Helicobacter pylori induces macrophage apoptosis by activation of arginase II

Inducible nitric oxide synthase polymorphism is associated with the increased risk of differentiated gastric cancer in a Japanese population

AIM: To examine the association of inducible nitric oxide synthase (iNOS) C150T polymorphism with gastric cancer, as well as with gastric atrophy and H pylori seropositivity.

METHODS: A single nucleotide polymorphism of iNOS C150T was examined for 454 Japanese health checkup examinees (126 males and 328 females) aged 35 to 85 years without a history of cancer and 202 gastric cancer patients (134 males and 68 females) aged 33 to 94 years with pathologically confirmed diagnosis of gastric adenocarcinoma.

RESULTS: The iNOS C150T polymorphism was not associated with gastric atrophy or with H pylori seropositivity. The odds ratio (OR) of the C/T + T/T for gastric cancer was increased without statistical significance (OR=1.19, 95% confidence interval (CI): 0.68-2.08). In the differentiated subgroup (n = 113), however, the OR of the C/T genotype for gastric cancer was significant (OR = 2.02, 95% CI: 1.04-3.92) relative to the C/C genotype. In addition, considering the location of gastric cancer (n = 105), there were significant differences between the controls and non-cardia group with the OR of 2.13 (95% CI: 1.08-4.18) for C/T and 1.94 (95% CI: 1.00-3.78) for C/T + T/T.

CONCLUSION: The iNOS C150T polymorphism is associated with the risk of H pylori-related gastric cancer in a Japanese population. This polymorphism may play an important role in increasing the risk of gastric cancer in Asian countires with the highest rates of gastric cancer.

Distinct patterns of mucosal apoptosis in H pylori-associated gastric ulcer are associated with altered FasL and perforin cytotoxic pathways

AIM: To analyze the level of apoptosis in different mucosal compartments and the differential expression of Fas/Fas-ligand and perforin in H pylori-associated gastric ulcer.

METHODS: Antral specimens from patients with H pylori-related active gastric ulcer (GU), H pylori-related gastritis, and non-infected controls were analysed for densities and distribution of apoptotic cells determined by the TdT-mediated dUDP-biotin nick-end-labelling method. GU patients were submitted to eradication therapy with follow-up biopsy after 60 d. Fas, FasL, and perforin-expressing cells were assessed by immunoperoxidase, and with anti-CD3, anti-CD20 and anti-CD68 by double immunofluorescence and confocal microscopy. Quantitative analysis was performed using a computer-assisted image analyser.

RESULTS: H pylori-infected antrum showed greater surface epithelial apoptosis which decreased after eradication therapy. In the lamina propria, higher rates of mononuclear cell apoptosis were observed in H pylori-gastritis. Co-expression of Fas with T-cell and macrophage markers was reduced in GU. FasL- and perforin-expressing cells were increased in H pylori-infection and correlated with epithelial apoptosis. Perforin-expressing cells were also increased in GU compared with H pylori-gastritis.

CONCLUSION: Epithelial apoptosis is increased in H pylori-infection and correlates to FasL- and perforin-expression by T cells. Expression of perforin is correlated with the tissue damage, and may represent the enhancement of a distinct cytotoxic pathway in GU. Increased expression of FasL not paralleled by Fas on T-cells and macrophages may indicate a reduced susceptibility to the Fas/FasL-mediated apoptosis of lymphoid cells in H pylori-infection.

Immune response to H pylori

The gastric mucosa separates the underlying tissue from the vast array of antigens that traffic through the stomach lumen. While the extreme pH of this environment is essential in aiding the activation of enzymes and food digestion, it also renders the gastric epithelium free from bacterial colonization, with the exception of one important human pathogen, H pylori. This bacterium has developed mechanisms to survive the harsh environment of the stomach, actively move through the mucosal layer, attach to the epithelium, evade immune responses, and achieve persistent colonization. While a hallmark of this infection is a marked inflammatory response with the infiltration of various immune cells into the infected gastric mucosa, the host immune response is unable to clear the infection and may actually contribute to the associated pathogenesis. Here, we review the host responses involved during infection with H pylori and how they are influenced by this bacterium.

Therapeutic and preventive properties of quercetin in experimental arthritis correlate with decreased macrophage inflammatory mediators

Pentahydroxyflavone dihydrate, quercetin (QU) is one of common flavonols biosynthesized by plants and has been suggested to modulate inflammatory responses in various models. In the present study, we investigated in vivo effects of oral or intra-cutaneous QU in chronic rat adjuvant-induced arthritis (AA). Growth delay and arthritic scores were evaluated daily after AA induction in Lewis rats. Oral administration of QU (5 x 160 mg/kg) to arthritic rats resulted in a clear decrease of clinical signs compared to untreated controls. Intra-cutaneous injections of lower doses (5 x 60 mg/kg) of QU gave similar anti-arthritic effects, while 5 x 30 mg/kg concentrations were inefficient in this respect. Finally, injection of relatively low QU doses (5 x 30 mg/kg) prior to AA induction significantly reduced arthritis signs. As QU was suggested to inhibit macrophage-derived cytokines and nitric oxide (NO), we then analyzed macrophage response ex vivo. Anti-arthritic effects of QU correlated with significant decrease of inflammatory mediators produced by peritoneal macrophages, ex vivo and in vitro. These data indicate that QU is a potential anti-inflammatory therapeutic and preventive agent targeting the inflammatory response of macrophages.

