Gastric protection by meciadanol. A new synthetic flavonoid inhibiting histidine decarboxylase

Gastric antiulcerogenic and hypokinetic activities of Terminalia fagifolia Mart. & Zucc. (Combretaceae)

The acute toxicity, the antioxidant activity, and the pharmacological activity on the gastrointestinal tract of rodents of the ethanolic extract (TFEE) from the bark of Terminalia fagifolia Mart. & Zucc. (Combretaceae) and of its aqueous (TFAqF), hydroalcoholic (TFHAF), and hexanic (TFHEXF) partition fractions have been evaluated. TFEE presented low acute toxicity, antioxidant, and antiulcerogenic activity against ethanol-induced ulcers, which was partially blocked by pretreatment with L-NAME and indomethacin. It reduced the total acidity and raised the pH of gastric secretion. Additionally, TFEE delayed gastric emptying and slightly inhibited the small intestinal transit and also presented a weakly antidiarrheal activity. The antiulcerogenic and antioxidant activity were also detected in TFAqF and TFHAF but not in TFHEXF. The antisecretory and gastroprotective activity of TFEE partially involve the nitric oxide and prostaglandin participation. Nevertheless, TFEE, TFAqF, and TFHAF drastically reduced the mucus layer adhered to the gastric wall of rats treated with ethanol or indomethacin. Complementary studies are required in order to clarify the paradox of the presence of a gastroprotector activity in this plant that, at the same time, reduces the mucus layer adhered to the gastric wall.

Selective histamine H₃ and H₄ receptor agonists exert opposite effects against the gastric lesions induced by HCl in the rat stomach

The present study investigated the role of histamine H(3) and H(4) receptors in gastric mucosal defense, by the use of selective ligands. Firstly, the affinities of several histaminergic agonists for the rat histamine H(3) and H(4) receptors were checked in HEK 293T cells transfected with either receptor subtype. Next, functional activities were determined in conscious rat against the ulcerogenic effect of 0.6N HCl. Radioligand binding studies showed that immethridine and methimepip were the most selective agonists at rat H(3) receptors, whereas VUF10460 displayed approximately a 50-fold selectivity for the rat H(4) receptor over the H(3) receptor. In conscious rats, immethridine and methimepip significantly reduced (66% and 48% inhibition, respectively) the gastric lesions induced by HCl; the effect of immethridine was antagonized by the H(3) receptor antagonist A-331440, but not by the H(4) receptor antagonist JNJ7777120. The mixed H(3)/H(4) receptor agonist immepip induced a significant aggravation of HCl damage, which was prevented by JNJ7777120; HCl-induced lesions were also significantly enhanced by the H(4) receptor agonists VUF10460 and VUF8430; however, this effect was not modified by JNJ7777120. Overall, this study indicates that, whereas the histamine H(3) receptor is involved in the protection of rat stomach against concentrated HCl, the functional role of the H(4) receptor is still to be defined, although selective agonists induce proulcerogenic effects under HCl challenge. Finally, the species-dependent variations in affinity and receptor selectivity observed for most ligands need to be carefully addressed in the pharmacological characterization of histamine H(3) and H(4) receptor functions in vivo.

Gastroprotective activity of the hydroalcoholic extract obtained from Polygala paniculate L. in rats

The possible gastroprotective effects of the hydroalcoholic extract of Polygala paniculata in rats have been evaluated. We have investigated the effects of this hydroalcoholic extract on acute lesions induced by ethanol (70%, p.o.) and indometacin (20 mg kg−1, s.c). Its influence on mucus secretion was investigated, measured as the amount of Alcian blue dye estimated by colorimetry, and antisecretory effects were assessed in the pylorus ligature model. The treatment of rats with a crude hydroalcoholic extract of P. paniculata (HEPP; 30, 100, 300 mg kg−1, p.o., or 3, 10 and 30 mg kg−1, i.p.) decreased the ulcer index, and maintained the gastric mucus production in acute gastric lesions caused by ethanol 70%. In addition, the extract partially protected the mucosa against indometacin-induced lesions. The extract did not change the volume and acidity of gastric secretion in the pylorus-ligated rat. An additional antioxidant activity of the extract and its isolated flavonoid compound rutin, in the DPPH free radical scavenging assay, was observed. In conclusion, HEPP exhibited marked gastroprotection; these effects may have involved prostaglandins and be related to cytoprotective factors, such as antioxidant activity and maintenance of mucus production.

