Gastric mucosal injury induced by local ischemia-reperfusion in rats. Role of endogenous endothelin-1 and free radical

L-Carnitine and Potential Protective Effects Against Ischemia-Reperfusion Injury in Noncardiac Organs: From Experimental Data to Potential Clinical Applications

The mechanism of ischemia-reperfusion (I/R) injury is complex and multifactorial. In this condition, systemic event results in morbidity and mortality in several pathologies, including myocardial infarction, ischemic stroke, acute kidney injury, trauma, and circulatory arrest. Hypoxia over ischemia phase leads to energy imbalance and changes of cellular homeostasis and functional or structural alterations. In addition, during the reperfusion period, some events, including calcium influx, release of intracellular enzymes, and cell membrane integrity breakdown, cause cell death. L-carnitine (LC) and its derivatives have been suggested to improve tolerance against I/R injury in various tissues. The favorable effects of LC are possibly mediated by its antioxidant and anti-inflammatory effects or by other capability due to increase in the intracellular carnitine content. In this article, anti-ischemic properties of LC and its derivative in noncardiac organs are reviewed using relative animal and human research. Although most of the studies on noncardiac internal organs have shown protective effects of LC administration against I/R injury, more clinical trials are needed to clarify the clinical importance of LC as a treatment option for I/R-induced injury.

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

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

Gastric mucosa injury quantification in an ischemia - Reperfusion experimental model

Gastric ischemia - reperfusion (I/R) injury is an important clinical problem, which is developed in more than 80% of critically ill patients. I/R is caused by interruption of blood supply to an organ or tissue followed by blood reflow into the exposed area, leading to multiple organ failure and death. Gastric reactance has been proposed to measure tissue injury caused by ischemia. The present study evaluates a new method to quantify gastric tissue damage due to I/R, and assess its relation to gastric reactance changes. Twenty Wistar rats were randomly assigned to 4 groups: control, ischemia, I/R 30 min, I/R 1 h. Local gastric ischemia was induced by clamping the celiac artery for 30 min and reperfusion was done for 30-60 min. In all groups, gastric impedance was measured, and then gastric mucosa samples were taken for light microscopy. There were statistical significant differences (p <;0.05) among the groups with respect to the index of gastric injury proposed, which was greater in I/R 1 h group. Also, impedance parameters increased in I/R groups with respect to control, and ischemia groups. The proposed index of gastric injury allowed gastric mucosa damage quantification, and it was related with gastric impedance increase, which is an objective method to evaluate tissue injury.

Theoretical Studies of Substitutionally Doped Single-Walled Nanotubes

The rich chemistry of single-walled carbon nanotubes (SWCNTs) is enhanced by substitutional doping, a process in which a single atom of the nanotube sidewall is replaced by a heteroatom. These so-called heteroatom-substituted SWCNTs (HSWCNTs) exhibit unique chemical and physical properties not observed in their corresponding undoped congeners. Herein, we present theoretical studies of both main group element and transition metal-doped HSWCNTs. Within density functional theory (DFT), we discuss mechanistic details of their proposed synthesis from vacancy-defected SWCNTs and describe their geometric and electronic properties. Additionally, we propose applications for these nanomaterials in nanosensing, nanoelectronics, and nanocatalysis.

Administration of angiotensin II in the paraventricular nucleus protects gastric mucosa from ischemia-reperfusion injury

