Maintenance Of Gastric Mucosal Integrity Research Articles

Influence of the Novel Histamine H3 Receptor Antagonist/Inverse Agonist M39 on Gastroprotection and PGE2 Production Induced by (R)-Alpha-Methylhistamine in C57BL/6 Mice.

The role of histamine H3 receptors (H3Rs) in the regulation of gastroprotection and production of prostaglandin E2 (PGE2) as well as somatostatin remains contradictory. Therefore, the effects of the H3R antagonist/inverse agonist M39 on in vivo acidified ethanol-induced gastric ulcers and gastric acid secretion in the C57BL/6 mice were assessed. Results showed that acute systemic administration of H3R agonist (R)-α-methylhistamine (RAMH, 100 mg/kg, i.g.) significantly reduced the severity of ulcer index, increased gastric acid output, and increased mucosal PGE2 production without any alteration of somatostatin concentration in gastric juice. However, only acute systemic administration of the H2R agonist dimaprit (DIM, 10 mg/kg, p.o.) significantly decreased the level of somatostatin measured in gastric juice. Moreover, acute systemic administration of M39 (0.3 mg/kg, i.g.) abrogated the RAMH-induced increase of acid output as well as PGE2 production, but not the DIM (10 mg/kg, i.g.)-stimulated acid secretion, indicating that RAMH as well as M39 modulate the gastroprotective effects through interactions with histamine H3Rs. The present findings indicate that agonistic interaction with H3Rs is profoundly involved in the maintenance of gastric mucosal integrity by modulating PGE2 as well as gastric acid secretion, with no apparent role in the regulation of the inhibitory influence of somatostatin.

Role of Glucocorticoids in Gastroprotection Induced by Capsaicin

The pivotal role of capsaicin‐sensitive peptidergic sensory fibers in maintaining of gastric mucosal integrity against injurious interventions has been well established in rats and then in human. Clinical finding suggests that capsaicin‐induced gastric mucosal protection against the injurious effects of ethanol or indomethacin is due to the acute stimulatory effect of the compound. It was concluded that patients taking non‐steroidal anti‐inflammatory drugs (NSAID) regularly can decrease the incidence and severity of gastric ulceration, if they have moderate spicy foods. Opposite effect has been observed in rats desensitized by capsaicin. Functional blockade of gastric sensory nerve endings elicited by systemic capsaicin application was resulted in impaired mucosal protection against various ulcerogenic agents. Our previous findings suggest a pivotal compensatory role of glucocorticoids in maintenance of gastric mucosal integrity in rats desensitized by capsaicin. In this study, we tested if glucocorticoids can participate in capsaicin‐caused gastroprotection during NSAID‐caused gastropathy accompanied by prostaglandin deficiency in rats. Gastric injury was induced by indomethacin (IM). A single IM administration (35 mg/kg, sc) into fasting (24 h) rats caused the formation of gastric erosions 4 h after injection. The effects of small doses (0.1, 0.5, 1.0, 2.0, 3.0, 5.0, 10.0 mg/kg, sc) of capsaicin on the blood corticosterone and glucose levels and IM‐induced gastric injury were tested. A single capsaicin administration was performed one hour before IM administration. To test the participation of corticosterone in the gastroprotective effect of capsaicin, the pretreatment by the inhibitor of glucocorticoid synthesis, metyrapone (30 mg/kg, i.p., 30 min before capsaicin) was used. We found that the pretreatment with capsaicin (0.5–10.0 mg/kg, sc) reduced dose dependently the area of IM‐induced erosions. This protection was accompanied by a gradual increase in blood corticosterone and glucose levels. Metyrapone injected shortly before capsaicin administration (1.0 mg/kg) caused a fast inhibition of capsaicin‐induced corticosterone response and reversed the protective effect of capsaicin on the gastric mucosa against the IM‐produced injury. The present study confirms evidence for the powerful gastroprotective potency of capsaicin during NSAID‐caused gastropathy. The findings obtained demonstrate that capsaicin administration resulted in an increase in plasma corticosterone levels which in turn plays a pivotal role in maintaining of gastric mucosal integrity against injurious intervention of IM.Support or Funding InformationThe study was supported by grants of RSF N 19‐15‐00430 (NSAID‐caused gastropathy with prostaglandin deficiency) and RFBR N 19‐015‐00514a (capsaicin‐induced gastroprotection)This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Time-dependent course of gastric ulcer healing and molecular markers profile modulated by increased gastric mucosal content of carbon monoxide released from its pharmacological donor

