Effects of vanilloid receptor agonists and antagonists on gastric antral ulcers in rats

Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN) is a debilitating side effect of many common anti-cancer agents that can lead to dose reduction or treatment discontinuation, which decrease chemotherapy efficacy. Long-term CIPN can interfere with activities of daily living and diminish the quality of life. The mechanism of CIPN is not yet fully understood, and biomarkers are needed to identify patients at high risk and potential treatment targets. Metabolomics can capture the complex behavioral and pathophysiological processes involved in CIPN. This chapter is to review the CIPN metabolomics studies to find metabolic pathways potentially involved in CIPN. These potential CIPN metabolites are then investigated to determine whether there is evidence from studies of other neuropathy etiologies such as diabetic neuropathy and Leber hereditary optic neuropathy to support the importance of these pathways in peripheral neuropathy. Six potential biomarkers and their putative mechanisms in peripheral neuropathy were reviewed. Among these biomarkers, histidine and phenylalanine have clear roles in neurotransmission or neuroinflammation in peripheral neuropathy. Further research is needed to discover and validate CIPN metabolomics biomarkers in large clinical studies.

Distribution of transient receptor potential vanilloid-1 channels in gastrointestinal tract of patients with morbid obesity

BACKGROUND

Transient receptor potential vanilloid-1 (TRPV1), a nonselective cation channel, is activated by capsaicin, a pungent ingredient of hot pepper. Previous studies have suggested a link between obesity and capsaicin-associated pathways, and activation of TRPV1 may provide an alternative approach for obesity treatment. However, data on the TRPV1 distribution in human gastric mucosa are limited, and the degree of TRPV1 distribution in the gastric and duodenal mucosal cells of obese people in comparison with normal-weight individuals is unknown.

AIM

To clarify gastric and duodenal mucosal expression of TRPV1 in humans and compare TRPV1 expression in obese and healthy individuals.

METHODS

Forty-six patients with a body mass index (BMI) of > 40 kg/m2 and 20 patients with a BMI between 18-25 kg/m2 were included. Simultaneous biopsies from the fundus, antrum, and duodenum tissues were obtained from subjects between the ages of 18 and 65 who underwent esophagogastroduodenoscopy. Age, sex, history of alcohol and cigarette consumption, and past medical history regarding chronic diseases and medications were accessed from patient charts and were analyzed accordingly. Evaluation with anti-TRPV1 antibody was performed separately according to cell types in the fundus, antrum, and duodenum tissues using an immunoreactivity score. Data were analyzed using SPSS 17.0.

RESULTS

TRPV1 expression was higher in the stomach than in the duodenum and was predominantly found in parietal and chief cells of the fundus and mucous and foveolar cells of the antrum. Unlike foveolar cells in the antrum, TRPV1 was relatively low in foveolar cells in the fundus (4.92 ± 0.49 vs 0.48 ± 0.16, P < 0.01, Mann-Whitney U test). Additionally, the mucous cells in the duodenum also had low levels of TRPV1 compared to mucous cells in the antrum (1.33 ± 0.31 vs 2.95 ± 0.46, P < 0.01, Mann-Whitney U test). TRPV1 expression levels of different cell types in the fundus, antrum, and duodenum tissues of the morbidly obese group were similar to those of the control group. Staining with TRPV1 in fundus chief cells and antrum and duodenum mucous cells was higher in patients aged ≥ 45 years than in patients < 45 years (3.03 ± 0.42, 4.37 ± 0.76, 2.28 ± 0.55 vs 1.9 ± 0.46, 1.58 ± 0.44, 0.37 ± 0.18, P = 0.03, P < 0.01, P < 0.01, respectively, Mann-Whitney U test). The mean staining levels of TRPV1 in duodenal mucous cells in patients with diabetes and hypertension were higher than those in patients without diabetes and hypertension (diabetes: 2.11 ± 0.67 vs 1.02 ± 0.34, P = 0.04; hypertension: 2.42 ± 0.75 vs 1.02 ± 0.33, P < 0.01 Mann-Whitney U test).

