Helicobacter pylori lipopolysaccharide: Biological activities in vitro and in vivo, pathological correlation to human chronic gastritis and peptic ulcer

Helicobacter pylori antigens as immunomodulators of immune system

Helicobacter pylori (H. pylori) is one of the most prevalent human pathogens and the leading cause of chronic infection in almost half of the population in the world (~59%). The bacterium is a major leading cause of chronic gastritis, gastric and duodenal ulcers, and two type of malignancies, gastric adenocarcinoma and mucosa-associated lymphoid tissue (MALT) lymphoma. Despite the immune responses mounted by the host, the bacteria are not cleared from the body resulting in a chronic infection accompanied by a chronic inflammation. Herein, a review of the literature discussing H. pylori antigens modulating the immune responses is presented. The mechanisms that are involved in the modulation of innate immune response, include modulation of recognition by pattern recognition receptors (PRRs) such as modulation of recognition by toll like receptors (TLR)4 and TLR5, modulation of phagocytic function, and modulation of phagocytic killing mediated by reactive oxygen species (ROS) and nitric oxide (NO). On the other hands, H. pylori modulates acquired immune response by the induction of tolerogenic dendritic cells (DCs), modulation of apoptosis, induction of regulatory T cells, modulation of T helper (Th)1 response, and modulation of Th17 response.

An Overview of Helicobacter pylori Survival Tactics in the Hostile Human Stomach Environment

Helicobacter pylori is well established as a causative agent for gastritis, peptic ulcer, and gastric cancer. Armed with various inimitable virulence factors, this Gram-negative bacterium is one of few microorganisms that is capable of circumventing the harsh environment of the stomach. The unique spiral structure, flagella, and outer membrane proteins accelerate H. pylori movement within the viscous gastric mucosal layers while facilitating its attachment to the epithelial cells. Furthermore, secretion of urease from H. pylori eases the acidic pH within the stomach, thus creating a niche for bacteria survival and replication. Upon gaining a foothold in the gastric epithelial lining, bacterial protein CagA is injected into host cells through a type IV secretion system (T4SS), which together with VacA, damage the gastric epithelial cells. H. pylori does not only establishes colonization in the stomach, but also manipulates the host immune system to permit long-term persistence. Prolonged H. pylori infection causes chronic inflammation that precedes gastric cancer. The current review provides a brief outlook on H. pylori survival tactics, bacterial-host interaction and their importance in therapeutic intervention as well as vaccine development.

Helicobacter pylori modulates cisplatin sensitivity in gastric cancer by down-regulating miR-141 expression

BACKGROUND

Recent studies found that gastric cancer patients with Helicobacter pylori infection had a better response to chemotherapy and had an improved overall prognosis compared with those without. However, the underlying mechanism remains unknown.

METHODS

Quantitative real-time PCR (qRT-PCR) was utilized to determine the expression profile of miR-141 in H. pylori infected cells and tissues and their respective controls. qRT-PCR and Western blot were used to determine the expression level of KEAP-1. Luciferase reporter assays were used to determine whether KEAP-1 was a direct target of miR-141 in the gastric cancer cells. MTT and apoptosis assay were performed to detect the survival of cells under cisplatin treatment.

RESULT

We found that H. pylori infection can significantly down-regulate miR-141 expression. Knockdown miR-141 expression in 7901/DDP and 7901 cells could significantly improve cisplatin sensitivity. Over-expression of miR-141 resulted in enhanced resistance to cisplatin in both gastric cancer cells. We also demonstrated that miR-141 directly targets KEAP1 by luciferase reporter assay, and that down-regulation of KEAP1 induces cisplatin resistance. Conversely, over-expression of KEAP1 significantly enhanced cisplatin sensitivity. Our 75 pairs of tissues also showed that KEAP1 was significantly up-regulated in H. pylori-positive tissues.

CONCLUSION

Altogether, these findings demonstrated that the H. pylori infection could modulate cisplatin sensitivity through miR-141-mediated regulation of KEAP1.

Bioactivity and immunological evaluation of LPS from different serotypes of Helicobacter pylori

BACKGROUND AND OBJECTIVES

Helicobacter pylori is the causative agent of peptic ulcer disease and a co-factor in development of gastric malignancies. LPS are among toxic substances produced by H. pylori exhibiting low endotoxic activity compared to typical bacterial LPS. The aim of this study was to investigate bioactivity of LPS produced by different serotypes of Helicobacter pylori compared to Escherichia coli and Brucella abortus LPS.

MATERIALS AND METHODS

Bacterial LPS was extracted by the hot phenol-water method. Biological activities of LPS were determined via the limulus lysate assay, pyrogenic assay, and blood pressure and PBMC induction test in rabbits.

