Comparative analysis of the Hom family of outer membrane proteins in isolates from two geographically distinct regions: The United States and South Korea

Helicobacter pylori Outer Membrane Proteins and Virulence Factors: Potential Targets for Novel Therapies and Vaccines

Helicobacter pylori is a gastric oncopathogen that infects over half of the world's human population. It is a Gram-negative, microaerophilic, helix-shaped bacterium that is equipped with flagella, which provide high motility. Colonization of the stomach is asymptomatic in up to 90% of people but is a recognized risk factor for developing various gastric disorders such as gastric ulcers, gastric cancer and gastritis. Invasion of the human stomach occurs via numerous virulence factors such as CagA and VacA. Similarly, outer membrane proteins (OMPs) play an important role in H. pylori pathogenicity as a means to adapt to the epithelial environment and thereby facilitate infection. While some OMPs are porins, others are adhesins. The epithelial cell receptors SabA, BabA, AlpA, OipA, HopQ and HopZ have been extensively researched to evaluate their epidemiology, structure, role and genes. Moreover, numerous studies have been performed to seek to understand the complex relationship between these factors and gastric diseases. Associations exist between different H. pylori virulence factors, the co-expression of which appears to boost the pathogenicity of the bacterium. Improved knowledge of OMPs is a major step towards combatting this global disease. Here, we provide a current overview of different H. pylori OMPs and discuss their pathogenicity, epidemiology and correlation with various gastric diseases.

Biofilm of Helicobacter pylori: Life Cycle, Features, and Treatment Options

Helicobacter pylori is a gastric pathogen that infects nearly half of the global population and is recognized as a group 1 carcinogen by the Word Health Organization. The global rise in antibiotic resistance has increased clinical challenges in treating H. pylori infections. Biofilm growth has been proposed to contribute to H. pylori's chronic colonization of the host stomach, treatment failures, and the eventual development of gastric diseases. Several components of H. pylori have been identified to promote biofilm growth, and several of these may also facilitate antibiotic tolerance, including the extracellular matrix, outer membrane proteins, shifted morphology, modulated metabolism, efflux pumps, and virulence factors. Recent developments in therapeutic approaches targeting H. pylori biofilm have shown that synthetic compounds, such as small molecule drugs and plant-derived compounds, are effective at eradicating H. pylori biofilms. These combined topics highlight the necessity for biofilm-based research in H. pylori, to improve current H. pylori-targeted therapeutic approaches and alleviate relative public health burden. In this review we discuss recent discoveries that have decoded the life cycle of H. pylori biofilms and current biofilm-targeted treatment strategies.

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.

Distribution characteristics of the sabA, hofC, homA, homB and frpB-4 genes of Helicobacter pylori in different regions of China

Background

Helicobacter pylori (H. pylori) encodes numerous outer membrane proteins (OMPs), with considerable geographic heterogeneity and related to different clinical outcomes. This study aimed to investigate the distribution characteristics of five important OMP genes (sabA, hofC, homA, homB and frpB-4) in different regions of China.

Materials and method

A total of 266 strains were isolated from 348 stomach biopsy specimens in Shandong, Guangxi, Heilongjiang, Hunan, and Qinghai provinces. The presence of sabA, hofC, homA, homB and frpB-4 gene was detected by polymerase chain reaction (PCR) from H. pylori genomic DNA.

Results

Among the strains in five regions, the prevalence of frpB-4 was 100% and that of hofC was 97.7%. The prevalence of homB in the isolates from Qinghai (45.5%) was significantly lower than that in Shandong (75.3%), Guangxi (76.9%) and Hunan (69.6%) (P<0.05). The frequency of homA in Shandong (30.1%) was significantly lower than in Guangxi (57.7%) and Qinghai (63.6%) (P<0.05). The prevalence of the sabA gene in Shandong, Guangxi, Heilongjiang, Hunan and Qinghai provinces was 21.9%, 59.7%, 45.9%, 52.2%, and 18.2%, respectively (P<0.05). The sabA “on” status was significantly more frequent in isolates from Guangxi (46.8%), Heilongjiang (37.8%), and Hunan (47.8%) than Qinghai (3.0%) (P<0.05). The presence of homA and sabA genes may be negatively correlated with the development of gastritis. There was no significant association between the frpB-4, hofC, homB gene and clinical outcomes.

