Potential therapeutic role of melatonin in hepatobiliary diseases: current evidence and clinical observations

Melatonin (MEL) is produced and secreted by the pineal gland as well as the small intestine, liver, retina, lymphocytes, and melanocytes in the skin in both experimental animals as well as in humans. While pineal and retinas MEL is closely related to the light/dark cycle, the production of MEL by other so called extrapineal tissues is independent of such circadian rhythm. Among the primary mechanisms of action of MEL in humans, the most important are interaction of MEL with specific receptors (M1, M2, M3) and the MEL 'scavenging' activity against the formation of free oxygen metabolites as a result of MEL's ability to transfer free electrons and stimulation of the expression of redox reaction enzymes. In addition, MEL binds to intracellular proteins such as calmodulin, thereby affecting the course of cell cycle, and it has been shown to activate of nuclear receptors belonging to the retinoid orphan receptors/retinoid Z receptors (ROR/RZR) subfamily. MEL exerts regulatory effects on the master clock regulating diurnal rhythms. This updated review presents current view on the synthesis and metabolism of MEL and the growing body of experimental evidence transferable to the practical medicine supporting a pleiotropic molecule beneficial effects on the health including protection against various organ abnormalities, including internal organs such as the liver. Although the beneficial effects of MEL in various types of liver damage have been well documented in experimental studies, there are relatively few studies on liver dysfunction in humans. Considering the worldwide obesity pandemic often associated with the occurrence of steatohepatitis and cirrhosis, the beneficial effects of MEL in liver pathology should be proven in randomized trials involving patients presenting with hepatic disorders.

Evidence for Cytoprotective Effect of Carbon Monoxide Donor in the Development of Acute Esophagitis Leading to Acute Esophageal Epithelium Lesions

Exposure to acidic gastric content due to malfunction of lower esophageal sphincter leads to acute reflux esophagitis (RE) leading to disruption of esophageal epithelial cells. Carbon monoxide (CO) produced by heme oxygenase (HMOX) activity or released from its donor, tricarbonyldichlororuthenium (II) dimer (CORM-2) was reported to protect gastric mucosa against acid-dependent non-steroidal anti-inflammatory drug-induced damage. Thus, we aimed to investigate if CO affects RE-induced esophageal epithelium lesions development. RE induced in Wistar rats by the ligation of a junction between pylorus and forestomach were pretreated i.g. with vehicle CORM-2; RuCl₃; zinc protoporphyrin IX, or hemin. CORM-2 was combined with NG-nitro-L-arginine (L-NNA), indomethacin, capsazepine, or capsaicin-induced sensory nerve ablation. Esophageal lesion score (ELS), esophageal blood flow (EBF), and mucus production were determined by planimetry, laser flowmetry, histology. Esophageal Nrf-2, HMOXs, COXs, NOSs, TNF-α and its receptor, IL-1 family and IL-1 receptor antagonist (RA), NF-κB, HIF-1α, annexin-A1, suppressor of cytokine signaling (SOCS3), TRPV1, c-Jun, c-Fos mRNA/protein expressions, PGE₂, 8-hydroxy-deoxyguanozine (8-OHdG) and serum COHb, TGF-β1, TGF-β2, IL-1β, and IL-6 content were assessed by PCR, immunoblotting, immunohistochemistry, gas chromatography, ELISA or Luminex platform. Hemin or CORM-2 alone or combined with L-NNA or indomethacin decreased ELS. Capsazepine or capsaicin-induced denervation reversed CORM-2 effects. COHb blood content, esophageal HMOX-1, Nrf-2, TRPV1 protein, annexin-A1, HIF-1α, IL-1 family, NF-κB, c-Jun, c-Fos, SOCS3 mRNA expressions, and 8-OHdG levels were elevated while PGE₂ concentration was decreased after RE. CO donor-maintained elevated mucosal TRPV1 protein, HIF-1 α, annexin-A1, IL-1RA, SOCS3 mRNA expression, or TGF-β serum content, decreasing 8-OHdG level, and particular inflammatory markers expression/concentration. CORM-2 and Nrf-2/HMOX-1/CO pathway prevent esophageal mucosa against RE-induced lesions, DNA oxidation, and inflammatory response involving HIF-1α, annexin-A1, SOCS3, IL-1RA, TGF-β-modulated pathways. Esophagoprotective and hyperemic CO effects are in part mediated by afferent sensory neurons and TRPV1 receptors activity with questionable COX/PGE₂ or NO/NOS systems involvement.

Mechanisms of curcumin-induced gastroprotection against ethanol-induced gastric mucosal lesions

BACKGROUND

Curcumin, a pleiotropic substance used for centuries in traditional medicine, exhibits antioxidant, anti-inflammatory and antiproliferative efficacy against various tumours, but the role of curcumin in gastroprotection is little studied. We determined the effect of curcumin against gastric haemorrhagic lesions induced by 75% ethanol and alterations in gastric blood flow (GBF) in rats with cyclooxygenase-1 (COX-1) and COX-2 activity inhibited by indomethacin, SC-560 or rofecoxib, inhibited NO-synthase activity, capsaicin denervation and blockade of TRPV1 receptors by capsazepine.

METHODS

One hour after ethanol administration, the gastric mucosal lesions were assessed by planimetry, the GBF was examined by H2 gas clearance, plasma gastrin was determined by radioimmunoassay, and the gastric mucosal mRNA expression of Cdx-2, HIF-1α, HO-1 and SOD 2 was analysed by RT-PCR.

RESULTS

Curcumin, in a dose-dependent manner, reduced ethanol-induced gastric lesions and significantly increased GBF and plasma gastrin levels. Curcumin-induced protection was completely reversed by indomethacin and SC-560, and significantly attenuated by rofecoxib, L-NNA, capsaicin denervation and capsazepine. Curcumin downregulated Cdx-2 and Hif-1α mRNA expression and upregulated HO-1 and SOD 2, and these effects were reversed by L-NNA and further restored by co-treatment of L-NNA with L-arginine.

CONCLUSIONS

Curcumin-induced protection against ethanol damage involves endogenous PG, NO, gastrin and CGRP released from sensory nerves due to activation of the vanilloid TRPV1 receptor. This protective effect can be attributed to the inhibition of HIF-1α and Cdx-2 expression and the activation of HO-1 and SOD 2 expression.

Carbon monoxide released from its pharmacological donor, tricarbonyldichlororuthenium (II) dimer, accelerates the healing of pre-existing gastric ulcers

BACKGROUND AND PURPOSE

Carbon monoxide (CO), a gaseous mediator produced by haem oxygenases (HOs), has been shown to prevent stress-, ethanol-, aspirin- and alendronate-induced gastric damage; however, its role in gastric ulcer healing has not been fully elucidated. We investigated whether CO released from tricarbonyldichlororuthenium (II) dimer (CORM-2) can affect gastric ulcer healing and determined the mechanisms involved in this healing action.

EXPERIMENTAL APPROACH

Gastric ulcers were induced in Wistar rats by serosal application of acetic acid. Animals received 9 days of treatment with RuCl₃ [2.5 mg·kg^-1 intragastrically (i.g.)], haemin (5 mg·kg^-1 i.g.), CORM-2 (0.1-10 mg·kg^-1 i.g.) administered alone or with zinc protoporphyrin IX (ZnPP, 10 mg·kg^-1 i.g.), 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 5 mg·kg^-1 i.g.), N^G -nitro-l-arginine (l-NNA, 15 mg·kg^-1 i.g.), indomethacin (5 mg·kg^-1 i.g.) or glibenclamide (10 mg·kg^-1 i.g.). Gastric ulcer area and gastric blood flow (GBF) were assessed planimetrically, microscopically and by laser flowmeter respectively. Gastric mRNA/protein expressions of EGF, EGF receptors, VEGFA, HOs, nuclear factor (erythroid-derived 2)-like 2 (Nrf2), COX-2, hypoxia-inducible factor (HIF)-1α and pro-inflammatory iNOS, IL-1β and TNF-α were determined by real-time PCR or Western blots.

KEY RESULTS

CORM-2 and haemin but not RuCl₃ or ZnPP decreased ulcer size while increasing GBF. These effects were reduced by ODQ, indomethacin, l-NNA and glibenclamide. CORM-2 significantly decreased the expression of pro-inflammatory markers, Nrf2/HO1 and HIF-1α, and up-regulated EGF.

CONCLUSIONS AND IMPLICATIONS

CO released from CORM-2 or endogenously produced by the HO1/Nrf2 pathway accelerates gastric ulcer healing via an increase in GBF, an up-regulation in EGF expression and down-regulation of the inflammatory response.

Exogenous and Endogenous Hydrogen Sulfide Protects Gastric Mucosa against the Formation and Time-Dependent Development of Ischemia/Reperfusion-Induced Acute Lesions Progressing into Deeper Ulcerations

Hydrogen sulfide (H₂S) is an endogenous mediator, synthesized from l-cysteine by cystathionine γ-lyase (CSE), cystathionine β-synthase (CBS) or 3-mercaptopyruvate sulfurtransferase (3-MST). The mechanism(s) involved in H₂S-gastroprotection against ischemia/reperfusion (I/R) lesions and their time-dependent progression into deeper gastric ulcerations have been little studied. We determined the effect of l-cysteine, H₂S-releasing NaHS or slow H₂S releasing compound GYY4137 on gastric blood flow (GBF) and gastric lesions induced by 30 min of I followed by 3, 6, 24 and 48 h of R. Role of endogenous prostaglandins (PGs), afferent sensory nerves releasing calcitonin gene-related peptide (CGRP), the gastric expression of hypoxia inducible factor (HIF)-1α and anti-oxidative enzymes were examined. Rats with or without capsaicin deactivation of sensory nerves were pretreated i.g. with vehicle, NaHS (18–180 μmol/kg) GYY4137 (90 μmol/kg) or l-cysteine (0.8–80 μmol/kg) alone or in combination with (1) indomethacin (14 μmol/kg i.p.), SC-560 (14 μmol/kg), celecoxib (26 μmol/kg); (2) capsazepine (13 μmol/kg i.p.); and (3) CGRP (2.5 nmol/kg i.p.). The area of I/R-induced gastric lesions and GBF were measured by planimetry and H₂-gas clearance, respectively. Expression of mRNA for CSE, CBS, 3-MST, HIF-1α, glutathione peroxidase (GPx)-1, superoxide dismutase (SOD)-2 and sulfide production in gastric mucosa compromised by I/R were determined by real-time PCR and methylene blue method, respectively. NaHS and l-cysteine dose-dependently attenuated I/R-induced lesions while increasing the GBF, similarly to GYY4137 (90 μmol/kg). Capsaicin denervation and capsazepine but not COX-1 and COX-2 inhibitors reduced NaHS- and l-cysteine-induced protection and hyperemia. NaHS increased mRNA expression for SOD-2 and GPx-1 but not that for HIF-1α. NaHS which increased gastric mucosal sulfide release, prevented further progression of acute I/R injury into deeper gastric ulcers at 6, 24 and 48 h of R. We conclude that H₂S-induced gastroprotection against I/R-injury is due to increase in gastric microcirculation, anti-oxidative properties and afferent sensory nerves activity but independent on endogenous prostaglandins.

Mechanisms by which Stress Affects the Experimental and Clinical Inflammatory Bowel Disease (IBD): Role of Brain-Gut Axis

Background

Stress of different origin is known to alter so called “brain-gut axis” and contributes to a broad array of gastrointestinal disorders including inflammatory bowel disease (IBD), irritable bowel syndrome (IBS) and other functional gastrointestinal diseases. The stressful situations and various stressors including psychosocial events, heat, hypo- and hyperthermia may worsen the course of IBD via unknown mechanism. The aims of this paper were to provide an overview of experimental and clinical evidences that stress activates the brain-gut axis which results in a mucosal mast cells activation and an increase in the production of proinflammatory cytokines and other endocrine and humoral mediators.

Methods

Research and online content related to effects of stress on lower bowel disorders are reviewed and most important mechanisms are delineated.

Results

Brain conveys the neural, endocrine and circulatory messages to the gut via brain-gut axis reflecting changes in corticotrophin releasing hormone, mast cells activity, neurotransmission at the autonomic nerves system and intestinal barrier function all affecting the pathogenesis of animal colitis and human IBD. Stress triggers the hypothalamus-pituitary axis and the activation of the autonomic nervous system, an increase in cortisol levels and proinflammatory cytokines such as tumor necrosis factor-alpha, interleukin-8, interleukin-1beta and interleukin-6.

Conclusion

The acute or chronic stress enhances the intestinal permeability weakening of the tight junctions and increasing bacterial translocation into the intestinal wall. An increased microbial load in the colonic tissue, excessive cytokine release and a partially blunted immune reactivity in response to stress result in its negative impact on IBD.

