Vascular and microvascular changes--key factors in the development of acetic acid-induced gastric ulcers in rats

The role of thromboxane prostanoid receptor signaling in gastric ulcer healing

The process of gastric ulcer healing includes cell migration, proliferation, angiogenesis and re-epithelialization. Platelets contain angiogenesis stimulating factors that induce angiogenesis. Thromboxane A2 (TXA2 ) not only induces platelet activity but also angiogenesis. This study investigated the role of TXA2 in gastric ulcer healing using TXA2 receptor knockout (TPKO) mice. Gastric ulcer healing was suppressed by treatment with the TXA2 synthase inhibitor OKY-046 and the TXA2 receptor antagonist S-1452 compared with vehicle-treated mice. TPKO showed delayed gastric ulcer healing compared with wild-type mice (WT). The number of microvessels and CD31 expression were lower in TPKO than in WT mice, and TPKO suppressed the expression of transforming growth factor beta (TGF-β) and vascular endothelial growth factor A (VEGF-A) in areas around gastric ulcers. Immunofluorescence assays showed that TGF-β and VEGF-A co-localized with platelets. Gastric ulcer healing was significantly reduced in WT mice transplanted with TPKO compared with WT bone marrow. These results suggested that TP signalling on platelets facilitates gastric ulcer healing through TGF-β and VEGF-A.

The Critical Role of Growth Factors in Gastric Ulcer Healing: The Cellular and Molecular Mechanisms and Potential Clinical Implications

In this article we review the cellular and molecular mechanisms of gastric ulcer healing. A gastric ulcer (GU) is a deep defect in the gastric wall penetrating through the entire mucosa and the muscularis mucosae. GU healing is a regeneration process that encompasses cell dedifferentiation, proliferation, migration, re-epithelialization, formation of granulation tissue, angiogenesis, vasculogenesis, interactions between various cells and the matrix, and tissue remodeling, all resulting in scar formation. All these events are controlled by cytokines and growth factors (e.g., EGF, TGFα, IGF-1, HGF, bFGF, TGFβ, NGF, VEGF, angiopoietins) and transcription factors activated by tissue injury. These growth factors bind to their receptors and trigger cell proliferation, migration, and survival pathways through Ras, MAPK, PI3K/Akt, PLC-γ, and Rho/Rac/actin signaling. The triggers for the activation of these growth factors are tissue injury and hypoxia. EGF, its receptor, IGF-1, HGF, and COX-2 are important for epithelial cell proliferation, migration, re-epithelialization, and gastric gland reconstruction. VEGF, angiopoietins, bFGF, and NGF are crucial for blood vessel regeneration in GU scars. The serum response factor (SRF) is essential for VEGF-induced angiogenesis, re-epithelialization, and blood vessel and muscle restoration. Local therapy with cDNA of human recombinant VEGF165 in combination with angiopoietin1, or with the NGF protein, dramatically accelerates GU healing and improves the quality of mucosal restoration within ulcer scars. The future directions for accelerating and improving healing include local gene and protein therapies with growth factors, their combinations, and the use of stem cells and tissue engineering.

Effects of artemisinin, with or without lumefantrine and amodiaquine on gastric ulcer healing in rat

Background

Antimalarial drugs have been shown to predispose the stomach to ulceration in rats. However, their role in the modulation of gastric ulcer healing is not known. The aim of the present study is to investigate the effect of artemisinin-based combination therapies on ulcer healing.

Methods

Gastric kissing ulcers were induced in 40 male albino rats (150–180 g) using 0.2 mL 50% acetic acid. One day after the ulcer induction, experimental rats were divided into four groups and treated once daily orally for 3 days as follows: (1) normal saline, (2) artemether-lumefantrine (2/12 mg/kg), (3) artesunate-amodiaquine (4/10 mg/kg), and (4) artesunate (2 mg/kg) only. A fifth group of 10 rats served as overall control with no ulcer induced and no treatment given. Ulcer healing was determined on days 4 and 7 post induction using ulcer score and planimetry.

Results

Artesunate decreased ulcer severity by 12.5% and 52.0% on days 4 and 7, respectively. Significant increases in severity were observed in rats treated with artemether-lumefantrine (25.0% and 40.0%) and artesunate-amodiaquine (50.0% and 95.0%). Lipid peroxidation was decreased by artesunate by day 7 (27%; p<0.05) but increased in artemether-lumefantrine and artesunate-amodiaquine administered rats (63.6% and 55%; p<0.05). The activity of superoxide dismutase was reduced by artesunate-amodiaquine on day 7 (22%; p<0.05) but no effect in the artemether-lumefantrine treatment. Neutrophil infiltration, total leukocyte count, neutrophil-lymphocyte ratio, and C-reactive protein values were significantly increased in the artemether-lumefantrine and artesunate-amodiaquine treated groups when compared with the untreated ulcer control group (p<0.05). These variables were all reduced by artesunate (p<0.05).

Conclusions

This study revealed that although artesunate may be beneficial in gastric ulcer healing, its combination with either lumefantrine or amodiaquine may delay healing of gastric mucosal injury.

Reduced NGF in Gastric Endothelial Cells Is One of the Main Causes of Impaired Angiogenesis in Aging Gastric Mucosa

BACKGROUND & AIMS

Aging gastric mucosa has increased susceptibility to injury and delayed healing owing to impaired angiogenesis, but the mechanisms are not fully known. We examined whether impairment of angiogenesis in aging gastric mucosa is caused by deficiency of nerve growth factor (NGF) in gastric endothelial cells (ECs), and whether NGF therapy could reverse this impairment.

METHODS

In gastric mucosal ECs (GECs) isolated from young and aging rats we examined the following: (1) in vitro angiogenesis, (2) NGF expression, and (3) the effect of NGF treatment on angiogenesis, GEC proliferation and migration, and dependence on serum response factor. In in vivo studies in young and aging rats, we examined NGF expression in gastric mucosa and the effect of NGF treatment on angiogenesis and gastric ulcer healing. To determine human relevance, we examined NGF expression in gastric mucosal biopsy specimens of aging (≥70 y) and young (≤40 y) individuals.

RESULTS

In cultured aging GECs, NGF expression and angiogenesis were reduced significantly by 3.0-fold and 4.1-fold vs young GECs. NGF therapy reversed impairment of angiogenesis in aging GECs, and serum response factor silencing completely abolished this response. In gastric mucosa of aging rats, NGF expression in GECs was reduced significantly vs young rats. In aging rats, local NGF treatment significantly increased angiogenesis and accelerated gastric ulcer healing. In aging human subjects, NGF expression in ECs of gastric mucosal vessels was 5.5-fold reduced vs young individuals.

CONCLUSIONS

NGF deficiency in ECs is a key mechanism underlying impaired angiogenesis and delayed ulcer healing in aging gastric mucosa. Local NGF therapy can reverse these impairments.

