Role of mucus in ischemia/reperfusion-induced gastric mucosal injury in rats

Gastric mucus plays an important role in gastric mucosal protection. Apart from its "barrier" function, it has been demonstrated that mucus protects gastric epithelial cells against toxic oxygen metabolites derived from the xanthine/ xanthine oxidase system. In this study, we investigated the effect of malotilate and sucralfate (mucus production stimulators) and N-acetylcysteine (mucolytic agent) on ischemia/reperfusion-induced gastric mucosal injury. Gastric ischemia was induced by 30 min clamping of the coeliac artery followed by 30 min of reperfusion. The mucus content was determined by the Alcian blue method. Sucralfate (100 mg/kg), malotilate (100 mg/kg), and N-acetylcysteine (100 mg/kg) were given orally 30 min before surgery. Both sucralfate and malotilate increased the mucus production in control rats. On the other hand, N-acetyloysteine significantly decreased mucus content in control (sham) group. A significant decrease of mucus content was found in the control and the N-acetylcysteine pretreated group during the period of ischemia. On the other hand, sucralfate and malotilate prevented the decrease the content of mucus during ischemia. A similar result can be seen after ischemia/reperfusion. In the control group and N-acetylcysteine pretreated group a significant decrease of adherent mucus content was found. However, sucralfate and malotilate increased mucus production (sucralfate significantly). Sucralfate and malotilate also significantly protected the gastric mucosa against ischemia/reperfusion-induced injury. However, N-acetylcysteine significantly increased gastric mucosal injury after ischemia/reperfusion. These results suggest that gastric mucus may be involved in the protection of gastric mucosa after ischemia/reperfusion.     

Role of salivary epidermal growth factor in the maintenance of physicochemical characteristics of oral and gastric mucosal mucus coat

The involvement of salivary epidermal growth factor (EGF) in the maintenance of oral and gastric mucosal mucus coat dimension and chemical characteristics was investigated using sialoadenectomized rats. Examination of the oral and gastric mucosal surface by phase contrast microscopy and Alcian blue uptake revealed that deprivation of salivary EGF caused a 31-36% reduction in mucus coat thickness and a 38-43% reduction in adherent mucin content. Chemical analyses indicated that the mucus coat of sialoadenectomized group exhibited a 21-28% increase in protein and a 67% decrease in covalently bound fatty acids, a 30% decrease in carbohydrates, and a 32-37% decrease in lipids. Sialoadenectomy also evoked changes in the chemical composition of mucus glycoprotein component of oral and gastric mucus coat reflected in the lower content of sulfate (25-26%), associated lipids (24-25%), and covalently bound fatty acids (67-75%). Intragastric supplementation of EGF had no effect on the physicochemical changes caused by sialoadenectomy in the oral mucosal mucus coat, while nearly complete restoration to normal characteristics occurred in the gastric mucosal mucus coat. The results suggest that salivary EGF is essential for the maintenance of mucus coat dimension and quality needed in the protection of alimentary tract epithelium.     

The gastric mucus layers: constituents and regulation of accumulation

The mucus layer continuously covering the gastric mucosa consists of a loosely adherent layer that can be easily removed by suction, leaving a firmly adherent mucus layer attached to the epithelium. These two layers exhibit different gastroprotective roles; therefore, individual regulation of thickness and mucin composition were studied. Mucus thickness was measured in vivo with micropipettes in anesthetized mice [isoflurane; C57BL/6, Muc1-/-, inducible nitric oxide synthase (iNOS)-/-, and neuronal NOS (nNOS)-/-] and rats (inactin) after surgical exposure of the gastric mucosa. The two mucus layers covering the gastric mucosa were differently regulated. Luminal administration of PGE(2) increased the thickness of both layers, whereas luminal NO stimulated only firmly adherent mucus accumulation. A new gastroprotective role for iNOS was indicated since iNOS-deficient mice had thinner firmly adherent mucus layers and a lower mucus accumulation rate, whereas nNOS did not appear to be involved in mucus secretion. Downregulation of gastric mucus accumulation was observed in Muc1-/- mice. Both the firmly and loosely adherent mucus layers consisted of Muc5ac mucins. In conclusion, this study showed that, even though both the two mucus layers covering the gastric mucosa consist of Muc5ac, they are differently regulated by luminal PGE(2) and NO. A new gastroprotective role for iNOS was indicated since iNOS-/- mice had a thinner firmly adherent mucus layer. In addition, a regulatory role of Muc1 was demonstrated since downregulation of gastric mucus accumulation was observed in Muc1-/- mice.     