Interaction between endogenous carbon monoxide and hydrogen sulfide in the mechanism of gastroprotection against acute aspirin-induced gastric damage

Acetylsalicylic acid (ASA) is mainly recognized as painkiller or anti-inflammatory drug. However, ASA causes serious side effects towards gastrointestinal (GI) tract which limits its usefulness. Carbon monoxide (CO) and hydrogen sulfide (H₂S) have been described to act as important endogenous messengers and mediators of gastroprotection but whether they can interact in gastroprotection against acute ASA-induced gastric damage remains unknown. In this study male Wistar rats were pretreated with 1) vehicle (saline, i.g.), 2) tricarbonyldichlororuthenium (II) dimer (CORM-2, 5mg/kg i.g.), 3) sodium hydrosulfide (NaHS, 5mg/kg i.g.), 4) zinc protoporphyrin (ZnPP, 10mg/kg i.p.), 5) D,L-propargylglycine (PAG, 30mg/kg i.g.), 6) ZnPP combined with NaHS, 7) PAG combined with CORM-2 or 8) 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ, 10mg/kg i.p.) combined with CORM-2 or NaHS and 30min later ASA was administered i.g. in a single dose of 125mg/kg. After 1h, gastric blood flow (GBF) was determined by H₂ gas clearance technique and gastric lesions were assessed by planimetry and histology. CO content in gastric mucosa and COHb concentration in blood were determined by gas chromatography and H₂S production was assessed in gastric mucosa using methylene blue method. Protein and/or mRNA expression for cystathionine-γ-lyase (CSE), cystathionine-β-synthase (CBS), 3-mercaptopyruvate sulfurtransferase (3-MST), heme oxygenase (HO)-1, HO-2, hypoxia inducible factor-alpha (HIF)-1α, nuclear factor (erythroid-derived 2)-like 2 (Nrf-2), cyclooxygenase (COX)-1 and COX-2, inducible nitric oxide synthase (iNOS) and interleukin (IL)-1β were determined by Western blot or real-time PCR, respectively. ASA caused hemorrhagic gastric mucosal damage and significantly decreased GBF, H₂S production, CO content, mRNA or protein expression for CSE, 3-MST, HO-2 and increased mRNA and/or protein expression for CBS, HO-1, Nrf-2, HIF-1α, iNOS, IL-1β, COX-2 in gastric mucosa and COHb concentration in blood. Pretreatment with CORM-2 or NaHS but not with PAG decreased ASA-damage and increased GBF. ZnPP reversed protective and hyperemic effect of NaHS but PAG failed to affect CORM-2-induced gastroprotection. CORM-2 elevated CO content, mRNA or protein expression for HO-1, Nrf-2, and decreased expression of CBS, HIF-1α, COX-2, IL-1β, iNOS, the H₂S production in gastric mucosa and COHb concentration in blood. NaHS raised mRNA or protein expression for CSE, COX-1 and decreased mRNA expression for IL-1β and COHb level in blood. We conclude that CO is involved in gastroprotection induced by H₂S while beneficial protective action of CO released from CORM-2 in gastric mucosa seems to be H₂S-independent. In contrast to H₂S, CO ameliorates hypoxia, regulates Nrf-2 expression but similarly to H₂S acts on sGC-dependent manner to restore gastric microcirculation and exhibit anti-inflammatory activity in gastric mucosa compromised by ASA.

Role of sensory afferent nerves, lipid peroxidation and antioxidative enzymes in the carbon monoxide-induced gastroprotection against stress ulcerogenesis

Carbon monoxide (CO) is a physiological gaseous mediator recently implicated in the mechanism of gastric mucosal defense due to its vasodilatory and antioxidative properties. Small quantities of endogenous CO are produced during heme degradation by heme oxygenase (HO-1), however, the involvement of the capsaicin-sensitive afferent neurons releasing calcitonin gene related peptide (CGRP) and anti-oxidative factors and mechanisms in the CO-induced gastroprotection against stress ulcerogenesis has been little studied. We investigated the possible role of CO released from the CO donor, tricarbonyldichlororuthenium (II) dimer (CORM-2) in the protection against water immersion and restraint stress (WRS)-induced lesions in rats with intact sensory nerves and those with capsaicin denervation and the accompanying changes in malondialdehyde (MDA) content considered as an index of lipid peroxidation, the activity of GSH and SOD-2 and gastric mucosal expression of antioxidative enzymes glutathione peroxidase (GPx) and SOD-2. Wistar rats with intact sensory nerves or those with capsaicin administered in total dose of 125 mg/kg s.c. within 3 days (capsaicin denervation) were pretreated either with 1) vehicle (saline) or 2) CORM-2 (0.1 - 0 mg/kg i.g.) with or without exogenous CGRP (10 μg/kg i.p.) and 30 min later exposed to 3.5 h of WRS. At the termination of WRS, the number of gastric lesions was counted and gastric blood flow (GBF) was assessed by H2-gas clearance technique. The mucosal content of MDA and reduced glutathione (GSH) and the activity of SOD-2 were determined and the expression of GPx-1 and SOD-2 mRNA in the gastric mucosa was analyzed by real-time PCR. The exposure of rats to 3.5 h of WRS resulted in numerous hemorrhagic gastric lesions and significantly decreased the GBF, raised MDA content and significantly decreased the mucosal SOD and GSH contents compared with intact gastric mucosa and these changes were exacerbated in rats with capsaicin denervation. Pretreatment with CORM-2 (1 mg/kg i.g.) which in our previous studies significantly reduced the ethanol and aspirin-induced gastric damage, significantly decreased the number of WRS-induced gastric lesions while raising the GBF and significantly increasing the activity of SOD and GSH (P < 0.05). The pretreatment with CORM-2 significantly decreased MDA content as compared with vehicle-pretreated rats exposed to WRS (P < 0.05). The reduction of WRS damage and the accompanying increase in the GBF as well as the significant decrease in MDA content and the increase in GSH content and SOD activity induced by CORM-2 (1 μg/kg i.g.) were all significantly altered in rats with capsaicin denervation (P < 0.05). The concurrent treatment of CORM-2 with exogenous CGRP in rats with or without sensory nerves tended to decrease the number of WRS lesions as compared with CORM-2 alone pretreated animals and significantly increased the GBF over the values measured in gastric mucosa of CORM-2 alone pretreated rats with or without capsaicin denervation. Such combined administration of CORM-2 and CGRP in rats with capsaicin denervation significantly inhibited an increase in MDA and 4-HNE content and evoked a significant increase in the GSH concentration (P < 0.05) remaining without significant effect on the increase in SOD activity observed with CORM-2 alone. The gastric mucosal expression of SOD-2- and GPx-1 mRNA was significantly increased as compared with those in intact gastric mucosa (P < 0.05). The pretreatment with CORM-2 applied with or without CGRP failed to significantly alter the mRNA expression for SOD-2 and GPx in the gastric mucosa of rats exposed to WRS. Both, the expression of SOD-2- and GPx-1 mRNA was significantly increased in capsaicin denervated rats exposed to WRS rats (P < 0.05) and this effect was abolished by the pretreatment with CORM-2. The expression of SOD-2 tended to decrease, though insignificantly, in rats pretreated with the combination of CORM-2 and CGRP as compared with that detected in CORM-2 alone in rats with capsaicin denervation. In contrast, the mRNA expression of GPx-1 was significantly decreased in gastric mucosa of capsaicin-denervated rats treated with the combination of CORM-2 and CGRP as compared with CORM-2 alone pretreated animals. We conclude that 1) CORM-2 releasing CO exerts gastroprotective activity against stress ulcerogenesis and this effect depends upon an increase in the gastric microcirculation and the vasodilatory activity of this gaseous mediator, and 2) the sensory nerve endings releasing CGRP can contribute, at least in part, to the CO-induced gastric hyperemia, the attenuation of gastric mucosal lipid peroxidation and prevention of oxidative stress as indicated by the CORM-2-induced normalization of the antioxidative enzyme expression enhanced in gastric mucosa of capsaicin-denervated rats.

The renin-angiotensin system and its vasoactive metabolite angiotensin-(1-7) in the mechanism of the healing of preexisting gastric ulcers. The involvement of Mas receptors, nitric oxide, prostaglandins and proinflammatory cytokines

The inhibition of angiotensin-converting enzyme (ACE) or the blockade of angiotensin (Ang) AT-1 receptors affords protection against acute gastric mucosal injury, but whether the major metabolite of renin-angiotensin system (RAS), Ang-(1-7), accelerates the healing process of preexisting gastric ulcers remains unknown. Previous studies documented that Ang-(1-7) acting via its own Mas receptor exerts vascular responses opposing those of Ang II. We studied the effects of the Ang-(1-7)/Mas receptor axis on the healing rate of acetic-acid-induced gastric ulcers with or without the blockade of Mas receptors by A 779 and compared it with the effects of activation and blockade of the AT-1 receptor by the treatment with Ang II and losartan, respectively, the inhibition of ACE by lisinopril, the NO/cNOS inhibition by L-NAME and inhibition of prostaglandin/COX system by indomethacin in the presence of Ang-(1-7). Additionally, ex vivo metabolism of Ang I in gastric tissue was assessed by LC/MS method. At day 9 after ulcer induction, the area of these ulcers and the accompanying changes in total gastric blood flow (GBF) were determined as were gastric mucosal blood flow (GMBF) at ulcer margin and gastric oxygen uptake (GVO2). The gastric mucosal expression of mRNAs for constitutive nitric oxide synthase (cNOS), superoxide dismutase (SOD), and pro-inflammatory cytokines interleukin 1β (IL-1β) and tumor necrosis factor alpha (TNF-α) and plasma level of both cytokines were determined by RT-PCR and ELISA. The 9 days treatment with Ang II dose-dependently increased the area of gastric ulcers and this effect was accompanied by a significant fall in the GBF, GVO2 and GMBF at ulcer margin. In contrast, treatment with Ang-(1-7) which produced a significant rise in the luminal content of NO significantly reduced the area of gastric ulcer and significantly increased the GBF, GVO2 and the GMBF at ulcer margin. Similar GMBF changes and significant reduction the area of gastric ulcer was observed in rats with gastric ulcers treated with the agonist of Mas receptor, AVE 0991. These effects of Ang-(1-7) and AVE 0991 were eliminated by blockade of the Mas receptor with A779. Similarly to Ang-(1-7), treatment with losartan or lisinopril significantly reduced the area of gastric ulcers and the accompanying increase in the GMBF at ulcer margin and these effects were significantly attenuated by a concomitant administration of L-NAME and indomethacin. The rate of healing of ulcers was associated with a decrease in ex vivo Ang-(1-7) formation and this effect was attenuated by lisinopril. The treatment with Ang-(1- 7) or AVE 0991 increased the expression of mRNA for cNOS and SOD and downregulated that of IL-1β and TNF-α followed by the decrease in the plasma IL-1β and TNF-α levels. We conclude that the Ang-(1-7)/Mas receptor system accelerates the healing of preexisting gastric ulcers via an increase in the gastric macro- and microcirculations, and an increase in gastric tissue oxygenation. These effects are mediated by PG and NO derived from overexpression of cNOS, an increase in the expression of antioxidizing enzyme SOD 2 and an anti-inflammatory action involving the inhibition of expression and release of pro-inflammatory cytokines IL-1β and TNF-α. Our results seem to underlie the importance of the Ang-(1-7), AT-1 and Mas receptors in the regulation of local vascular and metabolic effects associated with mechanism of gastric ulcer healing.

Esophagoprotective activity of angiotensin-(1-7) in experimental model of acute reflux esophagitis. Evidence for the role of nitric oxide, sensory nerves, hypoxia-inducible factor-1alpha and proinflammatory cytokines

