Dual Roles of Helicobacter pylori NapA in inducing and combating oxidative stress

Reactive oxygen species and gastric carcinogenesis: The complex interaction between Helicobacter pylori and host

Helicobacter pylori (H. pylori) is a highly successful human pathogen that colonizes stomach in around 50% of the global population. The colonization of bacterium induces an inflammatory response and a substantial rise in the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS), mostly derived from host neutrophils and gastric epithelial cells, which play a crucial role in combating bacterial infections. However, H. pylori has developed various strategies to quench the deleterious effects of ROS, including the production of antioxidant enzymes, antioxidant proteins as well as blocking the generation of oxidants. The host's inability to eliminate H. pylori infection results in persistent ROS production. Notably, excessive ROS can disrupt the intracellular signal transduction and biological processes of the host, incurring chronic inflammation and cellular damage, such as DNA damage, lipid peroxidation, and protein oxidation. Markedly, the sustained inflammatory response and oxidative stress during H. pylori infection are major risk factor for gastric carcinogenesis. In this context, we summarize the literature on H. pylori infection-induced ROS production, the strategies used by H. pylori to counteract the host response, and subsequent host damage and gastric carcinogenesis.

How Long Will It Take to Launch an Effective Helicobacter pylori Vaccine for Humans?

Helicobacter pylori infection often occurs in early childhood, and can last a lifetime if not treated with medication. H. pylori infection can also cause a variety of stomach diseases, which can only be treated with a combination of antibiotics. Combinations of antibiotics can cure H. pylori infection, but it is easy to relapse and develop drug resistance. Therefore, a vaccine is a promising strategy for prevention and therapy for the infection of H. pylori. After decades of research and development, there has been no appearance of any H. pylori vaccine reaching the market, unfortunately. This review summarizes the aspects of candidate antigens, immunoadjuvants, and delivery systems in the long journey of H. pylori vaccine research, and also introduces some clinical trials that have displayed encouraging or depressing results. Possible reasons for the inability of an H. pylori vaccine to be available over the counter are cautiously discussed and some propositions for the future of H. pylori vaccines are outlined.

Identification of anti-Helicobacter pylori antibody signatures in gastric intestinal metaplasia

BACKGROUND

Chronic Helicobacter pylori infection may induce gastric intestinal metaplasia (IM). We compared anti-H. pylori antibody profiles between IM cases and non-atrophic gastritis (NAG) controls.

METHODS

We evaluated humoral responses to 1528 H. pylori proteins among a discovery set of 50 IM and 50 NAG using H. pylori protein arrays. Antibodies with ≥ 20% sensitivity at 90% specificity for either group were selected and further validated in an independent set of 100 IM and 100 NAG using odds ratios (OR). A validated multi-signature was evaluated using the area under the receiver operating characteristics curve (AUC) and net reclassification improvement (NRI).

RESULTS

Sixty-two immunoglobulin (Ig) G and 11 IgA antibodies were detected in > 10%. Among them, 22 IgG and 6 IgA antibodies were different between IM and NAG in the discovery set. Validated antibodies included 11 IgG (anti-HP1177/Omp27/HopQ [OR = 8.1, p < 0.001], anti-HP0547/CagA [4.6, p < 0.001], anti-HP0596/Tipα [4.0, p = 0.002], anti-HP0103/TlpB [3.8, p = 0.001], anti-HP1125/PalA/Omp18 [3.1, p = 0.001], anti-HP0153/RecA [0.48, p = 0.03], anti-HP0385 [0.41, p = 0.006], anti-HP0243/TlpB [0.39, p = 0.016], anti-HP0371/FabE [0.37, p = 0.017], anti-HP0900/HypB/AccB [0.35, p = 0.048], and anti-HP0709 [0.30, p = 0.003]), and 2 IgA (anti-HP1125/PalA/Omp18 [2.7, p = 0.03] and anti-HP0596/Tipα [2.5, p = 0.027]). A model including all 11 IgG antibodies (AUC = 0.81) had better discriminated IM and NAG compared with an anti-CagA only (AUC = 0.77) model (NRI = 0.44; p = 0.001).

CONCLUSIONS

Our study represents the most comprehensive assessment of anti-H. pylori antibody profiles in IM. The target antigens for these novel antibodies may act together with CagA in the progression to IM. Along with other biomarkers, specific H. pylori antibodies may identify IM patients, who would benefit from surveillance.

The Role of Helicobacter pylori Neutrophil-Activating Protein in the Pathogenesis of H. pylori and Beyond: From a Virulence Factor to Therapeutic Targets and Therapeutic Agents

Helicobacter pylori neutrophil-activating protein (HP-NAP), a major virulence factor of H. pylori, plays a role in bacterial protection and host inflammation. HP-NAP activates a variety of innate immune cells, including neutrophils, monocytes, and mast cells, to induce their pro-oxidant and pro-inflammatory activities. This protein also induces T-helper type 1 (Th1) immune response and cytotoxic T lymphocyte (CTL) activity, supporting that HP-NAP is able to promote gastric inflammation by activation of adaptive immune responses. Thus, HP-NAP is a potential therapeutic target for the treatment of H. pylori-induced gastric inflammation. The inflammatory responses triggered by HP-NAP are mediated by a PTX-sensitive G protein-coupled receptor and Toll-like receptor 2. Drugs designed to block the interactions between HP-NAP and its receptors could alleviate the inflammation in gastric mucosa caused by H. pylori infection. In addition, HP-NAP acts as a promising therapeutic agent for vaccine development, allergy treatment, and cancer immunotherapy. The high antigenicity of HP-NAP makes this protein a component of vaccines against H. pylori infection. Due to its immunomodulatory activity to stimulate the Th1-inducing ability of dendritic cells, enhance Th1 immune response and CTL activity, and suppress Th2-mediated allergic responses, HP-NAP could also act as an adjuvant in vaccines, a drug candidate against allergic diseases, and an immunotherapeutic agent for cancer. This review highlights the role of HP-NAP in the pathogenesis of H. pylori and the potential for this protein to be a therapeutic target in the treatment of H. pylori infection and therapeutic agents against H. pylori-associated diseases, allergies, and cancer.

Positive Selection of Mutations in the Helicobacter pylori katA 5' Untranslated Region in a Mongolian Gerbil Model of Gastric Disease

To evaluate potential effects of gastric inflammation on Helicobacter pylori diversification and evolution within the stomach, we experimentally infected Mongolian gerbils with an H. pylori strain in which Cag type IV secretion system (T4SS) activity is controlled by a TetR/tetO system. Gerbils infected with H. pylori under conditions in which Cag T4SS activity was derepressed had significantly higher levels of gastric inflammation than gerbils infected under conditions with repressed Cag T4SS activity. Mutations in the 5' untranslated region (UTR) of katA (encoding catalase) were detected in strains cultured from 8 of the 17 gerbils infected with Cag T4SS-active H. pylori and none of the strains from 17 gerbils infected with Cag T4SS-inactive H. pylori. Catalase enzymatic activity, steady-state katA transcript levels, and katA transcript stability were increased in strains with these single nucleotide polymorphisms (SNPs) compared to strains in which these SNPs were absent. Moreover, strains harboring these SNPs exhibited increased resistance to bactericidal effects of hydrogen peroxide, compared to control strains. Experimental introduction of the SNPs into the wild-type katA 5' UTR resulted in increased katA transcript stability, increased katA steady-state levels, and increased catalase enzymatic activity. Based on site-directed mutagenesis and modeling of RNA structure, increased katA transcript levels were correlated with higher predicted thermal stability of the katA 5' UTR secondary structure. These data suggest that high levels of gastric inflammation positively select for H. pylori strains producing increased levels of catalase, which may confer survival advantages to the bacteria in an inflammatory gastric environment.

HP-NAP of Helicobacter pylori: The Power of the Immunomodulation

The miniferritin HP-NAP of Helicobacter pylori was originally described as a neutrophil-activating protein because of the capacity to activate neutrophils to generate oxygen radicals and adhere to endothelia. Currently, the main feature for which HP-NAP is known is the ability to promote Th1 responses and revert the immune suppressive profile of macrophages. In this review, we discuss the immune modulating properties of the protein regarding the H. pylori infection and the evidence that support the potential clinical application of HP-NAP in allergy and cancer immunotherapy.