Low multiplicity of infection of Helicobacter pylori suppresses apoptosis of B lymphocytes

Helicobacter pylori infection of the human stomach causes chronic gastritis that can lead to gastric cancer. Because activated lymphocytes persist in the gastric mucosa, and because a high multiplicity of infection (MOI) of H. pylori is needed to induce apoptosis in vitro, we speculated that resistance of lymphocytes to apoptosis is an important feature of the immune response to H. pylori. Freshly isolated mouse splenocytes underwent substantial spontaneous apoptosis and displayed a biphasic response to H. pylori, in which low MOI (1-10) markedly inhibited apoptosis, whereas high MOI (> or =75) potentiated apoptosis. Low MOI reduced mitochondrial membrane depolarization, caspase-3 and caspase-9 activation, and cytochrome c release and increased Bcl-2 levels. Low MOI also induced cellular proliferation. When cells were subjected to fluorescence-activated cell sorting after coculture with H. pylori, CD19+ B cells were found to be protected from apoptosis and undergoing proliferation at low MOI, whereas CD3+ T cells did not exhibit this pattern. The protective effect of low MOI on apoptosis persisted even when B cells were isolated before activation. Immunophenotyping showed that all B-cell subsets examined were protected from apoptosis at low MOI. Additionally, gastric infection with H. pylori resulted in protection of splenic B cells from spontaneous apoptosis. Our results suggest that the low levels of H. pylori infection that occur in vivo are associated with B-cell survival and proliferation, consistent with their potential to evolve into mucosa-associated lymphoid tissue lymphoma.

Arginine homeostasis in J774.1 macrophages in the context of Mycobacterium bovis BCG infection

The competition for L-arginine between the inducible nitric oxide synthase and arginase contributes to the outcome of several parasitic and bacterial infections. The acquisition of L-arginine, however, is important not only for the host cells but also for the intracellular pathogen. In this study we observe that strain AS-1, the Mycobacterium bovis BCG strain lacking the Rv0522 gene, which encodes an arginine permease, perturbs l-arginine metabolism in J774.1 murine macrophages. Infection with AS-1, but not with wild-type BCG, induced l-arginine uptake in J774.1 cells. This increase in L-arginine uptake was independent of activation with gamma interferon plus lipopolysaccharide and correlated with increased expression of the MCAT1 and MCAT2 cationic amino acid transport genes. AS-1 infection also enhanced arginase activity in resting J774.1 cells. Survival studies revealed that AS-1 survived better than BCG within resting J774.1 cells. Intracellular growth of AS-1 was further enhanced by inhibiting arginase and ornithine decarboxylase activities in J774.1 cells using L-norvaline and difluoromethylornithine treatment, respectively. These results suggest that the arginine-related activities of J774.1 macrophages are affected by the arginine transport capacity of the infecting BCG strain. The loss of Rv0522 gene-encoded arginine transport may have induced other cationic amino acid transport systems during intracellular growth of AS-1, allowing better survival within resting macrophages.

Mining the mouse transcriptome of receptive endometrium reveals distinct molecular signatures for the luminal and glandular epithelium

Epithelia coat most tissues where they sense and respond to the environment and participate in innate immune responses. In the adult mouse uterus, columnar epithelium lines the central lumen and the glands that penetrate the underlying stroma. A nidatory surge of estrogen causes differentiation of the luminal epithelium to the receptive state that permits blastocyst attachment and allows subsequent implantation. Here, using laser-capture microdissection to isolate the luminal and glandular epithelia separately, we have profiled gene expression 2 h before embryo attachment to determine whether there are unique roles for these two epithelial structures in this process. Although most genes were expressed in both compartments, there was greater expression of 153 and 118 genes in the lumen and glands, respectively. In the luminal epithelium, there is enrichment in lipid, metal-ion binding, and carbohydrate-metabolizing enzymes, whereas in the glands, immune response genes are emphasized. In situ hybridization to uterine sections obtained from mice during the preimplantation period validated these data and indicated an array of previously undocumented genes expressed with unique patterns in these epithelia. The data show that each epithelial compartment has a distinct molecular signature and that they act differentially and synergistically to permit blastocyst implantation.

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori Infection

SUMMARY

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori .

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori is the first formally recognized bacterial carcinogen and is one of the most successful human pathogens, as over half of the world's population is colonized with this gram-negative bacterium. Unless treated, colonization usually persists lifelong. H. pylori infection represents a key factor in the etiology of various gastrointestinal diseases, ranging from chronic active gastritis without clinical symptoms to peptic ulceration, gastric adenocarcinoma, and gastric mucosa-associated lymphoid tissue lymphoma. Disease outcome is the result of the complex interplay between the host and the bacterium. Host immune gene polymorphisms and gastric acid secretion largely determine the bacterium's ability to colonize a specific gastric niche. Bacterial virulence factors such as the cytotoxin-associated gene pathogenicity island-encoded protein CagA and the vacuolating cytotoxin VacA aid in this colonization of the gastric mucosa and subsequently seem to modulate the host's immune system. This review focuses on the microbiological, clinical, immunological, and biochemical aspects of the pathogenesis of H. pylori.

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.

Expression of B7-H1 on gastric epithelial cells: its potential role in regulating T cells during Helicobacter pylori infection

Helicobacter pylori infection is associated with gastritis, ulcers, and gastric cancer. The infection becomes chronic as the host response is unable to clear it. Gastric epithelial cells (GEC) play an important role during the host response, and their expression of class II MHC and costimulatory molecules such as CD80 and CD86 suggests their role in local Ag presentation. Although T cells are recruited to the infected gastric mucosa, they have been reported to be hyporesponsive. In this study, we detected the expression of B7-H1 (programmed death-1 ligand 1), a member of B7 family of proteins associated with T cell inhibition on GEC. Quantitative real-time RT-PCR revealed that B7-H1 expression increased significantly on GEC after H. pylori infection. Western blot analysis showed that B7-H1 expression was induced by various H. pylori strains and was independent of H. pylori virulence factors such as Cag, VacA, and Urease. The functional role of B7-H1 in the cross talk between GEC and T cells was assessed by coculturing GEC or H. pylori-infected GEC with CD4+ T cells isolated from peripheral blood. Using blocking Abs to B7-H1 revealed that B7-H1 was involved in the suppression of T cell proliferation and IL-2 synthesis, and thus suggested a role for B7-H1 on the epithelium as a contributor in the chronicity of H. pylori infection.

Helicobacter pylori induces apoptosis of T- and B-cell lines and translocates mitochondrial apoptosis-inducing factor to nucleus

Immune cell apoptosis may play a role in human persistent Helicobacter pylori infection. We planned to study the apoptosis of T and B cells by H. pylori strains. T (Jurkat) and B (Raji) cell lines were co-cultured with cagA-positive H. pylori strains carrying different vacA genotypes (s1a/m1, s1a/m2, and s2/m2). Apoptosis was detected by microscopy, DNA fragmentation assay, and flow cytometry. Apoptosis-inducing factor (AIF) transfer from mitochondria to nucleus was studied by immunoblot analysis. Apoptosis of T and B cells was significantly higher in H. pylori-infected cells than in uninfected controls (s1a/m1 80%, s1a/m2 78%, s2m2 69% vs. control 16% for T cells, P < 0.001; s1 a/m1 78%, s1a/m2 73%, s2m2 62% vs. control 24% for B cells, P < 0.001 by flow cytometry) with no difference among the genotypes. AIF transfer from mitochondria to nucleus was demonstrated in both apoptotic cell lines. Thus, H. pylori induces apoptosis in T- and B-cell lines and translocates AIF. T and B cells deletion through apoptosis may explain the persistence of H. pylori infection; its role in pathogenesis needs further research.

The biology of Helicobacter pylori infection, a major risk factor for gastric adenocarcinoma

Helicobacter pylori infection of the human stomach is the most important risk factor for development of gastric cancer. Whereas persistent viral infection leads to a number of cancers, H. pylori was the first bacteria linked to a human cancer. The exact mechanisms that lead to cancer induction are not clear, but study of the bacterial factors important for colonization and the host responses to the infection are starting to yield important clues.

Comparative analyses of Xanthomonas and Xylella complete genomes

Computational analyses of four bacterial genomes of the Xanthomonadaceae family reveal new unique genes that may be involved in adaptation, pathogenicity, and host specificity. The Xanthomonas genus presents 3636 unique genes distributed in 1470 families, while Xylella genus presents 1026 unique genes distributed in 375 families. Among Xanthomonas-specific genes, we highlight a large number of cell wall degrading enzymes, proteases, and iron receptors, a set of energy metabolism genes, second copy of the type II secretion system, type III secretion system, flagella and chemotactic machinery, and the xanthomonadin synthesis gene cluster. Important genes unique to the Xylella genus are an additional copy of a type IV pili gene cluster and the complete machinery of colicin V synthesis and secretion. Intersections of gene sets from both genera reveal a cluster of genes homologous to Salmonella's SPI-7 island in Xanthomonas axonopodis pv citri and Xylella fastidiosa 9a5c, which might be involved in host specificity. Each genome also presents important unique genes, such as an HMS cluster, the kdgT gene, and O-antigen in Xanthomonas axonopodis pv citri; a number of avrBS genes and a distinct O-antigen in Xanthomonas campestris pv campestris, a type I restriction-modification system and a nickase gene in Xylella fastidiosa 9a5c, and a type II restriction-modification system and two genes related to peptidoglycan biosynthesis in Xylella fastidiosa temecula 1. All these differences imply a considerable number of gene gains and losses during the divergence of the four lineages, and are associated with structural genome modifications that may have a direct relation with the mode of transmission, adaptation to specific environments and pathogenicity of each organism.