Apple polyphenol extracts prevent aspirin-induced damage to the rat gastric mucosa

Aspirin causes gastroduodenal ulcers and complications. Food bioactive compounds could exert beneficial effects in the gastrointestinal tract. We evaluated whether apple polyphenol extract (APE) reduced aspirin-induced injury to the rat gastric mucosa. Rats were treated with APE (10(-4) m catechin equivalent) before oral aspirin (200 mg/kg). Cyclo-oxygenase-2 (COX-2), transforming growth factor-alpha (TGF alpha) and heparin-binding epidermal-growth-factor-like growth factor (HB-EGF) mRNA and protein expression were assessed by RT-PCR and Western blot analysis, respectively; malondialdehyde (MDA) was determined by HPLC; gastric secretion was evaluated in pylorus-ligated rats. APE decreased acute and chronic aspirin injury both macroscopically and microscopically (approximately 50 % decrease in lesion score; P < 0.05). Aspirin up-regulated mRNA and protein expression of COX-2 and HB-EGF, but not of TGF alpha; APE reduced aspirin-induced mRNA and protein over-expression of COX-2 and HB-EGF; aspirin significantly increased gastric MDA and this effect was counteracted by APE pre-treatment. APE did not significantly affect gastric acid secretion. In conclusion, APE reduces aspirin-induced gastric injury independently of acid inhibition. We speculate that APE might be of therapeutic use in the prophylaxis of aspirin-related gastropathy.

(-)-epigallocatechin gallate inhibits the pacemaker activity of interstitial cells of cajal of mouse small intestine

The effects of (-)-epigallocatechin gallate (EGCG) on pacemaker activities of cultured interstitial cells of Cajal (ICC) from murine small intestine were investigated using whole-cell patch-clamp technique at 30 and Ca(2+) image analysis. ICC generated spontaneous pacemaker currents at a holding potential of -70 mV. The treatment of ICC with EGCG resulted in a dose-dependent decrease in the frequency and amplitude of pacemaker currents. SQ-22536, an adenylate cyclase inhibitor, and ODQ, a guanylate cyclase inhibitor, did not inhibit the effects of EGCG. EGCG-induced effects on pacemaker currents were not inhibited by glibenclamide, an ATP-sensitive K(+) channel blocker and TEA, a Ca(2+)-activated K(+) channel blocker. Also, we found that EGCG inhibited the spontaneous [Ca(2+)](i) oscillations in cultured ICC. In conclusion, EGCG inhibited the pacemaker activity of ICC and reduced [Ca(2+)](i) oscillations by cAMP-, cGMP-, ATP-sensitive K+ channel-independent manner.

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.

The effect of epigallocatechin gallate on intestinal motility in mice

OBJECTIVES

The epigallocatechin-3-gallate (EGCg) that is present in human diet originates mainly from tea leaves. Catechins have a number of possible application as medicines, however, there is no consistent evidence showing their influence on the gastrointestinal tract. Thus, the aim of the present study was to investigate the effect of EGCg on the motility of the murine isolated intestine.

METHODS

Segments of jejunum submerged in Krebs buffer were exposed to EGCg and the response was recorded under isometric conditions.

RESULTS

EGCg induced a dose-dependent inhibition of spontaneous activity in the jejunum. EGCg induced a decrease in the amplitude and frequency of jejunal contractions. moreover, the rythmicity of spontaneous, activity was altered in the presence of EGCg. A significant effect of EGCg was observed in the presence of 10(-4) M. The effect of EGCg was in part inhibited by pretreatment with methylene blue (guanylate cyclase inhibitor), while tetrodotoxin, (sodium channel blocker), L-nitro arginine methyl ester (nitric oxide synthase inhibitor), and N-ethylmaleimide (adenylate cyclase inhibitor) showed no effect.

CONCLUSIONS

The results of the present study suggest that EGCg inhibits the motility of the jejunum by direct action on smooth muscle cells where a guanylate cyclase-dependent mechanism may be partly involved.

A natural flavonoid and synthetic analogues protect the gastric mucosa from aspirin-induced erosions

The anti-ulcerogenic properties of plantain banana have been well established even though the active ingredient has only recently been identified as the flavonoid leucocyanidin. The aim of this study was to evaluate the ability of the natural flavonoid leucocyanidin and synthetic analogues to protect the gastric mucosa against aspirin challenge. Natural and synthetic flavonoids were added to the diet of rats, and their anti-ulcerogenic potential evaluated using a prophylactic animal model. Leucocyanidin and its synthetic hydroxyethylated and tetrallyl derivatives were found to protect the gastric mucosa from aspirin-induced erosions. Leucocyanidin and its hydroxyethylated and tetraallyl derivatives significantly increased mucus thickness. Whilst the mechanism by which the natural and synthetic flavonoids protect the gastric mucosa remains to be fully elucidated, it may, as indicated in this study, involve an increase in mucus thickness.

