Alkylhydroperoxide reductase of Helicobacter pylori as a biomarker for gastric patients with different pathological manifestations

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.

Proteomic Applications in Antimicrobial Resistance and Clinical Microbiology Studies

Sequences of the genomes of all-important bacterial pathogens of man, plants, and animals have been completed. Still, it is not enough to achieve complete information of all the mechanisms controlling the biological processes of an organism. Along with all advances in different proteomics technologies, proteomics has completed our knowledge of biological processes all around the world. Proteomics is a valuable technique to explain the complement of proteins in any organism. One of the fields that has been notably benefited from other systems approaches is bacterial pathogenesis. An emerging field is to use proteomics to examine the infectious agents in terms of, among many, the response the host and pathogen to the infection process, which leads to a deeper knowledge of the mechanisms of bacterial virulence. This trend also enables us to identify quantitative measurements for proteins extracted from microorganisms. The present review study is an attempt to summarize a variety of different proteomic techniques and advances. The significant applications in bacterial pathogenesis studies are also covered. Moreover, the areas where proteomics may lead the future studies are introduced.

Immunization with alkyl hydroperoxide reductase subunit C reduces Fusobacterium nucleatum load in the intestinal tract

Fusobacterium nucleatum (Fn) is an important tumour-associated bacterium in colorectal cancer (CRC). The antioxidant protein alkyl hydroperoxide reductase subunit C (AhpC) can induce strong antibacterial immune response during various pathogen infections. Our study aimed to evaluate the efficacy of Fn-AhpC as a candidate vaccine. In this work, by western blot analysis, we showed that Fn-AhpC recombinant protein could be recognized specifically by antibodies present in the sera of CRC patients; using the mouse Fn-infection model, we observed that systemic prophylactic immunization with AhpC/alum conferred significant protection against infection in 77.3% of mice. In addition, we measured the anti-AhpC antibody level in the sera of CRC patients and found that there was no obvious increase of anti-AhpC antibodies in the early-stage CRC group. Furthermore, we treated Fn with the sera from both immunized mice and CRC patients and found that sera with high anti-AhpC antibodies titre could inhibit Fn growth. In conclusion, our findings support the use of AhpC as a potential vaccine candidate against inhabitation or infection of Fn in the intestinal tract, which could provide a practical strategy for the prevention of CRC associated with Fn infection.

Functional disruption of peroxiredoxin by bismuth antiulcer drugs attenuates Helicobacter pylori survival

Bismuth drugs have been used clinically to treat infections from Helicobacter pylori, a pathogen that is strongly related to gastrointestinal diseases even stomach cancer. Despite extensive studies, the mechanisms of action of bismuth drugs are not fully understood. Alkyl hydroperoxide reductase subunit C (AhpC) is the most abundant 2-cysteine peroxiredoxin, crucial for H. pylori survival in the host by defense of oxidative stress. Herein we show that a Bi(III) antiulcer drug (CBS) binds to the highly conserved cysteine residues (Cys49 and Cys169) with a dissociation constant (K _d) of Bi(III) to AhpC of 3.0 (±1.0) × 10^-24 M. Significantly the interaction of CBS with AhpC disrupts the peroxiredoxin and chaperone activities of the enzyme both in vitro and in bacterial cells, leading to attenuated bacterial survival. Moreover, using a home-made fluorescent probe, we demonstrate that Bi(III) also perturbs AhpC relocation between the cytoplasm and membrane region in decomposing the exogenous ROS. Our study suggests that disruption of redox homeostasis by bismuth drugs via interaction with key enzymes such as AhpC contributes to their antimicrobial activity.

Serum Helicobacter pylori KatA and AhpC antibodies as novel biomarkers for gastric cancer

AIM: To investigate catalase (KatA) and alkyl hydroperoxide reductase (AhpC) antibodies of Helicobacter pylori as biomarkers for gastric cancer (GC).