RESULTS

Biological activity of O2 serotype LPS of H. pylori was less than the biological activity of other H. pylori serotypes.

CONCLUSION

Our data supported the hypothesis that the unique bacterial LPS of the O2 serotype must be included in the formulation of a multivalent H. pylori vaccine.

Comparison of Helicobacter pylori and Escherichia coli in induction of TNF-alpha mRNA from human peripheral blood mononuclear cells

PURPOSE

To investigate the difference between the abilities of Helicobacter pylori and Escherichia coli to induce expression of TNF-alpha in human peripheral blood mononuclear cells (PBMC).

MATERIALS AND METHODS

H pylori was isolated from gastric biopsy specimens. The mononuclear cells were isolated from human blood, cultured, and treated with either intact or sonicated E coli or H pylori, and mRNA expression for TNF-alpha was detected using semi-quantitative reverse transcriptase-polymerase chain reaction (RT-PCR).

RESULTS

TNF-alpha mRNA expression levels were significantly higher in PBMCs stimulated with E coli compared to those stimulated with H pylori at the same number and identical conditions (P < .001). The results also suggest that sonicated bacteria were significantly (P < .001) less stimulatory for PBMCs than intact bacteria for both E coli and H pylori.

CONCLUSIONS

The ability of different H pylori strains isolated from biopsy samples to stimulate TNF-alpha from PBMCs was significantly lower than that of E coli. Sonicated bacteria, as compared to intact bacteria, was a very poor inducer of TNF-alpha mRNA expression, suggesting that the conformation of lipopolysaccharides (LPS) on the outer leaflet of the outer membrane is not totally conserved in sonicated bacteria.

Helicobacter pylori augments growth of gastric cancers via the lipopolysaccharide-toll-like receptor 4 pathway whereas its lipopolysaccharide attenuates antitumor activities of human mononuclear cells

PURPOSE

Helicobacter pylori is reportedly involved in the development of gastric cancer. We investigated the mechanisms by which H. pylori affects gastric cancer growth and antitumor immunities in the host, focusing on H. pylori-derived lipopolysaccharide (LPS).

EXPERIMENTAL DESIGN

H. pylori and four gastric cancer cell lines (MKN28, MKN45, NUGC3, and KATOIII) were used. We examined the effect of H. pylori or its LPS stimulation on cancer growth and the involvement of the H. pylori LPS-toll-like receptor 4 (TLR4) pathway. We also examined the cytotoxicities of H. pylori/LPS-stimulated human mononuclear cells (MNC) against gastric cancer cells and the effect of H. pylori LPS stimulation on cytokine production by MNC.

RESULTS

H. pylori, as well as its LPS, augmented the growth of gastric cancers, all of which expressed TLR4. Neutralization of TLR4 almost completely abrogated the H. pylori-induced proliferative activity of cancer cells. Escherichia coli LPS also augmented cancer growth via the LPS-TLR4 pathway. However, only H. pylori-derived LPS attenuated the cytotoxicity of MNC against gastric cancer cells. Stimulation with H. pylori/LPS also down-regulated perforin production in cancer cell-cocultured CD56+ natural killer cells. H. pylori LPS induced neither interleukin-12 nor IFN-gamma production by MNC, although E. coli LPS did induce production of both significantly. Nevertheless, interleukin-12 stimulation restored the IFN-gamma-producing capacity of H. pylori LPS-stimulated MNC.

CONCLUSION

H. pylori augmented the growth of gastric cancers via the LPS-TLR4 pathway, whereas it attenuated the antitumor activity and IFN-gamma-mediated cellular immunity of MNC. H. pylori infection might thereby promote proliferation and progression of gastric cancers.

Patients with duodenal ulcer have lower levels of serum cholesterol compared to other dyspeptic patients independently of Helicobacter pylori status

OBJECTIVE

The association between Helicobacter pylori (H. pylori) infection and serum lipid profile is still controversial. The aim of this study was to determine any possible relationship between H. pylori infection and the lipid profile of patients with upper gastrointestinal symptoms.

MATERIAL AND METHODS

Consecutively selected 20-70 year-old dyspeptic patients who had undergone esophagogastroduodenoscopy were evaluated for H. pylori infection using both the CLO test and Giemsa staining. Serum total cholesterol (C), HDL-C, LDL-C, apo-A1, apo-B and triglyceride levels were measured.

RESULTS

A total of 137 patients (median age 52.0 years) were studied. Total cholesterol levels were lower in H. pylori-infected patients than in H. pylori-negative patients (mean +/- SEM: 199.3 +/- 5.9 versus 212.6 +/- 4.6 mg/dl, p = 0.08). Patients with duodenal ulcer (DU) had significantly lower levels of all measured lipidemic parameters including cholesterol, with the exception of triglycerides, in comparison with either H. pylori-positive or -negative dyspeptic patients (cholesterol: 177.6 +/- 6.5 versus 214.6 +/- 4.2 mg/dl, p < 0.0001). However, there was no difference in the total cholesterol/HDL-C ratio between DU patients and the rest of the dyspeptic patients.

