Helicobacter pylori generates superoxide radicals and modulates nitric oxide metabolism

Functional roles and cancer variants of the bifunctional glycosylase NEIL2

Over 70,000 DNA lesions occur in the cell every day, and the inability to properly repair them can lead to mutations and destabilize the genome, resulting in carcinogenesis. The base excision repair (BER) pathway is critical for maintaining genomic integrity by repairing small base lesions, abasic sites and single-stranded breaks. Monofunctional and bifunctional glycosylases initiate the first step of BER by recognizing and excising specific base lesions, followed by DNA end processing, gap filling, and finally nick sealing. The Nei-like 2 (NEIL2) enzyme is a critical bifunctional DNA glycosylase in BER that preferentially excises cytosine oxidation products and abasic sites from single-stranded, double-stranded, and bubble-structured DNA. NEIL2 has been implicated to have important roles in several cellular functions, including genome maintenance, participation in active demethylation, and modulation of the immune response. Several germline and somatic variants of NEIL2 with altered expression and enzymatic activity have been reported in the literature linking them to cancers. In this review, we provide an overview of NEIL2 cellular functions and summarize current findings on NEIL2 variants and their relationship to cancer.

Anti-inflammatory and urease inhibitory iridoid glycosides from Nyctanthes arbor-tristis Linn

ETHNOPHARMACOLOGICAL RELEVANCE

Nyctanthes arbor-tristis Linn. has been used by Ayruvedic physicians for the cure of different diseases including ulcers, gastric and inflammatory diseases.

AIM OF THE STUDY

To isolate and identify compounds from this source and investigate their therapeutic potential for the treatment of gastric ulcer and related disorders.

MATERIAL AND METHODS

The ethanol extract of fresh aerial parts of N. arbor-tristis was used in the present studies which was subjected to a bio-assay guided fractionation followed by chromatographic separations. The structures of pure compounds were elucidated using various spectroscopic techniques. The inhibition of urease enzyme was evaluated by weatherburn indophenol method. Molecular docking studies were determined by using Molecular Operating Environment (MOE) version 2020.0901 version. The intracellular ROS production from phagocytes was determined by chemiluminescence assay and NO generation was detected by Griess method. The proinflammatory cytokine TNF-α was quantified by ELISA. Cytotoxic activity was assessed by MTT assay.

RESULTS

One previously undescribed iridoid glycoside arborside F (1) and four known iridoid glycosides arborside A (2), arborside C (3), loganin (4) and 7-O-trans-cinnamoyl-6β-hydroxyloganin (5) were isolated and characterized in the present studies and their urease inhibitory activity was determined. Among these, 2 and 5 showed strong urease inhibition (IC50 = 12.1 ± 1.74 and 14.1 ± 0.59 μM respectively) (standard acetohydroxamic acid IC50 = 20.3 ± 0.42 μM), whereas rest of compounds showed moderate to low inhibition. Kinetic studies revealed that compounds 2 and 5 possess competitive type of inhibition. Molecular docking showed polar and non-polar interactions of compounds 2 and 5 with urease enzyme residues. Compounds 2 and 3 showed inhibition of ROS from whole blood (IC50 = 1.6 ± 0.3 and 2.5 ± 0.09 μg/mL respectively) and PMNs (IC50 = 1.5 ± 0.03 and 1.4 ± 0.0 μg/mL respectively). Compound 2 significantly inhibited nitric oxide and proinflammatory cytokine TNF-α (IC50 = 18.2 ± 3.0 and 73.8 ± 6.6 μg/mL respectively). Compounds 1, 4 and 5 were inactive on ROS. All isolated compounds were non-toxic on normal mouse fibroblasts (NIH-3T3) cells.

CONCLUSIONS

The ethno pharmacological repute of N. arbor-tristis in treating gastric and anti-inflammatory ailments is supported by present studies which resulted in isolation of a potent urease inhibitory and anti-inflammatory agent arborside A (2) a potential anti-ulcer and anti-inflammatory drug lead.

Helicobacter pylori infection-A risk factor for lipid peroxidation and superoxide dismutase over-activity: A cross-sectional study among patients with dyspepsia in Cameroon

Background and Aim

There is an intimate relationship between oxidative stress and inflammation. Helicobacter pylori (H. pylori) infection leads to gastritis in almost all the hosts. So, we hypothesize that gastritis in H. pylori infection may be described as the accumulation of continuous oxidative damage.

Methods

The study was conducted from October 2020 to October 2021 at three reference health facilities in Cameroon. A total of 266 participants (131 males and 135 females) ranging from 15 to 88 years old with 48.28 ± 17.29 years as mean age were enrolled. Each participant gave a written informed consent and ethical committees approved the protocol. Biopsies samples were collected for H. pylori detection using histological examination and rapid urease test. Malondialdehyde (MDA) and glutathione (GSH) content, and catalase (CAT) and superoxide dismutase (SOD) activities were evaluated in serum as biomarkers of oxidative stress.

Results

Helicobacter pylori was detected in 71.80% of our sample population. Low income level was associated with higher GSH level (P = 0.0249) and having family history of gastric cancer to higher SOD activity (P = 0.0156). A significant higher MDA content (P < 0.0001) and SOD activity (P = 0.0235) was recorded among infected individuals compared with noninfected ones. A significantly higher MDA content and SOD activity was recorded among smokers (P = 0.0461) and participants older than 50 years old (P = 0.0491) with H. pylori positivity.

Conclusion

Our findings showed that H. pylori infection is associated with overproduction of reactive oxygen species and oxidative stress. The presence of this pathogen in elderly individuals or in smokers increased their risk for oxidative stress.

Everolimus ameliorates Helicobacter pylori infection-induced inflammation in gastric epithelial cells

Helicobacter pylori (H.pylori) infection caused by gastric mucosal inflammation plays a pivotal role in the progression of gastric diseases. The recruitment and attachment of monocytes to the gastric mucosal epithelium are a major event in the early stages of H. pylori-associated gastric diseases. Everolimus is a mechanistic/mammalian target of rapamycin (mTOR) inhibitor used to prevent tumor growth by inhibiting the PI3K signaling pathway. Here, we examined the pharmacological role of Everolimus against H.pylori-induced damage in gastric epithelial cells. Firstly, we found that Everolimus ameliorated H.pylori-induced oxidative stress by reducing reactive oxygen species (ROS) and malondialdehyde (MDA). Secondly, Everolimus significantly reduced the expressions of the pro-inflammatory cytokines interleukin (IL)-6, tumor necrosis factor-α (TNF-α), and IL-8. Moreover, it decreased the production of the pro-inflammatory chemokines C-X-C motif ligand 1 (CXCL1) and macrophage chemoattractant protein-1 (MCP-1). Importantly, Everolimus suppressed the induction of the adhesion molecule intracellular adhesion molecule-1 (ICAM-1) and the attachment of THP-1 monocytes to gastric epithelial AGS cells. Our data also shows that Everolimus inhibited the activation of the NF-κB signaling pathway. Therefore, we conclude that Everolimus could protect gastric epithelial cells by mitigating H.pylori-induced inflammatory response and the attachment of monocytes to epithelial cells.

Helicobacter pylori FabX contains a [4Fe-4S] cluster essential for unsaturated fatty acid synthesis

Unsaturated fatty acids (UFAs) are essential for functional membrane phospholipids in most bacteria. The bifunctional dehydrogenase/isomerase FabX is an essential UFA biosynthesis enzyme in the widespread human pathogen Helicobacter pylori, a bacterium etiologically related to 95% of gastric cancers. Here, we present the crystal structures of FabX alone and in complexes with an octanoyl-acyl carrier protein (ACP) substrate or with holo-ACP. FabX belongs to the nitronate monooxygenase (NMO) flavoprotein family but contains an atypical [4Fe-4S] cluster absent in all other family members characterized to date. FabX binds ACP via its positively charged α7 helix that interacts with the negatively charged α2 and α3 helices of ACP. We demonstrate that the [4Fe-4S] cluster potentiates FMN oxidation during dehydrogenase catalysis, generating superoxide from an oxygen molecule that is locked in an oxyanion hole between the FMN and the active site residue His182. Both the [4Fe-4S] and FMN cofactors are essential for UFA synthesis, and the superoxide is subsequently excreted by H. pylori as a major resource of peroxide which may contribute to its pathogenic function in the corrosion of gastric mucosa.