Background and purposeBesides hydrogen sulfide (H2S) and nitric oxide (NO), carbon monoxide (CO) contributes to the maintenance of gastric mucosal integrity. We investigated increased CO bioavailability effects on time-dependent dynamics of gastric ulcer healing mediated by particular growth factors, anti-inflammatory and molecular pathways. Experimental approachWistar rats with gastric ulcers induced by serosal acetic acid application (day 0) were treated i.g. throughout 3, 6 or 14 days with vehicle or CO-releasing tricarbonyldichlororuthenium (II) dimer (CORM-2, 2.5 mg/kg). Gross and microscopic alterations in gastric ulcer size and gastric blood flow (GBF) at ulcer margin were determined by planimetry, histology and laser flowmetry, respectively. Gastric mRNA/protein expressions of platelet derived growth factors (PDGFA-D), insulin-like growth factor (IGF-1), epidermal growth factor (EGF), hepatocyte growth factor (HGF), vascular endothelial growth factor (VEGFA) and their receptors, heme oxygenases (HMOX), nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), cyclooxygenase (COX-2), hypoxia inducible factor (HIF)-1α, anti-inflammatory annexin-1 and transforming growth factor (TGF-β1) were assessed by real-time PCR or Western blot. TGF-β1-3 and IL-10 plasma concentration were measured using Luminex platform. Prostaglandin E2 content at ulcer margin was assessed by ELISA. Key resultsCORM-2 decreased ulcer area and increased GBF after 6 and 14 days of treatment comparing to vehicle. CO donor upregulated HGF, HGFr, VEGFR1, VEGFR2, TGF-β1, annexin-1 and maintained increased IGF-1, PDGFC and EGF expression at various time-intervals of ulcer healing. TGF-β3 and IL-10 plasma concentration were significantly increased after COMR-2 vs. vehicle. ConclusionsCO time-dependently accelerates gastric ulcer healing and raises GBF at ulcer margin by mechanism involving subsequent upregulation of anti-inflammatory, growth promoting and angiogenic factors response, not observed physiologically.

Alterations in Gastric Mucosal Expression of Calcitonin Gene-Related Peptides, Vanilloid Receptors, and Heme Oxygenase-1 Mediate Gastroprotective Action of Carbon Monoxide against Ethanol-Induced Gastric Mucosal Lesions.

Carbon monoxide (CO) has been reported to contribute to the maintenance of gastric mucosal integrity, gastroprotection, and ulcer healing. However, involvement of transient receptor potential vanilloid receptor type 1 (TRPV1) located on afferent sensory fibers endings and sensory neuropeptide calcitonin gene-related peptide (CGRP) in CO-mediated gastroprotection against ethanol-induced gastric damage has not been explored. Male Wistar rats with and without denervation of afferent sensory neurons induced by capsaicin (total dose 125 mg/kg within 3 days) were pretreated with vehicle, CO donor tricarbonyldichlororuthenium (II) dimer (CORM-2, 5 mg/kg i.g.), administered alone or with CGRP-α (10 μg/kg i.p.) or TRPV1 antagonist capsazepine (5 mg/kg i.g.), followed 30 min later by intragastric (i.g.) administration of 75% ethanol. The area of gastric damage and gastric blood flow (GBF) were assessed planimetrically and by laser flowmetry, respectively. Microscopic evaluation of ethanol-induced gastric lesions was performed after haematoxylin/eosin (H&E) or alcian blue/periodic acid-Schiff/alcian blue (AB/PAS) staining. Gastric mucosal mRNA fold change for heme oxygenase (HMOX)-1, HMOX-2, CGRP-α, CGRP-β, inducible nitric oxide synthase (iNOS), endothelial (e)NOS, neuronal (n)NOS, cyclooxygenase (COX)-1, COX-2, and protein expression for HMOX-1 and TRPV1 was determined by real-time PCR or Western blot, respectively. Pretreatment with CORM-2 combined or not with CGRP reduced ethanol-induced gastric lesions and elevated GBF. Capsaicin-denervation or co-treatment with capsazepine or CGRP and CORM-2 in capsaicin-denervated animals failed to affect these beneficial effects of CO donor. In rats with intact sensory nerves, CORM-2 increased gastric mRNA level for HMOX-1 and CGRP-α. In capsaicin-denervated rats, CORM-2 increased eNOS mRNA fold change and TRPV1 protein expression while capsaicin denervation itself decreased HMOX-1 protein expression and eNOS mRNA level. We conclude that CO prevents gastric mucosa from ethanol-induced lesions due to activation of TRPV1/CGRP-α system and accompanying increase in gastric microcirculation but independently on afferent sensory nerve activity despite the stimulation of TRPV1 protein and CGRP-α mRNA expression.