CONCLUSIONS

Among H. pylori-positive and H. pylori-negative patients there was no difference in lipid profile apart from a trend towards total cholesterol levels being lower in H. pylori-positive patients. However, cholesterol, HDL-C, LDL-C, apo-A and apo-B were all decreased in DU patients even though this reduction did not result in a fall in the total cholesterol/HDL-C ratio. The etiologic factor differentiating the lipid profiles among dyspeptics only in H. pylori-positive patients carrying a DU could be dietetic, microbial, genetic or a combination of all three.

Acyl chain specificity of the acyltransferases LpxA and LpxD and substrate availability contribute to lipid A fatty acid heterogeneity in Porphyromonas gingivalis

Porphyromonas gingivalis lipid A is heterogeneous with regard to the number, type, and placement of fatty acids. Analysis of lipid A by matrix-assisted laser desorption ionization-time of flight mass spectrometry reveals clusters of peaks differing by 14 mass units indicative of an altered distribution of the fatty acids generating different lipid A structures. To examine whether the transfer of hydroxy fatty acids with different chain lengths could account for the clustering of lipid A structures, P. gingivalis lpxA (lpxA(Pg)) and lpxD(Pg) were cloned and expressed in Escherichia coli strains in which the homologous gene was mutated. Lipid A from strains expressing either of the P. gingivalis transferases was found to contain 16-carbon hydroxy fatty acids in addition to the normal E. coli 14-carbon hydroxy fatty acids, demonstrating that these acyltransferases display a relaxed acyl chain length specificity. Both LpxA and LpxD, from either E. coli or P. gingivalis, were also able to incorporate odd-chain fatty acids into lipid A when grown in the presence of 1% propionic acid. This indicates that E. coli lipid A acyltransferases do not have an absolute specificity for 14-carbon hydroxy fatty acids but can transfer fatty acids differing by one carbon unit if the fatty acid substrates are available. We conclude that the relaxed specificity of the P. gingivalis lipid A acyltransferases and the substrate availability account for the lipid A structural clusters that differ by 14 mass units observed in P. gingivalis lipopolysaccharide preparations.

Shift of homeostasis from parenchymal regeneration to fibroblast proliferation induced by lipopolysaccharide-activated macrophages in gastric mucosal healing in vitro

Wound healing in the gastrointestinal tract is an orderly process involving orchestrated responses of various cell types. Lipopolysaccharides (LPS) are major components of the outer membrane of Gram-negative bacteria, which are known to impair gastric ulcer healing in animals. The influence of LPS on intercellular communication in wound healing, however, is unknown. We examined the effects of LPS-induced macrophage activation on the proliferative response in cultured rat gastric epithelial cells (RGM-1) and fibroblasts JHU-25. Rat peritoneal resident macrophages were activated with increasing doses of LPS. The supernatant from the activated macrophage preparation, designated as macrophage-conditioned medium, was then used to treat RGM-1 or JHU-25 cells. Cell proliferation and migration were determined by [(3)H]-thymidine incorporation and a monolayer wound-healing assay, respectively. Macrophage-conditioned medium significantly suppressed RGM-1 cell proliferation but had no effect on cell migration. The same medium, however, increased JHU-25 cell proliferation. LPS treatment alone suppressed JHU-25 cell proliferation while it had no effect on RGM-1 cell proliferation, indicating that the differential effects of the macrophage-conditioned medium on cell proliferation were elicited by the factors derived from macrophages. In this regard, tumor necrosis factor (TNF)-alpha stimulated while interleukin (IL)-1beta suppressed RGM-1 cell proliferation, suggesting that IL-1beta but not TNF-alpha may play a part in the mediation of the antiproliferative effect of macrophage-conditioned medium on gastric epithelial cells. In contrast, IL-1beta suppressed while TNF-alpha had no effect on JHU-25 cell proliferation. Collectively, LPS-activated macrophages delay gastric mucosal regeneration but promote fibroblast proliferation in vitro. Such changes may partly elucidate the detrimental effect of bacterial infection on tissue repair in the stomach.