Gastric Helicobacter suis Infection Partially Protects against Neurotoxicity in A 6-OHDA Parkinson's Disease Mouse Model

The exact etiology of Parkinson’s disease (PD) remains largely unknown, but more and more research suggests the involvement of the gut microbiota. Interestingly, idiopathic PD patients were shown to have at least a 10 times higher prevalence of Helicobacter suis (H. suis) DNA in gastric biopsies compared to control patients. H. suis is a zoonotic Helicobacter species that naturally colonizes the stomach of pigs and non-human primates but can be transmitted to humans. Here, we investigated the influence of a gastric H. suis infection on PD disease progression through a 6-hydroxydopamine (6-OHDA) mouse model. Therefore, mice with either a short- or long-term H. suis infection were stereotactically injected with 6-OHDA in the left striatum and sampled one week later. Remarkably, a reduced loss of dopaminergic neurons was seen in the H. suis/6-OHDA groups compared to the control/6-OHDA groups. Correspondingly, motor function of the H. suis-infected 6-OHDA mice was superior to that in the non-infected 6-OHDA mice. Interestingly, we also observed higher expression levels of antioxidant genes in brain tissue from H. suis-infected 6-OHDA mice, as a potential explanation for the reduced 6-OHDA-induced cell loss. Our data support an unexpected neuroprotective effect of gastric H. suis on PD pathology, mediated through changes in oxidative stress.

The beneficial health effects of Nigella sativa on Helicobacter pylori eradication, dyspepsia symptoms, and quality of life in infected patients: A pilot study

The aim of this study was to evaluate the effects of Nigella sativa (N. sativa) in addition to quadruple-therapy on Helicobacter pylori eradication, dyspepsia, biochemical-markers, and quality of life in infected patients. In this double-blind placebo-controlled clinical-trial, 51 H. pylori infected patients with functional dyspepsia were randomly assigned to treatment (quadruple-therapy with 2 g/day N. sativa) or placebo groups (quadruple-therapy with 2 g/day placebo) for 8 weeks. Serum levels of interleukin-8 (IL-8), high-sensitivity C-reactive protein (hs-CRP) and malondialdehyde, quality of life, dyspepsia, food-intake, body-weight, and body mass index (BMI) were evaluated at the baseline and at the end of the study. H. pylori eradication was evaluated at the end of the intervention. At the end of the study, H. pylori eradication was more in the N. sativa group compared with the placebo (p = .01). Weight, BMI, and dietary-intake (p < .05) increased significantly as compared with placebo. A significant improvement was also observed in patients' quality of life in the treatment group compared with the placebo (p < .05). The differences of biochemical-markers and dyspepsia between the two groups were not significant. So, N. sativa supplementation with medical treatment may have beneficial effects on H. pylori eradication, weight, BMI, dietary-intake, and quality of life in infected patients.

DNA Hypermethylation Downregulates Telomerase Reverse Transcriptase (TERT) during H. pylori-Induced Chronic Inflammation

Helicobacter pylori infection causes chronic gastritis and is the major risk factor of gastric cancer. H. pylori induces a chronic inflammation-producing reactive oxygen species (ROS) which is a source of chromosome instabilities and contributes to the development of malignancy. H. pylori also promotes DNA hypermethylation, known to dysregulate essential genes that maintain genetic stability. The maintenance of telomere length by telomerase is essential for chromosome integrity. Telomerase reverse transcriptase (TERT) is the catalytic component of telomerase activity and an important target during host-pathogen interaction. We aimed to investigate the consequences of H. pylori on the regulation of TERT gene expression and telomerase activity. In vitro, hTERT mRNA levels and telomerase activity were analysed in H. pylori-infected human gastric epithelial cells. In addition, C57BL/6 and INS-GAS mice were used to investigate the influence of H. pylori-induced inflammation on TERT levels. Our data demonstrated that, in vitro, H. pylori inhibits TERT gene expression and decreases the telomerase activity. The exposure of cells to lycopene, an antioxidant compound, restores TERT levels in infected cells, indicating that ROS are implicated in this downregulation. In vivo, fewer TERT-positive cells are observed in gastric tissues of infected mice compared to uninfected, more predominantly in the vicinity of large aggregates of lymphocytes, suggesting an inflammation-mediated regulation. Furthermore, H. pylori appears to downregulate TERT gene expression through DNA hypermethylation as shown by the restoration of TERT transcript levels in cells treated with 5′-azacytidine, an inhibitor of DNA methylation. This was confirmed in infected mice, by PCR-methylation assay of the TERT gene promoter. Our data unraveled a novel way for H. pylori to promote genome instabilities through the inhibition of TERT levels and telomerase activity. This mechanism could play an important role in the early steps of gastric carcinogenesis.

Artemisinin and its derivatives prevent Helicobacter pylori-induced gastric carcinogenesis via inhibition of NF-κB signaling

BACKGROUND

Gastric cancer has a high morbidity and is a leading cause of cancer-related mortality worldwide. Helicobacter pylori (H. pylori) infection is commonly found in the early stage of gastric cancer pathogenesis, which induces chronic gastritis. Artemisinin (ART) and its derivatives (ARTS, artesunate and DHA, dihydroartemisinin), a new class of potent antimalarials, have been reported to exert both preventive and anti-gastric cancer effects. However, the underlying mechanisms of the chemopreventive effects of ART and its derivatives in H. pylori infection induced-gastric cancer are not fully elucidated.

PURPOSE

We investigated the effects of H. pylori infection in gastric cancer; and the preventive mechanisms of ART, ARTS and DHA.

METHODS

The H. pylori growth was determined by the broth macro-dilution method, and its adhesion to gastric cancer cells was evaluated by using the urease assay. The protein and mRNA levels, reactive oxygen species (ROS) production, as well as the production of inflammatory cytokines were evaluated by Western blot, real-time PCR, flow cytometry and ELISA, respectively. Moreover, an in vivo MNU (N-methyl-N-nitroso-urea) and H. pylori-induced gastric adenocarcinoma mouse model was established for the investigation of the cancer preventive effects of ART and its derivaties, and the underlying mechanisms of action.

RESULTS

ART, DHA and ARTS inhibited the growth of H. pylori and gastric cancer cells,suppressed H. pylori adhesion to the gastric cancer cells, and reduced the H. pylori-enhanced ROS production. Moreover, ART, DHA and ARTS significantly reduced tumor incidence, number of tumor nodules and tumor size in the mouse model. Among these three compounds, DHA exerted the most potent chemopreventive effect. Mechanistic studies showed that ART and its derivatives potently inhibited the NF-κB activation.

CONCLUSION

ART, DHA and ARTS have potent preventive effects in H. pylori-induced gastric carcinogenesis. These effects are, at least in part, attributed to the inhibition of NF-κB signaling pathway. Our findings provide a molecular justification of using ART and its derivatives for the prevention and treatment of gastric cancer.

Inhibition of polarity-regulating kinase PAR1b contributes to Helicobacter pylori inflicted DNA Double Strand Breaks in gastric cells

The serine/threonine kinase Par1 is a core component of the machinery that sets up polarity in the embryo and regulates cell fate decisions but its role in the homeostasis of adult tissues is poorly understood. Inhibition of Par1 by the bacterium Helicobacter pylori (H. pylori) represents the only established pathology that affects Par1 function in an adult epithelium. Thus, during chronic H. pylori infection of the gastric mucosa Par1 is one of the targets of the non-obligate H.pylori cytotoxic protein and oncogene CagA, which stimulates inflammation and triggers morphological changes, both believed to contribute to the gastric cancer risk imposed by H. pylori infection. Based on Par1's role in cell polarity, it has been speculated that Par1 inhibition affects epithelial polarity. Here we report the unexpected finding that CagA-mediated Par1-inhibition promotes the generation of DNA Double Strand Breaks in primary gastric epithelial cells, which likely contributes to the reported accumulation of mutations in chronically infected mucosal cells. Abbreviations: AGS: human gastric adenocarcinoma cell line; CM: CagA Multimerization (and Par1 binding) domain; H. pylori: Helicobacter pylori; DSB: Double Strand Break; HGECs: human (primary) gastric epithelial cells; IB: immunoblot; IF: immunofluorescence; MOI: Multiplicity of Infection; ROS: reactive oxygen species; Par1: Partitioning Defective 1 kinase; WT: wild type.

Unraveling the Novel Protective Effect of Patchouli Alcohol Against Helicobacter pylori-Induced Gastritis: Insights Into the Molecular Mechanism in vitro and in vivo

