Involvement of endothelin-1 in up-regulation of gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide

Effect of ebrotidine on Helicobacter pylori lipopolysaccharide-induced up-regulation of endothelin-1 in gastric mucosa

Helicobacter pylori is recognized as a primary etiologic factor in the development of gastric disease. We applied the animal model of H. pylori lipopolysaccharide-induced acute gastritis to study the effect of the anti-ulcer agent, ebrotidine, on the course of mucosal inflammatory responses by analyzing over a period of 10 days the extent of epithelial cell apoptosis and the mucosal expression of endothelin-1 (ET-1), tumor necrosis factor α (TNFα), and the activity of constitutive (cNOS) and inducible (NOS-2) nitric oxide synthase. Rats, pretreated twice daily for 3 days with ebrotidine at 100 mg/kg or the vehicle, were subjected to intragastric application of H. pylori lipopolysaccharide at 50 µg/animal, and after 2, 4, and 10 additional days on the drug or vehicle regimen their mucosal tissue was used for histological and biochemical assessment. In the absence of ebrotidine, H. pylori lipopolysaccharide elicited within 2 days extensive mucosal inflammation accompanied by a significant increase in epithelial cell apoptosis (13.5-fold) and the mucosal expression of TNFα (11.7-fold), NOS-2 (9.3-fold), and ET-1 (2.9-fold), while cNOS activity showed a 5.5-fold decrease. The extent of mucosal inflammatory involvement reached a maximum by the 4th day and showed a decline by the 10th day. This was reflected in a marked reduction in epithelial cell apoptosis, a decrease in the mucosal expression of ET-1, TNFα and NOS-2, and the recovery in cNOS activity. Treatment with ebrotidine caused a reduction in the extent of mucosal inflammatory involvement elicited by the lipopolysaccharide and this effect of ebrotidine was reflected at the end of a 10 day period in a 61.3% reduction in inflammation, and a decrease in apoptosis (83%), TNFα (51.8%), ET-1 (27.6%) and NOS-2 (62.9%), while the expression of cNOS increased by 78.6%. The findings indicate that an increase in the ET-1 level elicited by H. pylori lipopolysaccharide, combined with a decline in cNOS, trigger the induction of TNFα which propagates the inflammatory process. We also show that ebrotidine is capable of suppressing the H. pylori-induced gastric mucosal inflammatory responses.

Integrin-linked kinase modulates lipopolysaccharide- and Helicobacter pylori-induced nuclear factor κB-activated tumor necrosis factor-α production via regulation of p65 serine 536 phosphorylation

Integrin-linked kinase (ILK) is a ubiquitously expressed and highly conserved serine-threonine protein kinase that regulates cellular responses to a wide variety of extracellular stimuli. ILK is involved in cell-matrix interactions, cytoskeletal organization, and cell signaling. ILK signaling has also been implicated in oncogenesis and progression of cancers. However, its role in the innate immune system remains unknown. Here, we show that ILK mediates pro-inflammatory signaling in response to lipopolysaccharide (LPS). Pharmacological or genetic inhibition of ILK in mouse embryonic fibroblasts and macrophages selectively blocks LPS-induced production of the pro-inflammatory cytokine tumor necrosis factor α (TNF-α). ILK is required for LPS-induced activation of nuclear factor κB (NF-κB) and transcriptional induction of TNF-α. The modulation of LPS-induced TNF-α synthesis by ILK does not involve the classical NF-κB pathway, because IκB-α degradation and p65 nuclear translocation are both unaffected by ILK inhibition. Instead, ILK is involved in an alternative activation of NF-κB signaling by modulating the phosphorylation of p65 at Ser-536. Furthermore, ILK-mediated alternative NF-κB activation through p65 Ser-536 phosphorylation also occurs during Helicobacter pylori infection in macrophages and gastric cancer cells. Moreover, ILK is required for H. pylori-induced TNF-α secretion in macrophages. Although ILK-mediated phosphorylation of p65 at Ser-536 is independent of the phosphatidylinositol 3-kinase (PI3K)/Akt pathway during LPS stimulation, upon H. pylori infection this event is dependent on the PI3K/Akt pathway. Our findings implicate ILK as a critical regulatory molecule for the NF-κB-mediated pro-inflammatory signaling pathway, which is essential for innate immune responses against pathogenic microorganisms.

