Activation of genes for growth factors and cyclooxygenases in rat gastric mucosa during recovery from stress damage

(1) H NMR Metabolic Profiling of Biofluids from Rats with Gastric Mucosal Lesion and Electroacupuncture Treatment

Gastric mucosal lesion (GML) is a common gastrointestinal disorder with multiple pathogenic mechanisms in clinical practice. In traditional Chinese medicine (TCM), electroacupuncture (EA) treatment has been proven as an effective therapy for GML, although the underlying healing mechanism is not yet clear. Here, we used proton nuclear magnetic resonance- (¹H NMR-) based metabolomic method to investigate the metabolic perturbation induced by GML and the therapeutic effect of EA treatment on stomach meridian (SM) acupoints. Clear metabolic differences were observed between GML and control groups, and related metabolic pathways were discussed by means of online metabolic network analysis toolbox. By comparing the endogenous metabolites from GML and GML-SM groups, the disturbed pathways were partly recovered towards healthy state via EA treated on SM acupoints. Further comparison of the metabolic variations induced by EA stimulated on SM and the control gallbladder meridian (GM) acupoints showed a quite similar metabolite composition except for increased phenylacetylglycine, 3,4-dihydroxymandelate, and meta-hydroxyphenylacetate and decreased N-methylnicotinamide in urine from rats with EA treated on SM acupoints. The current study showed the potential application of metabolomics in providing further insight into the molecular mechanism of acupuncture.

Tocotrienol Attenuates Stress-Induced Gastric Lesions via Activation of Prostaglandin and Upregulation of COX-1 mRNA

The present study aims to distinguish the effect of tocotrienol on an important gastric protective factor, prostaglandin E2 (PGE2), in stress-induced gastric injury. Twenty-eight Wistar rats were divided into four groups of seven rats each. Two control groups were fed commercial rat diet, and two treatment groups were fed the same diet but with additional dose of omeprazole (20 mg/kg) or tocotrienol (60 mg/kg). After 28 days, rats from one control group and both treated groups were subjected to water-immersion restraint stress for 3.5 hours once. The rats were then sacrificed, their stomach isolated and gastric juice collected, lesions examined, and gastric PGE2 content and cyclooxygenase (COX) mRNA expression were determined. Both the regimes significantly attenuated the total lesion area in the stomach compared to the control. Gastric acidity, which was increased in stress, was significantly reduced in rats supplemented with omeprazole and tocotrienol. The PGE2 content was also significantly higher in the rats given tocotrienol supplementation compared to the control followed by an increase in COX-1 mRNA expression. We conclude that tocotrienol supplementation protected rat gastric mucosa against stress-induced lesions possibly by reducing gastric acidity and preserving gastric PGE2 by increasing COX-1 mRNA.

The effects of palm vitamin E on stress hormone levels and gastric lesions in stress-induced rats

INTRODUCTION

This study examines the effects of palm vitamin E (PVE) or α-tocopherol (α-TF) supplementation on adrenocorticotropin hormone (ACTH), corticosterone and gastric lesions in rats exposed to water-immersion restraint stress (WIRS).

MATERIAL AND METHODS

Sixty male Sprague-Dawley rats (200-250 g) were divided into three groups. Group I: 20 rats as a control group were given a normal diet. Group II: 20 rats received oral supplementation of PVE at 60 mg/kg body weight. Group III: 20 rats received oral supplementation of α-TF at 60 mg/kg body weight. After the treatment period of 28 days, each group was further subdivided into two groups: 10 rats not exposed to stress, and the other 10 rats subjected to WIRS for 3.5 h. Blood samples were taken to measure the ACTH and corticosterone levels. The rats were then sacrificed and the stomach excised and opened along the greater curvature and examined for lesions.

RESULTS

Rats exposed to WIRS had lesions in their stomach mucosa. Our findings showed that dietary supplementation of PVE or α-TF was able to reduce gastric lesions significantly in comparison to the stressed controls. The WIRS increased plasma ACTH and corticosterone significantly. Palm vitamin E and α-TF treatments reduced these parameters significantly compared to the stressed controls.

CONCLUSIONS

Supplementation with either PVE or α-TF reduces the formation of gastric lesions, probably by inhibiting the elevation of ACTH and corticosterone levels induced by stress.

Inflammatory changes of the gastric mucosa and serum concentration of chosen growth factors in children

PURPOSE

To assess whether there is a correlation between the severity of gastritis and concentration of chosen growth factors in the serum of children infected with H. pylori.

MATERIAL AND METHODS

The study included 64 children of whom 50% (Group I) were infected with H. pylori and had gastritis; 18.7% (Group II) of the examined children had a positive titre of IgG against H. pylori and normal gastric mucosa. Controls (Group III) comprised 31.3%. The gastric mucosa was evaluated histopathologically according to the Sydney System. The serum concentrations of growth factors: EGF, TGF-alpha, VEGF, were determined using ELISA.

RESULTS

Mean concentrations of the growth factors were also the highest in Group I compared to Group II and Group III (EGF - 137.3+/-10.4 pg/mL, TGF-alpha - 0.4+/-1.2 pg/mL, VEGF - 146.8 pg/mL). Analysis of correlations between growth factors and the severity of gastritis as well as the activity of antral gastric mucosa inflammation proved that mean EGF concentration in H. pylori infected children was the highest (149.5+/-84.8 pg/mL) in severe gastritis, whereas mean concentrations of TGF-alpha (2.0+/-4.3 pg/mL) and of VEGF (148.1+/-92.6 pg/mL) were the highest in moderate gastritis. Mean concentrations of EGF (155.1+/-116.4 pg/mL) and of VEGF (156.0+/-118.9 pg/mL) were the highest in high activity antral gastritis, whereas the mean concentration of TGF-alpha was the highest (2.0+/-4.2 pg/ml) in moderate activity gastritis.

