Modulating phagocyte activation: the pros and cons of Helicobacter pylori virulence factors

Inflammatory microenvironment in gastric premalignant lesions: implication and application

Gastric precancerous lesions (GPL) are a major health concern worldwide due to their potential to progress to gastric cancer (GC). Understanding the mechanism underlying the transformation from GPL to GC can provide a fresh insight for the early detection of GC. Although chronic inflammation is prevalent in the GPL, how the inflammatory microenvironment monitored the progression of GPL-to-GC are still elusive. Inflammation has been recognized as a key player in the progression of GPL. This review aims to provide an overview of the inflammatory microenvironment in GPL and its implications for disease progression and potential therapeutic applications. We discuss the involvement of inflammation in the progression of GPL, highlighting Helicobacter pylori (H. pylori) as a mediator for inflammatory microenvironment and a key driver to GC progression. We explore the role of immune cells in mediating the progression of GPL, and focus on the regulation of inflammatory molecules in this disease. Furthermore, we discuss the potential of targeting inflammatory pathways for GPL. There are currently no specific drugs for GPL treatment, but traditional Chinese Medicine (TCM) and natural antioxidants, known as antioxidant and anti-inflammatory properties, exhibit promising effects in suppressing or reversing the progression of GPL. Finally, the challenges and future perspectives in the field are proposed. Overall, this review highlights the central role of the inflammatory microenvironment in the progression of GPL, paving the way for innovative therapeutic approaches in the future.

Role of amoebae for survival and recovery of 'non-culturable' Helicobacter pylori cells in aquatic environments

Helicobacter pylori is a fastidious Gram-negative bacterium that infects over half of the world's population, causing chronic gastritis and is a risk factor for stomach cancer. In developing and rural regions where prevalence rate exceeds 60%, persistence and waterborne transmission are often linked to poor sanitation conditions. Here we demonstrate that H. pylori not only survives but also replicates within acidified free-living amoebal phagosomes. Bacterial counts of the clinical isolate H. pylori G27 increased over 50-fold after three days in co-culture with amoebae. In contrast, a H. pylori mutant deficient in a cagPAI gene (cagE) showed little growth within amoebae, demonstrating the likely importance of a type IV secretion system in H. pylori for amoebal infection. We also demonstrate that H. pylori can be packaged by amoebae and released in extracellular vesicles. Furthermore, and for the first time, we successfully demonstrate the ability of two free-living amoebae to revert and recover viable but non-cultivable coccoid (VBNC)-H. pylori to a culturable state. Our studies provide evidence to support the hypothesis that amoebae and perhaps other free-living protozoa contribute to the replication and persistence of human-pathogenic H. pylori by providing a protected intracellular microenvironment for this pathogen to persist in natural aquatic environments and engineered water systems, thereby H. pylori potentially uses amoeba as a carrier and a vector of transmission.

Relationship between Helicobacter pylori Infection and Plasmacytoid and Myeloid Dendritic Cells in Peripheral Blood and Gastric Mucosa of Children

PURPOSE

To investigate the frequency and activation status of peripheral plasmacytoid DCs (pDCs) and myeloid DCs (mDCs) as well as gastric mucosa DC subset distribution in Helicobacter pylori- (H. pylori-) infected and noninfected children.

MATERIALS AND METHODS

Thirty-six children were studied; twenty-one had H. pylori. The frequencies of circulating pDCs (lineage-HLA-DR+CD123+) and mDCs (lineage-HLA-DR+CD11c+) and their activation status (CD83, CD86, and HLA-DR expression) were assessed by flow cytometry. Additionally, the densities of CD11c+, CD123+, CD83+, CD86+, and LAMP3+ cells in the gastric mucosa were determined by immunohistochemistry.

RESULTS

The frequency of circulating CD83+ mDCs was higher in H. pylori-infected children than in the noninfected controls. The pDCs demonstrated upregulated HLA-DR surface expression, but no change in CD86 expression. Additionally, the densities of gastric lamina propria CD11c+ cells and epithelial pDCs were increased. There was a significant association between frequency of circulating CD83+ mDCs and gastric lamina propria mDC infiltration.

CONCLUSION

This study shows that although H. pylori-infected children had an increased population of mature mDCs bearing CD83 in the peripheral blood, they lack mature CD83+ mDCs in the gastric mucosa, which may promote tolerance to local antigens rather than immunity. In addition, this may reduce excessive inflammatory activity as reported for children compared to adults.

Effect of patchouli alcohol on Helicobacter pylori-induced neutrophil recruitment and activation

Neutrophil infiltration typically occurs in Helicobacter pylori (H. pylori)-induced acute gastritis; however, this immune response fails to eradicate H. pylori in vivo. Moreover, reactive oxygen species (ROS), which are generated by neutrophils, cause severe damage to gastric mucosa. Patchouli alcohol (PA) has been reported to have effective anti-oxidative and anti-H. pylori activities, and we investigated its effects on H. pylori-induced neutrophil recruitment and activation in this research. In neutrophil recruitment experiment, H. pylori was injected into rat air pouch to explore the effects of PA (10, 20 and 40 mg/kg) on acute inflammatory response. The results revealed that PA significantly reduced the weight of exudate and the number of neutrophils in the air pouch. Meanwhile, remarkable decrements in TNF-α and IL-8 levels in exudates were observed. In neutrophil activation experiment, rat neutrophils were isolated and activated by using 50 μg/mL H. pylori water-soluble surface protein with or without the treatment of PA (5, 10 or 20 μmol/L). Results indicated that PA not only significantly inhibited the production of ROS, but also reduced the gene and protein expressions of p22/p47-phoxes, and the binding of p22/p47-phoxes. Furthermore, the influence of PA on the neutrophil activation genes of H. pylori (h-nap and sabA) was investigated, and the results showed that expressions of h-nap and sabA were remarkably decreased after PA treatment. In conclusion, PA reduced the recruitment and activation of neutrophils induced by H. pylori, as shown by its inhibition of pro-inflammatory factor generation, p22/p47-phoxes function and H. pylori neutrophil activation-related gene expression.