Regulation of arginase II by interferon regulatory factor 3 and the involvement of polyamines in the antiviral response

The innate antiviral response requires the induction of genes and proteins with activities that limit virus replication. Among these, the well-characterized interferon beta (IFNB) gene is regulated through the cooperation of AP-1, NF-kappaB and interferon regulatory factor 3 (IRF-3) transcription factors. Using a constitutively active form of IRF-3, IRF-3 5D, we showed previously that IRF-3 also regulates an IFN-independent antiviral response through the direct induction of IFN-stimulated genes. In this study, we report that the arginase II gene (ArgII) as well as ArgII protein concentrations and enzymatic activity are induced in IRF-3 5D-expressing and Sendai virus-infected Jurkat cells in an IFN-independent manner. ArgII is a critical enzyme in the polyamine-biosynthetic pathway. Of the natural polyamines, spermine possesses antiviral activity and mediates apoptosis at physiological concentrations. Measurement of intracellular polyamine content revealed that expression of IRF-3 5D induces polyamine production, but that Sendai virus and vesicular stomatitis virus infections do not. These results show for the first time that the ArgII gene is an early IRF-3-regulated gene, which participates in the IFN-independent antiviral response through polyamine production and induction of apoptosis.

Immune subversion by Helicobacter pylori

To maintain prolonged colonization of the human gastric mucosa, Helicobacter pylori must avoid both innate and adaptive immune responses. During its long coexistence with humans, it has evolved complex strategies to maintain a mild inflammation of the gastric epithelium while limiting the extent of immune effector activity. Severe disease, associated with bacterial colonization, might reflect loss of this control. Several mechanisms and the bacterial factors involved in immune subversion have, in recent years, been elucidated, thus opening the possibility of a better understanding of the pathogenicity of this microorganism.

Helicobacter pylori-induced macrophage apoptosis requires activation of ornithine decarboxylase by c-Myc

Helicobacter pylori infection causes chronic inflammation of the gastric mucosa that results from an ineffective immune response. We have demonstrated that one underlying mechanism is induction of macrophage apoptosis mediated by polyamines. The transcription factor c-Myc has been linked to induction of ornithine decarboxylase (ODC), the rate-limiting enzyme in polyamine synthesis. We determined whether H. pylori stimulates transcriptional activation of ODC in macrophages, whether this occurs via c-Myc, and whether these events regulate activation of apoptosis. H. pylori induced a significant increase in ODC promoter activity that peaked at 6 h after stimulation and was closely paralleled by similar increases in ODC mRNA, protein, and enzyme activity. By 2 h after stimulation, c-Myc mRNA and protein expression was induced, protein was translocated to the nucleus, and there was specific binding of a consensus probe for c-Myc to nuclear extracts. Both an antennapedia-linked inhibitor of c-Myc binding (Int-H1-S6A,F8A) and transfection of a c-Myc dominant-negative construct significantly attenuated H. pylori-induced ODC promoter activity, mRNA, enzyme activity, and apoptosis in parallel. Transfection of ODC small interfering RNA inhibited ODC activity and apoptosis to the same degree as inhibition of c-Myc binding. These studies indicate that c-Myc is an important mediator of macrophage activation and may contribute to the mucosal inflammatory response to pathogens such as H. pylori by its effect on ODC.

Murine macrophage transcriptional responses to Bacillus anthracis infection and intoxication

Interactions between Bacillus anthracis and host macrophages represent critical early events in anthrax pathogenesis, but their details are not clearly understood. Here we report the first genomewide characterization of the transcriptional changes within macrophages infected with B. anthracis and the identification of several hundred host genes that were differentially expressed during this intracellular stage of infection. These loci included both genes that are known to be regulated differentially in response to many other bacterial pathogens and those that appear to be differentially regulated in response to B. anthracis but not other bacterial species that have been tested. These data provide a transcriptional basis for a variety of physiological changes observed during infection, including the induction of apoptosis caused by the infecting bacteria. The expression patterns underlying B. anthracis-induced apoptosis led us to test further the importance of one very highly induced macrophage gene, that for ornithine decarboxylase. Our data show that this enzyme plays an important and previously unrecognized role in suppressing apoptosis in B. anthracis-infected cells. We have also characterized the transcriptional response to anthrax lethal toxin in activated macrophages and found that, following toxin treatment, many of the host inflammatory response pathways are dampened. These data provide insights into B. anthracis pathogenesis as well as potential leads for the development of new diagnostic and therapeutic options.