METHODS: This study included 232 cases and 264 controls. Recombinant KatA and AhpC proteins were constructed and the levels of antibodies were tested by indirect enzyme-linked immunosorbent assay (ELISA). Logistic regression was applied to analyze the relationships between KatA, AhpC and GC. The χ² trend test was used to evaluate the dose-response relationships between serum KatA and AhpC antibody levels and GC. Receiver operating characteristic (ROC) curve was used to evaluate the screening accuracy of KatA and AhpC as biomarkers. Combined analysis was used to observe screening accuracy of predictors for GC.

RESULTS: In all subjects, the association between KatA and AhpC and GC risk was significant (P < 0.001) with odds ratio (OR) = 12.84 (95%CI: 7.79-21.15) and OR = 2.4 (95%CI: 1.55-3.73), respectively. KatA and AhpC antibody levels were strongly related to GC risk with a dose-dependent effect (P for trend < 0.001). The area under the ROC (AUC) for KatA was 0.806, providing a sensitivity of 66.81% and specificity of 86.36%; and the AUC for AhpC was 0.615, with a sensitivity of 75.65% and specificity of 45.49%. The AUC was 0.906 for KatA and flagella protein A (FlaA) combined analysis.

CONCLUSION: Serum KatA and AhpC antibodies are associated with GC risk and KatA may serve as a biomarker for GC. KatA/FlaA combined analysis improved screening accuracy.

Analysis of lifespan-promoting effect of garlic extract by an integrated metabolo-proteomics approach

The beneficial effects of garlic (Allium sativum) consumption in treating human diseases have been reported worldwide over a long period of human history. The strong antioxidant effect of garlic extract (GE) has also recently been claimed to prevent cancer, thrombus formation, cardiovascular disease and some age-related maladies. Using Caenorhabditis elegans as a model organism, aqueous GE was herein shown to increase the expression of longevity-related FOXO transcription factor daf-16 and extend lifespan by 20%. By employing microarray and proteomics analysis on C. elegans treated with aqueous GE, we have systematically mapped 229 genes and 46 proteins with differential expression profiles, which included many metabolic enzymes and yolky egg vitellogenins. To investigate the garlic components functionally involved in longevity, an integrated metabolo-proteomics approach was employed to identify metabolites and protein components associated with treatment of aqueous GE. Among potential lifespan-promoting substances, mannose-binding lectin and N-acetylcysteine were found to increase daf-16 expression. Our study points to the fact that the lifespan-promoting effect of aqueous GE may entail the DAF-16-mediated signaling pathway. The result also highlights the utility of metabolo-proteomics for unraveling the complexity and intricacy involved in the metabolism of natural products in vivo.

Clinical proteomics identifies urinary CD14 as a potential biomarker for diagnosis of stable coronary artery disease

Inflammation plays a key role in coronary artery disease (CAD) and other manifestations of atherosclerosis. Recently, urinary proteins were found to be useful markers for reflecting inflammation status of different organs. To identify potential biomarker for diagnosis of CAD, we performed one-dimensional SDS-gel electrophoresis followed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS). Among the proteins differentially expressed in urine samples, monocyte antigen CD14 was found to be consistently expressed in higher amounts in the CAD patients as compared to normal controls. Using enzyme-linked immunosorbent assays to analyze the concentrations of CD14 in urine and serum, we confirmed that urinary CD14 levels were significantly higher in patients (n = 73) with multi-vessel and single vessel CAD than in normal control (n = 35) (P < 0.001). Logistic regression analysis further showed that urinary CD14 concentration level is associated with severity or number of diseased vessels and SYNTAX score after adjustment for potential confounders. Concomitantly, the proportion of CD14+ monocytes was significantly increased in CAD patients (59.7 ± 3.6%) as compared with healthy controls (14.9 ± 2.1%) (P < 0.001), implicating that a high level of urinary CD14 may be potentially involved in mechanism(s) leading to CAD pathogenesis. By performing shotgun proteomics, we further revealed that CD14-associated inflammatory response networks may play an essential role in CAD. In conclusion, the current study has demonstrated that release of CD14 in urine coupled with more CD14+ monocytes in CAD patients is significantly correlated with severity of CAD, pointing to the potential application of urinary CD14 as a novel noninvasive biomarker for large-scale diagnostic screening of susceptible CAD patients.

