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

Helicobacter pylori AddAB helicase-nuclease and RecA promote recombination-related DNA repair and survival during stomach colonization

Helicobacter pylori colonization of the human stomach is characterized by profound disease-causing inflammation. Bacterial proteins that detoxify reactive oxygen species or recognize damaged DNA adducts promote infection, suggesting that H. pylori requires DNA damage repair for successful in vivo colonization. The molecular mechanisms of repair remain unknown. We identified homologues of the AddAB class of helicase-nuclease enzymes, related to the Escherichia coli RecBCD enzyme, which, with RecA, is required for repair of DNA breaks and homologous recombination. H. pylori mutants lacking addA or addB genes lack detectable ATP-dependent nuclease activity, and the cloned H. pylori addAB genes restore both nuclease and helicase activities to an E. coli recBCD deletion mutant. H. pylori addAB and recA mutants have a reduced capacity for stomach colonization. These mutants are sensitive to DNA damaging agents and have reduced frequencies of apparent gene conversion between homologous genes encoding outer membrane proteins. Our results reveal requirements for double-strand break repair and recombination during both acute and chronic phases of H. pylori stomach infection.

Immunomodulator effect of picroliv and its potential in treatment against resistant Plasmodium yoelii (MDR) infection in mice

PURPOSE

The present study was envisaged to evaluate potential of combination therapy comprising of immunomodulator picroliv and antimalarial chloroquine against drug resistant Plasmodium yoelii (P. yoelii) infection in BALB/c mice.

METHODS

The immunomodulatory potential of picroliv was established by immunizing animals with model antigen along with picroliv. Immune response was assessed using T-cell proliferation assay and also by determining the antibody isotype-profile induced in the immunized mice. In the next set of experiment, prophylactic potential of picroliv to strengthen antimalarial properties of chloroquine against P. yoelii (MDR) infection in BALB/c mice was assessed.

RESULTS

T-cell proliferation as well as antibody production study reveals that picroliv helps in evoking strong immuno-potentiating response against model antigen in the immunized mice. Co-administration of picroliv enhances efficacy of CHQ against experimental murine malaria.

CONCLUSION

The activation of host immune system can increase the efficacy of chloroquine for suppression of drug resistant malaria infection in BALB/c mice.

Nuclear localization of human spermine oxidase isoforms - possible implications in drug response and disease etiology

The recent discovery of the direct oxidation of spermine via spermine oxidase (SMO) as a mechanism through which specific antitumor polyamine analogues exert their cytotoxic effects has fueled interest in the study of the polyamine catabolic pathway. A major byproduct of spermine oxidation is H2O2, a source of toxic reactive oxygen species. Recent targeted small interfering RNA studies have confirmed that SMO-produced reactive oxygen species are directly responsible for oxidative stress capable of inducing apoptosis and potentially mutagenic DNA damage. In the present study, we describe a second catalytically active splice variant protein of the human spermine oxidase gene, designated SMO5, which exhibits substrate specificities and affinities comparable to those of the originally identified human spermine oxidase-1, SMO/PAOh1, and, as such, is an additional source of H2O2. Importantly, overexpression of either of these SMO isoforms in NCI-H157 human non-small cell lung carcinoma cells resulted in significant localization of SMO protein in the nucleus, as determined by confocal microscopy. Furthermore, cell lines overexpressing either SMO/PAOh1 or SMO5 demonstrated increased spermine oxidation in the nucleus, with accompanying alterations in individual nuclear polyamine concentrations. This increased oxidation of spermine in the nucleus therefore increases the production of highly reactive H2O2 in close proximity to DNA, as well as decreases nuclear spermine levels, thus altering the protective roles of spermine in free radical scavenging and DNA shielding, and resulting in an overall increased potential for oxidative DNA damage in these cells. The results of these studies therefore have considerable significance both with respect to targeting polyamine oxidation as an antineoplastic strategy, and in regard to the potential role of spermine oxidase in inflammation-induced carcinogenesis.