[Glutamate as a potential protective drug in the gastrointestinal mucosa]

Monosodium glutamate (MSG) is known to provide the umami taste in the food. We have recently reported that glutamate has the potential to protect the small intestine against non-steroidal anti-inflammatory drugs (NSAIDs)-induced lesions in rats. In this paper, we examined this protective effect using sodium loxoprofen, one of the NSAIDs frequently used in Asian countries, to determine whether MSG accelerates the healing of loxoprofen-induced small intestinal lesions in rats. Loxoprofen at 60 mg/kg caused hemorrhagic lesions in the small intestine, mainly in the jejunum and ileum. These lesions spontaneously healed within 7 days, but this healing process was delayed by repeated administration of loxoprofen at low doses (10, 30 mg/kg) for 5 d after lesion induction. The healing-impairment action of loxoprofen was accompanied by the down-regulation of vascular endothelium-derived growth factor (VEGF) expression and an angiogenic response. The impaired healing caused by loxoprofen was significantly restored by co-treatment with a diet containing 5% MSG for 5 d, accompanied by the enhancement of VEGF expression and angiogenesis. We suggest that daily intake of MSG not only protects the small intestine against NSAIDs-induced damage but also exerts healing-promoting effects on these lesions.

Results of the 2nd scientific workshop of the ECCO (III): basic mechanisms of intestinal healing

The second scientific workshop of the European Crohn's and Colitis Organization (ECCO) focused on the relevance of intestinal healing for the disease course of inflammatory bowel disease (IBD). The objective was to better understand basic mechanisms, markers for disease prediction, detection and monitoring of intestinal healing, impact of intestinal healing on the disease course of IBD as well as therapeutic strategies. The results of this workshop are presented in four separate manuscripts. This section describes basic mechanisms of intestinal healing, identifies open questions in the field and provides a framework for future studies.

Loss of RegI in conjunction with gastrin deficiency in mice facilitates efficient gastric ulcer healing but is dispensable for hyperplasia and tumourigenesis

RegI (Regenerating islet derived-1) was originally characterized as a growth factor involved in pancreatic islet cell regeneration. It is also considered a gastrointestinal mitogen as its expression is increased during pathologies involving aberrant cell proliferation that can lead to neoplasia. However, the absolute requirement for RegI to directly stimulate gastric mucosal cell proliferation in vivo requires further investigation. We used RegI-deficient mice to determine the requirement for RegI in normal gastric mucosal development, wound healing, hyperplasia and tumourigenesis. We found that epithelial repair of acetic acid ulcers in compound mutant RegI/gastrin-deficient mice was significantly reduced compared to wild type, RegI-deficient or gastrin-deficient mice. In contrast, RegI was dispensable for normal gastric mucosal development, hyperplasia in HKbeta-deficient mice and tumourigenesis in gp130(F/F) mice. Although RegI was not required for proliferation in these pathological models, expression of multiple Reg family members were increased during gp130(F/F) tumourigenesis. Interestingly, loss of RegI in gp130(F/F) mice resulted in decreased expression of other Reg family members. Our results indicate that RegI and gastrin may synergistically regulate gastric mucosal proliferation during certain pathological settings like wound healing while gastric epithelial proliferation in other pathologies may require coordinated expression of multiple Reg genes.

Amylin prevents TRAIL-mediated apoptotic effects of reserpine in the rat gastric mucosa

We have previously shown that amylin has a protective effect upon the damaged rat gastric mucosa via a cytokine-mediated mechanism. Here, the effects of amylin on the proapoptotic cytokine TNF-related-apoptosis-inducing-ligand (TRAIL) were tested in the rat gastric mucosa damaged by reserpine administration in vivo. Intraperitoneal administration of reserpine in adult male Sprague-Dawley rats resulted in increased TRAIL expression in the gastric mucosa. Immunohistochemistry showed that the TRAIL death-receptor 5 (DR5) was constitutively expressed by the mucosa cells. Western blot showed that pretreatment of reserpine-treated rats with amylin was associated with attenuated expression of TRAIL. In the same samples, we also investigated about TRAIL-related signaling and observed that activation of caspases-8 and -3 occurs in parallel to increased TRAIL expression in rats treated with reserpine. Similarly to the latter, activation of caspases was attenuated in rats pretreated with amylin. Treatment with reserpine was associated with increased expression of the proapoptotic protein Bax, whereas that of the antiapoptotic protein Bcl-2 was significantly decreased. Amylin prevented the effects of reserpine on these genes. Reserpine sets into motion mechanisms of apoptosis in the rat gastric mucosa, which appear mediated, at least in part, by TRAIL. In addition, TRAIL downstream signaling is activated along with subversion of gene expression related to apoptosis. Amylin was able to prevent detrimental effects of reserpine. Finally, amylin and related molecules may be envisioned as protective agent in gastric mucosa damage.

Involvement of voltage-gated K+ and Na+ channels in gastric epithelial cell migration

Epithelial cell migration plays an important role in gastrointestinal mucosal repair. We previously reported that multiple functional ion channels, including a Ba(2+)-sensitive K(+) inward rectifier K(ir)1.2, 4-aminopyridine (4-AP)-sensitive voltage-gated K(+) channels K(v)1.1, K(v)1.6 and K(v)2.1, and a nifedipine-sensitive, tetrodotoxin (TTX)-insensitive voltage-gated Na(+) channel Na(v)1.5 were expressed in a non-transformed rat gastric epithelial cell line (RGM-1). In the present study, we further investigated whether these ion channels are involved in the modulation of gastric epithelial cell migration. Cell migration was determined by monolayer wound healing assay. Results showed that blockade of K(v) with 4-AP or Na(v)1.5 with nifedipine inhibited RGM-1 cell migration in the absence or presence of epidermal growth factor (EGF), which effectively stimulated RGM-1 cell migration. Moreover, high concentration of TTX mimicked the action of nifedipine, suggesting that the action of nifedipine was mediated through specific blockade of Na(v)1.5. In contrast, inhibition of K(ir)1.2 with Ba(2+), either in basal or EGF-stimulated condition, had no effect on RGM-1 cell migration. In conclusion, the present study demonstrates for the first time that voltage-gated K(+) and Na(+) channels are involved in the modulation of gastric epithelial cell migration.

Cellular and molecular mechanisms of gastrointestinal ulcer healing

This paper reviews cellular and molecular mechanisms of gastrointestinal ulcer healing. Ulcer healing, a genetically programmed repair process, includes inflammation, cell proliferation, re-epithelialization, formation of granulation tissue, angiogenesis, interactions between various cells and the matrix and tissue remodeling, all resulting in scar formation. All these events are controlled by the cytokines and growth factors (EGF, PDGF, KGF, HGF, TGFbeta, VEGF, angiopoietins) and transcription factors activated by tissue injury in spatially and temporally coordinated manner. These growth factors trigger mitogenic, motogenic and survival pathways utilizing Ras, MAPK, PI-3K/Akt, PLC-gamma and Rho/Rac/actin signaling. Hypoxia activates pro-angiogenic genes (e.g., VEGF, angiopoietins) via HIF, while serum response factor (SRF) is critical for VEGF-induced angiogenesis, re-epithelialization and muscle restoration. EGF, its receptor, HGF and Cox2 are important for epithelial cell proliferation, migration re-epithelializaton and reconstruction of gastric glands. VEGF, angiopoietins, nitric oxide, endothelin and metalloproteinases are important for angiogenesis, vascular remodeling and mucosal regeneration within ulcer scar. Circulating progenitor cells are also important for ulcer healing. Local gene therapy with VEGF + Ang1 and/or SRF cDNAs dramatically accelerates esophageal and gastric ulcer healing and improves quality of mucosal restoration within ulcer scar. Future directions to accelerate and improve healing include the use of stem cells and tissue engineering.

