The signal conversion strategy using the lytic transglycosylase Cag4-double nanoporous gold co-catalysis for the rapid screening of drugs against Helicobacter pylori infection

The cag pathogenicity island (cagPAI) is the main virulence factor of gastric carcinoma induced by Helicobacter pylori (H. pylori). The lytic transglycosylase Cag4 is an important component that assists in the translocation of the bacterial oncoprotein CagA and maintains the peptidoglycan cycle. The allosteric regulation of Cag4 has been preliminarily demonstrated to inhibit H. pylori infection. Unfortunately, a rapid screening technology for allosteric regulators of Cag4 has not been established. In this study, a novel Cag4-double nanoporous gold (NPG) biosensor based on enzyme-inorganic co-catalysis was constructed using the heterologously expressed H. pylori 26695 Cag4 as the biological recognition element for screening Cag4 allosteric regulators. The results showed that chitosan or carboxymethyl chitosan was a mixed Cag4 inhibitor combining non-competition with uncompetition. The inhibition constants were K_i' _Chitosan = 0.88909 mg/mL and K_i' _{Carboxymethyl chitosan} = 1.13480 mg/mL, respectively. Surprisingly, D-(+)-cellobiose showed the activation effect of Cag4 on E. coli MG1655 cell wall lysis by decreasing the K_a value by 29.7% and increasing the V_max value by 71.3%. In addition, molecular docking revealed the importance of the polarity of the C₂ substituent group with glucose as the main structure in the Cag4 allosteric regulator. This study provides a fast and useful platform for screening potential new drugs based on the Cag4 allosteric regulator.

Crystal structure of CagV, the Helicobacter pylori homologue of the T4SS protein VirB8

The VirB/D type IV secretion system (T4SS) plays an essential role in materials transport between host cells and pathogenic Helicobacter pylori and is considered the major pathogenic mediator of H. pylori-associated gastric disease. VirB8, an inner membrane protein that interacts with many other proteins, is a crucial component for secretory function. Here, we present a crystal structure of the periplasmic domain of CagV, the VirB8 counterpart in the H. pylori Cag-T4SS. The structure reveals a fold similar to that of other VirB8 members except for the absence of the α5 helix, a discontinuous β1 strand, a larger angle between the α2 and α3 helices, a more hydrophobic surface groove, but exhibits a different dimer interface. Whether the dimerization occurs in solution was proved by mutagenesis, size-exclusion chromatography and cross-linking assays. Unlike the classical dimerization mode, the interface of the CagV dimer is principally formed by several hydrogen bonds, which indicates instability of dimerization. The structure here demonstrates the difference in dimerization among VirB8 homologues and indicates the considerable compositional and functional diversity of them in T4SS. DATABASE: Coordinates and structure factors have been deposited in the Protein Data Bank under accession codes 6IQT.

Attenuation of Helicobacter pylori-induced gastric inflammation by prior cag- strain (AM1) infection in C57BL/6 mice

BACKGROUND

Helicobacter pylori, colonize in stomach of ~50% of the world population. cag pathogenicity Island of H. pylori is one of the important virulent factors that attributed to gastric inflammation. Coinfection with H. pylori strain with different genetic makeup alters the degree of pathogenicity and susceptibility towards antibiotics. The present study investigates host immunomodulatory effects of H. pylori infection by both cag⁺ strain (SS1) and cag^- strain (AM1). C57BL/6 mice were infected with AM1 or SS1 strain as well as AM1 followed by SS1 (AM1/SS1) and vice versa.

