Michal Pawlik

Therapeutic Potential of 1-Methylnicotinamide against Acute Gastric Lesions Induced by Stress : Role of Endogenous Prostacyclin and Sensory Nerves

1-Methylnicotinamide (MNA) is one of the major derivatives of nicotinamide, which was recently shown to exhibit antithrombotic and antiinflammatory actions. However, it is not yet known whether MNA affects gastric mucosal defense. The effects of exogenous MNA were studied on gastric secretion and gastric lesions induced in rats by 3.5 h of water immersion and water restraint stress (WRS) or in rats administered 75% ethanol. MNA [6.25–100 mg/kg intragastrically (i.g.)] led to a dose-dependent rise in the plasma MNA level, inhibited gastric acid secretion, and attenuated these gastric lesions induced by WRS or ethanol. The gastroprotective effect of MNA was accompanied by an increase in the gastric mucosal blood flow and plasma calcitonin gene-related peptide (CGRP) levels, the preservation of prostacyclin (PGI2) generation (measured as 6-keto-PGF1α), and an overexpression of mRNAs for cyclooxygenase (COX)-2 and CGRP in the gastric mucosa. R-3-(4-Fluoro-phenyl)-2-[5-(4-fluoro-phenyl)-benzofuran-2-ylmethoxycarbonylamino]-propionic acid (RO 324479), which is the selective antagonist of IP/PGI2 receptors, reversed the effects of MNA on gastric lesions and GBF. MNA-induced gastroprotection was attenuated by suppression of COX-1 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole; SC-560] and COX-2 [4-(4-methylsulfonylphenyl)-3-phenyl-5H-furan-2-one; rofecoxib] activity, capsaicin denervation, and by the pretreatment with CGRP8-37 or capsazepine. Addition of exogenous PGI2 or CGRP restored the MNA-induced gastroprotection in rats treated with COX-1 and COX-2 inhibitors or in those with capsaicin denervation. WRS enhanced MDA content while decreasing superoxide dismutase (SOD) activity in the gastric mucosa, but pretreatment with MNA reversed these changes. MNA exerts potent gastroprotection against WRS damage via mechanisms involving cooperative action of PGI2 and CGRP in preservation of microvascular flow, antioxidizing enzyme SOD activity, and reduction in lipid peroxidation.

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.

Gastroprotective and ulcer healing effects of nitric oxide-releasing non-steroidal anti-inflammatory drugs

BACKGROUND & AIM New class of nitric oxide-releasing non-steroidal anti-inflammatory drugs was shown to inhibit cyclooxygenase and prostaglandin generation without causing mucosal damage but whether these agents are capable of affecting gastric mucosal damage induced by strong irritants and healing of chronic gastric ulcers remains to be studied. In this investigation, effects of nitric oxide-releasing aspirin and nitric oxide-releasing naproxen were compared with those of native agents on gastric lesions provoked by 100% ethanol and on healing of chronic acetic acid ulcers. RESULTS Both, nitric oxide-releasing aspirin and naproxen dose-dependently attenuated ethanol-induced damage and produced a significant rise in gastric blood flow but did not delay healing of gastric ulcers while native aspirin and naproxen had no influence on ethanol-induced gastric damage but significantly prolonged ulcer healing, reduced gastric blood flow and suppressed mucosal generation of prostaglandin E2. The gastroprotective and hyperaemic effects of both nitric oxide-non-steroidal anti-inflammatory drugs were completely abolished by ODQ, an inhibitor of guanylyl cyclase-cGMP system but not influenced by suppression of nitric oxide-synthase with L-NNA. The damaging effects of native acetyl salicylate acid or naproxen were aggravated by acidification of these non-steroidal anti-inflammatory drugs but the exogenous acid added to nitric oxide-acetyl salicylate acid or nitric oxide-naproxen failed to influence their effect. Despite inhibiting of PGE2 generation, both nitric oxide-releasing derivatives and native aspirin and naproxen failed to affect expression of cyclooxygenase-1 mRNA but upregulated the cyclooxygenase-2 mRNA. Concurrent inhibition of cyclooxygenase-2 by selective inhibitor NS-398 which by itself delayed ulcer healing and attenuated the gastric blood flow at ulcer margin, significantly worsened the effects of these nitric oxide-non-steroidal anti-inflammatory drugs and their parent drugs on ulcer healing and the gastric blood flow at the ulcer margin. CONCLUSIONS 1) Coupling of nitric oxide to aspirin or naproxen attenuates ethanol-induced damage, possibly due to an increase in gastric microcirculation mediated by excessive release and action of nitric oxide that probably compensates for PG deficiency induced by non-steroidal anti-inflammatory drugs; and 2) nitric oxide-non-steroidal anti-inflammatory drug, unlike classic non-steroidal anti-inflammatory drugs, does not affect intact gastric mucosa and fails to delay the healing of pre-existing ulcers.