Helicobacter pylori invades the gastric mucosa and translocates to the gastric lymph nodes

Helicobacter pylori has been considered to be non-invasive and to rarely infiltrate the gastric mucosa, even though there is an active Th1 immune response in the lamina propria of the H. pylori-infected stomach. To elucidate whether H. pylori invades the lamina propria and translocates to the gastric lymph nodes, we examined H. pylori in formalin-fixed and paraffin-embedded tissue sections of stomach and gastric lymph nodes obtained from 51 cancer patients using real-time PCR and immunohistochemistry (IHC) with a novel anti-H. pylori monoclonal antibody that recognizes lipopolysaccharides. Fresh gastric lymph nodes were used to culture for H. pylori. In 46 patients with H. pylori in the stomach, the bacterium was found in the lymph nodes from 21 patients by culture, 37 patients by PCR, and 29 patients by IHC. H. pylori captured by macrophages was found in the lamina propria of 39 patients. In the lymph nodes, the bacterium was found in many macrophages and a few interdigitating dendritic cells at the paracortical areas. H. pylori was also found in the intracellular canaliculi of parietal cells in 21 patients, but intracytoplasmic invasion into gastric epithelial cells was not identified. When compared to the commercially available anti-H. pylori antibodies, the novel antibody showed the highest sensitivity to detect H. pylori-positive macrophages, whereas no difference was found for H. pylori in the mucous layer. The H. pylori-positive macrophages in the lamina propria correlated with chronic gastritis as well as translocation of such cells to the lymph nodes. These results suggest that H. pylori-induced gastric epithelial damage allows the bacteria to invade the lamina propria and translocate to the gastric lymph nodes, which may chronically stimulate the immune system. The bacteria captured by macrophages, whether remaining alive or not, may contribute to the induction and development of H. pylori-induced chronic gastritis.

The apolipoprotein E-mimetic peptide COG112 inhibits the inflammatory response to Citrobacter rodentium in colonic epithelial cells by preventing NF-kappaB activation

Inflammatory bowel disease arises from the interplay between luminal bacteria and the colonic mucosa. Targeted inhibition of pro-inflammatory pathways without global immunosuppression is highly desirable. Apolipoprotein (apo) E has immunomodulatory effects and synthetically derived apoE-mimetic peptides are beneficial in models of sepsis and neuroinflammation. Citrobacter rodentium is the rodent equivalent of enteropathogenic Escherichia coli, and it causes colitis in mice by colonizing the surface of colonic epithelial cells and inducing signaling events. We have reported that mice deficient in inducible nitric-oxide (NO) synthase (iNOS) have attenuated C. rodentium-induced colitis. We used young adult mouse colon (YAMC) cells that mimic primary colonic epithelial cells to study effects of an antennapedia-linked apoE-mimetic peptide, COG112, on C. rodentium-activated cells. COG112 significantly attenuated induction of NO production, and iNOS mRNA and protein expression, in a concentration-dependent manner. COG112 inhibited the C. rodentium-stimulated induction of iNOS and the CXC chemokines KC and MIP-2 to the same degree as the NF-kappaB inhibitors MG132 or BAY 11-7082, and there was no additive effect when COG112 and these inhibitors were combined. COG112 significantly reduced nuclear translocation of NF-kappaB, when assessed by electromobility shift assay, immunoblotting, and immunofluorescence for p65. This correlated with inhibition of both C. rodentium-stimulated IkappaB-alpha phosphorylation and degradation, and IkappaB kinase activity, which occurred by inhibition of IkappaB kinase complex formation rather than by a direct effect on the enzyme itself. These studies indicate that apoE-mimetic peptides may have novel therapeutic potential by inhibiting NF-kappaB-driven proinflammatory epithelial responses to pathogenic colonic bacteria.

Physiological polyamines: simple primordial stress molecules

Physiological polyamines are ubiquitous polycations with pleiotropic biochemical activities, including regulation of gene expression, cell proliferation and modulation of cell signalling. Reports that the polyamines with cytoprotective activities were induced by diverse stresses raised the hypothesis that physiological polyamines may play a role in inducing stress response. In a wide range of organisms, physiological polyamines were not only induced by diverse stresses, such as reactive oxygen species (ROS), heat, ultraviolet (UV) and psychiatric stress but were able to confer beneficial effects for survival. Recent biochemical and genetic evidences show that polyamines can function as an ROS scavenger, acid tolerance factor and chemical chaperone, and positive regulators for expression of stress response genes which may explain their protective functions against diverse stresses. Taken together, these data suggest that physiological polyamines can function as primordial stress molecules in bacteria, plants and mammals, and may play an essential role in regulation of pathogen-host interactions.