Gastroesophageal reflux disease (GERD) is a global disease rapidly increasing among world population. The pathogenesis of reflux esophagitis which is considered as the early stage of GERD is complex, resulting from an imbalance between aggressive factors damaging the esophagus and a number of the natural defense mechanisms. The esophageal mucosa is in a state of continuous exposure to potentially damaging endogenous and exogenous factors. Important aggressive components of gastric refluxate include acid and pepsin and also pancreatic enzymes and bile. Among aggressive factors of exogenous origin, cigarette smoking, non-steroidal anti-inflammatory drugs (NSAID), and steroids are of the utmost importance. The basic level of esophageal defense against acid-pepsin damage consists of the anti-reflux mechanisms such as the luminal acid clearance and removal of the esophageal contents and neutralization of luminal acidity. In addition the esophageal mucosal protection includes the presence of pre-epithelial, epithelial and post-epithelial cellular and functional components. Recently, the progress have been made in the understanding of role of the heptapeptide member of the renin-angiotensin system (RAS), angiotensin-(1-7) (Ang-(1-7)) in the control of gastrointestinal functions. It has been shown that all components of local RAS including Ang-(1-7) are detectable in the gastrointestinal wall including not only the stomach but also the esophagus. Previous studies revealed that Ang-(1-7), which is an important component of the RAS, exerts vasodilatory, anti-inflammatory and antioxidant activities in the stomach. Ang-(1-7) was recently implicated in gastroprotection, but its effects on esophageal mucosa in a rodent model of reflux esophagitis and in human subjects presenting GERD symptoms have not been explored. The present study was aimed to evaluate the possible protective effects of Ang-(1-7) and Mas-receptors upon esophageal mucosal damage in acute reflux esophagitis (RE) induced in anesthetized rats by ligating the pylorus and the limiting ridge (a transitional region between the forestomach and the corpus of stomach). Consequently, the total gastric reservoir to store gastric juice was greatly diminished, resulting in the reflux of this juice into the esophagus. Because Mas receptors are functionally linked to nitric oxide (NO) formation, we also studied involvement of endogenous NO in the mediation of protective and circulatory effects of exogenous Ang-(1-7). Moreover, an attempt was made to assess the possible role of sensory neurons in the modulation of the protective effects exerted by Ang-(1-7)/Mas receptor system. Six series of rats were pretreated 30 min before induction of RE with 1) vehicle (saline), 2) Ang-(1-7) (5-50 μg/kg i.p.), 3) A779 (50 μg/kg i.p.), the selective Mas receptor antagonist applied alone, 4) Ang-(1-7) (50 μg/kg i.p.) combined with A779, 5) L-NNA (20 mg/kg i.p.) administered alone, and 6) Ang-(1-7) (50 μg/kg i.p.) combined with L-NNA. In separate group of rats, capsaicin (total dosage of 125 mg/kg within three days) was administered s.c. 2 weeks before the induction of RE to induce functional ablation of sensory nerves. Rats with intact sensory nerves and those with capsaicin-induced sensory denervation received vehicle (saline) or Ang-(1-7) (50 μg/kg i.p.) to determine whether this vasoactive metabolite of angiotensin I could be also effective in rats with capsaicin-induced impairment of the synthesis and release of sensory neuropeptides such as CGRP. Four hours after induction of RE, the mucosal damage was graded with mucosal lesion index (LI) from 0 to 6, the esophageal microcirculatory blood flow (EBF) was determined by H2-gas clearance technique and plasma level of pro-inflammatory cytokines interleukin-1b (IL-1β), and tumor necrosis factor-α (TNF-α) was determined by ELISA. The expression of proinflammatory factors including COX-2, cytokine IL-1β and hypoxia inducible factor 1alpha (Hif1α) was analyzed in the esophageal mucosal biopsies. In rats with RE, the esophageal LI was significantly elevated comparing its value observed in intact rats, and the EBF was significantly decreased as compared with intact mucosa. Pretreatment with Ang-(1-7) of control rats without esophagitis induced increase in EBF by about 25% without any macroscopic changes in the esophageal mucosa or in the plasma level of cytokines. In animals with RE, pretreatment with Ang-(1-7) significantly reduced gross and histological esophageal mucosal injury and significantly increased EBF in comparison to vehicle-pretreated animals. The observed gross and histologic esophagoprotective effect of Ang-(1-7) was totally abolished by A779 so in rats with combined treatment of A779 with Ang-(1-7), the LI was identical with this observed in control RE and the EBF was decreased in these animals by about 39%. Inhibition of NO synthase by L-NNA significantly reduced the LI and the rise in EBF caused by Ang-(1-7). Similarly, the capsaicin denervation also significantly attenuated the vasodilatory and the esophagoprotective effects of Ang-(1-7). The expression of proinflammatory factors COX-2, Hif1α and IL-1β which was negligible in intact esophageal mucosa, was upregulated in esophageal mucosa of rats with RE. In contrast, the administration of Ang-(1-7) resulted in a downregulation of mRNA for COX-2, Hif1 and IL-1β in esophageal mucosa an this effect was abolished in A779-dependent manner. The Ang-(1-7) significantly decreased the RE-induced elevation of plasma levels of IL-1β and TNF-α, and this effect was also reversed by pretreatment with A779, and significantly attenuated by pretreatment with L-NNA and capsaicin-induced sensory denervation. The present study indicates that the protective effect of Ang-(1-7) observed in the esophageal mucosa during early acute stage of gastroesophageal reflux depends upon the enhancement of esophageal microcirculatory blood flow via the activation of Mas receptor possibly due to NO synthase/NO system activation, stimulation of sensory nerves, the inhibition of expression of pro-inflammatory factors including COX-2, Hif1α and IL-1β and release of proinflammatory cytokines IL-1β and TNF-α.

Lipid peroxidation, reactive oxygen species and antioxidative factors in the pathogenesis of gastric mucosal lesions and mechanism of protection against oxidative stress - induced gastric injury

The gastric mucosa plays an important role in the physiological function of the stomach. This mucosa acts as gastric barrier, which protects deeper located cells against the detrimental action of the gastric secretory components, such as acid and pepsin. Integrity of the gastric mucosa depends upon a variety of factors, such as maintenance of microcirculation, mucus-alkaline secretion and activity of the antioxidizing factors. The pathogenesis of gastric mucosal damage includes reactive oxygen species (ROS), because of their high chemical reactivity, due to the presence of uncoupled electron within their molecules. Therefore they cause tissue damage, mainly due to enhanced lipid peroxidation. Lipid peroxides are metabolized to malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE). The local increase of MDA and 4-HNE concentration indicates ROS-dependent tissue damage. Superoxide dismutase (SOD) is the main enzyme, which neutralizes ROS into less noxious hydrogen peroxide. A decrease of SOD activity is an indicator of impairment of the protective mechanisms and significantly contributes to cell damage. Hydrogen peroxide is further metabolized to water in the presence of reduced glutathione (GSH). GSH can also work synergetically with SOD to neutralize ROS. The reactions between GSH and ROS yields glutathione free radical (GS(•)), which further reacts with GSH leading to free radical of glutathione disulphide (GSSG(•)). This free radical of GSSG can then donate an electron to the oxygen molecule, producing O2 (•-) Subsequently, O2 (•-) is eliminated by SOD. Adecrease of the GSH level has detrimental consequences for antioxidative defense cellular properties. Gastric mucosa, exposed to stress conditions, exhibits an enhancement of lipid peroxidation (increase of MDA and 4-HNE), as well as a decrease of SOD activity and GSH concentration. This chain reaction of ROS formation triggered by stress, appears to be an essential mechanism for understanding the pathogenesis of stress - induced functional disturbances in the gastric mucosa leading to ulcerogenesis.

New satiety hormone nesfatin-1 protects gastric mucosa against stress-induced injury: mechanistic roles of prostaglandins, nitric oxide, sensory nerves and vanilloid receptors

Nesfatin-1 belongs to a family of anorexigenic peptides, which are responsible for satiety and are identified in the neurons and endocrine cells within the gut. These peptides have been implicated in the control of food intake; however, very little is known concerning its contribution to gastric secretion and gastric mucosal integrity. In this study the effects of nesfatin-1 on gastric secretion and gastric lesions induced in rats by 3.5h of water immersion and restraint stress (WRS) were determined. Exogenous nesfatin-1 (5-40μg/kg i.p.) significantly decreased gastric acid secretion and attenuated gastric lesions induced by WRS, and this was accompanied by a significant rise in plasma NUCB2/nefatin-1 levels, the gastric mucosal blood flow (GBF), luminal NO concentration, generation of PGE2 in the gastric mucosa, an overexpression of mRNA for NUBC2 and cNOS, as well as a suppression of iNOS and proinflammatory cytokine IL-1β and TNF-α mRNAs. Nesfatin-1-induced protection was attenuated by suppression of COX-1 and COX-2 activity, the inhibition of NOS with L-NNA, the deactivation of afferent nerves with neurotoxic doses of capsaicin, and the pretreatment with capsazepine to inhibit vanilloid VR1 receptors. This study shows for the first time that nesfatin-1 exerts a potent protective action in the stomach of rats exposed to WRS and these effects depend upon decrease in gastric secretion, hyperemia mediated by COX-PG and NOS-NO systems, the activation of vagal and sensory nerves and vanilloid receptors.

Experimental healing of preexisting gastric ulcers induced by hormones controlling food intake ghrelin, orexin-A and nesfatin-1 is impaired under diabetic conditions. A key to understanding the diabetic gastropathy?

Hormonal peptides like ghrelin, orexin A (OXA) or nesfatin-1 not only regulate appetite, which is their basic biological function, but also contribute to mechanisms responsible for maintaining integrity of the gastric mucosa. Previous studies including those from our laboratory have revealed that their gastroprotective effect results from cooperation with other factors responsible for protection of the gastric mucosa, including prostaglandin (PG) synthesis pathway, nitric oxide (NO) and the sensory afferent fibres releasing the vasoactive neurotransmitters. The aim of the present study was to determine whether ghrelin, orexin-A (OX-A) or nesfatin-1 with their protective effect on the gastric mucosa, also can modify the healing of chronic gastric ulcers. Furthermore, an attempt was made to explain participation of these peptides in healing processes of chronic gastric ulcers with comorbid conditions for the human beings resulted from diabetes mellitus. In our study, a model of gastric ulcers caused by concentrated acetic acid to induce the chronic gastric ulcers was used, while the clinical condition corresponding to diabetes was induced by single injection of streptozotocin (STZ). We found that ghrelin, OX-A and nesfatin-1 accelerate dynamics of the acetic acid ulcers healing, confirmed by a reduction in the ulcer area and this effect was accompanied by an increase in gastric blood flow at the ulcer margin. Destruction of sensory afferent fibres with capsaicin or blocking of vanilloid receptors with capsazepine resulted in a significant reduction of ghrelin, OX-A and nesfatin-1-induced acceleration of ulcer healing. Similar results were obtained when an NO-synthase blocker, L-NNA was used in a combination with these peptides. Moreover, it was found that OX-A and nesfatin-1 failed to accelerate the healing process under diabetic condition because both these hormones induced reduction in the ulcer area and the increase in blood flow in normal, non-diabetic rats were completely lost in the group of animals with diabetes. Treatment with OX-A and nesfatin-1 increased superoxide dismutase (SOD) mRNA expression even in acetic acid ulcers concurrent with diabetes. However, the treatment with OX-A and nesfatin-1 failed to alter the increase in gastric mucosal mRNA expression for ghrelin and hypoxia-inducible factor 1-alpha (HIF-1α), this latter effect that had been strongly pronounced in diabetic animals. We conclude that the hormonal peptides involved in the regulation of satiety and hunger such as ghrelin, OX-A and nesfatin-1 contribute to the process of chronic gastric ulcers healing cooperating with NO and sensory afferent nerve endings releasing vasoactive neuropeptide CGRP. Furthermore, OX-A and nesfatin-1, the two relatively unrecognized peptides, play an essential role in healing process of chronic gastric ulcers activating the gastric blood flow at ulcer margin and the mucosal regeneration and both ulcer healing and accompanying hyperemia at ulcer margin are greatly impaired during diabetes. Possibly, loss of the healing effect of these peptides during diabetes results from an interaction with radical generation processes as reflected by an increase of mRNA expression for SOD as well as the failure of their attenuating activity on proinflammatory factors such as HIF-1α.

The impact of asymmetric dimethylarginine (ADAMA), the endogenous nitric oxide (NO) synthase inhibitor, to the pathogenesis of gastric mucosal damage

This review was designed to provide an update on the role of asymmetric arginine (ADMA), the endogenous inhibitor of nitric oxide (NO) synthase in the pathophysiology of the upper gastrointestinal (GI) tract. Numerous studies in the past confirmed that NO is a multifunctional endogenous gas molecule involved in most of the body organs' functional and metabolic processes including the regulation of gastrointestinal (GI) secretory functions, motility, maintenance of GI integrity, gastroprotection and ulcer healing. NO is metabolized from L-arginine by enzymatic reaction in the presence of constitutive NO synthase. In upper GI tract, NO acts as a potent vasodilator known to increase gastric mucosa blood flow, regulates the secretion of mucus and bicarbonate, inhibits the gastric secretion and protects the gastric mucosa against the damage induced by a variety of damaging agents and corrosive substances. In contrast, ADMA first time described by Vallance and coworkers in 1992, is synthesized by the hydrolysis of proteins containing methylated arginine amino acids located predominantly within the nucleus of cells. This molecule has been shown to competitively inhibit NO synthase suggesting its regulatory role in the functions of vascular endothelial cells and systemic circulation in humans and experimental animals. Nowadays, ADMA is a potentially important risk factor for coronary artery diseases and a marker of cardiovascular risk. Increased plasma levels of ADMA have been documented in several conditions that are characterized by endothelial dysfunction, including hypertension, hypercholesterolemia, hyperglycemia, renal failure and tobacco exposure. The role of ADMA in other systems including GI-tract has been so far less documented. Nevertheless, ADMA was shown to directly induce oxidative stress and cell apoptosis in gastric mucosal cells in vitro and to contribute to the inflammatory reaction associated with major human pathogen to gastric mucosa, Helicobacter pylori (H.pylori). Infection of gastric mucosa with this germ or H. pylori water extract led to marked increase in the plasma concentration of ADMA and significantly inhibited bicarbonate secretion, considered as one of the important components of upper GI-tract defense system. When administered to rodents, ADMA aggravated gastric mucosal lesions injury induced by cold stress, ethanol and indomethacin and this worsening effect on gastric lesions was accompanied by the significant increase in the plasma level of ADMA. This exaggeration of gastric lesions by ADMA was coincided with the inhibition of NO, the suppression of gastric blood flow and excessive release of proinflammatory cytokine TNF-α. This metabolic analog of L-arginine applied to rats was exposed to water immersion and restraint stress and ischemia-reperfusion, causing an elevation of plasma levels of ADMA and gastric MDA content, which is the marker of lipid peroxidation. These effects, including the rise in the plasma levels of ADMA in rats with stress and ischemia-reperfusion-induced gastric lesions, were attenuated by concomitant treatment with L-arginine, the substrate for NO-synthase, and superoxide dismutase (SOD), a reactive oxygen metabolite scavenger added to ADMA. We conclude that ADMA could be considered as an important factor contributing to the pathogenesis of gastric mucosal damage and inflammatory reaction in H. pylori-infected stomach due to inhibition of NO, suppression of GI microcirculation, and the proinflammatory and proapoptotic actions of this arginine analog.