Transforming Non‐Ulcerogenic Stress Stimuli into Gastric Ulcerogenic Ones under the Circumstances of Inhibition of the Hypothalamic‐Pituitary‐Adrenocortical Axis

To investigate contribution of glucocorticoids to the maintenance of gastric mucosal integrity during stress we predominantly used ulcerogenic stress models. Using these models we demonstrated that glucocorticoids released in response to the ulcerogenic stimuli attenuated their harmful action on the gastric mucosa.In the present study we hypothesized that mild stressors does not damage the gastric mucosa due to gastroprotective action of glucocorticoids released in response to these stimuli. To verify the hypothesis the effects of normally non‐ulcerogenic mild stimuli (15‐30 min cold‐restraint) on the gastric mucosa have been studied under the circumstances of inhibition ofthe hypothalamic‐pituitary‐adrenocortical (HPA) axis in rats. The HPA axis was inhibited by: 1) fast inhibitory action of NBI 27914, the selective antagonist of cortricotropin‐releasing factor receptor type 1; 2) fast inhibitory action of metyrapone, inhibitor glucocoricoid synthesis; 3) delayed inhibitory action of a single pharmacological dose of cortisol injected one week before the onset of stress stimulus. Each of these pretreatments decreased 15‐30 min cold‐restraint‐produced corticosterone levels and resulted in an appearance of gastric lesions after the onset of this mild stress. The results suggest that in rats with glucocorticoid deficiency non‐ulcerogenic stimuli are transformed into ulcerogenic ones and confirm the hypothesis. The findings further support for the point of view that glucocorticoids released during acute stress are gastroprotective factors. Supported by the Russian Scientific Foundation (grant N 14‐15‐00790).

Mechanisms of Esophageal Protection, Gastroprotection and Ulcer Healing by Melatonin. Implications for the Therapeutic use of Melatonin in Gastroesophageal Reflux Disease (GERD) and Peptic Ulcer Disease

Melatonin is a potent reactive oxygen metabolite scavenger and antioxidant that has been shown to influence many physiological functions of the gastrointestinal (GI) tract including secretion, motility, digestion and absorption of nutrients. The role of melatonin in gastroduodenal defense and ulcer healing has been the subject of recent investigations. Melatonin produced in the GI mucosa plays an important role in protection against noxious agents thus contributing to the maintenance of GI integrity and to esophageal protection, gastroprotection and ulcer healing. This review was designed to summarize the involvement of melatonin, conventionally considered as a major hormone of the pineal gland, in the maintenance of gastric mucosal integrity, gastroprotection, ulcer healing and intestinal disorders. Melatonin was originally shown to attenuate gastric mucosal lesions but controversy exists in the literature as to whether melatonin derived from the pineal gland, considered as the major source of this indole, or rather gastrointestinal melatonin plays predominant role in gastroprotection. Intragastric and central administration of exogenous melatonin and L-tryptophan, this indoleamine precursor, affords protection against gastric hemorrhagic damage caused by the exposure of gastric mucosa to variety of non-topical and topical ulcerogens such as stress, ethanol and ischemia-reperfusion. The speed of ulcer healing in experimental animals and humans is accelerated by melatonin. This indoleamine could be also effective against the esophageal lesions provoked by reflux esophagitis in animal models and prevents the incidence of GERD in humans. The melatonin-induced gastroprotection is accompanied by an increase in gastric blood flow, plasma melatonin concentration, enhancement in mucosal generation of PGE2, luminal NO content and plasma gastrin levels. Melatonin scavenges reactive oxygen metabolites, exerts anti-oxidizing and anti-inflammatory actions and inhibits the formation of metalloproteinases- 3 and -9; both implicated in the pathogenesis of gastrointestinal injury and formation of gastric ulcers. Blockade of MT2 receptors by luzindole, significantly attenuated melatonin- and L-tryptophan-induced protection and increased the speed of ulcer healing and these effects were accompanied by an increase in the GBF and luminal content of NO suggesting that melatonin exhibits gastroprotection and hyperemia via activation of MT2 receptors and release of NO. The accumulated evidence indicates that the melatonin-induced gastroprotection and the enhancement in healing rate of gastric ulcers may involve the gastroprotective factors derived from the activation of PG/COX and NO/NOS systems as well as gastrin which also was shown to exhibit protective and trophic effects in the upper GItract. Interestingly, pinealectomy, which suppressed plasma melatonin levels, markedly exacerbated gastric lesions induced by topical and non-topical ulcerogens and these effects are counteracted by a concurrent supplementation with melatonin. Evidence is provided that exogenous melatonin and that converted from its precursor, L-tryptophan, attenuates acute gastric lesions and accelerates ulcer healing via interaction with MT2 receptors due to an enhancement of gastric microcirculation, probably mediated by NO and PG derived from NOS and COX-1 and COX-2 overexpression and activity. The pineal gland plays an important role in the limitation of gastric mucosal injury and the acceleration of ulcer healing via releasing endogenous melatonin, which attenuates oxidative stress and exerts anti-inflammatory action.