Our previous study demonstrated that electrical stimulation of the hypothalamic paraventricular nucleus (PVN) protects against gastric ischemia-reperfusion (GI-R) injury, but it is still unknown whether angiotensin II (Ang II) in the PVN plays a role in the development of GI-R. The purpose of this study was to investigate the effect of Ang II in the PVN on GI-R injury. GI-R injury was induced in rats by clamping the celiac artery for 30 min, and then reperfusing for 30 min, 1 h, 3 h, 6 h or 24 h, respectively. A cannula was inserted into the unilateral PVN for microinjection of Ang II. The extent of gastric mucosal damage was determined by gross and histological methods. We found that microinjection of pharmacological doses of Ang II (3, 30, and 300 ng) into the PVN dose-dependently inhibited GI-R injury, and that Ang II (30 ng) markedly attenuated GI-R injury at 1 h and 3 h after reperfusion. The effect of Ang II was prevented by pretreatment with the Ang II AT1 receptor antagonist losartan (5 microg) into the lateral cerebral ventricle. Furthermore, the protective effect of Ang II on GI-R injury was abolished by propranolol (1 mg/kg, i.v.) or disconnection of the nerves innervating the adrenal glands, was augmented by sympathectomy or phentolamine (1 mg/kg, i.v.), and was not affected by subdiaphragmatic vagotomy or atropine (1 mg/kg, i.v.). These results indicate that the PVN is a responsive site for central Ang II-induced protection against GI-R injury. The central effects of Ang II are mediated by AT1 receptors in the PVN, and the peripheral effects by a sympathetic-adrenal gland/beta-adrenoceptor pathway.

Effects of L-carnitine on neutrophil-mediated ischemia-reperfusion injury in rat stomach

Reactive oxygen metabolites play an important role in ischemia-reperfusion related gastric injury. Primary sources of reactive oxygen metabolites seem to be the xanthine/xanthine oxidase system and neutrophils accumulating within the reperfused tissue. Tissue myeloperoxidase activity is an important index of neutrophil accumulation. The purpose of the present study was to clarify the effect of L-carnitine on the accumulation of neutrophils and neutrophil-induced gastric mucosal damage in rats exposed to ischemia-reperfusion. Rats were randomly divided into three groups: sham-operated, ischemia-reperfusion and ischemia-reperfusion plus L-carnitine groups. Ischemia was induced by clamping the celiac artery for 30 min and then reperfusion was established for 60 min. Gastric injury was assessed by measuring myeloperoxidase activity in gastric tissue. The neutrophil accumulation and hemorrhagic lesions due to ischemia-reperfusion in gastric mucosa were ascertained in a histological study. L-Carnitine (100 mg kg(-1)) administrated intravenously 5 min before ischemia significantly reduced both the gastric injury and myeloperoxidase activity compared with the ischemia-reperfusion group. The results suggest that L-carnitine provides marked protection against ischemia-reperfusion-related gastric injury which could be due to its ability to reduce neutrophil accumulation in ischemic tissue.

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

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

Changes in endothelin-1 gene expression in the gastric mucosa of rats under cold-restraint-stress

OBJECTIVE

To investigate in rats the role of endothelin (ET)-1 gene expression in the development and progression of acute gastric mucosal lesions (AGML) induced by stress, and the effect of BQ-123 (a special ETA receptor antagonist) on the AGML.

METHODS

A rat model of gastric ulcer induced by cold-restraint-stress (CRS) was used. ET-1 concentrations in the plasma and gastric mucosa were determined by radioimmunoassay (RIA), gastric mucosa blood flow (GMBF) was measured with a laser Doppler flow meter, the ulcer index (UI) was used to estimate the degree of gastric mucosa damage and the expression levels of ET-1 mRNA in the gastric mucosa were measured using dot blot and reverse transcription polymerase chain reaction (RT-PCR). Different doses of BQ-123 were administered via the left femoral vein prior to the stress in order to observe the effects of BQ-123 on the ET-1 concentrations in the plasma and gastric mucosa, the GMBF and the UI.

RESULTS

Compared with the normal controls, the ET-1 concentrations in the plasma and gastric mucosa of the stressed rats were increased significantly (P < 0.05), the GMBF was decreased markedly (P < 0.01), and the UI increased dramatically (P < 0.01). There was a significant positive correlation between the gastric mucosal EF-1 concentration and the UI (r = 0.98, P < 0.01), and a significant negative correlation between the gastric mucosal ET-1 concentration and GMBF (r = -0.89, P < 0.01) and also between the UI and GMBF (r = -0.98, P < 0.01). The expression level of ET-1 mRNA in the gastric mucosa of the stressed rats increased significantly compared with that of the normal controls (P < 0.01), and there was a positive correlation between the expression of ET-1 mRNA and the ET-1 concentration in the gastric mucosa (r = 0.93, P < 0.01). Compared with the untreated animals, the GMBF was increased (P < 0.01) and the UI decreased significantly (P < 0.01) in the BQ-123-treated rats, and the dose of BQ-123 correlated with the degree of change in the GMBF and UI; however, the ET-1 concentrations of either the plasma or the gastric mucosa did not change markedly in the BQ-123-treated animals (P > 0.05).

