Histidine-rich protein Hpn from Helicobacter pylori forms amyloid-like fibrils in vitro and inhibits the proliferation of gastric epithelial AGS cells

The mechanisms of metronidazole resistance of Helicobacter pylori: A transcriptomic and biochemical study

Helicobacter pylori (H. pylori) is a bacterial pathogen in the stomach, causing gastritis, gastric ulcer, duodenal ulcer and even gastric cancer. The triple therapy containing one bismuth-containing compound or a proton-pump inhibitor with two antibiotics was the cornerstone of the treatment of H. pylori infections. However the drug resistance of Helicobacter pylori is more and more common, which leads to the continued decline in the radical cure rate. The purpose of this study was to investigate the mechanism of metronidazole resistance of H. pylori through transcriptomics and biochemical characterizations. In this study, a 128-time-higher metronidazole-resistant H. pylori strain compared to the sensitive strain was domesticated, and 374 significantly differential genes were identified by transcriptomic sequencing as compared to the metronidazole-sensitive strain. Through GO and KEGG enrichment analysis, antibiotic-resistance pathways were found to be mainly involved in redox, biofilm formation and ABC transportation, and the results were verified by qRT-PCR. The subsequent biochemical analysis found that the urease activity of the drug-resistant strain decreased, and whereas the capabilities of bacterial energy production, membrane production and diffusion ability increased. The work here will drop hints for the mechanisms of antibiotic-resistance of H. pylori and provide promising biomarkers for the further development of new-kind drugs to treat metronidazole-resistant H. pylori.

In vitro transcytosis of Helicobacter pylori histidine-rich protein through gastric epithelial-like cells and the blood-brain barrier

Recent epidemiological studies have supported the correlation between Helicobacter pylori infection and the development of Alzheimer's disease. HpHpn, a histidine-rich H. pylori protein, forms amyloid-like oligomers; it may be a pathogenic factor for Alzheimer's disease progression. HpHpn may also be transported from the gastric epithelium to the brain. However, HpHpn is secreted from H. pylori on the outer surface of gastric epithelia; therefore, the hypothesized movement of HpHpn across the gastric epithelium to the blood remains controversial. Here, we found the HpHpn showed acidic pH-dependent cellular uptake and subsequent secretion in human gastric epithelial-like carcinoma cells. Furthermore, HpHpn exhibited in vitro permeability across the blood-brain barrier. Although further in vivo experiments are required, our findings suggest that in vitro transcytosis of HpHpn in gastric epithelial cells and the blood-brain barrier may provide new insights into the correlation between H. pylori infections and Alzheimer's disease progression.

Nickel, an essential virulence determinant of Helicobacter pylori: Transport and trafficking pathways and their targeting by bismuth

Metal acquisition and intracellular trafficking are crucial for all cells and metal ions have been recognized as virulence determinants in bacterial pathogens. Nickel is required for the pathogenicity of H. pylori. This bacterial pathogen colonizes the stomach of about half of the human population worldwide and is associated with gastric cancer that is responsible for 800,000 deaths per year. H. pylori possesses two nickel-enzymes that are essential for in vivo colonization, a [NiFe] hydrogenase and an abundant urease responsible for resistance to gastric acidity. Because of these two enzymes, survival of H. pylori relies on an important supply of nickel, implying tight control strategies to avoid its toxic accumulation or deprivation. H. pylori possesses original mechanisms for nickel uptake, distribution, storage and trafficking that will be discussed in this review. During evolution, acquisition of nickel transporters and specific nickel-binding proteins has been a decisive event to allow Helicobacter species to become able to colonize the stomach. Accordingly, many of the factors involved in these mechanisms are required for mouse colonization by H. pylori. These mechanisms are controlled at different levels including protein interaction networks, transcriptional, post-transcriptional and post-translational regulation. Bismuth is another metal used in combination with antibiotics to efficiently treat H. pylori infections. Although the precise mode of action of bismuth is unknown, many targets have been identified in H. pylori and there is growing evidence that bismuth interferes with the essential nickel pathways. Understanding the metal pathways will help improve treatments against H. pylori and other pathogens.