Brain neuropeptides in gastric mucosal protection.

The centrally induced gastroprotective effect of neuropeptides has been intensively studied. Besides many similarities, however, differences can also be observed in their gastroprotective actions. The gastroprotective dose-response curve proved to be either sigmoid, or bell-shaped. Additional gastrointestinal effects of neuropeptides can contribute to their mucosal protective effect. Part of the neuropeptides induces gastroprotection by peripheral administration as well. Besides vagal nerve the sympathetic nervous system may also be involved in conveying the central effect to the periphery. Better understanding of the complex mechanism of the maintenance of gastric mucosal integrity may result in the development of new strategy to enhance gastric mucosal resistance against injury.

Both supraspinal and spinal mechanisms may be involved in the maintenance of gastric mucosal integrity in the rat.

Several neuropeptides given intracerebroventricularly (i.c.v.) or into motor nucleus of vagus induce gastric mucosal defense in the rat.AimTo study 1. if central modulation of the level of endogenous gastroprotective compounds may affect gastric mucosal defense, 2. if gastroprotection can be elicited also by microinjection of neuropeptides into lateral hypothalamus (LH) or intrathecallally (i.t.).MethodsGastric mucosal damage was induced by acidified ethanol. β‐endorphin level was determined by RIA.Results1. Gastroprotection was induced via inhibition of the degradation of anandamide and 2‐arachidonoyl‐glycerol by URB 597 (1.5–29.5 nmol i.c.v) and JZL 184; (0.3–1.3 nmol i.c.v.) resp., as well as by the inhibition of the degradation of endomorphins by diprotin A (1 μmol i.c.v.). 2. Neonatal monosodium glutamate treatment reduced significantly the immunoreactive β‐endorphin content in the nucleus of the solitary tract and the mucosal protective effect of opioid peptides. 3. Gastric mucosal protection was elicited both by i.t. administration of endomorphins and β‐endorphin (10 pmol) and by microinjection of different neuropeptides into LH.Conclusion1. Elevation of the level of endocannabinoids and endomorphins resulted in gastric mucosal defense, while reduction of the level of β‐endorphin counteracted the gastroprotective action of opioid peptides. 2. Gastroprotection could be elicited also by spinal mechanism.

IMMUNOHISTOCHEMICAL APPROACH REVEALS LOCALIZATION OF CYSTATHIONINE-?-LYASE AND CYSTATHIONINE-ß-SYNTHETASE IN ETHANOL-INDUCED GASTRIC MUCOSA DAMAGE IN MICE

Hydrogen sulphide (H2S) has been proved to be a neuromodulator and contributes to the maintenance of gastric mucosal integrity in damage caused by anti-inflammatory nonsteroidal drugs. Previously, we demonstrated that H2S synthesis is essential to gastric protection against ethanol. To better understanding the role of H2S and the detailed localization of its production in both normal and injured stomach due to ethanol injection, we studied the expression of cystathionine-γ-lyase (CSE) and cystathionine-β-synthetase (CBS) isoforms in gastric mucosa of mice treated with saline or 50% ethanol. Mice were treated by gavage with saline or 50% ethanol (0.5 mL/25 g). After 1 hour, mice were sacrificed, and gastric tissue was evaluated by histological and immunohistochemical analysis specific for CSE and CBS. We have demonstrated a non-specific expression of CBS in the normal gastric mucosa and expression of CSE occurring mainly in the parietal cells of the animals treated with ethanol. Thus, we demonstrated that the expression of CBS appears to be constitutive and diffuse across the gastric epithelium, while the expression of CSE appears to be induced in parietal cells by damage agents such as ethanol.