Patchouli alcohol (PA), a natural tricyclic sesquiterpene extracted from Pogostemon cablin (Blanco) Benth. (Labiatae), has been found to exhibit anti-Helicobacter pylori and anti-inflammatory properties. In this study, we investigated the protective effect of PA against H. pylori-induced gastritis in vitro and in vivo, and determined the underlying mechanism. In the in vivo experiment, a C57BL/6 mouse model of gastritis was established using H. pylori SS1, and treatments with standard triple therapy or 5, 10, and 20 mg/kg PA were performed for 2 weeks. Results indicated that PA effectively attenuated oxidative stress by decreasing contents of intracellular reactive oxygen species (ROS) and malonyldialdehyde (MDA), and increasing levels of non-protein sulfhydryl (NP-SH), catalase and glutathione (GSH)/glutathione disulphide (GSSG). Additionally, treatment with PA significantly attenuated the secretions of interleukin 1 beta (IL-1β), keratinocyte chemoattractant and interleukin 6 (IL-6). PA (20 mg/kg) significantly protected the gastric mucosa from H. pylori-induced damage. In the in vitro experiment, GES-1 cells were cocultured with H. pylori NCTC11637 at MOI = 100:1 and treated with different doses of PA (5, 10, and 20 μg/ml). Results indicated that PA not only significantly increased the cell viability and decreased cellular lactate dehydrogenase (LDH) leakage, but also markedly elevated the mitochondrial membrane potential and remarkably attenuated GES-1 cellular apoptosis, thereby protecting gastric epithelial cells against injuries caused by H. pylori. PA also inhibited the secretions of pro-inflammatory factors, such as monocyte chemotactic protein 1 (MCP-1), tumor necrosis factor-α (TNF-α) and IL-6. Furthermore, after PA treatment, the combination of NACHT, LRR, and PYD domains-containing protein 3 (NLRP3) and cysteine-aspartic proteases 1 (CASPASE-1), the expression levels of NLRP3 inflammasome-related proteins, such as thioredoxin-interacting protein (TXNIP), pro-CASPASE-1, cle-CASPASE-1, and NLRP3 and genes (NLRP3 and CASPASE1) were significantly decreased as compared to the model group. In conclusion, treatment with PA for 2 weeks exhibited highly efficient protective effect against H. pylori-induced gastritis and related damages. The underlying mechanism might involve antioxidant activity, inhibition of pro-inflammatory factor and regulation of NLRP3 inflammasome function. PA exerted anti-H. pylori and anti-gastritis effects and thus had the potential to be a promising candidate for treatment of H. pylori-related diseases.

Impact of Klebsiella pneumoniae in lower gastrointestinal tract diseases

The 2016 Global Burden of Disease report by WHO revealed that diseases of the gastrointestinal tract (GIT) had one of the highest incidence rates worldwide. The plethora of factors that contribute to the development of GIT-related illnesses can be divided into genetic, environmental and lifestyle factors. Apart from that, the role that infectious agents play in the development of GIT diseases has piqued the interest of researchers worldwide. The human gut harbors approximately 10¹⁴ bacteria in it with increasing concentration toward the lower GIT. Among the various microbiota that colonize the human gut, Gram-negative bacteria have been most notoriously linked to GIT-related diseases such as inflammatory bowel disease (IBD) including Crohn's disease and ulcerative colitis and colorectal cancer (CRC). Some of the notable culprits that have been attributed to these diseases are Bacteroides fragilis, Fusobacterium nucleatum, Escherichia coli and Helicobacter pylori. However, studies in recent years are beginning to recognize a new player, Klebsiella pneumoniae (K. pneumoniae) in the causation and progression of GIT diseases. Once synonymous with infections and diseases of the upper respiratory tract, K. pneumoniae has now emerged as one of the pathogens commonly isolated from patients with GIT diseases. However, extensive studies attributing K. pneumoniae to GIT diseases, particularly that of CRC are scanty. Therefore, this review intends to shed light on the association of K. pneumoniae in gastrointestinal diseases such as Crohn's disease, ulcerative colitis as well as CRC.

Helicobacter pylori and 17β-estradiol induce human intrahepatic biliary epithelial cell abnormal proliferation and oxidative DNA damage

BACKGROUND

Biliary cancers are more common in females, and previous studies have suggested that Helicobacter pylori (H. pylori) exists in the biliary system. However, the effects of H. pylori infection and estrogen on the biological behaviors of human biliary epithelium mucosa remain unknown. The present study aimed to clarify their effects on the proliferation, apoptosis, migration and oxidative DNA damage of a human intrahepatic biliary epithelial cell (HIBEC) line in vitro.

METHODS

HIBECs were co-cultured with 17β-estradiol (at 10^-9 mol/L, 10^-7 mol/L, and 10^-5 mol/L) and H. pylori (at MOI=0.5:1, 1:1, and 2:1) and continuously passaged until the 15th generation (approximately 45 days). Then, the following assays were performed. HIBEC proliferation was measured using the CCK-8 assay, plate clone-formation assay and by determining Ki-67 expression with immunocytochemistry; cell apoptosis and migration were investigated using Annexin-V/PI and transwell assays, respectively; and reactive oxygen species (ROS) and 8-hydroxy-2'-deoxyguanosine (8-OHdG) production were detected by flow cytometry and immunofluorescence staining combined with confocal laser scanning microscopy, respectively. The results were the basis for evaluating the level of oxidative stress and the related DNA damage in HIBECs.

RESULTS

HIBECs maintained a normal morphology and vitality when treated with 17β-estradiol (at 10^-9 mol/L) and H. pylori (at MOI=0.5:1 and 1:1). 17β-estradiol at 10^-7 mol/L and 10^-5 mol/L and H. pylori at MOI=2:1, by contrast, caused cell death. Compared with controls, HIBECs treated with 17β-estradiol (10^-9 mol/L) and H. pylori (MOI=1:1) had a higher up-regulation of proliferation, Ki-67 expression, clone formation, migration activity and the expression of ROS and 8-OHdG and exhibited a down-regulation of apoptosis. The above effects were further increased when 17β-estradiol and H. pylori were combined (P<0.05).

CONCLUSIONS

H. pylori and 17β-estradiol, separately or in combination, promoted cell proliferation and suppressed apoptosis of HIBECs in vitro. The above phenomena might be related to oxidative stress and its subsequent DNA damage with H. pylori and 17β-estradiol.

Redox signaling in the gastrointestinal tract

Redox signaling regulates physiological self-renewal, proliferation, migration and differentiation in gastrointestinal epithelium by modulating Wnt/β-catenin and Notch signaling pathways mainly through NADPH oxidases (NOXs). In the intestine, intracellular and extracellular thiol redox status modulates the proliferative potential of epithelial cells. Furthermore, commensal bacteria contribute to intestine epithelial homeostasis through NOX1- and dual oxidase 2-derived reactive oxygen species (ROS). The loss of redox homeostasis is involved in the pathogenesis and development of a wide diversity of gastrointestinal disorders, such as Barrett's esophagus, esophageal adenocarcinoma, peptic ulcer, gastric cancer, ischemic intestinal injury, celiac disease, inflammatory bowel disease and colorectal cancer. The overproduction of superoxide anion together with inactivation of superoxide dismutase are involved in the pathogenesis of Barrett's esophagus and its transformation to adenocarcinoma. In Helicobacter pylori-induced peptic ulcer, oxidative stress derived from the leukocyte infiltrate and NOX1 aggravates mucosal damage, especially in HspB+ strains that downregulate Nrf2. In celiac disease, oxidative stress mediates most of the cytotoxic effects induced by gluten peptides and increases transglutaminase levels, whereas nitrosative stress contributes to the impairment of tight junctions. Progression of inflammatory bowel disease relies on the balance between pro-inflammatory redox-sensitive pathways, such as NLRP3 inflammasome and NF-κB, and the adaptive up-regulation of Mn superoxide dismutase and glutathione peroxidase 2. In colorectal cancer, redox signaling exhibits two Janus faces: On the one hand, NOX1 up-regulation and derived hydrogen peroxide enhance Wnt/β-catenin and Notch proliferating pathways; on the other hand, ROS may disrupt tumor progression through different pro-apoptotic mechanisms. In conclusion, redox signaling plays a critical role in the physiology and pathophysiology of gastrointestinal tract.

The Immune Battle against Helicobacter pylori Infection: NO Offense

Helicobacter pylori is a successful pathogen of the human stomach. Despite a vigorous immune response by the gastric mucosa, the bacterium survives in its ecological niche, thus favoring diseases ranging from chronic gastritis to adenocarcinoma. The current literature demonstrates that high-output of nitric oxide (NO) production by the inducible enzyme NO synthase-2 (NOS2) plays major functions in host defense against bacterial infections. However, pathogens have elaborated several strategies to counteract the deleterious effects of NO; this includes inhibition of host NO synthesis and transcriptional regulation in response to reactive nitrogen species, allowing the bacteria to face the nitrosative stress. Moreover, NO is also a critical mediator of inflammation and carcinogenesis. In this context, we review the recent findings on the expression of NOS2 in H. pylori-infected gastric tissues and epithelial cells, the role of NO in H. pylori-related diseases and H. pylori gene expression, and the mechanisms whereby H. pylori regulates NO synthesis by host cells.

Regulation of Rac1 and Reactive Oxygen Species Production in Response to Infection of Gastrointestinal Epithelia

Generation of reactive oxygen species (ROS) during infection is an immediate host defense leading to microbial killing. APE1 is a multifunctional protein induced by ROS and after induction, protects against ROS-mediated DNA damage. Rac1 and NAPDH oxidase (Nox1) are important contributors of ROS generation following infection and associated with gastrointestinal epithelial injury. The purpose of this study was to determine if APE1 regulates the function of Rac1 and Nox1 during oxidative stress. Gastric or colonic epithelial cells (wild-type or with suppressed APE1) were infected with Helicobacter pylori or Salmonella enterica and assessed for Rac1 and NADPH oxidase-dependent superoxide production. Rac1 and APE1 interactions were measured by co-immunoprecipitation, confocal microscopy and proximity ligation assay (PLA) in cell lines or in biopsy specimens. Significantly greater levels of ROS were produced by APE1-deficient human gastric and colonic cell lines and primary gastric epithelial cells compared to control cells after infection with either gastric or enteric pathogens. H. pylori activated Rac1 and Nox1 in all cell types, but activation was higher in APE1 suppressed cells. APE1 overexpression decreased H. pylori-induced ROS generation, Rac1 activation, and Nox1 expression. We determined that the effects of APE1 were mediated through its N-terminal lysine residues interacting with Rac1, leading to inhibition of Nox1 expression and ROS generation. APE1 is a negative regulator of oxidative stress in the gastrointestinal epithelium during bacterial infection by modulating Rac1 and Nox1. Our results implicate APE1 in novel molecular interactions that regulate early stress responses elicited by microbial infections.