CONCLUSIONS

In the children with H. pylori infection, serum concentrations of EGF, TGF-alpha, VEGF were the highest in moderate and severe antral gastritis.

The antiulcer effect of Croton cajucara Benth in normoproteic and malnourished rats

The aim of the present study is to investigate the antiulcerogenic effects of the essential oil (EO) of Croton cajucara Benth in rats fed with a normal protein (NP) and low-protein diet (MN). NP and MN rats were treated with the essential oil for 15 days after chronic ulceration was induced. The EO accelerated healing of acetic acid-induced gastric lesions in NP and MN rats (p<0.05). In a similar experiment on chronic ulceration, Epidermal Growth Factor (EGF) mRNA expression increased in NP rats but not in MN rats. In assays of acute antiulcerogenic activity, C. cajucara increased somatostatin plasma levels and decreased gastrin plasma levels in both animal groups. The EO significantly prevented ethanol-induced gastric ulcers in NP and MN rats (p<0.001). Histological examination showed initial regeneration, formation of inflammatory infiltrate and angiogenesis in the epithelium surface of acetic acid-induced ulcers in NP and MN rats. C. cajucara prevented gastric lesions in both animal groups when ethanol methodology was used. We concluded that the EO showed an antiulcerogenic activity mediated by increased somatostatin secretion and EGF mRNA expression.

[Expressions of epidermal growth factor receptor signaling substances in gastric mucosal cells influenced by serum derived from rats treated with electroacupuncture at stomach meridian acupoints]

OBJECTIVE

To study the effects of serum derived from rats treated with electroacupuncture at stomach meridian acupoints on the expressions of epidermal growth factor receptor (EGFR) signaling substances phospholipase C gamma-1 (PLC gamma-1), protein kinase C (PKC) and c-myc in gastric mucosal cells.

METHODS

Sixty rats were randomly divided into normal group, stomach meridian group, gallbladder meridian group, stomach meridian plus PD153035 group and gallbladder meridian plus PD153035 group. Water-immersion and restrained stress methods were adopted for inducing gastric mucosal injury in the rats. Gastric mucosal cells were separated by using pronase digestion method, and incubated by PD153035, a EGFR inhibitor, and 100 ml/L serum. The expression of PLC gamma-1 in the gastric mucosal cells was tested by enzyme linked-immunosorbent assay (ELISA), while the expression of PKC by isotope incorporate assay and the expression of c-myc by reverse transcription polymerase chain reaction assay (RT-PCR).

RESULTS

In gastric mucosal cells, weak expressions of PLC gamma-1, PKC and c-myc were seen in the normal group, and relatively strong expressions of PLC gamma-1, PKC and c-myc were seen in the stomach meridian group and the gallbladder meridian group, among which, the expressions of PLC gamma-1, PKC and c-myc in the stomach meridian group were the strongest, and there was a significant difference between the stomach meridian group and the gallbladder meridian group (P<0.01). Relative weak expressions of PLC gamma-1, PKC and c-myc were seen in the stomach meridian plus PD153035 group and the gallbladder meridian plus PD153035 group, and there was a significant difference between the stomach meridian group and the stomach meridian plus PD153035 group (P<0.01).

CONCLUSIONS

The serum derived from the rats treated with electroacupuncture at stomach meridian acupoints can activate the EGFR singling pathway, and this provides an evidence for the theory of "relative particularity between meridians and viscera" in traditional Chinese medicine.

Enhanced expression of epidermal growth factor receptor gene in gastric mucosal cells by the serum derived from rats treated with electroacupuncture at stomach meridian acupoints

AIM: To investigate the effect of serum derived from rats treated with electroacupuncture at stomach meridian acupoints on the expression of epidermal growth factor receptor (EGFR) gene in gastric mucosal cells.

METHODS: The stress-induced gastric mucosal injury in rat model was established by water-immersion and restrained stress methods. 52 rats were randomly divided into: normal group (n = 8), model group (n = 8), model serum group (n = 12), stomach serum group (n = 12), and gallbladder serum group (n = 12). The gastric mucosal cells were separated by pronase-EDTA digestion method and incubated with serum. The EGFR gene expression in gastric mucosal cells was detected by reverse transcription-polymerase chain reaction (RT-PCR) method.

RESULTS: Compared with normal group (0.6860 ± 0.0594), the serum derived from rats of the stomach group (1.2272 ± 0.0813, P = 0.00 < 0.01) and gallbladder group (0.9640 ± 0.0387, P = 0.00 < 0.01) had a tendency to enhance the EGFR gene expression in gastric mucosal cells. Such tendency existed in the model group (0.7104 ± 0.0457) but with no significant difference (P = 0.495 > 0.05) and in model serum group (0.8516 ± 0.0409) with an extremely obvious difference (P = 0.001 < 0.01). Furthermore, the EGFR gene expression in stomach serum group was significantly higher than that in gallbladder serum group (P = 0.00 < 0.01).

CONCLUSION: The present study shows that serum derived from rats treated with electroacupuncture at stomach meridian acupoints can distinctly increase the EGFR gene expression of gastric mucosal cells. Therefore, there is certain meridian specificity in the serum, which could provide a proof for the TCM theory “particular relation between meridian and internal organ”.