Enhancement of the physicochemical qualities of gastric mucus by sofalcone.

The effect of prolonged administration of an antiulcer drug, sofalcone, on the physicochemical properties of gastric mucus was investigated. The experiments were conducted with groups of rats receiving twice daily for three consecutive days a dose of 100 mg/kg sofalcone, while the control group received daily doses of vehicle. The rats were sacrificed 16 h after the last dose and gastric mucosa subjected to physicochemical measurements. The results revealed that sofalcone evoked a 23% increase in mucus gel dimension, while sulfo- and sialomucins content of the gel increased by 54 and 25%, respectively. These changes were accompanied by a 16% increase in mucus H+ retardation capacity, 2-fold increase in viscosity, and a 39% increase in the gel hydrophobicity. The mucus elaborated in the presence of sofalcone contained 67% more covalently bound fatty acids, exhibited 10% lower content of protein, 30% higher content of carbohydrate, and 18% higher content of lipids. The mucus of the sofalcone group also showed an increase in the proportion of the high molecular weight mucus glycoprotein form, which in the control group accounted for about 30% of gel mucin, while its content in mucus gel of animals receiving sofalcone reached the value of 50%. The results indicate that sofalcone enhances the protective qualities of mucus component of gastric mucosal barrier.     

Biosynthesis of proteins by human gastric mucosa in vitro.

Incorporation of L-[U-14C]leucine and of D[U-14C]glucose into proteins of fresh human gastric mucosa in vitro was studied after incubation of homogenized tissue and of intact mucosal pieces. CsCl centrifugation was used to separate high-density mucus glycoproteins from other mucosal proteins, and the macromolecular nature of radioactive mucosal glycoprotein fractions was confirmed by SDS/polyacrylamide-gel electrophoresis and autoradiography of the polyacrylamide gels. In all experiments a substantial proportion of total incorporated radioactivity was associated with gastric-mucosal glycoprotein fractions (CsCl fraction L3), indicating their biosynthesis. Radioactivity of these fractions was shown to co-chromatograph with carbohydrates when fractionated either directly or after reduction and alkylation (1) Sephadex G-200 chromatography in the excluded fractions and (2) by DEAE-cellulose ion-exchange chromatography. On incubation of intact mucosa, the major portion of radioactivity associated with the glycoprotein fractions of both leucine- and glucose-labelled specimens was secreted into the mucosal media during the course of the experiment. It is suggested that biosynthesis of mucus in vivo by gastric mucosa may be associated with rapid secretion of the synthesized macromolecules into the lumen of the stomach and that investigations of the metabolic processes within the mucosa should consider the products of secretion of the tissue. Incorporation of L-[U-14C]leucine implies biosynthesis of the polypeptide components of the macromolecules.     

Biosynthesis, processing and secretion of mucus glycoprotein in the rat stomach

For the study of the biosynthesis, processing and secretion of mucus glycoproteins in rat gastric mucous cells, antibodies were raised against purified gastric mucus glycoproteins and against deglycosylated gastric mucus glycoproteins. Indirect immunofluorescence analysis of gastric mucosa sections revealed that both antibodies specifically labelled the mucus glycoprotein-synthesizing cells in the gastric mucosa. Stomach segments were pulse-labelled with [35S]cysteine and chased for various times. The radioactively labelled (glyco)proteins were quantitatively immunoprecipitated and analyzed by SDS-polyacrylamide gel electrophoresis. Less than 3% of the total radioactivity incorporated in protein was found to be present in mucus glycoproteins. Antibodies raised against native mucus glycoproteins recognized only high-molecular-weight mucus glycoproteins, while the antibodies against deglycosylated glycoproteins also bound to probable precursor forms. The synthesis of mature mucus glycoproteins (Mr greater than 300 000) required about 90 min. After 3 h of chase, only a small portion of the pulse-labelled mucus glycoproteins had been secreted; the majority of the radioactive glycoproteins at that time was still associated with the tissue. Immature (glyco)proteins were not secreted into the medium.     