Conclusion

The prevalence of homA, homB, and sabA genes and the sabA “on” or “off” status have significant geographical differences among five provinces in China. The presence of homA and sabA genes may be protective factors of gastritis.

Biomarker Characterization and Prediction of Virulence and Antibiotic Resistance from Helicobacter pylori Next Generation Sequencing Data

The Gram-negative bacterium Helicobacter pylori colonizes c.a. 50% of human stomachs worldwide and is the major risk factor for gastric adenocarcinoma. Its high genetic variability makes it difficult to identify biomarkers of early stages of infection that can reliably predict its outcome. Moreover, the increasing antibiotic resistance found in H. pylori defies therapy, constituting a major human health problem. Here, we review H. pylori virulence factors and genes involved in antibiotic resistance, as well as the technologies currently used for their detection. Furthermore, we show that next generation sequencing may lead to faster characterization of virulence factors and prediction of the antibiotic resistance profile, thus contributing to personalized treatment and management of H. pylori-associated infections. With this new approach, more and permanent data will be generated at a lower cost, opening the future to new applications for H. pylori biomarker identification and antibiotic resistance prediction.

Helicobacter pylori cagA status and gastric mucosa-associated lymphoid tissue lymphoma: a systematic review and meta-analysis

Background

Recent studies have investigated the role of Helicobacter pylori infection in the development of gastric mucosa-associated lymphoid tissue (MALT) lymphoma. It is estimated that approximately 0.1% of people infected with H. pylori develop gastric MALT lymphoma. However, the role of the CagA antigen, the highest causative agent of H. pylori, in increasing the risk of gastric MALT lymphoma remains unclear and controversial. A systematic review and meta-analysis were conducted to evaluate the effect of cagA status on the development of gastric MALT lymphoma.

Methods

All articles evaluating the status of the cagA gene in the development of gastric MALT lymphoma were collected using systematic searches in online databases, including PubMed, Scopus, Embase, and Google Scholar, regardless of publication date. The association between cagA and gastric MALT lymphoma was assessed using the odds ratio (OR) summary. In addition, a random-effects model was used in cases with significant heterogeneity.

Results

A total of 10 studies met our inclusion criteria, among which 1860 patients participated. No association between cagA status and the development of MALT lymphoma (extranodal marginal zone B-cell lymphoma) was found in this study (OR 1.30; 0.906–1.866 with 95% CIs; I²: 45.83; Q-value: 12.92). Surprisingly, a meaningful association was observed between cagA status and diffuse large B-cell lymphoma (OR 6.43; 2.45–16.84 with 95% CIs). We also observed an inverse association between vacA and gastric MALT lymphoma risk (OR 0.92; 0.57–1.50 with 95% CIs).

Conclusions

It seems that the infection with cagA-positive H. pylori strains does not have a meaningful effect on the gastric MALT lymphoma formation, while translocated CagA antigen into the B cells plays a crucial role in the development of diffuse large B-cell lymphoma.