Dynamic functional and ultrastructural changes of gastric parietal cells induced by water immersion-restraint stress in rats

AIM: To investigate the dynamic functional and ultrastructural changes of gastric parietal cells induced by water immersion-restraint stress (WRS) in rats.

METHODS: WRS model of Sprague-Dawley (SD) rats was established. Fifty-six male SD rats were randomly divided into control group, stress group and post-stress group. The stress group was divided into 1, 2 and 4 h stress subgroups. The post-stress group was divided into 24, 48 and 72 h subgroups. The pH value of gastric juice, ulcer index (UI) of gastric mucosa and H⁺, K⁺-ATPase activity of gastric parietal cells were measured. Ultrastructural change of parietal cells was observed under transmission electron microscope (TEM).

RESULTS: The pH value of gastric juice decreased time-dependently in stress group and increased in post-stress group. The H⁺, K⁺-ATPase activity of gastric parietal cells and the UI of gastric mucosa increased time-dependently in stress group and decreased in post-stress group. Compared to control group, the pH value decreased remarkably (P = 0.0001), the UI and H⁺, K⁺-ATPase activity increased significantly (P = 0.0001, P = 0.0174) in 4 h stress subgroup. UI was positively related with stress time (r = 0.9876, P < 0.01) but negatively with pH value (r = -0.8724, P < 0.05). The parietal cells became active in stress group, especially in 4 h stress subgroup, in which plenty of intracellular canalicular and mitochondria were observed under TEM. In post-stress group, the parietal cells recovered to resting state.

CONCOUSION: The acid secretion of parietal cells is consistent with their ultrastructural changes during the development and healing of stress ulcer induced by WRS and the degree of gastric mucosal lesions, suggesting gastric acid play an important role in the development of stress ulcer and is closely related with the recovery of gastric mucosal lesions induced by WRS.

Worsening effect of partial sleep deprivation on indomethacin-induced gastric mucosal damage

The present study was to investigate the roles of cyclooxygenase-1 and -2 (COX-1 and COX-2) and prostaglandin (PG) on gastric mucosal integrity of partially sleep deprived (PSD) rats. A slowly moving drum was used to induce PSD. The PG levels in the gastric mucosa of PSD rats, with or without indomethacin or rofecoxib treatment, were determined. Exogenous prostaglandin E (PGE) analog, misoprostol, was administered to PSD rats to investigate the modulating effect of PG in indomethacin-induced gastric damage. It was observed that COX-1 mRNA and protein were up-regulated in the gastric mucosa of PSD rats. Selective COX-2 inhibition by rofecoxib failed to decrease mucosal PGE2 levels nor to affect mucosal integrity in both PSD and sleep undisturbed rats. However, indomethacin, a COX-1 preferential non-selective COX inhibitor, significantly reduced mucosal PGE2 content and produced more severe mucosal damage in PSD rats than in the controls. The deleterious effect of indomethacin on gastric mucosal integrity of PSD rats was significantly attenuated with the administration of misoprostol. These results suggest that PSD enhances COX-1 biosynthesis of gastroprotective PGE2 as an adaptive response of the stomach to stress. The administration of non-selective COX inhibitors to subjects with chronic sleep deprivation may induce more gastric damages.

Is gastric ulceration different in normal and malnourished rats?

Protein malnutrition can adversely affect all tissues. The aim of the present study was to test the hypothesis that protein deprivation influences gastric ulcer formation, as well as metabolism and organ growth, in rats. In the present study, there was a significant reduction in the body and organ weight of rats fed a low-protein diet (P<0.001). Malnourished rats were less susceptible to ulceration of the gastric mucosa in ethanol and indomethacin models of acute gastric ulcers when compared with rats fed a normoproteic diet (17 % protein). Mucus production and prostaglandin E2 formation increased in malnourished rats, possibly explaining the lower number of acute ulcers in these animals. Pylorus ligature altered gastric juice composition (increased pH and gastric volume, and decreased total acid concentration) in the animal group fed a low-protein diet compared with the group fed a diet containing 17 % protein (P<0.05). The gastric mucosa was more damaged in malnourished rats than in normal rats evaluated for 14 d after acetic acid injection (P<0.001). Malnourished rats exhibited resistance to acute gastric lesions, owing to an increase in prostaglandin GE2 release and mucus secretion, which protected their gastric mucosa. This phenomenon was not seen in subchronic gastric ulceration.

Insights into the mechanisms of gastric adaptation to aspirin-induced injury: a role for regenerating protein but not trefoil peptides

The phenomenon of reduced gastric mucosal injury despite repeated doses of a damaging agent is termed adaptation. Adaptation to nonsteroidal anti-inflammatory drug-induced injury has been clearly demonstrated in both humans and experimental animals; however, the precise mechanisms remain unclear. We hypothesized that mediators of adaptation might be the regenerating protein (RegI) and the trefoil peptides TFF1 and TFF2, because these proteins play pivotal roles in gastric mucosal protection and repair. The gene expression and the protein levels of these proteins were measured and compared in normal, aspirin-injured, and aspirin-adapted rat stomachs. TFF gene and protein expression levels were similar in all three groups, whereas RegI gene expression and protein levels in adapted stomach were increased. A time course analysis of RegI expression during the onset and offset of adaptation showed that mucosal RegI increased during the development of adaptation, was maintained during subsequent aspirin dosing, and returned to baseline levels once dosing had ceased and adaptation was lost-indicative of a causal role in the adaptation process. Colocalization of increased RegI with gastric epithelial areas showing increased proliferation also suggests that RegI may be an important mediator of the resolution of mucosal injury that is characteristic of gastric adaptation to aspirin.