Rebamipide, a mucoprotective drug, inhibits NSAIDs-induced gastric mucosal injury: possible involvement of the downregulation of 15-hydroxyprostaglandin dehydrogenase

Prostaglandin E2 plays an important role in the maintenance of gastric mucosal integrity. The level of biologically active prostaglandin E2 in the tissue is regulated by the balanced expression of its synthetic enzymes, such as cyclooxygenase, and its catabolic enzyme, 15-hydroxyprostaglandin dehydrogenase. We examined the effect of rebamipide, a mucoprotective drug, on prostaglandin E2 production and metabolism in the gastric tissue and its effect on indomethacin-induced gastric mucosal injury in mice. Rebamipide suppressed indomethacin-induced gastric mucosal injury. Suppressive effect of rebamipide on indomethacin-induced gastric mucosal injury was also observed in cyclooxygenase-2-knockout mice. The mice that were treated with rebamipide showed a 2-fold increase in cyclooxygenase-2 mRNA expression in the gastric tissue, whereas 15-hydroxyprostaglandin dehydrogenase mRNA expression markedly decreased as compared to vehicle-treated control mice. Rebamipide did not affect the expression of cyclooxygenase-1 in the gastric tissue. Rebamipide did not increase prostaglandin E2 production in the gastric tissue; however, it induced a 1.4-fold increase in the concentration of prostaglandin E2 in the gastric tissue as compared to vehicle-treated control mice. These results suggest that the suppressive effect of rebamipide on non-steroidal anti-inflammatory drugs-induced gastric mucosal injury can be attributed to reduced 15-hydroxyprostaglandin dehydrogenase expression, which increases the prostaglandin E2 concentration in the gastric tissue.

Methods to Measure Gastric Mucosal Lesions in the Rat

The maintenance of gastric mucosal integrity is ensured by a dynamic balance between protective and noxious factors. The gastric mucosa has multiple protective mechanisms that allow the mucosa to withstand frequent exposure to potentially damaging agents such as acid and peptic secretions, bacterial products, ingested food, alcoholic beverages, and certain drugs. The imbalance between defensive and aggressive factors is at the basis of the formation of erosions/lesions or ulcerations of the gastric mucosa. The difference between an erosion/lesion and ulceration is that the former is confined to the mucosa, while an ulceration penetrates to the muscularis mucosae. This unit presents two models of acute mucosal lesions induced in the rat by gastrotoxic agents acting through different mechanisms of action. The protocols explain how to measure gastric mucosal lesions by microscopic examination of the stomach by light microscopy and by scanning electron microscopy.

Cytosolic phospholipase A2 S-nitrosylation in ghrelin protection against detrimental effect of ethanol cytotoxicity on gastric mucin synthesis ——Ghrelin in gastric mucosal protection

Ghrelin, a peptide hormone produced mainly in the stomach, has emerged recently as an important regulator of nitric oxide synthase (NOS) and cyclooxygenase (COX) enzyme systems, the products of which play direct cytoprotective function in the maintenance of gastric mucosal integrity. In this study, using gastric mucosal cells, we report on the role of ghrelin in countering the cytotoxic effect of ethanol on mucin synthesis. We show that the countering effect of ghrelin on mucin synthesis was associated with the increase in NO and PGE2 production, and characterized by a marked up-regulation in cytosolic phospholipase A2 (cPLA2) activity. The ghrelin-induced up-regulation in mucin synthesis, like that of cPLA2 activity, was subject to suppression by Src inhibitor, PP2 and ERK inhibitor, PD98059, as well as ascorbate. Moreover, the loss in countering effect of ghrelin on the ethanol cytotoxicity and mucin synthesis was attained with cNOS inhibitor, L-NAME as well as COX-1 inhibitor SC-560. The effect of L-NAME was reflected in the inhibition of ghrelin-induced mucosal cell capacity for NO production, cPLA2 S-nitrosylation and PGE2 generation, whereas COX-1 inhibitor caused only the inhibition in PGE2 generation. Our findings suggest that the activation of gastric mucosal cPLA2 through cNOS-induced S-nitrosylation plays an essential role in the countering effect of ghrelin on the disturbances in gastric mucin synthesis caused by ethanol cytotoxicity.

Ghrelin Protection against Lipopolysaccharide-Induced Gastric Mucosal Cell Apoptosis Involves Constitutive Nitric Oxide Synthase-Mediated Caspase-3 S-Nitrosylation

Ghrelin, a peptide hormone produced mainly in the stomach, has emerged as an important modulator of the inflammatory responses that are of significance to the maintenance of gastric mucosal integrity. Here, we report on the role of ghrelin in controlling the apoptotic processes induced in gastric mucosal cells by H. pylori lipopolysaccharide (LPS). The countering effect of ghrelin on the LPS-induced mucosal cell apoptosis was associated with the increase in constitutive nitric oxide synthase (cNOS) activity, and the reduction in caspase-3 and inducible nitric oxide synthase (NOS-2). The loss in countering effect of ghrelin on the LPS-induced changes in apoptosis and caspase-3 activity was attained with Src kinase inhibitor, PP2, as well as Akt inhibitor, SH-5, and cNOS inhibitor, L-NAME. Moreover, the effect of ghrelin on the LPS-induced changes in cNOS activity was reflected in the increased cNOS phosphorylation that was sensitive to SH-5. Furthermore, the ghrelin-induced up-regulation in cNOS activity was associated with the increase in caspase-3 S-nitrosylation that was susceptible to the blockage by L-NAME. Therefore, ghrelin protection of gastric mucosal cells against H. pylori LPS-induced apoptosis involves Src/Akt-mediated up-regulation in cNOS activation that leads to the apoptotic signal inhibition through the NO-induced caspase-3 S-nitrosylation.