Dynamics of Oxidative Stress in Helicobacter pylori-Positive Patients with Atrophic Body Gastritis and Various Stages of Gastric Cancer

Gastric cancer is a global health problem. The pathogenesis of this disease remains unclear. This study included 198 H. pylori (+) men aged 45 to 60 years old. Group A included 63 practically healthy men, group B included 45 men with severe atrophic body gastritis, group C included 37 men with epithelial gastric cancer stages I–II according to TNM, and group D included 54 men with epithelial gastric cancer stages III–IV according to the TNM scale. The content of malondialdehyde (MDA), diene conjugates (DCs), superoxide dismutase (SOD), catalase (CAT), glutathione S-transferase (GST), and glutathione peroxidase (GPO) was detected using an enzyme immunoassay (ELISA) or spectrophotometric methods in the blood plasma. The concentrations of MDA and DC were increased in the patients of group B compared with group A, and in patients of groups C and D compared with groups A and B. The ratio of MDA/SOD and MDA/CAT was decreased in the patients in group D compared with the patients in group C, and was significantly higher compared with group A. The ratios of MDA/GPO and MDA/GST increased linearly and were at a maximum in groups C and D. Our work determined that indicators of oxidative stress may be the biochemical substrate, which brings together the various stages of the Correa cascade, and may explain disease progression. The dynamics of changes in the content of SOD and CAT in the plasma in patients with gastric cancer may be a target of future investigations.

Helicobacter pylori-induced DNA double-strand break in the development of gastric cancer

Infection with cagA-positive Helicobacter pylori strains plays an etiological role in the development of gastric cancer. The CagA protein is injected into gastric epithelial cells through a bacterial Type IV secretion system. Inside the host cells, CagA promiscuously associates with multiple host cell proteins including the prooncogenic phosphatase SHP2 that is required for full activation of the RAS-ERK pathway. CagA-SHP2 interaction aberrantly activates SHP2 and thereby deregulates RAS-ERK signaling. Cancer is regarded as a disease of the genome, indicating that H. pylori-mediated gastric carcinogenesis is also associated with genomic alterations in the host cell. Indeed, accumulating evidence has indicated that H. pylori infection provokes DNA double-strand breaks (DSBs) by both CagA-dependent and -independent mechanisms. DSBs are repaired by either error-free homologous recombination (HR) or error-prone non-homologous end joining (NHEJ) or microhomology-mediated end joining (MMEJ). Infection with cagA-positive H. pylori inhibits RAD51 expression while dampening cytoplasmic-to-nuclear translocalization of BRCA1, causing replication fork instability and HR defects (known as "BRCAness"), which collectively provoke genomic hypermutation via non-HR-mediated DSB repair. H. pylori also subverts multiple DNA damage responses including DNA repair systems. Infection with H. pylori additionally inhibits the function of the p53 tumor suppressor, thereby dampening DNA damage-induced apoptosis while promoting proliferation of CagA-delivered cells. Thus, H. pylori cagA-positive strains promote abnormal expansion of cells with BRCAness, which dramatically increases the chance of generating driver gene mutations in the host cells. Once such driver mutations are acquired, H. pylori CagA is no longer required for subsequent gastric carcinogenesis (Hit-and-Run carcinogenesis).

Transient recombinant expression of highly immunogenic CagA, VacA and NapA in Nicotiana benthamiana

Interest in the plant-based transient production of recombinant immunogenic antigens has tremendously progressed because plants are cost-effective, easily selectable, free of mammalian contamination, and support complex post-translational modifications. Nicotiana benthamiana is a convenient system for transient expression of recombinant antigens. The present study documented a platform for rapid production of Helicobacter pylori CagA, VacA and NapA antigens three days (first harvest, FH) and six days (second harvest, SH) after agro-infiltration using a syringe. In this study, CagA, VacA and NapA antigen genes from Helicobacter pylori were cloned into the binary vector pBI121 and transformed into Nicotiana benthamiana by the Agrobacterium-mediated process. Leaves of four to five weeks old Nicotiana benthamiana plants were agroinfiltrated with EHA105 subtype of Agrobacterium tumefaciens strain containing cloned CagA (pBI121-CagA), VacA (pBI121-VacA) and NapA (pBI121-NapA) constructs. The transient expression and accumulation of the recombinant genes containing CagA, VacA and NapA expression cassettes were confirmed using qRT-PCR by comparing the relative expression at FH and SH post-infiltration with the non-infiltrated (control) samples and using ELISA at 1/5 and 1/10 dilution ratios. The qRT-PCR findings showed that Agrobacterium-mediated syringe infiltration of leaves of four to five weeks old Nicotiana benthamiana plants produced significantly higher transcript levels of CagA (about 8-fold and 7-fold), VacA (38-fold and 24-fold) and NapA (7-fold and 5-fold) genes at FH and SH compared to the control sample. Besides, the maximum amount of CagA, VacA and NapA antigens were detected at the FH stage compared to the SH stage, when the antibody concentrations of the agro-infiltrated leaf extracts containing these recombinant antigens were diluted in a 1/5 ratio. This study has developed evidence to support that recombinant CagA, VacA and NapA can be transiently produced in Nicotiana benthamiana plants.

The peptidoglycan-associated protein NapA plays an important role in the envelope integrity and in the pathogenesis of the lyme disease spirochete

The bacterial pathogen responsible for causing Lyme disease, Borrelia burgdorferi, is an atypical Gram-negative spirochete that is transmitted to humans via the bite of an infected Ixodes tick. In diderms, peptidoglycan (PG) is sandwiched between the inner and outer membrane of the cell envelope. In many other Gram-negative bacteria, PG is bound by protein(s), which provide both structural integrity and continuity between envelope layers. Here, we present evidence of a peptidoglycan-associated protein (PAP) in B. burgdorferi. Using an unbiased proteomics approach, we identified Neutrophil Attracting Protein A (NapA) as a PAP. Interestingly, NapA is a Dps homologue, which typically functions to bind and protect cellular DNA from damage during times of stress. While B. burgdorferi NapA is known to be involved in the oxidative stress response, it lacks the critical residues necessary for DNA binding. Biochemical and cellular studies demonstrate that NapA is localized to the B. burgdorferi periplasm and is indeed a PAP. Cryo-electron microscopy indicates that mutant bacteria, unable to produce NapA, have structural abnormalities. Defects in cell-wall integrity impact growth rate and cause the napA mutant to be more susceptible to osmotic and PG-specific stresses. NapA-linked PG is secreted in outer membrane vesicles and augments IL-17 production, relative to PG alone. Using microfluidics, we demonstrate that NapA acts as a molecular beacon-exacerbating the pathogenic properties of B. burgdorferi PG. These studies further our understanding of the B. burgdorferi cell envelope, provide critical information that underlies its pathogenesis, and highlight how a highly conserved bacterial protein can evolve mechanistically, while maintaining biological function.

SpoT-mediated NapA upregulation promotes oxidative stress-induced Helicobacter pylori biofilm formation and confers multidrug resistance

Recently, there is increased incidence of drug-resistant Helicobacter pylori infection. Biofilm formation confers multidrug resistance to bacteria. Moreover, it has been found that the formation of biofilm on the surface of gastric mucosa is an important reason for the difficulty of eradication of H. pylori The mechanisms underlying H. pylori biofilm formation in vivo have not been elucidated. Reactive oxygen species (ROS) released by the host immune cells in response to H. pylori infection cannot effectively clear the pathogen. Moreover, the extracellular matrix of the biofilm protects the bacteria against ROS-mediated toxicity. This study hypothesized that ROS can promote H. pylori biofilm formation and treatment with low concentrations of hydrogen peroxide (H₂O₂) promoted this process in vitro The comparative transcriptome analysis of planktonic and biofilm-forming cells revealed that the expression of SpoT, a (p)ppGpp (guanosine 3'-diphosphate 5'-triphosphate and guanosine 3',5'-bispyrophosphate) synthetase/hydrolase, is upregulated in H₂O₂-induced biofilms and that knockout of spoT inhibited H. pylori biofilm formation. Additionally, this study examined the key target molecules involved in SpoT regulation using weighted gene co-expression network analysis. The analysis revealed that neutrophil-activating protein (NapA; HP0243) promoted H₂O₂-induced biofilm formation and conferred multidrug resistance. Furthermore, vitamin C exhibited anti-H. pylori biofilm activity and downregulated the expression of napA in vitro These findings provide novel insight into the clearance of H. pylori biofilms.

