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

Taurine modulates host cell responses to Helicobacter pylori VacA toxin

Colonization of the human stomach with Helicobacter pylori strains producing active forms of the secreted toxin VacA is associated with an increased risk of peptic ulcer disease and gastric cancer, compared with colonization with strains producing hypoactive forms of VacA. Previous studies have shown that active s1m1 forms of VacA cause cell vacuolation and mitochondrial dysfunction. In this study, we sought to define the cellular metabolic consequences of VacA intoxication. Untargeted metabolomic analyses revealed that several hundred metabolites were significantly altered in VacA-treated gastroduodenal cells (AGS and AZ-521) compared with control cells. Pathway analysis suggested that VacA caused alterations in taurine and hypotaurine metabolism. Treatment of cells with the purified active s1m1 form of VacA, but not hypoactive s2m1 or Δ6-27 VacA-mutant proteins (defective in membrane channel formation), caused reductions in intracellular taurine and hypotaurine concentrations. Supplementation of the tissue culture medium with taurine or hypotaurine protected AZ-521 cells against VacA-induced cell death. Untargeted global metabolomics of VacA-treated AZ-521 cells or AGS cells in the presence or absence of extracellular taurine showed that taurine was the main intracellular metabolite significantly altered by extracellular taurine supplementation. These results indicate that VacA causes alterations in cellular taurine metabolism and that repletion of taurine is sufficient to attenuate VacA-induced cell death. We discuss these results in the context of previous literature showing the important role of taurine in cell physiology and the pathophysiology or treatment of multiple pathologic conditions, including gastric ulcers, cardiovascular disease, malignancy, inflammatory diseases, and other aging-related disorders.

Autophagy induced by Helicobacter Pylori infection can lead to gastric cancer dormancy, metastasis, and recurrence: new insights

According to the findings of recent research, Helicobacter Pylori (H. pylori) infection is not only the primary cause of gastric cancer (GC), but it is also linked to the spread and invasion of GC through a number of processes and factors that contribute to virulence. In this study, we discussed that H. pylori infection can increase autophagy in GC tumor cells, leading to poor prognosis in such patients. Until now, the main concerns have been focused on H. pylori's role in GC development. According to our hypothesis, however, H. pylori infection may also lead to GC dormancy, metastasis, and recurrence by stimulating autophagy. Therefore, understanding how H. pylori possess these processes through its virulence factors and various microRNAs can open new windows for providing new prevention and/or therapeutic approaches to combat GC dormancy, metastasis, and recurrence which can occur in GC patients with H. pylori infection with targeting autophagy and eradicating H. pylori infection.

There Are No Insurmountable Barriers: Passage of the Helicobacter pylori VacA Toxin from Bacterial Cytoplasm to Eukaryotic Cell Organelle

The Gram-negative bacterium Helicobacter pylori is a very successful pathogen, one of the most commonly identified causes of bacterial infections in humans worldwide. H. pylori produces several virulence factors that contribute to its persistence in the hostile host habitat and to its pathogenicity. The most extensively studied are cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA). VacA is present in almost all H. pylori strains. As a secreted multifunctional toxin, it assists bacterial colonization, survival, and proliferation during long-lasting infections. To exert its effect on gastric epithelium and other cell types, VacA undergoes several modifications and crosses multiple membrane barriers. Once inside the gastric epithelial cell, VacA disrupts many cellular-signaling pathways and processes, leading mainly to changes in the efflux of various ions, the depolarization of membrane potential, and perturbations in endocytic trafficking and mitochondrial function. The most notable effect of VacA is the formation of vacuole-like structures, which may lead to apoptosis. This review focuses on the processes involved in VacA secretion, processing, and entry into host cells, with a particular emphasis on the interaction of the mature toxin with host membranes and the formation of transmembrane pores.

Host cell sensing and restoration of mitochondrial function and metabolism within Helicobacter pylori VacA intoxicated cells

IMPORTANCE

Persistent human gastric infection with Helicobacter pylori is the single most important risk factor for development of gastric malignancy, which is one of the leading causes of cancer-related deaths worldwide. An important virulence factor for Hp colonization and severity of gastric disease is the protein exotoxin VacA, which is secreted by the bacterium and modulates functional properties of gastric cells. VacA acts by damaging mitochondria, which impairs host cell metabolism through impairment of energy production. Here, we demonstrate that intoxicated cells have the capacity to detect VacA-mediated damage, and orchestrate the repair of mitochondrial function, thereby restoring cellular health and vitality. This study provides new insights into cellular recognition and responses to intracellular-acting toxin modulation of host cell function, which could be relevant for the growing list of pathogenic microbes and viruses identified that target mitochondria as part of their virulence strategies.

Review of Phytochemical Potency as a Natural Anti-Helicobacter pylori and Neuroprotective Agent

Phytochemicals are plant secondary metabolites that show health benefits for humans due to their bioactivity. There is a huge variety of phytochemicals that have already been identified, and these compounds can act as antimicrobial and neuroprotection agents. Due to their anti-microbial activity and neuroprotection, several phytochemicals might have the potency to be used as natural therapeutic agents, especially for Helicobacter pylori infection and neurodegenerative disease, which have become a global health concern nowadays. According to previous research, there are some connections between H. pylori infection and neurodegenerative diseases, especially Alzheimer's disease. Hence, this comprehensive review examines different kinds of phytochemicals from natural sources as potential therapeutic agents to reduce H. pylori infection and improve neurodegenerative disease. An additional large-scale study is needed to establish the connection between H. pylori infection and neurodegenerative disease and how phytochemicals could improve this condition.

Restoration of mitochondrial structure and function within Helicobacter pylori VacA intoxicated cells

The Helicobacter pylori vacuolating cytotoxin (VacA) is an intracellular, mitochondrial-targeting exotoxin that rapidly causes mitochondrial dysfunction and fragmentation. Although VacA targeting of mitochondria has been reported to alter overall cellular metabolism, there is little known about the consequences of extended exposure to the toxin. Here, we describe studies to address this gap in knowledge, which have revealed that mitochondrial dysfunction and fragmentation are followed by a time-dependent recovery of mitochondrial structure, mitochondrial transmembrane potential, and cellular ATP levels. Cells exposed to VacA also initially demonstrated a reduction in oxidative phosphorylation, as well as increase in compensatory aerobic glycolysis. These metabolic alterations were reversed in cells with limited toxin exposure, congruent with the recovery of mitochondrial transmembrane potential and the absence of cytochrome c release from the mitochondria. Taken together, these results are consistent with a model that mitochondrial structure and function are restored in VacA-intoxicated cells.

Gastric microbiota in gastric cancer: Different roles of Helicobacter pylori and other microbes

Gastric cancer (GC) is one of the leading causes of cancer-related deaths worldwide. The gastric microbiota plays a critical role in the development of GC. First, Helicobacter pylori (H. pylori) infection is considered a major risk factor for GC. However, recent studies based on microbiota sequencing technology have found that non-H. pylori microbes also exert effects on gastric carcinogenesis. Following the infection of H. pylori, gastric microbiota dysbiosis could be observed; the stomach is dominated by H. pylori and the abundances of non-H. pylori microbes reduce substantially. Additionally, decreased microbial diversity, alterations in the microbial community structure, negative interactions between H. pylori and other microbes, etc. occur, as well. With the progression of gastric lesions, the number of H. pylori decreases and the number of non-H. pylori microbes increases correspondingly. Notably, H. pylori and non-H. pylori microbes show different roles in different stages of gastric carcinogenesis. In the present mini-review, we provide an overview of the recent findings regarding the role of the gastric microbiota, including the H. pylori and non-H. pylori microbes, in the development of GC.

