Receptor for VacA toxin and pathogenesis of gastric ulcer

The vacuolating cytotoxin VacA produced by Helicobacter pylori causes massive cellular vacuolation in vitro, and gastric tissue damage in vivo leading to gastric ulcers when administered intragastrically. We found that mice deficient in protein tyrosine phosphatase receptor type Z(Ptprz) do not show mucosal damage by VacA, although VacA is incorporated into the gastric epithelial cells to the same extent as in wild-type mice. Primary cultures of gastric epithelial cells from Ptprz+/+ and Ptprz-/- mice showed similar cellular vacuolation, but only Ptprz+/+ cells showed marked detachment from a reconstituted basement membrane from 24 h after treatment with VacA. VacA bound to Ptprz, and the tyrosine-phosphorylation level of Git1, a Ptprz substrate, was elevated by VacA, indicating that VacA behaves as a ligand for Ptprz. These data indicate that erroneous Ptprz signaling by VacA, but not cellular vacuolation, induces gastric ulcers.     

CagA^＋幽门螺杆菌菌株培养滤液对胃黏膜上皮细胞生长及DNA的影响

目的研究CagA^＋Hp菌株培养滤液对胃黏膜上皮细胞（GES-1）生长的作用。方法分为CagA^＋组、CagA^-组、布氏肉汤组（空白对照组）,Hp菌株制备培养滤液处理GES-1细胞,连续培养1个月。MTT法观察GES-1细胞生长,单细胞微凝胶电泳检测GES-1细胞DNA的损伤,并采用电镜观察GES-1细胞的形态变化。结果 CagA^＋培养滤液可使GES-1细胞增生活跃,GES-1细胞出现彗星现象显著高于CagA^-组（41.2%vs.12.5%）（P〈0.05）。经CagA^＋组处理的GES-1细胞,细胞核增大、畸形、核染色质变粗、核仁肥大、核分裂。结论 CagA在Hp培养滤液促使GES-1细胞呈肿瘤细胞的形态学改变及生长特征中起重要作用。DNA损伤可能是CagA诱导GES-1生长特征改变的机制之一。     

Anti-inflammatory effect of activated protein C in gastric epithelial cells

It has been previously demonstrated that activated protein C (APC) plays an important role in the inhibition of inflammation in the gastric mucosa from patients with Helicobacter pylori infection. However, the role of gastric epithelial cells in the anti-inflammatory activity of APC remains unknown. In the present study, we evaluated the anti-inflammatory activity of APC and the expression of thrombomodulin (TM) and endothelial protein C receptor (EPCR) in gastric epithelial cells. The gastric epithelial cell lines, MKN-1 and AGS, and gastric biopsy samples from patients with and without H. pylori infection were used in the experiments. Polymerase chain reaction showed that gastric epithelial cell lines express EPCR and TM. Flow cytometry analysis also showed EPCR expression in both cells. H. pylori infection significantly increased EPCR expression compared with non-infected cells. Similar results were observed in vivo when samples from patients with and without H. pylori infection were analyzed for EPCR protein expression. Significant TM activity was found on AGS and MKN-1 cells stimulated with LPS from Escherichia coli and VacA antigen. APC was able to significantly inhibit the secretion of MCP-1 and IL-1beta induced by H. pylori homogenate in AGS cells. APC also remarkably suppressed the mRNA expression and secretion of MCP-1 from AGS cells infected with H. pylori. These results demonstrated the expression of components of the protein C pathway on gastric epithelial cells and that APC may play a critical role in the protection against gastric mucosal inflammation.     

Polyphenols reduce gastritis induced by Helicobacter pylori infection or VacA toxin administration in mice

Helicobacter pylori colonizes the human gastric mucosa, causing inflammation that leads to atrophic gastritis, and it can cause peptic ulcer and gastric cancer. We show that polyphenol administration to mice experimentally infected by H. pylori or treated with VacA toxin can limit gastric epithelium damage, an effect that may be linked to VacA inhibition.     

