New frontiers in gut nutrient sensor research: prophylactic effect of glutamine against Helicobacter pylori-induced gastric diseases in Mongolian gerbils

Gamma-glutamyl transferase secreted by Helicobacter pylori promotes the development of gastric cancer by affecting the energy metabolism and histone methylation status of gastric epithelial cells

BACKGROUND

Helicobacter pylori (H. pylori) infection is critical in the development and occurrence of gastric cancer. H. pylori secretes gamma-glutamyl transferase (GGT), which affects energy metabolism and histone methylation in mesenchymal stem cells. However, its effect on human gastric epithelial cells remains unclear. This study aimed to investigate the effects of GGT on energy metabolism and histone methylation in gastric epithelial cells and determine its role in the development and progression of H. pylori-induced gastric cancer.

METHODS

A GGT knockout H. pylori strain and mouse gastric cancer model were constructed, and alpha-ketoglutarate (α-KG) was added. The underlying mechanism was investigated using proteomics, immunohistochemistry, Western blotting, and other experimental assays.

RESULTS

H. pylori can colonize the host's stomach and destroy the gastric epithelium. GGT secreted by H. pylori decreased the concentration of glutamine in the stomach and increased H3K9me3 and H3K27me3 expression, which promoted the proliferation and migration of gastric epithelial cells. Additionally, α-KG reversed this effect. GGT increased the tumorigenic ability of nude mice. GGT, secreted by H. pylori, promoted the expression of ribosomal protein L15 (RPL15), while GGT knockout and supplementation with α-KG and trimethylation inhibitors reduced RPL15 expression and Wnt signaling pathway expression.

CONCLUSIONS

H. pylori secreted GGT decreased the expression of glutamine and α-KG in gastric epithelial cells, increased the expression of histones H3K9me3 and H3K27me3, and activated the Wnt signaling pathway through RPL15 expression, ultimately changing the biological characteristics of the gastric epithelium and promoting the occurrence of gastric cancer. Altered energy metabolism and histone hypermethylation are important factors involved in this process.

Strategies adopted by gastric pathogen Helicobacter pylori for a mature biofilm formation: Antimicrobial peptides as a visionary treatment

Enormous efforts in recent past two decades to eradicate the pathogen that has been prevalent in half of the world's population have been problematic. The biofilm formed by Helicobacter pylori provides resistance towards innate immune cells, various combinatorial antibiotics, and human antimicrobial peptides, despite the fact that these all are potent enough to eradicate it in vitro. Biofilm provides the opportunity to secrete various virulence factors that strengthen the interaction between host and pathogen helping in evading the innate immune system and ultimately leading to persistence. To our knowledge, this review is the first of its kind to explain briefly the journey of H. pylori starting with the chemotaxis, the mechanism for selecting the site for colonization, the stress faced by the pathogen, and various adaptations to evade these stress conditions by forming biofilm and the morphological changes acquired by the pathogen in mature biofilm. Furthermore, we have explained the human GI tract antimicrobial peptides and the reason behind the failure of these AMPs, and how encapsulation of Pexiganan-A(MSI-78A) in a chitosan microsphere increases the efficiency of eradication.

A comprehensive evaluation of an animal model for Helicobacter pylori-associated stomach cancer: Fact and controversy

Even though Helicobacter pylori infection was the most causative factor of gastric cancer, numerous in vivo studies failed to induce gastric cancer using H. pylori infection only. The utilization of established animal studies in cancer research is crucial as they aim to investigate the coincidental association between suspected oncogenes and pathogenesis as well as generate models for the development and testing of potential treatments. The methods to establish gastric cancer using infected animal models remain limited, diverse in methods, and showed different results. This study investigates the differences in animal models, which highlight different pathological results in gaster by literature research. Electronic databases searched were performed in PubMed, Science Direct, and Cochrane, without a period filter. A total of 135 articles were used in this study after a full-text assessment was conducted. The most frequent animal models used for gastric cancer were Mice, while Mongolian gerbils and Transgenic mice were the most susceptible model for gastric cancer associated with H. pylori infection. Additionally, transgenic mice showed that the susceptibility to gastric cancer progression was due to genetic and epigenetic factors. These studies showed that in Mongolian gerbil models, H. pylori could function as a single agent to trigger stomach cancer. However, most gastric cancer susceptibilities were not solely relying on H. pylori infection, and numerous factors are involved in cancer progression. Further study using Mongolian gerbils and Transgenic mice is crucial to conduct and establish the best models for gastric cancer associated H. pylori.