Complete subunit structure of serotype C and D botulinum progenitor toxin complex induces vacuolation in the specific epithelial cell line

Clostridium botulinum produces seven botulinum neurotoxin (BoNT) serotypes. In nature, BoNT exists as a part of the progenitor toxin complex (PTC) through associations with neurotoxin associated proteins (NAPs), including nontoxic nonhemagglutinin and hemagglutinin (HA) complex, consists of HA-70, HA-17 and HA-33. Because PTC displays higher oral toxicity than pure BoNTs, NAPs play a critical role in food poisoning. In a previous study, we demonstrated that the NAP complex in mature large-sized PTC (L-PTC) from serotypes C and D concomitantly induced cell death and cytoplasmic vacuolation in the rat intestinal epithelial cell line IEC-6. Here, we found that the serotype D NAP complex induces only cytoplasmic vacuolation in the normal rat kidney cell line NRK-52E without reducing cell viability. NAP complexes from serotype A and B L-PTCs did not affect cell viability or cytoplasmic vacuolation in IEC-6 and NRK-52E cells. Furthermore, we assessed the effect of immature L-PTCs with fewer HA-33/HA-17 trimers (two HA-33 and one HA-17) than mature L-PTCs on cell viability and cytoplasmic vacuolation in IEC-6 and NRK-52E cells. As a result, mature L-PTCs with the maximum number of HA-33/HA-17 trimers displayed the greatest potency. Consequently, the reduction in cell viability and vacuolation induction are related to the number of HA-33/HA-17 trimers in PTC. The discovery of an epithelial cell model where botulinum PTC specifically induces vacuolization may help clarify the unknown cytotoxicity of PTC, which plays an important role in the trans-epithelial transport of the toxin.

An Overview of Autophagy in Helicobacter pylori Infection and Related Gastric Cancer

Helicobacter pylori (H. pylori) infection is considered a class I carcinogen in the pathogenesis of gastric cancer. In recent years, the interaction relationship between H. pylori infection and autophagy has attracted increasing attention. Most investigators believe that the pathogenesis of gastric cancer is closely related to the formation of an autophagosome-mediated downstream signaling pathway by H. pylori infection-induced cells. Autophagy is involved in H. pylori infection and affects the occurrence and development of gastric cancer. In this paper, the possible mechanism by which H. pylori infection affects autophagy and the progression of related gastric cancer signaling pathways are reviewed.

Escherichia coli vacuolating factor, involved in avian cellulitis, induces actin contraction and binds to cytoskeleton proteins in fibroblasts

Background

Avian pathogenic Escherichia coli (APEC) isolated from avian cellulitis lesions produces a toxin, named Escherichia coli vacuolating factor (ECVF), that causes cell vacuolization and induces inflammatory response in broiler chicken.

Methods

We investigated the intracellular activities of ECVF in avian fibroblasts using fluorescence staining, electron microscopy, MTT and LDH measurements. As ECVF act specifically in avian cells, we performed blotting assay followed by mass spectrometry to better understand its initial intracellular protein recognition.

Results

ECVF induced actin contraction, mitochondrial damage and membrane permeability alterations. Ultrastructural analysis showed intracellular alterations, as nuclear lobulation and the presence of degraded structures inside the vacuoles. Moreover, ECVF induced cell death in fibroblasts. ECVF-biotin associates to at least two proteins only in avian cell lysates: alpha-actinin 4 and vinculin, both involved in cytoskeleton structure.

Conclusion

These findings demonstrated that ECVF plays an important role in avian cellulitis, markedly in initial steps of infection. Taken together, the results place this toxin as a target for drug and/or vaccine development, instead of the use of large amounts antibiotics.

Chronic in vivo exposure to Helicobacter pylori VacA: Assessing the efficacy of automated and long-term intragastric toxin infusion

Helicobacter pylori (Hp) secrete VacA, a diffusible pore-forming exotoxin that is epidemiologically linked to gastric disease in humans. In vitro studies indicate that VacA modulates gastric epithelial and immune cells, but the in vivo contributions of VacA as an important determinant of Hp colonization and chronic infection remain poorly understood. To identify perturbations in the stomachs of C57BL/6 or BALB/C mice that result specifically from extended VacA exposure, we evaluated the efficacy of administering purified toxin using automated infusion via surgically-implanted, intragastric catheters. At 3 and 30 days of interrupted infusion, VacA was detected in association with gastric glands. In contrast to previously-reported tissue damage resulting from short term exposure to Hp extracts administered by oral gavage, extended infusion of VacA did not damage stomach, esophageal, intestinal, or liver tissue. However, several alterations previously reported during Hp infection were detected in animals infused with VacA, including reduction of the gastric mucus layer, and increased vacuolation of parietal cells. VacA infusion invoked an immune response, as indicated by the detection of circulating VacA antibodies. These foundational studies support the use of VacA infusion for identifying gastric alterations that are unambiguously attributable to long-term exposure to toxin.

Moringa oleifera leaf flavonoids protect bovine mammary epithelial cells from hydrogen peroxide-induced oxidative stress in vitro

Bovine mammary epithelial cells (BMECs) of high-producing dairy cows are subject to constant oxidative stress as a result of high metabolic rate and physiological adaptation to intensive farming. Moringa (Moringa oleifera) leaf has been proposed to have the antioxidant potential in scavenging free radicals due to the presence of flavonoids. In this study, we investigated the cytoprotective effects of moringa leaf flavonoids in alleviating oxidative stress in BMECs in vitro. Oxidative stress was established by exposing isolated BMECs to H₂ O₂ for 2 hr. Doses of moringa leaf flavonoids were evaluated by treating BMECs for 12 hr. The optimal concentrations of H₂ O₂ and moringa leaf flavonoids were 500 μmol/L and 1.0 mg/ml, respectively. The results showed that moringa leaf flavonoids increased the activities of superoxide dismutase, catalase, and glutathione peroxidase; and reduced malondialdehyde activity and intracellular accumulation of reactive oxygen species (ROS) in the H₂ O₂ -induced oxidative stress system. A Hoechst33258 staining assay revealed that moringa leaf flavonoids decreased the apoptosis rate in BMECs, while leaving membrane integrity and nucleolar morphology unchanged. We concluded that moringa leaf flavonoids have the antioxidant capacity to effectively reduce oxidative stress in BMECs.