Angiogenic effects of prostaglandin E2 are mediated by up-regulation of CXCR4 on human microvascular endothelial cells

Stimulation of vascular endothelial growth factor (VEGF) and basic fibroblast growth factor (bFGF) increases the expression of CXCR4 on endothelial cells, rendering these cells more responsive to stromal-derived factor 1 (SDF-1), an angiogenic CXC chemokine and unique ligand for CXCR4. Here, we show that prostaglandin E2 (PGE2) mediates the effects of bFGF and VEGF in up-regulating CXCR4 expression on human microvascular endothelial cells (HMECs). Forskolin or 3-isobutyl-1-methyl xanthine (IBMX), 2 inducers of adenylate cyclase, markedly enhanced, whereas cyclooxygenase (COX) inhibitors including aspirin, piroxicam, and NS398 markedly inhibited CXCR4 expression on HMECs. Furthermore, the ability of PGE2 to augment in vitro tubular formation in SDF-1alpha containing matrigel was inhibited completely by blocking CXCR4. Treatment of bFGF- or VEGF-stimulated HMECs with COX inhibitors blocked tubular formation by about 50% to 70%. Prostaglandin-induced human endothelial cell organization and subsequent vascularization can be inhibited to a greater extent by a neutralizing antibody to human CXCR4 in severe combined immunodeficient mice. Additionally, VEGF- and bFGF-induced angiogenesis in vivo was also inhibited by about 50% by NS-398 or piroxicam, and this inhibitory effect was accompanied by decreased expression of CXCR4 on murine endothelial cells. Consequently, by inducing CXCR4 expression, prostaglandin accounts for about 50% of the tubular formation in vitro and in vivo angiogenic effects of VEGF and bFGF. Moreover, augmentation of CXCR4 expression by VEGF, bFGF, and PGE2 involves stimulation of transcription factors binding to the Sp1-binding sites within the promoter region of the CXCR4 gene. These findings indicate that PGE2 is a mediator of VEGF- and bFGF-induced CXCR4-dependent neovessel assembly in vivo and show that angiogenic effects of PGE2 require CXCR4 expression.

Molecular and physiologic basis of obstructive sleep apnea

Obstructive sleep apnea-hypopnea syndrome occurs because of various combinations of anatomic, mechanical, and neurologic anomalies that jeopardize ventilation only when normal state-dependent reductions in drive to upper airway respiratory muscles and pump muscles occur. A well thought out and carefully described infrastructure of the normal and abnormal physiology in persons with OSAHS has been developed over the past few decades, which enables the development of innovative and largely effective therapies. The most recent data complement the infrastructure with the neurochemical changes underlying the state-dependent respiratory disorder and observations that the disease process itself can impair muscles, neural inputs, and soft tissue in a manner that has the potential to worsen disease. Oxidative and nitrosative stress from the repeated oxyhemoglobin desaturations and re-oxygenations is implicated in the injury to these tissues. An improved understanding of the mechanisms through which OSAHS progresses may lead to alternative therapies and aid in the identification of persons at risk for disease progression.

Transforming growth factor alpha-mediated gastroprotection against stress ulceration in the rat: involvement of capsaicin-sensitive sensory neurons

Exogenously administered TGF alpha has been shown to protect rodent gastric mucosa against injury caused by acid-dependent and acid-independent injury. The present study examined whether the gastroprotective effects of TGF alpha on stress-induced gastric ulceration in the rat involves activation of capsaicin-sensitive sensory neurons. Fasted male SD rats were subjected to water restraint stress (WRS) for four hours. Thereafter, rats were euthanized; the stomach opened and macroscopic areas of gastric ulceration quantitated (mm(2)). Gastric tissue contents of TGF alpha and the sensory neuropeptide, calcitonin gene-related peptide (CGRP) were determined by radioimmunoassay. Prior to stress rats received TGF alpha 50, 100 or 200 microg/kg by intraperitoneal injection. Sensory denervation was accomplished by high dose capsaicin treatment. WRS caused severe ulceration in the gastric corpus; 46.1 + 6.6 mm(2). Parenteral administration of TGF alpha caused dose-dependent reduction in gastric injury: 34.7 + 4.9 mm(2) with 50 microg/kg (p < 0.05); 25.4 + 3.6 mm(2) with 100 microg/kg (p < 0.001) and 9.4 + 0.8 mm(2) with 200 microg/kg (p < 0.001). The gastroprotective action of TGF alpha (200 microg/kg, i.p.) was abolished by capsaicin-induced sensory denervation. In addition, WRS ulceration was associated with significant reduction in gastric CGRP (-42%) and TGF alpha (-48%) content. Reduction in CGRP content was prevented by TGF alpha pretreatment. We conclude that: 1) TGF alpha caused dose-dependent gastroprotection against WRS ulceration, 2) TGF alpha-mediated gastric mucosal protection was prevented by capsaicin-induced sensory denervation and, 3) stress-induced injury was associated with significant reduction in gastric content of both TGF alpha and CGRP.

Pioglitazone, a Specific Ligand of the Peroxisome Proliferator-Activated Receptor Gamma Reduces Gastric Mucosal Injury Induced by Ischaemia/Reperfusion in Rat

BACKGROUND

The peroxisome proliferator-activated receptor gamma (PPARγ) is a ligand-dependent nuclear receptor that has been implicated in the control of metabolism and numerous cellular processes, including cell cycle control, carcinogenesis, and inflammation. The present study was designed to investigate the effect of the specific PPARγ ligand, pioglitazone, on the mucosal lesions induced by ischaemia and reperfusion (I/R) in rats.