Helicobacter pylori-induced apoptosis in T cells is mediated by the mitochondrial pathway independent of death receptors

BACKGROUND: Chronic infection with Helicobacter pylori is related to the pathogenesis of the noncardia carcinoma of the stomach. In this study we investigated the mechanisms of H. pylori-induced apoptosis in T lymphocytes, which could explain a mechanism of immune evasion facilitating chronic inflammation of the mucosa and gastric carcinogenesis. MATERIALS AND METHODS: The supernatant of H. pylori culture was used to study the mechanism of apoptosis induction in human leukaemia T cell lines Jurkat and CEM and in primary T cells. The cytotoxin associated gene A (CagA) and vacuolating cytotoxin A (Vac A) positive bacterial strain H. pylori 60190 (CagA(+), VacA(+)) and as a control the less toxic H. pylori strain Tx30a (CagA(-), VacA(-)) were used to produce the supernatant. Cell death was determined by DNA fragmentation and protein expression by Western blot. RESULTS: H. pylori 60190-induced apoptosis was neither blocked by inhibition of the death ligands TRAIL (TNF-related apoptosis-inducing ligand), CD95L/FasL and TNF-alpha (tumour necrosis factor-a) in wild type Jurkat cells nor in FADD(def) (Fas-associated death domain protein) and caspase-8(def) subclones of the Jurkat cell line. Yet, the pancaspase inhibitor zVAD-fmk could inhibit up to 90% of H. pylori-induced apoptosis. Stable transfection of Jurkat wild type cells with Bcl-x(L and) Bcl-2 resulted in marked reduction of H. pylori-induced apoptosis, showing that the mitochondrial pathway is the key regulator. This is supported by the finding that surviving primary human lymphocytes upregulate Bcl-2 when exposed to H. pylori supernatant. CONCLUSIONS: H. pylori-induced apoptosis of T cells is mediated by the mitochondrial pathway and could create a local environment that facilitates life-long infection by immune evasion.     

VacA and HP-NAP, Ying and Yang of Helicobacter pylori-associated gastric inflammation

Helicobacter pylori is a Gram-negative bacterium which infects almost half of the population worldwide and represents the major cause of gastroduodenal pathologies, such as duodenal and gastric ulcer, gastric cancer, B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) and autoimmune gastritis. H. pylori colonization is followed by infiltration of the gastric mucosa by polymorphonuclear cells, macrophages and lymphocytes. Two of the major H. pylori virulence factors are the vacuolating cytotoxin (VacA) and the H. pylori neutrophil-activating protein (HP-NAP). VacA has been proposed as a modulator of immune cell function because of its capacity to interfere with antigen presentation and to inhibit T-cell activation. HP-NAP was designated as neutrophil-activating protein because it stimulates high production of oxygen radicals from neutrophils. We have recently demonstrated that HP-NAP is able to recruit leukocytes in vivo and to stimulate either neutrophils or monocytes to release IL-12, a key cytokine for the differentiation of naive Th cells into the Th1 phenotype. Altogether these evidences indicate that both VacA and HP-NAP play a major role in generating and maintaining the gastric inflammatory response associated with the H. pylori infection.     

幽门螺杆菌感染及其毒力因子和胃十二指肠疾病关系的研究

目的 探讨幽门螺杆菌（Hp)感染病人中Hp细胞毒相关蛋白（CagA)、细胞空泡毒素（VacA)抗体在胃十二指肠疾病的比例，并评估不同类型幽门螺杆菌感染对胃窦粘膜炎症程度的影响。方法 应用免疫印迹法测定Hp感染者病人体内的CagA、VacA抗体。结果 73％的Hp感染者病人中出现CagA抗体，61％Hp感染者病人中出现VacA抗体。CagA抗体和VacA抗体在各疾病之间差异无显著性（P＞0．05）。在胃溃疡、十二指肠溃疡和复合性溃疡三类病人中，具CagA和VacA双阳性的比例较CagA和VacA双阴性的比例差异有显著性（P＜0．05）。胃窦萎缩病变在CagA和VacA双阳性的病人中比CagA和VacA双阴性的病人严重（P＜0．05）。结论 具有高毒力因子（CagA和VacA)的Hp是胃肠疾病病人感染的常见菌株，具有CagA和VacA的Hp可能在诱导胃粘膜发展到萎缩病变过程中起重要作用。但不能作为特异性指标来判断胃十二指肠疾病。     