Molecular mechanism of Helicobacter pylori-induced autophagy in gastric cancer

Helicobacter pylori (H. pylori) is a gram-negative pathogen that colonizes gastric epithelial cells. The drug resistance rates of H. pylori have dramatically increased, causing persistent infections. Chronic infection by H. pylori is a critical cause of gastritis, peptic ulcers and even gastric cancer. In host cells, autophagy is stimulated to maintain cellular homeostasis following intracellular pathogen recognition by the innate immune defense system. However, H. pylori-induced autophagy is not consistent during acute and chronic infection. Therefore, a deeper understanding of the association between H. pylori infection and autophagy in gastric epithelial cells could aid the understanding of the mechanisms of persistent infection and the identification of autophagy-associated therapeutic targets for H. pylori infection. The present review describes the role of H. pylori and associated virulence factors in the induction of autophagy by different signaling pathways during acute infection. Additionally, the inhibition of autophagy in gastric epithelial cells during chronic infection was discussed. The present review summarized H. pylori-mediated autophagy and provided insights into its mechanism of action, suggesting the induction of autophagy as a novel therapeutic target for persistent H. pylori infection.

Helicobacter pylori VacA, a distinct toxin exerts diverse functionalities in numerous cells: An overview

BACKGROUND

Helicobacter pylori, gastric cancer-causing bacteria, survive in their gastric environment of more than 50% of the world population. The presence of H. pylori in the gastric vicinity promotes the development of various diseases including peptic ulcer and gastric carcinoma. H. pylori produce and secret Vacuolating cytotoxin A (VacA), a major toxin facilitating the bacteria against the host defense system. The toxin causes multiple effects in epithelial cells and immune cells, especially T cells, B cells, and Macrophages.

METHODS

This review describes the diverse functionalities of protein toxin VacA. The specific objective of this review is to address the overall structure, mechanism, and functions of VacA in various cell types. The recent advancements are summarized and discussed and thus conclusion is drawn based on the overall reported evidences.

RESULTS

The searched articles on H. pylori VacA were evaluated and limited up to 66 articles for this review. The articles were divided into four major categories including articles on vacA gene, VacA toxin, distinct effects of VacA toxin, and their effects on various cells. Based on these studies, the review article was prepared.

CONCLUSIONS

This review describes an overview of how VacA is secreted by H. pylori and contributes to colonization and virulence in multiple ways by affecting epithelial cells, T cells, Dendritic cells, B cells, and Macrophages. The reported evidence suggests that the comprehensive outlook need to be developed for understanding distinctive functionalities of VacA.

Helicobacter pylori Infection Modulates Host Cell Metabolism through VacA-Dependent Inhibition of mTORC1

Helicobacter pylori (Hp) vacuolating cytotoxin (VacA) is a bacterial exotoxin that enters host cells and induces mitochondrial dysfunction. However, the extent to which VacA-dependent mitochondrial perturbations affect overall cellular metabolism is poorly understood. We report that VacA perturbations in mitochondria are linked to alterations in cellular amino acid homeostasis, which results in the inhibition of mammalian target of rapamycin complex 1 (mTORC1) and subsequent autophagy. mTORC1, which regulates cellular metabolism during nutrient stress, is inhibited during Hp infection by a VacA-dependent mechanism. This VacA-dependent inhibition of mTORC1 signaling is linked to the dissociation of mTORC1 from the lysosomal surface and results in activation of cellular autophagy through the Unc 51-like kinase 1 (Ulk1) complex. VacA intoxication results in reduced cellular amino acids, and bolstering amino acid pools prevents VacA-mediated mTORC1 inhibition. Overall, these studies support a model that Hp modulate host cell metabolism through the action of VacA at mitochondria.

Helicobacter pylori Vacuolating Toxin and Gastric Cancer

Helicobacter pylori VacA is a channel-forming toxin unrelated to other known bacterial toxins. Most H. pylori strains contain a vacA gene, but there is marked variation among strains in VacA toxin activity. This variation is attributable to strain-specific variations in VacA amino acid sequences, as well as variations in the levels of VacA transcription and secretion. In this review, we discuss epidemiologic studies showing an association between specific vacA allelic types and gastric cancer, as well as studies that have used animal models to investigate VacA activities relevant to gastric cancer. We also discuss the mechanisms by which VacA-induced cellular alterations may contribute to the pathogenesis of gastric cancer.

Helicobacter pylori outer inflammatory protein A (OipA) suppresses apoptosis of AGS gastric cells in vitro

Outer inflammatory protein A (OipA) is an important virulence factor associated with gastric cancer and ulcer development; however, the results have not been well established and turned out to be controversial. This study aims to elucidate the role of OipA in Helicobacter pylori infection using clinical strains harbouring oipA "on" and "off" motifs. Proteomics analysis was performed on AGS cell pre-infection and postinfection with H. pylori oipA "on" and "off" strains, using liquid chromatography/mass spectrometry. AGS apoptosis and cell cycle assays were performed. Moreover, expression of vacuolating cytotoxin A (VacA) was screened using Western blotting. AGS proteins that have been suggested previously to play a role or associated with gastric disease were down-regulated postinfection with oipA "off" strains comparing to oipA "on" strains. Furthermore, oipA "off" and ΔoipA cause higher level of AGS cells apoptosis and G0/G1 cell-cycle arrest than oipA "on" strains. Interestingly, deletion of oipA increased bacterial VacA production. The capability of H. pylori to induce apoptosis and suppress expression of proteins having roles in human disease in the absence of oipA suggests that strains not expressing OipA may be less virulent or may even be protective against carcinogenesis compared those expressing OipA. This potentially explains the higher incidence of gastric cancer in East Asia where oipA "on" strains predominates.

Structural organization of membrane-inserted hexamers formed by Helicobacter pylori VacA toxin

Helicobacter pylori colonizes the human stomach and is a potential cause of peptic ulceration or gastric adenocarcinoma. H. pylori secretes a pore-forming toxin known as vacuolating cytotoxin A (VacA). The 88 kDa secreted VacA protein, composed of an N-terminal p33 domain and a C-terminal p55 domain, assembles into water-soluble oligomers. The structural organization of membrane-bound VacA has not been characterized in any detail and the role(s) of specific VacA domains in membrane binding and insertion are unclear. We show that membrane-bound VacA organizes into hexameric oligomers. Comparison of the two-dimensional averages of membrane-bound and soluble VacA hexamers generated using single particle electron microscopy reveals a structural difference in the central region of the oligomers (corresponding to the p33 domain), suggesting that membrane association triggers a structural change in the p33 domain. Analyses of the isolated p55 domain and VacA variants demonstrate that while the p55 domain can bind membranes, the p33 domain is required for membrane insertion. Surprisingly, neither VacA oligomerization nor the presence of putative transmembrane GXXXG repeats in the p33 domain is required for membrane insertion. These findings provide new insights into the process by which VacA binds and inserts into the lipid bilayer to form membrane channels.

An Overview of Helicobacter pylori VacA Toxin Biology

The VacA toxin secreted by Helicobacter pylori enhances the ability of the bacteria to colonize the stomach and contributes to the pathogenesis of gastric adenocarcinoma and peptic ulcer disease. The amino acid sequence and structure of VacA are unrelated to corresponding features of other known bacterial toxins. VacA is classified as a pore-forming toxin, and many of its effects on host cells are attributed to formation of channels in intracellular sites. The most extensively studied VacA activity is its capacity to stimulate vacuole formation, but the toxin has many additional effects on host cells. Multiple cell types are susceptible to VacA, including gastric epithelial cells, parietal cells, T cells, and other types of immune cells. This review focuses on the wide range of VacA actions that are detectable in vitro, as well as actions of VacA in vivo that are relevant for H. pylori colonization of the stomach and development of gastric disease.