The nickel-chelator dimethylglyoxime inhibits human amyloid beta peptide in vitro aggregation

One of the hallmarks of the most common neurodegenerative disease, Alzheimer's disease (AD), is the extracellular deposition and aggregation of Amyloid Beta (Aβ)-peptides in the brain. Previous studies have shown that select metal ions, most specifically copper (Cu) and zinc (Zn) ions, have a synergistic effect on the aggregation of Aβ-peptides. In the present study, inductively coupled plasma mass spectrometry (ICP-MS) was used to determine the metal content of a commercial recombinant human Aβ40 peptide. Cu and Zn were among the metals detected; unexpectedly, nickel (Ni) was one of the most abundant elements. Using a fluorescence-based assay, we found that Aβ40 peptide in vitro aggregation was enhanced by addition of Zn2+ and Ni2+, and Ni2+-induced aggregation was facilitated by acidic conditions. Nickel binding to Aβ40 peptide was confirmed by isothermal titration calorimetry. Addition of the Ni-specific chelator dimethylglyoxime (DMG) inhibited Aβ40 aggregation in absence of added metal, as well as in presence of Cu2+ and Ni2+, but not in presence of Zn2+. Finally, mass spectrometry analysis revealed that DMG can coordinate Cu or Ni, but not Fe, Se or Zn. Taken together, our results indicate that Ni2+ ions enhance, whereas nickel chelation inhibits, Aβ peptide in vitro aggregation. Hence, DMG-mediated Ni-chelation constitutes a promising approach towards inhibiting or slowing down Aβ40 aggregation.

Mixed Borrelia burgdorferi and Helicobacter pylori Biofilms in Morgellons Disease Dermatological Specimens

BACKGROUND

Morgellons disease (MD) is a dermopathy that is associated with tick-borne illness. It is characterized by spontaneously developing skin lesions containing embedded or projecting filaments, and patients may also experience symptoms resembling those of Lyme disease (LD) including musculoskeletal, neurological and cardiovascular manifestations. Various species of Borrelia and co-infecting pathogens have been detected in body fluids and tissue specimens from MD patients. We sought to investigate the coexistence of Borrelia burgdorferi (Bb) and Helicobacter pylori (Hp) in skin specimens from MD subjects, and to characterize their association with mixed amyloid biofilm development.

METHODS

Testing for Bb and Hp was performed on dermatological specimens from 14 MD patients using tissue culture, immunohistochemical (IHC) staining, polymerase chain reaction (PCR) testing, fluorescent in situ hybridization (FISH) and confocal microscopy. Markers for amyloid and biofilm formation were investigated using histochemical and IHC staining.

RESULTS

Bb and Hp were detected in dermatological tissue taken from MD lesions. Bb and Hp tended to co-localize in foci within the epithelial tissue. Skin sections exhibiting foci of co-infecting Bb and Hp contained amyloid markers including β-amyloid protein, thioflavin and phosphorylated tau. The biofilm marker alginate was also found in the sections.

CONCLUSIONS

Mixed Bb and Hp biofilms containing β-amyloid and phosphorylated tau may play a role in the evolution of MD.

Ubiquitin specific peptidase 5 mediates Histidine-rich protein Hpn induced cell apoptosis in hepatocellular carcinoma through P14-P53 signaling

Hpn is a small histidine-rich cytoplasmic protein from Helicobacter pylori and has been recognized as a high-risk factor for several cancers including gastric cancer, colorectal cancer, and MALT lymphoma. However, the relationship between Hpn and cancers remains elusive. In this study, we discovered that Hpn protein effectively suppressed cell growth and induced apoptosis in hepatocellular carcinoma (HCC). A two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomics was performed to find the molecular targets of Hpn in HCC cells. It was identified that twelve proteins were differentially expressed, with USP5 being one of the most significantly downregulated protein. The P14^ARF -P53 signaling was activated by USP5 knockdown in HCC cells. Furthermore, USP5 overexpression significantly rescued the suppressive effect of Hpn on the viability of HCC cells. In conclusion, our study suggests that Hpn plays apoptosis-inducing roles through suppressing USP5 expression and activating the P14^ARF -P53 signaling. Therefore, Hpn may be a potential candidate for developing novel anti-HCC drugs.

Modification of drug delivery to improve antibiotic targeting to the stomach

The obstacles to the successful eradication of Helicobacter pylori infections include the presence of antibiotic-resistant bacteria and therapy requiring multiple drugs with complicated dosing schedules. Other obstacles include bacterial residence in an environment where high antibiotic concentrations are difficult to achieve. Biofilm production by the bacteria is an additional challenge to the effective treatment of this infection. Conventional oral formulations used in the treatment of this infection have a short gastric residence time, thus limiting the duration of exposure of drug to the bacteria. This review summarizes the current research in the development of gastroretentive formulations and the prospective future applications of this approach in the targeted delivery of drugs such as antibiotics to the stomach.