Inflammation and polyamine catabolism: the good, the bad and the ugly

The induction of polyamine catabolism by specific anti-tumour polyamine analogues has increased interest in the roles polyamine catabolism play in cell growth, death and response to various anti-tumour agents. The relatively recent finding of an inducible mammalian spermine oxidase (SMO/PAOh1), in addition to the two-step spermidine/spermine N(1)-acetyltransferanse (SSAT)/N(1)-acetylpolyamine oxidase (APAO) catabolic pathway, underscores the complexities of the regulation of polyamine catabolism by various stimuli. Furthermore, recent data indicate that infectious agents and mediators of inflammation can also up-regulate polyamine catabolism. Induction of SSAT by these agents can reduce intracellular polyamine concentrations and cell growth rate, thus providing a beneficial mechanism by which cells may adapt to inflammatory stress. However, increased polyamine catabolism can also result in substantial increases in intracellular reactive oxygen species (ROS) through the production of H(2)O(2) as a by-product of either APAO or SMO/PAOh1 activity. This increased generation of ROS can have different results, depending on the mechanism of induction and cell types involved. Targeted killing of tumour cells by agents that stimulate SSAT/APAO and/or SMO/PAOh1 is obviously a 'good' effect. However, induction of SMO/PAOh1 by inflammation or infectious agents has the potential to produce sufficient ROS in normal, non-tumour cells to lead to DNA damage, mutation and, potentially, carcinogenic transformation ('bad'). The variation in the induction of these polyamine catabolic enzymes, as well as the level and timing of this induction will dictate the cellular outcome in the presence of both desirable and undesirable effects ('ugly'). Here we discuss the relative role of each of the steps in polyamine catabolism in response to inflammatory stress.

Immunology of Helicobacter pylori: insights into the failure of the immune response and perspectives on vaccine studies

Helicobacter pylori infects the stomach of half of the human population worldwide and causes chronic active gastritis, which can lead to peptic ulcer disease, gastric adenocarcinoma, and mucosa-associated lymphoid tissue lymphoma. The host immune response to the infection is ineffective, because the bacterium persists and the inflammation continues for decades. Bacterial activation of epithelial cells, dendritic cells, monocytes, macrophages, and neutrophils leads to a T helper cell 1 type of adaptive response, but this remains inadequate. The host inflammatory response has a key functional role in disrupting acid homeostasis, which impacts directly on the colonization patterns of H pylori and thus the extent of gastritis. Many potential mechanisms for the failure of the host response have been postulated, and these include apoptosis of epithelial cells and macrophages, inadequate effector functions of macrophages and dendritic cells, VacA inhibition of T-cell function, and suppressive effects of regulatory T cells. Because of the extent of the disease burden, many strategies for prophylactic or therapeutic vaccines have been investigated. The goal of enhancing the host's ability to generate protective immunity has met with some success in animal models, but the efficacy of potential vaccines in humans remains to be demonstrated. Aspects of H pylori immunopathogenesis are reviewed and perspectives on the failure of the host immune response are discussed. Understanding the mechanisms of immune evasion could lead to new opportunities for enhancing eradication and prevention of infection and associated disease.

Polyamine biosynthesis as a target to inhibit apoptosis of non-tumoral cells

Growing evidence suggests a role for polyamines in apoptosis, although the relationship appears to be complex. alpha-Difluoromethylornithine (DFMO), a largely used ornithine decarboxylase inhibitor, is cytostatic, hardly cytotoxic and may even increase the resistance of tumour cells to some apoptotic stimuli. This may represent a problem in cancer therapy, where the killing of tumoral cells would be a desired effect, but could be an advantage in other pathological contexts related to an excess of apoptosis, such as cardiovascular diseases, stem cell transplantation, arthritis and infections. In different cellular models, polyamine depletion following treatment with polyamine biosynthesis inhibitors appears to inhibit mitochondrial and death receptor pathways of apoptosis by affecting key proteins. These studies indicate that inhibition of polyamine biosynthesis may prevent or reduce the apoptotic response triggered by a variety of stimuli in non-tumoral cells, such as cardiac cells, stem cells, chondrocytes, macrophages and intestinal epithelial cells.

