Role of activated protein C in Helicobacter pylori-associated gastritis

Activated protein C based therapeutic strategies in chronic diseases

Activated protein C (aPC) is a natural anticoagulant and a potent anti-inflammatory and cytoprotective agent. At the expense of increased bleeding risk aPC has been used - with some success - in sepsis. The design of cytoprotective-selective aPC variants circumvents this limitation of increased bleeding, reviving the interest in aPC as a therapeutic agent. Emerging studies suggest that aPC`s beneficial effects are not restricted to acute illness, but likewise relevant in chronic diseases, such as diabetic nephropathy, neurodegeneration or wound healing. Epigenetic regulation of gene expression, reduction of oxidative stress, and regulation of ROS-dependent transcription factors are potential mechanisms of sustained cytoprotective effects of aPC in chronic diseases. Given the available data it seems questionable whether a unifying mechanism of aPC dependent cytoprotection in acute and chronic diseases exists. In addition, the signalling pathways employed by aPC are tissue and cell specific. The mechanistic insights gained from studies exploring aPC`s effects in various diseases may hence lay ground for tissue and disease specific therapeutic approaches. This review outlines recent investigations into the mechanisms and consequences of long-term modulation of aPC-signalling in models of chronic diseases.

A new type of intrabacterial nanotransportation system for VacA in Helicobacter pylori

Helicobacter pylori possesses intrabacterial nanotransportation systems (ibNoTSs) for CagA and urease. Both systems are UreI-dependent and urea-independent, and activated by extrabacterial acid. The activation occurs/appears within 15 min after exposure to extrabacterial acid stimulation. Although it has been clarified that VacA is secreted via the type-V secretion machinery, it remains unclear how this toxin is transported toward the machinery. To clarify the intrabacterial nanotransportation system for H. pylori VacA, immunoelectron microscopic analysis was performed in this study. VacA shifted to the periphery of the bacterial cytoplasm at 30 min after the extracellular pH change, whereas CagA and urease did so within 15 min. Studies using an ureI-deletion mutant revealed that unlike CagA and urease transport, VacA transport was not UreI-dependent. VacA secretion was accelerated without an increase in the production of VacA 30 min after the exposure to extrabacterial acid. These findings indicated that H. pylori possesses a novel type of ibNoTS for VacA, which is different from that for CagA or urease, in response time and dependency of UreI.

Presence of thrombin-activatable fibrinolysis inhibitor in Helicobacter pylori-associated gastroduodenal disease

Thrombin-activatable fibrinolysis inhibitor (TAFI) plays a role in the regulation of coagulation and inflammation. In addition to inhibiting the fibrinolytic system, TAFI may also regulate the bradykinin and complement systems. We hypothesized that TAFI also plays a role in defense mechanisms of the gastric mucosa during Helicobacter pylori infection. This study comprised 65 patients with gastroduodenal disorders: 41 patients with H. pylori infection, 13 without, and 11 patients with cured H. pylori infection. The gastric intramucosal concentrations of TAFI were measured by enzyme immunoassay. The gastric levels of TAFI and plasminogen activator inhibitor-1 were significantly increased in patients with H. pylori compared to those without infection or cured H. pylori. The presence of TAFI was detected in gastric mucosal epithelial cells. The concentration of TAFI was correlated with the degree of gastric mucosal atrophy, inflammation, and disease activity. These results show that TAFI is present in the gastric mucosa and that it may play a role in the pathogenesis of H. pylori infection-associated gastroduodenal disorders.

Changes in coagulation-fibrinolysis balance in blood mononuclear cells and in gastric mucosa from patients with Helicobacter pylori infection

INTRODUCTION

Helicobacter pylori and some of its virulence factors stimulate human blood mononuclear cells (MNC) in vitro to produce tissue factor (TF) and plasminogen activator inhibitor-2 (PAI-2). In this study we investigated the procoagulant-fibrinolytic potential of blood MNC in patients with H. pylori infection. In the same patients we also evaluated the coagulation-fibrinolysis profile in gastric tissue and in plasma.

METHODS AND RESULTS

The production of TF and PAI-2 was evaluated in 61 patients with dyspepsia, 31 positive and 30 negative for H. pylori infection. TF expressed by MNC and PAI-2 accumulation in cell culture medium after incubation for 20 h at 37 degrees C were significantly higher in H. pylori(+) than in H. pylori(-) patients and were significantly correlated. TF and PAI-2 content in extracts of gastric mucosa was similar in the two groups whereas lower levels of tissue plasminogen activator (t-PA) and thrombomodulin (TM) antigens were found in the antrum of H. pylori(+) patients. No difference between the groups was observed in plasma thrombus precursor protein, prothrombin fragment 1+2, D-dimer, t-PA, PAI-1, TM and thrombin activatable fibrinolysis inhibitor.

CONCLUSIONS

H. pylori infection is associated with functional abnormalities of blood MNC resulting in the coordinate expression of TF and antifibrinolytic activity. Changes in cell coagulation-fibrinolysis balance may represent a link between H. pylori infection and ischemic heart disease.

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.