Pathobiology of Helicobacter pylori-Induced Gastric Cancer

Colonization of the human stomach by Helicobacter pylori and its role in causing gastric cancer is one of the richest examples of a complex relationship among human cells, microbes, and their environment. It is also a puzzle of enormous medical importance given the incidence and lethality of gastric cancer worldwide. We review recent findings that have changed how we view these relationships and affected the direction of gastric cancer research. For example, recent data have indicated that subtle mismatches between host and microbe genetic traits greatly affect the risk of gastric cancer. The ability of H pylori and its oncoprotein CagA to reprogram epithelial cells and activate properties of stemness show the sophisticated relationship between H pylori and progenitor cells in the gastric mucosa. The observation that cell-associated H pylori can colonize the gastric glands and directly affect precursor and stem cells supports these observations. The ability to mimic these interactions in human gastric organoid cultures as well as animal models will allow investigators to more fully unravel the extent of H pylori control on the renewing gastric epithelium. Finally, our realization that external environmental factors, such as dietary components and essential micronutrients, as well as the gastrointestinal microbiota, can change the balance between H pylori's activity as a commensal or a pathogen has provided direction to studies aimed at defining the full carcinogenic potential of this organism.

Mitochondrial channels: ion fluxes and more

The field of mitochondrial ion channels has recently seen substantial progress, including the molecular identification of some of the channels. An integrative approach using genetics, electrophysiology, pharmacology, and cell biology to clarify the roles of these channels has thus become possible. It is by now clear that many of these channels are important for energy supply by the mitochondria and have a major impact on the fate of the entire cell as well. The purpose of this review is to provide an up-to-date overview of the electrophysiological properties, molecular identity, and pathophysiological functions of the mitochondrial ion channels studied so far and to highlight possible therapeutic perspectives based on current information.

Methuosis: nonapoptotic cell death associated with vacuolization of macropinosome and endosome compartments

Apoptosis is the most widely recognized form of physiological programmed cell death. During the past three decades, various nonapoptotic forms of cell death have gained increasing attention, largely because of their potential importance in pathological processes, toxicology, and cancer therapy. A recent addition to the panoply of cell death phenotypes is methuosis. The neologism is derived from the Greek methuo (to drink to intoxication) because the hallmark of this form of cell death is displacement of the cytoplasm by large fluid-filled vacuoles derived from macropinosomes. The demise of the cell resembles many forms of necrosis, insofar as there is a loss of metabolic capacity and plasma membrane integrity, without the cell shrinkage and nuclear fragmentation associated with apoptosis. Methuosis was initially defined in glioblastoma cells after ectopic expression of activated Ras, but recent reports have described small molecules that can induce the features of methuosis in a broad spectrum of cancer cells, including those that are resistant to conventional apoptosis-inducing drugs. This review summarizes the available information about the distinguishing morphological characteristics and underlying mechanisms of methuosis. We compare and contrast methuosis with other cytopathological conditions in which accumulation of clear cytoplasmic vacuoles is a prominent feature. Finally, we highlight key questions that need to be answered to determine whether methuosis truly represents a unique form of regulated cell death.

Endoplasmic reticulum stress contributes to Helicobacter pylori VacA-induced apoptosis

Vacuolating cytotoxin A (VacA) is one of the important virulence factors produced by H. pylori. VacA induces apoptotic cell death, which is potentiated by ammonia. VacA also causes cell death by mitochondrial damage, via signaling pathways that are not fully defined. Our aim was to determine whether endoplasmic reticulum (ER) stress is associated with VacA-induced mitochondrial dysfunction and apoptosis. We found that C/EBP homologous protein (CHOP), a key signaling protein of ER stress-induced apoptosis, was transcriptionally up-regulated following incubation of gastric epithelial cells with VacA. The effect of VacA on CHOP induction was significantly enhanced by co-incubation with ammonium chloride. Phosphorylation of eukaryotic initiation factor 2 (eIF2)-alpha, which is known to occur downstream of the ER stress sensor PKR-like ER-localized eIF2-alpha kinase (PERK) and to regulate CHOP expression, was also observed following incubation with VacA in the presence of ammonium chloride. Knockdown of CHOP by siRNA resulted in inhibition of VacA-induced apoptosis. Further studies showed that silencing of the PERK gene with siRNA attenuated VacA-mediated phosphorylation of eIF2-alpha, CHOP induction, expression of BH3-only protein Bim and Bax activation, and cell death induced by VacA with ammonium chloride, indicating that ER stress may lead to mitochondrial dysfunction during VacA-induced toxicity. Activation of ER stress and up-regulation of BH3-only proteins were also observed in human H. pylori-infected gastric mucosa. Collectively, this study reveals a possible association between VacA-induced apoptosis in gastric epithelial cells, and activation of ER stress in H. pylori-positive gastric mucosa.

Role of connexin 43 in Helicobacter pylori VacA-induced cell death

Helicobacter pylori colonizes the human stomach and confers an increased risk for the development of peptic ulceration, noncardia gastric adenocarcinoma, and gastric lymphoma. A secreted H. pylori toxin, VacA, can cause multiple alterations in gastric epithelial cells, including cell death. In this study, we sought to identify host cell factors that are required for VacA-induced cell death. To do this, we analyzed gene trap and short hairpin RNA (shRNA) libraries in AZ-521 human gastric epithelial cells and selected for VacA-resistant clones. Among the VacA-resistant clones, we identified multiple gene trap library clones and an shRNA library clone with disrupted expression of connexin 43 (Cx43) (also known as gap junction protein alpha 1 [GJA1]). Further experiments with Cx43-specific shRNAs confirmed that a reduction in Cx43 expression results in resistance to VacA-induced cell death. Immunofluorescence microscopy experiments indicated that VacA did not colocalize with Cx43. We detected production of the Cx43 protein in AZ-521 cells but not in AGS, HeLa, or RK-13 cells, and correspondingly, AZ-521 cells were the most susceptible to VacA-induced cell death. When Cx43 was expressed in HeLa cells, the cells became more susceptible to VacA. These results indicate that Cx43 is a host cell constituent that contributes to VacA-induced cell death and that variation among cell types in susceptibility to VacA-induced cell death is attributable at least in part to cell type-specific differences in Cx43 production.