Spermine oxidation induced by Helicobacter pylori results in apoptosis and DNA damage: implications for gastric carcinogenesis

Oxidative stress is linked to carcinogenesis due to its ability to damage DNA. The human gastric pathogen Helicobacter pylori exerts much of its pathogenicity by inducing apoptosis and DNA damage in host gastric epithelial cells. Polyamines are abundant in epithelial cells, and when oxidized by the inducible spermine oxidase SMO(PAOh1) H(2)O(2) is generated. Here, we report that H. pylori up-regulates mRNA expression, promoter activity, and enzyme activity of SMO(PAOh1) in human gastric epithelial cells, resulting in DNA damage and apoptosis. H. pylori-induced H(2)O(2) generation and apoptosis in these cells was equally attenuated by an inhibitor of SMO(PAOh1), by catalase, and by transient transfection with small interfering RNA targeting SMO(PAOh1). Conversely, SMO(PAOh1) overexpression induced apoptosis to the same levels as caused by H. pylori. Importantly, in H. pylori-infected tissues, there was increased expression of SMO(PAOh1) in both human and mouse gastritis. Laser capture microdissection of human gastric epithelial cells demonstrated expression of SMO(PAOh1) that was significantly attenuated by H. pylori eradication. These results identify a pathway for oxidative stress-induced epithelial cell apoptosis and DNA damage due to SMO(PAOh1) activation by H. pylori that may contribute to the pathogenesis of the infection and development of gastric cancer.

Spermine causes loss of innate immune response to Helicobacter pylori by inhibition of inducible nitric-oxide synthase translation

Helicobacter pylori infection of the stomach elicits a vigorous but ineffective host immune and inflammatory response, resulting in persistence of the bacterium for the life of the host. We have reported that in macrophages, H. pylori up-regulates inducible NO synthase (iNOS) and antimicrobial NO production, but in parallel there is induction of arginase II, generating ornithine, and of ornithine decarboxylase (ODC), generating polyamines. Spermine, in particular, has been shown to restrain immune response in activated macrophages by inhibiting proinflammatory gene expression. We hypothesized that spermine could prevent the antimicrobial effects of NO by inhibiting iNOS in macrophages activated by H. pylori. Spermine did not affect the up-regulation of iNOS mRNA levels but in a concentration-dependent manner significantly attenuated iNOS protein levels and NO production. Reduction in iNOS protein was due to inhibition of iNOS translation and not due to iNOS degradation. ODC knockdown with small interfering (si) RNA resulted in increased H. pylori-stimulated iNOS protein expression and NO production without altering iNOS mRNA levels. When macrophages were cocultured with H. pylori, killing of bacteria was enhanced by transfection of ODC siRNA and prevented by addition of spermine. These results identify a mechanism of immune dysregulation induced by H. pylori in which stimulated spermine synthesis by the arginase-ODC pathway inhibits iNOS translation and NO production, leading to persistence of the bacterium and risk for peptic ulcer disease and gastric cancer.

Protective role of arginase in a mouse model of colitis

Arginase is the endogenous inhibitor of inducible NO synthase (iNOS), because both enzymes use the same substrate, l-arginine (Arg). Importantly, arginase synthesizes ornithine, which is metabolized by the enzyme ornithine decarboxylase (ODC) to produce polyamines. We investigated the role of these enzymes in the Citrobacter rodentium model of colitis. Arginase I, iNOS, and ODC were induced in the colon during the infection, while arginase II was not up-regulated. l-Arg supplementation of wild-type mice or iNOS deletion significantly improved colitis, and l-Arg treatment of iNOS(-/-) mice led to an additive improvement. There was a significant induction of IFN-gamma, IL-1, and TNF-alpha mRNA expression in colitis tissues that was markedly attenuated with l-Arg treatment or iNOS deletion. Treatment with the arginase inhibitor S-(2-boronoethyl)-l-cysteine worsened colitis in both wild-type and iNOS(-/-) mice. Polyamine levels were increased in colitis tissues, and were further increased by l-Arg. In addition, in vivo inhibition of ODC with alpha-difluoromethylornithine also exacerbated the colitis. Taken together, these data indicate that arginase is protective in C. rodentium colitis by enhancing the generation of polyamines in addition to competitive inhibition of iNOS. Modulation of the balance of iNOS and arginase, and of the arginase-ODC metabolic pathway may represent a new strategy for regulating intestinal inflammation.

Effects of L-Ornithine on Metabolic Processes of the Urea Cycle in Human Keratinocytes

The complex metabolic function of L-ornithine has led to a great interest in studying its pharmacotherapeutic potential. L-Ornithine is known to be crucial for the metabolism of keratinocytes, especially in the synthesis of urea, polyamines and precursors of collagen synthesis. In this study, we investigated in vitro the cytotoxicity of L-ornithine, and its influence on urea synthesis and arginase expression in primary human keratinocytes. L-Ornithine (> or =1 mM) induced a decrease in the de novo urea synthesis of keratinocytes and an increase (> or =10 mM) in the expression of the urea-generating enzyme arginase. Up to 20 mM, L-ornithine showed no cytotoxic potential, whereas higher concentrations induced apoptosis in keratinocytes in a concentration- and time-dependent manner.

