Jolanta Majka

Inhibition of nitric oxide synthase delays healing of chronic gastric ulcers

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

Role of salivary glands and epidermal growth factor (EGF) in gastric secretion and mucosal integrity in rats exposed to stress

EGF, produced mainly by salivary glands, inhibits gastric acid secretion, stimulates the proliferation of gastric mucosal cells and protects the mucosa against various ulcerogens, but its role in the pathogenesis of stress ulcerations is unknown. In this study, rats with intact or resected salivary glands were exposed to water immersion and restraint stress (WRS) without and with pretreatment with exogenous EGF or dimethyl PGE2 (dmPGE2) at doses which were shown previously to protect the mucosa against topical irritants. During 1.5-12 h of WRS, the formation of gastric ulcerations increased progressively with the duration of stress reaching peak after 6 h of stress and being significantly higher in rats with removed salivary glands than in intact animals. Gastric acid secretion and DNA synthesis in oxyntic mucosa declined with the duration of WRS, but after sialoadenectomy a significant increase in gastric acid secretion and a further decline in DNA synthesis were observed after WRS. EGF contents in the gastric lumen and the gastric mucosa were several times higher in rats subjected to stress than in control unstressed animals, indicating that stress causes an extensive release of EGF. Both exogenous EGF (17 nmol/kg/h) and dmPGE2 (143 nmol/kg) prevented, in part, the formation of gastric lesions, while inhibiting gastric acid secretion both in rats with intact or resected salivary glands. We conclude that water immersion and restraint stress is accompanied by an excessive release of EGF, which appears to attenuate gastric secretion, enhances the DNA synthesis and may limit the formation of stress-induced gastric ulcerations.

Epidermal growth factor, polyamines, and prostaglandins in healing of stress-induced gastric lesions in rats

Previous studies demonstrated that epidermal growth factor (EGF) and polyamines (PA) are capable of protecting gastric mucosa against topical irritants. This study was designed to examine whether EGF, PA, and PG affect the healing of acute gastric lesions induced by water immersion and restraint stress. It was found that the healing process of stress lesions in sham-operated rats was significant after 6 hr after stress, and after 24 hr the number of stress lesions was reduced by about 75%. In sham-operated rats, the healing of ulcerations observed at 6, 12, and 24 hr after the stress was accompanied by gradual restoration of DNA synthesis, and both these processes were significantly reduced by administration of DFMO (an inhibitor of ornithine decarboxylase activity) or indomethacin (an inhibitor of cyclooxygenase). In salivectomized rats, the healing was significantly delayed and the DNA was lowered at all time intervals after the stress. Administration of EGF, spermine, aminoguanidine (an inhibitor of degradation of PA), or 16,16-dmPGE2 after stress promoted significantly the healing and DNA synthesis, but pretreatment with DFMO abolished the effect of EGF but not that of spermine. We conclude that EGF, PA, and PG are implicated in healing of stress lesions and that EGF acts, at least in part, by the stimulation of PA formation in the gastric mucosa.