Role of childhood infection in the sequelae of H. pylori disease

The persistence of Helicobacter pylori infection plays a fundamental role in the development of H. pylori-associated complications. Since the majority of infected persons acquire the bacteria during early childhood, an examination of the immunobiology of H. pylori infection in children compared with that of adults may help identify host factors that contribute to persistent infection. Therefore, we begin our review of the role of persistence in H. pylori disease with an assessment of the clinical features of H. pylori infection in children. We next review the bacterial factors that promote colonization and evasion of host defense mechanisms. We then focus our attention on the early host immunological factors that promote persistence of the infection and its complications in humans and mouse models. We also highlight topics in which further research is needed. An examination of how immunological factors cause divergent manifestations of H. pylori infection in children compared with adults may provide new insight for therapeutic modification or prevention of persistent H. pylori infection and its complications.

The impact of autophagic processes on the intracellular fate of Helicobacter pylori: more tricks from an enigmatic pathogen?

Helicobacter pylori is a Gram-negative pathogen that colonizes the gastric epithelium of 50-60% of the world's population. Approximately one-fifth of the infected individuals manifest severe diseases such as peptic ulcers or gastric cancer. H. pylori infection has proven difficult to cure despite intensive antibiotic treatment. One possible reason for the relatively high resistance to antimicrobial therapy is the ability of H. pylori to reside inside host cells. Although considered by most as an extracellular pathogen, H. pylori can invade both gastric epithelial cells and immunocytes to some extent. The intracellular survival of H. pylori has been implicated in its ability to persist in the stomach, evade host immune responses and resist eradication by membrane-impermeable antibiotics. Interestingly, recent evidence suggests that macroautophagy, a cellular self-degradation process characterized by the formation of double-membraned autophagosomes, plays an important role in determining the intracellular fate of H. pylori. Detailed understanding of the interaction between H. pylori and host cell autophagic processes is anticipated to provide novel insights into the molecular mechanisms of macroautophagy and H. pylori pathogenesis, opening new avenues for the therapeutic intervention of autophagy-related and H. pylori-related disorders.

Proteomic analysis of the function of spot in Helicobacter pylori anti-oxidative stress in vitro and colonization in vivo

As a microaerobe, Helicobacter pylori employs the global regulator SpoT for defending against oxidative stress in vitro. However, the mechanisms how SpoT affects bacterial gene expression is still unknown. Moreover, the function of SpoT in H. pylori colonization in the host is remaining undetermined. To explore the functions of the SpoT in H. pylori pathogenesis, we constructed H. pylori 26695 spoT-deficient mutant (ΔspoT). While grown in ambient atmosphere, protein expression profile of the ΔspoT was analyzed with 2D gel electrophoresis and real-time PCR. Compared to the wild type, the spoT-deficient strain downregulated its transcription of the oxidative-induced genes, as well as the genes responsible for protein degradation and that related to energy metabolism. Meanwhile, the colonization ability of ΔspoT strains in Mongolian gerbil was tested, the results demonstrated a decayed colonization in the mouse stomach with ΔspoT than the wild type. As a matter of facts, the AGS cells infected with the ΔspoT strains excreted increased level of the gastric inflammation cytokines IL-8, and the ΔspoT strains showed poor survival ability when treated with reactive oxygen stress (sodium nitroprusside). The elevated capacity of stimulating cytokines and fragility to reactive oxygen stress may be contribute to decreased colonization of the spoT-deficient mutant in the mouse stomach. Conclusively, we speculate that spoT is a key regulator of the genes for H. pylori spreading in the air and colonization in host stomach.

Antimicrobial HPA3NT3 peptide analogs: placement of aromatic rings and positive charges are key determinants for cell selectivity and mechanism of action

In an earlier study, we determined that HP(2-20) (residues 2-20 of parental HP derived from the N-terminus of the Helicobacter pylori ribosomal protein L1) and its analog, HPA3NT3, had potent antimicrobial effects. However, HPA3NT3 also showed undesirable cytotoxicity against HaCaT cells. In the present study, we designed peptide analogs including HPA3NT3-F1A (-F1A), HPA3NT3-F8A (-F8A), HPA3NT3-F1AF8A (-F1AF8A), HPA3NT3-A1 (-A1) and HPA3NT3-A2 (-A2) in an effort to investigate the effects of amino acid substitutions in reducing their hydrophobicity or increasing their cationicity, and any resulting effects on their selectivity in their interactions with human cells and pathogens, as well as their mechanism of antimicrobial action. With the exception of HPA3NT3-A1, all of these peptides showed potent antimicrobial activity. Moreover, substitution of Ala for Phe at positions 1 and/or 8 of the HPA3NT3 peptides (-F1A, -F8A and -F1AF8A) dramatically reduced their cytotoxicity. Thus the cytotoxicity of HPA3NT3 appears to be related to its Phe residues (positions 1 and 8), which strongly interact with sphingomyelin in the mammalian cell membrane. HPA3NT3 exerted its bactericidal effects through membrane permeabilization mediated by pore formation. In contrast, fluorescent dye leakage and nucleic acid gel retardation assays showed that -A2 acted by penetrating into the cytoplasm, where it bound to nucleic acids and inhibited protein synthesis. Notably, Staphylococcus aureus did not develop resistance to -A2 as it did with rifampin. These results suggest that the -A2 peptide could potentially serve as an effective antibiotic agent against multidrug-resistant bacterial strains.