METHODS

I/R lesions were induced in Wistar rats by applying a small clamp to the coeliac artery for 30 min (ischaemic phase), followed by the removal of the clamp for 3 h (reperfusion phase). Vehicle (saline) or increasing doses of pioglitazone (2.5, 10, and 30 mg/kg i.g.) were given 30 min before exposure to I/R. The animals were killed immediately after the end of the reperfusion phase (time 0) and at 12 and 24 h after I/R. The area of gastric lesions was measured by planimetry, and the gastric blood flow was determined by the H[Formula: See Text] gas clearance method. The gastric mucosal gene expressions of PPARγ, interleukin-1beta (IL-1β), tumour necrosis factor alpha (TNF-α), leptin, cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2) were examined by RT-PCR. In addition, protein expression of COX-2 and leptin was assessed by Western blot.

RESULTS

The pretreatment with pioglitazone reduced in a dose-dependent manner the mean lesion area induced by I/R, and this effect was accompanied by a significant increase in the gastric blood flow. The decrease in gastric ulcerations by pioglitazone was also observed 12 and 24 h after the I/R. The PPARγ mRNA was weakly expressed in the intact gastric mucosa, but significantly up-regulated after exposure to I/R at each time interval studied. The expression of IL-1β was not changed significantly after pioglitazone applied i.g. at doses 2.5 and 10 mg/kg, but it was down-regulated at the dose 30 mg/kg. TNFα mRNA was strongly increased after the exposure to I/R, but it was down-regulated after pioglitazone pretreatment. In contrast, both leptin and COX-2 mRNA and protein expression were increased in the gastric mucosa after exposure to I/R. The pretreatment with pioglitazone caused a significant up-regulation of mRNA and protein expression of leptin, reaching its peak at the dose 30 mg/kg i.g. In contrast, COX-2 expression did not change significantly after the 2.5 and 10 mg/kg of pioglitazone, but it significantly decreased after pioglitazone at dose 30 mg/kg given to rats before exposure to I/R.

CONCLUSIONS

Pioglitazone reduces the acute erosions and deeper gastric lesions induced by I/R. The beneficial effect of this PPARγ ligand on I/R-induced gastric damage may be due to its anti-inflammatory properties, especially to the reduction in TNF-α expression and to up-regulation of leptin mRNA in the gastric mucosa. The inhibition of COX-2 expression by pioglitazone may reflect the anti-inflammatory properties of this compound.

Effect of Helicobacter pylori on delay in ulcer healing induced by aspirin in rats

Helicobacter pylori and nonsteroidal anti-inflammatory drugs (NSAIDs) are major pathogenic factors in peptic ulcer disease but whether these two factors exert synergistic or antagonistic effects on ulcer healing has been a subject of controversy. We compared the effect of aspirin alone with that of aspirin combined with H. pylori on gastric acid secretion and healing of acetic acid gastric ulcers in rats. The H. pylori colonization of gastric mucosa was determined by viable H. pylori culture, histology and assessment of bacterial DNA using polymerase chain reaction (PCR). The area of ulcers, gastric blood flow, mucosal generation of prostaglandin E(2) and plasma gastrin levels and expression of cyclooxygenase-1, cyclooxygenase-2 and growth factors was determined. Aspirin delayed significantly the healing of chronic gastric ulcers, decreased the gastric blood flow at the ulcer margin and gastric mucosal prostaglandin E(2) generation being without significant influence on gastric acid output. H. pylori acquisition that produced moderate gastric inflammation at the ulcer margin delayed significantly the healing of gastric ulcers, decreased significantly both the gastric blood flow at the ulcer margin and the gastric secretion while raising significantly the gastric mucosal prostaglandin E(2) generation and plasma gastrin levels. H. pylori infection attenuated the aspirin-induced inhibition of ulcer healing and accompanying fall in the gastric blood flow. Both aspirin and H. pylori up-regulated significantly cyclooxygenase-2 messenger RNA (mRNA) and protein but not that of cyclooxygenase-1 at the ulcer margin. Aspirin reduced significantly the transforming growth factor alpha- and vascular endothelial growth factor mRNAs, but these effects were significantly attenuated by H. pylori. We conclude that H. pylori antagonizes, in part, aspirin-induced delay of ulcer healing due to suppression of acid secretion, the enhancement in prostaglandin E(2) possibly derived from cyclooxygenase-2 and the overexpression of transforming growth factor alpha and vascular endothelial growth factor in the ulcer area.

Regulation and function of COX-2 gene expression in isolated gastric parietal cells

We examined expression, function, and regulation of the cyclooxygenase (COX)-2 gene in gastric parietal cells. COX-2-specific mRNA was isolated from purified (>95%) canine gastric parietal cells in primary culture and measured by Northern blots using a human COX-2 cDNA probe. Carbachol was the most potent inducer of COX-2 gene expression. Gastrin and histamine exhibited minor stimulatory effects. Carbachol-stimulated expression was inhibited by intracellular Ca(2+) chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid-AM (90%), protein kinase C (PKC) inhibitor GF-109203X (48%), and p38 kinase inhibitor SB-203580 (48%). Nuclear factor (NF)-kappaB inhibitor 1-pyrrolidinecarbodithioic acid inhibited carbachol-stimulated expression by 80%. Similar results were observed in the presence of adenoviral vector Ad.dom.neg.IkappaB, which expresses a repressor of NF-kappaB. Addition of SB-203580 with Ad.dom.neg.IkappaB almost completely blocked carbachol stimulation of COX-2 gene expression. We examined the effect of carbachol on PGE(2) release by enzyme-linked immunoassay. Carbachol induced PGE(2) release. Ad.dom.neg.IkappaB, alone or with SB-203580, produced, respectively, partial (70%) and almost complete (>80%) inhibition of carbachol-stimulated PGE(2) production. Selective COX-2 inhibitor NS-398 blocked carbachol-stimulated PGE(2) release without affecting basal PGE(2) production. In contrast, indomethacin inhibited both basal and carbachol-stimulated PGE(2) release. Carbachol induces COX-2 gene expression in the parietal cells through signaling pathways that involve intracellular Ca(2+), PKC, p38 kinase, and activation of NF-kappaB. The functional significance of these effects seems to be stimulation of PGE(2) release.