Induction of polyamine oxidase 1 by Helicobacter pylori causes macrophage apoptosis by hydrogen peroxide release and mitochondrial membrane depolarization

Helicobacter pylori infects the human stomach by escaping the host immune response. One mechanism of bacterial survival and mucosal damage is induction of macrophage apoptosis, which we have reported to be dependent on polyamine synthesis by arginase and ornithine decarboxylase. During metabolic back-conversion, polyamines are oxidized and release H(2)O(2), which can cause apoptosis by mitochondrial membrane depolarization. We hypothesized that this mechanism is induced by H. pylori in macrophages. Polyamine oxidation can occur by acetylation of spermine or spermidine by spermidine/spermine N(1)-acetyltransferase prior to back-conversion by acetylpolyamine oxidase, but recently direct conversion of spermine to spermidine by the human polyamine oxidase h1, also called spermine oxidase, has been demonstrated. H. pylori induced expression and activity of the mouse homologue of this enzyme (polyamine oxidase 1 (PAO1)) by 6 h in parallel with ornithine decarboxylase, consistent with the onset of apoptosis, while spermidine/spermine N(1)-acetyltransferase activity was delayed until 18 h when late stage apoptosis had already peaked. Inhibition of PAO1 by MDL 72527 or by PAO1 small interfering RNA significantly attenuated H. pylori-induced apoptosis. Inhibition of PAO1 also significantly reduced H(2)O(2) generation, mitochondrial membrane depolarization, cytochrome c release, and caspase-3 activation. Overexpression of PAO1 by transient transfection induced macrophage apoptosis. The importance of H(2)O(2) was confirmed by inhibition of apoptosis with catalase. These studies demonstrate a new mechanism for pathogen-induced oxidative stress in macrophages in which activation of PAO1 leads to H(2)O(2) release and apoptosis by a mitochondrial-dependent cell death pathway, contributing to deficiencies in host defense in diseases such as H. pylori infection.

Mouse strain susceptibility to trypanosome infection: an arginase-dependent effect

We previously reported that macrophage arginase inhibits NO-dependent trypanosome killing in vitro and in vivo. BALB/c and C57BL/6 mice are known to be susceptible and resistant to trypanosome infection, respectively. Hence, we assessed the expression and the role of inducible NO synthase (iNOS) and arginase in these two mouse strains infected with Trypanosoma brucei brucei. Arginase I and arginase II mRNA expression was higher in macrophages from infected BALB/c compared with those from C57BL/6 mice, whereas iNOS mRNA was up-regulated at the same level in both phenotypes. Similarly, arginase activity was more important in macrophages from infected BALB/c vs infected C57BL/6 mice. Moreover, increase of arginase I and arginase II mRNA levels and of macrophage arginase activity was directly induced by trypanosomes, with a higher level in BALB/c compared with C57BL/6 mice. Neither iNOS expression nor NO production was stimulated by trypanosomes in vitro. The high level of arginase activity in T. brucei brucei-infected BALB/c macrophages strongly inhibited macrophage NO production, which in turn resulted in less trypanosome killing compared with C57BL/6 macrophages. NO generation and parasite killing were restored to the same level in BALB/c and C57BL/6 macrophages when arginase was specifically inhibited with N(omega)-hydroxy-nor-L-arginine. In conclusion, host arginase represents a marker of resistance/susceptibility to trypanosome infections.

Helicobacter pylori induces apoptosis of human monocytes but not monocyte-derived dendritic cells: role of the cag pathogenicity island

Monocytes are circulating precursors of the dendritic cell subset, professional antigen-presenting cells with a unique ability to initiate the innate and adaptive immune response. In this study, we have investigated the effects of wild-type Helicobacter pylori strains and their isogenic mutants with mutations in known bacterial virulence factors on monocytes and monocyte-derived dendritic cells. We show that H. pylori strains induce apoptosis of human monocytes by a mechanism that is dependent on the expression of a functional cag pathogenicity island. This effect requires an intact injection organelle for direct contact between monocytes and the bacteria but also requires a still-unidentified effector that is different from VacA or CagA. The exposure of in vitro-generated monocyte-derived dendritic cells to H. pylori stimulates the release of inflammatory cytokines by a similar mechanism. Of note is that dendritic cells are resistant to H. pylori-induced apoptosis. These phenomena may play a critical role in the evasion of the immune response by H. pylori, contributing to the persistence of the infection.