Vacuolating cytotoxin A (VacA), a key toxin for Helicobacter pylori pathogenesis

More than 50% of the world's population is infected with Helicobacter pylori (H. pylori). Chronic infection with this Gram-negative pathogen is associated with the development of peptic ulcers and is linked to an increased risk of gastric cancer. H. pylori secretes many proteinaceous factors that are important for initial colonization and subsequent persistence in the host stomach. One of the major protein toxins secreted by H. pylori is the Vacuolating cytotoxin A (VacA). After secretion from the bacteria via a type V autotransport secretion system, the 88 kDa VacA toxin (comprised of the p33 and p55 subunits) binds to host cells and is internalized, causing severe “vacuolation” characterized by the accumulation of large vesicles that possess hallmarks of both late endosomes and early lysosomes. The development of “vacuoles” has been attributed to the formation of VacA anion-selective channels in membranes. Apart from its vacuolating effects, it has recently become clear that VacA also directly affects mitochondrial function. Earlier studies suggested that the p33 subunit, but not the p55 subunit of VacA, could enter mitochondria to modulate organelle function. This raised the possibility that a mechanism separate from pore formation may be responsible for the effects of VacA on mitochondria, as crystallography studies and structural modeling predict that both subunits are required for a physiologically stable pore. It has also been suggested that the mitochondrial effects observed are due to indirect effects on pro-apoptotic proteins and direct effects on mitochondrial morphology-related processes. Other studies have shown that both the p55 and p33 subunits can indeed be efficiently imported into mammalian-derived mitochondria raising the possibility that they could re-assemble to form a pore. Our review summarizes and consolidates the recent advances in VacA toxin research, with focus on the outstanding controversies in the field and the key remaining questions that need to be addressed.

Remodeling the host environment: modulation of the gastric epithelium by the Helicobacter pylori vacuolating toxin (VacA)

Virulence mechanisms underlying Helicobacter pylori persistence and disease remain poorly understood, in part, because the factors underlying disease risk are multifactorial and complex. Among the bacterial factors that contribute to the cumulative pathophysiology associated with H. pylori infections, the vacuolating cytotoxin (VacA) is one of the most important. Analogous to a number of H. pylori genes, the vacA gene exhibits allelic mosaicism, and human epidemiological studies have revealed that several families of toxin alleles are predictive of more severe disease. Animal model studies suggest that VacA may contribute to pathogenesis in several ways. VacA functions as an intracellular-acting protein exotoxin. However, VacA does not fit the current prototype of AB intracellular-acting bacterial toxins, which elaborate modulatory effects through the action of an enzymatic domain translocated inside host cells. Rather, VacA may represent an alternative prototype for AB intracellular acting toxins that modulate cellular homeostasis by forming ion-conducting intracellular membrane channels. Although VacA seems to form channels in several different membranes, one of the most important target sites is the mitochondrial inner membrane. VacA apparently take advantage of an unusual intracellular trafficking pathway to mitochondria, where the toxin is imported and depolarizes the inner membrane to disrupt mitochondrial dynamics and cellular energy homeostasis as a mechanism for engaging the apoptotic machinery within host cells. VacA remodeling of the gastric environment appears to be fine-tuned through the action of the Type IV effector protein CagA which, in part, limits the cytotoxic effects of VacA in cells colonized by H. pylori.

Helicobacter pylori vacuolating toxin A and apoptosis

VacA, the vacuolating cytotoxin A of Helicobacter pylori, induces apoptosis in epithelial cells of the gastic mucosa and in leukocytes. VacA is released by the bacteria as a protein of 88 kDa. At the outer surface of host cells, it binds to the sphingomyelin of lipid rafts. At least partially, binding to the cells is facilitated by different receptor proteins. VacA is internalized by a clathrin-independent mechanism and initially accumulates in GPI-anchored proteins-enriched early endosomal compartments. Together with early endosomes, VacA is distributed inside the cells. Most of the VacA is eventually contained in the membranes of vacuoles. VacA assembles in hexameric oligomers forming an anion channel of low conductivity with a preference for chloride ions. In parallel, a significant fraction of VacA can be transferred from endosomes to mitochondria in a process involving direct endosome-mitochondria juxtaposition. Inside the mitochondria, VacA accumulates in the mitochondrial inner membrane, probably forming similar chloride channels as observed in the vacuoles. Import into mitochondria is mediated by the hydrophobic N-terminus of VacA. Apoptosis is triggered by loss of the mitochondrial membrane potential, recruitment of Bax and Bak, and release of cytochrome c.

Helicobacter pylori vacuolating cytotoxin A (VacA) engages the mitochondrial fission machinery to induce host cell death

A number of pathogenic bacteria target mitochondria to modulate the host's apoptotic machinery. Studies here revealed that infection with the human gastric pathogen Helicobacter pylori disrupts the morphological dynamics of mitochondria as a mechanism to induce host cell death. The vacuolating cytotoxin A (VacA) is both essential and sufficient for inducing mitochondrial network fragmentation through the mitochondrial recruitment and activation of dynamin-related protein 1 (Drp1), which is a critical regulator of mitochondrial fission within cells. Inhibition of Drp1-induced mitochondrial fission within VacA-intoxicated cells inhibited the activation of the proapoptotic Bcl-2-associated X (Bax) protein, permeabilization of the mitochondrial outer membrane, and cell death. Our data reveal a heretofore unrecognized strategy by which a pathogenic microbe engages the host's apoptotic machinery.

The Human Gastric Pathogen Helicobacter pylori and Its Association with Gastric Cancer and Ulcer Disease

With the momentous discovery in the 1980's that a bacterium, Helicobacter pylori, can cause peptic ulcer disease and gastric cancer, antibiotic therapies and prophylactic measures have been successful, only in part, in reducing the global burden of these diseases. To date, ~700,000 deaths worldwide are still attributable annually to gastric cancer alone. Here, we review H. pylori's contribution to the epidemiology and histopathology of both gastric cancer and peptic ulcer disease. Furthermore, we examine the host-pathogen relationship and H. pylori biology in context of these diseases, focusing on strain differences, virulence factors (CagA and VacA), immune activation and the challenges posed by resistance to existing therapies. We consider also the important role of host-genetic variants, for example, in inflammatory response genes, in determining infection outcome and the role of H. pylori in other pathologies—some accepted, for example, MALT lymphoma, and others more controversial, for example, idiopathic thrombocytic purpura. More recently, intriguing suggestions that H. pylori has protective effects in GERD and autoimmune diseases, such as asthma, have gained momentum. Therefore, we consider the basis for these suggestions and discuss the potential impact for future therapeutic rationales.

Helicobacter pylori VacA induces programmed necrosis in gastric epithelial cells

Helicobacter pylori is a Gram-negative bacterium that colonizes the human stomach and contributes to the development of peptic ulcer disease and gastric cancer. The secreted pore-forming toxin VacA is one of the major virulence factors of H. pylori. In the current study, we show that AZ-521 human gastric epithelial cells are highly susceptible to VacA-induced cell death. Wild-type VacA causes death of these cells, whereas mutant VacA proteins defective in membrane channel formation do not. Incubation of AZ-521 cells with wild-type VacA results in cell swelling, poly(ADP-ribose) polymerase (PARP) activation, decreased intracellular ATP concentration, and lactate dehydrogenase (LDH) release. VacA-induced death of these cells is a caspase-independent process that results in cellular release of histone-binding protein high mobility group box 1 (HMGB1), a proinflammatory protein. These features are consistent with the occurrence of cell death through a programmed necrosis pathway and suggest that VacA can be included among the growing number of bacterial pore-forming toxins that induce cell death through programmed necrosis. We propose that VacA augments H. pylori-induced mucosal inflammation in the human stomach by causing programmed necrosis of gastric epithelial cells and subsequent release of proinflammatory proteins and may thereby contribute to the pathogenesis of gastric cancer and peptic ulceration.