Effect of methanolic extract of Terminalia arjuna against Helicobacter pylori 26695 lipopolysaccharide-induced gastric ulcer in rats

Helicobacter pylori lipopolysaccharide (HP-LPS) is a potent virulence factor in the causation of gastric ulcer and gastritis. H. pylori-induced gastric pathology is prevalent throughout the world. Herbal medicines are attracting attention because of their traditional values, popularity and belief, as well as for their advantages such as less toxicity, affordability and medicinal value. The present study aimed to evaluate the anti-ulcer effect of a methanolic extract of Terminalia arjuna (TA) against HP-LPS-induced gastric damage in rats. Ulcers were induced with HP-LPS (50 μg per animal) administered orally daily for 3 days. The efficacy of TA on gastric secretory parameters such as volume of gastric juice, pH, free and total acidity, pepsin concentration, and the cytoprotective parameters such as protein-bound carbohydrate complexes in gastric juice and gastric mucosa was assessed. The protective effect of TA was also confirmed by histopathological examination of gastric mucosa. HP-LPS-induced alterations in gastric secretory parameters were altered favourably in rats treated with TA, suggesting that TA has an anti-secretory role. Furthermore, HP-LPS-induced impairments in gastric defence factors were also prevented by treatment with TA. These results suggest that the severe cellular damage and pathological changes caused by HP-LPS are mitigated by TA; these effects are comparable with those of sucralfate. The anti-ulcer effect of TA may reflect its ability to combat factors that damage the gastric mucosa, and to protect the mucosal defensive factors.

Crevicular fluid endothelin-1 levels in periodontal health and disease

BACKGROUND AND OBJECTIVE

Endothelin-1 is a 21-amino-acid peptide with multifunctional regulation. Initial research indicated that endothelin-1 levels in the gingival crevicular fluid from patients with chronic periodontitis were higher than those in the gingival crevicular fluid from healthy subjects. The aim of the present study was to assess the relationship between the clinical parameters and the concentrations of endothelin-1 within the gingival crevicular fluid from inflamed gingiva and periodontitis sites and, subsequently, after the treatment of periodontitis sites.

MATERIAL AND METHODS

A total of 60 subjects were divided into three groups - healthy (group I), gingivitis (group II) and chronic periodontitis (group III) - based on gingival index, pocket probing depth and clinical attachment loss. A fourth group consisted of 20 subjects from group III, 6-8 wk after treatment (i.e. scaling and root planing). Gingival crevicular fluid samples collected from each patient were quantified for endothelin-1 using an enzymatic immunometric assay.

RESULTS

Endothelin-1 was not detected in any sample from any of the study groups.

CONCLUSION

The results showed that all the gingival crevicular fluid samples were negative for the endothelin-1 molecule. Therefore, endothelin-1 cannot be considered as a potential biomarker of periodontal disease progression.

Association of endothelin-converting enzyme-1b C-338A polymorphism with gastric cancer risk: a case-control study

To investigate the association between endothelin-converting enzyme-1b (ECE-1b) C-338A polymorphism and gastric cancer risk, we conducted a hospital-based case-control study of 256 gastric cancer cases and 256 controls matched on age and gender. The genotypes were identified by polymerase chain reaction-restriction fragment length polymorphism. We found that the genotype frequencies were significantly different (P=0.005) between cases and controls. Compared with the wild genotype CC, the variant genotypes (CA+AA) were associated with a 64% increased risk of gastric cancer [adjusted odds ratio (OR)=1.64, 95% confidence interval (CI) 1.15-2.33]. Further stratification analyses indicated that the increased risk was especially noteworthy in older subjects (age 58) (adjusted OR=1.91, 95% CI 1.18-3.09), women (adjusted OR=2.30, 95% CI 1.11-4.79) and non-smokers (adjusted OR=1.79, 95% CI 1.19-2.67). Our results suggest that the ECE-1b C-338A polymorphism may be associated with increased risk of gastric cancer.