Evolution of Helicobacter: Acquisition by Gastric Species of Two Histidine-Rich Proteins Essential for Colonization

Metal acquisition and intracellular trafficking are crucial for all cells and metal ions have been recognized as virulence determinants in bacterial pathogens. Virulence of the human gastric pathogen Helicobacter pylori is dependent on nickel, cofactor of two enzymes essential for in vivo colonization, urease and [NiFe] hydrogenase. We found that two small paralogous nickel-binding proteins with high content in Histidine (Hpn and Hpn-2) play a central role in maintaining non-toxic intracellular nickel content and in controlling its intracellular trafficking. Measurements of metal resistance, intracellular nickel contents, urease activities and interactomic analysis were performed. We observed that Hpn acts as a nickel-sequestration protein, while Hpn-2 is not. In vivo, Hpn and Hpn-2 form homo-multimers, interact with each other, Hpn interacts with the UreA urease subunit while Hpn and Hpn-2 interact with the HypAB hydrogenase maturation proteins. In addition, Hpn-2 is directly or indirectly restricting urease activity while Hpn is required for full urease activation. Based on these data, we present a model where Hpn and Hpn-2 participate in a common pathway of controlled nickel transfer to urease. Using bioinformatics and top-down proteomics to identify the predicted proteins, we established that Hpn-2 is only expressed by H. pylori and its closely related species Helicobacter acinonychis. Hpn was detected in every gastric Helicobacter species tested and is absent from the enterohepatic Helicobacter species. Our phylogenomic analysis revealed that Hpn acquisition was concomitant with the specialization of Helicobacter to colonization of the gastric environment and the duplication at the origin of hpn-2 occurred in the common ancestor of H. pylori and H. acinonychis. Finally, Hpn and Hpn-2 were found to be required for colonization of the mouse model by H. pylori. Our data show that during evolution of the Helicobacter genus, acquisition of Hpn and Hpn-2 by gastric Helicobacter species constituted a decisive evolutionary event to allow Helicobacter to colonize the hostile gastric environment, in which no other bacteria persistently thrives. This acquisition was key for the emergence of one of the most successful bacterial pathogens, H. pylori.

Helicobacter pylori is a bacterium that persistently colonizes the stomach of half of the human population. Infection by H. pylori is associated with gastritis, peptic ulcer disease and adenocarcinoma. To resist gastric acidity and proliferate in the stomach, H. pylori relies on urease, an enzyme that contains a nickel-metallocenter at its active site. Thus, nickel is a virulence determinant for H. pylori. Our aim is to characterize how H. pylori controls the intracellular nickel concentration to avoid toxicity, which protein partners are involved, and how they impact urease activity and virulence. We characterized two H. pylori proteins, Hpn and Hpn-2 that are rich in Histidine residues. We demonstrated that Hpn is involved in nickel sequestration, that the two proteins interact with each other and that their combined activities participate in a nickel transfer pathway to urease. Hpn is only expressed in gastric Helicobacter species able to colonize the stomach and Hpn-2 is restricted to the H. pylori and its close relative H. acinonychis. We found that both proteins are essential for colonization of a mouse model by H. pylori. We conclude that during evolution, the acquisition of Hpn and Hpn-2 by gastric Helicobacter species was decisive for their capacity to colonize the stomach.

Beyond the stomach: An updated view of Helicobacter pylori pathogenesis, diagnosis, and treatment

Helicobacter pylori (H. pylori) is an extremely common, yet underappreciated, pathogen that is able to alter host physiology and subvert the host immune response, allowing it to persist for the life of the host. H. pylori is the primary cause of peptic ulcers and gastric cancer. In the United States, the annual cost associated with peptic ulcer disease is estimated to be $6 billion and gastric cancer kills over 700000 people per year globally. The prevalence of H. pylori infection remains high (> 50%) in much of the world, although the infection rates are dropping in some developed nations. The drop in H. pylori prevalence could be a double-edged sword, reducing the incidence of gastric diseases while increasing the risk of allergies and esophageal diseases. The list of diseases potentially caused by H. pylori continues to grow; however, mechanistic explanations of how H. pylori could contribute to extragastric diseases lag far behind clinical studies. A number of host factors and H. pylori virulence factors act in concert to determine which individuals are at the highest risk of disease. These include bacterial cytotoxins and polymorphisms in host genes responsible for directing the immune response. This review discusses the latest advances in H. pylori pathogenesis, diagnosis, and treatment. Up-to-date information on correlations between H. pylori and extragastric diseases is also provided.

The interaction of a histidine-rich protein hpn with the membrane mimics: implications for pathologic roles of Hpn in Helicobacter pylori

BACKGROUND

Hpn is a small histidine-rich protein in Helicobacter pylori. This protein has been shown to play roles in nickel storage and detoxification and to exhibit cytotoxicity to gastric epithelial cells. Hpn can be secreted outside of the bacterium and forms amyloid-like structures.

OBJECTIVE

To study the interactions between Hpn and membrane mimics, which may further our understanding of the pathologic roles of this bacterium.