CONCLUSION

The expression of TRPV1 is unchanged in the gastroduodenal mucosa of morbidly obese patients demonstrating that drugs targeting TRPV1 may be effective in these patients.

Proton Pump Inhibitors Prevent Gastric Antral Ulcers Induced by NSAIDs via Activation of Capsaicin-Sensitive Afferent Nerves in Mice

BACKGROUND/AIMS

We examined the effects of proton pump inhibitors (PPIs) on gastric antral ulcers induced by non-steroidal anti-inflammatory drugs in re-fed mice and the role of capsaicin-sensitive afferent nerves (CSANs) in the protective effects of PPIs on the antral mucosa.

METHODS

Male mice were administered indomethacin after 2 h of re-feeding of diet after a 24-h fast, and gastric lesions were examined 24 h after indomethacin dosing. The effects of PPIs (lansoprazole and omeprazole), histamine H₂-receptor antagonists (H₂-RAs, famotidine, ranitidine), capsaicin and misoprostol on the formation of antral ulcers induced by indomethacin were examined. Functional ablation of CSANs was caused by pretreatment of mice with a high dose of capsaicin.

RESULTS

Indomethacin produced lesions selectively in the gastric antrum in re-fed conditions. Formation of antral ulcers was not affected by H₂-RAs, but inhibited by PPIs, capsaicin and misoprostol. The anti-ulcer effect of lansoprazole was 30 times stronger than that of omeprazole. Antral ulcers induced by indomethacin were markedly aggravated in mice with ablated CSANs. The effects of PPIs and capsaicin on ulcer formation were inhibited by ablation of CSANs, pretreatment with a capsaicin receptor antagonist (capsazepine/ruthenium red) and an inhibitor of nitric oxide synthesis (L-NAME). However, the inhibitory effect of misoprostol was not prevented by the ablation of CSANs or drugs.

CONCLUSIONS

The results suggested that CSANs play an important role in protection of the antral mucosa and that both lansoprazole and omeprazole are capable of preventing NSAID-induced antral ulcers by activating CSANs.

[Gastrointestinal Spice Sensors and Their Functions]

 Capsaicin is a constituent of chili pepper, and induces the burning sensation on the tongue. The site of action for capsaicin has been discovered as transient receptor potential vanilloid receptor subtype 1 (TRPV1) that resides on the membranes of pain- and heat-sensing primary afferent nerves. The immunohistochemical study on the stomach revealed that nerve fibers expressing TRPV1 exist along gastric glands in the mucosa, around blood vessels in the submucosa, in the myenteric plexus, and in the smooth muscle layers. High numbers of TRPV1-immunoreactive axons were observed in the rectum and distal colon. Therefore, capsaicin stimulates TRPV1 not only on the tongue but also in the gut. In this review, the mechanism of gastrointestinal mucosal defense enhanced by capsaicin was summarized. TRPV1 plays a protective role in gastrointestinal mucosal defensive mechanism. Hypersensitivity of afferent fibers occurs during gastrointestinal inflammation. Abnormalities of primary afferent nerve fibers are strongly associated with the visceral hypersensitive state in inflammatory bowel disease (IBD). The alteration of TRPV1 channels in mucosa contributes to the visceral hypersensitivity in colitis model mice. TRPV1-expressing neurons in the gut are thought to be extrinsic sensory afferent neurons that operate to maintain gastrointestinal functions under physiological and inflammatory states.

Capsaicin receptor as target of calcitonin gene-related peptide in the gut

Calcitonin gene-related peptide (CGRP), a 37 aminoacid-residue peptide, is a marker of afferent fibers in the upper gastrointestinal tract, being almost completely depleted following treatment with the selective neurotoxin capsaicin that targets these fibers via transient receptor potential vanilloid type-1 (TRPV-1). It is widely distributed in the peripheral nervous system of mammals where it is present as alpha isoform, while intrinsic neurons of the enteric nervous systems express predominantly CGRP-beta. Many gastrointestinal functions involve CGRP-containing afferent fibers of the enteric nervous system such as defense against irritants, intestinal nociception, modulation of gastrointestinal motility and secretion, and healing of gastric ulcers. The main effects on stomach homeostasis rely on local vasodilator actions during increased acid-back diffusion. In humans, release of CGRP through the activation of TRPV-1 has been shown to protect from gastric damage induced by several stimuli and to be involved in gastritis. In both dyspepsia and irritable bowel syndrome the repeated stimulation of TRPV-1 induced an improvement in epigastric pain of these patients. The TRPV-1/CGRP pathway might be a novel target for therapeutics in gastric mucosal injury and visceral sensitivity.