Aluminium hydroxide uptake in the stomach and in the intestine of the rat: a histochemical study.

Using the histochemical stains aluminon, solochrome azurine and solochrome cyanine, intracellular binding of aluminium was examined in the mucosa of the stomach, duodenum, jejunum and ileum of adult rats. A first group of rats (n = 42) was sacrificed 1, 3, 6, 12, 24, 48 and 96 h after a single (300 mg x kg-1) oral administration of aluminium hydroxide. A second group of animals (n = 30) received daily the same dose of Al(OH)3 and was euthanatized after 3, 4, 5, 6 and 7 days of treatment. Aluminium deposits occurred only in the antral glands of the stomach and in rats treated for at least 3 days. The reactive deposits are located in the cytoplasm of the upper glandular cells and in the lumen of the antral glands. These results suggest that aluminium is absorbed through the antral mucosa and may be re-excreted through the glandular mucus flow into the digestive lumen where it will be absorbed again. We hypothesize that the metal could act as a delayed-effect drug.     

Protection from nonsteroidal anti-inflammatory drug (NSAID)-induced gastric ulcers by dietary nitrate

Nitrate is abundant in our diet with particularly high levels in many vegetables. Ingested nitrate is concentrated in saliva and reduced to nitrite by bacteria in the oral cavity. We recently reported that application of nitrite-containing saliva to the gastric mucosa increases superficial blood flow and mucus generation via acid-catalyzed formation of bioactive nitrogen oxides including nitric oxide. Here we studied if dietary supplementation with nitrate would protect against gastric damage caused by a nonsteroidal anti-inflammatory drug. Rats received sodium nitrate in the drinking water for 1 week in daily doses of 0.1 or 1 mmol kg(-1). Control rats received 1 mmol kg(-1) sodium chloride. Diclofenac (30 mg kg(-1)) was then given orally and the animals were examined 4 h later. In separate experiments we studied the effects of dietary nitrate on intragastric NO levels and mucus formation. Luminal levels of NO gas were greatly increased in nitrate-fed animals. The thickness of the mucus layer increased after nitrate supplementation and gene expression of MUC6 was upregulated in the gastric mucosa. Nitrate pretreatment dose dependently and potently reduced diclofenac-induced gastric lesions. Inflammatory activity was reduced in the rats receiving nitrate as indicated by lower mucosal myeloperoxidase activity and expression of inducible NO synthase. We conclude that dietary nitrate protects against diclofenac-induced gastric ulcers likely via enhanced nitrite-dependent intragastric NO formation and concomitant stimulation of mucus formation. Future studies will reveal if a diet rich in nitrate can offer an additional nutritional approach to preventing and treating peptic ulcer disease.     

Gastric mucosal lesions in streptozotocin-diabetic rats

Formation of gastric mucosal lesions by streptozotocin-induced diabetes was investigated in rats. A single intravenous administration of streptozotocin in a dose of 65 mg/kg effectively produced hyperglycemia and damaged the gastric mucosa. Incidence and severity of mucosal lesions were progressively increased with time, from one to six weeks posttreatment. Microscopic lesions of the mucosa included hyperemia, desquamation of the surface epithelium with diffuse hemorrhage, and severe hemorrhage with localized erosion. Concurrent to the hyperglycemia, the histamine stimulated gastric H+-secretion was significantly decreased whereas pepsin secretion was not affected. Both soluble mucus and surface mucus gel were increased. The result suggests that the early lesion of gastric mucosa may be associated with the direct action of streptozotocin, the severity of which may be further aggravated by diabetic state.     

Protective effect of human epidermal growth factor against the experimental gastric mucosal lesions in rats

The protective effect of human epidermal growth factor (hEGF) on the gastric mucosal lesions in rats was examined in relation to the immunoreactive concentration of plasma. Human EGF (30 micrograms/kg) was administered intravenously, intraperitoneally or subcutaneously. At different times following the administration of hEGF, rats received acidified ethanol solution to induce an experimental gastric mucosal lesion. Sum of lesion length in the gastric mucosa was used as a lesion index. Human EGF administered parenterally markedly decreased the gastric mucosal lesions in 10 min after administration of necrotizing solution, and 10 to 30 min delay was observed in the development of maximal protective action. Profiles of protective potency against the hEGF dose administered intraperitoneally or subcutaneously 30 min before administration of necrotizing solution revealed that the effective dose of hEGF (ED50) was about 5.2 and 2.6 micrograms/kg, for intraperitoneal and subcutaneous administrations, respectively.     