A role for altered phagosome maturation in the long-term persistence of Helicobacter pylori infection

The vigorous host immune response that is mounted against Helicobacter pylori is unable to eliminate this pathogenic bacterium from its niche in the human gastric mucosa. This results in chronic inflammation, which can develop into gastric or duodenal ulcers in 10% of infected individuals and gastric cancer in 1% of infections. The determinants for these more severe pathologies include host (e.g., high IL-1β expression polymorphisms), bacterial [e.g., cytotoxicity-associated gene (cag) pathogenicity island], and environmental (e.g., dietary nitrites) factors. However, it is the failure of host immune effector cells to eliminate H. pylori that underlies its persistence and the subsequent H. pylori-associated disease. Here we discuss the mechanisms used by H. pylori to survive the host immune response and, in particular, the role played by altered phagosome maturation.

Fluorescent probes detecting the phagocytic phase of apoptosis: enzyme-substrate complexes of topoisomerase and DNA

In apoptosis, the initial self-driven suicide phase generates cellular corpses which are digested in the phagolysosomes of professional and amateur phagocytes during the subsequent waste-management phase. This ensures the complete elimination of the genetic material which often contains pathological, viral or cancerous DNA sequences. Although the phagocytic phase is critical for the efficient execution of apoptosis, there are currently few methods specifically adapted for its detailed visualization in the fixed tissue section format. To resolve this we developed new fluorescent probes for in situ research. The probes selectively visualize active phagocytic cells of any lineage (professional, amateur phagocytes or surrounding tissue cells) which engulf and digest apoptotic cell DNA. These fluorescent probes are the covalently-bound enzyme-DNA intermediates produced in a topoisomerase reaction with specific “starting” oligonucleotides. They detect a specific marker of DNase II cleavage activity, which occurs exclusively in phagolysosomes of the cells that engulfed apoptotic nuclei. The probes provide snap-shot images of the digestion process occurring in cellular organelles responsible for the actual execution of phagocytic degradation of apoptotic cell corpses. We applied the probes for visualization of the phagocytic reaction in tissue sections of normal thymus and in several human lymphomas. We also discuss the nature, stability and properties of DNase II-type breaks as a marker of phagocytic activity. This development provides a useful fluorescent tool for studies of pathologies where clearance of dying cells is essential, such as cancers, inflammation, infection and auto-immune disorders.

Transcript profiling and inference of Escherichia coli K-12 ArcA activity across the range of physiologically relevant oxygen concentrations

Oxygen availability is the major determinant of the metabolic modes adopted by Escherichia coli. Although much is known about E. coli gene expression and metabolism under fully aerobic and anaerobic conditions, the intermediate oxygen tensions that are encountered in natural niches are understudied. Here, for the first time, the transcript profiles of E. coli K-12 across the physiologically significant range of oxygen availabilities are described. These suggested a progressive switch to aerobic respiratory metabolism and a remodeling of the cell envelope as oxygen availability increased. The transcriptional responses were consistent with changes in the abundance of cytochrome bd and bo' and the outer membrane protein OmpW. The observed transcript and protein profiles result from changes in the activities of regulators that respond to oxygen itself or to metabolic and environmental signals that are sensitive to oxygen availability (aerobiosis). A probabilistic model (TFInfer) was used to predict the activity of the indirect oxygen-sensing two-component system ArcBA across the aerobiosis range. The model implied that the activity of the regulator ArcA correlated with aerobiosis but not with the redox state of the ubiquinone pool, challenging the idea that ArcA activity is inhibited by oxidized ubiquinone. The amount of phosphorylated ArcA correlated with the predicted ArcA activities and with aerobiosis, suggesting that fermentation product-mediated inhibition of ArcB phosphatase activity is the dominant mechanism for regulating ArcA activity under the conditions used here.

Oxidative stress by Helicobacter pylori causes apoptosis through mitochondrial pathway in gastric epithelial cells

Helicobacter pylori is a gram negative bacterium that infects the human stomach of approximately half of the world's population. It produces oxidative stress, and mitochondria are one of the possible targets and the major intracellular source of free radicals. The present study was aimed at determining mitochondrial alterations in H. pylori-infected gastric epithelial cells and its relationship with oxidative stress, one of the recognized causes of apoptotic processes. Cells were treated with a strain of H. pylori for 24 h. Cellular oxidative burst, antioxidant defense analysis, mitochondrial alterations and apoptosis-related processes were measured. Our data provide evidence on how superoxide acts on mitochondria to initiate apoptotic pathways, with these changes occurring in the presence of mitochondrial depolarization and other morphological and functional changes. Treatment of infected cells with Vitamin E prevented increases in intracellular ROS and mitochondrial damage consistent with H. pylori inducing a mitochondrial ROS mediated programmed cell death pathway.