The protective effects of lafutidine for bortezomib induced peripheral neuropathy

Peripheral neuropathy (PN) caused by bortezomib is an important complication of multiple myeloma. Subcutaneous injection of bortezomib reduced PN, but 24% of cases were grade 2 PN and 6% of cases were grade 3 PN. PN higher than grade 2 was not resolved by subcutaneous injection. PN higher than grade 3 has serious dose limiting toxicity and is the cause of discontinuing bortezomib treatment. Lafutidine is an H2-blocker with gastroprotective activity and is thought to function by increasing mucosal blood flow via capsaicin sensitive neurons. The same activity of lafutidine is considered to improve glossodynia and taxane induced PN. We hypothesized that lafutidine prevents or improves PN that is caused by bortezomib. In the current study, bortezomib was administered in the usual manner (intravenous administration of bortezomib 1.3 mg/m², twice a week for 2 weeks, followed by 1 week without treatment) for up to four cycles to compare our data with other studies. Lafutidine was administered orally at a dose of 10 mg twice daily. In our eight evaluated cases, the total occurrence of PN was four out of eight patients (50%). There were only grade 1 PN (4 out of 8) cases, and no cases higher than grade 2. We conclude that (1) the total occurrence of PN was not improved, (2) there was no PN after the first course, (3) there were only grade 1 cases and there were no cases higher than grade 2, and (4) no cases discontinued bortezomib treatment because of PN. This is the first report showing that lafutidine is useful for the amelioration of bortezomib induced PN.

Protective effect of a novel rice extract against ethanol-induced gastric mucosal injury in rat

The aim of this study was to investigate the protective action of rice extract on ethanol-induced mucosal damage in vivo and wound healing of epithelial cells in vitro. Also, the effect of rice extract on gastric mucosal prostaglandin E(2) level, HSP72 expression, gastric acid secretion, and contribution of vanilloid receptor-mediated action was studied. In addition, using cultured gastric mucosal cells (RGM-1), the effect of rice extract on cytoprotection and wound healing of epithelial cells was evaluated. Rice extract significantly reduced gastric mucosal damage produced by ethanol in vivo, and heat treatment (80 degrees C, 3 min) of this agent did not alter its protective effect. Rice extract also protected RGM-1 from ethanol-induced damage in a dose-dependent manner. Rice extract accelerated wound healing of gastric epithelial cells. Our results demonstrate that rice extract could be an alternative ulcer treatment that provides cytoprotection and enhancement of wound healing not dependent on acid secretion, prostaglandin E(2) level, HSP72 expression, or vanilloid receptors.

Effects of allyl isothiocyanate from horseradish on several experimental gastric lesions in rats

Allyl isothiocyanate is well known to be a principal pungent constituent of horseradish and an agonist for transient receptor potential (TRP) A1. Ally isothiocyanate markedly inhibited the formation of gastric lesions induced by ethanol (1.5 ml/rat, p.o.), 0.6 M HCl (1.5 ml/rat, p.o.), 1% ammonia (1.5 ml/rat, p.o.), and aspirin (150 mg/kg, p.o.) (ED(50)=1.6, 2.2, 1.7, ca. 6.5 mg/kg, p.o.). It also significantly inhibited the formation of gastric lesions induced by indomethacin (20 mg/kg, p.o.), though the inhibition was ca. 60% at a high dose (40 mg/kg, p.o.). Furthermore, several synthetic isothiocyanate compounds also significantly inhibited ethanol and indomethacin-induced gastric lesions. Whereas, TRPV1 agonists, capsaicin and piperine, inhibited gastric lesions induced by ethanol, 1% ammonia, and aspirin, but had less of an effect on 0.6 M HCl-induced gastric lesions. With regard to mode of action, the protective effects of ally isothiocyanate on ethanol-induced gastric lesions were attenuated by pretreatment with indomethacin, but not with N(G)-nitro-L-arginine methyl ester hydrochloride (L-NAME), or ruthenium red. Pretreatment with indomethacin reduced the protective effects of piperine, and L-NAME reduced the effects of capsaicin and omeprazole. Furthermore, ruthenium red reduced the effects of capsaicin, piperine, and omeprazole. These findings suggest that endogenous prostaglandins play an important role in the protective effect of allyl isothiocyanate in ethanol-induced gastric lesions different from capsaicin, piperine, and omeprazole.