Cytosolic phospholipase A2 activation in Helicobacter pylori lipopolysaccharide-induced interference with gastric mucin synthesis

Release of arachidonic acid from membrane glycerophospholipids by cytosolic phospholipase A2 (cPLA2) is a key step in the generation of platelet-activating factor (PAF), recognized as the most proximal mediator of inflammatory events triggered by bacterial infection. Here, we report on the role of cPLA2 in the disturbances in gastric mucin synthesis evoked by the LPS of H. pylori, a bacterium identified as a primary cause of gastric disease. Using rat gastric mucosal cells, we show that H. pylori LPS detrimental effect on gastric mucin synthesis, associated with up-regulation in PAF and endothelin-1 (ET-1) generation, was subject to suppression by a specific inhibitor of cPLA2, MAFP. Moreover, the LPS-induced changes in mucin synthesis and ET-1 generation were countered by PAF receptor antagonist, BN52020. The impedance by PAF antagonist of the LPS-induced reduction in mucin synthesis was countered by wortmannin, an inhibitor of PI3K, as well as by ERK inhibitor, PD98059. The blockade of ERK caused also inhibition of the LPS-induced cPLA2 activation and amplification in the impedance capacity of PAF antagonist on the LPS-induced ET-1 generation, while the inhibitor of PI3K had no effect. Our findings are the first to demonstrate that the detrimental consequences of H. pylori LPS on gastric mucin synthesis involve ERK-dependent cPLA2 activation that leads to up-regulation in PAF generation and ET-1 production.

Endothelin-1-dependent leptin induction in gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide

Leptin, a multifunctional hormone that regulates food intake and energy expenditure, has emerged recently as an important modulator of gastric mucosal responses to Helicobacter pylori infection. We applied the animal model of H. pylori LPS-induced gastritis to investigate the role of endothelin-1 (ET-1) in the mucosal leptin production. We show that the histologic pattern of inflammation reached a maximum on the fourth day following the LPS and was reflected in a marked increase in the mucosal level of ET-1 and leptin. Therapeutic administration of phosphoramidon, an inhibitor of ECE-1 activity, led to a 61.2% decline in the mucosal ET-1 level and a 64.1% reduction in leptin, while the severity of mucosal inflammatory involvement increased by 28.6%. A drop in the level of leptin and the increase in severity of the inflammatory involvement elicited by the LPS was also attained in the presence of ET(A) receptor antagonist BQ610, but not the ET(B) receptor antagonist BQ788. Moreover, administration of ERK inhibitor, PD98059, in the presence of ET(B) receptor antagonist, but not the ET(A) receptor antagonist, caused reduction in the mucosal leptin level. Our findings are the first to implicate ET-1 as a key factor in up-regulation of gastric mucosal leptin-associated H. pylori infection. We also show that the effect of ET-1 on leptin production is a consequence of ET(A) receptor activation.

Endothelin-1-dependent up-regulation of leptin production in gastric mucosal injury by indomethacin

Leptin, a multifunctional hormone that regulates food intake and metabolic and endocrine responses, has emerged recently as an important modulatory factor in gastric mucosal resistance to injury. In this study, we applied the animal model of gastric mucosal injury caused by indomethacin to investigate the role of endothelin-1 (ET-1) in the mucosal leptin production. Using groups of rats subjected to intragastric administration of indomethacin (at 0-60 mg/kg), we show that gastric mucosal damage reached a maximum 4 h following the drug, and was accompanied by a marked elevation (up to 3.5-fold) in the mucosal leptin level, up to 4-fold enhancement in the expression of endothelin-converting enzyme-1 (ECE-1) activity and up to 4.5-fold increase in ET-1 generation. Pretreatment with phosphoramidon, an inhibitor of ECE-1 activity, not only led to a decline in ECE-1 and ET-1 generation, but also produced a dose-dependent reduction in the mucosal level of leptin and the extent of mucosal damage caused by indomethacin. This effect of phosphoramidon, however, was subject to suppression by the exogenous ET-1 administration. Moreover, a marked drop in the mucosal level of leptin and the reduction in the severity of mucosal damage was attained following pretreatment with ET(A) receptor antagonist BQ610, but not by ET(B) receptor antagonist BQ788. The results implicate ET-1 as a key factor in the regulation of leptin production associated with gastric mucosal response to injury, and show that the stimulatory effect of ET-1 on leptin production occurs via ET(A) receptor activation.