The autophagic induction in Helicobacter pylori-infected macrophage

Helicobacter pylori has developed several mechanisms to evade the intracellular killing after phagocytosis. In this study, we reported that some Taiwanese clinical isolated H. pylori can multiply in human monocytic cells, such as THP-1 or U937 cells, but not in murine macrophage Raw264.7 cells. After internalization, there was a 5- to 10-fold increment of re-cultivable H. pylori from the infected THP-1 cells at 12 hrs post infection. The dividing H. pylori was found in a double-layer vesicle, which is characteristic of autophagosome. The formation of autophagosomes is associated with the multiplication of H. pylori in THP-1 cells. Its modulation with rapamycin or 3-MA affects the level of H. pylori replication. Furthermore, the VacA or CagA mutants of H. pylori have lower levels of multiplication in macrophages. We conclude that H. pylori infection induces autophagosome formation, and these autophagic vesicles were adapted for the multiplication of H. pylori in the host.

Rate and extent of Helicobacter pylori phagocytosis

Helicobacter pylori is a Gram-negative bacterium that colonizes the gastric epithelium and plays a causative role in the development of peptic ulcers and gastric cancer. Phagocytosis is an element of innate defense used by macrophages and neutrophils to engulf microorganisms. We and others have shown that strains of H. pylori that contain the cag pathogenicity island actively retard their entry into phagocytes. Consequently, there is a lag of several minutes between bacterial binding and the onset of engulfment, and relative to other particles and microbes, the rate of internalization is slow. Herein, we describe in detail the use of synchronized phagocytosis and indirect immunofluorescence microscopy to quantify the rate and extent of H. pylori phagocytosis. This method is appropriate for primary phagocytes as well as transformed cell lines. More importantly, the effects of opsonins, virulence factors, and other agents on infection can be measured independent of bacterial viability or intracellular locale.

Nox enzymes and oxidative stress in the immunopathology of the gastrointestinal tract

Chronic inflammation caused by Helicobacter pylori infection or inflammatory bowel disease (IBD) is closely linked to cancer development. Innate immune abnormalities and enhanced production of reactive oxygen species through a phagocyte NADPH oxidase (Nox2) are key issues in understanding the pathogenesis of inflammation-dependent carcinogenesis. Besides Nox2, functionally distinct homologues (Nox1, Nox3, Nox4, Nox5, Duox1, and Duox2) have been identified. Nox1 and Duox2 are highly expressed in the gastrointestinal tract. Although the functional roles of Nox/Duox in the gastrointestinal tract are still unclear, we will review their potential roles in the gastrointestinal immunopathology, particularly in H. pylori-induced inflammation, IBD, and malignancy.

Amphipathic alpha-helical peptide, HP (2-20), and its analogues derived from Helicobacter pylori: pore formation mechanism in various lipid compositions

In a previous study, we determined that HP(2-20) (residues 2-20 of parental HP derived from the N-terminus of Helicobacter pylori Ribosomal Protein L1) and its analogue, HPA3, exhibit broad-spectrum antimicrobial activity. The primary objective of the present study was to gain insight into the relevant mechanisms of action using analogues of HP(2-20) together with model liposomes of various lipid compositions and electron microscopy. We determined that these analogues, HPA3 and HPA3NT3, exert potent antibacterial effects in low-salt buffer and antifungal activity against chitin-containing fungi, while having little or no hemolytic activity or cytotoxicity against mammalian cell lines. Our examination of the interaction of HP(2-20) and its analogues with liposomes showed that the peptides disturb both neutral and negatively-charged membranes, as demonstrated by the release of encapsulated fluorescent markers. The release of fluorescent markers induced by HP(2-20) and its analogues was inversely related to marker size. The pore created by HP(2-20) shows that the radius is approximately 1.8 nm, whereas HPA3, HPA3NT3, and melittin have apparent radii between 3.3 and 4.8 nm. Finally, as shown by electron microscopy, the liposomes and various microbial cells treated with HPA3 and HPA3NT3 showed oligomerization and blebbing similar to that seen with melittin, while HP(2-20) exhibited flabbiness. These results suggest that HP(2-20) may exert its antibiotic effects through a small pore (about 1.8 nm), whereas HPA3 and HPA3NT3 formed pores of a size consistent with those formed by melittin.

To activate or not to activate: distinct strategies used by Helicobacter pylori and Francisella tularensis to modulate the NADPH oxidase and survive in human neutrophils

Neutrophils accumulate rapidly at sites of infection, and the ability of these cells to phagocytose and kill microorganisms is an essential component of the innate immune response. Relatively few microbial pathogens are able to evade neutrophil killing. Herein, we describe the novel strategies used by Helicobacter pylori and Francisella tularensis to disrupt neutrophil function, with a focus on assembly and activation of the nicotinamide adenine dinucleotide phosphate (NADPH) oxidase.