Helicobacter pylori arginase inhibits T cell proliferation and reduces the expression of the TCR zeta-chain (CD3zeta)

Helicobacter pylori infects approximately half the human population. The outcomes of the infection range from gastritis to gastric cancer and appear to be associated with the immunity to H. pylori. Patients developing nonatrophic gastritis present a Th1 response without developing protective immunity, suggesting that this bacterium may have mechanisms to evade the immune response of the host. Several H. pylori proteins can impair macrophage and T cell function in vitro through mechanisms that are poorly understood. We tested the effect of H. pylori extracts and live H. pylori on Jurkat cells and freshly isolated human normal T lymphocytes to identify possible mechanisms by which the bacteria might impair T cell function. Jurkat cells or activated T lymphocytes cultured with an H. pylori sonicate had a reduced proliferation that was not caused by T cell apoptosis or impairment in the early T cell signaling events. Instead, both the H. pylori sonicate and live H. pylori induced a decreased expression of the CD3zeta-chain of the TCR. Coculture of live H. pylori with T cells demonstrated that the wild-type strain, but not the arginase mutant rocF(-), depleted L-arginine and caused a decrease in CD3zeta expression. Furthermore, arginase inhibitors reversed these events. These results suggest that H. pylori arginase is not only important for urea production, but may also impair T cell function during infection.

Helicobacter pylori induces apoptosis of macrophages in association with alterations in the mitochondrial pathway

Helicobacter pylori is a gastric bacterial pathogen that evades host immune responses in vivo and is associated with the development of gastritis, peptic ulcer disease, and gastric cancers. Induction of macrophage apoptosis is a method employed by multiple pathogens to escape host immune responses. Therefore, we hypothesized that H. pylori induces apoptosis of infected macrophages. RAW 264.7 cells were infected with H. pylori strain 60190, and apoptosis was assessed. Transmission electron microscopy and fluorescence microscopy showed that infected macrophages displayed morphological features characteristic of apoptosis. Quantification by acridine orange-ethidium bromide fluorescent-dye staining showed that apoptosis was dose and time dependent, and apoptosis was further confirmed by increased binding of annexin V-fluorescein isothiocyanate (FITC) to externalized phosphatidylserine of infected but not of control macrophages. Macrophages infected with isogenic mutants of H. pylori strain 60190 deficient in either cagA or vacA induced significantly less apoptosis than the parental strain, as assessed by increased binding of annexin V-FITC. Western blot analysis of whole-cell protein lysates revealed that infection with strain 60190 induced a time-dependent increase in cleavage of procaspase 8 and disappearance of full-length Bid compared with uninfected cells. Furthermore, pharmacological inhibition of caspase 8 caused a decrease in levels of apoptosis. Finally, infection caused a time-dependent increase in mitochondrial-membrane permeability and release of cytochrome c into the cytosol. These results suggest that H. pylori induces apoptosis of macrophages in association with alterations in the mitochondrial pathway. Elimination of this key immunomodulatory cell may represent a mechanism employed by the bacterium to evade host immune responses.

Up-regulation of inducible nitric oxide synthase in Helicobacter pylori-associated gastritis may represent an increased risk factor to develop gastric carcinoma of the intestinal type

The enzyme inducible nitric oxide synthase (iNOS) is part of the host innate defense system against bacterial infection. During chronic inflammation, like that seen with a Helicobacter pylori infection, constant nitric oxide production may lead to tissue and DNA damage, thus increasing the patient's risk for developing cancer. Several investigations on iNOS expression in H. pylori-associated gastritis have resulted in conflicting data. Therefore, we investigated the association between chronic H. pylori infection and iNOS expression in samples from stomach carcinoma patients as well as in antral biopsies from patients with H. pylori-associated gastritis. iNOS expression was analyzed by means of reverse transcriptase (RT)-PCR and quantified by competitive RT-PCR. To study in situ localization of iNOS in biopsy samples, immunohistochemistry was performed. iNOS enzyme activity was quantified using an arginine/citrulline assay. A significant increase in iNOS mRNA signal was only present in one-third of the analyzed patient biopsies with H. pylori-associated gastritis. These biopsies showed a 90% association with intestinal metaplasia and a 100% association with CagA-positive H. pylori. Intestinal metaplasia is discussed to be one step in the carcinogenesis of stomach cancer. Quantitation of iNOS transcripts and iNOS enzyme activity in non-cancerous mucosa of gastric cancer patients revealed a significant increase in iNOS transcripts and iNOS activity only in the mucosa of patients with stomach cancer of the intestinal type but not in the diffuse type. Our results support the hypothesis that CagA-positive H. pylori strains are associated with the expression and activity of iNOS, and therefore might contribute to the development of intestinal metaplasia leading to gastric cancer of the intestinal type.