Mechanisms of persistence, innate immune activation and immunomodulation by the gastric pathogen Helicobacter pylori

The gastric bacterium Helicobacter pylori efficiently evades innate immune detection and persistently colonizes its human host. Understanding the genetic determinants that H. pylori uses to establish and maintain persistence, along with their cellular targets, is key to our understanding of the pathogenesis of this extraordinarily successful bacterial colonizer of the human stomach. This review highlights recent advances in elucidating innate immune recognition of H. pylori, its interactions with myeloid cells and the consequences that this very local infection has for immune responses at extragastric sites in models of allergy, autoimmunity and parasitic infection. The human-specific, gram-negative gastric colonizer and carcinogen H. pylori represents the prototype of a persistent bacterial pathogen. It is transmitted during early childhood, typically from mother to infant, and is believed to persist in its human host from the cradle to the grave. The tremendous success of H. pylori in infecting and colonizing half of the world's population, and in continuously accompanying humans since they migrated out of Africa over 60000 years ago, can largely be attributed to its ability to manipulate the host immune system to its own advantage, and to thereby ensure its own persistence and chronicity. In his final years as an active PI, Stanley Falkow increasingly recognized the need to understand bacterial persistence strategies as a prerequisite of understanding the pathogenesis of chronic bacterial infections, and, inspired in large part by Denise Monack's work on Salmonella persistence, many of our discussions at the time revolved around this topic. Multiple labs have since made important contributions to our understanding of innate immune detection of H. pylori, the types and polarization of adaptive immune responses that ensue, the ability of H. pylori to skew such immune responses to its advantage, and its ability to manipulate the host immune system with far-reaching, even systemic consequences. This review attempts to cover some of these topics, with a particular focus on the most recent contributions by researchers in the field.

Helicobacter pylori γ-glutamyl transferase contributes to colonization and differential recruitment of T cells during persistence

Helicobacter pylori γ-glutamyl transferase (gGT) is a key bacterial virulence factor that is not only important for bacterial gastric colonization but also related to the development of gastric pathology. Despite accumulating evidence for pathogenic and immunologic functions of H. pylori gGT, it is still unclear how it supports gastric colonization and how its specific effects on the host’s innate and adaptive immune responses contribute to colonization and pathology. We have compared mice showing similar bacterial load after infection with gGT-proficient or gGT-deficient H. pylori to analyse the specific role of the enzyme during infection. Our data indicate that H. pylori gGT supports initial colonization. Nevertheless, bacteria lacking gGT can still colonize and persist. We observed that the presence of gGT during infection favoured a proinflammatory innate and adaptive immune response. Notably, H. pylori gGT activity was linked to increased levels of IFNγ, which were attributed to a differential recruitment of CD8⁺ T cells to the stomach. Our data support an essential role for H. pylori gGT in gastric colonization and further suggest that gGT favours infiltration of CD8⁺ cells to the gastric mucosa, which might play an important and yet overlooked role in the pathogenesis of H. pylori.

Helicobacter pylori γ-Glutamyltranspeptidase Induces Tolerogenic Human Dendritic Cells by Activation of Glutamate Receptors

Helicobacter pylori infection is characterized by chronic persistence of the bacterium. Different virulence factors, including H. pylori γ-glutamyltranspeptidase (gGT), have been reported to induce tolerogenicity by reprogramming dendritic cells (DCs). gGT is present in all bacterial isolates, indicating an important role for gGT in the course of infection. In the current study, we have analyzed the effect of H. pylori gGT on human DCs and the subsequent adaptive immune response. We show that glutamate produced due to H. pylori gGT enzymatic activity tolerizes DCs by inhibiting cAMP signaling and dampening IL-6 secretion in response to the infection. Together, our results provide a novel molecular mechanism by which H. pylori manipulates the host's immune response to persist within its host.