Co-localization of TRPV1-expressing nerve fibers with calcitonin-gene-related peptide and substance P in fundus of rat stomach

The localization of vanilloid receptor TRPV1 was studied in rat gastric fundus by an immunohistochemical technique. Numerous TRPV1-immunoreactive nerve fibers were found around arterioles in the submucosal layer. A large number of the nerve fibers were also seen in the smooth muscle layer and in the myenteric nerve plexus, but the cell bodies could not be found. TRPV1 nerve fibers within the circular muscle layers were running parallel to the muscle fibers. Virtually all TRPV1 axons were immunoreactive for calcitonin-gene-related peptide (CGRP), with particularly extensive double labeling seen in axons of the submucosa around blood vessels. TRPV1 nerve fibers containing substance P were found running in longitudinal muscle and circular muscle. The TRPV1 axons seem to be predominantly extrinsic and contain CGRP and substance P in gastric fundus. TRPV1 neurons are thought to be sensory afferent neurons that operate to maintain gastric motility and blood flow.

Distribution of the vanilloid (capsaicin) receptor type 1 in the human stomach

Vanilloid receptor type 1 (TRPV1) is expressed in a capsaicin-sensitive and peptide-containing sub-population of primary sensory nerves that in the rat stomach seems involved in regulation of chlorhydropeptic secretion and gastroprotection. Our aim was to identify which cell types express TRPV1 in the human stomach in order to gain a better insight in the role of this receptor in the regulation of HCl secretion. Immunohistochemistry, by using three different commercially available anti-capsaicin antibodies, in situ hybridisation and Western blot analysis were performed on fragments surgically obtained from the gastric body on the large curvature. TRPV1 labelling was found in the parietal cells at the level of intra-cytoplasmatic granules matching mitochondrial features and distribution. Immunolabelled neurons and nerve fibres were also seen, the latter numerous in the submucosa and mucosa and often ending close to the parietal cells. TRPV1 presence was confirmed by Western blot analysis and in situ hybridisation. TRPV1 presence in nerve structures and parietal cells suggests the possibility of a combined effect of both neuronal and epithelial TRPV1 on chlorhydropeptic secretion. The presumed TRPV1 mitochondrial location inside parietal cells is in favour of the existence of a local pathway of auto-regulation of HCl secretion. Therefore, TRPV1 might modulate chlorhydropeptic secretion in the human stomach through more complex pathways than previously thought.

Expression of vanilloid receptor-1 in epithelial cells of human antral gastric mucosa

OBJECTIVE

Capsaicin, which acts by binding to the vanilloid receptor-1 (VR1), has been shown to give protection against gastric mucosal injury and to enhance healing of gastric ulcers. Although VR1 has recently been reported to be present in non-neural tissues, it is primarily considered to be expressed in nociceptor sensory neurons of small diameter. The aim of the present study was to evaluate the distribution of VR1 immunoreactivity in the normal human gastric mucosa.

MATERIALS AND METHODS

Ten volunteers underwent gastroscopy and biopsies were obtained from the corpus and the antrum. The specimens were labelled immunohistochemically using polyclonal goat anti-VR1 and evaluated at the light- and electronmicroscopic level. Moreover, post-embedding immunogold labelling was performed and subsequently analysed at the electronmicroscopic level.