CONCLUSION

The present study showed that the level of expression of ET-1 mRNA and the synthesis of ET-1 in the gastric mucosa both increased significantly, which suggests that the increased concentration of endogenous ET-1 may be involved in the development and progression of stress ulcer (acute gastric mucosa lesion). The mechanism of action may be associated with a reduction of GMBF induced by ETAR-mediated vasoconstriction. BQ-123 can dose-dependently attenuate significantly the degree of damage to the gastric mucosa induced by stress, and may have therapeutic benefits for stress ulcer.

Gastroprotective effect of leptin on gastric mucosal injury induced by ischemia-reperfusion is related to gastric histamine content in rats

Leptin has cytoprotective effect to gastric mucosal injury in rats. We aimed to test the hypothesis that leptin induced histamine is involved in the prevention of ischemia-reperfusion (I/R) induced gastric mucosal injury in rats. At the end of the 30 min celiac artery occlusion and 12h reperfusion process, serum and gastric tissue samples were taken from three group of rats to measure oxidative status, histamine levels and for histological examinations. Leptin decreased ulcer and polymorphonuclear leukocyte (PMNL) index, and serum malondialdehyde (MDA) and protein carbonyl content but increased gastric tissue histamine levels. We concluded that leptin exerts a protective effect on gastric mucosa to I/R induced gastric injury probably through increasing tissue histamine content which, in turn, maintain the gastric mucosal blood flow.

Endothelin receptor blockers reduce I/R-induced intestinal mucosal injury: role of blood flow

The aim of the present study was to assess the role of endothelin (ET) in ischemia-reperfusion (I/R)-induced mucosal injury. Mucosal permeability ((51)Cr-EDTA clearance) and tissue myeloperoxidase (MPO) activity were significantly increased after 30 min of ischemia followed by 30 min of reperfusion. The I/R-induced increases in mucosal permeability and polymorphonuclear leukocyte (PMN) infiltration were significantly attenuated by pretreatments with ET(A) (BQ-485) and/or ET(B) (BQ-788) receptor antagonists. Monoclonal antibody (MAb) directed against intercellular adhesion molecule-1 (ICAM-1; MAb 1A29) and superoxide dismutase (SOD) pretreatments significantly attenuated the increased mucosal permeability and PMN infiltration in a similar manner as with ET receptor antagonists. Superior mesenteric artery blood flow was significantly reduced during the reperfusion period. Both ET receptor antagonists caused a significant rise in blood flow compared with an untreated I/R group. In conclusion, our data suggest that ET(A) and/or ET(B) receptors, ICAM-1, and superoxide play an important role in I/R-induced mucosal dysfunction and PMN infiltration. Furthermore, ET is involved in the pathogenesis of post-reperfusion-induced damage and beneficial effects of ET receptor antagonism are related to an improvement of disturbed blood flow during the reperfusion period.