Helicobacter pylori infection of the gastric mucosa is largely lifelong leading to continued stimulation of immune cells. This results in the generation of reactive oxygen species (ROS) which are produced to kill bacteria, but at the same time ROS regulate cellular events in the host. However, prolonged generation of ROS has been implicated in damage of DNA, which ultimately could lead to the development of cancer. We studied a molecule known as APE-1 in gastric and intestinal cells, which is activated upon encounter of ROS. Our results show that APE1 limits the production of ROS in cells that form the lining of the gastrointestinal tract. APE1 regulates ROS production by inhibiting activation of the molecule Rac1. Inhibition of ROS production by APE1 occurred after infection of gastric cells with Helicobacter pylori and after Salmonella infection of intestinal cells. These data demonstrate that APE1 inhibits production of ROS in cells that line the inside of the digestive tract.

Diphenyleneiodonium Inhibits Apoptotic Cell Death of Gastric Epithelial Cells Infected with Helicobacter pylori in a Korean Isolate

NADPH oxidase produces a large amount of reactive oxygen species (ROS) in Helicobacter pylori (H. pylori)-induced gastric epithelial cells. Even though ROS mediate apoptotic cell death, direct involvement of NADPH oxidase on H. pylori-induced apoptosis remains unclear. Besides, H. pylori isolates show a high degree of genetic variability. The predominant genotype of H. pylori in Korea has been reported as cagA⁺, vacA s1b, m2, iceA genotype. Present study aims to investigate whether NADPH oxidase-generated ROS mediate apoptosis in human gastric epithelial AGS cells infected with H. pylori in a Korean isolate. AGS cells were pretreated with or without an NADPH oxidase inhibitor diphenyleneiodonium (DPI) and cultured in the presence of H. pylori at a bacterium/cell ratio of 300:1. Cell viability, hydrogen peroxide level, DNA fragmentation, and protein levels of p53, Bcl-2, and Bax were determined. Results showed that H. pylori inhibited cell viability with the density of H. pylori added to the cells. Inhibition of NADPH oxidase by DPI suppressed H. pylori-induced cell death, increased hydrogen peroxide, DNA fragmentation, and the ratio of Bax/Bcl-2, and p53 induction in AGS cells dose-dependently. The results suggest that targeting NADPH oxidase may prevent the development of gastric inflammation associated with H. pylori infection by suppressing abnormal apoptotic cell death of gastric epithelial cells.

Role of ROS in DNA damage caused by Helicobacter pylori in gastric epithelial cells

AIM: To explore the relationship between the change of reactive oxygen species (ROS) and DNA damage caused by Helicobacter pylori (H. pylori) infection in gastric epithelial cells.

METHODS: H. pylori ACTC43504 (CagA⁺, VacA⁺) infected GES-1 cells were used in this study. Live cell imaging system was used to observe the change of intracellular ROS, and a microplate reader was used to detect intracellular ROS level. Single cell gel electrophoresis comet assay was used to detect DNA damage.

RESULTS: ROS level was proportional to H. pylori concentration, and the ROS level was the highest when the MOI of H. pylori was 300:1. Various concentrations of N-acety-L-cysteine (NAC) could significantly inhibit the generation of ROS caused by H. pylori infection. H. pylori could cause DNA damage. After NAC pretreatment, the values of tail length, comet length, tail moment, and Olive tail moment had a clear downward trend compared with the H. pylori group.

CONCLUSION: H. pylori infection in GES-1 cells increases intracellular ROS level and results in DNA damage. Inhibition of the generation of ROS could reduce DNA damage.

Impact of bacterial infections on aging and cancer: impairment of DNA repair and mitochondrial function of host cells

The commensal floras that inhabit the gastrointestinal tract play critical roles in immune responses, energy metabolism, and even cancer prevention. Pathogenic and out of place commensal bacteria, can however have detrimental effects on the host, by introducing genomic instability and mitochondrial dysfunction, which are hallmarks of both aging and cancer. Helicobacter pylori and Enterococcus faecalis are bacteria of the gastrointestinal tract that have been demonstrated to affect these two hallmarks. These, and other bacteria, have been shown to decrease the transcription and translation of essential DNA repair subunits of major DNA repair pathways and increase production of reactive oxygen species (ROS). Defects in DNA repair cause mutations and genomic instability and are found in several cancers as well as in progeroid syndromes. This review describes our contemporary view on how bacterial infections impact DNA repair and damage, and the consequence on the mitochondrial and nuclear genomes. We argue that in the gastrointestinal tract, these mechanisms can contribute to tumorigenesis as well as cellular aging of the digestive system.

Interplay between DNA repair and inflammation, and the link to cancer

DNA damage and repair are linked to cancer. DNA damage that is induced endogenously or from exogenous sources has the potential to result in mutations and genomic instability if not properly repaired, eventually leading to cancer. Inflammation is also linked to cancer. Reactive oxygen and nitrogen species (RONs) produced by inflammatory cells at sites of infection can induce DNA damage. RONs can also amplify inflammatory responses, leading to increased DNA damage. Here, we focus on the links between DNA damage, repair, and inflammation, as they relate to cancer. We examine the interplay between chronic inflammation, DNA damage and repair and review recent findings in this rapidly emerging field, including the links between DNA damage and the innate immune system, and the roles of inflammation in altering the microbiome, which subsequently leads to the induction of DNA damage in the colon. Mouse models of defective DNA repair and inflammatory control are extensively reviewed, including treatment of mouse models with pathogens, which leads to DNA damage. The roles of microRNAs in regulating inflammation and DNA repair are discussed. Importantly, DNA repair and inflammation are linked in many important ways, and in some cases balance each other to maintain homeostasis. The failure to repair DNA damage or to control inflammatory responses has the potential to lead to cancer.

Expression of adhesion and activation molecules on circulating monocytes in children with Helicobacter pylori infection

OBJECTIVES

The aim of this study was to assess the cell surface expression of adhesion (CD11a, CD11b, CD11c, CD18, CD54, and CD58) and activation (CD14, HLA-DR, and CD16) molecules on the circulating monocytes in Helicobacter pylori (H. pylori)-infected and noninfected children with gastritis, with the goal of comparing the results with those obtained from the controls.

MATERIALS AND METHODS

 Ninety-four children were studied: 47 of them with H. pylori infection (of those 25 children after the failure of eradication therapy) and 26 children with gastritis where H. pylori infection was excluded, as well as 21 controls. H. pylori infection status was assessed based on [¹³C] urea breath test, rapid urease test, and histology. Analysis of the monocyte surface molecule expression was carried out by flow cytometry.

RESULTS

 H. pylori-infected children and children who experienced a failure of the eradication therapy differed significantly in the expression of adhesion and activation molecule on circulating monocytes. A decrease, both in the proportion of CD11c- and CD14-bearing monocytes, and the expression of CD11c and CD14 molecules on circulating monocytes, was found in children in whom the eradication therapy failed (p < .05). Low expression of CD11b (p = .04) and CD18 (p = .02) integrins on monocytes was also observed. Additionally, the percentage of HLA-DR-bearing monocytes was decreased (p = .04), while the CD16 density receptor was increased (p = .02). Compared with the controls, low percentage of CD16-positive monocytes was noted in noninfected children with gastritis (p = .01).

CONCLUSION

H. pylori eradication therapy in children causes inhibition of inflammatory response via a reduction in CD11b, CD11c, and CD18 beta2 integrin monocyte expression.

Dynamic aspect of reactive oxygen and nitric oxide in oral cavity

Oral mucosa is a critical protective interface between external and internal environments. Therefore, it must serve as a barrier to a huge number of microbial species present in the environment. Saliva is an important factor that provides for the environment in the oral cavity, and it is indispensable to the host defense reaction in this manner. Oral neutrophils are also important contributors to maintaining the balance between health and disease in this complex environment. These produce reactive oxygen species, nitric oxide, and several antimicrobial peptides, and enzymes. Neutrophils and saliva all contribute to the maintaining the health of the oral cavity in overlapping but independent ways. In addition to production by neutrophils and macrophage, some bacteria can also generate superoxide, hydrogen peroxide, and nitric oxide. Dietary intake of nitrate-enriched vegetables might play important roles in the protection of the oral and stomach against hazardous pathogens via the gastro-intestinal-salivary cycle of nitric oxide (NO) and related metabolites. This review will focus on defense system of the human oral cavity and metabolism of reactive oxygen and NO.