RESULTS

In the antrum, VR1 immunoreactivity was located in epithelial cells that fulfilled the criteria of endocrine cells of the "open type". These cells were located primarily in the neck region of the antral glands and the labelling was concentrated on the microvilli of these cells. At the ultrastructural level, round granulae with differences in electron density were identified in the basal compartment of the labelled cells. VR1 immunoreactivity was also identified in axon-like structures that were located in the lamina propria, often in close vicinity of vessels, in the corpus as well as in the antrum.

CONCLUSIONS

VR1-immunoreactivity was evident in antral epithelial cells exhibiting characteristics of endocrine-like cells. This may indicate that the gastroprotective effects of capsaicin, which hitherto have been attributed to primary afferent neurons, at least partly may be explained by an action on specific epithelial cells in the antrum.

The role of the vanilloid (capsaicin) receptor (TRPV1) in physiology and pathology

The cloning of the vanilloid receptor 1 opened a floodgate for discoveries regarding the function of this complex molecule. It has been found that, in addition to heat, protons and vanilloids, this receptor also responds to various endogenous ligands. Furthermore, it has been also emerged that, through associations with other molecules, the vanilloid receptor 1 plays an important role in the integration of various stimuli and modulation of cellular excitability. Although, originally, the vanilloid receptor 1 was associated with nociceptive primary afferent fibres, it has been gradually revealed that it is broadly expressed in the brain, epidermis and visceral cells. The expression pattern of the vanilloid receptor 1 indicates that it could be involved in various physiological functions and in the pathomechanisms of diverse diseases. Here, we summarise the molecular, pharmacological and physiological characteristics, and putative functions, of the vanilloid receptor 1, and discuss the therapeutic potential of this molecule.

Lafutidine-induced increase in intracellular ca(2+) concentrations in PC12 and endothelial cells

Lafutidine, a histamine H(2) receptor antagonist, exerts gastroprotective effects in addition to gastric antisecretory activity. The gastrointestinal protective effects of lafutidine are mediated by capsaicin-sensitive neurons, where capsaicin excites neurons by opening a member of the transient receptor potential channel family (TRPV1). Since the effect of lafutidine on the intracellular Ca(2+) concentration ([Ca(2+)](i)) in cells has not been elucidated, we investigated the lafutidine response to [Ca(2+)](i) in rat pheochromocytoma PC12 and human endothelial cells. Lafutidine at pharmacological concentrations greater than 1 mM induced a sustained increase in [Ca(2+)](i) in the presence of extracellular CaCl(2) in PC12 cells, while capsaicin showed dual effects on [Ca(2+)](i) in PC12 cells, where it activated TRPV1 and inhibited store-operated Ca(2+) entry. The thapsigargin (an activator of store-operated Ca(2+) entry)-induced increase in [Ca(2+)](i) in PC12 cells was inhibited by capsaicin and SKF96365, an inhibitor of store-operated Ca(2+) entry, and the lafutidine response was inhibited by capsaicin but not by SKF96365. In endothelial cells, lafutidine induced an increase in [Ca(2+)](i) in a SKF96365-insensitive manner. These results suggest that lafutidine stimulates Ca(2+) entry via the capsaicin-sensitive pathway but not the SKF96365-sensitive pathway. The possible role of store-operated Ca(2+) entry induced by lafutidine on gastrointestinal function is also discussed.

Protective role of vanilloid receptor type 1 in HCl-induced gastric mucosal lesions in rats

BACKGROUND

Effects of vanilloid-receptor agonists and antagonists on HCl-induced gastric lesions in rats were investigated to elucidate the role of vanilloid receptor type 1 (VR1) in gastric mucosal defense mechanisms.

METHODS

Gastric lesions in rats were evaluated after intragastric administration of 0.6 N HCl. The localization of VR1 in the stomach was investigated immunohistochemically.