Expression of three essential antioxidants of Helicobacter pylori in clinical isolates

OBJECTIVE

Helicobacter pylori maintains long-term persistence in the host and combats oxidative stress via many antioxidant proteins, which are expected to be relevant to bacterial-associated gastric diseases. We aimed to investigate the expression of three essential antioxidants in H. pylori strains isolated from patients with different clinical outcomes.

METHODS

Forty H. pylori strains were isolated from endoscopic biopsy specimens of gastric mucosa from 13 patients with gastric cancer, 13 with peptic ulcer, and 14 with gastritis. The expression of thioredoxin 1 (Trx1), arginase (RocF), and alkyl hydroperoxide reductase (AhpC) in H. pylori was measured by real-time PCR. Comparisons among multiple sample sets were analyzed using a one-way ANOVA test. Pearson's correlation test was used to assess relationships among multiple continuous variables.

RESULTS

Trx1 expression of H. pylori in gastric cancer and peptic ulcer tissues was higher than that in tissues with gastritis. RocF expression of H. pylori in gastric cancer tissues was higher than that in tissues exhibiting peptic ulcer and gastritis. However, we did not find any differences in AhpC expression in samples from patients with different clinical outcomes. The expression of Trx1 and RocF had a positive, linear correlation. The expression of Trx1 and AhpC had a positive correlation without a linear trend. We found no correlation between the expression of RocF and AhpC.

CONCLUSIONS

Our observations indicate that the expression of Trx1 and RocF in H. pylori might be related to gastric carcinogenesis. In H. pylori, the expression of members of the antioxidant system may be correlated and relevant to gastric cancer.

Clinical proteomics identifies potential biomarkers in Helicobacter pylori for gastrointestinal diseases

The development of gastrointestinal diseases has been found to be associated with Helicobacter pylori (H. pylori) infection and various biochemical stresses in stomach and intestine. These stresses, such as oxidative, osmotic and acid stresses, may bring about bi-directional effects on both hosts and H. pylori, leading to changes of protein expression in their proteomes. Therefore, proteins differentially expressed in H. pylori under various stresses not only reflect gastrointestinal environment but also provide useful biomarkers for disease diagnosis and prognosis. In this regard, proteomic technology is an ideal tool to identify potential biomarkers as it can systematically monitor proteins and protein variation on a large scale of cell’s translational landscape, permitting in-depth analyses of host and pathogen interactions. By performing two-dimensional polyacrylamide gel electrophoresis (2-DE) followed by liquid chromatography-nanoESI-mass spectrometry (nanoLC-MS/MS), we have successfully pinpointed alkylhydroperoxide reductase (AhpC), neutrophil-activating protein and non-heme iron-binding ferritin as three prospective biomarkers showing up-regulation in H. pylori under oxidative, osmotic and acid stresses, respectively. Further biochemical characterization reveals that various environmental stresses can induce protein structure change and functional conversion in the identified biomarkers. Especially salient is the antioxidant enzyme AhpC, an abundant antioxidant protein present in H. pylori. It switches from a peroxide reductase of low-molecular-weight (LMW) oligomers to a molecular chaperone of high-molecular-weight (HMW) complexes under oxidative stress. Different seropositivy responses against LMW or HMW AhpC in H. pylori-infected patients faithfully match the disease progression from disease-free healthy persons to patients with gastric ulcer and cancer. These results has established AhpC of H. pylori as a promising diagnostic marker for gastrointestinal maladies, and highlight the utility of clinical proteomics for identifying disease biomarkers that can be uniquely applied to disease-oriented translational medicine.

Immunodot blot assay to detect Helicobacter pylori using monoclonal antibodies against the 26 kDa protein