Serum response factor is a critical requirement for VEGF signaling in endothelial cells and VEGF-induced angiogenesis

Angiogenesis, new capillary blood vessel formation, is essential for embryonic development, wound healing, and cancer growth. Vascular endothelial growth factor (VEGF) induces angiogenesis by activating endothelial cell migration and proliferation. Serum response factor (SRF) is a transcription factor important for embryonic development and activation of immediate early gene expression. The roles of SRF in endothelial cell biology and angiogenesis have not been explored. Here we demonstrate that SRF is a downstream mediator of VEGF signaling in endothelial cells and a critical requirement for VEGF-induced angiogenesis. Knockdown of SRF protein levels in human and rat endothelial cells abolished VEGF-induced in vitro angiogenesis, impaired endothelial cell migration and proliferation, and inhibited VEGF-induced actin polymerization and immediate early gene expression. Injection of SRF antisense expression plasmid into gastric ulcers in rats significantly inhibited in vivo angiogenesis in granulation tissue. Mechanistically, this study also revealed that VEGF promotes SRF expression and nuclear translocation and increases SRF binding activity to DNA in endothelial cells through both Rho-actin and MEK-ERK dependent signaling pathways. These findings have potential therapeutic implications, e.g., local anti-SRF treatment may inhibit angiogenesis crucial for tumor growth.

Evaluation of anti-ulcerogenic and ulcer-healing properties of Ocimum sanctum Linn

Ocimum sanctum (OS) is known to possess various therapeutic properties. We evaluated its anti-ulcerogenic activity in cold restraint (CRU), aspirin (ASP), alcohol (AL), pyloric ligation (PL) induced gastric ulcer models in Sprague-Dawley rats, histamine-induced duodenal (HST) ulcer in guinea pigs, and ulcer-healing activity, in acetic acid-induced (AC) chronic ulcer model. We found that OS, decreased the incidence of ulcers and also enhanced the healing of ulcers. OS at a dose of 100 mg/kg was found to be effective in CRU (65.07%), ASP (63.49%), AL (53.87%), PL (62.06%), and HST (61.76%) induced ulcer models and significantly reduced free, total acidity and peptic activity by 72.58, 58.63, 57.6%, respectively, and increased mucin secretion by 34.61%. Additionally, OS completely healed the ulcers within 20 days of treatment in AC. We observed that anti-ulcer effect of OS may be due to its cytoprotective effect rather than antisecretory activity. Conclusively, OS was found to possess potent anti-ulcerogenic as well as ulcer-healing properties and could act as a potent therapeutic agent against peptic ulcer disease.

Vessel injury and capillary leak

OBJECTIVE

To understand the mechanism of pathologic capillary leak in the critically ill patient.

DESIGN

Review of normal and altered physiology of the microvasculature. Review of recent literature describing pathogenesis, mediators, and interventions influencing capillary leak and microvascular repair.

SETTING

In vitro and in vivo studies, the latter including animal and human subjects.

MEASUREMENTS AND MAIN RESULTS

Capillary leak with resultant edema develops in the critical care setting on the basis of perturbations in Starling's equation, primarily as a result of increased capillary permeability to larger molecules. This process is most likely fueled by inflammatory mediators or mechanical stress. Attempts to prevent or treat this process remain largely unsuccessful; resuscitation is more often symptomatic than therapeutic. Models of microvascular repair focus on discrete injury and may not be applicable to the recovery of capillary damage secondary to a systemic leak

CONCLUSIONS

Our understanding of capillary leak syndrome remains fragmented and weighted toward specific mediators contributing to the leak. The implications of extensive edema and the mechanism by which it resolves continue to be the subject of speculation rather than study.

Esophageal ulceration triggers expression of hypoxia-inducible factor-1 alpha and activates vascular endothelial growth factor gene: implications for angiogenesis and ulcer healing

Our previous studies demonstrated that enhanced epithelial cell proliferation is important for healing of experimental esophageal ulcers. However, the roles of angiogenesis, its major mediator, vascular endothelial growth factor (VEGF), and the mechanism(s) regulating VEGF expression during esophageal ulcer healing remain unknown. Esophageal ulcers were induced in rats by focal application of acetic acid. We studied expressions of hypoxia-inducible transcription factor-1 alpha (HIF-1 alpha), an activator of the VEGF gene, and VEGF by reverse transcriptase-polymerase chain reaction, Western blotting, and immunostaining. To determine the efficacy of VEGF gene therapy in esophageal ulcer healing, we studied whether a single local injection of plasmid cDNA encoding recombinant human VEGF(165) affects ulcer healing and angiogenesis. Esophageal ulceration induced HIF-1 alpha protein expression and VEGF gene activation reflected by increased VEGF mRNA (240%) and VEGF protein (310%) levels. HIF-1 alpha protein was expressed in microvessels bordering necrosis where it co-localized with VEGF. Injection of cDNA encoding VEGF(165) significantly enhanced angiogenesis and accelerated esophageal ulcer healing. These results: 1) suggest that HIF-1 alpha may mediate esophageal ulceration-triggered VEGF gene activation, 2) indicate an essential role of VEGF and angiogenesis in esophageal ulcer healing, and 3) demonstrate the feasibility of gene therapy for the treatment of esophageal ulcers.

von Hippel Lindau tumor suppressor and HIF-1alpha: new targets of NSAIDs inhibition of hypoxia-induced angiogenesis

Nonsteroidal anti-inflammatory drugs (NSAIDs) block prostaglandin synthesis and impair healing of gastrointestinal ulcers and growth of colonic tumors, in part, by inhibiting angiogenesis. The mechanisms of this inhibition are incompletely explained. Here we demonstrate that both nonselective (indomethacin) and COX-2-selective (NS-398) NSAIDs inhibit hypoxia-induced in vitro angiogenesis in gastric microvascular endothelial cells via coordinated sequential events: 1) increased expression of the von Hippel-Lindau (VHL) tumor suppressor, which targets proteins for ubiquitination leading to 2) reduced accumulation of hypoxia-inducible factor-1alpha (HIF-1alpha) and, as a result, 3) reduced expression of vascular endothelial growth factor (VEGF) and its specific receptor Flt-1. Because HIF-1alpha is the major trigger for hypoxia-induced activation of the VEGF and Flt-1 genes, this could explain how NSAIDs inhibit hypoxia-induced angiogenesis. Exogenous VEGF and, to a lesser extent, exogenous prostaglandins partly reversed the NSAIDs inhibition of hypoxia-induced angiogenesis. Taken together, these results indicate that NSAIDs inhibit hypoxia-induced angiogenesis in endothelial cells by inhibiting VEGF and Flt-1 expression through increased VHL expression and the resulting ubiquitination and degradation of HIF-1alpha. This action of NSAIDs has both prostaglandin-dependent and prostaglandin-independent components.