RESULTS

Intragastric administration of capsaicin inhibited the formation of gastric lesions in a dose-dependent manner (0.1-2.5 mg/kg). The functional VR1 antagonists ruthenium red and capsazepine markedly aggravated HCl-induced gastric lesions in rats. The gastroprotective effect of capsaicin was attenuated by ruthenium red or capsazepine. It is reported that resiniferatoxin, [6]-gingerol and lafutidine are compounds that activate VR1 and/or capsaicin-sensitive afferent neurons. These compounds significantly inhibited the formation of HCl-induced gastric lesions, and their gastroprotective effects were inhibited by treatment with ruthenium red. The immunohistochemical studies revealed that nerve fibers expressing VR1 exist along gastric glands in the mucosa, around blood vessels in the submucosa, in the myenteric plexus, and in the smooth muscle layers, especially the circular muscle layer.

CONCLUSION

The results of this study suggest that VR1 plays a protective role in the gastric defensive mechanism in rats.

Expression of vanilloid receptors in rat gastric epithelial cells: role in cellular protection

Vanilloid receptors subtype 1 (VR1), a nonselective cation channel responsive to capsaicin, protons, and noxious heat, has been recently identified in not only neural but also non-neural cells. In the present study, we demonstrated the peripheral expression of VR1 in gastric mucosal epithelial cells and investigated the role of the receptor in cellular protection. The rat gastric mucosal epithelial cell line was used. The expression of VR1 was examined by Western blotting and RT-PCR. Cell damage was induced by immersion in 10% ethanol or acid (pH 4.0) for 30 min, and cell viability was determined by MTT assay. Capsaicin or resiniferatoxin was added 30 min before the challenge with ethanol or acid, while capsazepine or ruthenium red (a VR1 antagonist) was added simultaneously with capsaicin. The distinct expression of VR1 protein and mRNA was detected in rat gastric mucosal epithelial cell line as well as in the rat stomach and spinal cord by Western blotting and RT-PCR, respectively. The cDNA sequence of the PCR product was found to be almost identical to that of the authentic VR1 (99.8%) when the product was subcloned and sequenced. On the other hand, the cell damage induced by ethanol or acid was dose-dependently prevented by pretreatment with capsaicin. The protective effect of capsaicin was mimicked by resiniferatoxin and almost totally abolished by co-addition of capsazepine or ruthenium red. These findings suggest that VR1 is expressed peripherally in gastric mucosal epithelial cells and plays a cellular protective role.

Modifications of capsaicin-sensitive neurons in isolated guinea pig ileum by [6]-gingerol and lafutidine

A segment of guinea pig ileum was used to confirm the hypothesis that [6]-gingerol and lafutidine interact with capsaicin-sensitive neurons. Addition of 30 and 100 microM [6]-gingerol (a pungent constituent of ginger) induced contraction of the ileum immediately. Like capsaicin, [6]-gingerol-induced contraction was inhibited by antagonists of the vanilloid receptor (capsazepine and ruthenium red), tetrodotoxin, and atropine. Treatment with [6]-gingerol up to 0.3 microM, which alone had no effect, enhanced 3 microM capsaicin-induced contraction, but greater than 3 microM [6]-gingerol significantly inhibited capsaicin-induced contraction. Treatment with lafutidine (a new type of antagonist of the histamine H(2) receptor), which was suggested to interact with capsaicin-sensitive neurons in vivo, also showed both stimulatory and inhibitory effects on capsaicin-induced contraction depending on the concentrations. Lafutidine alone had no effect. The enhanced contraction induced by capsaicin in the [6]-gingerol- or lafutidine-treated ileum was also inhibited by antagonists of the vanilloid receptor, tetrodotoxin, and atropine. Capsaicin and [6]-gingerol, but not lafutidine, at 30 microM stimulated [(3)H]choline release from the prelabeled slices of the ileum. These findings suggest that [6]-gingerol and lafutidine act on capsaicin-sensitive cholinergic neurons and modulate the contraction in isolated guinea pig ileum.