Effects of TGF-alpha gene knockout on epithelial cell kinetics and repair of methotrexate-induced damage in mouse small intestine

While previous studies have indicated that exogenous TGF-alpha stimulates epithelial growth, maintenance, and repair of the gut, roles of endogenous TGF-alpha are less well-defined particularly in the small bowel. The current study examined effects of TGF-alpha knockout on adult small intestinal epithelial cell proliferation, migration, apoptosis, and damage/repair response after methotrexate treatment. Compared to normal mice, TGF-alpha gene knockout did not affect crypt cell production, mitosis position, migration, and apoptosis in non-injured intestine. RT-PCR gene expression analysis revealed presence of four out of six TGF-alpha related EGF family ligands in the normal intestine, suggesting a possible functional redundancy of the EGF family in maintenance of the intestine. Although TGF-alpha gene knockout did not significantly impair the overall mucosal repair in methotrexate-induced acute damage in the small intestine, it resulted in a higher apoptotic response in the early hours following methotrexate challenge, and a delayed and reduced crypt cell proliferation during repair. Consistently, after methotrexate challenge, intestinal TGF-alpha mRNA was found to be markedly upregulated in the early hours and during repair in the wild type, and there were similar profiles in the increased expression of all other ligands (except EGF) between the wild type and knockout intestines. Therefore, despite a possible functional redundancy among the EGF family ligands in the normal small intestine, TGF-alpha may play a role in modulating the early apoptotic events and in enhancing the subsequent reparative proliferative response in the methotrexate-damaged intestine.

Circadian rhythm of melatonin and prostaglandin in modulation of stress-induced gastric mucosal lesions in rats

BACKGROUND

We previously demonstrated the circadian variation of water-immersion restraint stress (WRS)-induced gastric mucosal lesions in rats.

AIM

To investigate the roles of melatonin and prostaglandin in the gastric mucosa in circadian modulation of WRS.

METHODS

Fasted rats were subjected to 4-h WRS during both the diurnal and nocturnal phases of a light/dark cycle. Mucosal lesions, serum melatonin concentrations, mucosal generation of prostaglandin E2 (PGE2) and mucosal gene expressions of cyclooxygenase (COX)-1 and -2 were evaluated.

RESULTS

Lesion area after 4-h stress during the dark phase was significantly smaller than that in light-phase controls. Serum melatonin concentration in control rats during the light phase was significantly increased 4 h after WRS, but PGE2 generation was decreased by 48% as compared to that in intact mucosa before stress. In the dark phase, melatonin concentration after 4-h WRS was significantly depressed as compared with the control level at the corresponding time. PGE2 concentrations after 4-h WRS in the dark phase were not decreased compared with the control level at the corresponding time, although PGE2 level was significantly lower than that in light-phase controls. Expression of COX-1 and COX-2 mRNA was detected after exposure to stress in both the light and dark phases.

CONCLUSION

These results suggest that circadian rhythm has an important role in the formation of stress-induced gastric mucosal lesions in rats. The circadian rhythm of melatonin responses and PGE2 generation may contribute to nocturnal/diurnal rhythmicity of gastric mucosal defences between day and night.

Secretory phospholipase A2 mediates cooperative prostaglandin generation by growth factor and cytokine independently of preceding cytosolic phospholipase A2 expression in rat gastric epithelial cells

Transforming growth factor (TGF)-alpha and interleukin (IL)-1beta are responsible for the healing of gastric lesions through, in part, prostaglandin (PG) generation. We examined the contribution of cytosolic and secretory phospholipase A(2)s (cPLA(2) and sPLA(2)) to the PG generation by rat gastric epithelial cells in response to both stimuli. Stimulation with TGF-alpha for 24 h increased cPLA(2) and cyclooxygenase (COX)-2 markedly, PGE(2) slightly, and type IIA sPLA(2) and COX-1 not at all, whereas IL-1beta increased sPLA(2) only. Both stimuli synergistically increased PGE(2), sPLA(2), and the two COXs but not cPLA(2). The onset of the PGE(2) generation paralleled the sPLA(2) release but was apparently preceded by increases in cPLA(2) and the two COXs. The increase in PGE(2) was impaired by inhibitors for sPLA(2) and COX-2 but not COX-1. cPLA(2) inhibitors suppressed PGE(2) generation by TGF-alpha alone but not augmentation of PGE(2) generation or sPLA(2) release by IL-1beta in combination with TGF-alpha. Furthermore, despite an increase in cPLA(2) including its phosphorylated form (phosphoserine), -induced arachidonic acid liberation was impaired in the TGF-alpha/IL-1beta-stimulated cells, in which p11, a putative cPLA(2) inhibitory molecule, was also increased and co-immunoprecipitated with cPLA(2). These results suggest that synergistic stimulation of sPLA(2) and COX-2 expression by TGF-alpha and IL-1beta results in an increase in PGE(2). Presumably, the preceding cPLA(2) expression is not involved in the PGE(2) generation, because of impairment of its hydrolytic activity in the stimulated cells.