A natural flavonoid present in unripe plantain banana pulp (Musa sapientum L. var. paradisiaca) protects the gastric mucosa from aspirin-induced erosions

The active anti-ulcerogenic ingredient was extracted from unripe plantain banana by solvent fractionation and identified by chromatography, spectroscopy and high performance liquid chromatography as the flavonoid leucocyanidin. Dried unripe plantain banana powder, the extracted leucocyanidin and a purified synthetic leucocyanidin demonstrated a significant (P < 0.05) protective effect against aspirin-induced erosions.

Protection against necrotizing agents-induced gastric lesions in rats. Unrelated to inhibition of gastric motility

Effects of necrotizing agents, blockers of gastric motility, and mild irritants on gastric mucosa and gastric motility were investigated in conscious rats. Gastric motor activity was recorded using a miniature balloon placed in the glandular part of the stomach, which was connected to a pressure transducer and polygraph. Necrotizing agents, such as 96% ethanol, 0.6 N hydrochloric acid, 0.2 N sodium hydroxide, or 4 M sodium chloride, were given intragastrically through a fistula on the forestomach. One milliliter of these agents produced hemorrhagic bandlike lesions in the corpus mucosa along the long axis of the stomach with the occurrence of a complete inhibition of gastric motility (smooth muscle relaxation). Blockers of gastric motility alone, such as subcutaneous papaverine HCl (50 mg/kg), and intraperitoneal verapamil (20 mg/kg), or mild irritants (1 ml/rat, orally) such as 20% ethanol or 1 M NaCl, which by themselves suppressed gastric motility, have no effect on gastric mucosa and on the inhibited gastric motility induced by necrotizing agents. Bandlike lesions were significantly prevented by pretreatment with 20% ethanol or 1 M NaCl but not with papaverine HCl or verapamil administered 30 min before necrotizing agents. The gastroprotection offered by 20% ethanol or 1 M NaCl was significantly diminished by pretreatment with subcutaneous indomethacin (30 mg/kg), but the inhibited gastric motility was not reversed by indomethacin. These results indicate that it seems unlikely that gastric contractile activity would play a major role in the development and prevention of gastric lesions after the administration of necrotizing agents.

Ulcer-protecting effects of naringenin on gastric lesions induced by ethanol in rat: role of endogenous prostaglandins

This study was designed to determine the cytoprotective properties of naringenin and the involvement of endogenous prostaglandins on mucosal injury produced by absolute ethanol. Gastric glands were also histologically analysed. Oral pretreatment with the highest dose of naringenin (200 mg kg-1), 240 min before absolute ethanol, was the most effective in ulcer prevention. Subcutaneous administration of indomethacin (10 mg kg-1) to the animals treated with naringenin (200 mg kg-1) partially inhibited the gastric protection but there was no increase in prostaglandin E2. All treated groups showed a marked increase in gastric mucus, although this increase was less in animals pretreated with indomethacin. Total proteins and hexosamine content decreased in the groups receiving indomethacin. Histomorphometric evaluation of the gastric damage, with the highest dose of naringenin (200 mg kg-1), confirmed a significant increase of mucus production accompanied by a parallel reduction of gastric lesion.

Effect of DS-4574, a novel peptidoleukotriene antagonist with mast cell stabilizing action, on acute gastric lesions and gastric secretion in rats

DS-4574 is a peptidoleukotriene antagonist with mast cell stabilizing activity. In the present study, we studied the effects of this compound on gastric secretion and various acute gastric lesions in rats. Intraduodenal administration of DS-4574 at doses of 5 to 10 mg/kg significantly and dose-dependently inhibited gastric acid secretion in pylorus-ligated rats, but a further increase in the dose up to 50 mg/kg did not cause any further inhibition. Shay ulceration in response to pylorus ligation was dose-dependently prevented by DS-4574 (10-25 mg/kg, i.d.). Water-immersion restraint stress- and aspirin-induced gastric ulcers were also significantly prevented in a dose-related manner by oral pretreatment with DS-4574 (10-50 mg/kg). The lower doses of DS-4574 (1-10 mg/kg, p.o.) significantly and dose-dependently protected the gastric mucosa against the necrotizing action of either absolute ethanol or concentrated hydrochloric acid, indicating that this compound possesses a potent gastroprotective activity. These antiulcer and gastric protective effects of DS-4574 were more potent than those of cimetidine used as a reference drug. These findings suggest that DS-4574 is useful for peptic ulcer therapy, as well as for the therapy of various allergic diseases, including asthma.