Gene expression and gene therapy in experimental duodenal ulceration

Gastroduodenal ulceration is still poorly understood and changes in gene expression may provide new mechanistic insights. Previously, we demonstrated that angiogenic growth factors are potent ulcer healing agents, and the synthesis of bFGF, PDGF and VEGF is enhanced early in duodenal ulcer healing. The initial molecular event in duodenal ulceration seems to be the organ-specific early release of ET-1 in the pre-ulcerogenic stages after the administration of duodenal ulcerogen cysteamine in rats. We also briefly review here data from literature indicating a central role of ET-1 in gastroduodenal ulceration. After studying the involvement of immediate early genes (e.g. egr-1, Sp1) in ulcer development, we now investigated expression of other genes in the duodenal mucosa in the early stages of chemically induced duodenal ulceration in rats. Following a brief review of principles of gene expression and gene therapy, we review our preliminary gene expression studies, involving monitoring about 1200 genes which revealed about 160 signals and prominent changes in about 30 genes in the early stages of experimental duodenal ulceration. Cysteamine enhanced ET-B receptor gene expression in 30 min, while transcription factors (MAX, STAT 3) showed increased expression in 12 h. We recently also initiated gene therapy studies to enhance the local synthesis of PDGF and VEGF to accelerate duodenal ulcer healing, using a single dose of naked DNA (ND) or adenoviral (AV) vectors of VEGF and PDGF in rats with cysteamine-induced duodenal ulcers. Gene therapy with ND or AV of VEGF or PDGF significantly accelerated chronic duodenal ulcer healing, and increased levels of VEGF and PDGF were detected by Western blotting and ELISA in duodenal mucosa after both VEGF and PDGF gene therapy. Thus, gene expression studies provide new insights into the molecular mechanisms of duodenal ulceration and VEGF or PDGF gene therapy seems to be a new option to achieve a rapid ulcer healing.

Role of endothelin-converting enzyme-1 in the suppression of constitutive nitric oxide synthase in rat gastric mucosal injury by indomethacin

BACKGROUND

Disturbances in nitric oxide generation and the release of a vasoactive peptide, endothelin-1 (ET-1), are well recognized early events in pathogenesis of NSAID-induced gastropathy. In this study using phosphoramidon, a potent inhibitor of endothelin-converting enzyme-1 (ECE-1), we investigated the influence of ET-1 on the expression of constitutive (cNOS) and inducible nitric oxide synthase (NOS-2) during gastric mucosal injury caused by indomethacin.

METHODS

The experiments were conducted with groups of rats pretreated intragastrically with phosphoramidon (10, 20, and 40 mg/kg) or vehicle, followed 30 min later by an intragastric dose of indomethacin (60 mg/kg). The animals were killed 4 h later and their mucosal tissue subjected to macroscopic damage assessment and biochemical measurements.

RESULTS

In the absence of phosphoramidon, indomethacin caused extensive multiple hemorrhagic lesions of glandular mucosa, accompanied by a 29.9-fold increase in epithelial cell apoptosis, a 13.3-fold increase in NOS-2 and a 5.5-fold decline in the activity of cNOS, while the mucosal expression of ECE-1 activity increased 4-fold and the level of ET-1 showed a 4.8-fold increase. Pretreatment with phosphoramidon produced dose-dependent reduction in the extent of mucosal damage caused by indomethacin, accompanied by a significant recovery in the expression of cNOS, and a marked decline in ECE-1, epithelial cell apoptosis and the mucosal level of ET-1. Phosphoramidon, however, had no effect on the indomethacin-induced increase in the mucosal expression of NOS-2.

CONCLUSIONS

The results suggest that suppression of ET-1 generation counters the mucosal drop in cNOS and the extent of gastric mucosal damage caused by indomethacin, but has no effect on the mucosal responses associated with up-regulation of NOS-2 expression. Hence, only cNOS plays a role in the protection of gastric mucosa against damage by NSAIDs.

Endogenous endothelin in a rat model of acute colonic mucosal injury

BACKGROUND

Endothelin (ET) is involved in various biologic activities in non-vascular and vascular tissues. While ET has some significant effects on gastrointestinal functions, the possible role of endogenous ET in the host response to mucosal injury has not been well clarified.

METHODS

The present study describes an investigation of the effects of an endothelin A receptor antagonist, BQ-123, on lactate dehydrogenase (LDH), mucus and albumin flux into the perfusate in a rat model of acute colonic injury, induced by acetic acid perfusion. The present study also examined localization of ET in damaged rat colons by using immunohistochemistry.