3-Pentylcatechol, a Non-Allergenic Urushiol Derivative, Displays Anti-Helicobacter pylori Activity In Vivo

We previously reported that 3-pentylcatechol (PC), a synthetic non-allergenic urushiol derivative, inhibited the growth of Helicobacter pylori in an in vitro assay using nutrient agar and broth. In this study, we aimed to investigate the in vivo antimicrobial activity of PC against H. pylori growing in the stomach mucous membrane. Four-week-old male C57BL/6 mice (n = 4) were orally inoculated with H. pylori Sydney Strain-1 (SS-1) for 8 weeks. Thereafter, the mice received PC (1, 5, and 15 mg/kg) and triple therapy (omeprazole, 0.7 mg/kg; metronidazole, 16.7 mg/kg; clarithromycin, 16.7 mg/kg, reference groups) once daily for 10 days. Infiltration of inflammatory cells in gastric tissue was greater in the H. pylori-infected group compared with the control group and lower in both the triple therapy- and PC-treated groups. In addition, upregulation of cytokine mRNA was reversed after infection, upon administration of triple therapy and PC. Interestingly, PC was more effective than triple therapy at all doses, even at 1/15th the dose of triple therapy. In addition, PC demonstrated synergism with triple therapy, even at low concentrations. The results suggest that PC may be more effective against H. pylori than established antibiotics.

Helicobacter pylori Immunoproteomic Profiles in Gastric Cancer

Chronic Helicobacter pylori infection is the major risk factor for gastric cancer (GC). However, only some infected individuals develop this neoplasia. Previous H. pylori serology studies have been limited by investigating small numbers of candidate antigens. Therefore, we evaluated humoral responses to a nearly complete H. pylori immunoproteome (1527 proteins) among 50 GC cases and 50 controls using Nucleic Acid Programmable Protein Array (NAPPA). Seropositivity was defined as median normalized intensity ≥2 on NAPPA, and 53 anti-H. pylori antibodies had >10% seroprevalence. Anti-GroEL exhibited the greatest seroprevalence (77% overall), which agreed well with ELISA using whole-cell lysates of H. pylori cells. After an initial screen by H. pylori-NAPPA, we discovered and verified that 12 antibodies by ELISA in controls had ≥15% of samples with an optical reading value exceeding the 95th percentile of the GC group. ELISA-verified antibodies were validated blindly in an independent set of 100 case-control pairs. As expected, anti-CagA seropositivity was positively associated with GC (odds ratio, OR = 5.5; p < 0.05). After validation, six anti-H. pylori antibodies showed lower seropositivity in GC, with ORs ranging from 0.44 to 0.12 (p < 0.05): anti-HP1118/Ggt, anti-HP0516/HsIU, anti-HP0243/NapA, anti-HP1293/RpoA, anti-HP0371/FabE, and anti-HP0875/KatA. Among all combinations, a model with anti-Ggt, anti-HslU, anti-NapA, and anti-CagA had an area under the curve of 0.73 for discriminating GC vs. controls. This study represents the first comprehensive assessment of anti-H. pylori humoral profiles in GC. Decreased responses to multiple proteins in GC may reflect mucosal damage and decreased bacterial burden. The higher prevalence of specific anti-H. pylori antibodies in controls may suggest immune protection against GC development.

Helicobacter pylori infection downregulates the DNA glycosylase NEIL2, resulting in increased genome damage and inflammation in gastric epithelial cells

Infection with the Gram-negative, microaerophilic bacterium Helicobacter pylori induces an inflammatory response and oxidative DNA damage in gastric epithelial cells that can lead to gastric cancer (GC). However, the underlying pathogenic mechanism is largely unclear. Here, we report that the suppression of Nei-like DNA glycosylase 2 (NEIL2), a mammalian DNA glycosylase that specifically removes oxidized bases, is one mechanism through which H. pylori infection may fuel the accumulation of DNA damage leading to GC. Using cultured cell lines, gastric biopsy specimens, primary cells, and human enteroid-derived monolayers from healthy human stomach, we show that H. pylori infection greatly reduces NEIL2 expression. The H. pylori infection-induced downregulation of NEIL2 was specific, as Campylobacter jejuni had no such effect. Using gastric organoids isolated from the murine stomach in coculture experiments with live bacteria mimicking the infected stomach lining, we found that H. pylori infection is associated with the production of various inflammatory cytokines. This response was more pronounced in Neil2 knockout (KO) mouse cells than in WT cells, suggesting that NEIL2 suppresses inflammation under physiological conditions. Notably, the H. pylori-infected Neil2-KO murine stomach exhibited more DNA damage than the WT. Furthermore, H. pylori-infected Neil2-KO mice had greater inflammation and more epithelial cell damage. Computational analysis of gene expression profiles of DNA glycosylases in gastric specimens linked the reduced Neil2 level to GC progression. Our results suggest that NEIL2 downregulation is a plausible mechanism by which H. pylori infection impairs DNA damage repair, amplifies the inflammatory response, and initiates GC.

The synergy of resveratrol and alcohol against Helicobacter pylori and underlying anti-Helicobacter pylori mechanism of resveratrol

AIMS

To determine individual antibacterial and synergistic antibacterial effects of resveratrol and alcohol against Helicobacter pylori 26695 in vitro, and to elucidate the underlying mechanism of action of resveratrol against H. pylori.

METHODS AND RESULTS

The minimum inhibitory concentrations (MICs) and time-killing curve of resveratrol and alcohol were determined. Transcriptome analysis by RNA sequencing was used to elucidate the underlying mechanism of action of resveratrol against H. pylori. Our results showed that the MICs of resveratrol and alcohol against H. pylori 26695 are about 64 μg ml^-1 and 4% (v/v) respectively. The synergy was found: resveratrol at concentration of 64 μg ml^-1 in combination with alcohol at concentration of 4% (v/v) showed >10 000-fold decrease in the mount of viable bacteria compared with resveratrol and alcohol used alone. Transcriptome analysis showed 152 genes were downregulated and 111 genes were upregulated in the presence of resveratrol. Genes involved in protein translation (17·1%), outer membrane proteins (OMPs) (9·9%) and transports (11·2%) comprise 38·2% of the downregulated genes. In comparison, genes involved in redox (13·5%), pathogenesis and motility (9·9%) and iron homeostasis (4·5%) comprise 27·9% of the upregulated genes.

CONCLUSIONS

The synergy of resveratrol and alcohol against H. pylori was found in this study. The underlying mechanism of action of resveratrol against H. pylori may be mainly attributed to its inhibitory effect on translation, OMPs, transports, ATP synthase and possible oxidative damage.

SIGNIFICANCE AND IMPACT OF THIS STUDY

Our study provides a global insight into the anti-H. pylori mechanism of resveratrol. Both resveratrol and alcohol can contribute to inhibition of ribosomes, changes in OMPs and oxidative damage, which may be the explanations of synergistic effect against H. pylori elicited by resveratrol and alcohol.

Chaperone activity of serine protease HtrA of Helicobacter pylori as a crucial survival factor under stress conditions

BACKGROUND

Serine protease HtrA exhibits both proteolytic and chaperone activities, which are involved in cellular protein quality control. Moreover, HtrA is an important virulence factor in many pathogens including Helicobacter pylori, for which the crucial stage of infection is the cleavage of E-cadherin and other cell-to-cell junction proteins.

METHODS

The in vitro study of H. pylori HtrA (HtrA_Hp) chaperone activity was carried out using light scattering assays and investigation of lysozyme protein aggregates. We produced H. pylori ∆htrA deletion and HtrA_Hp point mutants without proteolytic activity in strain N6 and investigated the survival of the bacteria under thermal, osmotic, acidic and general stress conditions as well as the presence of puromycin or metronidazole using serial dilution tests and disk diffusion method. The levels of cellular and secreted proteins were examined using biochemical fraction and Western blotting. We also studied the proteolytic activity of secreted HtrA_Hp using zymography and the enzymatic digestion of β-casein. Finally, the consequences of E-cadherin cleavage were determined by immunofluorescence microscopy.