Mechanisms of gastroprotection

Gastric mucosa is constantly exposed to various irritants, but it usually maintains its integrity owing to several lines of defense, including mucus-alkaline secretion, mucosal hydrophobicity, rich mucosal blood flow, stabilization of tissue lysosomes, maintenance of mucosal sulfhydryls, and rapid proliferation and renewal of mucosal cells. Prostaglandins (PG) inhibit experimental gastric mucosal damage and ulcerations induced by a wide variety of agents, hence PG have been proposed to contribute to the overall protective process by activation of various mucosal defence lines--particularly by prevention of vasocongestion, ischemia, and deep hemorrhagic necrosis. The relation between tissue PG generation and mucosal protection does not appear to be closely related, and probably only minute amounts of PG are required to maintain mucosal integrity. In contrast to PG, other products of arachidonate metabolism, such as TxA2, LTC4 or LTD4, and the related lipid, platelet-activating factor, appear to mediate mucosal damage mainly by the disturbance in mucosal microcirculation and tissue ischemia. Gastroprotection can be achieved by stimulation of mucosal biosynthesis of protective PG or by the inhibition of the release or action of the proulcerogenic arachidonate metabolites. Certain natural substances, such as sulfhydryls, epidermal growth factor, or polyamines, protect the mucosa via a PG-independent mechanism, probably by enhancing the tissue repair processes.(ABSTRACT TRUNCATED AT 250 WORDS)

Bile salt binding by maalox, sucralfate, and meciadanol: in vitro and clinical comparisons

Inhibition of gastric acid secretion is a major factor in protecting the gastric mucosa, although other mechanisms such as bile salt binding may contribute to the protective properties of individual agents. Sucralfate, antacid (Maalox), and Meciadanol, a new flavonoid, were compared with cholestyramine resin for binding bile salts. The free, glycine, and taurine conjugates of the human bile salts, cholate, chenodeoxycholate, and deoxycholate, were incubated with each of the above. Cholestyramine resin adsorbed 91-97% of all bile salts tested. Meciadanol adsorbed all of the bile salts fairly well except for the free forms of chenodeoxycholate and deoxycholate. Meciadanol (53 to 84%) adsorbed bile salts better than sucralfate (4.2 to 61%), and significantly (P less than 0.05) better than Maalox (10 to 47%). In our in vitro studies, sucralfate was not as effective in binding bile salts as previously reported. Patients in the surgical intensive care unit were randomized prospectively to receive nasogastric instillation of Maalox, sucralfate, or Meciadanol to prevent gastrointestinal bleeding. The gastric aspirates were analyzed for bile salt concentration. The mean bile salt concentration of those treated with Maalox (0.24 mM), Meciadanol (0.24 mM), or sucralfate (0.35 mM) was significantly lower than those treated with nasogastric aspiration (0.87 mM) alone (P less than 0.01). This suggests that these substances bind bile salts and may provide additional protection to the gastric mucosa along with their ability to neutralize gastric acid.

Protection against absolute-ethanol-induced gastric antral and corpus mucosal injury. A gross and histologic study

The purpose of this study was to systematically assess 100% ethanol-induced gross and histologic injury of the antral and the corpus mucosa of the rat stomach and the effect of two protective agents, a prostaglandin analog and meciadanol (a flavenoid) on this injury. The gross antral injury was much more subtle than the corpus injury. Therefore, different scoring criteria were developed for the antrum. Surprisingly, however, the extent and severity of histologic injury was similar in both areas. Pretreatment with either meciadanol or 16,16-dimethyl prostaglandin E2 significantly protected against this injury in the antrum as well as in the corpus.

The protective effect of Meciadanol (O-methyl-3(+)-catechin) on experimental ulceration

Meciadanol, (O-methyl-3(+)-catechin), a histidine decarboxylase inhibitor was shown to have a marked protective action against experimental peptic ulceration in three rat models. The three methods used to induce ulceration were the instillation of absolute alcohol, pyloric ligation following an ulcerogenic South Indian diet and the instillation of rice bran oil into the stomach after pyloric ligation. Meciadanol was shown to reduce incidence, numbers and areas of ulceration and protected mast cells against degranulation and to preserve a normal vascular patterns. Furthermore, Meciadanol reduced gastric acid output and concentration in the pylorus ligation model. These results indicate that Meciadanol may be useful for the treatment of peptic ulcers in humans.

Mucosal coating agents and other nonantisecretory agents. Are they cytoprotective?

Gastric cytoprotection is protection against gross and histological gastric mucosal injury by a mechanism other than inhibition of neutralization of gastric acid secretion. Animal studies have shown that a variety of agents afford such a protective effect. With some of these agents, a similar protective effect has been shown in man. This protective effect must be distinguished from an action that enhances healing of an already established mucosal lesion as an ulcer. It is yet to be established that the cytoprotective effect of an agent enhances ulcer healing. Agents other than prostaglandins that have been shown to possess such a cytoprotective effect in animals are reviewed. Some, such as sucralfate, act via stimulation of endogenous prostaglandin synthesis, while others, such as DeNol, neomycin, and meciadanol, do not. Investigation of the mechanism through which these agents enhance gastric mucosal defense is a fertile field for investigation.