Roles of Calcitonin Gene–Related Peptide in Maintenance of Gastric Mucosal Integrity and in Enhancement of Ulcer Healing and Angiogenesis

The gastrointestinal tract is known to be rich in neural systems, among which afferent neurons are reported to exhibit protective actions. We tested whether an endogenous neuropeptide, calcitonin gene-related peptide (CGRP), can prevent gastric mucosal injury elicited by ethanol and enhance healing of acetic acid-induced ulcer using CGRP knockout mice (CGRP(-/-)). The stomach was perfused with 1.6 mmol/L capsaicin or 1 mol/L NaCl, and gastric mucosal injury elicited by 50% ethanol was estimated. Levels of CGRP in the perfusate were determined by enzyme immunoassay. Gastric ulcers were induced by serosal application of absolute acetic acid. Capsaicin inhibited injured area dose-dependently. Fifty percent ethanol containing capsaicin immediately increased intragastric levels of CGRP in wild-type (WT) mice, although 50% ethanol alone did not. The protective action of capsaicin against ethanol was completely abolished in CGRP(-/-). Preperfusion with 1 mol/L NaCl increased CGRP release and reduced mucosal damage during ethanol perfusion. However, 1 mol/L NaCl was not effective in CGRP(-/-). Healing of ulcer elicited by acetic acid in CGRP(-/-) mice was markedly delayed, compared with that in WT. In WT, granulation tissues were formed at the base of ulcers, and substantial neovascularization was induced, whereas those were poor in CGRP(-/-). Expression of vascular endothelial growth factor was more markedly reduced in CGRP(-/-) than in WT. CGRP has a preventive action on gastric mucosal injury and a proangiogenic activity to enhance ulcer healing. These results indicate that the CGRP-dependent pathway is a good target for regulating gastric mucosal protection and maintaining gastric mucosal integrity.

Gastroprotective action of glucocorticoid hormones in rats with desensitization of capsaicin-sensitive sensory neurons

The ability of glucocorticoid hormones to protect gastric mucosa during desensitization of capsaicin-sensitive afferent neurons has been investigated in rats. Functional ablation of the afferent neurons was performed by pre-treatment with neurotoxic doses of capsaicin (100 mg/kg s.c.). After 1 week of recovery, capsaicin-desensitized, as well as control rats were adrenalectomized or sham-operated. Seven days later, indomethacin at an ulcerogenic dose (35 mg/kg s.c.) was given to each group of rats. One half of adrenalectomized capsaicin-pre-treated rats were injected by corticosterone for replacement (4 mg/kg s.c., 15 min before indomethacin). Gastric lesions, plasma corticosterone and blood glucose levels were estimated 4 h after indomethacin administration. Indomethacin caused gastric erosions that were aggravated by adrenalectomy or desensitization of capsaicin-sensitive afferent neurons approximately with the same extension. Combination of adrenalectomy with the sensory desensitization profoundly potentiated the effect of sensory desensitization alone on indomethacin-induced gastric erosions: the mean gastric erosion area was increased approximately 10-fold. Corticosterone replacement completely prevented this profound effect of adrenalectomy. The results suggest a pivotal role of glucocorticoid hormones in the maintenance of gastric mucosal integrity in the case of impaired gastroprotective mechanisms provided by PGs and capsaicin-sensitive sensory neurons.

Are All COX-2 Inhibitors Created Equal?