RESULTS

We demonstrate that HtrA_Hp displays chaperone activity that inhibits the aggregation of lysozyme and is stable under various pH and temperature conditions. Next, we could show that N6 expressing only HtrA chaperone activity grow well under thermal, pH and osmotic stress conditions, and in the presence of puromycin or metronidazole. In contrast, in the absence of the entire htrA gene the bacterium was more sensitive to a number of stresses. Analysing the level of cellular and secreted proteins, we noted that H. pylori lacking the proteolytic activity of HtrA display reduced levels of secreted HtrA. Moreover, we compared the amounts of secreted HtrA from several clinical H. pylori strains and digestion of β-casein. We also demonstrated a significant effect of the HtrA_Hp variants during infection of human epithelial cells and for E-cadherin cleavage.

CONCLUSION

Here we identified the chaperone activity of the HtrA_Hp protein and have proven that this activity is important and sufficient for the survival of H. pylori under multiple stress conditions. We also pinpointed the importance of HtrA_Hp chaperone activity for E- cadherin degradation and therefore for the virulence of this eminent pathogen.

Immune Cell Signaling by Helicobacter pylori: Impact on Gastric Pathology

Helicobacter pylori represents a highly successful colonizer of the human stomach. Infections with this Gram-negative bacterium can persist lifelong, and although in the majority of cases colonization is asymptomatic, it can trigger pathologies ranging from chronic gastritis and peptic ulceration to gastric cancer. The interaction of the bacteria with the human host modulates immune responses in different ways to enable bacterial survival and persistence. H. pylori uses various pathogenicity-associated factors such as VacA, NapA, CGT, GGT, lipopolysaccharide, peptidoglycan, heptose 1,7-bisphosphate, ADP-heptose, cholesterol glucosides, urease and a type IV secretion system for controlling immune signaling and cellular functions. It appears that H. pylori manipulates multiple extracellular immune receptors such as integrin-β₂ (CD18), EGFR, CD74, CD300E, DC-SIGN, MINCLE, TRPM2, T-cell and Toll-like receptors as well as a number of intracellular receptors including NLRP3, NOD1, NOD2, TIFA and ALPK1. Consequently, downstream signaling pathways are hijacked, inducing tolerogenic dendritic cells, inhibiting effector T cell responses and changing the gastrointestinal microbiota. Here, we discuss in detail the interplay of bacterial factors with multiple immuno-regulatory cells and summarize the main immune evasion and persistence strategies employed by H. pylori.

Production and delivery of Helicobacter pylori NapA in Lactococcus lactis and its protective efficacy and immune modulatory activity

Helicobacter pylori neutrophil-activating protein A subunit (NapA) has been identified as a virulence factor, a protective antigen and a potent immunomodulator. NapA shows unique application potentials for anti-H. pylori vaccines and treatment strategies of certain allergic diseases and carcinomas. However, appropriate production and utilization modes of NapA still remain uncertain to date. This work has established a novel efficient production and utilization mode of NapA by using L. lactis as an expression host and delivery vector, and demonstrated immune protective efficacy and immune modulatory activity of the engineered L. lactis by oral vaccination of mice. It was observed for the first time that H. pylori NapA promotes both polarized Th17 and Th1 responses, which may greatly affect the clinical application of NapA. This report offers a promising anti-H. pylori oral vaccine candidate and a potent mucosal immune modulatory agent. Meanwhile, it uncovers a way to produce and deliver the oral vaccine and immunomodulator by fermentation of food like milk, which might have striking effects on control of H. pylori infection, gastrointestinal cancers, and Th2 bias allergic diseases, including many food allergies.

Helicobacter pylori and Gastric Cancer: Adaptive Cellular Mechanisms Involved in Disease Progression

Helicobacter pylori (H. pylori) infection is the major risk factor associated with the development of gastric cancer. The transition from normal mucosa to non-atrophic gastritis, triggered primarily by H. pylori infection, initiates precancerous lesions which may then progress to atrophic gastritis and intestinal metaplasia. Further progression to dysplasia and gastric cancer is generally believed to be attributable to processes that no longer require the presence of H. pylori. The responses that develop upon H. pylori infection are directly mediated through the action of bacterial virulence factors, which drive the initial events associated with transformation of infected gastric cells. Besides genetic and to date poorly defined environmental factors, alterations in gastric cell stress-adaptive mechanisms due to H. pylori appear to be crucial during chronic infection and gastric disease progression. Firstly, H. pylori infection promotes gastric cell death and reduced epithelial cell turnover in the majority of infected cells, resulting in primary tissue lesions associated with an initial inflammatory response. However, in the remaining gastric cell population, adaptive responses are induced that increase cell survival and proliferation, resulting in the acquisition of potentially malignant characteristics that may lead to precancerous gastric lesions. Thus, deregulation of these intrinsic survival-related responses to H. pylori infection emerge as potential culprits in promoting disease progression. This review will highlight the most relevant cellular adaptive mechanisms triggered upon H. pylori infection, including endoplasmic reticulum stress and the unfolded protein response, autophagy, oxidative stress, and inflammation, together with a subsequent discussion on how these factors may participate in the progression of a precancerous lesion. Finally, this review will shed light on how these mechanisms may be exploited as pharmacological targets, in the perspective of opening up new therapeutic alternatives for non-invasive risk control in gastric cancer.

Human and Helicobacter pylori Interactions Determine the Outcome of Gastric Diseases

The innate immune response is a critical hallmark of Helicobacter pylori infection. Epithelial and myeloid cells produce effectors, including the chemokine CXCL8, reactive oxygen species (ROS), and nitric oxide (NO), in response to bacterial components. Mechanistic and epidemiologic studies have emphasized that dysregulated and persistent release of these products leads to the development of chronic inflammation and to the molecular and cellular events related to carcinogenesis. Moreover, investigations in H. pylori-infected patients about polymorphisms of the genes encoding CXCL8 and inducible NO synthase, and epigenetic control of the ROS-producing enzyme spermine oxidase, have further proven that overproduction of these molecules impacts the severity of gastric diseases. Lastly, the critical effect of the crosstalk between the human host and the infecting bacterium in determining the severity of H. pylori-related diseases has been supported by phylogenetic analysis of the human population and their H. pylori isolates in geographic areas with varying clinical and pathologic outcomes of the infection.

Protein signature characterizing Helicobacter pylori strains of patients with autoimmune atrophic gastritis, duodenal ulcer and gastric cancer

Background

Helicobacter pylori (H. pylori) represents a key factor in the etiology of autoimmune atrophic gastritis (AAG), duodenal ulcer (DU) and gastric cancer (GC). The aim of this study was to characterize the differential protein expression of H. pylori isolated from gastric biopsies of patients affected by either AAG, DU or GC.

Methods

The H. pylori strains were isolated from endoscopic biopsies from the stomach of patients with gastric disease. Protein profiles of H. pylori were compared by two-dimensional difference in gel electrophoresis (2D-DIGE) coupled with mass spectrometry (MS) for the identification of significantly different spots (Student t-test, p < 0.05).

Results

A total of 47 differentially expressed spots were found between H. pylori isolated from patients with either DU or AAG diseases and those isolated from patients with GC (Anova < 0.05, log fold change >1.5). These spots corresponded to 35 unique proteins. The identity of 7 protein spots was validated after one-dimensional electrophoresis and MS/MS analyses of excised gel portions. In H. pylori isolated from DU-patients a significant increase in proteins with antioxidant activity emerged (AroQ, AspA, FldA, Icd, OorA and ScoB), together with a higher content of proteins counteracting the high acid environment (KatA and NapA). In H. pylori isolated from AAG-patients proteins neutralizing hydrogen concentrations through organic substance metabolic processes decreased (GroL, TrxB and Tuf). In addition, a reduction of bacterial motility (FlhA) was found to be associated with AAG-H. pylori isolates. In GC-H. pylori strains it was found an increase in nucleic acid-binding proteins (e.g. DnaG, Tuf, RpoA, RplU) which may be involved in a higher demand of DNA- and protein-related processes.

Conclusion

Our data suggest the presence of specific protein signatures discriminating among H. pylori isolated from either AAG, DU or GC. Changes in protein expression profiles evaluated by DIGE succeeded in deciphering part of the molecular scenarios associated with the different H. pylori-related gastric diseases.

Electronic supplementary material

The online version of this article (doi:10.1186/s13027-017-0133-x) contains supplementary material, which is available to authorized users.