L-arginine availability regulates inducible nitric oxide synthase-dependent host defense against Helicobacter pylori

Helicobacter pylori infection of the stomach causes an active immune response that includes stimulation of inducible nitric oxide (NO) synthase (iNOS) expression. Although NO can kill H. pylori, the bacterium persists indefinitely, suggesting that NO production is inadequate. We determined if the NO derived from iNOS in macrophages was dependent on the availability of its substrate, L-arginine (L-Arg). Production of NO by H. pylori-stimulated RAW 264.7 cells was dependent on the L-Arg concentration in the culture medium, and the 50% effective dose for L-Arg was 220 microM, which is above reported plasma L-Arg levels. While iNOS mRNA induction was L-Arg independent, iNOS protein increased in an L-Arg-dependent manner that did not involve changes in iNOS protein degradation. L-lysine, an inhibitor of L-Arg uptake, attenuated H. pylori-stimulated iNOS protein expression, translation, NO levels, and killing of H. pylori. While L-Arg starvation suppressed global protein translation, at concentrations of L-Arg at which iNOS protein was only minimally expressed in response to H. pylori, global translation was fully restored and eukaryotic translation initiation factor alpha was dephosphorylated. H. pylori lacking the gene rocF, which codes for a bacterial arginase, induced higher levels of NO production by increasing iNOS protein levels. When murine gastric macrophages were activated with H. pylori, supraphysiologic levels of L-Arg were required to permit iNOS protein expression and NO production. These findings indicate that L-Arg is rate limiting for iNOS translation and suggest that the levels of L-Arg that occur in vivo do not permit sufficient NO generation by the host to kill H. pylori.

Electrochemical detection of pathogen infection using cell chip

The immobilized cell using self-assembled synthetic oligopeptide was applied to the electrochemical detection of pathogen infection. Thin films based on cysteine-terminated synthetic oligopeptides were fabricated for the immobilization of HeLa cell on gold (Au) substrate. Layer formation and immobilization of the cell were investigated with surface plasmon resonance (SPR) and electrochemical impedance spectroscopy (EIS). Experimental results showed that the thin film of cysteine-terminated synthetic oligopeptide was successfully fabricated and it could be applied for the immobilization of HeLa cells. The adhered living cell was exposed to E. coli O157:H7, which induced the change of SPR angle and electrochemical impedance signal. The proposed cell immobilization method using self-assembly technique can be applied to construct the cell microarray for on-site pathogen monitoring.

Polyamine-mediated apoptosis of alveolar macrophages during Pneumocystis pneumonia

The number of alveolar macrophages is decreased during Pneumocystis pneumonia (Pcp), partly because of activation of apoptosis in these cells. This apoptosis occurs in both rat and mouse models of Pcp. Bronchoalveolar lavage (BAL) fluids from Pneumocystis-infected animals were found to contain high levels of polyamines, including spermidine, N1-acetylspermine, and N1-acetylspermidine. These BAL fluids and exogenous polyamines were able to induce apoptosis in alveolar macrophages. Apoptosis of alveolar macrophages during infection, after incubation with BAL fluids from Pneumocystis-infected animals, or after incubation with polyamines was marked by an increase in intracellular reactive oxygen species, activation of caspases-3 and -9, DNA fragmentation, and leakage of mitochondrial cytochrome c into the cytoplasm. When polyamines were depleted from the BAL fluids of infected animals, the ability of these BAL fluids to induce apoptosis was lost. Interestingly, the apoptosis inducing activity of the polyamine-depleted BAL fluids was restored when polyamines were added back. The results of this study suggested that Pneumocystis infection results in accumulation of high levels of polyamines in the lung. These polyamines activate apoptosis of alveolar macrophages, perhaps because of the ROS that are produced during polyamine metabolism.

Mammalian polyamine catabolism: a therapeutic target, a pathological problem, or both?

With the recent discovery of the polyamine catabolic enzyme spermine oxidase (SMO/PAOh1), the apparent complexity of the polyamine metabolic pathway has increased considerably. Alone or in combination with the two other known members of human polyamine catabolism, spermidine/spermine N(1)-acetyltransferase, and N(1)-acetylpolyamine oxidase (PAO), SMO/PAOh1 expression has the potential to alter polyamine homeostasis in response to normal cellular signals, drug treatment and environmental and/or cellular stressors. The activity of the oxidases producing toxic aldehydes and the reactive oxygen species (ROS) H(2)O(2), suggest a mechanism by which these oxidases can be exploited as an antineoplastic drug target. However, inappropriate activation of the pathways may also lead to pathological outcomes, including DNA damage that can lead to cellular transformation. The most recent data suggest that the two polyamine catabolic pathways exhibit distinct properties and understanding these properties should aid in their exploitation for therapeutic and/or chemopreventive strategies.