Phagocytosis and persistence of Helicobacter pylori

Helicobacter pylori is a spiral-shaped, flagellated, microaerophilic Gram-negative bacterium that colonizes the gastric epithelium of humans. All persons infected with H. pylori have gastritis, and some will develop severe disease such as peptic ulcers or gastric cancer. A characteristic feature of this infection is the pronounced accumulation of phagocytes, particularly neutrophils, in the gastric mucosa. H. pylori thrives in a phagocyte-rich environment, and we describe here how this organism uses an array of novel virulence factors to manipulate chemotaxis, phagocytosis, membrane trafficking and the respiratory burst as a means to evade elimination by the innate immune response.

Defenses against oxidative stress in Neisseria gonorrhoeae: a system tailored for a challenging environment

Neisseria gonorrhoeae is a host-adapted pathogen that colonizes primarily the human genitourinary tract. This bacterium encounters reactive oxygen and reactive nitrogen species as a consequence of localized inflammatory responses in the urethra of males and endocervix of females and also of the activity of commensal lactobacilli in the vaginal flora. This review describes recent advances in the understanding of defense systems against oxidative stress in N. gonorrhoeae and shows that while some of its defenses have similarities to the paradigm established with Escherichia coli, there are also some key differences. These differences include the presence of a defense system against superoxide based on manganese ions and a glutathione-dependent system for defense against nitric oxide which is under the control of a novel MerR-like transcriptional regulator. An understanding of the defenses against oxidative stress in N. gonorrhoeae and their regulation may provide new insights into the ways in which this bacterium survives challenges from polymorphonuclear leukocytes and urogenital epithelial cells.

Role of urease in megasome formation and Helicobacter pylori survival in macrophages

Previous studies have demonstrated that Helicobacter pylori (Hp) delays its entry into macrophages and persists inside megasomes, which are poorly acidified and accumulate early endosome autoantigen 1. Herein, we explored the role of Hp urease in bacterial survival in murine peritoneal macrophages and J774 cells. Plasmid-free mutagenesis was used to replace ureA and ureB with chloramphenicol acetyltransferase in Hp Strains 11637 and 11916. ureAB null Hp lacked detectable urease activity and did not express UreA or UreB as judged by immunoblotting. Deletion of ureAB had no effect on Hp binding to macrophages or the rate or extent of phagocytosis. However, intracellular survival of mutant organisms was impaired significantly. Immunofluorescence microscopy demonstrated that (in contrast to parental organisms) mutant Hp resided in single phagosomes, which were acidic and accumulated the lysosome marker lysosome-associated membrane protein-1 but not early endosome autoantigen 1. A similar phenotype was observed for spontaneous urease mutants derived from Hp Strain 60190. Treatment of macrophages with bafilomycin A1, NH4Cl, or chloroquine prevented acidification of phagosomes containing mutant Hp. However, only ammonium chloride enhanced bacterial viability significantly. Rescue of ureAB null organisms was also achieved by surface adsorption of active urease. Altogether, our data indicate a role for urease and urease-derived ammonia in megasome formation and Hp survival.

A bactericidal cecropin-A peptide with a stabilized alpha-helical structure possess an increased killing capacity but no proinflammatory activity

Antibacterial peptides are part of the innate immune system in a variety of different species including humans. Some of these peptides have also been shown to have effects on immune competent cells such as professional phagocytes. We have recently shown that a cecropin-like peptide from Helicobacter pylori, Hp(2-20), in addition to being bactericidal possesses proinflammatory effects and can recruit and activate neutrophils as well as monocytes. It is well established that cecropins have the ability to adopt amphipathic alpha-helices, which is thought to be required for their bactericidal activity. In this study we show the same structural requirements for Hp(2-20). Breaking the helical structure of Hp(2-20) reduced the antibacterial effect and abolished its proinflammatory activity. A C-terminal truncated cecropin A peptide that highly resembles Hp(2-20) failed to activate neutrophils and computer-based structural simulations revealed a difference between the two peptides in the stability of their helical structures. A hybrid peptide with amino acid substitutions stabilizing the alpha-helical structure of the truncated cecropin A peptide did not introduce any proinflammatory activity; the bactericidal activity was, however, increased. We thus conclude that the proinflammatory effect of Hp(2-20) is a unique sequence-specific feature of the peptide and the ability to adopt a stable amphipathic helix is a necessary but not sufficient criterion for the functional dualism of the peptide.

Novel action of gastric proton pump inhibitor on suppression of Helicobacter pylori induced angiogenesis

BACKGROUND

Although activation of mitogen activated protein kinases (MAPKs) by Helicobacter pylori infection is associated with induction of host angiogenesis, which may contribute to H pylori associated gastric carcinogenesis, the strategy for its prevention has not been identified. As we previously reported a strong inhibitory action of gastric proton pump inhibitors (PPIs) on MAPK extracellular signal regulated kinase (ERK)1/2 phosphorylation, we investigated whether PPIs could suppress the H pylori induced angiogenesis via inhibition of MAPK ERK1/2.

METHODS

To address the relationship between H pylori infection and angiogenesis, comparative analysis of density of CD34(+) blood vessel was performed in tissues obtained from 20 H pylori positive gastritis and 18 H pylori negative gastritis patients. Expression of hypoxia inducible factor 1 (HIF-1alpha) and vascular endothelial growth factor (VEGF) was tested by reverse transcription-polymerase chain reaction and secretion of interleukin 8, and VEGF was measured by ELISA. To evaluate the direct effect of H pylori infection on the tubular formation of human umbilical vein endothelial cells (HUVEC), an in vitro angiogenesis assay was employed. Activation of MAPK and nuclear factor kappaB (NFkappaB) was detected by immunoblotting.