RESULTS

A 4% acetic acid treatment induced mild mucosal damage of perfused rat colon and increased LDH as well as albumin and protein-bound hexose release into the perfusate. Pretreatment with BQ-123 significantly reduced LDH activity and protein-bound hexose concentration in the perfusate and delayed the reduction of albumin leakage from damaged mucosa. Vascular endothelial, neural and surface epithelial cells of the colon showed strong ET-like immunoreactivity. Mucosal damage markedly influenced ET expression by epithelial cells. Mild mucosal damage decreased the ET expression by surface epithelial cells while moderate mucosal damage induced a mosaic location of ET-positive epithelial cells in the crypt. Severe mucosal damage abolished the ET expression by epithelial cells.

CONCLUSIONS

Endothelin may play a role in the host response to acute mucosal damage. Mucosal ET production is significantly affected by mucosal injury.

Role of gastric acid secretion in progression of acute gastric erosions induced by ischemia-reperfusion into gastric ulcers

Ischemia followed by reperfusion is known to produce gastric lesions due to oxidative stress, but the role of gastric H(+) secretion in the formation of this mucosal injury remains unknown. We studied alterations in gastric acid secretion and gastric histamine content, as well as the expression of histidine-decarboxylase and interleukin-1beta during the mucosal recovery from ischemia-reperfusion erosions. Gastric secretion was studied in rats (series A) with gastric fistula before, during and after the ischemia induced by clamping of celiac artery for 0.5 h followed by reperfusion in animals pretreated with vehicle (saline), omeprazole, a proton pump inhibitor, or ranitidine, a histamine (H(2)) receptor antagonist. In series B, the animals were submitted to 0.5 h of ischemia followed by 1 h of reperfusion and then anesthetized at 0, 3, 12 and 24 h or 3, 5, 10 or 15 days after the end of ischemia-reperfusion to determine gastric blood flow by H(2)-gas clearance technique, area of gastric lesions, plasma gastrin and interleukin-1beta levels, histamine content by radioimmunoassay (RIA) and expression of histidine-decarboxylase and interleukin-1beta mRNA by reverse transcription polymerase chain reaction. Clamping of celiac artery caused cessation of gastric blood flow and almost complete suppression of basal gastric acid secretion (series A) that returned gradually to the control value at day 3 after ischemia-reperfusion, accompanied by the rise in plasma gastrin levels, pronounced expression of histidine-decarboxylase mRNA and increased mucosal histamine content. Ischemia, followed by 1 h of reperfusion, produced gastric erosions (series B) that reached maximum at 12 h, but then declined at 24 h. These erosions progressed at day 3 into deeper ulcers whose area declined progressively within the next 5-15 days. The gastric blood ceased to flow (series B) during 30 min of clamping and was reduced throughout the period of healing of acute erosions, being accompanied by a gradual rise in mucosal interleukin-1beta mRNA content and in plasma interleukin-1beta levels. Treatment with omeprazole or ranitidine, which completely suppressed gastric acid secretion and significantly raised plasma gastrin level, greatly reduced the formation of erosive lesions preventing the progression of these lesions to chronic gastric ulcers, and this was accompanied by the rise in gastric blood flow and plasma gastrin levels and the significant attenuation of plasma interleukin-1beta levels. The ranitidine and omeprazole-induced suppression of ischemia-reperfusion erosions were abolished by the instillation of exogenous 0.2 N HCl into the stomach of these rats. The histidine-decarboxylase was faintly expressed in the intact gastric mucosa, but strongly upregulated during mucosal recovery from the damage induced by ischemia-reperfusion. We conclude that following ischemia-reperfusion: (1) gastric acid secretion, gastric microcirculation and histamine production markedly decline, while interleukin-1beta release significantly increases, probably playing an important role in the progression of acute lesions into chronic gastric ulcerations; (2) the suppression of gastric acid secretion by omeprazole and ranitidine, that induces hypergastrinemia, prevents the progression of gastric erosions into ulcers; and (3) the addition of exogenous acid restores the progression of the acute lesions into gastric ulcers, indicating that gastric acid plays a key role in ulcerogenesis induced by ischemia-reperfusion.