Up-regulation in endothelin-1 by Helicobacter pylori lipopolysaccharide interferes with gastric mucin synthesis via epidermal growth factor receptor transactivation

OBJECTIVE

Endothelin-1 (ET-1), a key mediator of inflammatory processes associated with bacterial infection, is a 21-amino acid peptide produced from a biologically inactive big ET-1 by the action of endothelin-converting enzyme-1 (ECE-1) that acts through G protein-coupled ET(A) and ET(B) receptors. Here we report on the role of ET-1 in the mediation of the detrimental influence of Helicobacter pylori on the synthesis of gastric mucin.

MATERIAL AND METHODS

Rat gastric mucosal cells were exposed to H. pylori key virulence factor, lipopolysaccharide (LPS).

RESULTS

The LPS inhibitory effect on gastric mucin synthesis was accompanied by a marked increase in ET-1 generation and enhancement in ECE-1 activity. Inhibition of ECE-1 with phosphoramidon not only led to the impedance of LPS-induced ET-1 generation, but also countered the detrimental effect of LPS on mucin synthesis. Moreover, the LPS inhibitory effect on mucin synthesis was blocked by ET(A) receptor antagonist BQ610, but not by ET(B) receptor antagonist BQ788. Furthermore, the LPS-induced suppression in gastric mucin synthesis was countered in a concentration-dependent fashion by PD153035 (81.7%), a specific inhibitor of epidermal growth factor receptor (EGFR) kinase as well as PP2 (69.8%), a selective inhibitor of tyrosine kinase Src responsible for ligand-independent EGFR transactivation.

CONCLUSIONS

Our findings are the first to show that the detrimental effect of H. pylori on gastric mucin synthesis is intimately linked to the events associated with ECE-1 up-regulation, enhancement in ET-1 production, and G protein-coupled ET(A) receptor activation that triggers the EGFR transactivation.

Induction of cyclooxygenase 2 by Escherichia coli but not Helicobacter pylori lipopolysaccharide in gastric epithelial cells in vitro

BACKGROUND

Cyclooxygenase 2 (COX-2) is an inducible enzyme that plays a key role in the synthesis of prostaglandins in response to inflammatory stimuli. It is expressed in the gastric mucosa as part of the response to infection with Helicobacter pylori. The specific interaction between H. pylori and the gastric epithelium that results in COX-2 expression has not been identified.

METHODS

In order to investigate the hypothesis that lipopolysaccharide (LPS) from H. pylori plays a role in the induction of cyclooxygenase 2 in the stomach, gastric cell lines MKN-7 and MKN-45 were incubated with LPS from either H. pylori NCTC 11637 or Escherichia coli 055:B5. Incubation of cells with live H. pylori NCTC 11637 was also carried out as a positive control. Cells were then analysed for COX-2 protein and mRNA and prostaglandin E2 synthesis.

RESULTS

Cyclooxygenase 2 protein and mRNA expression was induced by E. coli LPS and live H. pylori, but not by H. pylori LPS. Prostaglandin E2 synthesis increased in a dose-dependent manner in both cell lines with E. coli but not H. pylori LPS.

CONCLUSIONS

H. pylori LPS is of low biological activity when compared with E. coli LPS in its ability to induce the expression of cyclooxygenase 2 and synthesis of prostaglandin E2. This may provide one mechanism by which H. pylori minimizes the inflammatory response in the gastric mucosa, allowing chronic infection.

Modulation of MUC1 and blood group antigen expression in gastric adenocarcinoma cells by cytokines

Immunohistological studies demonstrated that MUC1 expression in gastric cancer is associated with a poor prognosis. As a mediator of cell-cell interactions, MUC1 may also be involved in metastasis. However, these aspects are of relevance since cytokine levels are locally increased as a consequence of peritumorous inflammatory response and coexisting chronic gastritis. Therefore we analyzed the potential influence of several cytokines on the expression of tumor-associated MUC1 and Lewis blood group antigens in gastric carcinoma cells. Gastric cancer cell lines AGS and KATOIII were incubated with the cytokines interleukin-1beta, interferon-gamma, tumor necrosis factor-alpha (TNF-alpha), and hepatocyte growth factor over a period of 72 h. Expressions of mucin antigens and cytokine secretion were measured by immunocytochemistry and/or enzyme-linked immunosorbent assay (ELISA). Analysis by fluorescence-activated cell sorter (FACS) demonstrated that MUC1 and sialyl Lewis A reactivities of AGS cells were increased significantly following TNF-alpha stimulation but not by other cytokines. Expression of mucin-associated antigens by cell line KATOIII was not affected by any of the employed cytokines. These data provide evidence that TNF-alpha can raise the expression of important mucin peptide as well as mucin-associated carbohydrate antigens and thereby potentially influence the progression of gastric carcinomas.