RESULTS

Mice infected with AM1/SS1 strain exhibited less gastric inflammation and reduced proMMP9 and proMMP3 activities in gastric tissues as compared to SS1/SS1 and SS1/AM1 infected groups. The expression of both MMP9 and MMP3 followed similar trend like activity in infected tissues. Both Th1 and Th17 responses were induced by SS1 strain more profoundly than AM1 strain infection which induced solely Th1 response in spleen and gastric tissues. Moreover, IFN-γ, TNF-α, IL-1β and IL-12 were significantly downregulated in mice spleen and gastric tissues infected by AM1/SS1 compared to SS1/SS1 but not with SS1/AM1 coinfection. Surprisingly, IL-17 level was dampened significantly in AM1/SS1 compared to SS1/AM1 coinfected groups. Furthermore, number of Foxp3⁺ T-regulatory (Treg) cells and immunosuppressive cytokines like IL-10 and TGF-β were reduced in AM1/SS1 compared to SS1/SS1 and SS1/AM1 coinfected mice gastric tissues.

CONCLUSIONS

These data suggested that prior H. pylori cag^- strain infection attenuated the severity of gastric pathology induced by subsequent cag⁺ strain in C57BL/6 mice. Prior AM1 infection induced Th1 cytokine IFN-γ, which reduced the Th17 response induced by subsequent SS1 infection. The reduced gastritis in AM1/SS1-infected mice might also be due to enrichment of AM1- primed Treg cells in the gastric compartment which inhibit Th1 and Th17 responses to subsequent SS1 infection. In summary, prior infection by non-virulent H. pylori strain (AM1) causes reduction of subsequent virulent strain (SS1) infection by regulation of inflammatory cytokines and MMPs expression.

Role of Helicobacter pylori in gastric cancer: Updates

Helicobacter pylori (H. pylori) infection is highly prevalent in human, affecting nearly half of the world’s population; however, infection remains asymptomatic in majority of population. During its co-existence with humans, H. pylori has evolved various strategies to maintain a mild gastritis and limit the immune response of host. On the other side, presence of H. pylori is also associated with increased risk for the development of various gastric pathologies including gastric cancer (GC). A complex combination of host genetics, environmental agents, and bacterial virulence factors are considered to determine the susceptibility as well as the severity of outcome in a subset of individuals. GC is one of the most common cancers and considered as the third most common cause of cancer related death worldwide. Many studies had proved H. pylori as an important risk factor in the development of non-cardia GC. Although both H. pylori infection and GC are showing decreasing trends in the developed world, they still remain a major threat to human population in the developing countries. The current review attempts to highlight recent progress in the field of research on H. pylori induced GC and aims to provide brief insight into H. pylori pathogenesis, the role of major virulence factors of H. pylori that modulates the host environment and transform the normal gastric epithelium to neoplastic one. This review also emphasizes on the mechanistic understanding of how colonization and various virulence attributes of H. pylori as well as the host innate and adaptive immune responses modulate the diverse signaling pathways that leads to different disease outcomes including GC.

Interleukin-1 and TNF-α polymorphisms and Helicobacter pylori in a Brazilian Amazon population

AIM: To study the association between Interleukin-1 (IL-1) and tumor necrosis factor (TNF)-α polymorphisms, infection by Helicobacter pylori (H pylori) and the development of gastrointestinal diseases.

METHODS: Genomic DNA was extracted from the peripheral blood of 177 patients with various gastrointestinal diseases and from 100 healthy volunteers. The polymorphisms in IL-1β and TNF-α genes were analyzed using the polymerase chain reaction-restriction fragment length polymorphism method (PCR-RFLP) and those from IL-1RN with PCR. The presence of infection due to H pylori and the presence of the CagA toxin were detected by serology. The histopathological parameters in the gastric biopsies of the patients were according to the Sydney classification.

RESULTS: A comparison of the frequencies of the different polymorphisms studied among the patients and the control group demonstrated that the allele IL-1RN*2 was more frequent among patients with gastric ulcers and adenocarcinoma. Carriers of the allele IL-RN*2 and those with reactive serology for anti-CagA IgG had a greater risk of developing peptic ulcer and gastric adenocarcinoma, as well as a higher degree of inflammation and neutrophilic activity in the gastric mucosa.

CONCLUSION: Our results indicate a positive association between IL-1RN gene polymorphism and infection by positive H pylori CagA strains and the development of gastric ulcers and adenocarcinoma.