METHODS

Various biochemical and biophysical methods, such as secondary structure determination be CD, calcein release assay with fluorescence spectrometry, and Laurdan and Prodan generalized polarization determination have been used to characterize the interaction between Hpn and membrane mimics.

RESULTS

Membrane mimics induced the formation of α-helix in Hpn. The interaction disrupts the integrity of the membrane mimics and leads to the release of inner calcein probe. The experiments involving the Laurdan and Prodan fluorescence indicated that increasing the total protein/lipid ratio leads to a less ordered and more hydrated lipid membrane structure close to the water/lipid interface of lipid bilayers modeling the mitochondrial inner membrane.

CONCLUSION

The present data indicated that Hpn may take part in the pathological roles of Helicobacter pylori through membrane interactions.

Common themes and unique proteins for the uptake and trafficking of nickel, a metal essential for the virulence of Helicobacter pylori

Nickel is a virulence determinant for the human gastric pathogen Helicobacter pylori. Indeed, H. pylori possesses two nickel-enzymes that are essential for in vivo colonization, [NiFe] hydrogenase and urease, an abundant virulence factor that contains 24 nickel ions per active complex. Because of these two enzymes, survival of H. pylori relies on an important supply of nickel, implying a tight control of its distribution and storage. In this review, we will present the pathways of activation of the nickel enzymes as well as original mechanisms found in H. pylori for the uptake, trafficking and distribution of nickel between the two enzymes. These include (i) an outer-membrane nickel uptake system, the FrpB4 TonB-dependent transporter, (ii) overlapping protein complexes and interaction networks involved in nickel trafficking and distribution between urease and hydrogenase and, (iii) Helicobacter specific nickel-binding proteins that are involved in nickel storage and can play the role of metallo-chaperones. Finally, we will discuss the implication of the nickel trafficking partners in virulence and propose them as novel therapeutic targets for treatments against H. pylori infection.

Nickel trafficking system responsible for urease maturation in Helicobacter pylori

Helicobacter pylori (H. pylori) is a common human pathogen responsible for various gastric diseases. This bacterium relies on the production of urease and hydrogenase to inhabit the acidic environment of the stomach. Nickel is an essential cofactor for urease and hydrogenase. H. pylori has to uptake sufficient nickel ions for the maturation of urease, and on the other way, to prevent the toxic effects of excessive nickel ions. Therefore, H. pylori has to strike a delicate balance between the import of nickel ions, its efficient intracellular storage, and delivery to nickel-dependent metalloenzymes when required. The assembly and maturation of the urease enzyme is a complex and timely ordered process, requiring various regulatory, uptake, chaperone and accessory proteins. In this review, we focus on several nickel trafficking proteins involved in urease maturation: NikR, NixA, HypAB, UreEFGH, HspA, Hpn and Hpnl. The work will deepen our understanding of how this pathogenic bacterium adapts to severe habitant environments in the host.

Inhibition of Helicobacter pylori urease activity in vivo by the synthetic nickel binding protein Hpn

Helicobacter pylori infection is the most common cause of gastroduodenal ulcerations worldwide. Adaptation of H. pylori to the acidic environment is mediated by urease splitting urea into carbon dioxide and ammonia. Whereas neutralization of acid by ammonia is essential for gastric H. pylori colonization, the catalytic activity of urease is mediated by nickel ions. Therefore, nickel uptake and metabolism play key roles in H. pylori infection and urease is considered first line target for drug development and vaccination. Since nickel binding within H. pylori cells is mediated by the Histidine-rich protein designated Hpn, we investigated whether nickel binding by a synthetic Hpn is capable of abrogating urease activity of live H. pylori in liquid cultures. Supplementation of growth media with synthetic Hpn completely inhibited urease acitivity in live cells, indicating that H. pylori nickel uptake is effectively blocked by Hpn. Thus, nickel chelation by Hpn is stronger than nickel uptake of H. pylori offering therapeutic use of Hpn. Although the nickel binding of Hpn was confirmed by binding assays in vitro, its use in anti-H. pylori directed strategy will further need to be adapted to the gastric environment given that protons interfere with nickel binding and Hpn is degraded by pepsin.

The in vivo functions of a histidine-rich protein Hpn in Helicobacter pylori: linking gastric and Alzheimer's diseases together?

Helicobacter pylori causes such gastric diseases as gastritis, peptic ulcerations, gastric cancer and MALT lymphoma. Hpn is a histidine-rich protein abundant in this bacterium and forms amyloid-like oligomers in physiologically relevant conditions. Here we proposed the in vivo functions of this protein with relevance to its physical locations. The collective evidence presented here shed some light on the pathologic mechanisms of H. pylori infections, with emphasis on the bacterial colonization in the gastric environment, pathological effects to the gastric epithelial cells and the possible link to Alzheimer's disease.