Lipoxins, the novel mediators of gastroprotection and gastric adaptation to ulcerogenic action of aspirin

Previous studies revealed that prostaglandins contribute to the mechanism of maintenance of gastrointestinal integrity and mediate various physiological aspects of mucosal defense. The suppression of prostaglandin synthesis in the stomach is a critical event in terms of the development of mucosal injury after administration of various NSAID including aspirin (ASA). A worldwide use of ASA is now accepted due to its remarkable analgesic, antipyretic and anti-thrombotic prophylactics against myocardial infarct and coronary disorders despite the fact that the use of NSAIDs is associated with the risk of gastrointestinal bleedings, haemorrhagic lesions and ulcerations. It has become clear that other mediators besides prostaglandins can similarly act to protect the gastrointestinal mucosa of experimental animals and humans from injury induced by ASA. For instance, nitric oxide (NO) released from vascular epithelium, epithelial cells of gastrointestinal tract and sensory nerves can influence many of the same components of mucosal defense as do prostaglandins. This review was designed to provide an updated overview based on the experimental and clinical evidence on the involvement COX-2 derived products, lipoxins in the mechanism of gastric defense, gastroprotection and gastric adaptation to ASA. Lipoxins were recently considered as another group of lipid mediators that can protect the stomach similarly as NO-donors known to exert protective influence on the stomach from the injury under condition where the mucosal prostaglandin levels are suppressed. The new class of NO-releasing NSAIDs, including NO-aspirin or NO-naproxen, represent a very promising approach to reducing the toxicity of their parent NSAIDs. Aspirin-triggered lipoxin (ATL) synthesis, via COX-2, acts to reduce the severity of damage induced by this NSAID. Lipoxin analogues may prove to be useful for preventing mucosal injury and for modulating mucosal inflammation. Evidence presented in this review documents that ATL also play in important role in gastric adaptation during chronic ASA administration. Suppression of COX-2 activity by selective COX-2 inhibitors such as rofecoxib or celecoxib was shown to abolish the production of ATL and to diminish the gastric tolerability of ASA and gastric adaptation developed in response to repetitive administration of this NSAID. Synthetic analogues of lipoxins as well as newer class of NSAIDs releasing NO may be used in the future as the therapeutic approach to counteract adverse effects in the stomach associated with NSAIDs ingestion.

Effects of peripherally and centrally applied ghrelin in the pathogenesis of ischemia-reperfusion induced injury of the small intestine

Ghrelin is an important hormone involved in the control of the human appetite center. Recently, protective properties of this hormone have been recognized in various models of impairment of the gastric mucosa, including stress, ischemia and reperfusion (I/R). Ghrelin is predominantly secreted by the gastric mucosa of stomach, but there are other sources of ghrelin, for example in the hypothalamus and various parts of the central nervous system (CNS) that should be taken into consideration. This hormone exerts biological effects via the activation of growth hormone secretagogue receptor (GHSR), the presence of which was confirmed in different parts of the gastrointestinal (GI) tract and midbrain structures. Although substantial evidence of the divergent biological effects of ghrelin and the mechanism of its action has been emphasized, the precise mechanisms of ghrelin which affords GI protection is still unclear. Particularly, there is a sparse amount of evidence concerning its action on the GI system. The major aim of the present study was to evaluate the importance of peripherally and centrally administered ghrelin at different times of the ischemia and reperfusion (I/R period in the modulation of resistance of the intestinal mucosa to the injury induced by ischemia and subsequent reperfusion. Secondly, we wanted to evaluate the possible mechanism of the action of ghrelin with a particular focus on its influence on the intestinal blood flow. Male Wistar rats were divided into 4 series (A-D) of the experimental groups (n=7). In series A the importance of peripherally administered ghrelin at different time of I/R period was studied. In series B the importance of centrally administered ghrelin at different time of I/R period was evaluated. In series C and D, the mechanisms of peripherally and centrally administered hormone were examined, respectively. Two models of the I/R period were selected: short lasting (30/60 min) and long lasting (60/120 min). The following drugs were used: ghrelin (50 μg/kg i.p. or 1 nmol in 10 μl i.c.v.), 6 hydroxy dopamine (50 mg/kg i.p.), nadolol (0.5 mg/kg i.p.), calcitonin gene related peptide fragment (CGRP(8-37), 100 μg /kg i.p.), capsaicin (5-10 mg/100 ml solution s.c.). The mesenteric blood flow (MBF-ml/min), the intestinal microcirculatory blood flow (LDBF-PU), the arterio-venous oxygen difference (AVO(2)-ml/O(2)/100 ml blood), and the intestinal oxygen uptake (VO(2)) in ml O(2)/min were measured. Mucosal impairment was assessed planimetrically with the use of a digital photo analyzer (LA) and histologically with the use of the six-point Park/Chiu scale. Peripheral administration of ghrelin evoked marked increase of MBF and LDBF by 42% and 48%, respectively, with significant reduction of LA by 38%. When ghrelin was administered at the beginning of the reperfusion period during the short I/R period or prior to the long lasting I/R period, the vascular reactions and protective effects were reduced, but not completely abolished. The central administration of ghrelin before the short I/R period significantly increased the MBF and LDBF by about 32% and 35%, respectively, as well as LA reduction by about 20% in comparison to the control group. However, when ghrelin was administered prior to the long I/R period or after the onset of completed ischemia, neither vascular nor protective effects were noticed. Sensory denervation and the blockade of the CGRP1 receptors totally blocked the protective and hyperemic effects of the peripherally administered ghrelin. Selective blockade of the adrenergic system or blunting of the vagal nerves (vagotomy) significantly but not totally eliminated the effects of centrally applied ghrelin, which were abolished when both adrenergic and parasympathetic pathways were ablated. These results indicate that ghrelin applied centrally or peripherally markedly increases resistance of the intestinal tissue during the I/R period induced mucosal and hyperemic impairment evoked by I/R. Ghrelin is an important mediator of the increase in the intestinal microcirculation and elevation of the intestinal metabolism, which seems to be, at least in part, responsible for the observed protection of the intestine subjected to I/R. Impairment of this microvasculature response due to I/R seems to be responsible for a markedly observed weaker effect of ghrelin when this hormone was administered after the ischemic period. The lack of a protective effect observed after central administration of this peptide against a long lasting I/R period is probably due to damage of neural pathways caused by I/R. Finally, the peripheral activity of ghrelin in the intestine is mediated by the sensory neurons with a prominent role of CGRP released from their endings. However, this peripheral action of ghrelin depends upon the proper functioning of both the sympathetic and parasympathetic system.

Antibiotic treatment with ampicillin accelerates the healing of colonic damage impaired by aspirin and coxib in the experimental colitis. Importance of intestinal bacteria, colonic microcirculation and proinflammatory cytokines

Non-steroidal anti-inflammatory drugs (NSAIDs) are widely used for their anti-inflammatory, analgesic and antipyretic effects, however their use is associated with the broad spectrum of side effects observed in human as well as the experimental animals. Despite damaging activity of NSAIDs in upper gastrointestinal (GI) tract, these drugs exert deleterious influence in lower GI tract, including colon. The role of GI microflora in the pathogenesis of NSAIDs-induced experimental colonic damage is not completely understood. The aim of this study was 1) to evaluate the relative importance of the GI microflora on the experimental colonic damage in the presence of caused by NSAID, and 2) to assess the efficacy of antibiotic treatment with ampicillin on the process of healing of colitis. We compared the effect of vehicle, ASA applied 40 mg/kg intragastrically (i.g.) or the selective cyclooxygenase (COX)-2 inhibitor, celecoxib (25 mg/kg i.g.) without or with ampicillin treatment (800 mg/kg i.g.) administered throughout the period of 10 days, on the intensity of TNBS-induced colitis in rats. The severity of colonic damage, the alterations in the colonic blood flow (CBF) and myeloperoxidase (MPO) activity, the mucosal expression of TNF-α, IL-1β, COX-2, VEGF and iNOS and the plasma concentration of TNF-α and IL-1β were assessed. In all rats, the faeces samples as well as those from the colonic mucosa, blood, liver and spleen underwent microbiological evaluation for intestinal bacterial species including Escherichia coli and Enterococcus spp. The administration of TNBS resulted in macroscopic and microscopic lesions accompanied by the significant fall in the CBF, an increase in tissue weight and 4-5-fold rise in the MPO activity and a significant increase in the plasma IL-1β and TNF-α levels. ASA or celecoxib significantly increased the area of colonic lesions, enhanced MPO activity and caused the marked increase in colonic tissue weight and plasma IL-1β and TNF-α levels, as well as an overexpression of mRNA for IL-1β and TNF-α, COX-2, VEGF and iNOS in the colonic tissue. ASA and coxib also resulted also in a significant increase of E. coli counts in the stool at day 3 and day 10 day of the observation compared with the intact rats. Moreover, E. coli translocation from the colon to the blood and extraintestinal organs such as liver and spleen in the group of rats treated without or with ASA and coxib. E. coli was the most common bacteria isolated from these organs. Treatment with ampicillin significantly attenuated the ASA- or celecoxib-induced increase in plasma levels of IL-1β and TNF-α and suppressed the mucosal mRNA expression for IL-1β and TNF-β, COX-2, iNOS and VEGF in the colonic mucosa. Ampicillin administration caused a significant fall in the number of E. coli in the faeces at day 3 and day 10 of observation in ASA- and coxib-treated rats with colitis. Antibiotic therapy markedly reduced bacterial translocation to the colonic tissue and the extraintestinal organs such as the liver and spleen. We conclude that administration of ASA and to lesser extent of celecoxib, delays the healing of experimental colitis and enhances the alterations in colonic blood flow, proinflammatory markers such as IL-1β, TNF-α, COX-2, iNOS and VEGF and increased intestinal mucosal permeability resulting in the intestinal bacterial translocation to the blood, spleen and liver. Antibiotic treatment with ampicillin is effective in the diminishing of the severity of colonic damage, counteracts both the NSAID-induced fall in colonic microcirculation and bacterial E.coli translocation to the extraintestinal organs.

Nitric oxide (NO)-releasing aspirin exhibits a potent esophagoprotection in experimental model of acute reflux esophagitis. Role of nitric oxide and proinflammatory cytokines

The purpose of this study was to develop an acute animal model of reflux esophagitis, which would be suitable to induce the esophageal damage caused by gastric acid reflux, thus mimicking the esophageal injury of human gastroesophageal reflux disease (GERD). Global research indicates that GERD is rapidly increasing among the world's population. NSAIDs are known to induce gastrointestinal damage and low doses of aspirin (ASA) have been shown to increase the incidences of GERD in humans. Gastric acid and pepsin secretion and enhanced COX-2 expression were implicated in the pathogenesis of reflux esophagitis, but the effect of selective COX-2 inhibitors against lesions induced by the reflux of gastric acid content into esophagus has not been thoroughly studied. Here, we compared the effect of aspirin (ASA) and so called "safe" nitric oxide (NO) derivative of ASA with those of non-selective and selective cyclooxygenase (COX)-1 and COX-2 in rat model of reflux esophagitis. Reflux esophagitis was induced in anesthetized rats by ligating the pylorus and limiting ridge transitional region between the forestomach and the corpus of stomach. Subsequently, the total gastric reservoir to store gastric juice was greatly diminished, resulting in the reflux of this juice into the esophagus. Rats with esophagitis received intragastric (i.g.) pretreatment either with: 1) vehicle (saline), 2) ASA or NO-ASA (100 mg/kg); 3) the non-selective COX inhibitor, indomethacin (5 mg/kg); 4) the selective COX-1 inhibitor, SC-560 (10 mg/kg), and 5) the selective COX-2 inhibitor, celecoxib (5 mg/kg). In a separate series of rats with reflux oesophagitis, the efficacy of ASA combined with a donor of NO, glyceryl trinitrate (GTN; 10 mg/kg i.g.) to prevent esophageal mucosal injury was investigated. Four hours after induction of esophagitis the gross mucosal damage was graded with a macroscopic lesion index (LI) from 0-6. The esophageal blood flow (EBF) was determined by H₂-gas clearance technique, the oesophageal mucosal and blood samples were collected for histology and analysis of the RT-PCR expression and release of proinflammatory cytokines IL-1β, TNF-α and IL-6 using specific ELISA. The exposure of the esophagus to reflux of gastric acid time-dependently increased the esophageal LI and morphologic damage, and decreased EBF with the most significant changes observed at 4 hrs after the ligation procedure. The pretreatment with native ASA in the dose that suppressed the generation of mucosal PGE₂, enhanced gross and histologic esophageal damage and produced a significant fall in EBF. NO-ASA or ASA coupled with GTN counteracted the aggravation of the damage and accompanying fall in EBF when compared with native ASA applied alone to rats with esophagitis. The proinflammatory cytokines IL-1β and TNF-α were overexpressed in rats with esophagitis and those pretreated with ASA but this effect was significantly attenuated by NO-ASA. Plasma IL-1β, TNF-α and IL-6 were negligible in the intact rats but significantly increased in those with esophagitis, with this effect being further enhanced by non-selective (indomethacin) and selective (SC-560, celecoxib) COX-1 and COX-2 inhibitors. We conclude that conventional NSAID such as aspirin augments esophagitis, while NO-ASA exerts the beneficial protective effect against reflux esophagitis via the enhancement of esophageal microcirculation due to NO release and an inhibitory effect on expression and release of pro-inflammatory cytokines.