Helicobacter pylori persistence: an overview of interactions between H. pylori and host immune defenses

Helicobacter pylori is a gram-negative bacterium that persistently colonizes more than half of the global human population. In order to successfully colonize the human stomach, H. pylori must initially overcome multiple innate host defenses. Remarkably, H. pylori can persistently colonize the stomach for decades or an entire lifetime despite development of an acquired immune response. This review focuses on the immune response to H. pylori and the mechanisms by which H. pylori resists immune clearance. Three main sections of the review are devoted to (i) analysis of the immune response to H. pylori in humans, (ii) analysis of interactions of H. pylori with host immune defenses in animal models, and (iii) interactions of H. pylori with immune cells in vitro. The topics addressed in this review are important for understanding how H. pylori resists immune clearance and also are relevant for understanding the pathogenesis of diseases caused by H. pylori (peptic ulcer disease, gastric adenocarcinoma, and gastric lymphoma).

Effects of glucocorticoids on polyamine metabolism in liver and spleen of guinea pig during sensitization

Glucocorticoids are potent anti-inflammatory and immunosuppressive agents. As endogenous inhibitors of cytokine synthesis, glucocorticoids suppress immune activation and uncontrolled overproduction of cytokines, preventing tissue injury. Also, polyamine spermine is endogenous inhibitor of cytokine production (inhibiting IL-1, IL-6 and TNF synthesis). The idea of our work was to examine dexamethasone effects on the metabolism of polyamines, spermine, spermidine and putrescine and polyamine oxidase activity in liver and spleen during sensitization of guinea pigs. Sensitization was done by application of bovine serum albumin with addition of complete Freund's adjuvant. Our results indicate that polyamine amounts and polyamine oxidase activity increase during immunogenesis in liver and spleen. Dexamethasone application to sensitized and unsensitized guinea pigs causes depletion of polyamines in liver and spleen. Dexamethasone decreases polyamine oxidase activity in liver and spleen of sensitized guinea pigs, increasing at the same time PAO activity in tissues of unsensitized animals.

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.

Suppression of alveolar macrophage apoptosis prolongs survival of rats and mice with pneumocystis pneumonia

The number of alveolar macrophages is decreased in patients or animals with Pneumocystis pneumonia (Pcp). This loss of alveolar macrophages is in part due to apoptosis caused by Pneumocystis infection. The mechanism of apoptosis induction is unknown. Cell-free bronchoalveolar lavage fluids from Pneumocystis-infected rats or mice have the ability to induce apoptosis in normal alveolar macrophages. To characterize the mechanisms by which apoptosis proceeds in alveolar macrophages during Pcp, specific caspase inhibitors are tested for their ability to suppress the apoptosis. In vitro induction of apoptosis can be inhibited by the caspase-9 inhibitor (Z-LEHD-FMK) but not by the inhibitor to caspase-8 or -10. The caspase-9 inhibitor can also inhibit apoptosis of alveolar macrophages in vivo when it is intranasally instilled into dexamethasone-immunosuppressed, Pneumocystis-infected rats or L3T4 cell-depleted, Pneumocystis-infected mice. The number of alveolar macrophages rebounds in caspase-9 inhibitor-treated Pcp animals. Phagocytic activity of alveolar macrophages in treated animals is also recovered, and organism burden in these animals is reduced. Administration of caspase-9 inhibitor also clears the exudate that normally fills the alveoli during Pcp and decreases lung inflammation. Furthermore, caspase-9-treated Pcp animals survive for the entire 70-day period of the study, whereas nontreated Pcp animals die 40-60 days after initiation of infection. Depletion of recovered alveolar macrophages by intranasal administration of clodronate-containing liposomes in caspase-9 inhibitor-treated animals abrogates the effects of the inhibitor. Together, these results indicate that immunomodulation of the host response may be an alternative to current treatments for Pcp.