Expression of endothelin-1 in gingival epithelial cells

OBJECTIVES AND BACKGROUND

Endothelin-1 (ET-1) is a 21-amino acid peptide with multifunctional regulation. ET-1 expresses in various cells during inflammation. The present study aimed to examine the ET-1 expression in oral epithelial cells after infection with the periodontal pathogen and to investigate the presence of ET-1 in human inflamed and uninflamed gingival tissues.

MATERIALS AND METHODS

The KB cells were infected with Porphyromonas gingivalis and the expression level of ET-1 was examined using reverse transcription-polymerase chain reaction (RT-PCR) and enzyme-linked immunosorbent assay (ELISA). The immunohistochemical analysis of ET-1 was performed in gingival tissues obtained from patients. In addition, the ET-1 mRNA expression in each tissue was also investigated by RT-PCR.

RESULTS

The expression of ET-1 in KB cells was strongly induced by the P. gingivalis infection. On the other hand, the strong immunoreactivity for ET-1 was observed in the epithelium and vascular endothelial cells of the inflamed gingival tissue. Furthermore, the level of ET-1 mRNA was greater in the inflamed tissues.

CONCLUSION

These results suggested that the expression level of ET-1 in gingival epithelial cells might be enhanced during the periodontal inflammation.

Protective effects of endothelin-1 antibody on stress induced lesion of gastric mucosa in rats

AIM

To explore the protective effects of endothelin-1 antibody (ET-1Ab) on acute gastric mucosa lesions induced by stress in rats.

METHODS

Stress ulcer induced by cold-restraint-stress(CRS) was used as model in this study, different dose ET-1Ab were administered by left femoral vein prior to stress so as to observe the effects of the drug on ET-1 levels in plasma and gastric mucosa, gastric mucosa blood flow(GMBF)and ulcer index(UI) of CRS rats.

RESULTS

(1) Compared with the normal control group, ET-1 levels of plasma and gastric mucosa and UI were increased significantly in the stress groups (116.2±4.7 mv and 125.1±4.2 mv vs 49.1±9.7 mv, 113.8±9.3 mv and 122.9±19.6 mv vs 52.3±10.3 mv, 28.6±1.85 mv and 51.2±5.93 mv vs 0, P<0.01), while GMBF were decreased markedly in stress groups (227.8±13.5 mv and 150.8±11.5 mv vs 405.8±23.3 mv, P<0.01).There was significantly positive correlation between ET-1 and UI (r = 0.96, P<0.01), and significantly negative correlation between ET-1 and GMBF(r = -0.91, P<0.01). (2) However, compared with the single-stress groups, ET-1 levels of plasma and gastric mucosa and UI were decreased significantly in ET-1Ab-stress groups (69.2±7.3 mv vs 116.2±24.7 mv, 80.6±12.3 mv vs 125.1±24.2 mv, 58.5±6.3 mv vs 113.8±29.3 mv, 68.9±9.6 mvvs 122.9±19.6 mv, 13.2±2.05 mv vs 28.6±1.85 mv, 25.8±3.62 mv vs 51.2±5.93 mv, P<0.01), GMBF were increased dramatically (329.8±16.3 mv vs 227.8±13.5 mv, 251.9±11.3 mv vs 150.8±1.5 mv, P<0.01), ET-1Ab can dose-dependently reduce levels of the ET-1 and UI, and improve GMBF significantly in cold-restraint-stress.