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.

Esophagoprotection mediated by exogenous and endogenous melatonin in an experimental model of reflux esophagitis

Reflux esophagitis is a common clinical entity in western countries with approximately 30% of the population experiencing the symptoms at least once every month. The imbalance between the protective and aggressive factors leads to inflammation and damage of the esophageal mucosa. We compared the effect of exogenous melatonin and melatonin derived endogenously from L‐tryptophan with that of pantoprazole or ranitidine in acid reflux esophagitis due to ligation of the rat pylorus and the limiting ridge between the forestomach and the corpus. Four hours after the induction of gastric reflux, an increase in mucosal lesions associated with edema of the submucosa and with the infiltration of numerous neutrophils and the fall in esophageal blood flow (EBF) were observed. Both melatonin and L‐tryptophan or pantoprazole significantly reduced the lesion index (LI) and raised the EBF. Pinealectomy that significantly decreased plasma melatonin levels aggravated LI and these effects were reduced by melatonin and L‐tryptophan. Luzindole, the MT2 receptor antagonist, abolished the melatonin‐induced reduction in LI and the rise in EBF. L‐NNA and capsaicin that augmented LI and decreased EBF, also significantly reduced melatonin‐induced protection and hyperemia; both were restored with L‐arginine and calcitonin gene–related peptide (CGRP) added to melatonin. Upregulation of IL‐1β and TNF‐α mRNAs and plasma IL‐1β and TNF‐α levels were significantly attenuated by melatonin and L‐tryptophan. We conclude that melatonin protects against acid reflux‐induced damage via activation of MT2 receptors mediated by NO and CGRP released from sensory nerves and the suppression of expression and release of TNF‐α and IL‐1β.

Role of histamine in ghrelin-induced gastroprotection against acute gastric lesions

Ghrelin is an orexigenic gut peptide produced predominantly by the stomach. Besides the regulation of food intake, ghrelin is reported to have strong growth hormone-releasing activity and to regulate important gastrointestinal functions [1]. The majority of circulating ghrelin is produced in Gr-cells located in the oxyntic mucosa [2]. Plasma ghrelin concentrations increase before meals and decrease post-prandially, giving it a distinct meal-related diurnal profi le [3]. Recently, we have shown potent gastroprotective activity of ghrelin against acute gastric mucosal injury [4]. Since both histamine producing ECL-cells and ghrelin producing Gr-cells are located in the oxyntic mucosa we investigated whether histamine is involved in the gastroprotective action of ghrelin.

Involvement of gastrin in gastric secretory and protective actions of N-alpha-methyl histamine.