尖顶羊肚菌对急性酒精性胃黏膜损伤保护作用研究

研究尖顶羊肚菌菌丝体水提液对酒精引起的大鼠急性胃黏膜损伤的保护作用。以95%乙醇诱导的大鼠胃黏膜损伤为模型,测定各组胃黏膜损伤指数,并测定胃黏膜超氧化物歧化酶（SOD）、丙二醛（MDA）、谷胱甘肽（GSH）含量,采用幽门结扎法,测定大鼠胃酸、胃蛋白酶与胃黏液分泌的量。结果表明羊肚菌中、高剂量能明显降低胃黏膜损伤指数（p＜0.05）;羊肚菌不能抑制胃酸的分泌（p＞0.05）,但是能增加胃蛋白酶与胃黏液的分泌（p＜0.05）;95%乙醇能引起胃黏膜SOD活性与GSH的降低,MDA含量的增加,给予羊肚菌能明显抑制这一现象。结果说明羊肚菌对急性酒精性胃黏膜损伤的保护作用是与增加胃黏液分泌与提高机体抗氧化能力有关。     

Gastroprotective effect of Terminalia arjuna bark on diclofenac sodium induced gastric ulcer

AIM: The present study was aimed to evaluate the effect of methanolic extract of Terminalia arjuna (TA) on diclofenac sodium induced gastric ulcer in experimental rats. METHODS: Animals were induced for gastric ulcer with diclofenac sodium (DIC) (80mg/kg bodyweight in water, orally) and treated orally with TA in various doses ranging from 100mg/kg bodyweight to 500mg/kg bodyweight. The effective dose was 400mg/kg bodyweight, since this dose elicited a maximum reduction in lesion index. The gastroprotective effect of TA was assessed from volume of gastric juice, pH, free and total acidity, pepsin concentration, acid output in gastric juice, the levels of non-protein sulfhydryls (NP-SH), lipid peroxide (LPO), reduced glutathione (GSH), and activities of enzymic antioxidants--super oxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione-S-transferase (GST) and myeloperoxidase (MPO) in gastric mucosa. The levels of DNA, protein bound carbohydrate complexes--hexose, hexoseamine, sialic acid, fucose in gastric mucosa and gastric juice and the levels of RNA in gastric mucosa were assessed. The stomach tissues were used for adherent mucus content and also for the histological examination. RESULTS: A significant reduction in lesion index was observed in ulcer induced animals treated with TA (DIC+TA) compared to ulcerated rats (DIC). A significant increase was observed in pH, NP-SH, GSH, enzymic antioxidants, protein bound carbohydrate complexes, adherent mucus content, nucleic acids with a significant decrease in volume of gastric juice, free and total acidity, pepsin concentration, acid output, LPO levels and MPO activities in DIC+TA rats compared to DIC rats. Histological studies confirmed the gastroprotective activity of TA. CONCLUSION: From the data presented in this study it could be concluded that T. arjuna acts as an gastroprotective agent probably due to its free radical scavenging activity and cytoprotective nature.     

Enhancement of gastric mucosal integrity by Lactobacillus rhamnosus GG

The gastric mucosa is frequently exposed to different exogenous and endogenous ulcerative agents. Alcoholism is one of the risk factors for the development of mucosal damage in the stomach. This study aimed to assess if a probiotic strain Lactobacillus rhamnosus GG (LGG) is capable of protecting the gastric mucosa from acute damage induced by intragastric administration of ethanol. Pre-treatment of rats with LGG at 10(9) cfu/ml twice daily for three consecutive days markedly reduced ethanol-induced mucosal lesion area by 45%. LGG pre-treatment also significantly increased the basal mucosal prostaglandin E(2) (PGE(2)) level. In addition, LGG attenuated the suppressive actions of ethanol on mucus-secreting layer and transmucosal resistance and reduced cellular apoptosis in the gastric mucosa. It is suggested that the protective action of LGG on ethanol-induced gastric mucosal lesions is likely attributed to the up-regulation of PGE(2), which could stimulate the mucus secretion and increase the transmucosal resistance in the gastric mucosa. All these would protect mucosal cells from apoptosis in the stomach.     