Human cell line for study of damage to gastric epithelial cells in vitro

We evaluated whether monolayers from a well-differentiated human gastric epithelial cell line (MKN 28) are suitable for studying the effect of drugs on gastric mucosa. MKN 28 monolayers and monolayers of human gastric epithelial cells from surgical specimens were studied morphologically and functionally. The protective effect of acetaminophen against taurocholate-induced damage was evaluated as was its effect on prostaglandin production. Both types of cultures showed similar morphologic and histochemical characteristics. Indomethacin inhibited and arachidonic acid stimulated prostaglandin production by both types of monolayers similarly. Both monolayers responded similarly to drug-induced damage. Acetaminophen decreased taurocholate-induced damage by 33% and 40% in MKN 28 cells and in primary human gastric cell culture, respectively. Indomethacin did not prevent acetaminophen protection nor did the amount of prostaglandin produced by cells increase after incubation with acetaminophen. In conclusion: (1) in the MKN 28 cell line model acetaminophen protected against taurocholate-induced damage; the percentage of protection was similar to that in primary cultures of human gastric epithelial cells; (2) acetaminophen protection in both models was not related to increased prostaglandin production; (3) the MKN 28 cell line is a suitable model to study damage to and protection of gastric epithelial cells in vitro.     

Progress in study for mechanism of gastric mucosal injury

Inflammatory reactions mediated by leukocytes, cytokines, adhesion molecules, active oxygen species, nitric oxide(NO) or prostaglandins have been implicated in the pathogenesis of gastric mucosal injury induced by Helicobacter pylori(H. pylori) or nonsteroidal anti-inflammatory drugs(NSAID). The molecular mechanism of gastric mucosal injury has been investigated in view of cell proliferation, apoptosis or necrosis. Eradication therapy of H. pylori, Cox2 inhibitors or NO-releasing NSAID may become new strategy for protection against gastric mucosal injury.     

H. pylori infection: bacterial virulence factors and cytokine gene polymorphisms as determinants of infection outcome

The gram negative bacterium H. pylori infects the human stomach worldwide, invariably causing mucosal inflammation. In the majority of cases, H. pylori-associated gastritis remains the only clinical manifestation of the infection, which might cause, otherwise, peptic ulcer, gastric adenocarcinoma. or MALToma. The balance between the bacterial virulence machinery and the host response to the infection determines the different clinical outcomes. The main bacterial virulence factors comprise adhesins (BabA, SabA), the vacuolating cytotoxin VacA, and the products of cag pathogenicity island. The pattern of cytokine production in response to the infection is one of the main host determinants involved in limiting the infection outcome to gastritis or in favoring peptic ulcer or cancer onset. The polymorphisms of some cytokine genes (IL-1beta IL-1RN, TNF-alpha, IFN-gamma) have been correlated with H. pylori-associated gastric adenocarcinoma or peptic ulcer, possibly because they influence the amount of cytokine production in response to H. pylori infection. This review focuses on the role of H. pylori virulence genes and on host cytokines' genes polymorphisms in determining clinical outcome to H. pylori infection.     

Relationship between mucosal levels of Helicobacter pylori-specific IgA, interleukin-8 and gastric inflammation