Vacuolating cytotoxin A is associated with increased thrombin generation in gastric mucosa

BACKGROUND

Activation of the coagulation system is a critical response for both the repair of tissue injury and the host defense against microbial pathogens. Activation of the coagulation cascade culminates with the generation of thrombin. In vitro studies have shown that thrombin protects gastric epithelial cells from injury. The present study was undertaken to assess in vivo the relationship between gastric intramucosal generation of thrombin and Helicobacter pylori infection.

MATERIALS AND METHODS

This study comprised 59 patients with gastroduodenal disorders. There were 27 patients with H. pylori infection (Hp+), 14 without it (Hp-), and 18 patients with cured H. pylori infection (Hp c). The gastric intramucosal concentrations of thrombin-antithrombin complex (TAT), epidermal growth factor (EGF), prostaglandin E2 (PGE2), and vacuolating cytotoxin A (VacA) were measured by specific immunoassays.

RESULTS

The level of TAT was significantly increased in patients with Hp+ compared to Hp- and Hp c. The levels of TAT, EGF and PGE2 were higher in VacA (+) patients than in those with VacA (-). VacA induced significant expression of tissue factor in gastric epithelial cells in vitro. The gastric intramucosal level of VacA antigen was proportionally and significantly correlated with TAT, EGF and PGE2 in Hp+ patients. The level of TAT was proportionally and significantly correlated with EGF in Hp+ patients but not in Hp- and HP c patients.

CONCLUSIONS

These results showed that VacA produced by H. pylori is associated with increased thrombin generation, and that thrombin may play a protective role in H. pylori-associated gastroduodenal disorders.

Drotrecogin alfa (activated) prevents smoke-induced increases in pulmonary microvascular permeability and proinflammatory cytokine IL-1beta in rats

In an established rat model of smoke inhalation injury, we conducted a dose-response study to examine the protective effects of Xigris [drotrecogin alfa (activated) (DrotAA)], a recombinant form of human activated protein C (APC). DrotAA is a serine protease (approximately 55 kD molecular weight) with the same amino acid sequence and the glycosylation site as human plasma-derived APC. A total of 120 F344/NH rats (half each gender, approximately 175 g body weight) were randomly divided into five groups and exposed nose-only to air or diesel fuel smoke for 20 min. These rats were then i.v. administered with DrotAA in 0, 5, 10, and 20 mg/kg body weight, respectively, immediately following smoke exposure. Treatment with DrotAA significantly attenuated smoke inhalation injury in a dose-dependent manner at 2 hours after insult, as indicated by preserving microvascular permeability and proinflammatory cytokine IL-1beta (but not TNF-alpha and neuropeptide substance P) in bronchoalveolar lavage fluid (BALF). Moreover, the rats treated with 20 mg/ kg of DrotAA had an improvement of the expiration phase of pulmonary dynamic compliance. At all dosages, however, DrotAA also significantly increased all phases of pulmonary resistance compared with either the controls or to smoke inhalation alone. Generally, these data suggest that DrotAA may exert an anti-inflammatory effect by inhibiting cytokine-mediated inflammatory amplification. However, additional studies following a clinical course are needed to confirm the maximum efficiency and possible side effects of this recombined human activated protein C.

A cardioprotective role for the endothelial protein C receptor in lipopolysaccharide-induced endotoxemia in the mouse

A model of gram-negative lethal endotoxin shock, involving continuous peritoneal infusion of lipopolysaccharide (LPS), has been applied to wild-type (WT) mice and mice with a severe deficiency of endothelial protein C receptor (EPCR(delta/delta)). The survival of EPCR(delta/delta) mice was significantly diminished as compared to WT mice after administration of LPS via this route. Heart rates and central blood pressures also were significantly more depressed in EPCR(delta/delta) mice, indicating that the receptor-based protein C (PC) pathway functions in regulation of hemodynamic properties in the mouse. Further, heart muscle damage was more severe in EPCR(delta/delta) mice as compared to WT mice after endotoxin administration, as revealed by the more elevated plasma myoglobin levels in EPCR(delta/delta) mice and by microscopic examination of stained heart sections. Neutrophil infiltration was more pronounced in heart tissue of EPCR(delta/delta) mice, perhaps in response to the greatly increased expression level of the chemokine, MIP-2, which also significantly more up-regulated in the LPS-treated EPCR(delta/delta) mouse cohort. In conclusion, a severe deficiency of EPCR adversely affects survival of mice subjected to continuous infusion of endotoxin, via contributions of more responsive hemodynamic and cardiac alterations, thus suggesting that, among its other functions, the PC-based receptor system has a cardioprotective role after acute inflammatory challenge.

Reflux esophagitis after eradication of Helicobacter pylori is associated with the degree of hiatal hernia

BACKGROUND

Several studies have shown that reflux esophagitis (RE) occurs after eradication of Helicobacter pylori. However, endoscopic findings do not allow prediction of the development of RE after successful treatment. In this study, we evaluated the relationship between the prevalence of RE after eradication therapy and the degree of hiatal hernia.