Gastroduodenal mucus bicarbonate barrier: protection against acid and pepsin

Secretion of bicarbonate into the adherent layer of mucus gel creates a pH gradient with a near-neutral pH at the epithelial surfaces in stomach and duodenum, providing the first line of mucosal protection against luminal acid. The continuous adherent mucus layer is also a barrier to luminal pepsin, thereby protecting the underlying mucosa from proteolytic digestion. In this article we review the present state of the gastroduodenal mucus bicarbonate barrier two decades after the first supporting experimental evidence appeared. The primary function of the adherent mucus gel layer is a structural one to create a stable, unstirred layer to support surface neutralization of acid and act as a protective physical barrier against luminal pepsin. Therefore, the emphasis on mucus in this review is on the form and role of the adherent mucus gel layer. The primary function of the mucosal bicarbonate secretion is to neutralize acid diffusing into the mucus gel layer and to be quantitatively sufficient to maintain a near-neutral pH at the mucus-mucosal surface interface. The emphasis on mucosal bicarbonate in this review is on the mechanisms and control of its secretion and the establishment of a surface pH gradient. Evidence suggests that under normal physiological conditions, the mucus bicarbonate barrier is sufficient for protection of the gastric mucosa against acid and pepsin and is even more so for the duodenum. acid-base transporters; cystic fibrosis transmembrane conductance regulator channel; surface pH gradient; mucus gels; trefoil peptides     

Decreased colonic mucus in rats with loperamide-induced constipation

Constipation is a risk factor of colorectal cancer. Mucin is a major component of lumenal mucus, which protects the colorectal mucosa against mechanical and chemical damage. The aim of this study was to evaluate mucus production and to quantitate lumen mucus in a rat model of spastic constipation. We induced constipation with loperamide (1.5 mg/kg), and histochemically evaluated mucus production and the thickness of the mucus layer at the fecal surface. We quantitated the mucus attached to the mucosal surface using colonic perfusion with N-acetylcysteine. While more feces remained in the colon, there was less fecal excretion and lower fecal water content in loperamide-administered rats than in control rats. Crypt epithelial cells contained less mucus in constipated rats than in control rats. The mucus layer at the fecal surface was thinner and less mucus was recovered from the mucosal surface in constipated rats than in control rats. Mucus production of crypt epithelial cells and mucus at the fecal and mucosal surface were reduced by loperamide-induced constipation.     

Prevention of HCl-ethanol induced gastric mucosal injury in rats by Garcinia cambogia extract and its possible mechanism of action

Oral pretreatment of rats with G. cambogia fruit extract (1 g/kg body weight/day at interval of 7 and 15 days) protected gastric mucosa against HCl-ethanol induced damage by decreasing the volume and acidity of gastric juice. Increased lipid peroxidation, decreased activity of antioxidant enzymes, altered levels of protein and glycoproteins in the ulcerated mucosa, and gastric juice were maintained at near normal levels in G. cambogia pretreated rats. The results suggest the anti-ulcer activity of G. cambogia by virtue of its ability to decrease acidity and increase mucosal defense.     

Inhibition by 16,16-dimethyl PGE2 of ethanol-induced gastric mucosal damage and leukotriene B4 and C4 formation