Esophageal ulceration activates keratinocyte growth factor and its receptor in rats: implications for ulcer healing

BACKGROUND & AIMS

Cellular and molecular mechanisms of esophageal ulcer healing remain unexplored. We studied the sequential cellular events and the expression of keratinocyte growth factor (KGF) and its receptor (KGF-R) during the healing of experimental esophageal ulcers.

METHODS

Esophageal ulcers were produced in rats by local application of acetic acid. Studies included (1) ulcer size, (2) quantitative histology, and (3) KGF and KGF-R messenger RNA and protein expression by reverse-transcription polymerase chain reaction, Western blotting, and immunostaining. In separate groups, ulcer size and esophageal epithelial proliferation were evaluated after a single injection of recombinant human KGF (1 mg/kg) around the ulcer.

RESULTS

Ulcers were fully developed 3 days after induction, and 58% of ulcers were re-epithelialized by 9 days. At 3 days, in esophageal tissue bordering the ulcers, KGF messenger RNA and protein were increased by 191% and 151%, respectively, and KGF-R messenger RNA and protein were increased by 357% and 237%, respectively. KGF was expressed in stromal cells, whereas KGF-R was expressed in epithelial cells. At 6 days, epithelial proliferation at the ulcer margin was increased by 216%, and treatment with KGF further enhanced cell proliferation and accelerated ulcer healing.

CONCLUSIONS

KGF is a likely mediator of esophageal epithelial proliferation and ulcer healing.

Gene therapy for gastric ulcers with single local injection of naked DNA encoding VEGF and angiopoietin-1

BACKGROUND & AIMS

Angiogenesis, formation of new capillary blood vessels, is crucial for gastroduodenal ulcer healing because it enables delivery of oxygen and nutrients to the healing site. Because angiogenesis is stimulated by vascular endothelial growth factor (VEGF) and angiopoietin-1 (Ang1), we studied whether local gene therapy with nonviral DNA encoding VEGF and/or Ang1 into the ulcer base could accelerate ulcer healing through enhanced angiogenesis.

METHODS

Gastric ulcers were induced in rats by acetic acid applied to the serosal surface of the stomach, and the site around the ulcer was injected with nonviral plasmid-encoding full-length complementary DNA (cDNA) of human recombinant (rh) VEGF165, rhAng1, or their combination. For some studies, neutralizing anti-VEGF antibody was administered.

RESULTS

Single local injection of plasmids encoding VEGF165 and Ang1 significantly increased neovascularization and accelerated ulcer healing. A neutralizing anti-VEGF antibody significantly reduced the acceleration of ulcer healing resulting from the treatment. Coinjection of both plasmids encoding rhVEGF165 and rhAng1 resulted in formation of more mature vessels and to more complete restoration of gastric glandular structures within the ulcer scar. However, this did not result in further reduction of ulcer size.

CONCLUSIONS

VEGF and Ang1 gene therapy, with limited duration of target gene expression, significantly accelerates gastric ulcer healing. Coinjection of both plasmids leads to more complete structural restoration. Inhibition of accelerated healing by a neutralizing anti-VEGF antibody indicates an essential role for VEGF and enhanced angiogenesis in ulcer healing.

Histological characteristics of induced acute peptic injury in equine gastric squamous epithelium

The objective of the study reported here was to characterise the microscopic appearance of peptic-injured equine gastric squamous epithelium in relation to the duration of peptic injury. Erosions and ulcers were induced in equine gastric squamous epithelium using a feed deprivation protocol that results in prolonged increased gastric acidity. Specimens of normal gastric mucosa and mucosa with lesions created after 48 and 96 h of feed deprivation were compared for characteristics associated with angiogenesis and mucosal proliferation. Fifteen mature horses, 9 geldings and 6 mares, age 3-20 years, were divided into 3 groups. Group 1 (n = 5) had normal-appearing gastric squamous mucosal epithelium and had been killed due to problems unrelated to the gastrointestinal tract. Groups 2 (n = 5) and 3 (n = 5) had lesions induced in the gastric squamous epithelium by alternating 24 h periods of feed deprivation and ad libitum access to hay, for totals of 48 and 96 h feed deprivation, respectively. Following lethal injection of barbiturate, stomachs were removed and fixed by filling with 4-6 l 10% buffered formalin. Sections were made from lesions in the gastric squamous epithelium adjacent to the margo plicatus along the right side of the stomach/greater curvature and the lesser curvature. Measurements of total epithelial thickness, keratinised epithelium, nonkeratinised epithelium, epithelial projections, capillary extension into the epithelium and lamina propria thickness were made. The cross-sectional areas of arterial and venous vascular structures in the lamina propria at the lesions and their margins were measured using image analysis software. All horses, except one, in Group 2 developed erosions or ulcers in the gastric squamous epithelium after feed deprivation. There were several changes in the epithelium adjacent to erosions and ulcers, compared to normal epithelium, from horses in Groups 2 and 3: total epithelial thickness was significantly (P<0.05) greater, including both keratinised and nonkeratinised layers in most specimens; the length of epithelial projections and extent to which capillaries from the lamina propria extended toward the luminal surface, and the cross-sectional area of vascular structures (arterioles, capillaries, venules) in the lamina propria were significantly greater. Epithelial thickness of erosion beds was not significantly less than normal epithelium, although a greater proportion of the epithelium in erosions consisted of epithelial projections (Group 1, 23%; Group 2, 76%; Group 3, 72%). The cross-sectional area of vascular structures in the lamina propria beneath erosions was significantly greater than in normal mucosa only in Group 2 tissues, whereas in the lamina propria of ulcers it was significantly greater than in normal mucosa only in Group 3 tissues. The epithelial proliferation and increased vascular cross-sectional area in the lamina propria associated with peptic-induced gastric lesions are consistent with processes associated with the initiation of ulcer healing, and these changes temporally coincided with the initiation of peptic insult to the gastric squamous epithelium. These findings demonstrate that processes that promote ulcer healing begin soon after peptic injury and that they progress even with repeated peptic injury. Furthermore, our findings support observations that gastric ulcers often heal without medical intervention, and the theory that medications that reduce gastric acidity do not initiate healing, but rather facilitate ulcer healing by providing a microenvironment that is optimal for healing to proceed.