[An overview of acetic acid ulcer models and their utility for drug screening]

Since Takagi et al. reported an experimental chronic gastric ulcer model [acetic acid ulcers induced by submucosal injection of acetic acid (Type 1)], we further modified the methodology and subsequently devised three more models. The second model involves inducing ulcers by serosal application of an acetic acid solution (Type 2) and the third model achieves ulcer induction by intragastric application of an acetic acid solution (Type 3). The forth model was modification of the third model by giving the acetic acid solution and the same volume of air to make one ulcer in the stomach (Type 4). In general, animals accepted the procedures without problems and no undesirable effects were noticed. More importantly, this experimental animal model allows production of ulcers that highly resemble human ulcers in terms of both pathology and healing. Indeed, relapse is even endoscopically observed for 360 days after ulceration. The ulcers produced not only respond well to various anti-ulcer medications, such as antisecretory and mucosal protective drugs and growth factors, but also demonstrate appropriate responses to ulcerogenic agents such as NSAIDs. In addition, we have recently demonstrated that H. pylori infection resulted in delayed ulcer healing and recurrence of healed acetic acid ulcers induced in Mongolian gerbils. The present article gives a brief summary of the ulcer history before establishment of acetic acid ulcers and characteristic features of acetic acid ulcer, including both their merits and shortcomings.

Protective effects of polygodial on gastric mucosal lesions induced by necrotizing agents in rats and the possible mechanisms of action

The effects of polygodial isolated from the leaves of Tasmannia lanceolata on necrotizing agents-induced gastric lesions in rats were compared with capsaicin. Polygodial markedly inhibited the gastric mucosal lesions induced by several necrotizing agents, such as ethanol (ED(50)=0.029 mg/kg, p.o.), 0.6 M HCl (ED(50)=0.26 mg/kg, p.o.), and aspirin (ED(50)=0.38 mg/kg, p.o.), and partly inhibited the gastric mucosal lesions induced by indomethacin, but showed no significant effect on acid output in pylorus-ligated rats at doses of 0.05-0.5 mg/kg. The gastroprotection of polygodial was attenuated by pretreatment with indomethacin (10 mg/kg, s.c.), N(G)-nitro-L-arginine methyl ester (70 mg/kg, i.p.), N-ethylmaleimide (10 mg/kg, s.c.) and ruthenium red (3.5 mg/kg, s.c.). Polygodial (0.2 mg/kg, p.o.) increased the amount of reduced glutathione in gastric mucosa of ethanol-treated group. These results suggested that endogenous prostaglandins, nitric oxide, sulfhydryl compounds and vanilloid receptor-mediated effects are involved in the protective effect of polygodial.

Facilitation by endogenous prostaglandins of capsaicin-induced gastric protection in rodents through EP2 and IP receptors

We investigated the role that prostaglandins (PGs) and EP receptors play in facilitating the gastroprotective action of capsaicin against HCl/ethanol in rats and mice. Male Sprague-Dawley rats and C57BL/6 mice were used after 18 h of fasting. The animals were given HCl/ethanol (60% in 150 mM HCl) p.o. and killed 1 h later. Capsaicin or various EP agonists were given p.o. 30 min or i.v. 10 min before HCl/ethanol. In some cases, indomethacin or various EP agonists were given s.c. 30 min or i.v 10 min before capsaicin, respectively. Gastric lesions induced by HCl/ethanol were significantly inhibited by PGE(2) as well as capsaicin. The effect of PGE(2) was antagonized by ONO-AE-829 (EP1 antagonist), whereas the capsaicin action was mitigated by indomethacin as well as sensory deafferentation but not by ONO-AE-829. The generation of mucosal PGE(2) was not affected by either capsaicin or sensory deafferentation, but was significantly inhibited by indomethacin. Although neither butaprost (EP2), ONO-NT-012 (EP3), nor 11-deoxy PGE1 (EP4) alone had any effect on HCl/ethanol-induced gastric lesions, only butaprost restored the protective action of capsaicin in the presence of indomethacin. Capsaicin provided a protective action against HCl/ethanol-induced gastric lesions in wild-type (+/+) mice in an indomethacin-sensitive manner, and this action was similarly observed in EP1 (-/-) and EP3 (-/-) mice but not in the animals lacking IP receptors. These results suggest that capsaicin exhibits gastric cytoprotection, essentially by stimulating sensory neurons, and this action is facilitated by endogenous PGs through EP2/IP receptors, probably sensitizing the sensory neurons to capsaicin.