The unexpected link between infection-induced apoptosis and a TH17 immune response

Microbial pathogens can initiate MOMP in host cells and as such, initiate the mitochondrial pathway of apoptosis. Innate immune recognition of cells dying in this way by infection-induced apoptosis would involve recognition of ligands derived from the apoptotic host cell simultaneously with those derived from the infecting pathogen. The resultant signal transduction pathways engaged direct DCs to concomitantly synthesize TGF-β and IL-6, two cytokines that subsequently favor the differentiation of naïve CD4 T cells into T(h)17 cells. Citrobacter rodentium is one rodent pathogen that targets mitochondria and induces apoptosis, and blockade of apoptosis during enteric Citrobacter infection impairs the characteristic T(h)17 response in the intestinal LP. Here, we review these original findings. We discuss microbial infections other than Citrobacter that have been shown to induce T(h)17 responses, and we examine what is known about the ability of those pathogens to induce apoptosis. We also consider types of cell death other than apoptosis that can be triggered by microbial infection, and we highlight how little we know about the impact of various forms of cell death on the ensuing adaptive immune response.

Helicobacter pylori and gastric cancer: factors that modulate disease risk

Helicobacter pylori is a gastric pathogen that colonizes approximately 50% of the world's population. Infection with H. pylori causes chronic inflammation and significantly increases the risk of developing duodenal and gastric ulcer disease and gastric cancer. Infection with H. pylori is the strongest known risk factor for gastric cancer, which is the second leading cause of cancer-related deaths worldwide. Once H. pylori colonizes the gastric environment, it persists for the lifetime of the host, suggesting that the host immune response is ineffective in clearing this bacterium. In this review, we discuss the host immune response and examine other host factors that increase the pathogenic potential of this bacterium, including host polymorphisms, alterations to the apical-junctional complex, and the effects of environmental factors. In addition to host effects and responses, H. pylori strains are genetically diverse. We discuss the main virulence determinants in H. pylori strains and the correlation between these and the diverse clinical outcomes following H. pylori infection. Since H. pylori inhibits the gastric epithelium of half of the world, it is crucial that we continue to gain understanding of host and microbial factors that increase the risk of developing more severe clinical outcomes.

A Tale of Two Toxins: Helicobacter Pylori CagA and VacA Modulate Host Pathways that Impact Disease

Helicobacter pylori is a pathogenic bacterium that colonizes more than 50% of the world's population, which leads to a tremendous medical burden. H. pylori infection is associated with such varied diseases as gastritis, peptic ulcers, and two forms of gastric cancer: gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma. This association represents a novel paradigm for cancer development; H. pylori is currently the only bacterium to be recognized as a carcinogen. Therefore, a significant amount of research has been conducted to identify the bacterial factors and the deregulated host cell pathways that are responsible for the progression to more severe disease states. Two of the virulence factors that have been implicated in this process are cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA), which are cytotoxins that are injected and secreted by H. pylori, respectively. Both of these virulence factors are polymorphic and affect a multitude of host cellular pathways. These combined facts could easily contribute to differences in disease severity across the population as various CagA and VacA alleles differentially target some pathways. Herein we highlight the diverse types of cellular pathways and processes targeted by these important toxins.

Bacterial interactions with the host epithelium

The gastrointestinal epithelium deploys multiple innate defense mechanisms to fight microbial intruders, including epithelial integrity, rapid epithelial cell turnover, quick expulsion of infected cells, autophagy, and innate immune responses. Nevertheless, many bacterial pathogens are equipped with highly evolved infectious stratagems that circumvent these defense systems and use the epithelium as a replicative foothold. During replication on and within the gastrointestinal epithelium, gastrointestinal bacterial pathogens secrete various components, toxins, and effectors that can subvert, usurp, and exploit host cellular functions to benefit bacterial survival. In addition, bacterial pathogens use a variety of mechanisms that balance breaching the epithelial barrier with maintaining the epithelium in order to promote bacterial colonization. These complex strategies represent a new paradigm of bacterial pathogenesis.

Endosome-mitochondria juxtaposition during apoptosis induced by H. pylori VacA

The vacuolating cytotoxin (VacA) is an important virulence factor of Helicobacter pylori with pleiotropic effects on mammalian cells, including the ability to trigger mitochondria-dependent apoptosis. However, the mechanism by which VacA exerts its apoptotic function is unclear. Using a genetic approach, in this study we show that killing by VacA requires the proapoptotic Bcl-2 family members BAX and BAK at the mitochondrial level, but not adequate endoplasmic reticulum Ca²(+) levels, similarly controlled by BAX and BAK. A combination of subcellular fractionation and imaging shows that wild-type VacA, but not mutants in its channel-forming region, induces the accumulation of BAX on endosomes and endosome-mitochondria juxtaposition that precedes the retrieval of active BAX on mitochondria. It is noteworthy that in Bax- and Bak-deficient cells, VacA is unable to cause endosome-mitochondria juxtaposition and is not retrieved in mitochondria. Thus, VacA causes BAX/BAK-dependent juxtaposition of endosomes and mitochondria early in the process of cell death, revealing a new function for these proapoptotic proteins in the regulation of relative position of organelles.

Helicobacter pylori VacA toxin/subunit p34: targeting of an anion channel to the inner mitochondrial membrane

The vacuolating toxin VacA, released by Helicobacter pylori, is an important virulence factor in the pathogenesis of gastritis and gastroduodenal ulcers. VacA contains two subunits: The p58 subunit mediates entry into target cells, and the p34 subunit mediates targeting to mitochondria and is essential for toxicity. In this study we found that targeting to mitochondria is dependent on a unique signal sequence of 32 uncharged amino acid residues at the p34 N-terminus. Mitochondrial import of p34 is mediated by the import receptor Tom20 and the import channel of the outer membrane TOM complex, leading to insertion of p34 into the mitochondrial inner membrane. p34 assembles in homo-hexamers of extraordinary high stability. CD spectra of the purified protein indicate a content of >40% beta-strands, similar to pore-forming beta-barrel proteins. p34 forms an anion channel with a conductivity of about 12 pS in 1.5 M KCl buffer. Oligomerization and channel formation are independent both of the 32 uncharged N-terminal residues and of the p58 subunit of the toxin. The conductivity is efficiently blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid (NPPB), a reagent known to inhibit VacA-mediated apoptosis. We conclude that p34 essentially acts as a small pore-forming toxin, targeted to the mitochondrial inner membrane by a special hydrophobic N-terminal signal.