Helicobacter pylori induces mitochondrial DNA mutation and reactive oxygen species level in AGS cells

To investigate the role of ROS in the helicobacter pylori (Hp) induced mtDNA mutations, AGS cells were treated by extracts of Hp11638 or Hp11638M. The ROS levels, cytochrome C reductions, and intracellular ATP levels were measured. The coding region and the D-Loop region were amplified and sequenced. Results showed the ROS levels, cytochrome C reduction and mtDNA mutations were markedly increased and cell viability decreased after treatment with both Hp extracts, and 616 mutations were detected in D-Loop region and 3 heteroplasmic point mutations in the Cytb gene. No mutations were found in the coding region. The mutation rates of mtDNA D-Loop region were positively correlated with the ROS levels and negatively to the ATP levels.

Redox biology and gastric carcinogenesis: the role of Helicobacter pylori

Almost half the world's population is infected by Helicobacter pylori (H. pylori). This bacterium increases the production of reactive oxygen species (ROS) and reactive nitrogen species (RNS) in human stomach, and this has been reported to impact upon gastric inflammation and carcinogenesis. However, the precise mechanism by which H. pylori induces gastric carcinogenesis is presently unclear. Although the main source of ROS/RNS production is possibly the host neutrophil, H. pylori itself produces O₂•⁻. Furthermore, its cytotoxin induces ROS production by gastric epithelial cells, which might affect intracellular signal transduction, resulting in gastric carcinogenesis. Excessive ROS production in gastric epithelial cells can cause DNA damage and thus might be involved in gastric carcinogenesis. Understanding the molecular mechanism of H. pylori-induced carcinogenesis is important for developing new strategies against gastric cancer.

Diphenyleneiodonium inhibits the activation of mitogen-activated protein kinases and the expression of monocyte chemoattractant protein-1 in Helicobacter pylori-infected gastric epithelial AGS cells

OBJECTIVE

To investigate whether NADPH oxidase induces MCP-1 expression and the activation of mitogen-activated protein kinases (MAPKs) in H. pylori-infected gastric epithelial cells.

MATERIAL

H. pylori in Korean isolates, human gastric epithelial AGS cells

TREATMENT

AGS cells pretreated with or without an NADPH oxidase inhibitor diphenyleneiodonium (DPI) are cultured in the presence of H. pylori at a bacterium/cell ratio of 300:1.

METHODS

Reactive oxygen species (ROS) and MCP-1 were determined by confocal microscopy and enzyme-linked immonosorbent assay. NADPH oxidase activity was measured by lucigenin assay. mRNA expression of MCP-1 was analyzed by reverse transcription-polymerase chain reaction. Levels of MAPKs were assessed by Western blot analysis.

RESULTS

H. pylori induced increase in ROS, NADPH oxidase activity, MCP-1 expression, and the activation of MAPKs including extracellular signal-regulated kinases, p38, and jun N-terminal kinases in AGS cells, which was inhibited by DPI.

CONCLUSION

Inhibiting NADPH oxidase by DPI suppresses H. pylori-induced activation of MAPKs and MCP-1 expression in AGS cells.

Mechanisms linking pathogens-associated inflammation and cancer

It has been estimated that chronic infections with viruses, bacteria and parasites are the causative agents of 8-17% of global cancers burden. Carcinogenesis associated with infections is a complex process, often mediated by chronic inflammatory conditions and accumulating evidence indicate that a smouldering inflammation is a component of the tumor microenvironment and represents the 7th hallmark of cancer. Selected infectious agents promote a cascade of events culminating in chronic inflammatory responses, thus predisposing target tissues to increased cancer susceptibility. A causal link also exists between an inflammatory microenvironment, consisting of inflammatory cells and mediators, and tumor progression. Tumor-Associated Macrophages (TAM) represent the major inflammatory population present in tumors, orchestrating various aspects of cancer, including: diversion and skewing of adaptive responses; cell growth; angiogenesis; matrix deposition and remodelling; construction of a metastatic niche and actual metastasis; response to hormones and chemotherapeutic agents. Recent studies on human and murine tumors indicate that TAM show a remarkable degree of plasticity and functional heterogeneity, during tumour development. In established tumors, TAM acquire an M2 polarized phenotype are engaged in immunosuppression and the promotion of tumor angiogenesis and metastasis. Being a first line of the innate defence mechanisms, macrophages are also equipped with pathogen-recognition receptors, to sense the presence of danger signals, including onco-pathogens. Here we discuss the evidence suggesting a causal relationship between selected infectious agents and the pro-tumoral reprogramming of inflammatory cells, as well as its significance in tumor development. Finally, we discuss the implications of this phenomenon for both cancer prevention and therapy.

Helicobacter pylori: a ROS-inducing bacterial species in the stomach

BACKGROUND

Reactive oxygen species (ROS) and reactive nitrogen species (RNS) have been reported to impact gastric inflammation and carcinogenesis. However, the precise mechanism by which Helicobacter pylori induces gastric carcinogenesis is presently unclear.

AIM

This review focuses on H. pylori-induced ROS/RNS production in the host stomach, and its relationship with gastric carcinogenesis.

RESULTS

Activated neutrophils are the main source of ROS/RNS production in the H. pylori-infected stomach, but H. pylori itself also produces ROS. In addition, extensive recent studies have revealed that H. pylori-induced ROS production in gastric epithelial cells might affect gastric epithelial cell signal transduction, resulting in gastric carcinogenesis. Excessive ROS/RNS production in the stomach can damage DNA in gastric epithelial cells, implying its involvement in gastric carcinogenesis.

CONCLUSION

Understanding the molecular mechanism behind H. pylori-induced ROS, and its involvement in gastric carcinogenesis, is important for developing new strategies for gastric cancer chemoprevention.

Reactive oxygen species generated by NADPH oxidase are involved in neurodegeneration in the pilocarpine model of temporal lobe epilepsy

Reactive oxygen species (ROS) appear to be involved in several neurodegenerative disorders. We tested the hypothesis that oxidative stress could have a role in the hippocampal neurodegeneration observed in temporal lobe epilepsy induced by pilocarpine. We first determined the spatio-temporal pattern of ROS generation, by means of detection with dihydroethidium oxidation, in the CA1 and CA3 areas and the dentate gyrus of the dorsal hippocampus during status epilepticus induced by pilocarpine. Fluoro-Jade B assays were also performed to detect degenerating neurons. ROS generation was increased in CA1, CA3 and the dentate gyrus after pilocarpine-induced seizures, which was accompanied by marked cell death. Treatment of rats with a NADPH oxidase inhibitor (apocynin) for 7 days prior to induction of status epilepticus was effective in decreasing both ROS production (by an average of 20%) and neurodegeneration (by an average of 61%). These results suggest an involvement of ROS generated by NADPH oxidase in neuronal death in the pilocarpine model of epilepsy.

CAT C-262T and GPX1 Pro198Leu polymorphisms in a Turkish population

Oxidative stress is believed to play an important role in the pathogenesis of considerable number of complex diseases. The antioxidant enzymes catalase (CAT) and glutathione peroxidase (GPX) are important components of cell defense against oxidative stress, and polymorphisms in the genes which regulate their expression may contribute to differences in susceptibility of individuals to oxidative damage caused by reactive oxygen species. The aim of this study was to assess the distribution of CAT C-262T and GPX1 Pro198Leu genotypic variants in a Turkish population. Genotyping analyses of CAT and GPX1 were conducted in 250 unrelated, healthy volunteers by the PCR-RFLP assay. The allele frequencies were 0.784 (C) and 0.216 (T) for CAT and 0.636 (C) and 0.364 (T) for GPX1 Pro198Leu. The genotype frequencies were 0.632 (CC), 0.304 (CT), and 0.064 (TT) for CAT and 0.416 (CC), 0.44 (CT), and 0.144 (TT) for GPX1 Pro198Leu. The genotype frequencies did not deviate from Hardy-Weinberg equilibrium. The results are compared with those of other reported populations. They showed marked ethnic group differences.

Naringenin reduces tumor size and weight lost in N-methyl-N'-nitro-N-nitrosoguanidine-induced gastric carcinogenesis in rats

Carcinoma of the stomach is reportedly the second most common cancerous condition affecting the general population. Administration of antioxidants is reported to effectively alleviate the risk of gastric carcinoma. Therefore, we assessed the protective role of naringenin, an antioxidant and naturally occurring citrus flavanone, on gastric carcinogenesis induced by MNNG (200 mg/kg body weight) and S-NaCl (1 mL per rat) in Wistar rats (obtained from the Central Animal House Facility, University of Madras, Taramani Campus, Chennai, India). The animals were divided into 5 groups, and the effects of naringenin on simultaneous and posttreated stages of MNNG were tested. Cancer risk was analyzed along with their antioxidant status. The LPO levels in the experimental groups were assessed as an index of oxidative milieu. Altered redox status was subsequently investigated by assaying the superoxide and hydroxyl radicals, the enzymatic antioxidants (SOD, CAT, GPx), and the nonenzymatic antioxidants viz reduced GSH, vitamin C, and vitamin E. In the presence of MNNG, cancer incidence and LPO levels were significantly increased, whereas enzymatic (SOD, CAT, and GPx) and nonenzymatic antioxidant activities (GSH, Vitamins C, and E) were decreased in the treated rats compared with control rats. Administration of naringenin to gastric carcinoma-induced rats largely up-regulated the redox status to decrease the risk of cancer. We conclude that up-regulation of antioxidants by naringenin treatment might be responsible for the anticancer effect in gastric carcinoma.