Prostaglandins (PGs) are biologically active lipids derived from the cyclooxygenase (COX)-mediated metabolism of arachidonic acid. They are constitutively produced in certain tissues (eg, brain, gut, and kidney), and their synthesis is increased at sites of inflammation. Prostanoids function as important mediators of inflammation and modulate a variety of physiological processes, including maintenance of gastric mucosal integrity, renal hemodynamic regulation, renin synthesis and release, and tubular reabsorption of salt and water.1 Cyclooxygenase, or PG synthase G2/H2, is the rate-limiting enzyme responsible for the initial conversion of arachidonic acid to PGG2 and subsequently to PGH2. PGH2 is then metabolized by tissue-specific isomerases to produce prostaglandins and thromboxanes. There are 2 distinct isoforms of cyclooxygenase, COX-1 and COX-2, which share 66% homology in amino acid sequence 2–4 but have different patterns of expression and regulation. COX-1, traditionally termed the “constitutive” enzyme, is widely distributed in tissues, and its level of activity is not dynamically regulated. COX-2, the glucocorticoid-sensitive “inducible” enzyme, is more restricted in its basal expression and is upregulated in response to inflammation, resulting in increased prostanoid production at the site of inflammation. NSAIDs, which block both isoforms COX-1 and COX-2, have been widely used in the treatment of inflammatory conditions. However, the adverse effects of NSAIDs, especially gastrointestinal toxicity, have limited their long-term use in clinical settings. The hypothesis that NSAID-induced gastrointestinal toxicity was related to the inhibition of gastric COX-1, whereas the anti-inflammatory properties caused by COX-2 inhibition5 led to the development of the new antiinflammatory agents, the coxibs, which were designed to inhibit COX-2 selectively. It was anticipated that these selective COX-2 inhibitors would be as effective as the nonselective NSAIDs in the treatment of inflammatory diseases but would be better-tolerated with fewer gastrointestinal side effects. Rofecoxib (Vioxx) and celecoxib (Celebrex) were the first COX-2–selective inhibitors to be marketed as effective antiinflammatory agents without serious gastrointestinal toxicity, based on the results of the VIoxx Gastrointestinal Outcomes Research (VIGOR) trial6 and the Celecoxib Long term Arthritis Safety Study (CLASS) trial, 7 respectively. The VIGOR trial reported that patients with rheumatoid arthritis receiving rofecoxib (50 mg daily) had fewer gastrointestinal events compared with those taking naproxen (500 mg twice daily) (2.1% versus 4.5%; P0.001), but there was similar efficacy between the drugs. However, the incidence of myocardial infarction was increased by a factor of 5 in the rofecoxib-treated group compared with the naproxen group. In the CLASS trial, celecoxib (400 mg twice daily) was compared with ibuprofen (800 mg thrice daily) or diclofenac (75 mg twice daily) in patients with osteoarthritis or rheumatoid arthritis. Celecoxib had a lower gastrointestinal side effect profile compared with other NSAIDs, and there was no difference in the incidence of cardiovascular events between celecoxib and NSAIDs regardless of aspirin use. Questions regarding the cardiovascular risk of the various coxibs remained, and on September 30, 2004 rofecoxib was withdrawn from the market based on the data from the Adenomatous Polyp PRevention On Vioxx (APPROVe) study. 8 This trial was prematurely discontinued after it was discovered that 3.5% of the patients treated with rofecoxib (25 mg once daily) had serious thromboembolic adverse events compared with 1.9% of patients in the placebo group (P0.001).8,9 The

Preferential and non-selective cyclooxygenase inhibitors reduce inflammation during lipopolysaccharide-induced synovitis

Synovitis in horses is frequently treated by administration of non-steroidal anti-inflammatory drugs (NSAIDs), which inhibit cyclooxygenase isoforms (COX-1 and COX-2). Constitutively expressed COX-1 is involved in physiologic functions such as maintenance of gastric mucosal integrity, whereas COX-2 is up-regulated at sites of inflammation. Thus, COX-2 inhibitors reduce inflammation with reduced gastrointestinal side effects as compared to non-selective COX inhibitors. The objective of the present study was to compare the anti-inflammatory effects of the preferential COX-2 inhibitor etodolac with the non-selective COX inhibitor phenylbutazone in horses with lipopolysaccharide (LPS)-induced synovitis. Three groups of horses ( n = 6) received no treatment, phenylbutazone (4.4 mg/kg, IV, q12h), or etodolac (23 mg/kg, IV, q12h), respectively, 2-h following injection of LPS into one middle carpal joint. Synovial fluid was analyzed for white blood cell (WBC) count, and TXB 2 and PGE 2 levels. Phenylbutazone and etodolac significantly reduced WBC count 6 and 24-h following injection of LPS compared to untreated horses. In addition, both drugs significantly reduced PGE 2 levels ( P < 0.05) 6-h following LPS injection, whereas the probable COX-1 prostanoid TXB 2 was significantly reduced by phenylbutazone ( P < 0.05), but not etodolac. Etodolac may serve as a more selective anti-inflammatory agent than phenylbutazone for treatment of equine synovitis.