Characterization of East-Asian Helicobacter pylori encoding Western EPIYA-ABC CagA

The polymorphic bacterial oncoprotein, CagA shows geography-dependent variation in the C-terminal Glu-Pro-Ile-Tyr-Ala (EPIYA) motifs; East-Asian H. pylori isolates carry the ABD type while Western isolates carry the ABC type. In Western isolates, the EPIYA-C motif is sometimes found in multi-copy and this genotype is associated with disease severity. Interestingly, a small number of East-Asian H. pylori isolates have been found to carry Western ABC-type CagA. To gain a better understanding of these unusual isolates, the genomes of four Korean H. pylori clinical isolates carrying ABC-type CagA were sequenced via third generation (Pac-Bio SMRT) sequencing technology. The obtained data were utilized for phylogenetic analysis as well as comparison of additional virulence factors that are known to show geographic-dependent polymorphisms. Three of four isolates indeed belonged to the hpEastAsia group and showed typical East-Asian polymorphism in virulence factors such as homA/B/C, babA/B/C, and oipA. One isolate grouped to HpAfrica and showed typical Western polymorphism of virulence factors such as cagA, homA/B/C, and oipA. To understand the occurrence of the multi-copy EPIYA-C motif genotype in an East-Asian H. pylori background, the Korean clinical isolate, K154 was analyzed; this strain belonged to hpEastAsia but encoded CagA EPIYA-ABCCCC. Based on DNA sequence homology within the CagA multimerization (CM) sequence that flanked the EPIYA-C motifs, we predicted that the number of C motifs might change via homologous recombination. To test this hypothesis, K154 was cultured for one generation and 287 single colonies were analyzed for the number of EPIYA-C motifs using PCR-based screening and DNA sequencing verification. Three out of 284 (1%) single colony isolates showed changes in the number of EPIYA-C motifs in vitro; one isolate increased to five EPIYA-C motifs, one decreased to three EPIYA-C motifs, and one completely deleted the EPIYA-C motifs. The capacity for dynamic changes in the number of EPIYA-C repeats of CagA may play a role in generating important intraspecies diversity in East-Asian H. pylori.

Geographic diversity in Helicobacter pylori oipA genotype between Korean and United States isolates

Helicobacter pylori outer membrane inflammatory protein A (OipA) was originally named for its role in inducing inflammation in the host, as evidenced by high mucosal IL-8 levels. Expression of OipA is regulated by phase variation of a CT dinucleotide-repeat located in the 5' region of the gene. However, little is known about OipA geographic diversity across isolates. To address this gap, we conducted a large-scale molecular epidemiologic analysis using H. pylori clinical isolates obtained from two geographically distinct populations: Korea and the United States (US). Most Korean isolates (98.7%) possessed two copies of oipA located at two specific loci (A and B) while all US isolates contained only one copy of oipA at locus A. Furthermore, most Korean oipA (94.8%) possessed three or less CT repeats while most US oipA (96.6%) contained five or more CT repeats. Among the two copies, all Korean H. pylori possessed at least one oipA 'on' phase variant while the single copy of oipA in US isolates showed 56.2% 'on' and 43.8% 'off.' Thus, host differences seem to have driven geographic diversification of H. pylori across these populations such that OipA expression in US isolates is still regulated by phase variation with 5 or more CT repeats, while Korean isolates always express OipA; duplication of the oipA combined with a reduction of CT repeats to three or less ensures continued expression. En masse, these findings suggest that diversity in the oipA gene copy number, CT repeats, and phase variation among H. pylori from different populations may confer a benefit in adaptation to particular host populations.

CagL polymorphisms between East Asian and Western Helicobacter pylori are associated with different abilities to induce IL-8 secretion

Helicobacter pylori colonizes human gastric mucosa. Its infection is associated with gastric diseases including gastric cancer. CagA is one of the most important toxins produced by H. pylori. It is related to gastric cancer which can be injected into host cells via a type IV secretion system (T4SS). CagL is a structural component of T4SS apparatus, which triggers host cell signaling pathway. It has been reported that CagL polymorphisms may influence the severity of disease development. To explore the contribution of CagL polymorphisms between East Asian and Western H. pylori in pathogenesis, cagL gene in G27 H. pylori was swapped by K74 cagL which is identical to East Asian CagL consensus sequence and by Western 26695 H. pylori, resulting in G27 ΔcagL/cagL^K74 and G27 ΔcagL/cagL²⁶⁶⁹⁵, respectively. Intriguingly, G27 ΔcagL/cagL^K74 showed significantly less ability of IL-8 induction than G27 ΔcagL/cagL²⁶⁶⁹⁵ while displayed similar abilities of CagA phosphorylation, and cell elongation. Taken together, this study suggests that the CagL polymorphism may influence IL-8 induction, and K74 CagL has less ability to induce IL-8 secretion than G27 or 26695 CagL. Further research should address how the different capabilities of IL-8 induction between intraspecies-CagL are associated with the large differences of the incidence of gastric cancer between East Asian and Western countries.