Involvement of orexigenic peptides in the mechanism of gastric mucosal integrity and healing of chronic gastric ulcers

Orexigenic peptides are group of endocrine hormones exerting a pleiotropic influence on many physiological functions including regulation of the feeding behaviour and energy expenditure, release of growth hormone (GH) and inotropic effects on the heart. Some of these peptides such as ghrelin, originally identified in the gastric mucosa, has been involved not only in control of food intake and growth hormone release but also exerts the immunomodulatory and anti-inflammatory properties. This review summarizes the recent attempts to prove the concept that orexigenic peptides such as ghrelin, orexin-A and obestatin besides playing an important role in the mechanism of food intake, exhibit a potent gastroprotective action against the formation of acute gastric mucosal injury induced by various ulcerogens. This protective effect depends upon vagal activity and hyperemia mediated by NOS/NO and COX/PG systems and CGRP released from sensory afferent nerves. In addition, the appetite peptides such as ghrelin and orexin-A are implicated in the mechanism of the healing of preexisting gastric ulcers due to an activation of specific GHS-R1a and OX-R1 receptors and PG/COX system.

Mucosal strengthening activity of central and peripheral melatonin in the mechanism of gastric defense

This review summarizes the involvement of centrally and peripherally applied melatonin, a major hormone of pineal gland, in the mechanism of gastric mucosal integrity, gastroprotection and ulcer healing. Melatonin was originally shown to attenuate gastric mucosal lesions but the controversy exists in the literature as to whether melatonin derived from the pineal gland, considered as the major source of this indole or rather that locally generated from L-tryptophan within gastric mucosa, plays predominant role in the mechanism of gastrointestinal integrity. Both, intragastric (i.g.) and intracerebroventricular (i.c.v.) administration of melatonin and its precursor, L-tryptophan to rats without or with removed pineal gland by pinealectomy attenuates in the dose-dependent manner the formation of on gastric lesions induced by topical irritants and water immersion restraint stress (WRS). Melatonin accelerated the gastric ulcer healing and this was accompanied by the rise in gastric blood flow (GBF), the plasma melatonin and gastrin levels, the mucosal generation of PGE(2) and luminal NO content. Pinealectomy, which suppresses the plasma melatonin levels, markedly aggravated the gastric lesions induced by WRS. Concurrent supplementation of pinealectomized animals with melatonin or L-tryptophan, the melatonin precursor, attenuated the lesions induced by WRS. Treatment with luzindole, an antagonist of Mel(2) receptors, or with L-NNA, the NO-synthase inhibitor, significantly attenuated melatonin- and L-tryptophan-induced protection and the acceleration of ulcer healing and the accompanying increase in the GBF and luminal content of NO. We conclude that 1) exogenous melatonin and that released from the L-tryptophan attenuate lesions induced by topical irritant such as ethanol and WRS via interaction with MT(2) receptors and due to an enhancement of gastric microcirculation, probably mediated by NO and PG derived from cNOS, iNOS and COX-2 overexpression and activity, and 2) the pineal gland plays an important role in the limitation of WRS-induced gastric lesions and acceleration of ulcer healing via releasing melatonin predominately at night time, that exerts gastroprotective and ulcer healing actions.

Ghrelin ameliorates colonic inflammation. Role of nitric oxide and sensory nerves

Ghrelin is a novel growth hormone (GH)-releasing and orexigenic peptide with anti-inflammatory activities. However, the role of ghrelin in the colonic inflammation is still controversial. The aim of the present study was: 1) to examine the expression of ghrelin and TNF-alpha mRNA in the inflamed colonic mucosa of patients with ulcerative colitis (UC), 2) to analyze the effect of treatment with exogenous ghrelin on the healing of trinitrobenze sulphonic acid (TNBS)-induced colitis in rats, and 3) to assess the effects of ghrelin treatment on mRNA expression for iNOS and protein expression for COX-2 and PPARalpha in intact colonic mucosa and in that with TNBS-induced colitis. Fifteen patients with UC and fifteen healthy controls were enrolled in this study. Expression of ghrelin and TNF-alpha was assessed by semi-quantitative RT-PCR in the colonic mucosal biopsies from UC patients and healthy controls. In addition, the effect of exogenous ghrelin on healing of TNBS colitis was tested in rats without or with capsaicin-induced functional ablation of sensory nerves. Patients with UC showed a significant upregulation of mRNA for ghrelin and TNF-alpha in colonic mucosa as compared to that observed in healthy controls. The expression of ghrelin correlated with the grade of inflammation and expression of TNF-alpha. In rats the exogenous ghrelin administered daily at a dose of 20 microg/kg i.p. significantly accelerated the healing of TNBS colitis and this effect was accompanied by an increase in mRNA expression for iNOS and protein expression for COX-2 in the colonic mucosa. The protein expression for PPARgamma, which was down-regulated in rat colonic mucosa after exposure to TNBS as compared to that in intact colonic mucosa, was not significantly influenced by ghrelin treatment. We conclude that 1) patients with UC show an increased mucosal expression of mRNA for ghrelin in the colonic mucosa which could trigger protective response in inflamed colon; and 2) exogenous ghrelin accelerates healing of colonic lesions in animal model of ulcerative colitis via increased release of NO and PGE(2) due to an increase in iNOS and COX-2 expression and stimulation of sensory neuropeptides such as CGRP released from sensory afferent endings.

Physiological mediators in nonsteroidal anti-inflammatory drugs (NSAIDs)-induced impairment of gastric mucosal defense and adaptation. Focus on nitric oxide and lipoxins

Prostaglandins mediate various physiological aspects of mucosal defense and the suppression of prostaglandin synthesis in the stomach is a critical event in terms of the development of mucosal injury after NSAID administration. However, it has become clear that other mediators besides prostaglandins can similarly act to protect the stomach from injury. For instance, nitric oxide (NO) released from vascular epithelium, epithelial cells of gastrointestinal tract and sensory nerves can influence many of the same components of mucosal defense as do prostaglandins. Thus, administration of NO in a form of NO-donors exert protective influence on the stomach from the injury that usually occurs when mucosal prostaglandin levels are suppressed. The new class of NO releasing NSAIDs, including NO-aspirin, represent a very promising approach to reducing the toxicity of anti-inflammatory drugs. Lipoxins are another group of lipid mediators that can protect the stomach. Aspirin-triggered lipoxin synthesis, via COX-2, acts to reduce the severity of damage induced by this drug. Lipoxin analogues may prove to be useful for preventing mucosal injury and for modulating mucosal inflammation. Aspirin-triggered lipoxin also seems to play in important role in gastric adaptation during chronic aspirin administration. Suppression of COX-2 activity by selective COX-2 inhibitors abolishes the production of this endogenous gastroprotective substance and diminishes the gastric tolerability of NSAIDS and gastric adaptation to these drugs. This review was designed to give an updated overview on the physiological factors and experimental and clinical attempts that were used or may be used in the future as the therapeutic approach to counteract adverse effects in the stomach associated with NSAID ingestion.

[Protective role of leptin in acute gastric ulcers]

There are few data concerning protective effects of leptin on gastric epithelium treated with necrotic factors: ethanol, bile salts and hiperosmotic solutions. Further investigations are needed to establish the role of hormone leptin in gastroprotection and in the process of chronic gastric ulcers healing in animals. Exogenous leptin administration plays protective effects against 75% ethanol damage in gastric epithelium. Nitric oxide is involved in gastroprotective effects of leptin and CCK.

Neural aspects of ghrelin-induced gastroprotection against mucosal injury induced by noxious agents

Ghrelin, identified in oxyntic mucosa has been recently implicated in the control of food intake and growth hormone (GH) release but whether this hormone can influence the gastric secretion and gastric mucosal integrity have been little studied. We compared the effects of intraperitoneal (i.p.) and intracerebroventricular (i.c.v.) administration of ghrelin on gastric secretion in rats equipped with gastric fistula (GF) and gastric lesions induced in rats by 75% ethanol and ischemia-reperfusion (I/R) with or without vagotomy or functional ablation of afferent sensory nerves by capsaicin. The number and the area of gastric lesions was measured by planimetry, the GBF was assessed by H(2)-gas clearance method and blood was withdrawn for the determination of the plasma ghrelin and gastrin levels. Ghrelin (5-80 microg/kg i.p. or 600-5000 ng/rat i.c.v.) increased gastric acid secretion and attenuated gastric lesions induced by ethanol and I/R. These protective effects of ghrelin were accompanied by the significant rise in the gastric mucosal blood flow (GBF) and plasma ghrelin and gastrin levels. Ghrelin given i.p. or injected i.c.v. in standard doses 20 microg/kg or 5000 ng/kg, respectively, significantly attenuated the gastric mucosal damage and significantly raised the GBF. Ethanol applied i.g. in smaller concentrations (12.5% and 25%) produced a significant increase in plasma immunorective ghrelin levels and this effect was inhibited in rats receiving ethanol in higher concentrations (75% and 100%). Ghrelin-induced protection after its i.p. or i.c.v. administration and accompanying increase in the GBF were completely abolished by vagotomy and capsaicin-deactivation of sensory nerves. Concurrent treatment with CGRP added to ghrelin restored the gastroprotective and hyperemic effects of ghrelin applied i.p. or i.c.v. in rats with capsaicin denervation. We conclude that central and peripheral ghrelin exerts a potent protective and gastric secretory effects in rats exposed to ethanol and I/R, and that these actions involve vagal nerve integrity, partially depending upon afferent nerves and hyperemia mediated by sensory neuropeptides such as CGRP released from these nerves.

Are probiotics effective in the treatment of fungal colonization of the gastrointestinal tract? Experimental and clinical studies

The influence of fungal colonization and probiotic treatment on the course of gastric ulcer (GU) and ulcerative colitis (UC) was not explored. Our studies included: 1) clinical investigation of 293 patients with dyspeptic and ulcer complaints and 72 patients with lower gastrointestinal (GI) tract: 60 patients with UC, 12 with irritable bowel syndrome (IBS) - the control group. Significant fungal colonization (SFC), over 10(5) CFU/ml was evaluated. Mycological investigation was performed, including qualitative and quantitative examination, according to Muller method, 2) experimental studies in rats included estimation of the influence of inoculation of Candida isolated from human GI tract on the healing process of GU, induced by acetic acid with or without probiotic Lactobacillus acidophilus (10(6) CFU/ml) introduced intragastrically (i.g.). At 0, 4, 15 and 25 day after ulcer induction. Weight, damage area, gastric blood flow (GBF) (H2 clearance), expression of mRNA for cytokines IL-beta, TNF-alpha (ELISA) were evaluated. Mycology: qualitative and quantitative examination was performed. MPO serum activity was measured. Results of clinical studies: 1) SFC was more frequent in patients with GU: 54.2% of cases and patients with over 5 years history of UC: 33.3% cases. 2) SFC delayed GU healing and influenced the maintenance of clinical symptoms in both diseases. Results of animal studies: 3) In Candida inoculated rats, the GBF was significantly lower than in the vehicle controls (saline administered group). Upregulation of TNF-alpha, IL-1 beta was recorded. The GUs were still present till 25 day in all rats inoculated with Candida, in contrast to vehicle group (reduction of ulcer in 92% at day 25).

CONCLUSIONS

1) Fungal colonization delays process of ulcer and inflammation healing of GI tract mucosa. That effect was attenuated by probiotic therapy. 2) Probiotic therapy seems to be effective in treatment of fungal colonization of GI tract. 3) Lactobacillus acidophilus therapy shortens the duration of fungal colonization of mucosa (enhanced Candida clearance is associated with IL-4, INF-gamma response).

Prostaglandin/cyclooxygenase pathway in ghrelin-induced gastroprotection against ischemia-reperfusion injury

Ghrelin is involved in the control of food intake, but its role in gastroprotection against the formation of gastric mucosal injury has been little elucidated. We studied the effects of peripheral (i.p.) and central (i.c.v.) administration of ghrelin on gastric secretion and gastric mucosal lesions induced by 3 h of ischemia/reperfusion (I/R) with or without inhibition of ghrelin growth hormone secretagogue type 1a receptor (GHS-R1a) by using ghrelin antagonist, d-Lys(3)-GHRP-6; blockade of cyclooxygenase (COX)-1 (indomethacin, SC560 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-trifluoromethylpyrazole]) and COX-2 (rofecoxib); and bilateral vagotomy or capsaicin denervation. I/R produced typical gastric erosions, a significant fall in the gastric blood flow (GBF), an increase in gastric myeloperoxidase (MPO) activity and malonyldialdehyde (MDA) content, and the up-regulation of mucosal ghrelin mRNA. Ghrelin dose-dependently increased gastric acid secretion and significantly reduced I/R-induced gastric erosions, while producing a significant rise in the GBF and mucosal PGE(2) generation and a significant fall in MPO activity and MDA content. The protective and hyperemic activities of ghrelin were significantly attenuated in rats pretreated with d-Lys(3)-GHRP-6 and capsaicin denervation and completely abolished by vagotomy. Indomethacin, SC560, and rofecoxib, selective COX-1 and COX-2 inhibitors, attenuated ghrelin-induced protection that was restored by supplying the methyl analog of prostaglandin (PG) E(2). The expression of mRNA for COX-1 was unaffected by ghrelin, but COX-2 mRNA and COX-2 protein were detectable in I/R injured mucosa and further up-regulated by exogenous ghrelin. We conclude that ghrelin exhibits gastroprotective and hyperemic activities against I/R-induced erosions, the effects that are mediated by hormone activation of GHS-R1a receptors, COX-PG system, and vagal-sensory nerves.