Mucosal IgA is important in local immune defence. Helicobacter pylori induces a specific IgA response in antral mucosa, but its immunopathology is unknown. Interleukin-8 (IL-8) has been suggested to be important in H. pylori-induced inflammation. Current information on the relationship between H. pylori-induced IgA and mucosal inflammation is limited. To investigate possible associations between mucosal-specific IgA, the toxinogenicity of H. pylori, mucosal levels of IL-8 and gastric inflammation, 52 endoscoped patients were studied. These comprised 28 patients with peptic ulcer and 24 with non-ulcer dyspepsia. Of these patients, 38 had H. pylori infection: 28 with peptic ulcer and 10 with non-ulcer dyspepsia. Antral biopsies were taken for histology, H. pylori culture and measurement of mucosal levels of IL-8 (pg/mg) and specific IgA (A450x1000) by ELISA. Mucosal H. pylori IgA was detectable in 35 out of 38 patients with H. pylori infection, with a median (interquartile) level of 220 (147, 531) units. There was no significant difference in mucosal levels of the IgA antibodies between patients infected with cytotoxin-positive or cagA-positive strains of H. pylori and those with toxin-negative or cagA-negative strains. The IgA levels in those patients with severe neutrophil infiltration were lower than in those with mild or moderate infiltration (P<0.05). There was a weak inverse correlation between antral mucosal IgA and IL-8 in infected patients (r=-0.36; P=0.04). H. pylori infection induced a significant local mucosal IgA response in most infected patients. The level of IgA antibodies does not appear to be correlated with the toxinogenicity of H. pylori. However, patients with severe active inflammation appear to have decreased levels of IgA. An inverse correlation between mucosal IL-8 and IgA may suggest that IL-8-induced inflammation compromises the mucosal IgA defence and renders the mucosa susceptible to further damage.     

Mitogenic response of canine fundic epithelial cells in short-term culture to transforming growth factor alpha and insulinlike growth factor I.

We report methods allowing the culture of rapidly dividing gastric epithelial cells to investigate the regulation of mucosal cell replication. Cells from canine fundic mucosa were dispersed by enzyme treatment, enriched by filtration and elutriation, and cultured on collagen gel in DMEM/F12 medium. After 48 h, greater than 95% of the cells displayed immunoreactivity with antibody to cytokeratin, an epithelial marker. The cells formed confluent monolayers by 72 h with a transmembrane resistance of 1,600 ohm.cm2 when mounted in a Ussing chamber indicating retention of epithelial cell characteristics. Calf serum (0.1-2%) produced a dose-dependent mitogenic effect evident by increases in [3H]-thymidine incorporation into acid-precipitated material and in cell number. After an 18-24-h incubation with [3H]-thymidine, approximately 55% of the cells cultured in 2% serum showed evidence of DNA synthesis by autoradiography and all of the replicating cells were cytokeratin positive. Using comparable culture conditions, a similar proportion of cells incubated for 18-24 h with bromodeoxyuridine displayed nuclear anti-bromodeoxyuridine immunoreactivity, thus indicating that over half of the cells in these cultures synthesized DNA during this period. As with serum, epidermal growth factor and transforming growth factor alpha (TGF alpha) (10 pM to 1 nM), insulin (10 nM to 1 microM) and insulinlike growth factor-I (IGF-I, 1-100 nM) increased [3H]-thymidine uptake. The greater potency of IGF-I, compared to insulin, suggests the presence of IGF-I receptors. We conclude that this culture preparation is composed of fundic mucosal epithelial cells and contains a predominance of dividing epithelial cells. EGF/TGF alpha and IGF-I are potential factors directly regulating proliferation of fundic mucosal cells.     

The Helicobacter pylori VacA toxin is a urea permease that promotes urea diffusion across epithelia

Urease and the cytotoxin VacA are two major virulence factors of the human pathogen Helicobacter pylori, which is responsible for severe gastroduodenal diseases. Diffusion of urea, the substrate of urease, into the stomach is critically required for the survival of infecting H. pylori. We now show that VacA increases the transepithelial flux of urea across model epithelia by inducing an unsaturable permeation pathway. This transcellular pathway is selective, as it conducts thiourea, but not glycerol and mannitol, demonstrating that it is not due to a loosening of intercellular junctions. Experiments performed with different cell lines, grown in a nonpolarized state, confirm that VacA permeabilizes the cell plasma membrane to urea. Inhibition studies indicate that transmembrane pores formed by VacA act as passive urea transporters. Thus, their inhibition by the anion channel blocker 5-nitro-2-(3-phenylpropylamino) benzoic acid significantly decreases toxin-induced urea fluxes in both polarized and nonpolarized cells. Moreover, phloretin, a well-known inhibitor of eukaryotic urea transporters, blocks VacA-mediated urea and ion transport and the toxin's main biologic effects. These data show that VacA behaves as a low-pH activated, passive urea transporter potentially capable of permeabilizing the gastric epithelium to urea. This opens the novel possibility that in vivo VacA may favor H. pylori infectivity by optimizing urease activity.     