N alpha-methylhistamine (N alpha-MH) is one of an unusual metabolite of histamine that was found in Helicobacter pylori-infected stomachs and is believed to interact with specific histamine H(1), H(2) and H(3)-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 exogenous N alpha-MH with that of standard histamine on gastric secretion and plasma gastrin levels in rats equipped with gastric fistula (series A); and (2) to assess the action of N alpha-MH on gastric lesions induced by 100% ethanol (series B) in rats with or without removal of antral portion of the stomach (antrectomy). Rats of series B were pretreated intragastrically (i.g.) or intraperitoneally (i.p.) with N alpha-MH or histamine (0.1-2 mg/kg) 30 min prior to 100% ethanol (1.5 ml, i.g.) with or without: (1) vehicle (saline); (2) RPR 102681 (30 mg/kg i.p.), to block CCK-B/gastrin receptors; and (3) ranitidine (40 mg/kg s.c.) to inhibit histamine H(2)-receptors. The area of gastric lesions was determined planimetrically, gastric blood flow (GBF) was assessed by H(2)-gas clearance method and venous blood was collected for determination of plasma gastrin levels by radioimmunoassay (RIA). N alpha-MH and histamine dose-dependently increased gastric acid output (series A); the dose increasing this secretion by 50% (ED(50)) being 2 and 5 mg/kg i.g or i.p., respectively, and this effect was accompanied by a significant rise in plasma gastrin levels. Both, N alpha-MH and histamine attenuated dose-dependently the area of gastric lesions induced by 100% ethanol (series B) while producing significant rise in the GBF and plasma immunoreactive gastrin increments. These secretory, protective, hipergastrinemic and hyperemic effects of N alpha-MH and histamine were completely abolished by antrectomy, whereas pretreatment with RPR 102681 attenuated significantly the N alpha-MH and histamine-induced protection against ethanol damage and accompanying hyperemia. Ranitidine, that produced achlorhydria and a further increase in plasma gastrin levels, failed to influence the N alpha-MH- and histamine-induced protection and accompanying rise in the GBF. We conclude that (1) N alpha-MH stimulates gastric acid secretion and exhibit gastroprotective activity against acid-independent noxious agents in the manner similar to that afforded by histamine; and (2) this protection involves an enhancement in the gastric microcirculation and release of gastrin acting via specific CCK-B/gastrin receptors but unexpectedly, appears to be unrelated to histamine H(2)-receptors.

Gastroprotective Activity of Grapefruit (Citrus paridisi) Seed Extract Against Acute Gastric Lesions

Publisher Summary This chapter provides an outline of the antibacterial, antiviral, and antiparasitic activities of grapefruit seeds. Grapefruit seed extract (GSE) is a product of the grapefruit seed and pulps, and has been found to exert antibacterial, antiviral, and antiparasitic activities. Previous studies documented that grapefruit seeds are the major depositories for limonoids. Grapefruit also contains many flavonoid glycosides, naringenin, quercetin, kaempferol, hesperidin, and apigenin being the most abundant among their aglycones. Grapefruit seed extracts (GSEs), containing flavonoids, have been shown to possess antibacterial, antiviral, and antifungal properties. Furthermore, grapefruit-containing flavonoids such as naringenin were also recently implicated in cytoprotection against injury induced by algal toxins in isolated hepatocytes. The antimicrobiological properties of GSE against a wide range of gram-negative and gram-positive organisms were attributed to the disruption it caused to the bacterial membrane and the subsequent liberation by this extract of the bacterial cytoplasmic contents within a relatively short time. The underlying mechanism of the therapeutic efficacy of citrus seed extracts such as from grapefruits and red grapes seems to depend upon the presence of different classes of polyphenolic flavonoids, which were shown to inhibit platelet aggregation, thus decreasing the risk of coronary thrombosis and myocardial infarction. The mechanism of the gastroprotective activity of GSE appears to be dependent on endogenous PG and the functional activity of sensory nerves releasing CGRP. The major mechanism of protection against gastric mucosal damage involves enhancement of the gastric microcirculation mediated by increased generation of endogenous prostaglandins (PGs) and nitric oxide (NO) and activity of sensory neuropeptides such as CGRP. Interestingly, GSE in a formulation of Citricidal was demonstrated to be effective against more than 800 bacterial and viral strains, 100 strains of fungus, and a large number of single- or multi-celled parasites.

Involvement of nitric oxide (NO) in the mechanism of gastric preconditioning induced by short ischemia

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). Short ischemia significantly reduced the 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. The cNOS mRNA, but not iNOSmRNA, was detected in intact mucosa and only cNOS mRNA was strongly upregulated in the preconditioned mucosa. We conclude that overexpression of cNOS with the subsequent release of NO plays a key role in the mechanism of gastric preconditioning.