Correlation between the geographical origin of Helicobacter pylori homB-positive strains and their clinical outcomes: a systematic review and meta-analysis

BACKGROUND

In general, all virulence factors of Helicobacter pylori (H. pylori) are involved in its infections. However, recent studies have shown that the homB gene is one of the virulence genes that affects the severity of the clinical results of this bacterium.

METHODS

The main purpose of this study was to investigate the relationship between the presence of homB gene in H. pylori and the progression of its infection to peptic ulcer and gastric cancer. In the present study, we conducted a systematic search to collect all articles related to the effect of homB-positive strains on clinical outcomes. Finally, 12 eligible studies according to our criteria were included in this meta-analysis and the effect of homB gene on gastric ulcer and gastric cancer diseases was evaluated by summary odds ratio (OR).

RESULTS

Current results showed that the homB-positive strains significantly increase the risk of peptic ulcer (OR 1.36; 1.07-1.72 with 95% CIs), especially in western countries (OR 1.61; 1.20-2.14 with 95% CIs). Moreover, we observed a positive association between the homB gene and risk of gastric cancer (OR 2.16; 1.37-3.40 with 95% CIs). In addition, based on subgroup analysis, it was found that the presence of this gene in H. pylori strains increases the risk of gastric cancer in the Asian population (OR 3.71; 1.85-7.45 with 95% CIs).

CONCLUSIONS

Overall, in the present study we found that homB gene is responsible for the progressing of primary infection to severe complications, in particular peptic ulcer in western countries and gastric cancer in Asian countries.

Increased Risk of Severe Gastric Symptoms by Virulence Factors vacAs1c, alpA, babA2, and hopZ in Helicobacter pylori Infection

Two virulence factors of Helicobacter pylori, cagA and vacA, have been known to play a role in the development of severe gastric symptoms. However, they are not always associated with peptic ulcer or gastric cancer. To predict the disease outcome more accurately, it is necessary to understand the risk of severe symptoms linked to other virulence factors. Several other virulence factors of H. pylori have also been reported to be associated with disease outcomes, although there are many controversial descriptions. H. pylori isolates from Koreans may be useful in evaluating the relevance of other virulence factors to clinical symptoms of gastric diseases because the majority of Koreans are infected by toxigenic strains of H. pylori bearing cagA and vacA. In this study, a total of 116 H. pylori strains from Korean patients with chronic gastritis, peptic ulcers, and gastric cancers were genotyped. The presence of virulence factors vacAs1c, alpA, babA2, hopZ, and the extremely strong vacuolating toxin was found to contribute significantly to the development of severe gastric symptoms. The genotype combination vacAs1c/alpA/babA2 was the most predictable determinant for the development of severe symptoms, and the presence of babA2 was found to be the most critical factor. This study provides important information on the virulence factors that contribute to the development of severe gastric symptoms and will assist in predicting clinical disease outcomes due to H. pylori infection.