A proinflammatory peptide from Helicobacter pylori activates monocytes to induce lymphocyte dysfunction and apoptosis

Infection with Helicobacter pylori causes chronic gastritis, which is characterized by a dense mucosal infiltration by inflammatory cells such as monocytes/macrophages. H. pylori-induced inflammation is a risk factor for the development of gastric adenocarcinoma, but the mechanisms involved in H. pylori-associated carcinogenesis are poorly understood. A cecropin-like H. pylori peptide, Hp(2-20), was found to be a monocyte chemoattractant and activated the monocyte NADPH-oxidase to produce oxygen radicals. The receptors mediating monocyte activation were identified as FPRL1 and the monocyte-specific orphan receptor FPRL2. Hp(2-20)-activated monocytes inhibited lymphocytes with antitumor properties, such as CD56+ natural killer (NK) cells and CD3epsilon+ T cells. The changes observed in NK cells and T cells--a reduced antitumor cytotoxicity, downregulation of CD3zeta expression, and apoptosis--were mediated by Hp(2-20)-induced oxygen radicals. Histamine, a gastric mucosal constituent, rescued NK cells and T cells from inhibition and apoptosis by suppressing Hp(2-20)-induced oxygen radical formation. We conclude that H. pylori expression of this monocyte-activating peptide contributes to its ability to attract and activate monocytes and reduces the function and viability of antineoplastic lymphocytes. These novel mechanisms may be subject to local, histaminergic regulation in the gastric mucosa.     

Frequencies of serum antibodies to Helicobacter pylori CagA and VacA in a Turkish population with various gastroduodenal diseases

Infection with Helicobacter pylori (H. pylori) strains secreting cytotoxin-associated gene A (CagA) and vacuolating cytotoxin A (VacA) proteins is associated with more severe gastroduodenal pathologies. However, this association varies among geographical regions and ethnic groups. We investigated the frequencies of antibodies to CagA and VacA proteins in 131 H. pylori-infected dyspeptic patients [40 duodenal ulcer (DU), 19 gastric ulcer (GU), 28 gastric cancer (GC), and 44 non-ulcer dyspepsia (NUD)] across 30 H. pylori-infected and endoscopically normal asymptomatic subjects (AS). Anti-CagA and anti-VacA antibodies were detected by Western blotting. The positivity rates of anti-CagA and anti-VacA antibodies were higher in patients with DU (92.5 and 75%), GU (89.5 and 84.2%) and GC (96.4 and 85.7%) than patients with NUD (70.5 and 50%) and AS (50 and 23.3%) (p < 0.05). CagA+ VacA+ phenotype was more frequent in patients with DU, GU and GC than patients with NUD and AS (75, 84.2, 85.7 vs. 47.7 and 20%, respectively) (p < 0.01). Our results showed that there is a significantly positive association between the presence of anti-CagA and anti-VacA antibodies and DU, GU and GC in our region.     

儿童胃黏膜白细胞介素mRNA水平与幽门螺旋杆菌感染的研究

目的分析儿童胃黏膜白细胞介素(IL-1β)水平与幽门螺旋杆菌(H.pylori)及其高毒力亚型感染间的相关性。方法实时定量聚合酶链(real-time PCR)检测H.pylori的保守基因ure以判断H.pylori的感染,高毒力亚型基因vacA s1用real-time PCR检测,用PCR扩增另一高毒力基因cagA羧基端EPIYA基序所在区,然后测序确定其亚型。IL-1βmRNA使用PCR-荧光探针法检测,比较循环CT法分析。结果患儿中无论是低毒力还是高毒力的H.pylori感染都与胃黏膜IL-1βmRNA水平无显著相关性。结论 H.pylori对儿童胃黏膜IL-1β表达的影响作用并不明显,可能还有其他一些环境、遗传因素如IL-1基因簇多态性与H.pylori共同作用调节胃黏膜IL-1β的表达。     

