin levels were not affected by eradication therapy. Acid secretion was inhibited (-80%) in week 3, increased from weeks 5 to 9, and remained constant for up to 42 weeks after H. pylori infection. SR-27417A had no effect on acid secretion before week 8 but inhibited it thereafter, and thioperamide increased it (20%) only before week 7 in those cats. Helicobacter inhibits gastric acid via an H(3) receptor pathway. Inflammatory mediators are thus involved in adaptation to the inhibitory effects of H. pylori on acid secretion.

Adherence of Helicobacter pylori to gastric epithelial cells and mucosal inflammation

Adherence of Helicobacter pylori to the gastric epithelium is believed to be an important step in the induction of active inflammation of the mucosal layer. However, structural evidence showing a quantitative relationship between the adherence of H. pylori and severity of gastric mucosal inflammation is lacking. We therefore investigated the correlations between severity of gastritis and adherence of morphologically different forms of H. pylori. Fifty-seven biopsy specimens from the gastric bodies of patients with H. pylori-induced gastritis were examined. The severity of gastritis and the adherence and structure of H. pylori were determined with the use of light and scanning electron microscopy. We also investigated the ability of H. pylori organisms with different structural features to induce interleukin-8 secretion by human gastric adenocarcinoma (AGS) cells in vitro because production of interleukin-8 is related to H. pylori-associated gastritis. Furthermore, serum pepsinogen concentrations and cytotoxin-associated protein status in relation to adherence of H. pylori to the epithelial surface were examined. The results indicated that H. pylori organisms, which adhered firmly to the epithelial surface, were consistently long, tightly coiled bacilli. Histologically, those gastric mucosa samples with H. pylori firmly attached showed severe gastritis. H. pylori bacilli of greater length induced higher levels of interleukin-8 secretion. The serum pepsinogen I/II ratio showed a significant negative correlation with the grade of H. pylori adhesion (r = -0.401, P <.01). We also noted a significant correlation between cytotoxin-associated protein status and the adherence of H. pylori (r = 0.344, P <.05). A quantitative correlation was found between adherence of H. pylori and gastric inflammation. Both adherence and the induction of inflammation were found to be related to the structure of H. pylori.

Cutting edge: VacA, a vacuolating cytotoxin of Helicobacter pylori, directly activates mast cells for migration and production of proinflammatory cytokines

Mucosal mast cells strategically located at the optimal site interact with invading bacteria. Presence of VacA, the virulent Helicobacter pylori cytotoxin, is correlated with the severity of H. pylori-induced gastritis. To examine the mechanisms of inflammation in H. pylori-induced gastritis, we administered VacA to the mice. Inoculation of VacA resulted in epithelium vacuolization and marked infiltrations of mast cells and mononuclear cells into the mucosal epithelium within 24 h. In an in vitro study using bone marrow-derived mast cells, VacA directly bound and showed a chemotactic activity to the mast cell. In addition, VacA induced bone marrow-derived mast cells to produce proinflammatory cytokines, TNF-alpha, macrophage-inflammatory protein-1alpha, IL-1beta, IL-6, IL-10, and IL-13 in a dose-dependent manner without causing degranulation. The present study suggests that early activation of mast cells by VacA may be the host early response to clear the bacteria and also may contribute to the pathogenesis of H. pylori-induced gastritis.

Dynamics of bacterial phenotype selection in a colonized host

The population dynamics of Helicobacter pylori during colonization in an infected animal host provide a quantifiable experimental model of in vivo microbial phenotype evolution. Phenotype variability in H. pylori populations can be typed as polymorphic expression of Lewis antigens on their cell surfaces. The high mutational frequency of H. pylori for Lewis expression provides substrate for differential selection by the host. Experimental challenge and successful colonization of mice and gerbils allows tracking of H. pylori phenotype variability from the initial inoculation to the ultimate establishment of a quasispecies. Colonization data provide a quantitative experimental model of phenotype evolution in a relatively large population (>10(4) individuals) over a relatively long evolutionary time scale (>10(3) generations). A mathematical model is developed to interpret the data in terms of the dynamic processes occurring during colonization. The mathematical model distinguishes the roles of selection and mutation; quantifies the effects of initial phenotype diversity, mutational frequency, and selective advantage; and applies generally to phenotype evolution in biological populations.

Helicobacter pylori infection promotes gastric carcinogenesis in a mice model

BACKGROUND AND AIM

Debate that Helicobacter pylori might play a causative role in gastric carcinogenesis still exists in spite of the World Health Organization's definition of H. pylori as a class I carcinogen. In order to define the exact role of H. pylori infection in gastric carcinogenesis, we established a mice model of H. pylori infection.

METHODS

One hundred and forty-four female C57BL/6 mice were divided into nine groups according to N-methyl-N-nitrosourea (MNU) treatment and H. pylori infection. All mice were killed at the 50th or 80th week after treatment, and their histopathological changes were evaluated according to group.