Cyclooxygenase inhibitors--current status and future prospects

Prostaglandins are formed from arachidonic acid by the action of cyclooxygenase and subsequent downstream synthetases. Two closely related forms of the cyclooxygenase have been identified which are now known as COX-1 and COX-2. Both isoenzymes transform arachidonic acid to prostaglandins, but differ in their distribution and their physiological roles. Meanwhile, the responsible genes and their regulation have been clarified. COX-1, the pre-dominantly constitutive form of the enzyme, is expressed throughout the body and performs a number of homeostatic functions such as maintaining normal gastric mucosa and influencing renal blood flow and platelet aggregation. In contrast, the inducible form is expressed in response to inflammatory and other physiological stimuli and growth factors, and is involved in the production of the prostaglandins that mediate pain and support the inflammatory process. All the classic NSAIDs inhibit both COX-1 and COX-2 at standard anti-inflammatory doses. The beneficial anti-inflammatory and analgesic effects are based on the inhibition of COX-2, but the gastrointestinal toxicity and the mild bleeding diathesis are a result of the concurrent inhibition of COX-1. Agents that inhibit COX-2 while sparing COX-1 represent a new attractive therapeutic development and could represent a major advance in the treatment of rheumatoid arthritis and osteoarthritis. Apart from its involvement in inflammatory processes, COX-2 seems to play a role in angiogenesis, colon cancer and Alzheimer's disease, based on the fact that it is expressed during these diseases. The benefits of specific and selective COX-2 inhibitors are currently under discussion and offer a new perspective for a further use of COX-2 inhibitors.

Epidermal growth factor and prostaglandin E(2) accelerate mucosal recovery from stress-induced gastric lesions via inhibition of apoptosis

The repair of damaged gastric mucosa is a complex process involving prostaglandins (PG) and mucosal growth factors such as epidermal growth factor (EGF). Recently, we postulated that the increased occurrence of apoptosis in the gastric epithelium might be of pathophysiological importance in the development of stress lesions. The aim of the present study was to assess the effect of the pretreatment of rats, exposed to 3.5 h of water immersion and restraint stress (WRS), with EGF and PG (16,16 dmPGE(2)) on the number of stress lesions, recovery of gastric mucosa from stress and the expression of apoptosis related genes such as caspase-3 and antiapoptotic bcl-2. Rats were divided in following groups: (1) vehicle; (2) EGF 100 microg/kg i.p.; (3) 16,16 dm-PGE(2) (5 microg/kg i.g.) and caspase-1 inhibitor (ICE-I; 100 microg/kg i.p.). One hour later, the rats were exposed to 3.5 h of WRS and then sacrificed immediately (0 h) or at 6, 12, or 24 h after WRS. The number of acute gastric lesions was determined. Gastric epithelial apoptosis was assessed by TUNEL staining. In addition, mRNA expression of caspase-3, Bcl-2 and proinflammatory cytokines (IL-1 beta, TNFalpha) was assessed by RT-PCR. PGE(2) generation in gastric mucosa and luminal EGF were determined by RIA. Exposure to WRS resulted in the development of multiple acute stress erosions ( approximately 18) which almost completely healed during 24 h. The gastric blood flow was significantly reduced (approximately 70% of intact mucosa) immediately after WRS. The expression of mRNA for IL-1 beta and TNF alpha reached their peak at 12 h after stress exposure. The apoptosis rate was highest at 6 h after WRS and was accompanied by the highest caspase-3 expression. In rats pretreated with EGF or 16,16 dm-PGE(2), a significant decrease in caspase-3 mRNA and upregulation of bcl-2 mRNA as observed as compared to vehicle controls. Caspase-1 inhibitor significantly reduced the number of stress lesions. We conclude that EGF and PGE(2) accelerate healing of stress-induced lesions due to the attenuation of apoptosis via upregulation of bcl-2 in gastric mucosa. Inhibitors of apoptosis accelerate healing of stress lesions and may be potentially effective agents in the healing of damaged gastric mucosa.

Transforming growth factor-alpha stimulates prostaglandin generation through cytosolic phospholipase A(2) under the control of p11 in rat gastric epithelial cells

The regulatory effects of transforming growth factor (TGF)-alpha on phospholipase A(2) (PLA(2)) isozymes contributing to prostaglandin generation in rat gastric epithelial RGM1 cells were examined. Stimulation with TGF-alpha for 24 h time-dependently induced prostaglandin E(2) generation with an increase in cyclo-oxygenase-2 protein. The TGF-alpha-induced prostaglandin E(2) generation was suppressed by NS-398, a cyclo-oxygenase-2 inhibitor. TGF-alpha stimulated the activity and the protein synthesis of cytosolic PLA(2) (cPLA(2)). A time-dependent increase in cPLA(2) protein occurred in parallel with PGE(2) generation, which was inhibited by methyl arachidonyl fluorophosphonate (MAFP), a cPLA(2) inhibitor. However, no change in activity of secretory PLA(2) or Ca(+2)-independent PLA(2) was observed in the TGF-alpha-stimulated cells. Stimulation with the Ca(2+) ionophore A23187 for 10 min induced MAFP-sensitive arachidonic acid liberation. Interestingly, preincubation with TGF-alpha for 24 h diminished A23187-stimulated arachidonic acid liberation despite the increase in cPLA(2) protein. Under the conditions, TGF-alpha was found to increase p11, an endogenous cPLA(2) suppressor, also known as annexin II light chain. The TGF-alpha-induced increase in p11 was suppressed by tyrphostin AG1478, an inhibitor of tyrosine kinase of epidermal growth factor receptor, which was also found to restore the inhibition by TGF-alpha of A23187-stimulated arachidonic acid liberation. However, TGF-alpha did not alter protein levels of annexin II heavy chain. These results suggest that TGF-alpha stimulates prostaglandin generation through an increase in cPLA(2), the hydrolytic action of which may be under the control of p11.