Agonist of peroxisome proliferator-activated receptor gamma (PPAR-gamma): a new compound with potent gastroprotective and ulcer healing properties

Pioglitazone, a specific ligand for peroxisome proliferator-activated receptor gamma (PPAR-gamma), was recently implicated in the control of inflammatory processes and in the modulation of the expression of various cytokines such as tumor necrosis factor alpha (TNF-alpha), but its role in the mechanism of gastric mucosal integrity has not been studied extensively. This study was designed to determine the effect of pioglitazone on gastric mucosal lesions induced in rats by topical application of 100% ethanol and by 3.5 h of water immersion and restraint stress (WRS) with or without pretreatment with indomethacin (5 mg/kg i.p.) to inhibit cyclooxygenase-1 (COX-1) and COX-2 enzyme activities and L-NNA (20 mg/kg i.p.) to suppress nitric oxide (NO)-synthase. In addition, the effect of pioglitazone on ulcer healing in rats with chronic acetic acid ulcers (ulcer area 28 mm2) was determined. Rats were killed 1 h and 3.5 h after ethanol administration or WRS exposure or at day 9 upon ulcer induction, and the number and area of gastric lesions were measured by planimetry, the gastric blood flow (GBF) was determined by H2-gas clearance technique and the mucosal PGE2 generation and gene expression and plasma concentration of TNF-alpha and IL-1beta were also evaluated. Pre-treatment with pioglitazone dose-dependently attenuated gastric lesions induced by 100% ethanol and WRS; the dose reducing these lesions by 50% (ID50) being 10 mg/kg and 7 mg/kg, respectively. The protective effect of pioglitazone was accompanied by the significant rise in the GBF, an increase in PGE2 generation and the significant fall in the plasma TNF-alpha and IL-1beta levels. Strong signals for IL-1beta- and TNF-alpha mRNA were recorded in gastric mucosa exposed to ethanol or WRS, and these effects were significantly decreased by pioglitazone. Indomethacin which suppressed PG generation by about 90%, while augmenting WRS damage, and L-NNA, that suppressed NO-synthase activity, significantly attenuated the protective and hyperaemic activity of this PPAR-gamma ligand. In the chronic study, pioglitazone significantly reduced the area of gastric ulcers on day 9 and significantly raised the GBF at the ulcer margin. The acceleration of ulcer healing by PPAR-gamma ligand was accompanied by a significant increase in the expression of PECAM-1 protein, a marker of angiogenesis. We conclude that (1) pioglitazone exerts a potent gastroprotective and hyperaemic actions on the stomach involving endogenous PG and NO and attenuation of the expression and release of proinflammatory cytokines TNF-alpha and IL-1beta, and (2) PPAR-gamma ligand accelerates ulcer healing, possibly due to the enhancement in angiogenesis at ulcer margin.

Grapefruit-seed extract attenuates ethanol-and stress-induced gastric lesions via activation of prostaglandin, nitric oxide and sensory nerve pathways

AIM: Grapefruit-seed extract (GSE) containing flavonoids, possesses antibacterial and antioxidative properties but whether it influences the gastric defense mechanism and gastroprotection against ethanol- and stress-induced gastric lesions remains unknown.

METHODS: We compared the effects of GSE on gastric mucosal lesions induced in rats by topical application of 100% ethanol or 3.5 h of water immersion and restraint stress (WRS) with or without (A) inhibition of cyclooxygenase (COX)-1 activity by indomethacin and rofecoxib, the selective COX-2 inhibitor, (B) suppression of NO-synthase with L-NNA (20 mg/kg ip), and (C) inactivation by capsaicin (125 mg/kg sc) of sensory nerves with or without intragastric (ig) pretreatment with GSE applied 30 min prior to ethanol or WRS. One hour after ethanol and 3.5 h after the end of WRS, the number and area of gastric lesions were measured by planimetry, the gastric blood flow (GBF) was assessed by H₂-gas clearance technique and plasma gastrin levels and the gastric mucosal generation of PGE2, superoxide dismutase (SOD) activity and malonyldialdehyde (MDA) concentration, as an index of lipid peroxidation were determined.

RESULTS: Ethanol and WRS caused gastric lesions accompanied by the significant fall in the GBF and SOD activity and the rise in the mucosal MDA content. Pretreatment with GSE (8-64 mg/kg i g) dose-dependently attenuated gastric lesions induced by 100% ethanol and WRS; the dose reducing these lesions by 50% (ID₅₀) was 25 and 36 mg/kg, respectively, and this protective effect was similar to that obtained with methyl PGE2 analog (5 μg/kg i g). GSE significantly raised the GBF, mucosal generation of PGE₂, SOD activity and plasma gastrin levels while attenuating MDA content. Inhibition of PGE₂ generation with indomethacin or rofecoxib and suppression of NO synthase by L-NNA or capsaicin denervation reversed the GSE-induced protection and the accompanying hyperemia. Co-treatment of exogenous calcitonine gene-related peptide (CGRP) with GSE restored the protection and accompanying hyperemic effects of GSE in rats with capsaicin denervation.

CONCLUSION: GSE exerts a potent gastroprotective activity against ethanol and WRS-induced gastric lesions via an increase in endogenous PG generation, suppression of lipid peroxidation and hyperemia possibly mediated by NO and CGRP released from sensory nerves.

Ischemic preconditioning of remote organs attenuates gastric ischemia-reperfusion injury through involvement of prostaglandins and sensory nerves

Limitation of the stomach damage by its earlier brief ischemia and reperfusion before prolonged ischemia is defined as gastric ischemic preconditioning but whether such brief ischemia of remote organs like heart or liver can also attenuate the gastric damage caused by longer and severe ischemia-reperfusion remains unknown. The cardiac, hepatic and gastric preconditioning were induced by brief ischemia (occlusion of coronary, hepatic and celiac arteries twice for 5 min) applied 30 min before 3 h of ischemia/reperfusion. Standard 3 h ischemia-reperfusion of the stomach produced numerous gastric lesions, decreased gastric blood flow and mucosal prostaglandin E2 generation and increased expression and plasma release of interleukin-1beta and tumor necrosis factor-alpha (TNF-alpha). These effects were significantly attenuated by brief cardiac, hepatic and gastric preconditioning which upregulated cyclooxygenase-2 mRNA but not cyclooxygenase-1 mRNA. The protective effects of brief gastric, cardiac and hepatic preconditioning were attenuated by selective cyclooxygenase-1 and cyclooxygenase-2 inhibitors and capsaicin denervation. We conclude that brief ischemia of remote preconditioning such as heart or liver protects gastric mucosa against severe ischemia-reperfusion-induced gastric lesions as effectively as local preconditioning of the stomach itself via the mechanism involving prostaglandin derived from cyclooxygenase-1 and cyclooxygenase-2 and the activation of sensory nerves releasing calcitonin gene-related peptide (CGRP) combined with the suppression of interleukin-1beta and TNF-alpha expression and release.

Exogenous and endogenous ghrelin in gastroprotection against stress-induced gastric damage

Ghrelin, identified in the gastric mucosa has been involved in control of food intake and growth hormone (GH) release but little is known about its influence on gastric secretion and mucosal integrity. The effects of ghrelin on gastric secretion, plasma gastrin and gastric lesions induced in rats by 75% ethanol or 3.5 h of water immersion and restraint stress (WRS) were determined. Exogenous ghrelin (5, 10, 20, 40 and 80 microg/kg i.p.) increased gastric acid secretion and attenuated gastric lesions induced by ethanol and WRS and this was accompanied by the significant rise in plasma ghrelin level, gastric mucosal blood flow (GBF) and luminal NO concentrations. Ghrelin-induced protection was abolished by vagotomy and attenuated by suppression of COX, deactivation of afferent nerves with neurotoxic dose of capsaicin or CGRP(8-37) and by inhibition of NOS with L-NNA but not influenced by medullectomy and administration of 6-hydroxydopamine. We conclude that ghrelin exerts a potent protective action on the stomach of rats exposed to ethanol and WRS, and these effects depend upon vagal activity, sensory nerves and hyperemia mediated by NOS-NO and COX-PG systems.

Healing of chronic gastric ulcers in diabetic rats treated with native aspirin, nitric oxide (NO)-derivative of aspirin and cyclooxygenase (COX)-2 inhibitor

Previous studies have demonstrated that the gastric mucosa of diabetic rats is highly vulnerable to acute injury but the influence of nonsteroidal anti-inflammatory drugs (NSAID) and their new nitric oxide (NO) releasing derivatives of aspirin (NO-ASA) on the ulcer healing under diabetic conditions has been little studied. In this study streptozocin (STZ, 70 mg/kg injected intraperitoneally) was used to induce diabetes mellitus in rats. Four weeks after STZ injection, gastric ulcers were induced using the acetic acid method and rats with gastric ulcers received the treatment with 1) aspirin (ASA, 30 mg/kg-d i.g.), 2) NO-ASA applied in equimolar dose of 50 mg/kg-d i.g., 3) rofecoxib (5 mg/kg-d i.g.), the selective cyclooxygenase-(COX)-2 inhibitor and 4) SNAP (5 mg/kg-d i.g.), a donor of NO, combined with ASA (30 mg/kg-d i.g.). Ten days after the induction of the ulcers, the healing rate and the gastric blood flow (GBF) were measured by planimetry and hydrogen (H(2))-gas clearance method, respectively and the plasma cytokine such as IL-1beta, TNF-alpha and IL-10 were determined. In addition, the effect of insulin (4 IU/day/rat i.p.) with or without the blockade of NO-synthase by L-NNA (20 mg/kg-d i.p.) on the ulcer healing and the GBF in non-diabetic and diabetic rats was determined. In the diabetic rats, a significant delay in ulcer healing (approximately by 300%) was observed with an accompanied decrease in the GBF at ulcer margin. The prolongation of the healing in diabetic animals was associated with an increase in the plasma cytokine (IL-1beta, TNF-alpha and IL-10) levels. ASA and rofecoxib, that significantly suppressed the mucosal prostaglandin (PG) E(2) generation in ulcer area, delayed significantly the rate of ulcer healing and decreased the GBF at ulcer margin, while elevating plasma IL-1beta, TNF-alpha and IL-10 concentrations in non-diabetic rats and these alterations were significantly augmented in diabetic animals. In contrast to ASA, the treatment with NO-ASA failed to influence both, the ulcer healing and GBF at ulcer margin and significantly attenuated the plasma levels of IL-1beta, TNF-alpha and IL-10 as compared to those recorded in ASA- or rofecoxib-treated animals. Co-treatment of SNAP with native ASA abolished the deleterious effect of ASA on ulcer healing, GBF at ulcer margin and luminal NO release in diabetic rats. Administration of insulin in rats with diabetes, opposed the delay in ulcer healing, and the fall in the GBF at ulcer margin and these effects were counteracted by the concurrent treatment with L-NNA. We conclude that: 1) ulcer healing is dramatically impaired in experimental diabetes and this effect involves the fall in the gastric microcirculation at the ulcer margin and increased release of proinflammatory cytokines; 2) classic NSAID such as ASA and selective COX-2 inhibitors such as rofecoxib, prolong ulcer healing under diabetic conditions probably due to suppression of endogenous PG and the fall in the GBF at the ulcer margin suggesting that both COX isoforms, namely, COX-1 and COX-2, are important sources of PG during ulcer healing in diabetes; and 3) NO-ASA counteracts the impairment of ulcer healing in diabetic rats induced by ASA, mainly due to the release of NO that compensates for PG deficiency resulting in enhancement in the GBF at ulcer margin and suppression of cytokine release in the ulcer area.

Ghrelin-a new gastroprotective factor in gastric mucosa

Ghrelin, a novel peptide expressed in the gastrointestinal tract, especially in the gastric mucosa, exerts several biological activities including the stimulation of appetite and food intake, the stimulation of intestinal motility and the release of growth hormone. The aim of this study was to examine the expression of ghrelin in gastric mucosa after its exposure to ethanol and its effects on gastric lesions induced by ethanol with and without pretreatment with indomethacin. Acute gastric lesions were induced by intragastric administration of 75% ethanol in rats pretreated with saline-vehicle or ghrelin injected intraperitoneally (i.p.) without or with i.p. pretreatment with indomethacin. At the end of experiments, the rats were anesthetized, the stomach was exposed to measure gastric blood flow (GBF), to determine the area of gastric lesions and to take biopsy samples from the oxyntic mucosa for determination of transcripts of ghrelin, tumor necrosis alpha (TNF-alpha) and transforming growth factor alpha (TGFalpha) using RT-PCR and to assess the generation of PGE(2) by RIA. Exposure of gastric mucosa to 75% ethanol resulted in numerous mucosal lesions of an area of about 115 mm(2) and in the increase of mucosal expression of TNF-alpha, PGE(2), TGFalpha and ghrelin with concomitant decrease in GBF. Exogenous ghrelin reduced dose-dependently acute gastric lesions with simultaneous attenuation of GBF and a decrease in the expression of TNF-alpha but not TGFalpha. Pretreatment with indometahcin, which suppressed the generation of PGE(2) by about 85%, augmented ethanol-induced gastric lesions and eliminated the ghrelin-induced protection of mucosa against ethanol. We conclude that ghrelin, whose mucosal expression is enhanced after exposure to ethanol, exhibits a strong gastroprotection, at least in part, due to its anti-inflammatory action mediated by prostaglandins.