CONCLUSION

In the course of CRS-induced ulcers, endogenous ET-1 levels of plasma and gastric mucosa were increased significantly, and there were close relationship between ET-1 levels and UI. The increased ET-1 may involve in the pathogenesis of CRS-induced ulcers in rats by its vasoconstriction and marked reduction of GMBF. ET-1Ab can dose-dependently attenuate the degree of gastric mucosa lesions induced by CRS significantly. So it may have therapeutic effect for SU.

Expression of endothelins and their receptors in cells from human periodontal tissues

OBJECTIVE

The present study investigated the presence of ET-1 in gingival crevicular fluid (GCF) from patients with periodontitis, and the expression of endothelins (ETs) and their receptors mRNA in cultured cells from human periodontal tissues.

BACKGROUND

ET was originally discovered as a potent vasoconstrictive peptide from endothelial cells. It has been reported that ETs are produced by various cells besides endothelial cells. ETs are related to inflammatory and sclerotic lesions, such as arteriolosclerosis and hepatic cirrhosis. Therefore, ETs may be involved in periodontal disease. However, the roles of ETs in development and progression of periodontal disease are not clear.

METHODS

ET-1 released from the cultured cells was measured by enzyme-linked immunosorbent assay. mRNA expressions for ETs and their receptors were examined by reverse transcription-polymerase chain reaction and Northern blotting analysis.

RESULTS

ET-1 levels in GCF from patients with periodontitis were higher than those from healthy subjects. Human gingival keratinocytes (HGK) expressed mRNA for ETs and their receptors, ET-Ar and ET-Br. ET-1 mRNA expression and ET-1 peptide production from HGK were enhanced by interleukin-1beta and tumor necrosis factor-alpha.

CONCLUSIONS

These results suggest that ET-1 plays a significant role in periodontal disease.

Apoptosis in gastric epithelium induced by Helicobacter pylori infection: implications in gastric carcinogenesis

OBJECTIVES

Helicobacter pylori is an identified carcinogen for gastric cancer, however, the underlying mechanisms remain to be defined. In this review, we sought to elucidate the role of apoptosis in gastric carcinogenesis, to determine the influence of H. pylori infection on apoptosis, and finally to provide insights into the mechanisms by which H. pylori may lead to gastric carcinogenesis.

METHODS

A broad-based MEDLINE and Current Contents literature search was performed to identify relevant publications between 1966 and March 2000 addressing H. pylori infection, apoptosis, cell proliferation, gastric carcinoma, oncogenes, and tumor suppressor genes, as well as the products of these genes. Abstracts from recent major conferences that provided adequate additional data were also included.

RESULTS

Apoptotic cells are rare in the glandular neck region (the generative cell zone) of normal gastric mucosa. With progression of atrophic gastritis, the generative cell zone shifts downward and a relatively large number of apoptotic cells occur. In intestinalized glands, both apoptotic cells and proliferative cells are present in deeper portions of the glands, corresponding to the generative zone. A higher frequency of apoptosis has been observed in gastric dysplasia than in coexisting gastric carcinomas, whereas the number of proliferative cells is significantly higher in gastric carcinoma than in dysplasia. Upregulation of oncogene bcl-2 in premalignant lesions and "downregulation" of the gene after malignant change is probably a common event. Accumulation of p53 protein is first detected in dysplasia, although mutation of the pS3 gene may occur in intestinal metaplasia. H. pylori infection induces apoptosis in gastric epithelial cells, which returns to normal after eradication of the infection. Numerous molecules produced by H. pylori including cytotoxin (VacA), lipopolysaccharide, monochloramine, and nitric oxide may directly induce apoptosis. Moreover, H. pylori-stimulated host inflammatory/immune responses lead to release of a large amount of cytokines. Cytokines produced by type 1 T helper cells, such as TNF-alpha and IFN-gamma, markedly potentiate apoptosis. Gastric cell proliferation is significantly higher in patients with H. pylori infection than in normal controls, and eradication of the infection leads to a reduction in cell proliferation. Apoptosis and cell proliferation are also increased in precancerous lesions such as gastric atrophy, intestinal metaplasia, and dysplasia in the presence of H. pylori infection. However, H. pylori-induced apoptosis may no longer be cell cycle-dependent in these lesions because of the occurrence of alterations and mutations of apoptosis-regulating genes, resulting in a loss of balance between apoptosis and cell proliferation.