Remodeling of extracellular matrix in gastric ulceration

The quality of ulcer repair remains crucial for the stability of the injured tissue and for preventing recurrence. Therefore, we studied the temporo-spatial expression of the fibrillar and basement membrane collagens (types I, III, and IV), the collagenase MMP-2 as well as its inhibitor TIMP-1 before and after oral administration of basic fibroblast growth factor (b-FGF) over 30 days in acetic acid-induced rat gastric ulcers. The alterations and the exact location of the mRNA transcripts and their precipitated proteins were visualized by means of radioactive in situ hybridization and immunohistochemistry. Our data show that hybridization signals of procollagen I could first be identified 2 hours after ulcer induction. After 12 hours the ulcer was established and the mRNA was enhanced at the ulcer margin. After 24-48 hours the other procollagen transcripts were detected and all were further upregulated over the mesenchymal cells of all gastric layers up to 21 days, then declined at 30 days. In contrast, MMP-2 became prominent after 48 hours and up to 21 days. TIMP-1 was enhanced at 72 hours. After oral administration of b-FGF the transcriptional activity of the procollagens and MMP-2 was not significantly altered, while ulcer diameter was significantly reduced. We conclude that the early onset and long duration of collagens' expression points to their central structural and functional role in gastric ulcer healing. MMP-2 seems to be involved in both active ulceration and ECM remodeling. The timing of TIMP/MMP expression may be critical for proper restoration of gastric wall integrity.

Spatio-temporal expression of trefoil peptide following severe gastric ulceration in the rat implicates it in late-stage repair processes

BACKGROUND

The trefoil peptide (TFF1) is a member of a family of mucin-associated regulatory peptides that are widely distributed in gastrointestinal tissues and have been implicated in the maintenance of the gastric mucosa. The role of TFF1 in gastric mucosal repair was examined by analysis of the spatio-temporal expression of TFF1 following gastric ulceration in the rat.

METHODS

Gastric ulcers were induced in rats by application of glacial acetic acid to the serosa of the fundus. At various time points post injury (0-28 days), macroscopic and microscopic examination of the gastric mucosa was performed. In addition, the spatio-temporal expression of TFF1 protein and proliferating cell nuclear antigen were identified by immunohistochemistry, TFF1 message by in situ hybridization, and acidic/neutral secreting mucins by Alcian blue-periodic acid-Schiff staining.

RESULTS

In normal rat gastric tissue, TFF1 peptide and mRNA were expressed in mucosal cells of the superficial epithelium. Trefoil peptide and mRNA were significantly induced between 4 and 28 days post ulceration, with expression extending beyond the superficial epithelium and being localized to acidic mucin-producing cells deep within the repairing mucosa.

CONCLUSIONS

Spatio-temporal expression of TFF1 mRNA and peptide following macroscopic repair implicates TFF1 as a potential mediator of late stage-repair processes. Whether this is through direct stimulation of cellular differentiation or the enhancement of mucosal protective properties through an interaction with gastric mucins remains to be elucidated.

Augmented intestinal trefoil factor (TFF3) and loss of pS2 (TFF1) expression precedes metaplastic differentiation of gastric epithelium

The trefoil peptides spasmolytic polypeptide (SP), intestinal trefoil factor (ITF), and pS2 show lineage-specific expression in the normal gut and are strongly induced after mucosal injury. We assessed the relationship between this induction and the development of the regenerative epithelial lineage over time in the rat stomach and verified these observations in the metaplastic and dysplastic human stomach. Antral or colonic ulcers were induced in Wistar rats by application of serosal acetic acid and tissues harvested 2 hours to 125 days later. Human endoscopic biopsies or gastric resection specimens were also assessed. Tissues were examined by radioimmunoassay, immunoblotting, or immunohistochemistry for ITF, SP, and transforming growth factor alpha (rat) or ITF and pS2 (human) expression. ITF and SP mRNA in antral ulcer margins was localized by in situ hybridization. ITF and SP peptide expression rose steadily in ulcer margins after 4 days, with the rise in ITF being more pronounced. By 40 days, several hundred-fold elevations in ITF levels were present, with a field effect in uninvolved mucosa. Hyperproliferative, elongated glands of undifferentiated cells expressing abundant trefoil peptides and acid sulfomucins were present after day 12 and persisted after ulcer healing. ITF mRNA was aberrantly expressed in basal and mid-regions of these regenerative glands. In contrast, transforming growth factor alpha peptide expression rose promptly after injury then fell to baseline levels with healing. Seven months after injury, gastric atrophy, intestinal metaplasia, and severe dysplasia with conserved ITF expression were seen. ITF was also induced in human intestinal metaplasia and conserved in all gastric cancers, whereas expression of the gastric peptide pS2 was progressively reduced in the progression from metaplasia to dysplasia. Persistent, selective overexpression of ITF, possibly acting in an autocrine fashion, is a feature of regeneration after antral ulceration, and may provide insight into the nature of metaplastic phenotypes arising from chronic gastric injury. The loss of pS2 expression in metaplasia and cancer supports a role for this protein in gastric tumor suppression.

Regeneration of gastric mucosa during ulcer healing is triggered by growth factors and signal transduction pathways

An ulcer is a deep necrotic lesion penetrating through the entire thickness of the gastrointestinal mucosa and muscularis mucosae. Ulcer healing is a complex and tightly regulated process of filling the mucosal defect with proliferating and migrating epithelial and connective tissue cells. This process includes the re-establishment of the continuous surface epithelial layer, glandular epithelial structures, microvessels and connective tissue within the scar. Epithelial cells in the mucosa of the ulcer margin proliferate and migrate onto the granulation tissue to re-epithelialize the ulcer. Growth factors, such as epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), trefoil peptides (TP), platelet derived growth factor (PDGF) and other cytokines produced locally by regenerating cells, control re-epithelialization and the reconstruction of glandular structures. These growth factors, most notably EGF, trigger epithelial cell proliferation via signal transduction pathways involving EGF-R- MAP (Erk1/Erk2) kinases. Granulation tissue, which develops at the ulcer base, consists of fibroblasts, macrophages and proliferating endothelial cells, which form microvessels under the control of angiogenic growth factors. These growth factors [bFGF, vascular endothelial growth factor (VEGF) and angiopoietins] promote angiogenesis--capillary vessel formation--thereby allowing for the reconstruction of microvasculature in the mucosal scar, which is essential for delivery of oxygen and nutrients to the healing site. The primary trigger to activate expression of angiogenic growth factors and their receptors appears to be hypoxia. During ulcer healing expression of growth factor genes is tightly regulated in a temporally and spatially ordered manner.

Intragastric administration of heparin enhances gastric ulcer healing through a nitric oxide-dependent mechanism in rats

Our preliminary finding indicated that intravenous (i.v.) injection of heparin increased gastric ulcer healing in rats. However, the anticoagulant action of i.v. heparin could produce complications in ulcer patients if the drug was used as an anti-ulcer agent. The present study aimed to investigate whether intragastric (i.g.) administration of heparin, known to have no anticoagulant activity, would have the similar ulcer healing effect and the relationship of this effect, if any, with nitric oxide (NO), a substance suggested to be important for ulcer healing. Heparin (100, 500, 1000 U/kg, i.g. ) administered once daily for 4 days accelerated the healing of gastric ulcer induced by acetic acid in Sprague-Dawley rats, which was accompanied by an increase in mucosal proliferation and regeneration at the ulcer margin, microvessel number both at the ulcer margin and base, and the thickness of mucus layer. Both activity and content, but not the mRNA of constitutive nitric oxide synthase (cNOS) in the gastric mucosa were enhanced. L-N(G)-nitroarginine methyl ester (L-NAME), an inhibitor of NOS activity blocked the cNOS activity activated by heparin and reversed the beneficial effects of heparin on ulcer healing. The bleeding time was not altered by i.g. heparin. These findings demonstrate that i.g. heparin promotes the healing processes of gastric ulcer. Such effect is suggested to act through the stimulation of mucosal cNOS activity. In addition, i.g. heparin is better than i.v. heparin without the potential anticoagulation effect.