Polyamine- and NADPH-dependent generation of ROS during Helicobacter pylori infection: A blessing in disguise

Helicobacter pylori is a Gram-negative bacterium that specifically colonizes the gastric ecological niche. During the infectious process, which results in diseases ranging from chronic gastritis to gastric cancer, the host response is characterized by the activation of the innate immunity of gastric epithelial cells and macrophages. These cells thus produce effector molecules such as reactive oxygen species (ROS) to counteract the infection. The generation of ROS in response to H. pylori involves two canonical pathways: 1) the NADPH-dependent reduction of molecular oxygen to generate O₂^•-, which can dismute to generate ROS; and 2) the back-conversion of the polyamine spermine into spermidine through the enzyme spermine oxidase, leading to H₂O₂ production. Although these products have the potential to affect the survival of bacteria, H. pylori has acquired numerous strategies to counteract their deleterious effects. Nonetheless, ROS-mediated oxidative DNA damage and mutations may participate in the adaptation of H. pylori to its ecological niche. Lastly, ROS have been shown to play a major role in the development of the inflammation and carcinogenesis. It is the purpose of this review to summarize the literature about the production of ROS during H. pylori infection and their role in this infectious gastric disease.

Oxidative Stress Resulting From Helicobacter pylori Infection Contributes to Gastric Carcinogenesis

Helicobacter pylori is a gram-negative, microaerophilic bacterium that infects the stomach and can lead to, among other disorders, the development of gastric cancer. The inability of the host to clear the infection results in a chronic inflammatory state with continued oxidative stress within the tissue. Reactive oxygen species and reactive nitrogen species produced by the immune and epithelial cells damage the host cells and can result in DNA damage. H pylori has evolved to evoke this damaging response while blunting the host's efforts to kill the bacteria. This long-lasting state with inflammation and oxidative stress can result in gastric carcinogenesis. Continued efforts to better understand the bacterium and the host response will serve to prevent or provide improved early diagnosis and treatment of gastric cancer.

Oxidative and nitrosative stress defences of Helicobacter and Campylobacter species that counteract mammalian immunity

Helicobacter and Campylobacter species are Gram-negative microaerophilic host-associated heterotrophic bacteria that invade the digestive tract of humans and animals. Campylobacter jejuni is the major worldwide cause of foodborne gastroenteritis in humans, while Helicobacter pylori is ubiquitous in over half of the world's population causing gastric and duodenal ulcers. The colonisation of the gastrointestinal system by Helicobacter and Campylobacter relies on numerous cellular defences to sense the host environment and respond to adverse conditions, including those imposed by the host immunity. An important antimicrobial tool of the mammalian innate immune system is the generation of harmful oxidative and nitrosative stresses to which pathogens are exposed during phagocytosis. This review summarises the regulators, detoxifying enzymes and subversion mechanisms of Helicobacter and Campylobacter that ultimately promote the successful infection of humans.

Serum Antibodies against Helicobacter pylori Neutrophil Activating Protein in Carriers of IL-4 C-590T Genetic Polymorphism Amplify the Risk of Gastritis and Gastric Cancer

BACKGROUND

Gastric cancer arises, mainly, on an inflammatory background. Helicobacter pylori neutrophil activating (HP-NAP) protein functions as a potent pro-inflammatory mediator. Similarly, IL-4 plays a critical role in the inflammation pathway, the levels of which are altered by C to T transition at position -590 in its promoter region. Here, we have aimed to assess the risk of gastritis and gastric cancer in the co-presence of these two inflammation modulating mediators.

METHODS

Gastritis (n=58) and gastric cancer (n=31) patients were evaluated and compared with H. pylori-positive asymptomatic controls (n=46), for serum antibodies against recombinant HP-NAP and IL-4 C-590T single nucleotide polymorphism using immunoblotting and PCR-RFLP, respectively. Multivariable logistic regression, adjusting for age, gender and ethnicity, was used for data analysis.

RESULTS

In terms of susceptibility to gastritis, seropositivity to HP-NAP projected a risk impact of 4.62 fold (OR=4.62, 95% CI=1.50-14.22), which when present in IL-4 -590 T carriers augmented the risk up to 9.7 fold (OR=9.70, 95% CI=2.06-45.69). A similar pattern, but of a stronger magnitude, occurred for the risk of gastric cancer, which was estimated at 9.07 fold (OR=9.07, 95% CI=1.99-42.0) for HP-NAP-seropositive subjects and was drastically amplified (OR=33.64, 95% CI=2.06-548.68), when double-positive (HP-NAP seropositive/IL-4 -590 T carrier) subjects were examined against double negatives (HP-NAP seronegative/IL-4 -590 CC).

CONCLUSION

Our preliminary data indicate that serum antibodies against HP-NAP represent a state of risk, which is further exacerbated in IL-4 -590 T carriers. These biomarkers, if validated in larger prospective studies, can be used to screen for gastric cancer susceptibility.

Molecular interactions of UvrB protein and DNA from Helicobacter pylori: Insight into a molecular modeling approach

Helicobacter pylori (H. pylori) persevere in the human stomach, an environment in which they encounter many DNA-damaging conditions, including gastric acidity. The pathogenicity of H. pylori is enhanced by its well-developed DNA repair mechanism, thought of as 'machinery,' such as nucleotide excision repair (NER). NER involves multi-enzymatic excinuclease proteins (UvrABC endonuclease), which repair damaged DNA in a sequential manner. UvrB is the central component in prokaryotic NER, essential for damage recognition. Therefore, molecular modeling studies of UvrB protein from H. pylori are carried out with homology modeling and molecular dynamics (MD) simulations. The results reveal that the predicted structure is bound to a DNA hairpin with 3-bp stem, an 11-nucleotide loop, and 3-nt 3' overhang. In addition, a mutation of the Y96A variant indicates reduction in the binding affinity for DNA. Free-energy calculations demonstrate the stability of the complex and help identify key residues in various interactions based on residue decomposition analysis. Stability comparative studies between wild type and mutant protein-DNA complexes indicate that the former is relatively more stable than the mutant form. This predicted model could also be useful in designing new inhibitors for UvrB protein, as well as preventing the pathogenesis of H. pylori.

Comparison of Iron-Binding Ability Between Thr70-NapA and Ser70-NapA of Helicobacter pylori

BACKGROUND

The neutrophil-activating protein (NapA) of Helicobacter pylori (H. pylori), with DNA-binding and iron seizing properties, is a fundamental virulence factor involved in H. pylori-related diseases. Compared with Ser70-NapA strain, Thr70-NapA strain is more intimately correlated with iron-deficiency anemia.

METHODS

To investigate whether two types of proteins differ in iron-binding ability, mutated Thr70-NapA and Ser70-NapA strains were established. Isothermal titration calorimetry (ITC) method was conducted to measure the binding between the NapA protein and Fe(2+) . The structural changes of NapA protein were also tested during iron interaction by fast protein liquid chromatography (FPLC) and circular dichroism (CD) methods. DNA-binding assay was performed for evaluate the affinity of both mutated and wild types of NapA with DNA.

RESULTS

Mutated Thr70-NapA had higher iron-binding ability than wild Ser70-NapA. The structural stability of Thr70-NapA was disrupted and became more active along with the rising concentration of Fe(2+) , whereas no similar association was observed between Ser70-NapA and Fe(2+) level. When the iron/protein molar ratio ranged from 10 to 20, both Ser70-NapA and Thr70-NapA displayed weaker DNA-binding ability.

CONCLUSIONS

Thr70-NapA has much stronger ability to sequester ferrous ion compared with Ser70-NapA in H. pylori. In addition, the DNA-binding property of NapA is dependent upon the Fe(2+) concentration.

Helicobacter pylori infection: An overview of bacterial virulence factors and pathogenesis

Helicobacter pylori pathogenesis and disease outcomes are mediated by a complex interplay between bacterial virulence factors, host, and environmental factors. After H. pylori enters the host stomach, four steps are critical for bacteria to establish successful colonization, persistent infection, and disease pathogenesis: (1) Survival in the acidic stomach; (2) movement toward epithelium cells by flagella-mediated motility; (3) attachment to host cells by adhesins/receptors interaction; (4) causing tissue damage by toxin release. Over the past 20 years, the understanding of H. pylori pathogenesis has been improved by studies focusing on the host and bacterial factors through epidemiology researches and molecular mechanism investigations. These include studies identifying the roles of novel virulence factors and their association with different disease outcomes, especially the bacterial adhesins, cag pathogenicity island, and vacuolating cytotoxin. Recently, the development of large-scale screening methods, including proteomic, and transcriptomic tools, has been used to determine the complex gene regulatory networks in H. pylori. In addition, a more available complete genomic database of H. pylori strains isolated from patients with different gastrointestinal diseases worldwide is helpful to characterize this bacterium. This review highlights the key findings of H. pylori virulence factors reported over the past 20 years.