Nitric oxide protects macrophages from hydrogen peroxide-induced apoptosis by inducing the formation of catalase

We investigated the cytoprotective effect of NO on H2O2-induced cell death in mouse macrophage-like cell line RAW264. H2O2-treated cells showed apoptotic features, such as activation of caspase-9 and caspase-3, nuclear fragmentation, and DNA fragmentation. These apoptotic features were significantly inhibited by pretreatment for 24 h with NO donors, sodium nitroprusside and 1-hydroxy-2-oxo-3,3-bis-(2-aminoethyl)-1-triazene, at a low nontoxic concentration. The cytoprotective effect of NO was abrogated by the catalase inhibitor 3-amino-1,2,4-triazole but was not affected by a glutathione synthesis inhibitor, L-buthionine-(S,R)-sulfoximine. NO donors increased the level of catalase and its activity in a concentration-dependent manner. Cycloheximide, a protein synthesis inhibitor, inhibited both the NO-induced increase in the catalase level and the cytoprotective effect of NO. These results indicate that NO at a low concentration protects macrophages from H2O2-induced apoptosis by inducing the production of catalase.

Co-ordinate but disproportionate activation of apoptotic, regenerative and inflammatory pathways characterizes the liver response to acute amebic infection

The liver has the remarkable ability to respond to injury with repair and regeneration. The protozoan parasite Entamoeba histolytica is the major cause of liver abscess worldwide. We report a transcriptional analysis of the response of mouse liver to E. histolytica infection, the first study looking at acute liver infection by a non-viral pathogen. Focusing on early time points, we identified 764 genes with altered transcriptional levels in amebic liver abscess. The response to infection is rapid and complex, with concurrent increased expression of genes linked to host defence through IL-1, TLR2, or interferon-induced pathways, liver regeneration via activation of IL-6 pathways, and genes associated with programmed cell death possibly through TNFalpha or Fas pathways. A comparison of amebic liver infection with the liver response to partial hepatectomy or toxins reveals striking similarities between amebic liver abscess and non-infectious injury in key components of the liver regeneration pathways. However, the response in amebic liver abscess is biased towards apoptosis when compared with acute liver injury from hepatectomy, toxins, or other forms of liver infection. E. histolytica infection of the liver simultaneously activates inflammatory, regenerative and apoptotic pathways, but the sum of these early responses is biased towards programmed cell death.

Oxygen reactivity of PutA from Helicobacter species and proline-linked oxidative stress

Proline is converted to glutamate in two successive steps by the proline utilization A (PutA) flavoenzyme in gram-negative bacteria. PutA contains a proline dehydrogenase domain that catalyzes the flavin adenine dinucleotide (FAD)-dependent oxidation of proline to delta1-pyrroline-5-carboxylate (P5C) and a P5C dehydrogenase domain that catalyzes the NAD+-dependent oxidation of P5C to glutamate. Here, we characterize PutA from Helicobacter hepaticus (PutA(Hh)) and Helicobacter pylori (PutA(Hp)) to provide new insights into proline metabolism in these gastrointestinal pathogens. Both PutA(Hh) and PutA(Hp) lack DNA binding activity, in contrast to PutA from Escherichia coli (PutA(Ec)), which both regulates and catalyzes proline utilization. PutA(Hh) and PutA(Hp) display catalytic activities similar to that of PutA(Ec) but have higher oxygen reactivity. PutA(Hh) and PutA(Hp) exhibit 100-fold-higher turnover numbers (approximately 30 min(-1)) than PutA(Ec) (<0. 3 min(-1)) using oxygen as an electron acceptor during catalytic turnover with proline. Consistent with increased oxygen reactivity, PutA(Hh) forms a reversible FAD-sulfite adduct. The significance of increased oxygen reactivity in PutA(Hh) and PutA(Hp) was probed by oxidative stress studies in E. coli. Expression of PutA(Ec) and PutA from Bradyrhizobium japonicum, which exhibit low oxygen reactivity, does not diminish stress survival rates of E. coli cell cultures. In contrast, PutA(Hp) and PutA(Hh) expression dramatically reduces E. coli cell survival and is correlated with relatively lower proline levels and increased hydrogen peroxide formation. The discovery of reduced oxygen species formation by PutA suggests that proline catabolism may influence redox homeostasis in the ecological niches of these Helicobacter species.

Helicobacter pylori induces apoptosis of rat gastric epithelial cells in vitro

AIM: To investigate the effect of Helicobacter pylori (H. pylori) sonicated extract on the apoptosis of rat gastric epithelial cells as well as the expression of apoptosis-related genes in vitro.

METHODS: H. pylori sonicated extract from strain Sydney SS-1 was cultured with OUMS-37, a kind of immortalized rat gastric cell lines. Apoptosis of the cells was confirmed according to specific changes of morphology and DNA ladder 24-48 h after co-incubation. The expression of P53 protein was detected by Western blotting and the expression of bax and bcl-2 mRNA were observed by Northern blotting.