The ulcer healing effect of protamine sulphate in rat stomach

BACKGROUND

Protamine sulphate has been reported to stimulate nitric oxide production from blood vessels, which is a pivotal factor for gastric ulcer healing. Our preliminary study also showed that protamine sulphate potentiated the ulcer healing effect of heparin.

METHODS

Male SD rats with acetic acid-induced gastric ulcers were given protamine sulphate (40-80 mg/kg, s.c.) twice daily for 4 or 7 days. L-NG-nitroarginine methyl ester (L-NAME, 5 mg/kg), an inhibitor of nitric oxide synthase (NOS), was given s.c. prior to protamine sulphate (80 mg/kg) treatment. Ulcer healing, angiogenesis, mucosal histological changes, NOS activity and growth factors were determined.

RESULTS

Protamine sulphate dose-dependently accelerated gastric ulcer healing, which was accompanied by a significant increase in angiogenesis, mucosal regeneration and constitutive NOS activity. Inhibition of gastric secretion was observed. Epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), tumour necrosis factor-alpha (TNF-alpha) or inducible NOS activity was also affected. L-NAME completely blocked the beneficial effects of protamine sulphate.

CONCLUSIONS

Protamine sulphate accelerates gastric ulcer healing through a mucosal nitric oxide-dependent and possibly also the EGF-and bFGF-associated pathways, which are followed by an increase of angiogenesis and mucosal regeneration. Acid inhibition contributes in part to the ulcer healing action of protamine sulphate.

Effects of cigarette smoking on gastric ulcer formation and healing: possible mechanisms of action

Epidemiologic studies have shown that cigarette smoking is closely related to peptic ulcer disease. The mechanisms by which cigarette smoking adversely affects gastric mucosa have been suggested and elucidated. This article reviews some of the mechanisms involved in cigarette smoking-related gastric ulceration and healing. Experimental findings suggest that cigarette smoking increases xanthine oxidase activity, leukotrienes, and nitric oxide production and also neutrophil infiltration in the gastric mucosa. On the other hand, it reduces blood flow, prostaglandin production, epithelial cell proliferation, and formation of blood vessels in the tissue. These actions are important for ulcer formation and healing. The evidence thus far available strengthens the hypothesis that cigarette smoke is indeed harmful to gastric mucosa through defined mechanisms.

Cigarette smoking delays ulcer healing: role of constitutive nitric oxide synthase in rat stomach

Epidemiological studies have shown that cigarette smoking is associated with peptic ulceration. This study aims to investigate the mechanisms by which cigarette smoking delays ulcer healing in rats. Gastric ulcers were induced by applying acetic acid to the luminal surfaces in rats. Twenty-four hours later, rats were exposed to different concentrations of cigarette smoke (0, 2, or 4%) for a 1-h period once daily for 3 or 6 days. Cigarette smoke exposure delayed ulcer healing and decreased gastric blood flow and angiogenesis at the ulcer margin. These changes were accompanied by a significant reduction of constitutive nitric oxide synthase (cNOS) activity but not PGE2 production and vascular endothelial growth factor levels. Administration of L-arginine (10 mg/kg iv) completely reversed the adverse actions on ulcer healing, gastric blood flow, and angiogenesis in the mucosa at the ulcer margin but partially restored angiogenesis in granulation tissues. In conclusion, cigarette smoke exposure delays ulcer healing through depression of gastric blood flow and angiogenesis at the ulcer margin. Reduction of cNOS expression and activity is suggested to be involved in these ulcerogenic processes.

Induction of mitogen-activated protein kinase signal transduction pathway during gastric ulcer healing in rats

BACKGROUND & AIMS

Previous studies have shown that gastric ulceration stimulates epithelial cell proliferation and overexpression of epidermal growth factor (EGF) and EGF receptor (EGF-R) in the mucosa bordering necrosis. The aim of this study was to investigate whether extracellular signal-regulated kinase (ERK) cascade is involved in the healing of experimental gastric ulcers.

METHODS

We studied EGF-R levels, EGF-R phosphorylation levels, and ERK1 and ERK2 activity in normal and ulcerated rat gastric mucosa. We also examined the effect of Tyrphostin A46 (potent inhibitor of EGF-R and EGF-R kinase-dependent proliferation) on the above parameters.

RESULTS

During the initial stages of healing (3 and 7 days), ulcerated mucosa showed significant increase (vs. controls) in protein tyrosine kinase activity, EGF-R levels (510% and 550%), EGF-R phosphorylation levels, ERK1 activity (430% and 880%), and ERK2 activity (550% and 990%). Tyrphostin A46 treatment significantly inhibited ulcer healing and reduced EGF-R levels, EGF-R phosphorylation, and ERK1 and ERK2 activity.

CONCLUSIONS

These findings indicate that experimental gastric ulcer healing involves activation of EGF-R-ERK signal transduction pathway.

Expression of epidermal growth factor and transforming growth factor alpha during ulcer healing. Time sequence study

BACKGROUND

Growth factors such as epidermal growth factor (EGF) and transforming growth factor alpha (TGF alpha) have been shown to share common receptor (EGFR) and to accelerate ulcer healing due to stimulation of cell proliferation, but the time sequence of expression of EGF and TGF alpha during ulcer healing has not been investigated. In this study the rate of cell proliferation and the gastric secretion and gene expression of mRNA for EGF and TGF alpha were determined during ulcer healing.

METHODS

Gastric ulcers were induced in 150 Wistar rats by serosal application of 100% acetic acid (ulcer area, 14 mm2). Some of these animals were also equipped with a gastric fistula for the assessment of gastric secretion during ulcer healing. The animals were killed 0, 2, 4, 6, or 8 days after ulcer induction, and the ulcer area was determined. The mucosal sections with gastric ulcer were immunostained for proliferating cell nuclear antigen (PCNA) and for immunoexpression of EGF, TGF alpha, and EGFR. The expression of mRNA EGF and mRNA TGF alpha was also determined in the ulcer margin by reverse transcriptase (RT) polymerase chain reaction (PCR) using specific primers.

RESULTS

Two, 4, 6, and 8 days after ulcer induction the gastric ulcer area was gradually reduced from the initial size (day 0) by 47%, 70%, 80%, and 87%, respectively, and this was accompanied by an increase in PCNA with its maximum on day 4. The gastric acid and pepsin secretion was significantly reduced by 75% and 79%, respectively, on day 2 after ulcer induction but then the secretion tended to return to normal value by day 8. The expression of EGF, TGF alpha, and EGFR was negligible on day 0 but increased significantly during the healing, reaching maximum on day 4. Expression of EGF mRNA was detected on days 2, 4, and 6, and that of TGF alpha mRNA on days 2, 4, 6, and 8 after ulcer induction, with the most intense signals for both transcripts observed on day 2.