Multiplex H. pylori Serology and Risk of Gastric Cardia and Noncardia Adenocarcinomas

The reported associations with gastric adenocarcinoma and seropositivity to different Helicobacter pylori antigens using multiplex serology have not been consistent across studies. We aimed to investigate the association between 15 different multiplex serology antigens and the risk of gastric cardia (GCA) and gastric noncardia (GNCA) adenocarcinomas in northeastern Iran, a population with high rates of gastric adenocarcinoma. We included 272 cases of gastric adenocarcinoma (142 GCA, 103 GNCA, and 27 unspecified) and 524 controls who were individually matched to cases for age, sex, and place of residence in a population-based case-control study. Seropositivity to H. pylori was assessed using both multiplex serology and H. pylori IgG ELISA. Ninety-five percent of controls were seropositive to H. pylori. Of the 15 antibodies in the multiplex assay, 11 showed no significant association with gastric adenocarcinomas. CagA and VacA were associated with a significantly increased risk of all gastric adenocarcinoma and GNCA in multivariate models. Surprisingly, GroEL and NapA were significantly associated with a reduced risk of these tumors. Only CagA antigen was associated with significantly elevated risk of GCA. We found no associations between H. pylori seropositivity overall either by whole-cell ELISA test or multiplex serology, likely due to the high prevalence of seropositivity. Individual antigen testing showed that CagA positivity was associated with increased risk of both noncardia and cardia adenocarcinoma, which is similar to some other Asian populations, whereas two antigens were associated with lower risk of gastric cancer. This latter result was unexpected and should be retested in other populations.

A ferritin-like protein with antioxidant activity in Ureaplasma urealyticum

Background

Ureaplasma urealyticum is a major pathogen associated with many diseases. The ability of U. urealyticum to protect itself from oxidative stress is likely to be important for its pathogenesis and survival, but its oxidative stress tolerance mechanisms remain unclear. This study investigates the antioxidant activity of a ferritin-like protein from U. urealyticum.

Results

The uuferritin gene, which was up regulated when U. urealyticum was subjected to oxidative stress, was cloned from U. urealyticum and the corresponding recombinant protein uuferritin was purified. Uuferritin protein reduced the levels of hydroxyl radicals generated by the Fenton reaction as a consequence of its ferroxidase activity, and thus the protein protected DNA from oxidative damage. Furthermore, oxidation-sensitive Escherichia coli mutants transformed with pTrc99a-uuferritin showed significantly improved tolerance to oxidative stress compared to E. coli mutants transformed with an empty pTrc99a vector.

Conclusions

The present work shows that uuferritin protein confers resistance to oxidative stress in vitro and in E. coli. The protective role of uuferritin provides a foundation for understanding the mechanisms of oxidative stress tolerance in U. urealyticum.

Structures and metal-binding properties of Helicobacter pylori neutrophil-activating protein with a di-nuclear ferroxidase center

Helicobacter pylori causes severe diseases, such as chronic gastritis, peptic ulcers, and stomach cancers. H. pylori neutrophil-activating protein (HP-NAP) is an iron storage protein that forms a dodecameric shell, promotes the adhesion of neutrophils to endothelial cells, and induces the production of reactive oxygen radicals. HP-NAP belongs to the DNA-protecting proteins under starved conditions (Dps) family, which has significant structural similarities to the dodecameric ferritin family. The crystal structures of the apo form and metal-ion bound forms, such as iron, zinc, and cadmium, of HP-NAP have been determined. This review focused on the structures and metal-binding properties of HP-NAP. These metal ions bind at the di-nuclear ferroxidase center (FOC) by different coordinating patterns. In comparison with the apo structure, metal loading causes a series of conformational changes in conserved residues among HP-NAP and Dps proteins (Trp26, Asp52, and Glu56) at the FOC. HP-NAP forms a spherical dodecamer with 23 symmetry including two kinds of pores. Metal ions have been identified around one of the pores; therefore, the negatively-charged pore is suitable for the passage of metal ions.

At the Bench: Helicobacter pylori, dysregulated host responses, DNA damage, and gastric cancer

Helicobacter pylori infection is the strongest known risk factor for the development of gastric cancer. Given that ∼50% of the global population is infected with this pathogen, there is great impetus to elucidate underlying causes that mediate progression from infection to cancer. Recent evidence suggests that H. pylori-induced chronic inflammation and oxidative stress create an environment conducive to DNA damage and tissue injury. DNA damage leads to genetic instability and eventually, neoplastic transformation. Pathogen-encoded virulence factors induce a robust but futile immune response and alter host pathways that lower the threshold for carcinogenesis, including DNA damage repair, polyamine synthesis and catabolism, antioxidant responses, and cytokine production. Collectively, such dysregulation creates a protumorigenic microenvironment within the stomach. This review seeks to address each of these aspects of H. pylori infection and to call attention to areas of particular interest within this field of research. This review also seeks to prioritize areas of translational research related to H. pylori-induced gastric cancer based on insights garnered from basic research in this field. See related review by Dalal and Moss, At the Bedside: H. pylori, dysregulated host responses, DNA damage, and gastric cancer.

Helicobacter pylori neutrophil-activating protein: From molecular pathogenesis to clinical applications

Helicobacter pylori (H. pylori) neutrophil-activating protein (HP-NAP) was originally identified as a virulence factor of H. pylori for its ability to activate neutrophils to generate respiratory burst by releasing reactive oxygen species. Later on, HP-NAP was also found to be involved in the protection of H. pylori from DNA damage, supporting the survival of H. pylori under oxidative stress. This protein is highly conserved and expressed by virtually all clinical isolates of H. pylori. The majority of patients infected with H. pylori produced antibodies specific for HP-NAP, suggesting its important role in immunity. In addition to acting as a pathogenic factor by activating the innate immunity through a wide range of human leukocytes, including neutrophils, monocytes, and mast cells, HP-NAP also mediates adaptive immunity through the induction of T helper cell type I responses. The pro-inflammatory and immunomodulatory properties of HP-NAP not only make it play an important role in disease pathogenesis but also make it a potential candidate for clinical use. Even though there is no convincing evidence to link HP-NAP to a disease outcome, recent findings supporting the pathogenic role of HP-NAP will be reviewed. In addition, the potential clinical applications of HP-NAP in vaccine development, clinical diagnosis, and drug development will be discussed.

Helicobacter pylori antibody patterns in Germany: a cross-sectional population study

BACKGROUND

Helicobacter pylori infection that is usually acquired in childhood and lasts for lifetime is mostly asymptomatic but associated with severe gastrointestinal disease including cancer. During chronic infection, the gastric mucosa is histologically changing. This forces H. pylori to permanent adaptation in its gastric habitat by expression of different proteins which might be reflected in distinctive antibody patterns.

METHODS

To characterize dynamics of the immune response to H. pylori we analysed 1797 sera of a cross-sectional study representative for the German population (age range 1-82 years) with multiplex serology, a fluorescent bead-based antibody binding assay that allows simultaneous and quantitative detection of antibodies. Fifteen recombinant, affinity-purified H. pylori proteins (UreA, GroEL, Catalase, NapA, CagA, CagM, Cagδ, HP0231, VacA, HpaA, Cad, HyuA, Omp, HcpC and HP0305) were used as antigens.

RESULTS

H. pylori seroprevalence (positivity for at least three antigens) was 48% and increased with age from 12% in children <15 years to 69% in females and 90% in males >65 years. Prevalences were highest (>83%) for Omp, VacA and GroEL. For 11 proteins, seroprevalence was higher in males than females (P < 0.05) from age 55 onwards. For all antigens, the median prevalence increase per age decade was stronger in males (8.4%, range 3.8-12.9%) than females (6.1%, range 3.4-10.8%). However, among seropositives the median number of antigens recognized increased from children <15 years to individuals >65 years stronger in females (P = 0.02). Antibody reactivities to GroEL, HyuA, CagM, Catalase, NapA and UreA also increased stronger in females (average 1.7-fold/decade, SD 0.5) than in males (1.5-fold/decade, SD 0.4).