The pyrrole moiety as a template for COX-1/COX-2 inhibitors

Aroyl- and thiophene-substituted pyrrole derivatives have been synthesized as a new class of COX-1/COX-2 inhibitors. The inhibition of COX-1 was evaluated in a biological system using bovine PMNLs as the enzyme source, whereas LPS-stimulated human monocytes served as the enzyme source for inducible COX-2. The determination of the concentration of arachidonic acid metabolites was performed by HPLC for COX-1 and RIA for COX-2. Variation of the substitution pattern led to a series of active compounds which showed inhibition for COX-1 and COX-2. Structural requirements for the development of COX-1/COX-2 inhibitors are discussed.

Inhibitory effect of macrophage-derived factors on the recovery of wounds induced in rat gastric epithelial monolayers

The effect of macrophage supernatant on the recovery of wounds induced in rat gastric epithelial RGM1 monolayers was investigated. The repair of wounds induced in the monolayers of RGM1 cells was accelerated time-dependently by 10 ng/mL of transforming growth factor-alpha (TGF-alpha). TGF-alpha also significantly stimulated DNA synthesis in RGM1 cells for 24 hr. Upon treatment of the cells with the macrophage supernatant, spontaneous and TGF-alpha-stimulated restoration was inhibited in a time- and concentration-dependent manner. After 24 hr, TGF-alpha-enhanced restoration was eliminated completely by the supernatant at 10(6) cells/mL. Similarly, the macrophage supernatant suppressed the spontaneous and TGF-alpha-stimulated DNA syntheses in a concentration-dependent manner. The macrophage supernatant at 10(6) cells/mL contained 0.4 ng/mL of interleukin-1beta (IL-1beta). Interleukin-1 receptor antagonist (IL-1RA) reversed the inhibition induced by the macrophage supernatant in a concentration-dependent manner. Nonetheless, pretreatment with IL-1RA had no effects on the spontaneous and TGF-alpha-stimulated DNA syntheses. Reverse transcription-polymerase chain reaction analysis revealed that RGM1 cells express mRNA for IL-1 receptor type 1, but not for type 2. These results indicate that macrophages can inhibit the spontaneous and TGF-alpha-stimulated recovery of wounds induced in gastric epithelial monolayers. The inhibitory effects of the supernatant are suggested to be partially mediated through a IL-1beta/IL-1 receptor type 1 pathway.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Growth factors in inflammatory bowel disease

The pathogenesis of both ulcerative colitis and Crohn's disease is unknown but these forms of inflammatory bowel disease (IBD) may be associated with an inability of the intestinal mucosa to protect itself from luminal challenges and/or inappropriate repair following intestinal injury. Numerous cell populations regulate these broad processes through the expression of a complex array of peptides and other agents. Growth factors can be distinguished by their actions regulating cell proliferation. These factors also mediate processes such as extracellular matrix formation, cell migration and differentiation, immune regulation, and tissue remodeling. Several families of growth factors may play an important role in IBD including: epidermal growth factor family (EGF) [transforming growth factor alpha (TGF alpha), EGF itself, and others], the transforming growth factor beta (TGF beta) super family, insulin-like growth factors (IGF), fibroblast growth factors (FGF), hepatocyte growth factor (HGF), trefoil factors, platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF) and others. Collectively these families may determine susceptibility of IBD mucosa to injury and facilitate tissue repair.

Polyamines and epidermal growth factor in the recovery of gastric mucosa from stress-induced gastric lesions

Polyamines such as spermine or putrescine, resulting from increased activity of ornithine decarboxylase (ODC), are known for gastroprotective and mucosal growth-promoting effects. EGF exhibits similar effects, but little is known about the involvement of polyamines in acceleration of the healing of stress-induced gastric lesions by epidermal growth factor (EGF). In this study, rats with intact or suppressed ODC activity by alpha-difluoromethy-ornithine (DFMO, 400 mg/kg i.p.) were subjected to 3.5 h of water immersion and restraint stress (WRS) without or with addition of spermine or EGF. At 0, 2, 6, 12, or 24 h after stress, rats were sacrificed. The number of gastric lesions was determined and gastric blood flow (GBF) was recorded by the H2 gas clearance technique. Stress produced gastric lesions (mean number 18+/-2 per stomach) and decreased GBF (by approximately 43%), but at 2, 6, 12, and 24 h after stress, these lesions and the decrease in GBF were gradually attenuated. Pretreatment with DFMO or removal of an endogenous source of EGF by salivectomy resulted in a marked decrease in mucosal DNA synthesis and significantly delayed the healing of stress lesions. EGF or spermine significantly accelerated ulcer healing and increased the GBF in rats with intact or removed salivary glands. DFMO significantly reduced the enhancement of healing and the increase in GBF induced by EGF, but failed to influence those induced by exogenous spermine. We conclude that polyamines play an important role in mucosal recovery from stress lesions due to acceleration of mucosal repair and increase in gastric microcirculation and that increased ODC activity and resulting excessive polyamine release appear to act as primary mediators of EGF-induced acceleration of the healing of stress lesions.