Induction of endothelin-converting enzyme-1 in gastric mucosal injury by idomethacin

Endothelin-1 (ET-1) is a 21-amino acid vasoactive peptide produced from a 39-amino acid biologically inactive peptide, big ET-1, by the action of endothelin-converting enzyme-1 (ECE-1). We investigated gastric mucosal expression of ECE-1 during a 16 h course of inflammatory responses associated with gastric mucosal injury caused by indomethacin. The extent of gastric mucosal damage reached a maximum 4 h following the drug, and was accompanied by a 3.9-fold enhancement in the expression of ECE-1 activity and a significant elevation in ET-1 (4.5-fold), TNF-alpha (11.3-fold), and apoptosis (29.9-fold). A 37.2% decrease in the severity of lesion 16 h following the drug was associated with a 44.5% reduction in the mucosal expression of ECE-1 activity and a decline in TNF-alpha (64%), ET-1 (65.2%), and apoptosis (72.3%). The results demonstrate that gastric mucosal injury by indomethacin is associated with up-regulation of ECE-1 expression, which leads to the enhancement of ET-1 production, induction of TNF-alpha, and triggering apoptotic events that disrupt gastric mucosal homeostasis.

Downregulation of endothelin-1 by interleukin-4 during gastric ulcer healing

We investigated the course of events associated with gastric ulcer healing by analyzing mucosal expression of interleukin-4 (IL-4), endothelin-1 (ET-1), tumor necrosis factor-alpha (TNF-alpha), and the activity of constitutive (cNOS) and inducible nitric oxide synthase (NOS-2). Ulcer onset was characterized by a massive epithelial apoptosis associated with a 5.7-fold increase in TNF-alpha, a 17.5-fold increase in NOS-2, and a 3.9-fold increase in ET-1, while mucosal expression of cNOS showed a 7.6-fold drop and IL-4 fell by 37.2%. Healing was accompanied by a rapid raise in IL-4; decrease in apoptosis, TNF-alpha, ET-1, and NOS-2; and a slow recovery in cNOS. The expression of IL-4 returned to control levels by the 7th day of healing and that of ET-1 and TNF-alpha by the 14th day, while apoptotic DNA fragmentation and the activity of NOS-2 remained significantly elevated beyond the 14-day period. The results suggest that a decrease in the mucosal level of IL-4 at ulcer onset may well be a key factor causing dysregulation of ET-1 production, induction of TNF-alpha, and triggering the apoptotic events that affect the efficiency of mucosal repair.

Role of endothelin-1 and constitutive nitric oxide synthase in gastric mucosal resistance to indomethacin injury: effect of antiulcer agents

BACKGROUND

Endothelin-1 (ET-1) and nitric oxide, recognized key mediators implicated in the pathophysiology of gastric mucosal injury, are known to exert opposing effects on the inflammatory processes mediated by regulatory cytokines. In this study we investigated the mucosal expression of ET-1 and interleukin-4 (IL-4) and the activity of constitutive nitric oxide synthase (cNOS) during indomethacin-induced gastric mucosal injury and evaluated the effect of antiulcer agents, omeprazole and sucralfate, on this process.

METHODS

The experiments were conducted with groups of rats pretreated intragastrically with omeprazole (40 mg/kg), sucralfate (200 mg/kg), or vehicle, followed 30 min later by an intragastric dose of indomethacin (60 mg/kg). The animals were killed 2 h later, and their mucosal tissue subjected to macroscopic damage assessment, ET-1 and IL-4 expression assay, and the measurement of cNOS activity.