Host-interactive genes in Amerindian Helicobacter pylori diverge from their Old World homologs and mediate inflammatory responses

Helicobacter pylori is the dominant member of the gastric microbiota and has been associated with an increased risk of gastric cancer and peptic ulcers in adults. H. pylori populations have migrated and diverged with human populations, and health effects vary. Here, we describe the whole genome of the cag-positive strain V225d, cultured from a Venezuelan Piaroa Amerindian subject. To gain insight into the evolution and host adaptation of this bacterium, we undertook comparative H. pylori genomic analyses. A robust multiprotein phylogenetic tree reflects the major human migration out of Africa, across Europe, through Asia, and into the New World, placing Amerindian H. pylori as a particularly close sister group to East Asian H. pylori. In contrast, phylogenetic analysis of the host-interactive genes vacA and cagA shows substantial divergence of Amerindian from Old World forms and indicates new genotypes (e.g., VacA m3) involving these loci. Despite deletions in CagA EPIYA and CRPIA domains, V225d stimulates interleukin-8 secretion and the hummingbird phenotype in AGS cells. However, following a 33-week passage in the mouse stomach, these phenotypes were lost in isolate V225-RE, which had a 15-kb deletion in the cag pathogenicity island that truncated CagA and eliminated some of the type IV secretion system genes. Thus, the unusual V225d cag architecture was fully functional via conserved elements, but the natural deletion of 13 cag pathogenicity island genes and the truncation of CagA impaired the ability to induce inflammation.

Involvement of VDAC1 and Bcl-2 family of proteins in VacA-induced cytochrome c release and apoptosis of gastric epithelial carcinoma cells

OBJECTIVE

It is known that the vacuolating cytotoxin (VacA) could induce apoptosis. However, the mechanism remained to be elucidated. The aim of this study is to investigate the role of Bcl family of proteins (Bcl-2 and Bax) and the mitochondrial voltage-dependent anion channel (VDAC) in VacA-induced apoptosis of AGS cells.

METHODS

Plasmid pGBKT7-VacA p58 was constructed and transfected into the AGS cells. RT-PCR and Western blotting were used to determine the expressions of cytochrome c, caspase-3, Bax, Bcl-2 and VDAC1 mRNA and proteins.

RESULTS

VacA p58 can induce cytochrome c release and activate caspase-3 in AGS cells. It up-regulated the expressions of Bax and VDAC1 mRNA and proteins, and decreased the expression of Bcl-2 in AGS cells.

CONCLUSION

VacA p58 induces apoptosis in AGS cells. This apoptotic process is associated with the up-regulation of Bax/VDAC1 and downregulation of Bcl-2. These findings suggest that the release of cytochrome c by VacA p58 is mainly through VDAC-dependent and Bcl-2 family-dependent pathways.

Surreptitious manipulation of the human host by Helicobacter pylori

Microbial pathogens contribute to the development of more than 1 million cases of cancer per year. Gastric adenocarcinoma is the second leading cause of cancer-related death in the world, and gastritis induced by Helicobacter pylori is the strongest known risk factor for this malignancy. H. pylori colonizes the stomach for years, not days or weeks, as is usually the case for bacterial pathogens and it always induces inflammation; however, only a fraction of colonized individuals ever develop disease. Identification of mechanisms through which H. pylori co-opts host defenses to facilitate its own persistence will not only improve diagnostic and therapeutic modalities, but may also provide insights into other diseases that arise within the context of long-term pathogen-initiated inflammatory states, such as chronic viral hepatitis and hepatocellular carcinoma.

Targeting of Helicobacter pylori VacA to mitochondria

One of the major virulence factors of Helicobacter pylori is the vacuolating toxin vaca. It has been known for a long time that the toxin enters host cells by endocytosis. On the other hand there is ample evidence that vaca is able to trigger apoptosis and this effect has been attributed in part to interactions with mitochondria. However, for 10 years it was difficult to reconcile the obvious accumulation of vaca in endosomes with mitochondrial targeting. The accessibility of the mitochondria to the toxin was enigmatic. In our new study, we investigated the activities of p34, the toxic subunit of vaca, in more detail. We found that the p34 N-terminus carries a unique targeting sequence for import into mitochondria and for insertion into the mitochondrial inner membrane. By forming an anion channel in this membrane, the toxin has the ability to interfere directly with mitochondrial functions. Taking into account additional results from independent studies, we discuss the implications of our findings with respect to intracellular traffic, the remarkable possibility of a direct transfer of VacA from endosomes to mitochondria and vaca-dependent cell death.

Helicobacter pylori counteracts the apoptotic action of its VacA toxin by injecting the CagA protein into gastric epithelial cells

Infection with Helicobacter pylori is responsible for gastritis and gastroduodenal ulcers but is also a high risk factor for the development of gastric adenocarcinoma and lymphoma. The most pathogenic H. pylori strains (i.e., the so-called type I strains) associate the CagA virulence protein with an active VacA cytotoxin but the rationale for this association is unknown. CagA, directly injected by the bacterium into colonized epithelium via a type IV secretion system, leads to cellular morphological, anti-apoptotic and proinflammatory effects responsible in the long-term (years or decades) for ulcer and cancer. VacA, via pinocytosis and intracellular trafficking, induces epithelial cell apoptosis and vacuolation. Using human gastric epithelial cells in culture transfected with cDNA encoding for either the wild-type 38 kDa C-terminal signaling domain of CagA or its non-tyrosine-phosphorylatable mutant form, we found that, depending on tyrosine-phosphorylation by host kinases, CagA inhibited VacA-induced apoptosis by two complementary mechanisms. Tyrosine-phosphorylated CagA prevented pinocytosed VacA to reach its target intracellular compartments. Unphosphorylated CagA triggered an anti-apoptotic activity blocking VacA-induced apoptosis at the mitochondrial level without affecting the intracellular trafficking of the toxin. Assaying the level of apoptosis of gastric epithelial cells infected with wild-type CagA⁺/VacA⁺H. pylori or isogenic mutants lacking of either CagA or VacA, we confirmed the results obtained in cells transfected with the CagA C-ter constructions showing that CagA antagonizes VacA-induced apoptosis. VacA toxin plays a role during H. pylori stomach colonization. However, once bacteria have colonized the gastric niche, the apoptotic action of VacA might be detrimental for the survival of H. pylori adherent to the mucosa. CagA association with VacA is thus a novel, highly ingenious microbial strategy to locally protect its ecological niche against a bacterial virulence factor, with however detrimental consequences for the human host.

The gram-negative bacterium Helicobacter pylori is the main causative agent of peptic ulcer and gastric cancer in humans. Our work sheds light on a new molecular mechanism by which H. pylori would exert its highly efficient colonization strategy of the human host. In this paper, we show that the H. pylori CagA protein counteracts, by two distinct non-overlapping mechanisms, the apoptotic activity of the H. pylori VacA toxin on human gastric epithelial cells so as to allow a protection of the bacterium niche against VacA, giving a rationale for the association of these two virulence factors in the most pathogenic H. pylori strains. This is a new, highly ingenious mechanism by which a bacterium locally protects its ecological niche against the action of one of its own virulence factors. However, while exerting a beneficial role for survival and growth of the bacterium by counteracting VacA toxin, CagA injection in the gastric epithelial cells triggers proinflammatory and anti-apoptotic responses which are detrimental for the human host in the long-term and favor the development of ulcer and cancer.

Helicobacter pylori in health and disease

Helicobacter pylori is highly adapted for colonization of the human stomach and is present in about half of the human population. When present, H pylori is usually the numerically dominant gastric microorganism. H pylori typically does not cause any adverse effects, but it is associated with an increased risk of noncardia gastric adenocarcinoma, gastric lymphoma, and peptic ulcer. Disorders such as esophageal diseases and childhood-onset asthma were recently reported to occur more frequently in individuals who lack H pylori than in H pylori-positive persons. In this review, we discuss biologic factors that allow H pylori to colonize the human stomach, mechanisms by which H pylori increases the risk of peptic ulcer disease and noncardia gastric adenocarcinoma, and potential benefits that H pylori might confer to humans.