Involvement of Capsaicin-Sensitive Afferent Nerves and Cholecystokinin 2/Gastrin Receptors in Gastroprotection and Adaptation of Gastric Mucosa toHelicobacter pylori-Lipopolysaccharide

Lipopolysaccharide (LPS) is one of the virulence factors in the Helicobacter pylori (Hp)-infected stomach, but it remains unknown whether single and prolonged pretreatment with Hp-LPS can affect the course of gastric damage induced by aspirin (ASA). We compared the effects of Hp-LPS with those induced by LPSs isolated from intestinal Bacteroides fragilis, Yersinia enterocolitica, and Campylobacter jejuni applied for 4 days on acute ASA-induced gastric lesions in rats. The area of ASA-induced gastric lesions, gastric blood flow (GBF), expression of mRNA and protein of leptin and plasma leptin, gastrin, interleukin-1beta, and tumor necrosis factor-alpha levels were examined. Single (once) or repeated (five times) i.p. injections of Hp-LPS (1 mg/kg) or intestinal LPSs failed to produce macroscopic gastric damage and did not affect the GBF when compared with vehicle. Hp-LPS injected repeatedly suppressed the gastric acid secretion, up-regulated leptin mRNA and protein, and increased plasma leptin and gastrin levels. Hp-LPS significantly reduced the ASA-induced gastric damage and the accompanying decline in the GBF, and these effects were significantly attenuated by capsaicin denervation and selective antagonism of cholecystokinin-B (CCK2) receptors by RPR-102681 [N-(metoxy-3 phenyl) N-(N-methyl N-phenyl-carbamylmethyl) carbamoylmethyl]-3 ureido]-3 phenyl]-2 propronique] but not by loxiglumide, an antagonist of CCK1 receptors. We conclude that 1) daily application of Hp-LPS enhances gastric mucosal resistance against ASA damage due to the increase of GBF and the expression and release of leptin and gastrin exerting trophic and gastroprotective effects, and 2) this enhanced resistance to ASA damage in Hp-LPS-adapted stomach is mediated by the sensory afferents and specific CCK2/gastrin receptors.

Importance of brain-gut axis in the gastroprotection induced by gastric and remote preconditioning

Limitation of the damage to the organs such as heart, liver, intestine, stomach and brain by an earlier brief complete occlusion of their arteries is defined as ischemic preconditioning (IP). No study so for has been undertaken to check whether brain-gut axis is involved in the gastroprotection exhibited by gastric IP or in that induced by repeated brief episodes of ischemia of remote organs such as heart and liver. This study was designed to determine the possible involvement of vagal and sensory afferent nerves, in the mechanism of gastric and remote organ IP on the gastric mucosa in rats exposed to prolonged ischemia-reperfusion with or without functional ablation of sensory nerves by capsaicin or in those with removed vagal innervation by vagotomy. This gastric IP was induced by short ischemia episodes (occlusion of celiac artery 1-5 times for 5 min) applied 30 min before subsequent ischemia followed by 3 h of reperfusion (I/R) and compared with remote IP induced by occlusion of left descending coronary artery or hepatic artery plus portal vein. The area of gastric lesions was determined by planimetry, gastric blood flow (GBF) was measured by H(2)-gas clearance method and mucosal biopsy samples were taken for the assessment of calcitonin gene-related peptide (CGRP) by RIA. Exposure of gastric mucosa to standard 3 h of I/R produced numerous gastric lesions and significant fall in the GBF and mucosal CGRP content. Two 5 min short ischemic episodes by occlusion of coronary or hepatic arteries, significantly reduced gastric damage induced by I/R with the extent similar to that exhibited by two short (5 min) episodes of gastric ischemia. These protective effects of gastric and remote IPs were accompanied by a restoration of the fall in the CGRP content caused by I/R alone. Protection and hyperemia induced by gastric IP were significantly attenuated in capsaicin-denervated or vagotomized animals and completely removed in those exposed to the combination of vagotomy and capsaicin-denervation. The IP-induced protection and hyperemia were restored by the administration of exogenous CGRP to gastric IP in capsaicin-treated animals. Gastroprotective and hyperemic actions of remote IP were markedly diminished in capsaicin-denervated rats and in those subjected to vagotomy. We conclude that brief ischemia in remote organs such as heart and liver protects gastric mucosa against gastric injury induced by I/R as effectively as gastric IP via mechanism involving both vagal and sensory nerves releasing vasodilatatory mediators such as CGRP.

Enhanced resistance of gastric mucosa to damaging agents in the rat stomach adapted to Helicobacter pylori lipopolysaccharide

BACKGROUND AND AIM

Lipopolysaccharide (LPS) has been proposed to act as one of numerous virulence factors in the Helicobacter pylori (HP)-infected stomach. However, little is known as to whether the gastric mucosa can withstand the repeated LPS insult, and how the possible adaptation to this endotoxin influences the damage induced by strong irritants. We determined the effect of a single or repeated parenteral administration of LPS obtained from HP on acute gastric lesions induced by intragastric application of 100% ethanol (1.5 ml) and by water immersion and restraint stress (WRS).

METHODS

The area of the gastric lesions was measured by planimetry, mucosal gastric blood flow (GBF) was determined by H(2) gas clearance, and gastric luminal content was collected for the determination of luminal NO(2)(-)/NO(3)(-) levels by the Griess reaction. Biopsy samples were taken for the measurement of prostaglandin (PG) E(2) by radioimmunoassay and mucosal expression of constitutive and inducible nitric oxide synthase (cNOS and iNOS), constitutive (COX-1) and inducible cyclooxygenase (COX-2), heat shock protein 70 (HSP 70) mRNA and protein were analyzed by RT-PCR and Western blot.

RESULTS

HP LPS (1 mg/kg i.p.) injected once or 5 times produced negligible macroscopic injury and failed to influence GBF significantly compared to the injuries recorded in vehicle-controlled rats. Single and repeated (5 times) administration of HP LPS significantly reduced ethanol- and WRS-induced lesions, these protective effects were accompanied by a rise in GBF and excessive luminal release of NO. The suppression of NOS activity by L-NAME (20 mg/kg i.p.), a nonspecific NOS inhibitor, or L-NIL (30 mg/kg i.g.), a specific iNOS inhibitor, and of COX-2 activity by NS-398 reversed the protective and hyperemic effects of single or repeated LPS administrations against ethanol and WRS damage and the accompanying rise in NO and PGE(2) production. These effects of L-NAME were significantly antagonized by the addition of L-arginine, a substrate for NO synthesis. The signals for cNOS, COX-1 and HSP 70 mRNA were detected by RT-PCR in the vehicle-treated gastric mucosa, whereas gene and protein expression of iNOS, COX-2 and HSP 70 mRNA were significantly increased only in rats treated with 1 or 5 applications of HP LPS.

CONCLUSIONS

Repeated injections of HP LPS enhance gastric mucosal resistance to the mucosal damage induced by ethanol and WRS via a mechanism involving mucosal overexpression of iNOS, COX-2 and HSP 70 with subsequent excessive production of NO and PGE(2).

Pioglitazone, a specific ligand of peroxisome proliferator-activated receptor-gamma, accelerates gastric ulcer healing in rat

The peroxisome proliferator-activated receptor-gamma (PPAR-gamma) is a member of the nuclear hormone receptor superfamily that is involved in the control of inflammation and carcinogenesis. We determined the effect of the specific PPAR-gamma ligand, pioglitazone (5-40 mg/kg intragastrically), on the healing of acetic-acid gastric ulcers in rats. At day 8 after ulcer induction, the ulcer area, the gastric blood flow and mucosal expression of proinflammatory cytokines such as interleukin-1beta, tumour necrosis factor alpha (TNF-alpha) and cyclooxygenase-1, cyclooxygenase-2, constitutive nitric oxide synthase (cNOS), inducible nitric oxide synthase (iNOS) and heat shock protein 70 (HSP70) was determined. Pioglitazone reduced the area of gastric ulcers and raised significantly the gastric blood flow at the ulcer margin and downregulated the mRNA for interleukin-1beta, TNF-alpha, cyclooxygenase-2 and iNOS while cyclooxygenase-1 mRNA was not affected. The expression of PPAR-gamma mRNA was increased in the ulcerated gastric mucosa. We conclude that pioglitazone accelerates the healing of preexisting gastric ulcers due to the hyperemia at ulcer margin and the anti-inflammatory action including suppression of interleukin-1beta, TNF-alpha, cyclooxygenase-2 and iNOS and by an overexpression of HSP70.

Implications of reactive oxygen species and cytokines in gastroprotection against stress-induced gastric damage by nitric oxide releasing aspirin

BACKGROUND AND AIMS

Nitric oxide-releasing aspirin (NO-ASA) has been shown to inhibit cyclo-oxygenase and prostaglandin generation without causing mucosal damage, but the role of reactive oxygen species (ROS) and cytokines in the action of ASA and NO-ASA against acute gastric damage has been little studied.

METHODS AND MATERIALS

We compared the effect of NO-ASA and ASA on gastric lesions provoked by water-immersion and restraint stress (WRS), ischemia-reperfusion, and 100% ethanol. We determined the number and area of gastric lesions, gastric blood flow (GBF), plasma concentration of proinflammatory cytokines IL-1beta and TNFalpha, expression of superoxide dismutase (SOD) and glutathione peroxidase (GPx), ROS generation, and the malondialdehyde (MDA) concentration as an index of lipid peroxidation.

RESULTS

Pretreatment with NO-ASA attenuated dose-dependently gastric erosions provoked by WRS, ischemia-reperfusion, and ethanol. In contrast, ASA aggravated significantly WRS-induced lesions, and this was accompanied by a fall in the GBF, suppression of prostaglandin E(2) generation, and significant rise in ROS chemiluminescence and in plasma TNFalpha and IL-1beta levels. ASA also enhanced significantly the mucosal MDA content and downregulated SOD and GPx mRNA, and these effects were markedly reduced by NO-ASA.

CONCLUSION

Coupling of NO to ASA attenuates stress, ischemia-reperfusion, and ethanol-induced damage due to mucosal hyperemia mediated by NO, which compensates for prostaglandin deficiency induced by ASA. ASA aggravates WRS damage via enhancement of ROS and cytokine generation and suppression of SOD and GPx, and these effects are counteracted by NO released from NO-ASA.

Functional and morphological aspects of Helicobacter pylori-induced gastric cancer in Mongolian gerbils

BACKGROUND

Helicobacter pylori infection of Mongolian gerbils is an established model of gastric carcinogenesis, but gastric secretory aspects of this carcinogenesis have not been studied.

METHODS

The effects of single intragastric inoculation of gerbils with H. pylori strain (cagA+ vacA+, 5 x 10(6) CFU/ml) or vehicle (saline) were examined at 1, 2, 4, 6, 9, 12 and 30 weeks from inoculation. Gastric morphology, the presence of H. pylori using the rapid urease test, the density of H. pylori and 16S rRNA and the plasma gastrin and somatostatin were determined.

RESULTS

H. pylori was detected in gastric mucosa in all infected animals. Basal gastric acid in gerbils was reduced by about 50% after H. pylori inoculation. Early lesions seen at 4 weeks after H. pylori inoculation consisted of chronic gastritis with thickened mucosal folds, oedema, congestion and mucosal lymphocytic infiltration. Adenomatous hyperplasia with cellular atypia with increased mitotic activity and the formation of apoptotic bodies and visible erosions and ulcerations were observed at 12-30 weeks after inoculation. The atypical gastric glands were situated 'back-to-back', suggesting gastric pre-cancer. The gastric blood flow in H. pylori-infected gerbils was significantly lower than that in the controls. Six- to seven-fold increase in plasma gastrin levels combined with significant fall in gastric somatostatin contents and the intraepithelial neoplasia were noticed in gerbils at all tested periods.

CONCLUSION

H. pylori-infection in gerbils resulted in gastric pre-cancer associated with functional changes, such as suppression of gastric secretion and impairment of both gastric mucosal microcirculation and the gastrin-somatostatin link.