Oral glutathione supplementation drastically reduces Helicobacter-induced gastric pathologies

Helicobacter (H.) suis causes gastric pathologies in both pigs and humans. Very little is known on the metabolism of this bacterium and its impact on the host. In this study, we have revealed the importance of the glutamate-generating metabolism, as shown by a complete depletion of glutamine (Gln) in the medium during H. suis culture. Besides Gln, H. suis can also convert glutathione (GSH) to glutamate, and both reactions are catalyzed by the H. suis γ-glutamyltranspeptidase (GGT). Both for H. pylori and H. suis, it has been hypothesized that the degradation of Gln and GSH may lead to a deficiency for the host, possibly initiating or promoting several pathologies. Therefore the in vivo effect of oral supplementation with Gln and GSH was assessed. Oral supplementation with Gln was shown to temper H. suis induced gastritis and epithelial (hyper)proliferation in Mongolian gerbils. Astonishingly, supplementation of the feed with GSH, another GGT substrate, resulted in inflammation and epithelial proliferation levels returning to baseline levels of uninfected controls. This indicates that Gln and GSH supplementation may help reducing tissue damage caused by Helicobacter infection in both humans and pigs, highlighting their potential as a supportive therapy during and after Helicobacter eradication therapy.

Resveratrol Protects against Helicobacter pylori-Associated Gastritis by Combating Oxidative Stress

Helicobacter pylori (H. pylori)-induced oxidative stress has been shown to play a very important role in the inflammation of the gastric mucosa and increases the risk of developing gastric cancer. Resveratrol has many biological functions and activities, including antioxidant and anti-inflammatory effect. The purpose of this study was to probe whether resveratrol inhibits H. pylori-induced gastric inflammation and to elucidate the underlying mechanisms of any effect in mice. A mouse model of H. pylori infection was established via oral inoculation with H. pylori. After one week, mice were administered resveratrol (100 mg/kg body weight/day) orally for six weeks. The mRNA and protein levels of iNOS and IL-8 were assessed using RT-PCR, Western blot and ELISA. The expression levels of IκBα and phosphorylated IκBα (which embodies the level and activation of NF-κB), Heme Oxygenase-1 (HO-1; a potent antioxidant enzyme) and nuclear factor-erythroid 2 related factor 2 (Nrf2) were determined using Western blot, and lipid peroxide (LPO) level and myeloperoxidase (MPO) activity were examined using an MPO colorimetric activity assay, thiobarbituric acid reaction, and histological-grade using HE staining of the gastric mucosa. The results showed that resveratrol improved the histological infiltration score and decreased LPO level and MPO activity in the gastric mucosa. Resveratrol down-regulated the H. pylori-induced mRNA transcription and protein expression levels of IL-8 and iNOS, suppressed H. pylori-induced phosphorylation of IκBα, and increased the levels of HO-1 and Nrf2. In conclusion, resveratrol treatment exerted significant effects against oxidative stress and inflammation in H. pylori-infected mucosa through the suppression of IL-8, iNOS, and NF-κB, and moreover through the activation of the Nrf2/HO-1 pathway.

Helicobacter pylori γ-glutamyltranspeptidase impairs T-lymphocyte function by compromising metabolic adaption through inhibition of cMyc and IRF4 expression

Helicobacter pylori (H. pylori) is a human-specific pathogen that has evolved to cope with the immune response elicited against the infection. We previously reported that H. pylori γ-glutamyltranspeptidase (gGT) impairs T-lymphocyte proliferation and thus might act as immune regulatory factor. In this study, we analysed the underlying mechanism and its implications for H. pylori persistence. We found that H. pylori gGT compromised T-cell proliferation, activation and effector cytokine expression by specifically depriving the extracellular space of glutamine. When assessing signalling cascades and transcription factors affected by H. pylori gGT, we found that expression of cMyc and IRF4, both required for metabolic adaptation of T-lymphocytes, was highly sensitive to extracellular glutamine levels and downregulated upon gGT treatment. Moreover, we could confirm decreased IRF4 expression in T-lymphocytes infiltrating the stomach of infected individuals. Thus, our results suggest that H. pylori gGT-mediated glutamine deprivation in the gastric mucosa may suppress T-cell function thereby contributing to bacterial persistence.

Protective effect of Korean Red Ginseng extract against Helicobacter pylori-induced gastric inflammation in Mongolian gerbils