RESULTS

H pylori positive gastritis patients showed a higher density of CD34(+) blood vessels (mean 40.9 (SEM 4.4)) than H pylori negative gastritis patients (7.2+/-0.8), which was well correlated with expression of HIF-1alpha. Conditioned media from H pylori infected gastric epithelial cells directly induced tubular formation of HUVEC and the increase of in vitro angiogenesis was suppressed by PPI treatment. Infection of H pylori significantly upregulated expression of HIF-1alpha and VEGF in gastric epithelial cells and expression of proangiogenic factors was mediated by MAPK activation and partially responsible for NFkappaB activation. PPIs effectively inhibited the phosphorylation of MAPK ERK1/2 that is a principal signal for H pylori induced angiogenesis.

CONCLUSIONS

The fact that PPIs could downregulate H pylori induced angiogenesis indicates that antiangiogenic treatment using a PPI could be a promising protective therapeutic approach for H pylori associated carcinogenesis.

Investigation of oxidative stress defenses of Neisseria gonorrhoeae by using a human polymorphonuclear leukocyte survival assay

Neisseria gonorrhoeae has well-characterized oxidative stress defense systems that protect against oxidative killing in in vitro assays. In contrast, mutant strains of N. gonorrhoeae lacking oxidative stress defenses are identical to the wild type when tested in an ex vivo survival assay using human polymorphonuclear leukocytes.

Phosphoinositide3-kinase regulates actin polymerization during delayed phagocytosis of Helicobacter pylori

We have shown previously that ulcerogenic (type I) strains of Helicobacter pylori (Hp) retard their entry into macrophages. However, the signaling pathways that regulate Hp phagocytosis are largely undefined. We show here that Hp strongly activated class IA phosphoinositide3-kinases (PI3Ks) in macrophages, coincident with phagocytosis, and endogenous p85 and active protein kinase Balpha accumulated on forming phagosomes. PI3K inhibitors, wortmannin and LY294002, inhibited phagocytosis of Hp in a dose-dependent manner, and blockade of engulfment correlated directly with loss of 3'-phosphoinositides in the membrane subjacent to attached bacteria. During uptake of large immunoglobulin G (IgG)-coated particles, PI3Ks regulate pseudopod extension and phagosome closure. In marked contrast, we show here that 3'-phosphoinositides regulated actin polymerization at sites of Hp uptake. Moreover, Hp and IgG beads activated distinct PI3K isoforms. Phagosomes containing IgG-coated particles accumulated 3'-phosphatase and tensin homologue deleted on chromosome 10 and Src homology 2 domain-containing inositol 5'-phosphatase, yet Hp phagosomes did not. Finally, rapid uptake of IgG-opsonized Hp or a less-virulent type II Hp was PI3K-independent. We conclude that Hp and IgG beads are ingested by distinct mechanisms and that PI3Ks regulate the actin cytoskeleton during slow phagocytosis of ulcerogenic Hp.

Helicobacter pylori disrupts NADPH oxidase targeting in human neutrophils to induce extracellular superoxide release

Helicobacter pylori (Hp) infection triggers a chronic influx of polymorphonuclear leukocyte neutrophils (PMNs) into the gastric mucosa. Although Hp reside in a neutrophil-rich environment, how these organisms evade phagocytic killing is largely unexplored. We now show that live Hp (strains 11637, 60190, DT61A, and 11916) are readily ingested by PMNs and induce a rapid and strong respiratory burst that is comparable to PMA. Relative to other particulate stimuli, Hp are more potent activators of PMNs than opsonized zymosan, Staphylococcus aureus, or Salmonella. Strikingly, biochemical and microscopic analyses demonstrate that Hp disrupt NADPH oxidase targeting such that superoxide anions are released into the extracellular milieu and do not accumulate inside Hp phagosomes. Specifically, nascent Hp phagosomes acquire flavocytochrome b558 but do not efficiently recruit or retain p47phox or p67phox. Superoxide release peaks at 16 min coincident with the appearance of assembled oxidase complexes in patches at the cell surface. Oxidant release is regulated by formalin-resistant and heat-sensitive bacterial surface factors distinct from urease and Hp(2-20). Following opsonization with fresh serum, Hp triggers a modest respiratory burst that is confined to the phagosome, and ingested bacteria are eliminated. We conclude that disruption of NADPH oxidase targeting allows unopsonized Hp to escape phagocytic killing, and our findings support the hypothesis that bacteria and PMNs act in concert to damage the gastric mucosa.

Mechanisms of pathogenesis: evasion of killing by polymorphonuclear leukocytes

Few microorganisms evade killing by neutrophils. Summarized here are the mechanisms used by Yersinia, group A streptococci, Helicobacter, Ehrlichia and Francisella to block phagocytosis, disrupt phagosome maturation or perturb the respiratory burst. Also discussed are mechanisms used by neutrophils to control organisms that replicate inside macrophages.