Triple eradication therapy counteracts functional impairment associated with Helicobacter pylori infection in Mongolian gerbils

Gastric Helicobacter pylori (Hp) infection in Mongolian gerbils is an established experimental model of gastric carcinogenesis resulting from the long-term Hp infection but functional aspects accompanying this Hp-induced progression from gastritis to the cancer, especially changes in gastric acid secretion, gastric blood flow (GBF) and gastrin-somatostatin link have been little studied. It is unclear whether Hp eradication therapy alters the functional and the histopathological changes in this animal model of Hp-infection. We examined the effects of intragastric (i.g.) inoculation of Mongolian gerbils with Hp strain (cagA+ vacA+, 5 x 10(6) CFU/ml) that had been isolated from a patient with gastric ulcer as compared to those induced by vehicle (saline) in gerbils with or without gastric fistula (GF) at 1.2, 4, 6, 9, 12 and 30 wks upon gastric inoculation with this bacteria. An attempt was made to evaluate the influence of anti-Hp triple therapy with omeprazole, amoxicillin and tinidazol on gastric Hp-infection and Hp-induced functional impairment of the gastric mucosa. Gastric mucosal biopsy specimens were taken for the assessment of the morphological changes and the presence of Hp infection using rapid urease test (CLO-test) and the density of Hp-colonization were assessed by counting of the number of bacterial colonies per plate. Gastric blood flow (GBF) was measured by H2-gas clearance technique and the venous blood and the gastric content were collected for the measurement of plasma gastrin levels and the gastric luminal somatostatin level by radioimmunoassay (RIA). The Hp in gastric mucosa was detected in all animals by culture and rapid urease test at various periods upon Hp inoculation. Basal gastric acid in non-infected conscious gerbils with GF reached the level of about 28 +/- 4 micromol/h and this was reduced by over 50% immediately upon the Hp-inoculation and persisted for time intervals tested up to 30 wk. Early lesions were seen 4 wks after the Hp-inoculation and consisted of chronic gastritis with thickened gastric mucosal foldings and elongated interfoveolar ridges. Edema and congestion as well as significant mucosal inflammatory infiltration with lymphoid infiltrate in lamina propria of the mucosa occurred in all infected gerbils. Adenomatous hyperplasia with cellular atypia was observed at 12 wk upon Hp-inoculation together with increased mitotic activity and numerous apoptotic bodies formation, while lamina propria was reduced leaving dilated atypical gastric gland situated "back-to-back". This glandular atypia failed to show lamina propria or submucosa infiltration corresponding to gastric intraepithelial neoplasia. The GBF in Hp-infected gerbils was significantly lower, and a 6-7 fold increase in plasma gastrin levels combined with a significant fall in gastric luminal somatostatin contents observed at all tested periods as compared to vehicle-controls and these effects were counteracted by anti-Hp triple therapy. We conclude that: 1). Hp-infection in Mongolian gerbils in early stages before adenocarcinoma formation results in the development of typical functional and pathological changes such as suppression of gastric secretion and impairment of both, gastric mucosal microcirculation and gastrin-somatostatin link, and 2). this deleterious influence of Hp on gastric morphology and gastric functions is greatly attenuated in gerbils treated with Hp-eradication therapy.

Importance of nitric oxide (NO) and adenosine in the mechanism of gastric preconditioning induced by short ischemia

PURPOSE

Gastric mucosa subjected to repeated brief episodes of ischemia exhibits an increased resistance to damage caused by a subsequent prolonged ischemic insult and this is called gastric preconditioning. In this study, L-NNA, a non-selective NO-synthase inhibitor, and aminoguanidine, a relative inhibitor of inducible NO-synthase (iNOS), were applied prior to short ischemia (occlusion of celiac artery 1-5 times for 5 min) followed by a subsequent exposure to 0.5 h of ischemia and 3 h of reperfusion (I/R).

MATERIAL AND METHODS

Male Wistar rats were used in all studies.

RESULTS

Short ischemia reduced significantly I/R-induced lesions while raising significantly the GBF and luminal NO content. These effects were attenuated by L-NNA and aminoguanidine and restored by addition of L-arginine and SNAP to L-NNA and aminoguanidine. Pretreatment of with adenosine (10 mg/kg i.p.) significantly reduced I/R lesions and accompanying fall in the GBF induced by I/R. These protective and hyperemic effects of standard preconditioning and adenosine were significantly attenuated by pretreatment with 8-phenyl theophylline (SPT, 10 mg/kg i.g.), an antagonist of adenosine A1 and A2 receptors.

CONCLUSIONS

We conclude that gastric ischemic preconditioning is considered as one of the major protective mechanism in the stomach that involves key vasodilatory mediators such as NO and adenosine.

Role of prostaglandins, nitric oxide, sensory nerves and gastrin in acceleration of ulcer healing by melatonin and its precursor, L-tryptophan

Melatonin, a major hormone of pineal gland, was recently shown to attenuate acute gastric lesions induced by strong irritants because of the scavenging of free radicals but its role in ulcer healing has been little investigated. In this study we compared the effects of intragastric (i.g.) administration of melatonin and its precursor, L-tryptophan, with or without concurrent treatment with luzindole, a selective antagonist of melatonin MT2 receptors, on healing of chronic gastric ulcers induced by serosal application of acetic acid (ulcer area 28 mm2). The involvement of endogenous prostaglandins (PG), nitric oxide (NO) and sensory nerves in ulcer healing action of melatonin and L-tryptophan was studied in rats treated with indomethacin and NG-nitro-L-arginine (L-NNA) to suppress, respectively, cyclo-oxygenases (COX) and NO synthases or in those with functionally deactivated sensory nerves with capsaicin. The influence of melatonin on gastric secretion during ulcer healing was tested in separate group of rats with gastric ulcer equipped with gastric fistulas (GF). At day 8 and 15 upon the ulcer induction, the area of gastric ulcers was measured by planimetry, the mucosal blood flow (GBF) was determined by H2-gas clearance technique and gastric luminal NO2-/NO3- levels was assessed by Griess reaction. Plasma melatonin and gastrin levels were measured by specific radioimmunoassay (RIA). Biopsy mucosal samples were taken for expression of constitutive NO-synthase (cNOS) and inducible NOS (iNOS) by reverse transcriptase-polymerase chain reaction (RT-PCR). Melatonin (2.5-20 mg/kg-d i.g.) and L-tryptophan (25-100 mg/kg-d i.g.) dose-dependently accelerated ulcer healing, the dose inhibiting by 50% (ED50) of ulcer area being 10 and 115 mg/kg, respectively. This inhibitory effect of melatonin (10 mg/kg-d i.g.) and L-tryptophan (100 mg/kg-d i.g.) on ulcer healing was accompanied by a significant rise in the GBF at ulcer margin and an increase of plasma melatonin. luminal NO2-/NO3- and plasma gastrin levels. Gastric acid and pepsin outputs were significantly inhibited during the ulcer healing in melatonin-treated gastric mucosa as compared with those in vehicle-treated animals. Luzindole abolished completely the healing effects of melatonin and L-tryptophan and attenuated significantly the rise in plasma gastrin evoked by the hormone and its precursor. Indomethacin (5 mg/kg-d i.p). that blocked PG biosynthesis by 90% or L-NAME (20 mg/kg i.v), inhibitor of NOS. that suppressed luminal NO release, attenuated significantly melatonin and L-tryptophan-induced acceleration of ulcer healing and accompanying rise in GBF at ulcer margin and luminal NO release. The melatonin-induced acceleration of ulcer healing, hyperemia at ulcer margin and increase in the release of NO were enhanced when L-arginine but not D-arginine was added to L-NAME. The ulcer healing and the GBF effects of melatonin and L-tryptophan were significantly impaired in rats with capsaicin-induced denervation of sensory nerves and both, ulcer healing and the hyperemia at ulcer margin were restored in these rats by addition of exogenous CGRP to melatonin and L-tryptophan. Expression of cNOS mRNA was detected by RT-PCR in the intact gastric mucosa as well as at the edge of gastric ulcers treated with both, vehicle and melatonin, while iNOS mRNA that was undetectable in the intact gastric mucosa, appeared during ulcer healing and especially this was strongly up-regulated in the melatonin-treated gastric mucosa. We conclude that (1) exogenous melatonin and that derived from its precursor, L-tryptophan, accelerate ulcer healing probably via interaction with MT2 receptors; (2) this ulcer healing action is caused by an enhancement by melatonin of the microcirculation at the ulcer margin possibly mediated by COX-derived PG and NO because of overexpression of iNOS and (3) gastrin, which exhibits trophic activity in the gastric mucosa and calcitonin gene related peptide (CGRP), released from sensory nerves, may also contribute to the ulcer healing action of melatonin.

Brain-gut axis in gastroprotection by leptin and cholecystokinin against ischemia-reperfusion induced gastric lesions

Leptin, a product of ob gene controlling food intake, has recently been detected in the stomach and shown to be released by CCK and implicated in gastroprotection against various noxious agents but it is unknown whether centrally applied leptin influences ischemia-reperfusion (I/R)-induced gastric erosions that progress into deeper gastric ulcerations. In this study we compared the effects of leptin and CCK-8 applied intracerebroventricularly (i.c.v.) or intraperitoneally (i.p.) on gastric mucosal lesions induced by I/R and topical application of 75% ethanol. Several major series of Wistar rats were used to examine the effects of leptin and CCK applied centrally on gastroprotection against I/R and ethanol in rats with A) vagotomy by cutting of vagal nerves, B) suppression of NO-synthase with L-NNA (20 mg/kg i.p.), C) inactivation of sensory nerves by capsaicin (125 mg/kg s.c.) and D) inhibition of CGRP receptors with CGR(8-37) (100 microg/kg i.p.) applied with or without the i.c.v. pretreatment with leptin or CCK-8. Rats were anesthetized 1 h after ethanol administration or at 3 h and 3 days upon the end of ischemia to measure the gastric blood flow (GBF) and then to determine the area of gastric lesions by planimetry. Blood was withdrawn for the measurement of plasma leptin and gastrin levels by radioimmunoassay (RIA). Leptin (0.1-20 microg/kg i.p.) dose-dependently attenuated gastric lesions induced by 75% ethanol and I/R; the dose reducing these lesions by 50% (ED50) was 8 microg/kg and 6 microg/kg, respectively and this protective effect was similar to that obtained with CCK-8 applied in a standard dose of 10 microg/kg i.p. This protective effect of leptin was accompanied by a significant increase in GBF and plasma gastrin levels whereas CCK-8 increased plasma leptin levels but failed to affect plasma gastrin levels. Leptin and CCK-8 applied i.c.v. in a dose of 625 ng/rat reduced significantly the area of I/R induced gastric lesions and raised the GBF and plasma leptin levels with the extent similar to those achieved with peripheral administration of leptin or CCK-8 (10 microg/kg i.p.). The protective and hyperemic effects of centrally administered leptin or CCK-8 (625 ng/rat i.c.v.) were completely abolished by vagotomy and significantly attenuated by sensory denervation with capsaicin or by CGRP antagonist, CGRP(8-37). The pretreatment with L-NNA to inhibit NO-synthase activity attenuated significantly the protective and hyperemic effects of CCK but not those of leptin while capsaicin denervation counteracted leptin-induced protection and rise in the GBF but attenuated significantly those of CCK. We conclude that: 1) central leptin exerts a potent gastroprotective activity against I/R-induced gastric erosions that progress into deeper gastric lesions and this protection depends upon vagal activity and sensory nerves and involves hyperemia probably mediated by NO and 2) leptin mimics the gastroprotective effect of CCK and may be implicated in the protective and hyperemic actions of this peptide against mucosal damage evoked by I/R.

Effect of central and peripheral actions of histamine and its metabolite N-alpha methyl histamine on gastric secretion and acute gastric lesions

N alpha-methylhistamine (N alpha-MH) is one of unusual metabolite of histamine that was found in Helicobacter pylori-infected stomach and is believed to interact with specific histamine H1, H2 and H3-receptors to stimulate gastric acid secretion and gastrin release from isolated G-cells but the effects of N alpha-MH on gastric mucosal integrity have been little studied. This study was designed; 1) to compare the effect of intraperitoneal (i.p.), intracerebroventricular (i.c.v.) and gastric topical (intragastric i.g.) application of exogenous N alpha-MH with that of standard histamine on gastric secretion in rats equipped with gastric fistula (series A) and 2) to compare the effect of i.c.v. administration of histamine and N alpha-MH with that of peripheral (i.p. and i.g.) application of these amines on gastric lesions induced by 100% ethanol (series B) in rats with or without capsaicin-induced deactivation of sensory nerves. The area of gastric lesions was determined planimetrically, gastric blood flow (GBF) was assessed by H2-gas clearance method and venous blood was collected for determination of plasma gastrin levels by RIA. N alpha-MH and histamine (0.1-10 mg/kg i.p. or i.g.) dose-dependently increased gastric acid output (series A); whereas i.c.v. administration of histamine or N alpha-MH inhibited dose-dependently this secretion; the dose attenuating gastric acid output by 50% (ED50) being 4 and 6 microg/kg i.c.v. Both, N alpha-MH and histamine (2 mg/kg i.p. and i.g.) attenuated significantly the area of gastric lesions induced by 100% ethanol (series B) while producing significant rise in the GBF and plasma immunoreactive gastrin increments. Central application of N alpha-MH and histamine (0.01-5 microg/kg i.c.v.) inhibited ethanol-induced gastric damage whereas higher doses ranging from 10-100 microg/kg of histamine and N alpha-MH were significantly less effective. Capsaicin-induced deactivation of sensory nerves by itself augmented significantly ethanol damage and attenuated significantly the protective and hyperemic effects of histamine and its methylated analog applied i.p. but failed to affect significantly those caused by i.c.v. administration of these amines. We concluded that: 1) central histamine and N alpha-MH inhibits gastric acid secretion and exhibits gastroprotective activity against ethanol in similar manner to that afforded by parenteral and topical histamine and N-alphaMH, 2) central N-alphaMH- and histamine-induced protection involve the enhancement in gastric microcirculation unrelated to neuropeptides released from capsaicin-sensitive afferent nerves, and 3) the major difference between central and peripheral histamine and its methylated analog is the influence on gastric acid secretion which does not appear to play any major role in gastroprotective activity of these agents.