CONCLUSIONS

1) The enhancement in cell proliferation during ulcer healing may be mediated by increased release of EGF and TGF alpha; 2) the expression of EGF and TGF alpha mRNA precedes the overexpression of these growth factors at the ulcer margin during ulcer healing; and 3) the overexpression of growth factors coincides with the inhibition of gastric secretion and increased blood flow at the ulcer margin, indicating that these factors affect gastric secretion and blood flow in the course of ulcer healing.

Quality of gastric ulcer healing. Is it influenced by antiulcer drugs?

BACKGROUND

Chronic administration of sucralfate (SCR), a non-systemic ulcer-healing drug, exerts a trophic action on the gastric mucosa and prevents or reduces ulcer recurrence. The aim of this study was to determine whether SCR and/or the acid inhibiting drug omeprazole (OME) may affect the quality of ulcer healing, i.e., restoration of mucosal architecture.

METHODS

Gastric ulcers were produced in male rats by serosal application of acetic acid. Rats were gavaged twice daily for 14 days with 2 ml of: (a) Placebo (PLA), (b) SCR 500 mg/kg, or (c) OME, 50 mg/kg starting 48 h after ulcer induction. We determined ulcer size under a dissecting microscope, and performed quantitative histologic assessment of quality of healing score (QS) on a scale from 0 (normal) to 5 (most abnormal).

RESULTS

Ulcer size was 1.4 +/- 0.15 mm in the PLA group, 0.61 +/- 0.1 mm in the SCR group and 0.86 +/- 0.13 mm in the OME group (both OME and SCR p < 0.01 versus PLA). In the PLA group, histology showed (in rats with ulcers) a well-developed ulcer margin with cystically dilated glands. The QS of the ulcer scar in the PLA group was 3.3 +/- 0.22. IN the SCR-treated group, within the scar gastric glands were less dilated, more vertically oriented and the healing zone and granulation tissue were well developed and organized. The QS was 1.6 +/- 0.2, p < 0.001 versus PLA and OME. In the OME group, the ulcer margin and the scar were thinner-reduction of mucosal thickness by 43 +/- 2% (p < 0.005) and 18 +/- 1%, respectively, versus SCR and PLA groups. The number of dilated glands and connective tissue components in the scar was increased by 60%. The QS was 3.6 +/- 0.3.

CONCLUSIONS

(1) Both SCR and OME significantly reduced the size of the experimental gastric ulcer. (2) Restoration of mucosal architecture, assessed quantitatively, was much better in the SCR than in the OME and PLA-treated groups. (3) a trophic action of SCR on the gastric mucosa may be the basis of better quality of ulcer healing with SCR.

Cellular and molecular mechanisms of gastric ulcer healing. Is the quality of mucosal scar affected by treatment?

BACKGROUND

Ulcer healing, i.e. the reconstruction of the mucosal architecture, is an active process of filling the mucosal defect with proliferating and migrating epithelial cells and connective tissue.

METHODS

This article represents a summary of histologic and ultrastructural assessment of the cellular events occurring during healing of experimental gastric ulcer.

RESULTS

Mucosa adjacent to the ulcer crater forms a 'healing' zone. The gastric glands in this zone dilate and the epithelial cells lining these glands de-differentiate, express epidermal growth factor receptor, and proliferate. The latter is the result of local activation of genes encoding for EGF and its receptors. At the ulcer margin, proliferating and dividing epithelial cells migrate onto the granulation tissue to cover (re-epithelialize) the ulcer and bud into granulation tissue to reconstruct glandular structures within the ulcer scar. Re-epithelialization and reconstruction of epithelial structures is under control of epidermal growth factor (EGF) and related peptides which are produced locally by regenerating cells. Under control of fibroblast growth factors, granulation connective tissue grows extensively supplying (a) microvessels for restoration of the microvascular network and (b) connective tissue cells for restoration of the lamina propria within the mucosal scar. The final outcome of the healing process reflects a dynamic interaction between the epithelial component for the 'healing' zone at the ulcer margin and the connective tissue component (including microvessels) originating from the granulation tissue. Depending on these interactions, mucosal scar can be of good quality (restoration close to normal) or poor quality. While a number of pharmacologic agents affect gastric ulcer healing, it is unknown whether these drugs affect the quality of mucosal architecture reconstruction. In previous studies, we demonstrated that sucralfate exerts a trophic effect on gastric mucosa and, compared with omeprazole, improves the quality of restored mucosal structures within the scar of healed gastric ulcers. In the most recent studies, we demonstrated that treatment with sucralfate activates genes for EGF, bFGF, and their receptors, significantly increasing (vs placebo and omeprazole) expression of EGF and its receptor in ulcerated gastric mucosa.

CONCLUSION

Thus, the superior quality of ulcer healing by sucralfate (versus omeprazole) is most likely based on its capacity to induce and stimulate expression of EGF, bFGF, and their receptors.

Omentum and basic fibroblast growth factor in healing of chronic gastric ulcerations in rats

Omentum was shown to exhibit angiogenic activity, but its role in healing of chronic gastric ulcers is unknown. This study was designed to compare the effects of omentum and basic fibroblast growth factor (bFGF), a potent angiogenic factor, on healing of chronic gastric ulcers in rats. Several series of rats with gastric ulcers were used: series A with intact omentum (control), series B with omentum resected, and series C with omentum placed on the serosal side of the ulcer. Series A-C were divided into four groups treated with vehicle (I); indomethacin (II), an inhibitor of prostaglandin formation, difluoromethylornithine (DFMO) (III); an inhibitor of polyamine biosynthesis or bFGF (IV). Seven days after ulcer induction, the animals were anesthetized, the gastric blood flow (GBF) was determined by laser Doppler flowmetry (LDF), and the ulcer area was measured by planimetry. Biopsy samples of the ulcer margin were taken for determination of the number of capillaries and myofibroblasts in the granulation tissue. Attachment of omentum significantly accelerated ulcer healing, whereas omentectomy delayed this process. LDF revealed the decrease in the GBF at the ulcer margin to 45% and at the ulcer bed to 18% of the value recorded in the intact adjacent mucosa. Attachment of the omentum significantly increased the blood flow at the ulcer margin and increased the number of capillaries and myofibroblasts in the granulation tissue. Indomethacin (1 mg/kg/day) that inhibited mucosal PGE2 by about 85% delayed significantly ulcer healing without affecting the blood flow in the ulcer area.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of misoprostol on delayed ulcer healing induced by aspirin

Clinical studies have suggested that treatment with the prostaglandin E1 analog, misoprostol, leads to significant healing of ulcers in patients taking regular nonsteroidal antiinflammatory therapy. This study aimed to investigate mechanisms involved in this healing using a rat model. Gastric ulcers were induced by application of acetic acid using a standard technique. Rats were treated with 200 mg/kg aspirin, 100 micrograms/kg misoprostol, a combination of both treatments, or methylcellulose vehicle for up to two weeks, starting two days after ulcer induction. Ulcers were assessed by macroscopic measurements of area and by quantitative histological measurements. Aspirin delayed ulcer healing compared with controls, while misoprostol significantly reversed this effect. Quantitative histology revealed that misoprostol cotreatment significantly increased mucosal regeneration compared with aspirin treatment alone. However, misoprostol did not reverse the effects of aspirin on an index of wound contraction. We conclude that treatment with misoprostol significantly reverses the delayed healing effect of aspirin, and this may occur via an effect on epithelial regeneration.