Oral cavity as a potential source of gastric reinfection by Helicobacter pylori

Helicobacter pylori (Hp) is a common pathogen colonizing the a gastric mucosa, but some reports indicated that it may also be found in the oral cavity, which could serve as a reservoir of the bacteria and a source of gastric reinfection. Accordingly, we aimed to study whether the oral cavity, particularly gingival pockets, are colonized by Hp and whether it could be the source of gastric reinfection. We studied 329 patients with dyspeptic symptoms (257 with chronic gastritis, 15 with gastric ulcer, and 57 with duodenal ulcer). The [13C]urea breath test (UBT), gastroscopy, and Hp culture from gastric biopsies were carried out, and material was collected from the oral cavity (gingival pocket) for bacteriological culture and genomic DNA studies. The serum was obtained for anti-Hp IgG and anti-CagA assays and saliva for anti-Hp IgA determination using the ELISA technique. Bacteria in material from gingival pockets and biopsies from the corpus and antrum of stomach of 30 DU patients before and after Hp eradication were also examined by PCR technique, using primers specific for 16S rRNA. All Hp-positive patients (276) were subjected to one week of triple therapy (omeprazole 2 × 20 mg twice a day, clarithromycin 2 × 500 mg twice a day, and metronidazole 2 × 500 mg twice a day). The measurements described above were then repeated at four weeks and six months. Bacteriological culture showed the presence of Hp in the material from oral cavity in about 50% of patients, whereas UBT, used as a gold standard, revealed gastric Hp infection in about 84% of these patients. The eradication was successful in the majority of patients (87%), but about 13% of them were still Hp positive after four weeks and about 21% after six months. Four weeks after Hp therapy, Hp was found in culture from oral samples in 23% (P < 0.05 vs initial) and after six months in 35.1%. The IgA levels recorded in saliva were in a close agreement with UBT results. Hp DNA assessed by PCR in 30 DUs before eradication of Hp was detected in 95% of antral mucosa, 90% in corpus mucosa, and in 35% of gingival pocket material, and after eradication therapy Hp DNA values fell to 25%, 20%, and 10%, respectively. In conclusion, Hp is commonly detected in the oral cavity of patients with dyspeptic symptoms, but the gastric reinfection does not appear to occur in the patients despite oral Hp colonization.

Nitric oxide in gastroprotection by sucralfate, mild irritant, and nocloprost : role of mucosal blood flow

Pretreatment with sucralfate is known to protect gastric mucosa against the damaging effect of strong irritants, and this protection is accompanied by an increase in mucosal blood flow but the mechanisms underlying these effects have not been elucidated. Similar gastroprotective and hyperemic effects can be obtained with exogenous prostaglandins (PG), mild irritants such as dilute ethanol, and by capsaicin. In this study we investigated the role of nitric oxide (NO) in the prevention of ethanol-induced gastric damage and gastric blood flow by sucralfate, mild irritant such as 20% ethanol, capsaicin, and nocloprost, a stable PGE2 analog. Pretreatment withNG-nitro-l-arginine (l-NNA), an inhibitor of NO synthase, enhanced ethanol-induced mucosal damage and reduced dose-dependently the gastroprotective and hyperemic effects of sucralfate, dilute ethanol, and capsaicin. The doses ofl-NNA attenuating significantly the protective effects of sucralfate or 20% ethanol were 25–50 mg/kg, while those reducing the protection by capsaicin were 6.2–12.5 mg/kg. The attenuating effect ofl-NNA on gastroprotection was reversed byl-arginine but notd-arginine. For comparison, the gastroprotective (but not hyperemic) effect of nocloprost was not affected by the pretreatment withl-NNA and/or arginine. We conclude that sucralfate, mild irritant, and capsaicin activate the NO system that may contribute to their gastroprotective effect through enhancing mucosal circulation but that NO is not essential for the mucosal protection by PGE2 analog.

Role of nitric oxide and prostaglandins in sucralfate-induced gastroprotection

We investigated the role of nitric oxide (NO) and prostaglandins (PG) in the prevention by sucralfate of ethanol-induced gastric damage and the decrease of gastric blood flow and compared them with those obtained with nocloprost, a potent locally acting gastroprotective agent. Sucralfate and nocloprost given intragastrically (i.g.) protected dose dependently the gastric mucosa against the damage by absolute ethanol and prevented the decrease in blood flow induced by ethanol. Pretreatment with NG-nitro-L-arginine (L-NNA), an inhibitor of NO synthase decreased dose dependently the protection and the maintenance of blood flow provided by sucralfate but not by nocloprost. This decrease of sucralfate protection was antagonized by L-arginine but not D-arginine. Pretreatment with indomethacin also reversed, in part, the protective and hyperemic effects of sucralfate but the combination of both indomethacin and L-NNA completely abolished these effects. We conclude that sucralfate activates both the NO and PG systems that cooperate in the gastroprotective action of this drug and that NO is not involved in the protection induced by a PGE2 analog.