The effects of PGE2 and its stable analogue, 16,16 dimethyl PGE2 (dmPGE2) were investigated on ethanol-induced gastric mucosal haemorrhagic lesions and leukotriene formation in the rat. Exposure of the rat gastric mucosa to ethanol in-vivo, produced a concentration-related increase in the mucosal formation of leukotriene B4 (LTB4) which was correlated with macroscopically-apparent haemorrhagic damage to the mucosa. Challenge with absolute ethanol likewise enhanced the mucosal formation of LTC4 whereas the mucosal formation of 6-keto-PGF1 alpha was unaffected. Challenge of the rat gastric mucosa in vitro with ethanol induced a concentration-dependent increase in the formation of LTB4 and LTC4, but not 6-keto PGF1 alpha. Pretreatment with PGE2 (200-500 micrograms/kg p.o.) prevented the haemorrhagic mucosal damage induced by oral administration of absolute ethanol but not the increased formation of leukotrienes by the mucosa. In contrast, pretreatment with a high dose of dmPGE2 (20 micrograms/kg p.o.) prevented both the gastric mucosal lesions and the increase mucosal leukotriene formation. The differences in the effects of these prostaglandins may be related to the nature or degree of protection of the gastric mucosa. Thus, high doses of dmPGE2 but not PGE2 may protect the cells close to the luminal surface of the mucosa and hence reduce the stimulation of leukotriene synthesis by these cells.     

Effect of essential oil obtained from Croton cajucara Benth. on gastric ulcer healing and protective factors of the gastric mucosa.

The bark of Croton cajucara Benth. (Euphorbiaceae) is used widely in Amazonian folk medicine for the treatment of a wide range of gastrointestinal symptoms. Infusions of C. cajucara bark contain dehydrocrotonin (DHC), the furan diterpene, and an essential oil, a rich mixture of sesquiterpenes. Although the antiulcerogenic activity of the essential oil has been studied in different gastric ulcer models in mice and rats, its mechanism remains unclear. In this work, we examined the ability of this essential oil to increase PGE2 release from mucus cells, as well as its effects on the amount of gastric mucus and on the healing of acetic acid-induced gastric ulcers. The essential oil (100 mg/kg body wt., p.o), significantly increased PGE2 production by glandular cells (by 102% as compared to control) and the amount of Alcian blue binding to the gastric mucus. In chronic gastric ulcers, a single daily oral dose of essential oil (100 mg/kg body wt.) for 14 consecutive days accelerated ulcer healing to an extent similar to that seen with an equal dose of cimetidine. Thus, the protective and healing actions of the essential oil from C. cajucara bark on gastric lesions resulted mainly from an increase in PGE2 release and gastric mucus formation which would protect the gastric mucosa.     

Incorporation of radioactive proline and fucose in gastric mucosal biopsies. Correlation with histological findings

Human gastric mucosal biopsies incorporate in vitro radioactive proline and fucose into macromolecular glycoproteins (mucin). Differences were found between the incorporation pattern of antral and fundic mucosae according to their pathology, confirmed by histology. Antral mucosae with abnormal histology showed a significantly higher incorporation of proline than normal samples. Fucose incorporation was also increased. Similar results were found with fundic biopsies. The ratio of total fucose to total proline incorporated into mucin secreted during incubation also increased significantly in these samples. Biochemical analyses on the other hand showed no significant change. The results suggest a breakdown in the processing, storage and secretory processes of mucin-type glycoproteins in pathological mucosae, but not in their biosynthesis. The mucosal samples could be classified as A or B types according to their proline and fucose incorporation: A mucosae have a lower proline incorporation than B mucosae (greater than 380 cpm/micrograms DNA for the antrum and greater than 200 cpm/micrograms DNA for the fundus). These results confirm the possibility of studying abnormal mucus secretion using gastric biopsy samples.     

Suppressive effect of astaxanthin isolated from the Xanthophyllomyces dendrorhous mutant on ethanol-induced gastric mucosal injury in rats

Ethanol has been found to induce ulcerative gastric lesion in humans. The present study investigated the in vivo protective effect of astaxanthin isolated from the Xanthophyllomyces dendrorhous mutant against ethanol-induced gastric mucosal injury in rats. The rats were treated with 80% ethanol for 3 d after pretreatment with two doses of astaxanthin (5 and 25 mg/kg of body weight respectively) for 3 d, while the control rats received only 80% ethanol for 3 d. The oral administration of astaxanthin (5 and 25 mg/kg of body weight) showed significant protection against ethanol-induced gastric lesion and inhibited elevation of the lipid peroxide level in gastric mucosa. In addition, pretreatment with astaxanthin resulted in a significant increase in the activities of radical scavenging enzymes such as superoxide dismutase, catalase, and glutathione peroxidase. A histologic examination clearly indicated that the acute gastric mucosal lesion induced by ethanol nearly disappeared after pretreatment with astaxanthin.