白光胃镜下胃黏膜形态变化对幽门螺杆菌感染的诊断价值分析

目的探究白光胃镜下胃黏膜形态变化对幽门螺杆菌（H. pylori）感染相关性胃炎的诊断价值。 方法回顾性分析2018年7月至2020年7月在海南医学院第二附属医院进行白光胃镜检查和13-尿素呼气试验（¹³C-UBT）检查的1160例病例,依据¹³C-UBT检查结果分为2组：H. pylori感染组（812例）和无H. pylori感染组（348例）。比较2组白光胃镜下胃粘膜形态差异,进行Logistic回归分析筛选出H. pylori感染独立相关的胃黏膜形态特征,并应用受试者工作特征曲线（ROC）评价相关指标的预测价值。 结果H. pylori感染组白光胃镜下弥漫性胃黏膜充血、点状发红、胃黏膜肿胀、胃体皱襞肿大蛇形、胃体黏膜呈“龟纹样”等检出率均显著高于无H. pylori感染组。多因素Logistic回归分析显示,弥漫性胃黏膜充血（OR=116.280）、点状发红（OR=4.821）、胃黏膜肿胀（OR=3.432）、胃体皱襞肿大蛇形（OR=4.336）、胃体黏膜呈“龟纹样”（OR=9.346）是H. pylori感染的独立相关因子。ROC曲线分析显示,弥漫性胃黏膜充血、点状发红、胃黏膜肿胀、胃体皱襞肿大蛇形、胃体黏膜呈“龟纹样”预测H. pylori感染的曲线下面积分别为0.829（95%CI：0.796~0.859）、0.687（95%CI：0.648~0.725）、0.750（95%CI：0.713~0.785）、0.578（95%CI：0.537~0.619）、0.619（95%CI：0.578~0.619）,其中以弥漫性胃黏膜充血、胃黏膜肿胀较大,它们的敏感度和特异度分别为93.68%和72.17%、97.13%、52.96%。 结论白光胃镜下胃黏膜形态变化与H. pylori感染具有相关性,以弥漫性胃黏膜充血、胃黏膜肿胀对H. pylori感染的诊断价值较大。     

CpG ODN增强树突状细胞对胃癌细胞增殖周期和凋亡影响的实验研究

目的探讨CpG ODN1826增强树突状细胞(DC)抗胃癌效应的作用。方法分离正常人外周血DC,用GM-CSF和IL-4培养,于第5天加入TNF-α并分成Ⅰ、Ⅱ、Ⅲ、Ⅳ、Ⅴ、Ⅵ、Ⅶ、Ⅷ组继续培养。第6天各组均加入胃癌细胞冻融抗原50μl,Ⅱ、Ⅳ、Ⅵ、Ⅷ组再分别加入CpG ODN182610μg/ml,第10天ELISA检测IL-12和IFN-γ的水平,MTT法检测CTL对MKN45、MKN28、SGC7901和A549细胞的体外杀伤效应。流式细胞术检测CpG ODN1826增强DC对胃癌细胞增殖周期、凋亡的影响。结果体外培养第10天,加入CpG ODN1826后各组IL-12、IFN-γ的分泌量明显提高;CpG ODN1826协助DC对同种不同分化类型的胃癌细胞株MKN45、MKN28、SGC7901均有强烈的杀伤效应(P<0.01),杀伤活性显著高于A549(P<0.01)。体外应用CpG ODN1826对肿瘤细胞周期比例:G0/G1间期(MKN4568.35%、MKN2869.23%、SGC790169.80%),S期(MKN4539.45%、MKN2839.75%、SGC790139.55%),G2/M期(MKN456.50%、MKN286.30%、SGC79016.42%);与A549(G0/G1间期57.68%,S期25.13%,G2/M期18.46%)比较,差异有统计学意义(P<0.01);同时,不同肿瘤细胞株的凋亡率分别为MKN4575.20%、MKN2373.87%、SGC790172.43%、A54951.43%,表明CpG ODN1826能显著增强DC对胃癌细胞周期的抑制作用,促进胃癌细胞的早期凋亡(P<0.01)。结论 CpG ODN1826体外可显著增强DC诱导出高效而特异的抗胃癌效应,显著抑制胃癌细胞分裂增殖、促进凋亡,可作为胃癌免疫治疗的一种有效方法。