Helicobacter pylori-induced gastric inflammation includes induction of inflammatory mediators interleukin (IL)-8 and inducible nitric oxide synthase (iNOS), which are mediated by oxidant-sensitive transcription factor NF-κB. High levels of lipid peroxide (LPO) and increased activity of myeloperoxidase (MPO), a biomarker of neutrophil infiltration, are observed in H. pylori-infected gastric mucosa. Panax ginseng Meyer, a Korean herb medicine, is widely used in Asian countries for its biological activities including anti-inflammatory efficacy. The present study aims to investigate whether Korean Red Ginseng extract (RGE) inhibits H. pylori-induced gastric inflammation in Mongolian gerbils. One wk after intragastric inoculation with H. pylori, Mongolian gerbils were fed with either the control diet or the diet containing RGE (200 mg RGE/gerbil) for 6 wk. The following were determined in gastric mucosa: the number of viable H. pylori in stomach; MPO activity; LPO level; mRNA and protein levels of keratinocyte chemoattractant factor (KC, a rodent IL-8 homolog), IL-1β, and iNOS; protein level of phospho-IκBα (which reflects the activation of NF-κB); and histology. As a result, RGE suppressed H. pylori-induced mRNA and protein levels of KC, IL-1β, and iNOS in gastric mucosa. RGE also inhibited H. pylori-induced phosphorylation of IκBα and increases in LPO level and MPO activity of gastric mucosa. RGE did not affect viable H. pylori colonization in the stomach, but improved the histological grade of infiltration of polymorphonuclear neutrophils, intestinal metaplasia, and hyperplasia. In conclusion, RGE inhibits H. pylori-induced gastric inflammation by suppressing induction of inflammatory mediators (KC, IL-1β, iNOS), MPO activity, and LPO level in H. pylori-infected gastric mucosa.

New therapeutic strategy for amino acid medicine: prophylactic and healing promoting effect of monosodium glutamate against NSAID-induced enteropathy

We reviewed the effect of monosodium glutamate (MSG) on the development and healing of nonsteroidal anti-inflammatory drug (NSAID)-induced small intestinal lesions in rats. Loxoprofen (60 mg/kg, p.o.) induced lesions in the small intestine within 24 h, accompanied by a decrease of Muc2 expression and an increase in enterobacterial invasion and inducible nitric oxide synthase (iNOS) expression. These lesions were prevented when MSG was given as a mixture of powdered food for 5 days before the loxoprofen treatment. This effect of MSG was accompanied by an increase in Muc2 expression / mucus secretion as well as the suppression of bacterial invasion and iNOS expression. These intestinal lesions healed spontaneously within 6 days, but the process was impaired by the repeated administration of low-dose loxoprofen (30 mg/kg) for 5 days after the ulceration, with the decrease of vascular endothelial derived growth factor (VEGF) expression and angiogenesis. The healing-impairing effect of loxoprofen was prevented by feeding 5% MSG for 5 days after the ulceration. These results suggest that MSG not only prevents loxoprofen-induced small intestinal damage but also promotes a healing of these lesions; the former is functionally associated with the increase in Muc2 expression / mucus secretion and the suppression of bacterial invasion and iNOS expression, while the latter is associated with the stimulation of VEGF expression/angiogenesis.

N-methyl D-aspartate channels link ammonia and epithelial cell death mechanisms in Helicobacter pylori Infection

BACKGROUND & AIMS

Helicobacter pylori infection is a risk factor for gastric cancer. Ammonia/ammonium (A/A) is a cytotoxin generated by H pylori that kills gastric epithelial cells. We investigated whether A/A cytotoxicity occurs by activating N-methyl d-aspartate (NMDA) channels, which results in Ca(2+) permeation and epithelial cell death.

METHODS

Gastric epithelial cells were cultured to confluence and then incubated with A/A and NMDA channel or cell signaling antagonists. Cells were incubated with wild-type H pylori or mutant strains that do not produce A/A. Changes in intracellular Ca(2+) were examined in living cells by confocal microscopy. Biochemical and histochemical techniques were used to examine the relationship between A/A-induced cell death and intracellular levels of Ca(2+).

RESULTS

A/A increased Ca(2+) permeation in gastric epithelial cells; the increase was blocked by NMDA receptor and cell signaling antagonists. Wild-type, but not mutant H pylori, also caused extensive Ca(2+) permeation of gastric epithelial cells, which was blocked when NMDA-receptor expression was repressed. Ca(2+) that entered cells was initially cytoplasmic and activated proteases. Later, the Ca(2+) was sequestered to cytoplasmic vacuoles that are dilatations of the endoplasmic reticulum. Inositol-3-phosphate-dependent release of Ca(2+) from the endoplasmic reticulum and protease activity damaged mitochondria, reduced levels of adenosine triphosphate, and transcriptionally up-regulated cell death effectors. Expression of the NMDA receptor was altered in stomachs of mice infected with H pylori.

CONCLUSIONS

A/A affects gastric epithelial cell viability by allowing excessive Ca(2+) permeation through NMDA channels. NMDA channels might thereby regulate cell survival and death pathways during development of gastric cancers associated with H pylori infection.