Influence of capsaicin-sensitive afferent fibers on acetic acid-induced chronic gastric ulcers in rats

Accumulating evidence indicates that capsaicin-sensitive afferent fibers play a pivotal role in acute gastroprotection. However, whether they also influence healing of chronic gastric ulcers is still unknown. The effects of ablation of sensory neurons on acetic acid-induced chronic gastric ulcers in rats were investigated at morphologic and biochemical levels by computerized imaging analysis of the ulcerated area, histologic examination, and neuropeptide determination. Afferent nerve ablation, as a result of treating rats with a neurotoxic dose of capsaicin (50 + 50 mg/kg subcutaneously over 2 days), produced a significant increase in the ulcer area at 1 and 2 weeks after acetic acid injection. The delay in ulcer healing was associated with a marked and persistent decrease in tissue calcitonin gene-related peptide-like immunoreactivity, whereas gastric vasoactive intestinal polypeptide was unaffected by capsaicin pretreatment. Histologically, as compared with control rats, capsaicin-desensitized animals only differed in a slight increase in the inflammatory infiltrate during the early phase of ulcer formation. These findings suggest that capsaicin-sensitive afferent fibers may play a role in the healing of chronic experimental gastric ulcers in rats, but the underlying mechanisms remain to be elucidated and deserve further investigation.

Inhibition of nitric oxide synthase delays healing of chronic gastric ulcers

We investigated the influence of inhibition of nitric oxide (NO) synthase, using NG-nitro-L-arginine (L-NNA) or NG-mono-methyl-L-arginine (L-NMMA), and the effects of exogenous donor of NO, such as glyceryl trinitrate (GTN), on the healing of chronic gastric ulcers induced by acetic acid, on gastric blood flow around the ulcer and on the number of capillaries in the granulation tissue at the ulcer bed. The inhibition of NO synthase resulted in a delay in ulcer healing and in a reduction in blood flow at the ulcer margin and in the number of capillaries in the granulation tissue at the ulcer bed. These effects of inhibition of NO synthase were antagonized, in part, by the administration of GTN or L-arginine but not D-arginine. We conclude that endogenous NO plays an important role in the maintenance of blood flow around the ulcer, in the angiogenesis in the granulation tissue and, thus, in the healing of gastric ulcers.

Fibroblast growth factor in gastroprotection and ulcer healing: interaction with sucralfate

The study was designed to determine the gastroprotective and ulcer healing efficacy of basic transforming growth factor (bFGF) and to assess whether this peptide contributes to the action of sucralfate on the rat stomach. Application of human recombinant bFGF (1-100 micrograms/kg/hour subcutaneously) failed to affect the formation of acute gastric lesions induced by 100% ethanol and acidified aspirin but reduced the stress induced by gastric lesions. Sucralfate (100-200 mg/kg given orally) protected gastric mucosa against the ethanol, aspirin, and stress induced acute gastric lesions but the addition of bFGF (100 micrograms/kg subcutaneously or intragastrically) failed to affect sucralfate induced protection against ethanol or aspirin but increased that against stress. Administration of bFGF (3-300 micrograms/kg/day) by an intragastric or an intraperitoneal route or sucralfate (400 mg/kg/day) orally to rats with acetic acid induced gastric ulcers, enhanced the healing rate of these ulcers during seven day treatment in a dose dependent manner. This was accompanied by a pronounced increase in the number of capillaries and myofibroblasts and in DNA synthesis and DNA and RNA concentrations in the granulation tissue in the ulcer area. [125I]bFGF (1 microCi) applied subcutaneously or intragastrically accumulated in two to threefold higher amounts in the ulcer area than in the intact mucosa, particularly in rats treated with sucralfate. Concurrent treatment with indomethacin (2 mg/kg intraperitoneally) delayed ulcer healing and reduced the binding of labelled bFGF to the ulcer area, angiogenesis, and DNA synthesis by sucralfate. Addition of [125I]bFGF to sucralfate at various pHs resulted in the coprecipitation of bFGF by sucralfate in a pH dependent manner from about 10% at pH 7.0 to 90% at pH 1.5. Thus bFGF shows little protective activity and is not essential for gastroprotection afforded by sucralfate but plays an important part in healing of gastric ulcers possibly due to its growth promoting and angiogenic actions.

Increased expression of epidermal growth factor receptor during gastric ulcer healing in rats

Expression of epidermal growth factor receptor (EGFR) was studied immunohistochemically in rat gastric mucosa during healing of acetic acid-induced ulcers. In normal control gastric oxyntic mucosa, EGFR was expressed in proliferative zone cells and in some parietal cells. In mucosa of the ulcer margin, at 3, 7, and 16 days after ulcer induction, there was a 75-fold increase (over controls) in the number of cells expressing EGFR. Seventy percent of ulcers healed by the 16th day, and all were healed by the 25th day. The mucosal scar that replaced the ulcer was composed of dilated glands lined with poorly or aberrantly differentiated cells showing persistence of increased EGFR expression. An increased EGFR expression indicates an important role of EGF in ulcer healing and scar formation.

Quality of gastric ulcer healing: histological and ultrastructural assessment

It has long been assumed that the mucosa in areas of grossly 'healed' gastric or duodenal ulcers returns to normal, either spontaneously or after treatment. This assumption is based almost entirely upon visual, superficial examination by endoscopy. Few, if any, histological and ultrastructural studies examined the deeper mucosa in the areas of grossly healed ulcers. In several experimental studies, we analysed the development, evolution, and healing of acetic acid-induced gastric ulcers in rats and assessed the histological and ultrastructural features (structure and cellular composition) of the gastric mucosa in areas of grossly healed ulcers. The gastric mucosa of grossly 'healed' ulcers showed re-epithelialization of the mucosal surface at every study interval (2 weeks, 2, 3, and 4 months), but the subepithelial mucosa displayed prominent abnormalities. Two patterns of scarring were distinguished: (a) the mucosa in the area of healed ulcer was thinner (25-45% thinner than normal mucosa) with increased connective tissue and poor differentiation and/or degenerative changes in the glandular cells; and (b) the mucosa displayed a marked dilation of gastric glands with poor differentiation of the glandular cells and a reduction in the supportive microvascular network. It is theorized that these abnormalities could interfere with oxygenation, nutrient supply, and mucosal resistance and defence; therefore, they could be a basis for ulcer recurrence. These observations indicate that the quality of mucosal structural restoration rather than the speed of ulcer healing is the most important factor in determining risk of ulcer recurrence. The clinical relevance of these findings is supported by a preliminary study in which marked histological abnormalities were found in the subepithelial mucosa in patients with 'healed' duodenal ulcers.