Helicobacter pylori tissue tropism: mouse-colonizing strains can target different gastric niches

Studies with the mouse-adapted Helicobacter pylori strain SS1 had supported an idea that infections by this pathogen start in the gastric antrum and spread to the corpus after extensive mucosal damage. This paper shows that the unrelated strain X47 colonizes the corpus preferentially. Differences between strains in preferred gastric region were detected by co-inoculating mice with a mixture of SS1 and X47, and genotyping H. pylori recovered after 2-8 weeks of infection by vacA s allele PCR and RAPD fingerprinting. Mixed infections were found in each of 59 co-inoculated young C57BL/6J mice. On average, however, SS1 was fourfold more abundant than X47 in the antrum and X47 was threefold more abundant than SS1 in the corpus. Similar results were obtained in mice inoculated first with one strain and then the other strain 2 weeks later. SS1 was even more abundant in the antrum of elderly (>1 year old) mice (97 % of isolates). Qualitatively similar SS1 and X47 tissue distributions were seen using unrelated mouse lines (AKR/J, A/J, DBA/2J, BALB/cJ, LG/J, SM/J), but with significantly different SS1 : X47 ratios in some cases. These results suggest the existence of at least two distinct gastric niches whose characteristics may be affected by host genotype and age (physiology), and indicate that strains differ in how effectively they colonize each niche. Differences among gastric regions and the mixed infections that these allow may contribute to H. pylori diversity and genome evolution.

Modulation of host antimicrobial peptide (beta-defensins 1 and 2) expression during gastritis

BACKGROUND

beta-Defensins are a newly identified family of antimicrobial peptides that are expressed by epithelia on mucosal surfaces where their production is augmented by infection or inflammation. Helicobacter pylori colonises the gastric epithelium causing persistent gastric inflammation leading to antral and corpus gastritis, and peptic ulcer disease.

AIMS

To evaluate the role of beta-defensins in the innate immune response of the gastric epithelium to infection and inflammation, we have assessed mRNA expression and regulation of human beta-defensins 1 and 2 (hBD1, hBD2) by H pylori and proinflammatory stimuli. We have also compared gene and peptide expression of these bactericidal agents in H pylori induced gastritis with that in normal gastric mucosa.

METHODS

Modulation of expression of hBD1 and hBD2 by various stimuli was studied in three (AGS, MKN7, MKN45) gastric epithelial cell lines by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR). Defensin mRNA expression was measured by semiquantitative RT-PCR in gastritis tissue and compared with controls. Peptide localisation was assessed by immunohistochemistry.

RESULTS

Cytotoxic H pylori and interleukin 1 beta (IL-1 beta) markedly upregulated expression of hBD2 in a dose and time dependent manner in both AGS and MKN7 cell lines. A modest increase in hBD1 expression was also noted during infection. Interestingly, induction of hBD1 gene expression by IL-1 beta was only observed in MKN7 cells. The magnitude of this response was delayed and reduced compared with hBD2 expression. In gastric biopsies, hBD2 was undetectable in normal gastric antrum but a marked increase was observed in H pylori positive gastritis compared with control tissue (p<0.001). Constitutive expression of hBD1 was observed in normal gastric mucosa and there was a significant increase in gastritis (p<0.05). Immunohistochemistry revealed a parallel increase in hBD1 and hBD2 peptide expression in gastritis tissue with positive staining confined to the surface epithelium of the gastric glands.

CONCLUSIONS

Modulation of beta-defensin expression by pathogenic and/or inflammatory stimuli and their cellular localisation places these antimicrobial peptides in the front line of innate host defence in the human stomach.

Lipopolysaccharide-induced granule mobilization and priming of the neutrophil response to Helicobacter pylori peptide Hp(2-20), which activates formyl peptide receptor-like 1

The cecropin-like bactericidal peptide Hp(2-20) from Helicobacter pylori induces activation of the NADPH oxidase in human neutrophils via formyl peptide receptor-like 1 (FPRL1) (J. Bylund, T. Christophe, F. Boulay, T. Nyström, A. Karlsson, and C. Dahlgren, Antimicrob. Agents Chemother. 45:1700-1704, 2001). Here we investigated the ability of bacterial lipopolysaccharide (LPS) to prime this response. Neutrophils treated with LPS for 30 min at 37 degrees C produced substantially more superoxide anion than control cells upon stimulation with Hp(2-20). Hence, LPS primed the cells for subsequent stimulation through FPRL1. To study the molecular background of this priming phenomenon, we measured the degrees of granule mobilization and concomitant receptor upregulation to the cell surface in LPS-treated cells. Exposure of complement receptors 1 and 3 as well as the formyl peptide receptor (FPR) was markedly increased after LPS treatment. Since approximately 60% of the gelatinase granules were mobilized while the specific granules were retained, we hypothesized that the gelatinase granules were potential stores of FPRL1. The presence of FPRL1 mainly in the gelatinase granules was confirmed by Western blotting of subcellular fractions of resting neutrophils. These results suggest that the mechanism behind the LPS-induced priming of FPRL1-mediated responses lies at the level of granule (receptor) mobilization.