Lafutidine, a novel histamine H2-receptor antagonist, increases serum calcitonin gene-related peptide in rats after water immersion-restraint stress

Lafutidine is a novel histamine H(2)-receptor antagonist with a potent and long-lasting anti-acid secretory effect that has also been found to have a potent gastroprotective effect. We investigated the effect of lafutidine on gastric mucosal injury induced in rats with the use of water-immersion restraint stress (WRS) by examining serum calcitonin gene-related peptide (CGRP) concentrations, which we measured with the use of an enzyme immunometric assay. WRS-induced mucosal erosive injury in the stomach was reduced significantly by both lafutidine and famotidine pretreatment (from 7.79 +/- 2.02 mm(2) to 3.09 +/- 0.74 mm(2) and 4.05 +/- 1.18 mm(2), respectively). A single administration of lafutidine or famotidine did not change the serum CGRP concentration from the control value when these drugs were administered without WRS. Lafutidine pretreatment before WRS caused a significant increase in serum CGRP concentration compared with famotidine (lafutidine, 86.64 +/- 9.52 pg/mL; famotidine, 47.55 +/- 4.35 pg/mL; control, 58.43 +/- 6.07 pg/mL). Our results suggest that lafutidine augments CGRP release from the rat stomach when administered before the induction of WRS.

Irsogladine Prevents Monochloramine-Induced Gastric Mucosal Lesions by Improving the Decrease in Mucosal Blood Flow Due to the Disturbance of Nitric Oxide Synthesis in Rats

The inhibitory effect of an anti-ulcer drug irsogladine [2,4-diamino-6-(2,5-dichlorophenyl)-s-triazine maleate] on monochloramine (NH(2)Cl)-induced gastric mucosal lesions and its mechanisms of action were clarified in rats. Irsogladine dose-dependently prevented the formation of gastric mucosal lesions induced by 60 mM NH(2)Cl. The mucosal protective effect of irsogladine was not influenced by capsaicin-sensitive sensory defunctionalization. On the other hand, its protective effect was diminished by the inhibitor of nitric oxide synthase N(G)-nitro-L-arginine methylester (L-NAME), but not by the inducible nitric oxide synthase selective inhibitor aminoguanidine. Irsogladine restored the NH(2)Cl-induced decrease in the gastric cGMP formation as an index of nitric oxide synthesis, while it alone had no influence on the cGMP formation in intact tissues. Pretreatment with L-NAME abolished the recovery of cGMP by irsogladine. Furthermore, irsogladine ameliorated the NH(2)Cl-induced decrease in gastric mucosal blood flow, which was also reversed by pretreatment with L-NAME. These findings suggest that the improvement of the decrease in mucosal blood flow subsequent to the disturbance of gastric nitric oxide synthesis is involved in the protective effect of irsogladine on gastric mucosal lesions caused by NH(2)Cl.

Sensory neurone responses to mucosal noxae in the upper gut: relevance to mucosal integrity and gastrointestinal pain

The digestive tract is supplied by extrinsic and intrinsic sensory neurones that, together with endocrine and immune cells, form a surveillance network that is essential to gut function. This article focuses on the responses of extrinsic afferent neurones to chemical insults of the gastrointestinal mucosa and their pathophysiological relevance to mucosal integrity and abdominal pain. Within the gastroduodenal region, spinal afferents subserve an emergency function because, in case of alarm by influxing acid, they stimulate mechanisms of mucosal protection via an efferent-like release of transmitters. Other sensory neurones signal chemical noxae to the brain, a task that is not confined to spinal afferents because vagal afferents communicate gastric acid and peripheral immune challenges to the brainstem and in this way elicit autonomic, endocrine, affective and behavioural reactions. Emerging evidence indicates that hypersensitivity of extrinsic afferent pathways to mechanical and chemical stimuli makes an important contribution to the abdominal hyperalgesia seen in functional dyspepsia and irritable bowel syndrome. Sensitization may be brought about by inflammatory processes that lead to up-regulation and functional alterations of receptors and ion channels on sensory neurones. Such sensory neurone-specific molecules, which include vanilloid (capsaicin) receptors, may represent important targets for novel drugs to treat abdominal pain.