CONCLUSION

H. pylori antibody response accumulates qualitatively and quantitatively with age. This may reflect a lifelong stimulation of the immune response by chronically active infection.

Chronic inflammation and oxidative stress: the smoking gun for Helicobacter pylori-induced gastric cancer?

Helicobacter pylori is the leading risk factor associated with gastric carcinogenesis. H. pylori leads to chronic inflammation because of the failure of the host to eradicate the infection. Chronic inflammation leads to oxidative stress, deriving from immune cells and from within gastric epithelial cells. This is a main contributor to DNA damage, apoptosis and neoplastic transformation. Both pathogen and host factors directly contribute to oxidative stress, including H. pylori virulence factors, and pathways involving DNA damage and repair, polyamine synthesis and metabolism, and oxidative stress response. Our laboratory has recently uncovered a mechanism by which polyamine oxidation by spermine oxidase causes H 2O 2 release, DNA damage and apoptosis. Our studies indicate novel targets for therapeutic intervention and risk assessment in H. pylori-induced gastric cancer. More studies addressing the many potential contributors to oxidative stress, chronic inflammation, and gastric carcinogenesis are essential for development of therapeutics and identification of gastric cancer biomarkers.

Proteome variability among Helicobacter pylori isolates clustered according to genomic methylation

AIMS

To understand whether the variability found in the proteome of Helicobacter pylori relates to the genomic methylation, virulence and associated gastric disease.

METHODS AND RESULTS

We applied the Minimum-Common-Restriction-Modification (MCRM) algorithm to genomic methylation data of 30 Portuguese H. pylori strains, obtained by genome sensitivity to Type II restriction enzymes' digestion. All the generated dendrograms presented three clusters with no association with gastric disease. Comparative analysis of two-dimensional gel electrophoresis (2DE) maps obtained for total protein extracts of 10 of these strains, representative of the three main clusters, revealed that among 70 matched protein spots (in a universe of 300), 16 were differently abundant (P < 0·05) among clusters. Of these, 13 proteins appear to be related to the cagA genotype or gastric disease. The abundance of three protein species, DnaK, GlnA and HylB, appeared to be dictated by the methylation status of their gene promoter.

CONCLUSIONS

Variations in the proteome profile of strains with common geographic origin appear to be related to differences in cagA genotype or gastric disease, rather than to clusters organized according to strain genomic methylation.

SIGNIFICANCE AND IMPACT OF THE STUDY

The simultaneous study of the genomic methylation and proteome is important to correlate epigenetic modifications with gene expression and pathogen virulence.

Campylobacter jejuni Dps protein binds DNA in the presence of iron or hydrogen peroxide

Iron is an essential cofactor for many enzymes; however, this metal can lead to the formation of reactive oxygen species. Ferritin proteins bind and oxidize Fe(2+) to Fe(3+), storing this metal in a nonreactive form. In some organisms, a particular subfamily of ferritins, namely, Dps proteins, have the ability to bind DNA. Here we show that the Campylobacter jejuni Dps has DNA binding activity that is uniquely activated by Fe(2+) or H2O2 at below neutral pH. The Dps-DNA binding activity correlated with the ability of Dps to self-aggregate. The Dps-DNA interaction was inhibited by NaCl and Mg(2+), suggesting the formation of ionic interactions between Dps and DNA. Alkylation of cysteines affected DNA binding in the presence of H2O2 but not in the presence of Fe(2+). Replacement of all cysteines in C. jejuni Dps with serines did not affect DNA binding, excluding the participation of cysteine in H2O2 sensing. Dps was able to protect DNA in vitro from enzymatic cleavage and damage by hydroxyl radicals. A C. jejuni dps mutant was less resistant to H2O2 in vivo. The concerted activation of Dps-DNA binding in response to low pH, H2O2, and Fe(2+) may protect C. jejuni DNA during host colonization.

Up-regulation of neutrophil activating protein in Helicobacter pylori under high-salt stress: structural and phylogenetic comparison with bacterial iron-binding ferritins

It is generally accepted that most gastrointestinal diseases are probably caused by the bacterial pathogen Helicobacter pylori (H. pylori). In this study we have focused on the comparison of protein expression profiles of H. pylori grown under normal and high-salt conditions by a proteomics approach. We have identified about 190 proteins whose expression levels changed after growth at high salt concentration. Among these proteins, neutrophil-activating protein (NapA) was found to be consistently up-regulated under osmotic stress brought by high salts. We have investigated the effect of high salt on secondary and tertiary structures of NapA by circular dichroism spectroscopy followed by analytical ultracentrifugation to monitor the change of quaternary structure of recombinant NapA with increasing salt concentration. The loss of iron-binding activity of NapA coupled with noticeable energetic variation in protein association of NapA as revealed by isothermal titration calorimetry was found under high salt condition. The phylogenetic tree analysis based on sequence comparison of 16 protein sequences encompassing NapA proteins and ferritin of H. pylori and other prokaryotic organisms pointed to the fact that all H. pylori NapA proteins of human origin are more homologous to NapA of Helicobacter genus than to other bacterial NapA. Based on computer modeling, NapA proteins from H. pylori of human isolates are found more similar to ferritin from H. pylori than to NapA from other species of bacteria. Taken together, these results suggested that divergent evolution of NapA and ferritin possessing dissimilar and diverse sequences follows a path distinct from that of convergent evolution of NapA and ferritin with similar dual functionality of iron-binding and ferroxidase activities.

Helicobacter pylori peptidoglycan modifications confer lysozyme resistance and contribute to survival in the host

The prominent host muramidase lysozyme cleaves bacterial peptidoglycan (PG), and the enzyme is abundant in mucosal secretions. The lytic enzyme susceptibility of Gram-negative bacteria and mechanisms they use to thwart lytic enzyme activity are poorly studied. We previously characterized a Helicobacter pylori PG modification enzyme, an N-deacetylase (PgdA) involved in lysozyme resistance. In this study, another PG modification enzyme, a putative PG O-acetyltransferase (PatA), was identified. Mass spectral analysis of the purified PG demonstrated that a patA strain contained a greatly reduced amount of acetylated muropeptides, indicating a role for PatA in H. pylori PG O-acetylation. The PG modification mutant strains (pgdA, patA, or pgdA patA) were more susceptible to lysozyme killing than the parent, but this assay required high lysozyme levels (up to 50 mg/ml). However, addition of host lactoferrin conferred lysozyme sensitivity to H. pylori, at physiologically relevant concentrations of both host components (3 mg/ml lactoferrin plus 0.3 mg/ml lysozyme). The pgdA patA double mutant strain was far more susceptible to lysozyme/lactoferrin killing than the parent. Peptidoglycan purified from a pgdA patA mutant was five times more sensitive to lysozyme than PG from the parent strain, while PG from both single mutants displayed intermediate sensitivity. Both sensitivity assays for whole cells and for purified PGs indicated that the modifications mediated by PgdA and PatA have a synergistic effect, conferring lysozyme tolerance. In a mouse infection model, significant colonization deficiency was observed for the double mutant at 3 weeks postinoculation. The results show that PG modifications affect the survival of a Gram-negative pathogen.

Importance Pathogenic bacteria evade host antibacterial enzymes by a variety of mechanisms, which include resisting lytic enzymes abundant in the host. Enzymatic modifications to peptidoglycan (PG, the site of action of lysozyme) are a known mechanism used by Gram-positive bacteria to protect against host lysozyme attack. However, Gram-negative bacteria contain a thin layer of PG and a recalcitrant outer membrane permeability barrier to resist lysis, so molecular modifications to cell wall structure in order to combat lysis remain largely unstudied. Here we show that two Helicobacter pylori PG modification enzymes (PgdA and PatA) confer a clear protective advantage to a Gram-negative bacterium. They protect the bacterium from lytic enzyme degradation, albeit via different PG modification activities. Many pathogens are Gram negative, so some would be expected to have a similar cell wall-modifying strategy. Understanding such strategies may be useful for combating pathogen growth.

Pathogenic bacteria evade host antibacterial enzymes by a variety of mechanisms, which include resisting lytic enzymes abundant in the host. Enzymatic modifications to peptidoglycan (PG, the site of action of lysozyme) are a known mechanism used by Gram-positive bacteria to protect against host lysozyme attack. However, Gram-negative bacteria contain a thin layer of PG and a recalcitrant outer membrane permeability barrier to resist lysis, so molecular modifications to cell wall structure in order to combat lysis remain largely unstudied. Here we show that two Helicobacter pylori PG modification enzymes (PgdA and PatA) confer a clear protective advantage to a Gram-negative bacterium. They protect the bacterium from lytic enzyme degradation, albeit via different PG modification activities. Many pathogens are Gram negative, so some would be expected to have a similar cell wall-modifying strategy. Understanding such strategies may be useful for combating pathogen growth.