RESULTS

In the absence of antiulcer agents, indomethacin caused multiple hemorrhagic lesions and extensive epithelial cell apoptosis, accompanied by a 20.7% reduction in IL-4, a 3.1-fold increase in mucosal expression of ET-1, and a 4.2-fold decrease in cNOS. Pretreatment with a gastroprotective agent, sucralfate, produced a 59.7% reduction in the mucosal damage caused by indomethacin, a 41.2% decrease in epithelial cell apoptosis, and a 56.5% reduction in ET-1, whereas the expression of IL-4 increased by 29.3% and that of cNOS showed a 3.3-fold increase. In contrast, the pretreatment with a proton pump inhibitor, omeprazole, led to only a 10.5% reduction in the extent of mucosal damage caused by indomethacin and a 13% decrease in apoptosis, whereas the expression of cNOS increased by 68.7% and ET-1 by 12.2%, and the level of IL-4 remained essentially unchanged.

CONCLUSIONS

The results suggest that an increase in the vasoconstrictive ET-1 level combined with a decrease in regulatory cytokine, IL-4, and a loss of compensatory action by cNOS may be responsible for the gastric mucosal injury caused by indomethacin. Our findings also indicate the value of sucralfate in countering the untoward gastrointestinal side effects of nonsteroidal anti-inflammatory drug therapy.

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

In this study, we investigated gastric mucosal inflammatory responses during Helicobacter pylori lipopolysaccharide-induced gastritis by analyzing the interplay between mucosal expression of endothelin-1 (ET-1), interleukin-4 (IL-4) and tumor necrosis factor-alpha (TNF-alpha). The assays conducted 4 days after intragastric dose of H. pylori lipopolysaccharide demonstrated a pattern of acute mucosal reaction characterized by the inflammatory infiltration of the lamina propria, hyperemia, and epithelial hemorrhage. This was accompanied by a 3.1-fold increase in the mucosal expression of ET-1 and a 9-fold enhancement in TNF-alpha, while the level of IL-4 showed a 20.8% decline. The results implicate ET-1 in gastric mucosal responses to H. pylori, and suggest that an increase in its level, combined with a loss of compensatory action by IL-4, may be responsible for the induction of TNF-alpha and triggering apoptotic events that exacerbate the inflammatory process.

Anti-ulcerogenic properties of endothelin receptor antagonists in the rat

BACKGROUND

Endothelins have been implicated in gastric mucosal damage in a variety of animal models. Exogenous ET-1 and ET-3 are causally associated with experimental gastric ulcers. Furthermore, clinical reports also show elevated plasma and gastric mucosal endothelin-1 levels in patients suffering from peptic ulcers.

AIM

To study the possibility that endothelin receptor antagonists may have beneficial effects and prevent the development of gastric ulcers. We have tested in rats the orally-active endothelin antagonist bosentan (Ro 47-0203) and Ro 48-5695, which is 10-30 times more potent than bosentan on endothelin receptors.

METHODS

Water immersion restrained stress (WIRS) and indomethacin were used to provoke gastric mucosal damage. Endothelin receptor antagonists were administered orally prior to the induction of gastric damage. The gastric lesion index (mm), assessed macroscopically, and myeloperoxidase (MPO) activity were used as markers of the extent of mucosal injury.

RESULTS

Bosentan at 100 and 30 mg/kg administered orally caused attenuation of gastric damage in the WIRS model by 58% and 42%, respectively. Bosentan also caused complete reduction of MPO activity. In indomethacin-induced gastric damage, 100 mg/kg bosentan attenuated gastric damage by 45% and 61% as measured by the gastric lesion index and MPO activity respectively. Ro 48-5695 was at least 30 times more potent than bosentan in reducing indomethacin-induced mucosal damage and at 3 mg/kg, caused a decrease of 49% in the gastric lesion index and a reduction in MPO activity of 41%. Bosentan and Ro 48-5695 possess weak antisecretory properties as tested in the mouse gastric gland assay, than cannot, alone, account for their anti-ulcer properties.

CONCLUSIONS

Both endothelin receptor antagonists prevented the development of gastric mucosal injury in the rat. Disturbances in the gastric microcirculation are responsible for the development of experimental gastric ulcers. The anti-ulcer properties of these two endothelin antagonists suggest possible new therapeutic approaches to controlling gastric inflammation.