Effect of Nitric Oxide on the Oxygen Metabolism and Growth of E. faecalis

Gastro-intestinal mucosal cells have a potent mechanism to eliminate a variety of pathogens using enzymes that generate reactive oxygen species and/or nitric oxide (NO). However, a large number of bacteria survive in the intestine of human subjects. Enterococcus faecalis (E. faecalis) is a Gram-positive bacterium that survives not only in the intestinal lumen but also within macrophages generating NO. It has been reported that E. faecalis generated the superoxide radical (O₂⁻). To elucidate the role of O₂⁻ and NO in the mechanism for the pathogen surviving in the intestine and macrophages, we studied the role and metabolism of O₂⁻ and NO in and around E. faecalis. Kinetic analysis revealed that E. faecalis generated 0.5 µmol O₂⁻/min/10⁸ cells in a glucose-dependent manner as determined using the cytochrome c reduction method. The presence of NOC12, an NO donor, strongly inhibited the growth of E. faecalis without affecting in the oxygen consumption. However, the growth rate of NOC12-pretreated E. faecalis in NO-free medium was similar to that of untreated cells. Western blotting analysis revealed that the NOC12-treated E. faecalis revealed a large amount of nitrotyrosine-posititive proteins; the amounts of the modified proteins were higher in cytosol than in membranes. These observations suggested that O₂⁻ generated by E. faecalis reacted with NO to form peroxinitrite (ONOO⁻) that preferentially nitrated tyrosyl residues in cytosolic proteins, thereby reversibly inhibited cellular growth. Since E. faecalis survives even within macrophages expressing NO synthase, similar metabolism of O₂⁻ and NO may occur in and around phagocytized macrophages.

Homeostatic mass control in gastric non-neoplastic epithelia under infection of Helicobacter pylori: an immunohistochemical analysis of cell growth, stem cells and programmed cell death

We evaluated homeostatic mass control in non-neoplastic gastric epithelia under Helicobacter pylori (HP) infection in the macroscopically normal-appearing mucosa resected from the stomach with gastric cancer, immunohistochemically analyzing the proliferation, kinetics of stem cells and programmed cell death occurring in them. Ki67 antigen-positive proliferating cells were found dominantly in the elongated neck portion, sparsely in the fundic areas and sporadically in the stroma with chronic infiltrates. CD117 could monitor the kinetics of gastric stem cells and showed its expression in two stages of gastric epithelial differentiation, namely, in transient cells from the gastric epithelial stem cells to the foveolar and glandular cells in the neck portion and in what are apparently progenitor cells from the gastric stem cells in the stroma among the infiltrates. Most of the nuclei were positive for ssDNA in the almost normal mucosa, suggesting DNA damage. Cleaved caspase-3-positive foveolar cells were noted under the surface, suggesting the suppression of apoptosis in the surface foveolar cells. Besides such apoptosis of the foveolar cells, in the severely inflamed mucosa apoptotic cells were found in the neck portion where most of the cells were Ki67 antigen-positive proliferating cells. Beclin-1 was recognized in the cytoplasm and in a few nuclei of the fundic glandular cells, suggesting their autophagic cell death and mutated beclin-1 in the nuclei. Taken together, the direct and indirect effects of HP infection on the gastric epithelial proliferation, differentiation and programmed cell death suggested the in-situ occurrence of gastric cancer under HP infection.

Expression of apurinic/apyrimidinic endonuclease-1 (APE-1) in H. pylori-associated gastritis, gastric adenoma, and gastric cancer

BACKGROUND AND AIM

Apurinic/apyrimidinic endonuclease-1 (APE-1) is a key enzyme in DNA base excision repair (BER), linked to cancer chemosensitivity. However, little is known about the localization of APE-1 in Helicobacter pylori-infected gastric mucosa or its role in the development of gastric cancer. To investigate the role of APE-1 in the development of gastric cancer, we examined APE-1 expression and localization in cultured cells and gastric biopsies from patients with H. pylori-infected gastritis or gastric adenoma, and from surgically resected gastric cancer.

METHODS

APE-1 mRNA and protein expression were determined in H. pylori (CagA+) water-extract protein (HPWEP)-stimulated MKN-28 cells, gastric adenocarcinoma cell-line (AGS) cells, and human peripheral macrophages by real-time polymerase chain reaction and Western blot analysis. APE-1 expression and 8-OHdG as a measure of oxidative DNA damage were evaluated by immunostaining. Localization of APE-1 and IkappaBalpha phosphorylation in gastric adenoma and gastric cancer tissues were evaluated by single- and double-label immunohistochemistry.

RESULTS

In studies in vitro, HPWEP-stimulation significantly increased APE-1 mRNA expression levels in both MKN-28 cells and human peripheral macrophages. Hypo/reoxygenation treatment significantly increased APE-1 protein expression in HPWEP-stimulated MKN-28 cells. HPWEP stimulation significantly increased both APE-1 expression and IkappaBalpha phosphorylation levels in MKN-28 and AGS cells. In human tissues, APE-1 expression in H. pylori-infected gastritis without goblet cell metaplasia was significantly increased as compared to that in tissues from uninfected subjects. Eradication therapy significantly reduced both APE-1 and 8-OHdG expression levels in the gastric mucosa. APE-1 expression was mainly localized in epithelial cells within gastric adenoma and in mesenchymal cells of gastric cancer tissues. APE-1 expression in gastric cancer tissues was significantly reduced compared to that in H. pylori-infected gastric adenoma, while 8-OHdG index and IkappaBalpha phosphorylation levels did not differ between these two neoplastic tissue types. Co-localization of APE-1 and IkappaBalpha phosphorylation was observed not in gastric cancer cells but in gastric adenoma cells.

CONCLUSION

H. pylori infection is associated with increased APE-1 expression in human cell lines and in gastric tissues from subjects with gastritis and gastric adenomas. The observed distinct expression patterns of APE-1 and 8-OHdG in gastric adenoma and gastric cancer tissues may provide insight into the progression of these conditions and warrants further investigation.

The bactericidal and morphological effects of peroxynitrite on Helicobacter pylori

Peroxynitrite (ONOO-) is correlated with the pathogenesis of Helicobacter pylori-induced peptic ulcer diseases. We aimed to investigate the time- and concentration-dependent bactericidal and morphological effects of ONOO- on H. pylori. Authentic ONOO- was synthesized as quenched-flow method. A stock culture of H. pylori NCTC 11637 was exposed to different concentrations of ONOO- (0.1-40 micromol/L) or decomposed ONOO- or fresh medium. Samples were taken at 0, 15, 30, 60, and 120 minutes, for the evaluation of viable bacteria and bacterial morphology with gram strain and transmission electron microscopy. Decomposed ONOO- showed no bactericidal activity against H. pylori. ONOO- application caused a decrease in the number of viable bacteria within the first 15 minutes. The significant conversion of H. pylori from spiral form to coccoid form was determined with 10 micromol/L of ONOO-, and higher concentrations caused lysis of the cells. Separation of cell wall, bleb formation, vacuolization, decrease of secretory granules, and lysis of bacteria were the morphological effects of ONOO- on H. pylori. Because the morphology of the bacteria is one of the important factors in virulence; peroxynitrite-related morphological effects might have an impact in the progress of the H. pylori-induced peptic ulcer diseases.

Nitrite reductase in Streptoccocus mutans plays a critical role in the survival of this pathogen in oral cavity

BACKGROUND/AIMS

The mechanisms of nitric oxide (NO) production by bacteria in the oral cavity are still not clearly defined but salivary streptococci have been reported to generate NO. The aim of this study was to clarify the mechanism of nitrite metabolism and generation of NO by Streptococcus mutans, a major pathogen of dental caries.

METHODS

We searched the genomic database of oral pathogens for nitrite reductase and used a polymerase chain reaction (PCR) to clone the nirJ gene from S. mutans GS5. His-tagged recombinant NirJ protein was expressed in Escherichia coli BL21 and characterized. We constructed a nirJ gene-disrupted mutant strain of S. mutans (DeltanirJ) to analyze the physiological significance of nirJ.