RESULTS: The specific morphology of the cells such as shrinkage, condensation, margination of nuclear chromatin and apoptotic bodies were observed under light microscope. DNA ladder was manifested by fragment analysis. Western blotting showed a dose-dependent increased expression of wild-type P53 protein and Northern blotting showed a dose-pendent increased expression of bax mRNA and reduced expression of bcl-2 mRNA in the treated cells.

CONCLUSION: H. pylori sonicated extract induces the apoptosis in vitro through up-regulation of wild-type P53 protein and bax mRNA expression, and down-regulation of bcl-2 mRNA expression, suggesting that H. pylori infection may interrupt the balance between proliferation and apoptosis of the gastric epithelial cells, which plays a key role in gastric carcinogenesis.

Differential modulation of MAP kinases by zinc deficiency in IMR-32 cells: role of H(2)O(2)

The influence of zinc deficiency on the modulation of the mitogen-activated protein kinases (MAPKs) extracellular signal-regulated kinase (ERK1/2), p38, and c-Jun N-terminal kinase (JNK) was studied. Using human IMR-32 cells as a model of neuronal cells, the role of oxidants on MAPKs and activator protein-1 (AP-1) activation in zinc deficiency was investigated, characterizing the participation of these events in the triggering of apoptosis. Relative to controls, cells incubated in media with low zinc concentrations showed increased cell oxidants and hydrogen peroxide (H(2)O(2)) release, increased JNK and p38 activation, high nuclear AP-1-DNA binding activity, and AP-1-dependent gene expression. Catalase addition to the media prevented the increase of cellular oxidants and inhibited JNK, p38, and AP-1 activation. Low levels of ERK1/2 phosphorylation were observed in the zinc-deficient cells in association with a reduction in cell proliferation. Catalase treatment did not prevent the above events nor the increased rate of apoptosis in the zinc-deficient cells. It is first demonstrated that a decrease in cellular zinc triggers H(2)O(2)-independent, as well as H(2)O(2)-dependent effects on MAPKs. Zinc deficiency-induced increases in cellular H(2)O(2) can trigger the activation of JNK and p38, leading to AP-1 activation, events that are not involved in zinc deficiency-induced apoptosis.

Events at the host-microbial interface of the gastrointestinal tract IV. The pathogenesis of Helicobacter pylori persistence

Long-term interactions between Helicobacter pylori and humans significantly increase the risk for peptic ulcer disease and noncardia gastric adenocarcinoma. The vast majority of infected persons remain persistently colonized unless a targeted antibiotic regimen is employed; thus regulation of inflammation by H. pylori is governed by levels of host-bacteria equilibria that are not found during cellular interactions with acute enteric pathogens. It is important to gain insight into mechanisms that regulate immune evasion by H. pylori not only to develop more effective treatments for disease, but also because such knowledge may serve as a paradigm for the role that other chronic infectious agents play in the genesis of pathological lesions that arise from inflammatory foci.

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.

Direct oxidative DNA damage, apoptosis and radio sensitivity by spermine oxidase activities in mouse neuroblastoma cells

In mammals, the polyamines affect cell growth, differentiation, and apoptosis; their levels are increased in malignant and proliferating cells, thus justifying an interest in a chemotherapeutic approach to cancer. The flavoprotein SMO is the most recently characterized catabolic enzyme, preferentially oxidizing SPM to SPD, 3-aminopropanal and H(2)O(2). In this report, we describe a novel functional characterization of the recently cloned splice variant isoforms from mouse brain, encoding, among others, the nuclear co-localized spermine oxidase mSMOmu. The over-expression of the active isoforms mSMOalpha and mSMOmu, and the inactive mSMOdelta and mSMOgamma in mouse neuroblastoma cells, demonstrated the first evidence of the direct oxidative DNA damage by the SMO activities, either alone or, in a higher extent, when associated with radiation exposure, thus working as radio sensitizer. These effects were reverted by treatment with 50 muM and 100 muM doses of the inhibitor of SMO activity MDL 72,527. The over-expression of all SMO isoforms failed to influence the expression of the regulating enzymes of polyamines metabolism ODC and SSAT. Dealing with the unbalanced tissue specific SMO activities, these results could indicate a new direction to tailor chemotherapy-associated radiotherapy, improving dose-rate protocol and allowing the modulation of deleterious side effects on healthy tissues.

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.

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.