Cutting edge: cyclooxygenase-2 activation suppresses Th1 polarization in response to Helicobacter pylori

Helicobacter pylori infection causes a Th1-driven mucosal immune response. Cyclooxygenase (COX)-2 is up-regulated in lamina propria mononuclear cells in H. pylori gastritis. Because COX-2 can modulate Th1/Th2 balance, we determined whether H. pylori activates COX-2 in human PBMCs, and the effect on cytokine and proliferative responses. There was significant up-regulation of COX-2 mRNA and PGE(2) release in response to H. pylori preparations. Addition of COX-2 inhibitors or an anti-PGE(2) Ab resulted in a marked increase in H. pylori-stimulated IL-12 and IFN-gamma production, and a decrease in IL-10 levels. Addition of PGE(2) or cAMP, the second messenger activated by PGE(2), had the opposite effect. Similarly, stimulated cell proliferation was increased by COX-2 inhibitors or anti-PGE(2) Ab, and was decreased by PGE(2). Our findings indicate that COX-2 has an immunosuppressive role in H. pylori gastritis, which may protect the mucosa from severe injury, but may also contribute to the persistence of the infection.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori induces persistent inflammation in the human stomach, yet only a minority of colonized persons develop peptic ulcer disease or gastric malignancy. Numerous studies published in the last year have demonstrated that H. pylori isolates possess substantial phenotypic and genotypic diversity, which may engender differential host inflammatory responses that influence clinical outcome. Results from these recent investigations have more precisely delineated the mechanisms of H. pylori pathogenesis, which will ultimately help to define colonized persons bearing the highest risk for disease, and enable physicians to appropriately focus diagnostic testing and eradication therapy.

Nitric oxide in inflammatory bowel disease

Nitric oxide (NO) is a pleiotropic free radical messenger molecule. There is a large body of evidence that the inducible form of the NO synthase enzyme (iNOS) that is responsible for high-output production of NO from l-arginine is up-regulated in various forms of mucosal inflammation. Consistent with this, multiple detection strategies have demonstrated that iNOS expression, enzymatic activity, and NO production are increased in human inflammatory bowel disease tissues. There is also evidence that the level of iNOS-derived NO correlates well with disease activity in ulcerative colitis, while for Crohn's disease, the results are more variable. A substantial number of animal studies have assessed the role of inducible NO production. While the majority of studies have shown improvement in experimental inflammatory bowel disease with iNOS inhibition, there are also a significant number of reports of exacerbation of disease with inhibitors. Similarly, studies using iNOS-deficient mice in colitis models have shown improvement, worsening, or no effect on disease. The authors suggest that additional studies to assess the role of the competing biochemical pathway, namely the conversion of l-arginine to polyamines via the actions of arginase and ornithine decarboxylase, may provide important new insights into understanding the regulation of mucosal inflammation and inflammatory bowel disease.

Helicobacter pylori infection: pathogenesis

This review covers progress in identifying Helicobacter pylori-derived factors that are involved in survival and virulence of the organism and in elucidating host response pathways that can limit the infection but are also susceptible to dysregulation. Recent work has identified genes of the cytotoxin-associated gene (cag) pathogenicity island (PAI) involved in regulating signaling, interleukin-8 secretion, and phenotypic events in epithelial cells. New roles in pathogenesis have been recognized for vacuolating toxin A (VacA) and urease, H. pylori membrane and secreted factors, and host epithelial surface molecules. Molecular pathways involved in H. pylori-induced apoptosis in epithelial cells, T cells, and macrophages are being dissected. Activation of toll-like receptors and bacterial factors involved in nitric oxide (NO) and reactive oxygen species induction were also described. The ability of H. pylori to limit NO production by several mechanisms may be an important part of its ability to evade the host immune response.

Pathogenesis of Helicobacter pylori infection

Five years after publication of the complete genome sequence of Helicobacter pylori, research interest is shifting from the descriptive association of virulence factors with clinical outcome in infected patients to the molecular mechanisms of virulence factor action. This is particularly noticeable for VacA and CagA, for both of which detailed understanding of the interaction with host signalling pathways has accumulated over the last year. The role of H. pylori Lewis antigens for clinical outcome was further substantiated. Various strategies of H. pylori to fool or evade the human immune system are described, which all lead to the dysfunction of specific compartments of the host cellular immune system. Finally, a number of animal models indicate that inflammation is a key factor for gastric carcinogenesis, which is finally supported by a large prospective study identifying corpus atrophy and intestinal metaplasia as precancerous conditions.

Cutting edge: urease release by Helicobacter pylori stimulates macrophage inducible nitric oxide synthase

Inducible NO synthase (iNOS) expression and production of NO are both up-regulated with Helicobacter pylori infection in vivo and in vitro. We determined whether major pathogenicity proteins released by H. pylori activate iNOS by coculturing macrophages with wild-type or mutant strains deficient in VacA, CagA, picB product, or urease (ureA(-)). When filters were used to separate H. pylori from macrophages, there was a selective and significant decrease in stimulated iNOS mRNA, protein, and NO(2)(-) production with the ureA(-) strain compared with wild-type and other mutants. Similarly, macrophage NO(2)(-) generation was increased by H. pylori protein water extracts of all strains except ureA(-). Recombinant urease stimulated significant increases in macrophage iNOS expression and NO(2)(-) production. Taken together, these findings indicate a new role for the essential H. pylori survival factor, urease, implicating it in NO-dependent mucosal damage and carcinogenesis.