RESULTS

S. mutans generates NO from nitrite, probably as a result of the possession of nitrite reductase. We cloned the nirJ gene from S. mutans GS5 by PCR. The recombinant NirJ protein catalyzed the reduction of nitrite with a K(m) value of 3.37 microM and a specific activity of 2.5 micromol/min/mg of protein at 37 degrees C. Biochemical analysis revealed that the nitrite-reducing activity of the mutant (DeltanirJ) strain was significantly lower than that of the wild-type strain. The growth of the mutant strain, but not of the wild-type strain, was strongly suppressed by the presence of physiological levels of nitrite ( approximately 0.2 mM) in saliva.

CONCLUSION

These observations suggest that the elimination of nitrite and/or the generation of NO are important for the survival of S. mutans in the oral cavity.

The pathogenesis of Helicobacter pylori-induced gastro-duodenal diseases

Helicobacter pylori is the main cause of peptic ulceration, distal gastric adenocarcinoma, and gastric lymphoma. Only 15% of those colonized develop disease, and pathogenesis depends upon strain virulence, host genetic susceptibility, and environmental cofactors. Virulence factors include the cag pathogenicity island, which induces proinflammatory, pro-proliferative epithelial cell signaling; the cytotoxin VacA, which causes epithelial damage; and an adhesin, BabA. Host genetic polymorphisms that lead to high-level pro-inflammatory cytokine release in response to infection increase cancer risk. Pathogenesis is dependent upon inflammation, a Th-1 acquired immune response and hormonal changes including hypergastrinaemia. Antral-predominant inflammation leads to increased acid production from the uninflamed corpus and predisposes to duodenal ulceration; corpus-predominant gastritis leads to hypochlorhydria and predisposes to gastric ulceration and adenocarcinoma. Falling prevalence of H. pylori in developed countries has led to a falling incidence of associated diseases. However, whether there are disadvantages of an H. pylori-free stomach, for example increased risk of esosphageal adenocarcinoma, remains unclear.

Helicobacter pylori infection induces oxidative stress and programmed cell death in human gastric epithelial cells

Helicobacter pylori infection is associated with altered gastric epithelial cell turnover. To evaluate the role of oxidative stress in cell death, gastric epithelial cells were exposed to various strains of H. pylori, inflammatory cytokines, and hydrogen peroxide in the absence or presence of antioxidant agents. Increased intracellular reactive oxygen species (ROS) were detected using a redox-sensitive fluorescent dye, a cytochrome c reduction assay, and measurements of glutathione. Apoptosis was evaluated by detecting DNA fragmentation and caspase activation. Infection with H. pylori or exposure of epithelial cells to hydrogen peroxide resulted in apoptosis and a dose-dependent increase in ROS generation that was enhanced by pretreatment with inflammatory cytokines. Basal levels of ROS were greater in epithelial cells isolated from gastric mucosal biopsy specimens from H. pylori-infected subjects than in cells from uninfected individuals. H. pylori strains bearing the cag pathogenicity island (PAI) induced higher levels of intracellular oxygen metabolites than isogenic cag PAI-deficient mutants. H. pylori infection and hydrogen peroxide exposure resulted in similar patterns of caspase 3 and 8 activation. Antioxidants inhibited both ROS generation and DNA fragmentation by H. pylori. These results indicate that bacterial factors and the host inflammatory response confer oxidative stress to the gastric epithelium during H. pylori infection that may lead to apoptosis.

Oxidative stress expression status associated to Helicobacter pylori virulence in gastric diseases

OBJECTIVES

To analyze the status of expression of inflammation markers, antioxidant and oxidant enzymes in biopsies from patients diagnosed with gastritis, gastric ulcer (GU) and gastric cancer (GC) and the Helicobacter pylori virulence from these isolated biopsies in order to evaluate a possible association among these factors.

METHODS

H. pylori genotype from isolated biopsies was performed by PCR. The pattern of expression of inflammation (TNF-alpha, IL-1beta, IL-8, IL-10 and IL-12), oxidant (iNOS and Nox1) and antioxidant markers (MnSOD, GPX and CAT) of biopsies from gastritis, GU, GC and control groups was performed by RT-PCR.

RESULTS

Different from other gastric diseases studied here, gastritis is characterized by an oxidative stress with significant expression of TNF-alpha, IL-8, IL-12, iNOS and Nox and significant absence of MnSOD and GPX expression. Gastritis was the only condition where there was an association between TNF-alpha or IL-8 expression and H. pylori cagA+/vacAs1 genotype. In this case, TNF-alpha expression was about 3 times higher when compared to control subjects.

CONCLUSION

In this study, only gastritis was found to be associated with significant oxidative stress marker expression of TNF-alpha and IL-8 that was also related to H. pylori virulence, suggesting that they are the main oxidant stress markers responsible to trigger an increase in ROS level that contributes to decrease the expression of the MnSOD and GPX.

Interleukin-8 induction by Helicobacter pylori in gastric epithelial cells is dependent on apurinic/apyrimidinic endonuclease-1/redox factor-1

Helicobacter pylori infection causes inflammation and increases the expression of IL-8 in human gastric epithelial cells. H. pylori activates NF-kappaB and AP-1, essential transcriptional factors in H. pylori-induced IL-8 gene transcription. Although colonization creates a local oxidative stress, the molecular basis for the transition from infection to the expression of redox-sensitive cytokine genes is unknown. We recently reported that the expression of apurinic/apyrimidinic endonuclease-1/redox factor-1 (APE-1/Ref-1), which repairs oxidative DNA damage and reductively activates transcription factors including AP-1 and NF-kappaB, is increased in human gastric epithelia during H. pylori infection. In this study, we examine whether APE-1/Ref-1 functions in the modulation of IL-8 gene expression in H. pylori-infected human gastric epithelial cells. Small interfering RNA-mediated silencing of APE-1/Ref-1 inhibited basal and H. pylori-induced AP-1 and NF-kappaB DNA-binding activity without affecting the nuclear translocation of these transcription factors and also reduced H. pylori-induced IL-8 mRNA and protein. In contrast, overexpression of APE-1/Ref-1 enhanced basal and H. pylori-induced IL-8 gene transcription, and the relative involvement of AP-1 in inducible IL-8 promoter activity was greater in APE-1/Ref-1 overexpressing cells than in cells with basal levels of APE-1/Ref-1. APE-1/Ref-1 inhibition also reduced other H. pylori-induced chemokine expression. By implicating APE-1/Ref-1 as an important regulator of gastric epithelial responses to H. pylori infection, these data elucidate a novel mechanism controlling transcription and gene expression in bacterial pathogenesis.

Deficiency in OGG1 protects against inflammation and mutagenic effects associated with H. pylori infection in mouse

BACKGROUND

Helicobacter pylori infection is associated with gastric cancer. Study with the Big Blue mouse model has reported a mutagenic effect associated with the H. pylori infection, as a result in part of oxidative DNA damage. The present work investigates the consequences of a deficiency in the OGG1 DNA glycosylase, responsible for the excision of 8-oxo guanine, on the inflammatory and genotoxic host response to the infection.

MATERIALS AND METHODS

Big Blue Ogg1-/- C57BL/6 mice were orally inoculated with H. pylori strain SS1 or vehicle only, and sacrificed after 1, 3, or 6 months. The serologic response, histologic lesions, mutant frequency, and spectra of mutations were assessed in the stomach and compared to what observed in the wild-type (Wt) context.

RESULTS

Inflammatory lesions induced in the gastric mucosa of H. pylori-infected mice, corresponding to a moderate gastritis, were less severe in Ogg1-/- than in Wt Big Blue mice. Analysis of antimicrobial humoral immunity exhibited a lower IgG2a serum level (Th1 response) after 6 months of infection in Ogg1-/- than in the Wt mice. In these conditions, the H. pylori-SS1 infection in the Ogg1-/- mice did not induce a mutagenic effect at the gastric epithelial cells level, either after 3 or 6 months.

CONCLUSIONS

The inactivation of the OGG1 DNA glycosylase in mouse leads to less severe inflammatory lesions and abolished the mutagenic effect at the gastric epithelial cells level, induced by the H. pylori infection. These data suggest for the OGG1deficiency a protective role against inflammation and genotoxicity associated to the H. pylori infection.

The diverse antioxidant systems of Helicobacter pylori

The gastric pathogen Helicobacter pylori induces a strong inflammatory host response, yet the bacterium maintains long-term persistence in the host. H. pylori combats oxidative stress via a battery of diverse activities, some of which are unique or newly described. In addition to using the well-studied bacterial oxidative stress resistance enzymes superoxide dismutase and catalase, H. pylori depends on a family of peroxiredoxins (alkylhydroperoxide reductase, bacterioferritin co-migratory protein and a thiol-peroxidase) that function to detoxify organic peroxides. Newly described antioxidant proteins include a soluble NADPH quinone reductase (MdaB) and an iron sequestering protein (NapA) that has dual roles - host inflammation stimulation and minimizing reactive oxygen species production within H. pylori. An H. pylori arginase attenuates host inflammation, a thioredoxin required as a reductant for many oxidative stress enzymes is also a chaperon, and some novel properties of KatA and AhpC were discovered. To repair oxidative DNA damage, H. pylori uses an endonuclease (Nth), DNA recombination pathways and a newly described type of bacterial MutS2 that specifically recognizes 8-oxoguanine. A methionine sulphoxide reductase (Msr) plays a role in reducing the overall oxidized protein content of the cell, although it specifically targets oxidized Met residues. H. pylori possess few stress regulator proteins, but the key roles of a ferric uptake regulator (Fur) and a post-transcriptional regulator CsrA in antioxidant protein expression are described. The roles of all of these antioxidant systems have been addressed by a targeted mutant analysis approach and almost all are shown to be important in host colonization. The described antioxidant systems in H. pylori are expected to be relevant to many bacterial-associated diseases, as genes for most of the enzymes carrying out the newly described roles are present in a number of pathogenic bacteria.