RESULTS

The incidence of gastric adenocarcinoma at the 50th week was 80% in mice treated with both MNU 240 microg/L and H. pylori infection, whereas the incidence was only 27% in mice treated with only MNU 240 microg/L. Although H. pylori caused marked expansion of the proliferative zone at the surface epithelium, H. pylori infection alone caused only chronic atrophic gastritis without any evidence of carcinomas until 80 weeks. The combination of MNU and H. pylori infection also resulted in a significantly higher incidence of gastric adenoma and adenocarcinoma. Significantly higher expressions of proliferating cell nuclear antigen were noted in the gastric mucosa infected with H. pylori compared to controls.

CONCLUSIONS

These results clearly demonstrated the role of H. pylori infection, rather than direct carcinogens, in promoting gastric carcinogenesis in a mice model.

Functional complementation reveals the importance of intermolecular monomer interactions for Helicobacter pylori VacA vacuolating activity

The Helicobacter pylori vacuolating cytotoxin (VacA) induces degenerative vacuolation of sensitive mammalian cell lines. Although evidence is accumulating that VacA enters cells and functions from an intracellular site of action, the biochemical mechanism by which VacA mediates cellular vacuolation has not been established. In this study, we used functional complementation and biochemical approaches to probe the structure of VacA. VacA consists of two discrete fragments, p37 and p58, that are both required for vacuolating activity. Using a transient transfection system, we expressed genetically modified forms of VacA and identified mutations in either p37 or p58 that inactivated the toxin. VacA with an inactivating single-residue substitution in the p37 domain [VacA (P9A)] functionally complemented a second mutant form of VacA with an inactivating two-residue deletion in the p58 domain [VacA Delta(346-347)]. VacA (P9A) and VacA Delta(346-347) also co-immunoprecipitated from vacuolated monolayers, supporting the hypothesis that these two inactive mutants associate directly to function in trans. p37 and p58 interact directly when expressed as separate fragments within HeLa cells, suggesting that p37-p58 inter-actions facilitate VacA monomer associations. Collectively, these results support a model in which the active form of VacA requires assembly into a complex of two or more monomers to elaborate toxin function.

Recent developments in Helicobacter pylori vaccination

This reviews discusses the recent progress in the development of a vaccine against Helicobacter pylori. To date, this gram-negative, spiral-shaped bacterium is one of the most common infections of mankind. Infection usually occurs during childhood, and when left untreated results in lifelong colonization of the stomach. Helicobacter pylori infection is a chronic gastritis that can lead to peptic ulcer disease, gastric adenocarcinoma and gastric B-cell lymphoma. Antimicrobial therapy is currently the method of choice for curing H. pylori infection, but complex dosing, inconsistent efficiency, development of antibiotic resistance, costs and various side effects compromise widespread use. As a consequence, new strategies for the prevention and eradication of H. pylori infections are being explored. Vaccines are an attractive option, because they are both effective and economic in use. Natural infection with H. pylori usually results in a strong inflammatory Th1-type CD4(+)T-cell response that does not seem to have any protective effects. Successful vaccination studies indicate that a Th2-type response is required for protection, but the exact mechanisms involved in protective immunization are still poorly understood. Although commercial development of products for clinical trial is underway, many important issues, such as lack of a suitable mucosal adjuvant, and prevention of potential side effects, such as postimmunization gastritis, need to be resolved.

Vaccination of mice with live recombinant Salmonella typhimurium aroA against H. pylori: parameters associated with prophylactic and therapeutic vaccine efficacy

Previously we described a recombinant attenuated Salmonella typhimurium aroA strain (SL3261[pYZ97]) with constitutive expression of plasmid encoded Helicobacter pylori urease subunits A and B (UreAB). Single dose oral vaccination effectively induced prophylactic immunity against bacterial challenge in BALB/c mice. Here we successfully extended this approach to several mouse strains with allelic differences in NRAMP-1 and H-2 genes. The respective host determinants are known to influence the immune response against S. typhimurium. A comparative analysis of the vaccine efficacy in C57BL/6 and BALB/c mice showed that the live vaccine confers long lasting immunity in both strains (>18 weeks). In C57BL/6 mice, protection was still observed 54 weeks while not all vaccinated BALB/c were immune when challenged after this time. BALB/c mice also needed higher doses of SL3261[pYZ97] for full protection. We also demonstrate a therapeutic potential of SL3261[pYZ97] in H. pylori infected BALB/c and C57BL/6 mice. Urease- and carrier-specific serum antibody responses as well as the level of colonization by the Salmonella were analyzed in both mouse strains after immunization with low (4 x 10(7)CFU) or high (1 x 10(9)CFU) vaccine doses. The results are discussed in the context of inoculum size and the mode of antigen supply required for effective vaccination with recombinant Salmonella.