Expression of a Porphyromonas gingivalis lipid A palmitylacyltransferase in Escherichia coli yields a chimeric lipid A with altered ability to stimulate interleukin-8 secretion

In Escherichia coli the gene htrB codes for an acyltransferase that catalyses the incorporation of laurate into lipopolysaccharide (LPS) as a lipid A substituent. We describe the cloning, expression and characterization of a Porphyromonas gingivalis htrB homologue. When the htrB homologue was expressed in wild-type E. coli or a mutant strain deficient in htrB, a chimeric LPS with altered lipid A structure was produced. Compared with wild-type E. coli lipid A, the new lipid A species contained a palmitate (C16) in the position normally occupied by laurate (C12) suggesting that the cloned gene performs the same function as E. coli htrB but preferentially transfers the longer-chain palmitic acid that is known to be present in P. gingivalis LPS. LPS was purified from wild-type E. coli, the E. coli htrB mutant strain and the htrB mutant strain expressing the P. gingivalis acyltransferase. LPS from the palmitate bearing chimeric LPS as well as the htrB mutant exhibited a reduced ability to activate human embryonic kidney 293 (HEK293) cells transfected with TLR4/MD2. LPS from the htrB mutant also had a greatly reduced ability to stimulate interleukin-8 (IL-8) secretion in both endothelial cells and monocytes. In contrast, the activity of LPS from the htrB mutant bacteria expressing the P. gingivalis gene displayed wild-type activity to stimulate IL-8 production from endothelial cells but a reduced ability to stimulate IL-8 secretion from monocytes. The intermediate activation observed in monocytes for the chimeric LPS was similar to the pattern seen in HEK293 cells expressing TLR4/MD2 and CD14. Thus, the presence of a longer-chain fatty acid on E. coli lipid A altered the activity of the LPS in monocytes but not endothelial cell assays and the difference in recognition does not appear to be related to differences in Toll-like receptor utilization.

Characterization of the Helicobacter pylori cysteine-rich protein A as a T-helper cell type 1 polarizing agent

Predominant T-helper 1 (Th1) responses with increased gamma interferon (IFN-gamma) levels have been proposed to play an important role in Helicobacter pylori-induced gastritis and peptic ulceration. However, bacterial factors contributing to the initiation of Th1 polarization of H. pylori-specific immune responses have not been characterized in detail thus far. We report here on the identification of Helicobacter cysteine-rich protein A (HcpA) as a novel proinflammatory and Th1-promoting protein. The capacity of HcpA to induce immune activation was studied in splenocyte cultures of naive H. pylori-negative mice. HcpA stimulated the release of high concentrations of the proinflammatory and Th1-promoting cytokines interleukin-6 (IL-6) and IFN-gamma, in addition to significant levels of IL-12, tumor necrosis factor alpha, and IL-10. The observed cytokine profile was comparable to that induced by lipopolysaccharide but differed in the kinetics and maximum levels of cytokine production. In addition, HcpA-induced cytokine release resembled that observed upon incubation with H. pylori except for IL-10, which was only moderately released upon HcpA stimulation. Both HcpA- and H. pylori-mediated IFN-gamma production was drastically reduced by a neutralizing antibody against IL-12 but not by an anti-IL-2 antibody. Thus, HcpA seems to represent a novel bacterial virulence factor triggering the release of a concerted set of cytokines to instruct the adaptive immune system for the initiation of proinflammatory and Th1-biased immunity.

Impact of Helicobacter pylori virulence factors and compounds on activation and maturation of human dendritic cells

Recently, we and others have shown that Helicobacter pylori induces dendritic cell (DC) activation and maturation. However, the impact of virulence factors on the interplay between DCs and H. pylori remains elusive. Therefore, we investigated the contribution of cag pathogenicity island (PAI) and VacA status on cytokine release and up-regulation of costimulatory molecules in H. pylori-treated DCs. In addition, to characterize the stimulatory capacity of H. pylori compounds in more detail, we studied the effect of formalin-inactivated and sonicated H. pylori, as well as secreted H. pylori molecules, on DCs. Incubation of DCs with viable or formalin-inactivated H. pylori induced comparable secretion of interleukin-6 (IL-6), IL-8, IL-10, IL-12, IL-1beta, and tumor necrosis factor (TNF). In contrast, IL-12 and IL-1beta release was significantly reduced in DCs treated with sonicated bacteria and secreted bacterial molecules. Treatment of sonicated H. pylori preparations with polymyxin B resulted in a significant reduction of IL-8 and IL-6 secretion, suggesting that H. pylori-derived lipopolysaccharide at least partially contributes to activation of immature DCs. In addition, the capacity of H. pylori-pulsed DCs to activate allogeneic T cells was not affected by cag PAI and VacA. Pretreatment of DC with cytochalasin D significantly inhibited secretion of IL-12, IL-1beta, and TNF, indicating that phagocytosis of H. pylori contributes to maximal activation of DCs. Taken together, our results suggest that DC activation and maturation, as well as DC-mediated T-cell activation, are independent of the cag PAI and VacA status of H. pylori.