Roles of gastric mucin-type O-glycans in the pathogenesis of Helicobacter pylori infection

Helicobacter pylori is a Gram-negative bacterium that infects over 50% of the world's population. This organism causes various gastric diseases such as chronic gastritis, peptic ulcer, and gastric cancer. H. pylori possesses lipopolysaccharides that share structural similarity to Lewis blood group antigens in gastric mucosa. Such antigenic mimicry could result in immune tolerance against antigens of this pathogen. On the other hand, H. pylori colonizes gastric mucosa by utilizing adhesins that bind Lewis blood group antigen-related carbohydrates expressed on gastric epithelial cells. After colonization, H. pylori induces acute inflammatory responses mainly by neutrophils. This acute phase is gradually replaced by a chronic inflammatory response. In chronic gastritis, lymphocytes infiltrate the lamina propria, and such infiltration is facilitated by the interaction between L-selectin on lymphocytes and peripheral lymph node addressin (PNAd), which contains 6-sulfo sialyl Lewis X-capped O-glycans, on high endothelial venule (HEV)-like vessels. H. pylori barely colonizes gland mucous cell-derived mucin where alpha1,4-GlcNAc-capped O-glycans exist. In vitro experiments show that alpha1,4-GlcNAc-capped O-glycans function as a natural antibiotic to inhibit H. pylori growth. These findings show that distinct sets of carbohydrates expressed in the stomach are closely associated with pathogenesis and prevention of H. pylori-related diseases, providing therapeutic potentialities based on specific carbohydrate modulation.

Carbohydrate-dependent defense mechanisms against Helicobacter pylori infection

Helicobacter pylori is a Gram-negative bacterium that infects over 50% of the world's population. This organism causes various gastric diseases such as chronic gastritis, peptic ulcer, and gastric cancer. H. pylori possesses lipopolysaccharide, which shares structural similarity to Lewis blood group antigens in gastric mucosa. Such antigenic mimicry could result in immune tolerance against antigens of this pathogen. On the other hand, H. pylori colonize gastric mucosa by utilizing adhesins, which bind Lewis blood group antigen-related carbohydrates expressed on gastric epithelial cells. In chronic gastritis, lymphocytes infiltrate the lamina propria, and such infiltration is facilitated by 6-sulfo sialyl Lewis X-capped O-glycans, peripheral lymph node addressin (PNAd), on high endothelial venule (HEV)-like vessels. The number of HEV-like vessels increases as chronic inflammation progresses. Furthermore, PNAd formed on HEV-like vessels disappear once H. pylori is eradicated. These results indicate that PNAd plays an important role in H. pylori-associated inflammation. H. pylori barely colonizes gland mucous cell-derived mucin where alpha1,4-GlcNAc-capped O-glycans exist. In vitro experiments show that alpha1,4-GlcNAc-capped O-glycans function as a natural antibiotic to inhibit H. pylori growth. We recently identified cholesterol alpha-glucosyltransferase (CHLalphaGcT) using an expression cloning strategy and showed that this enzyme is specifically inhibited by mucin-type O-glycans like those present in deeper portions of the gastric mucosa. These findings show that a battery of carbohydrates expressed in the stomach is closely associated with pathogenesis and also prevention of H. pylori-related diseases.

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.

Helicobacter pylori-induced inhibition of vascular endothelial cell functions: a role for VacA-dependent nitric oxide reduction

Epidemiological and clinical studies provide compelling support for a causal relationship between Helicobacter pylori infection and endothelial dysfunction, leading to vascular diseases. However, clear biochemical evidence for this association is limited. In the present study, we have conducted a comprehensive investigation of endothelial injury in bovine aortic endothelial cells (BAECs) induced by H. pylori-conditioned medium (HPCM) prepared from H. pylori 60190 [vacuolating cytotoxin A (Vac(+))]. BAECs were treated with either unconditioned media, HPCM (0-25% vol/vol), or Escherichia coli-conditioned media for 24 h, and cell functions were monitored. Vac(+) HPCM significantly decreased BAEC proliferation, tube formation, and migration (by up to 44%, 65%, and 28%, respectively). Posttreatment, we also observed sporadic zonnula occludens-1 immunolocalization along the cell-cell border, and increased BAEC permeability to FD40 Dextran, indicating barrier reduction. These effects were blocked by 5-nitro-2-(3-phenylpropylamino)benzoic acid (VacA inhibitor) and were not observed with conditioned media prepared from either VacA-deleted H. pylori or E. coli. The cellular mechanism mediating these events was also considered. Vac(+) HPCM (but not Vac(-)) reduced nitric oxide (NO) by >50%, whereas S-nitroso-N-acetylpenicillamine, an NO donor, recovered all Vac(+) HPCM-dependent effects on cell functions. We further demonstrated that laminar shear stress, an endothelial NO synthase/NO stimulus in vivo, could also recover the Vac(+) HPCM-induced decreases in BAEC functions. This study shows, for the first time, a significant proatherogenic effect of H. pylori-secreted factors on a range of vascular endothelial dysfunction markers. Specifically, the VacA-dependent reduction in endothelial NO is indicated in these events. The atheroprotective impact of laminar shear stress in this context is also evident.

Differential regulation of ERK1/2 and p38 MAP kinases in VacA-induced apoptosis of gastric epithelial cells

Helicobacter pylori vacuolating cytotoxin A (VacA) has been considered as an apoptosis-inducing factor. Here, we investigated the mechanism of VacA-induced apoptosis in relation to the defense mechanism and MAP kinases pathway in gastric epithelial cells. AGS cells exposed to enriched VacA extracts affected the level of SOD-1 and villin. We further investigated the role of VacA in those inductions using a functional recombinant VacA (rVacA). Activation of p38 MAPK and Bax dimerization by rVacA were increased in a dose-dependent manner. rVacA-induced ERK1/2 MAPK activation was maximal at 30 min and 4 h and 1-4 microg/ml of rVacA. rVacA-induced SOD-1 expression was considerably diminished by inhibiting ERK1/2 MAPK and it was slightly increased by inhibiting p38 MAPK. rVacA increased or decreased villin expression depending on dose and exposure time and its expression was mainly appeared in the contractile actin ring of the dividing cells. Despite its cytoprotective effect, SB-203580, a p38 inhibitor, was unlikely to reduce VacA-induced Bax dimerization and rather inhibited villin and Bcl2 expression, indicating that p38 may also play a role in cell proliferation or differentiation for survival after VacA intoxication. Furthermore, p38 inhibitor accelerated rVacA-induced cell death after exposure of AGS cells to H(2)O(2) but ERK1/2 inhibitor protected cells from H(2)O(2) insult. These results suggest that SOD-1 and villin are expressed differentially upon VacA insult depending on dose and exposure time via ERK and p38 MAP kinases; decrease in SOD-1 and villin expression coupled with Bax dimerization leads to apoptosis of gastric epithelial cells.