Virulence of Helicobacter pylori outer membrane proteins: an updated review

Helicobacter pylori (H. pylori) infection is associated with some gastric diseases, such as gastritis, peptic ulcer, and gastric cancer. CagA and VacA are known virulence factors of H. pylori, which play a vital role in severe clinical outcomes. Additionally, the expression of outer membrane proteins (OMPs) helps H. pylori attach to gastric epithelial cells at the primary stage and increases the virulence of H. pylori. In this review, we have summarized the paralogs of H. pylori OMPs, their genomic loci, and the different receptors of OMPs identified so far. We focused on five OMPs, BabA (HopS), SabA (HopP), OipA (HopH), HopQ, and HopZ, and one family of OMPs: Hom. We highlight the coexpression of OMPs with other virulence factors and their relationship with clinical outcomes. In conclusion, OMPs are closely related to the pathogenic processes of adhesion, colonization, persistent infection, and severe clinical consequences. They are potential targets for the prevention and treatment of H. pylori–related diseases.

Roles of Adhesion to Epithelial Cells in Gastric Colonization by Helicobacter pylori

Helicobacter pylori adherence to host epithelial cells is essential for its survival against the harsh conditions of the stomach and for successful colonization. Adherence of H. pylori is achieved through several related families of outer membrane proteins and proteins of a type IV secretion system (T4SS), which bridge H. pylori to host cells through protein-protein and other protein-ligand interactions. Local environmental conditions such as cell type, available host cell surface proteins and/or ligands, as well as responses by the host immune system force H. pylori to alter expression of these proteins to adapt quickly to the local environment in order to colonize and survive. Some of these host-pathogen interactions appear to function in a "catch-and-release" manner, regulated by reversible binding at varying pH and allowing H. pylori to detach itself from cells or debris sloughed off the gastric epithelial lining in order to return for subsequent productive interactions. Other interactions between bacterial adhesin proteins and host adhesion molecules, however, appear to function as a committed step in certain pathogenic processes, such as translocation of the CagA oncoprotein through the H. pylori T4SS and into host gastric epithelial cells. Understanding these adhesion interactions is critical for devising new therapeutic strategies, as they are responsible for the earliest stage of infection and its maintenance. This review will discuss the expression and regulation of several outer membrane proteins and CagL, how they engage their known host cell protein/ligand targets, and their effects on clinical outcome.

ArsRS-Dependent Regulation of homB Contributes to Helicobacter pylori Biofilm Formation

One elusive area in the Helicobacter pylori field is an understanding of why some infections result in gastric cancer, yet others persist asymptomatically for the life-span of the individual. Even before the genomic era, the high level of intraspecies diversity of H. pylori was well recognized and became an intriguing area of investigation with respect to disease progression. Of interest in this regard is the unique repertoire of over 60 outer membrane proteins (OMPs), several of which have been associated with disease outcome. Of these OMPs, the association between HomB and disease outcome varies based on the population being studied. While the molecular roles for some of the disease-associated OMPs have been evaluated, little is known about the role that HomB plays in the H. pylori lifecycle. Thus, herein we investigated homB expression, regulation, and contribution to biofilm formation. We found that in H. pylori strain G27, homB was expressed at a relatively low level until stationary phase. Furthermore, homB expression was suppressed at low pH in an ArsRS-dependent manner; mutation of arsRS resulted in increased homB transcript at all tested time-points. ArsRS regulation of homB appeared to be direct as purified ArsR was able to specifically bind to the homB promoter. This regulation, combined with our previous finding that ArsRS mutations lead to enhanced biofilm formation, led us to test the hypothesis that homB contributes to biofilm formation by H. pylori. Indeed, subsequent biofilm analysis using a crystal-violet quantification assay and scanning electron microscopy (SEM) revealed that loss of homB from hyper-biofilm forming strains resulted in reversion to a biofilm phenotype that mimicked wild-type. Furthermore, expression of homB in trans from a promoter that negated ArsRS regulation led to enhanced biofilm formation even in strains in which the chromosomal copy of homB had been deleted. Thus, homB is necessary for hyper-biofilm formation of ArsRS mutant strains and aberrant regulation of this gene is sufficient to induce a hyper-biofilm phenotype. In summary, these data suggest that the ArsRS-dependent regulation of OMPs such as HomB may be one mechanism by which ArsRS dictates biofilm development in a pH responsive manner.