Helicobacter pylori infection and gastric cancer

The pathogenesis of gastric cancer (GC) includes a sequence of events that begins with Helicobacter pylori-induced chronic superficial gastritis, progressing towards atrophic gastritis, intestinal metaplasia, dysplasia and eventually GC. The association between H. pylori and GC is supported by experimental data showing a capacity of H. pylori to induce GC in animals, and the results of interventional studies showing that H. pylori eradication can lower the risk of GC and prevent development of pre-cancerous lesions in humans and in experimental animals. The "driving force" of gastric carcinogenesis is a chronic gastric inflammation, whose intensity and localisation depending on bacterial, host and environmental factors, determines the risk of GC. The mechanisms by which chronic inflammation lead to epithelial and pre-cancerous lesions include induction of oxidative stress, perturbation of the epithelial cells proliferation/apoptosis ratio, and cytokine secretion. Several molecular alterations associated with gastric carcinogenesis have also been described.

The translation of Helicobacter pylori basic research to patient care

In 1984, Barry Marshall and Robin Warren proposed a role for bacterial infections in the pathogenesis of gastroduodenal disease, which triggered an avalanche of research intended to prove or disprove their theory. The result has been a series of advances that have enhanced our understanding of these diseases and completely modernized the clinical approach to their management. In just over 20 years, many aspects of the immunopathogenesis of these diseases have been dissected at the molecular level, with key pathogenic mechanisms being validated by the identification of genes that are associated with the development of gastric cancer. There has been particular emphasis on understanding the molecular structures associated with Helicobacter pylori and their role in modifying the host responses. Gastric immune and inflammatory responses have emerged as key elements in the pathogenesis of gastritis and epithelial cell damage. This review summarizes important findings emanating from basic research primarily related to the immunopathogenesis of H pylori that have advanced the practice of medicine or our understanding of gastroduodenal disease.

The presence of thecagpathogenicity island is associated with increased superoxide anion radical scavenging activity byHelicobacter pylori

Reactive oxygen species (ROS) generated by Helicobacter pylori infection have been suggested to be important factors in induction of gastric malignancies. Utilizing electron spin resonance spectrometry, H. pylori-dependent radical formation and hydroxyl- and superoxide-anion radical scavenging activity was investigated. In contrast to previous reports, we found that H. pylori does not produce ROS, but displays superoxide scavenging activity. This scavenging activity was increased in cag-positive H. pylori strains when compared to strains lacking an intact cag pathogenicity island, and was dependent on enzyme activity. We hypothesize that the increased scavenging activity of cag-positive H. pylori strains is an adaptation to the increased inflammatory response associated with the cag-positive genotype of H. pylori.

Gastric helicobacter infection induces a Th2 phenotype but does not elevate serum cholesterol in mice lacking inducible nitric oxide synthase

Persistent Helicobacter felis infection in (C57BL/6 x 129SvEv)F1 mice induces chronic gastritis. Expression of inducible nitric oxide synthase (iNOS) is upregulated in response to Helicobacter infection. In this study, 20 10-week-old iNOS-/- mice and 20 wild-type [(C57BL/6 x 129SvEv)F1] mice were infected with H. felis by oral gavage and were assessed histologically and serologically at 32 weeks postinfection. Equal numbers of uninfected controls were sham inoculated. The mice were scored for severity of gastric inflammation, hyperplasia, glandular atrophy, and mucous metaplasia in the corpus and for the level of helicobacter colonization. The immunoglobulin G1 (IgG1), IgG2a, and IgG2c antibody responses to H. felis were determined. As a secondary measure, serum cholesterol levels were assessed. iNOS-/- mice have a propensity for increased serum cholesterol, and although controversial, several human epidemiologic studies have demonstrated an association between Helicobacter infection and several risk factors for cardiovascular disease, including elevated serum cholesterol. Nevertheless, no differences in serum cholesterol levels were observed between the H. felis-infected and -uninfected iNOS-/- mice in this study. The uninfected animals had minimal to no gastric pathology. The gastric pathology scores for the infected animals were reduced significantly in the iNOS-deficient mice relative to those for the wild-type mice (all P <0.01). Helicobacter-infected iNOS-/- mice had chronic lymphoid infiltration and negligible to mild glandular atrophy and mucous metaplasia in the fundic mucosa, while H. felis-infected wild-type mice had severe atrophic and metaplastic mucosal changes. The atrophic gastritis in the infected wild-type mice, particularly the female mice, was also accompanied by greater granulocytic infiltration, antral hyperplasia, and diminished antral colonization, unlike that in the infected iNOS-/- mice. iNOS-/- mice developed significantly lower Th1-associated IgG2c antibody responses to H. felis (P <0.0003); the Th2-associated IgG1 responses were similar (P=0.09), suggesting a greater effect of the iNOS defect on Th1 responses. H. felis colonization was significantly greater in the iNOS-deficient mice. These findings are indicative of an impaired Th1 component of the H. felis-induced inflammatory response when the influence of iNOS is removed.

Helicobacter pylori and H2O2 increase AP endonuclease-1/redox factor-1 expression in human gastric epithelial cells

BACKGROUND & AIMS

Helicobacter pylori infection causes inflammation, accumulation of reactive oxygen species, and oxidative DNA damage in the gastric mucosa. Apurinic/apyrimidinic endonuclease-1 (APE-1)/redox factor-1 (Ref-1) repairs damaged DNA and reductively activates transcription factors, including activator protein-1. Considering that H. pylori generate reactive oxygen species and that reactive oxygen species modulate APE-1/Ref-1 in other cell types, we examined the effect of H. pylori, oxidative stress, and antioxidants on APE-1/Ref-1 expression in human gastric epithelial cells.

METHODS

Human gastric epithelial cell lines or cells isolated from mucosal biopsy samples were stimulated with H. pylori, Campylobacter jejuni, and/or H 2 O 2 in the presence or absence of antioxidants. APE-1/Ref-1 expression was assayed by Western blot or reverse-transcription polymerase chain reaction, and its cellular distribution was determined by using indirect conventional and confocal immunofluorescence. New protein synthesis was detected by [S 35 ]methionine labeling. APE-1/Ref-1 function was assessed by using a luciferase-linked reporter construct containing 3 activator protein 1 binding sites.

RESULTS

APE-1/Ref-1 protein and messenger RNA were detected in resting gastric epithelial cells. APE-1/Ref-1 protein expression was increased after stimulation with H 2 O 2 or live cag pathogenicity island-bearing H. pylori, but not cag pathogenicity island-negative H. pylori or C. jejuni. H. pylori - or reactive oxygen species-mediated increases in APE-1/Ref-1 expression involved de novo protein synthesis that was inhibited by antioxidants. H. pylori or H 2 O 2 also induced nuclear accumulation of APE-1/Ref-1, and overexpression of APE-1/Ref-1 increased activator protein 1 binding activity.

CONCLUSIONS

The data show that H. pylori or reactive oxygen species enhance APE-1/Ref-1 protein synthesis and nuclear accumulation in human gastric epithelial cells and implicate APE-1/Ref-1 in the modulation of the pathogenesis of H. pylori infection.

Urinary 8-hydroxydeoxyguanosine excretion in children before and after therapy for eradication of Helicobacter pylori infection

AIM

A number of reports have implicated oxygen free radicals in the pathogenesis of Helicobacter pylori (H. pylori)-associated disease. 8-hydroxydeoxyguanosine (8-OHdG) has recently been accepted as a sensitive marker for reflecting the oxidative DNA damage. However, there have been no previous studies comparing the changes in urinary 8-OHdG excretions before and after therapy for eradication of H. pylori infection, or to examine 8-OHdG excretions in children with H. pylori infection. The aim of this study was therefore to examine the DNA damage in gastric mucosal cells in children with H. pylori infection.

METHODS

Urinary 8-OHdG excretions were measured before and after therapy for eradication of H. pylori infection in 15 children diagnosed with the H. pylori infection and 13 parents who were also suffering from the same infection.

RESULTS

In both the children and their parents, no significant differences were found in urinary 8-OHdG excretions either before or after the eradication therapy. Furthermore, there was no significant difference in urinary 8-OHdG excretions between 8 children with peptic ulcers and 7 children without ulcers, either before or after the therapy.

CONCLUSION

These results suggest that measurement of urinary 8-OHdG levels is not useful for evaluation of the DNA damage in H. pylori-infected gastric mucosa in children.