CONCLUSIONS

It is hypothesized that H. pylori-induced apoptosis may play a key role in gastric carcinogenesis by increasing cell proliferation and/or resulting in gastric atrophy.

Gastroduodenal mucosal defense

The gastroduodenal mucosa is a model system of defense with several structural levels and biologic strategies that are closely interrelated with each other to cope with the harmful ingredients of ingested food and the potentially deleterious effects of gastric acid and pepsin. Experimental and clinical research carried out during the review period added to the understanding of each component of the multiple mechanisms of gastroduodenal mucosal protection. In the first place, mucosal integrity is defended by the mucus gel barrier, the epithelial cell barrier, and the immune barrier. The properties of these barriers are maintained by adequate regulation of mucus production, bicarbonate secretion, mucosal microcirculation, and motor activity. These regulatory systems are alarmed by nociceptive neurons and the mucosal immune system which includes chemokine-secreting epithelial cells. The ultimate defense system is rapid repair of the injured mucosa under the control of several growth factors. Progressing insight into the network of mucosal defense not only will improve existing therapies of inflammation and ulceration but also will provide new leads for the management of functional diseases in the gastroduodenal region.

Up-regulation of endothelin-converting enzyme-1 in gastric mucosal inflammatory responses to Helicobacter pylori lipopolysaccharide

Endothelin-1 (ET-1) is a vasoactive peptide produced from a biologically inactive big ET-1 by the action of endothelin-converting enzyme-1 (ECE-1). We investigated gastric mucosal expression of ECE-1 during a 10-day course of inflammatory responses associated with acute gastritis elicited by Helicobacter pylori lipopolysaccharide. The ECE-1 activity was associated with microsomal fraction and the level of its expression reflected the extent of mucosal inflammatory involvement. The histologic pattern of inflammation reached a maximum on the 4th day following the lipopolysaccharide and was accompanied by a 4.1-fold enhancement in the expression of ECE-1 activity and a significant elevation in ET-1 (3.1-fold), TNF-alpha (8.8-fold), and apoptosis (11.6-fold). A 41.5% decrease in the severity of mucosal inflammation by the 10th day following the lipopolysaccharide was reflected in a 62.3% reduction in the mucosal expression of ECE-1 and a decline in TNF-alpha, ET-1, and apoptosis. Thus, H. pylori infection causes up-regulation of gastric mucosal ECE-1 expression, which leads to the enhancement of ET-1 production, induction of TNF-alpha, and triggering the apoptotic events that exacerbate the inflammatory process.

Pathogenesis of Helicobacter pylori infection

Helicobacter pylori, a gram-negative, microaerophilic, motile, spiral-shaped bacterium, has been established as the etiologic agent of gastritis and peptic ulcers and is a major risk factor for gastric adenocarcinoma and mucosa-associated lymphoid tissue lymphoma (MALT). The ability of H. pylori to cause this spectrum of diseases depends on host, bacterial, and environmental factors. Bacterial factors critical for H. pylori colonization of the gastric mucosa include urease, flagella, adhesins, and delta-glutamyltranspeptidase. Lipopolysaccharide, urease, and vacuolating cytotoxin are among the factors that allow H. pylori to persist for decades and invoke an intense inflammatory response, leading to damaged host cells. Genes in the cag pathogenicity island also contribute to the inflammatory response by initiating a signal transduction cascade, resulting in interleukin-8 production. Proinflammatory cytokines and a Th-1 cytokine response further exacerbates the inflammation. Products of the enzymes nitric oxide synthase (iNOS) and cyclooxygenase may perturb the balance between gastric epithelial cell apoptosis (ulcer formation) and proliferation (cancer). The host Th-1 response and antibodies directed against H. pylori do not eliminate the organism, which presents challenges to vaccine development. Vaccines that include urease have shown some promise, but improved adjuvants and animal models should hasten progress in vaccine research. H. pylori is the most genetically diverse organism known, and the panmictic population structure may contribute to the varying ranges of disease severity produced by different strains. The complete genome sequence of two strains of H. pylori has propelled this field forward, and numerous groups are now using genomic, proteomic, and mutagenetic approaches to identify new virulence genes. Discovered only in 1982, H. pylori is now among the most intensely investigated organisms. This review summarizes recent progress in this rapidly moving field.