Development of a specific immunoassay to detect Helicobacter pylori infection in stool samples requires monoclonal antibody against the specific antigen. The aims of this study were to establish monoclonal antibodies against the 26 kDa protein of H. pylori and develop an immunodot blot for their application to recognize H. pylori infection using stool samples. Mice were immunized intraperitoneally with homogenized gel containing the 26 kDa band of cell surface proteins of H. pylori in sodium dodecyl sulfate-polyacrylamide gel electrophoresis. The monoclonal antibodies were produced using the hybridoma technique. Reactivity of monoclonal antibodies was tested with the purified 26 kDa antigen and cell surface proteins from cultured H. pylori by ELISA. Furthermore reactivity of monoclonal antibodies was tested on negative and positive stool samples for H. pylori and suspensions of several major bacteria in stool by immunodot blot assay. Five stable hybridoma monoclones were obtained. The concordant reactivity of the monoclonal antibodies with H. pylori present in the stool samples, which had been tested previously using an ACON ELISA kit for H. pylori stool antigen testing, and unreactivity with several different major fecal bacteria in immunodot blotting indicates high specificity of the immunodot blot based on the reaction of produced monoclonal antibodies with the H. pylori antigen in stools. The findings indicate that the novel immunodot blot developed based on new monoclonal antibodies for stool antigens would be useful as a noninvasive method of diagnosing H. pylori infection.

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.

Construction and use of a prokaryotic expression system for Helicobacter pylori AhpC

Background

Helicobacter pylori is an important pathogen responsible for human gastric problems like inflammation, ulcers and cancer. It is widely prevalent in developing countries with low socioeconomic status. Since the infection remains asymptomatic in most individuals, efforts for efficient diagnostic markers to identify high risk patients are warranted. In this study, we constructed an expression vector that overexpresses the H. pylori AhpC protein as a glutathione S-transferase fusion protein. We furthermore examined whether this recombinant fusion protein retained immunogenicity and thus would be useful as a diagnostic marker.

Findings

The full-length tsaA gene from H. pylori strain G27, which encodes AhpC, was cloned in plasmid vector pGEX-6P-2 to create the recombinant plasmid vector pGEX-tsaA. The nucleotide sequence of the clone showed 100% homology with corresponding published sequence of original gene. Over-expression of the target protein GST-AhpC was achieved in E. coli BL21 (DE3) cells by induction with isopropyl-beta-D-thiogalactoside (IPTG). GST-AhpC was extracted and identified using SDS-PAGE as a 52 kDa protein. Western blotting results using commercial antibodies against whole cell H. pylori showed that the fusion protein retained immunogenecity.

Conclusion

A recombinant prokaryotic expression system was successfully established with high expression efficiency for target fusion gene pGEX-tsaA. The expressed GST-AhpC protein showed immunoreactivity against commercial anti-H. pylori antibodies. This recombinant fusion protein can be developed as a diagnostic marker for screening patients with chronic H. pylori infections.

Alkyl hydroperoxide reductase: a candidate Helicobacter pylori vaccine

Helicobacter pylori (H. pylori) is the most important etiological agent of chronic active gastritis, peptic ulcer disease and gastric cancer. The aim of this study was to evaluate the efficacy of alkyl hydroperoxide reductase (AhpC) and mannosylated AhpC (mAhpC) as candidate vaccines in the C57BL/6J mouse model of H. pylori infection. Recombinant AhpC was cloned, over-expressed and purified in an unmodified form and was also engineered to incorporate N and C-terminal mannose residues when expressed in the yeast Pichia pastoris. Mice were immunized systemically and mucosally with AhpC and systemically with mAhpC prior to challenge with H. pylori. Serum IgG responses to AhpC were determined and quantitative culture was used to determine the efficacy of vaccination strategies. Systemic prophylactic immunization with AhpC/alum and mAhpC/alum conferred protection against infection in 55% and 77.3% of mice, respectively. Mucosal immunization with AhpC/cholera toxin did not protect against infection and elicited low levels of serum IgG in comparison with systemic immunization. These data support the use of AhpC as a potential vaccine candidate against H. pylori infection.

Diagnosis of Helicobacter pylori Infection

When an endoscopy is performed, it now becomes easier to observe indirect evidence of the presence of a Helicobacter pylori infection, given the progress of new methods including magnifying narrow band imaging or confocal laser endomicroscopy. Out of the biopsy-based tests, the novel original method proposed concerned culture in a broth medium with or without antibiotics and ELISA detection of H. pylori. New stool antigen tests are still appearing with no major improvement in comparison with the monoclonal-based tests already on the market. The combination of pepsinogen detection to H. pylori serology is now more and more evaluated to detect preneoplastic lesions.