Nociceptin/orphanin FQ prevents ethanol-induced gastric lesions in the rat

Nociceptin/orphanin FQ (N/OFQ), the endogenous ligand of the NOP receptor, exerts a variety of effects on the gastrointestinal tract. The present study was aimed at evaluating the possible implication of N/OFQ in the maintenance of gastric mucosal integrity. N/OFQ was given either centrally or peripherally 30 min prior to intragastric administration (i.g.) of 1 ml/rat of ethanol (either 25% or 50%, v/v), which produces macroscopically visible gastric lesions. Intracerebroventricular (i.c.v.) injection of 2 μg/rat of N/OFQ significantly reduced lesions caused by 50% ethanol, while 1 μg/rat was enough to significantly reduce lesions caused by 25% ethanol. Intracerebroventricular injection of 5 μg/rat of the selective NOP receptor antagonist, UFP-101, completely reversed the protective effect of N/OFQ, 1 or 4 μg/rat against 25% or 50% ethanol, respectively. The intraperitoneal (i.p.) injection of N/OFQ produced a significant reduction of lesions induced by 50% ethanol, the peak effect being observed at 10 μg/kg. Intraperitoneal pretreatment with UFP-101, 120 μg/kg, completely abolished the protective effect of peripherally injected N/OFQ. Therefore, N/OFQ acts both centrally and peripherally as a protective agent against ethanol-induced gastric lesions, and its effect is mediated by NOP receptors.

Adaptive cytoprotection through modulation of nitric oxide in ethanol-evoked gastritis

To assess the mechanisms of protective action by different mild irritants through maintenance of gastric mucosal integrity and modulation of mucosal nitric oxide (NO) in experimental gastritis rats. Either 200 mL/L ethanol, 50 g/L NaCl or 0.3 mol/L HCl was pretreated to normal or 800 mL/L ethanol-induced acute gastritis Sprague-Dawley rats before a subsequent challenge with 500 mL/L ethanol. Both macroscopic lesion areas and histological damage scores were determined in the gastric mucosa of each group of animals. Besides, gastric mucosal activities of NO synthase isoforms and of superoxide dismutase, along with mucosal level of leukotriene (LT)C4 were measured. Macroscopic mucosal damages were protected by 200 mL/L ethanol and 50 g/L NaCl in gastritis rats. However, although 200 mL/L ethanol could protect the surface layers of mucosal cells in normal animals (protection attenuated by NG-nitro-L-arginine methyl ester), no cytoprotection against deeper histological damages was found in gastritis rats. Besides, inducible NO synthase activity was increased in the mucosa of gastritis animals and unaltered by mild irritants. Nevertheless, the elevation in mucosal LTC4 level following 500 mL/L ethanol administration and under gastritis condition was significantly reduced by pretreatment of all three mild irritants in both normal and gastritis animals. These findings suggest that the aggravated 500 mL/L ethanol-evoked mucosal damages under gastritis condition could be due to increased inducible NO and LTC4 production in the gastric mucosa. Only 200 mL/L ethanol is truly "cytoprotective" at the surface glandular level of non-gastritis mucosa. Furthermore, the macroscopic protection of the three mild irritants involves reduction of LTC4 level in both normal and gastritis mucosa, implicating preservation of the vasculature.

Capsaicin-sensitive afferents and their role in gastroprotection: an update

The pivotal role of capsaicin-sensitive peptidergic sensory fibers in the maintenance of gastric mucosal integrity against injurious interventions was suggested by the authors 20 years ago. Since then substantial evidence has accumulated for the local sensory-efferent function of the released CGRP, tachykinins and NO in this gastroprotective mechanism. This overview outlines some recent achievements which shed light on new aspects and further horizons in this field. (1) Cloning the capsaicin VR-1 receptor (an ion channel-coupled receptor) and raising the VR-1 knockout mice provided a definite molecular background for the existence of capsaicin-sensitive afferents with both sensory and mediator releasing functions in the stomach. This cation channel is also sensitive to hydrogen ions. (2) VR-1 agonists (capsaicin, resiniferatoxin, piperine) protect against gastric ulcer of the rat parallel with their sensory stimulating potencies. (3) Antidromic stimulation of capsaicin-sensitive vagal and somatic afferents results in the release of CGRP, tachykinins, NO and somatostatin. Somatostatin with gastroprotective effect is released from D cells and sensory nerve endings. (4) The recent theory for the existence of spinal afferents without sensory function [P. Holzer, C.A. Maggi, Dissociation of dorsal root ganglion neurons into afferent and efferent-like neurons, Neuroscience 86 (1998) 389–398] is discussed. Data proposed to support this theory are interpreted here on the basis of a dual sensory-efferent function of VR-1 positive afferents, characterized by a frequency optimum of discharges for release vasodilatory neuropeptides below the nociceptive threshold. (5) Recent data on the effect of capsaicin in healthy human stomach are summarized. These results indicate that the gastroprotective effect of capsaicin in the human stomach involves additional mechanisms to those already revealed in the rat.