Nocloprost, a unique prostaglandin E2 analog with local gastroprotective and ulcer-healing activity

Nocloprost (9 beta-chloro-16,16-dimethyl prostaglandin E2 (PGE2)) was examined for gastroprotective and ulcer-healing activity and compared to 16,16-dimethyl PGE2 (dmPGE) in rats. Nocloprost given intragastrically (i.g.) at various doses (0.01-10 micrograms/kg) 30 min before 100% ethanol, acidified aspirin (ASA), acidified taurocholate, water immersion, or restraint stress dose dependently prevented the formation of gastric lesions, the ID50 values being 0.25, 0.58, 0.06 and 0.12 micrograms/kg, respectively. The gastroprotection provided by nocloprost given i.g. was somewhat enhanced by the presence of acid in the stomach and was reduced by inhibition of gastric acid secretion. Nocloprost given s.c. also showed protective activity against ethanol damage but was ineffective when applied intraduodenally. The protective effect of nocloprost lasted about 8 h whereas that induced by dmPGE lasted 6 h. Nocloprost (0.01-100 micrograms/kg) given i.g. failed to affect gastric acid secretion or intestinal secretion (enteropooling) but prevented the increased gastroduodenal alkaline secretion. Nocloprost alone caused only a transient increase in the mucosal blood flow but prevented the fall in blood flow caused by 100% ethanol. [3H]Nocloprost was absorbed from the small intestine but was then taken up and metabolized by the liver and excreted into the bile so that very little reached the systemic circulation in an unchanged form. Nocloprost, unlike dmPGE, accelerated the healing of chronic gastric ulcerations and enhanced mucosal growth. We conclude that nocloprost is a locally active PGE2 analog with high cytoprotective and ulcer-healing efficacy.

Role of polyamines and prostaglandins in gastroprotective action of epidermal growth factor against ethanol injury.

Epidermal growth factor (EGF) exhibits its gastroprotective action against a variety of irritants and ulcerogens and plays an important role in healing of acute and chronic gastroduodenal ulcerations, but the mechanisms of these effects are not known. The present study was undertaken to determine whether polyamines (such as spermine or putrescine) and prostaglandins (PGs), which also show protective properties, contribute to the gastroprotective effect of EGF against ethanol injury in rats. It was found that both EGF and polyamines significantly and dose-dependently prevented the formation of gastric lesions induced by absolute ethanol, the effect being similar to that obtained with 16,16-dimethylprostaglandin E2. Pretreatment with indomethacin failed to affect the gastroprotective action of EGF and polyamines, suggesting that endogenous PGs may not play any major role in this protection. Our finding that the protective effect of EGF can be abolished by pretreatment with DFMO, an inhibitor of the polyamine biosynthetic pathway, suggests that gastroprotection by EGF is due, at least in part, to stimulation of biosynthesis of protective polyamines.

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.

Role of neurophils and mucosal blood flow in gastric adaptation to aspirin

Gastric mucosa adapts to ulcerogenic action of aspirin but the mechanism of this phenomenon is unknown. In this study, acute gastric lesions were produced by single or repeated oral administration of acidified aspirin in rats with intact or deactivated (by capsaicin) sensory nerves and with intact or suppressed synthase of nitric oxide (NO). Single oral dose of aspirin produced a dose-dependent increase in the area of gastric lesions accompanied by a significant increase in blood neutrophils, neutrophil infiltration into the mucosa, leukotriene B4 formation and almost complete suppression of prostaglandin synthesis. After repeated administration of aspirin, the mucosal damage progressively declined and this was accompanied by a significant augmentation in gastric blood flow. In addition, a reduction in blood neutrophil count, mucosal neutrophil infiltration and leukotriene B4 release was observed during this adaptation of the stomach to repeated aspirin insults. Capsaicin denervation of sensory nerves aggravated the damage induced by the first exposure of the stomach to aspirin and caused a significant reduction in gastric blood flow, but with repeated aspirin administration, gastric adaptation to this agent and a rise in gastric blood flow were observed. Pretreatment NG-nitro-L-arginine with (L-NNA), a specific inhibitor of nitric oxide synthase, eliminated the hyperemic response to repeated aspirin insults but failed to affect the adaptation to aspirin. We conclude that the rat stomach adapts readily to repeated aspirin insults despite sustained inhibition of prostaglandin biosynthesis and this adaptation appears to be mediated by a significant increase in gastric blood flow and a reduction in neutrophil activation and leukotriene B4 release.