The neutrophil-activating protein of Helicobacter pylori

Infection of the stomach mucosa by the gastric pathogen Helicobacter pylori is accompanied by a large infiltration of neutrophils and monocytes which are believed to contribute substantially to H. pylori-induced gastritis. A protein was identified (HP-NAP for neutrophil-activating protein from H. pylori) that was capable of increasing the adhesion of neutrophils to endothelial cells. We have demonstrated that HP-NAP is a dodecamer composed of identical 17-kDa subunits that induces the production of reactive oxygen radicals (ROIs) by neutrophils via a cascade of intracellular activation events. HP-NAP has also been shown to be chemotactic for neutrophils and monocytes, and a majority of H. pylori-infected patients have been found to produce antibodies specific for HP-NAP making it a strong vaccine candidate. More recently it has been shown that HP-NAP can stimulate tissue factor and plasminogen activator inhibitor-2 production by human monocytes. While structurally similar to the Escherichia coli DNA-binding protein Dps, HP-NAP has characteristics that are more similar to bacterioferritins being capable of binding up to 500 atoms of iron in vitro. Further study, however, has revealed that synthesis of HP-NAP in H. pylori is not altered by the addition or subtraction of metal ions from its growth medium suggesting that the primary role of the protein in vivo is not as a metal-binding protein. A number of other reports have proposed that HP-NAP acts as an adhesin being capable of binding several different compounds in vitro. Sequence analysis of the genomes of several other bacteria reveal that many possess Dps/HP-NAP-like proteins. The preliminary characterisation of some of these proteins will be discussed.

A proinflammatory peptide from Helicobacter pylori activates monocytes to induce lymphocyte dysfunction and apoptosis

Infection with Helicobacter pylori causes chronic gastritis, which is characterized by a dense mucosal infiltration by inflammatory cells such as monocytes/macrophages. H. pylori-induced inflammation is a risk factor for the development of gastric adenocarcinoma, but the mechanisms involved in H. pylori-associated carcinogenesis are poorly understood. A cecropin-like H. pylori peptide, Hp(2-20), was found to be a monocyte chemoattractant and activated the monocyte NADPH-oxidase to produce oxygen radicals. The receptors mediating monocyte activation were identified as FPRL1 and the monocyte-specific orphan receptor FPRL2. Hp(2-20)-activated monocytes inhibited lymphocytes with antitumor properties, such as CD56+ natural killer (NK) cells and CD3epsilon+ T cells. The changes observed in NK cells and T cells--a reduced antitumor cytotoxicity, downregulation of CD3zeta expression, and apoptosis--were mediated by Hp(2-20)-induced oxygen radicals. Histamine, a gastric mucosal constituent, rescued NK cells and T cells from inhibition and apoptosis by suppressing Hp(2-20)-induced oxygen radical formation. We conclude that H. pylori expression of this monocyte-activating peptide contributes to its ability to attract and activate monocytes and reduces the function and viability of antineoplastic lymphocytes. These novel mechanisms may be subject to local, histaminergic regulation in the gastric mucosa.

Proinflammatory activity of a cecropin-like antibacterial peptide from Helicobacter pylori

Helicobacter pylori, the bacterial pathogen associated with gastritis and peptic ulcers, is highly successful in establishing infection in the human gastric mucosa, a process typically associated with massive infiltration of inflammatory cells. Colonization of the mucosa is suggested to be facilitated by H. pylori-produced cecropin-like peptides with antibacterial properties, giving the microbe a competitive advantage over other bacteria. We show that a cecropin-like antibacterial peptide from H. pylori, Hp(2-20), not only has a potent bactericidal effect but also induces proinflammatory activities in human neutrophils, e.g., upregulation of integrins (Mac-1), induction of chemotaxis, and activation of the oxygen radical producing NADPH-oxidase. Furthermore, we show that these effects are mediated through binding of Hp(2-20) to the promiscuous, G-protein-linked lipoxin A(4) receptor-formyl peptide-like receptor 1.

The role of the neutrophil and phagocytosis in infection caused by Helicobacter pylori

Recent advances in our understanding of Helicobacter pylori-phagocyte interactions indicate that these organisms actively modulate phagocyte function in order to retard phagocytosis, while simultaneously inducing a strong respiratory burst. The central players in this dynamic include H. pylori neutrophil activating protein and factors that are associated with the cag pathogenicity island type IV secretion apparatus. Additionally, catalase, alkyl hydroperoxide reductase, and factors that are unique to type I strains allow bacteria to resist phagocytic killing.

Virulence factors of Helicobacter pylori

To date a number of virulence factors have been identified and characterised from the gastric pathogen Helicobacter pylori. The vacuolating toxin (VacA) is a major determinant of H. pylori-associated gastric disease. In non-polarised cells, VacA alters the endocytic pathway, resulting in the release of acid hydrolases and the reduction of both extracellular ligand degradation and antigen processing. The toxin forms trans-membrane anion-specific channels and reduces the transepithelial electrical resistance of polarized monolayers. Localization of the VacA channels in acidic intracellular compartments causes osmotic swelling which, together with membrane fusion, leads to vacuole formation. The neutrophil-activating protein of H. pylori (HP-NAP) induces the production of oxygen radicals in human neutrophils via a cascade of intracellular activation events which may contribute to the damage of the stomach mucosa. This protein has recently been shown to be an important antigen in the human immune response to H. pylori infection. In addition, mice vaccinated with recombinant HP-NAP were protected against H. pylori challenge. H. pylori strains that are associated with severe tissue damage and inflammation possess the cag pathogenicity island that contains several genes encoding factors involved in the induction of proinflammatory cytokines/chemokines and of a type IV secretion system involved in the delivery of a highly immunogenic protein, CagA, into eukaryotic cells. Recent advances in our understanding of the involvement of VacA, HP-NAP and the CagA/Type IV secretion system in the H. pylori-associated disease process are discussed in this review.