A histone-like protein of Helicobacter pylori protects DNA from stress damage and aids host colonization

Genomic DNA in a bacterial cell is folded into a compact structure called a nucleoid, and nucleoid-associated proteins are responsible for proper assembly of active higher-order genome structures. The human gastric pathogen Helicobacter pylori express a nucleoid-associated protein encoded by the hup gene, which is the homolog to the Escherichia coli histone-like protein HU. An H. pylori hup mutant strain (X47 hup:cat) showed a defect in stationary phase survival. The X47 hup:cat mutant was more sensitive to the DNA damaging agent mitomycin C, and displayed a decreased frequency of DNA recombination, indicating Hup plays a significant role in facilitating DNA recombinational repair. The X47 hup:cat mutant was also sensitive to both oxidative and acid stress, conditions that H. pylori commonly encounters in the host. The hup mutant cells survived significantly (7-fold) less upon exposure to macrophages than the wild type strain. In a mouse infection model, the hup mutant strain displayed a greatly reduced ability to colonize host stomachs. The geometric means of colonization number for the wild type and hup mutant were 6×10(5) and 1.5×10(4)CFU/g stomachs, respectively. Complementation of the hup strain by chromosomal insertion of a functional hup gene restored oxidative stress resistance, DNA transformation frequency, and mouse colonization ability to the wild type level. We directly demonstrated that the purified His-tagged H. pylori Hup protein can protect (in vitro) an H. pylori-derived DNA fragment from oxidative damage.

Crystal structure of Helicobacter pylori neutrophil-activating protein with a di-nuclear ferroxidase center in a zinc or cadmium-bound form

Helicobacter pylori neutrophil-activating protein (HP-NAP) is a Dps-like iron storage protein forming a dodecameric shell, and promotes adhesion of neutrophils to endothelial cells. The crystal structure of HP-NAP in a Zn(2+)- or Cd(2+)-bound form reveals the binding of two zinc or two cadmium ions and their bridged water molecule at the ferroxidase center (FOC). The two zinc ions are coordinated in a tetrahedral manner to the conserved residues among HP-NAP and Dps proteins. The two cadmium ions are coordinated in a trigonal-bipyramidal and distorted octahedral manner. In both structures, the second ion is more weakly coordinated than the first. Another zinc ion is found inside of the negatively-charged threefold-related pore, which is suitable for metal ions to pass through.

Helicobacter pylori defense against oxidative attack

Helicobacter pylori is a microaerophilic, gram-negative pathogen of the human stomach. Despite the chronic active gastritis that develops following colonization, H. pylori is able to persist unharmed in the stomach for decades. Much of the damage caused by gastric inflammation results from the accumulation of reactive oxygen/nitrogen species within the stomach environment, which can induce oxidative damage in a wide range of biological molecules. Without appropriate defenses, this oxidative damage would be able to rapidly kill nearby H. pylori, but the organism employs a range of measures, including antioxidant enzymes, biological repair systems, and inhibitors of oxidant generation, to counter the attack. Despite the variety of measures employed to defend against oxidative injury, these processes are intimately interdependent, and any deficiency within the antioxidant system is generally sufficient to cause substantial impairment of H. pylori viability and persistence. This review provides an overview of the development of oxidative stress during H. pylori gastritis and examines the methods the organism uses to survive the resultant damage.

The iron-binding protein Dps2 confers peroxide stress resistance on Bacillus anthracis

Iron is an essential nutrient that is implicated in most cellular oxidation reactions. However, iron is a highly reactive element that, if not appropriately chaperoned, can react with endogenously and exogenously generated oxidants such as hydrogen peroxide to generate highly toxic hydroxyl radicals. Dps proteins (DNA-binding proteins from starved cells) form a distinct class (the miniferritins) of iron-binding proteins within the ferritin superfamily. Bacillus anthracis encodes two Dps-like proteins, Dps1 and Dps2, the latter being one of the main iron-containing proteins in the cytoplasm. In this study, the function of Dps2 was characterized in vivo. A B. anthracis Δdps2 mutant was constructed by double-crossover mutagenesis. The growth of the Δdps2 mutant was unaffected by excess iron or iron-limiting conditions, indicating that the primary role of Dps2 is not that of iron sequestration and storage. However, the Δdps2 mutant was highly sensitive to H(2)O(2), and pretreatment of the cells with the iron chelator deferoxamine mesylate (DFM) significantly reduced its sensitivity to H(2)O(2) stress. In addition, the transcription of dps2 was upregulated by H(2)O(2) treatment and derepressed in a perR mutant, indicating that dps2 is a member of the regulon controlled by the PerR regulator. This indicates that the main role of Dps2 is to protect cells from peroxide stress by inhibiting the iron-catalyzed production of OH.

Ulcerogenic Helicobacter pylori strains isolated from children: a contribution to get insight into the virulence of the bacteria

Infection with Helicobacter pylori is the major cause for the development of peptic ulcer disease (PUD). In children, with no other etiology for the disease, this rare event occurs shortly after infection. In these young patients, habits of smoking, diet, consumption of alcohol and non-steroid anti-inflammatory drugs and stress, in addition to the genetic susceptibility of the patient, represent a minor influence. Accordingly, the virulence of the implicated H. pylori strain should play a crucial role in the development of PUD. Corroborating this, our in vitro infection assays comparing a pool of five H. pylori strains isolated from children with PUD to a pool of five other pediatric clinical isolates associated with non-ulcer dyspepsia (NUD) showed the greater ability of PUD strains to induce a marked decrease in the viability of gastric cells and to cause severe damage in the cells cytoskeleton as well as an impairment in the production/secretion of mucins. To uncover virulence features, we compared the proteome of these two groups of H. pylori strains. Two-dimensional gel electrophoresis followed by mass-spectrometry allowed us to detect 27 differentially expressed proteins between them. In addition to the presence of genes encoding well established virulence factors, namely cagA, vacAs1, oipA “on” status, homB and jhp562 genes, the pediatric ulcerogenic strains shared a proteome profile characterized by changes in the abundance of: motility-associated proteins, accounting for higher motility; antioxidant proteins, which may confer increased resistance to inflammation; and enzymes involved in key steps in the metabolism of glucose, amino acids and urea, which may be advantageous to face fluctuations of nutrients. In conclusion, the enhanced virulence of the pediatric ulcerogenic H. pylori strains may result from a synergy between their natural ability to better adapt to the hostile human stomach and the expression of the established virulence factors.

Change is good: variations in common biological mechanisms in the epsilonproteobacterial genera Campylobacter and Helicobacter

Microbial evolution and subsequent species diversification enable bacterial organisms to perform common biological processes by a variety of means. The epsilonproteobacteria are a diverse class of prokaryotes that thrive in diverse habitats. Many of these environmental niches are labeled as extreme, whereas other niches include various sites within human, animal, and insect hosts. Some epsilonproteobacteria, such as Campylobacter jejuni and Helicobacter pylori, are common pathogens of humans that inhabit specific regions of the gastrointestinal tract. As such, the biological processes of pathogenic Campylobacter and Helicobacter spp. are often modeled after those of common enteric pathogens such as Salmonella spp. and Escherichia coli. While many exquisite biological mechanisms involving biochemical processes, genetic regulatory pathways, and pathogenesis of disease have been elucidated from studies of Salmonella spp. and E. coli, these paradigms often do not apply to the same processes in the epsilonproteobacteria. Instead, these bacteria often display extensive variation in common biological mechanisms relative to those of other prototypical bacteria. In this review, five biological processes of commonly studied model bacterial species are compared to those of the epsilonproteobacteria C. jejuni and H. pylori. Distinct differences in the processes of flagellar biosynthesis, DNA uptake and recombination, iron homeostasis, interaction with epithelial cells, and protein glycosylation are highlighted. Collectively, these studies support a broader view of the vast repertoire of biological mechanisms employed by bacteria and suggest that future studies of the epsilonproteobacteria will continue to provide novel and interesting information regarding prokaryotic cellular biology.