METHODS

The study comprised 148 patients who had undergone H. pylori eradication therapy over the past 5 years. The degree of RE and hiatal hernia was evaluated based on endoscopic findings. Hiatal hernia was graded according to Hill's gastroesophageal flap valve (GEFV; grades I-IV) classification. RE after eradication therapy was graded according to the Los Angeles classification system. H. pylori infection was confirmed in all patients by culture, urease test and histological examination of antral and fundic biopsy specimens.

RESULTS

Among 148 patients, there were 122 patients (82.4%) with successful and 26 (17.6%) with failed eradication therapy. RE was diagnosed in 25 (20.5%) out of 122 patients with successful therapy but only in 1 (3.8%) out of 26 patients with failed therapy (P < 0.05). After successful eradication, 25 patients had mild RE (12 with grade A, 13 with grade B). Among patients of the successful eradication group (n = 122), RE was diagnosed in 2 (5.3%) out of 38 patients without hiatal hernia and in 23 (27.4%) out of 84 patients with hiatal hernia (P = 0.0051). Furthermore, RE was diagnosed in 2 (5.3%) out of 38 patients with GEFV grade I, 13 (24.1%) out of 54 with grade II, 7 (30.4%) among 23 with grade III, and 3 (42.9%) out of 7 patients with grade IV. The pH level of gastric juice after eradication therapy was lower in the group with successful eradication than in the group with failed therapy regardless of the incidence and degree of RE.

CONCLUSIONS

There is a high incidence of RE after successful H. pylori eradication therapy. This incidence of RE was closely associated with the presence and degree of hiatal hernia and with the decrease in gastric juice pH. These findings suggest that the presence of hiatal hernia together with increase in gastric acidity are important determinant factors for the development of RE after successful H. pylori eradication therapy.

Protective role of activated protein C in lung and airway remodeling

Recent studies have implicated the protein C pathway in the mechanism of lung and airway remodeling. The effector enzyme of this pathway is activated protein C (APC). Clinical studies have shown that APC generation is decreased in patients with lung injury and airway inflammation and that this decrease is associated with increased collagen deposition in the lung. In line with these findings, low APC activity has been observed in the bronchoalveolar lavage fluid in animal models of lung injury and airway inflammation. Treatment with APC significantly inhibits the development of lung fibrosis in bleomycin-induced lung injury and the development of airway hyperresponsiveness and allergic inflammation in ovalbumin-induced bronchial asthma. APC may protect the lung from fibrosis and airway remodeling by suppressing activation of coagulation, decreasing the secretion of inflammatory cytokines and platelet-derived growth factor, and promoting fibrinolysis. APC inhibits the expression of cytokines by decreasing the nuclear translocation of signal transducer and activator of transcription 6 and the nuclear factor-kappaB family of transcription factors. In view of its multiple functions, APC constitutes a potential therapeutic agent for inflammatory disorders of the lung and airways.

Activated protein C inhibits the expression of platelet-derived growth factor in the lung

The natural anticoagulant-activated protein C may inhibit inflammation and fibrosis in the lung. Platelet-derived growth factor is involved in the pathogenesis of lung fibrosis. This study assessed the effect of activated protein C on platelet-derived growth factor expression in human cell lines and in an in vivo model of lung fibrosis. Activated protein C significantly inhibited the secretion and expression of platelet-derived growth factor in human lung cell lines, primary bronchial epithelial cells, and macrophages. In vitro studies also showed that the endothelial activated protein C receptor is expressed by lung epithelial cells and macrophages, and that this receptor and the proteolytic activity of activated protein are implicated in the inhibition of platelet-derived growth factor expression. In the in vivo model of lung fibrosis, intratracheal administration of activated protein C decreased the expression of platelet-derived growth factor and suppressed the development of lung fibrosis. Concomitant intratracheal administration of activated protein C and anti-endothelial activated protein C receptor or anti-platelet-derived growth factor suppressed the inhibitory activity of activated protein C in vivo. In brief, this study describes a novel biological function of activated protein C that may further explain its inhibitory activity on lung inflammation and fibrosis.

Expression and cytoprotective effect of protease-activated receptor-1 in gastric epithelial cells

Thrombin is a serine protease involved in many physiological functions and its receptor. the protease-activated receptor-1 (PAR-1), has a wide tissue distribution. We hypothesized that PAR-1 is expressed in gastric epithelial cells and that thrombin can modulate defence mechanisms through PAR-1. The rat gastric epithelial cell line (RMG1) and gastric biopsy specimens from gastritis patients were used in the study. Reverse transcriptase polymerase chain reaction analysis showed that the thrombin receptors PAR-1, PAR3 and PAR-4 are expressed by RGM1 gastric epithelial cell line. Immunohistochemical and electron microspcopic studies also showed PAR-1 expression in human gastric epithelial cells. Thrombin stimulated the secretion of mucin and prostaglandin E2 (PGE2) formation in RGM1 cells in a dose-dependent manner. PAR-1 agonist also stimulated PGE2 formation. In addition, thrombin significantly increases the expression of the PGE2 receptors EP2-R and EP4-R in RGM1 cells. In conclusion, the results of the present study showed for the first time that gastric epithelial cells express thrombin receptors and that these receptors may play a protective role in the gastric mucosa.