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

Targeting TRPV1 and TRPA1: A feasible strategy for natural herbal medicines to combat postoperative ileus

Under physiological or pathological conditions, transient receptor potential (TRP) channel vanilloid type 1 (TRPV1) and TRP ankyrin 1 (TRPA1) possess the ability to detect a vast array of stimuli and execute diverse functions. Interestingly, increasing works have reported that activation of TRPV1 and TRPA1 could also be beneficial for ameliorating postoperative ileus (POI). Increasing research has revealed that the gastrointestinal (GI) tract is rich in TRPV1/TRPA1, which can be stimulated by capsaicin, allicin and other compounds. This activation stimulates a variety of neurotransmitters, leading to increased intestinal motility and providing protective effects against GI injury. POI is the most common emergent complication following abdominal and pelvic surgery, and is characterized by postoperative bowel dysfunction, pain, and inflammatory responses. It is noteworthy that natural herbs are gradually gaining recognition as a potential therapeutic option for POI due to the lack of effective pharmacological interventions. Therefore, the focus of this paper is on the TRPV1/TRPA1 channel, and an analysis and summary of the processes and mechanism by which natural herbs activate TRPV1/TRPA1 to enhance GI motility and relieve pain are provided, which will lay the foundation for the development of natural herb treatments for this disease.

Regional characterisation of TRPV1 and TRPA1 signalling in the mouse colon mucosa

Capsaicin and allyl isothiocyanate (AITC) activate transient receptor potential (TRP) vanilloid-1 (TRPV1) and TRP ankyrin-1 (TRPA1), respectively. TRPV1 and TRPA1 expression have been identified in the gastrointestinal (GI) tract. GI mucosal functions remain largely undefined for TRPV1 and TRPA1 with side-dependence and regional differences in signalling unclear. Here we investigated TRPV1- and TRPA1-induced vectorial ion transport as changes in short-circuit current (ΔIsc), in defined segments of mouse colon mucosa (ascending, transverse and descending) under voltage-clamp conditions in Ussing chambers. Drugs were applied basolaterally (bl) or apically (ap). Capsaicin responses were biphasic, with primary secretory and secondary anti-secretory phases, observed with bl application only, which predominated in descending colon. AITC responses were monophasic and secretory, with ΔIsc dependent on colonic region (ascending vs. descending) and sidedness (bl vs. ap). Aprepitant (neurokinin-1 (NK1) antagonist, bl) and tetrodotoxin (Na+ channel blocker, bl) significantly inhibited capsaicin primary responses in descending colon, while GW627368 (EP4 receptor antagonist, bl) and piroxicam (cyclooxygenase inhibitor, bl) inhibited AITC responses in ascending and descending colonic mucosae. Antagonism of the calcitonin gene-related peptide (CGRP) receptor had no effect on mucosal TRPV1 signalling, while tetrodotoxin and antagonists of the 5-hydroxytryptamine-3 and 4 receptors, CGRP receptor, and EP1/2/3 receptors had no effect on mucosal TRPA1 signalling. Our data demonstrates the regional-specificity and side-dependence of colonic TRPV1 and TRPA1 signalling, with involvement of submucosal neurons and mediation by epithelial NK1 receptor activation for TRPV1, and endogenous prostaglandins and EP4 receptor activation for TRPA1 mucosal responses.

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.

Effects of adding a commercial capsaicin fertilizer on the feeding behavior of sika deer (Cervus nippon)

We investigated the inhibitory effect of capsaicin fertilizer on feeding in deer. We tested four captive adult female deer. In Experiment 1, in addition to the treatment (intact) containing only a solid feed (HC), we mixed the fertilizer not containing capsaicin (F) or the capsaicin fertilizer (CF) in the solid feed. In addition, the solid feed was put on a wire net that capsaicin fertilizer was placed 5 cm below (SCF). We investigated their feeding behavior response. In Experiment 2, we changed the amount of substance (fertilizer and capsaicin fertilizer) mixed in the HC. We mixed different amounts (0, 50, 100, and 200 g) of the treatments other than the intact with HC and presented them to the deer, and investigated their feeding behavior response. In Experiment 1, intake in the F and CF decreased (p < .05). In Experiment 2, HC intake was significantly lower in the 100 and 200 g CF (p < .05). However, HC intake relatively increased by the last day in the CF 200 g too. The capsaicin fertilizer decreased the feeding behavior of deer by directly touching the mucous membranes of the deer nose and lips. However, the effects were decreased over time.

Effects of Chaihu-Shugan-San on Small Intestinal Interstitial Cells of Cajal in Mice

Chaihu-Shugan-San (CSS) has been widely used as an alternative treatment for gastrointestinal (GI) diseases in East Asia. Interstitial cells of Cajal (ICCs) are pacemakers in the GI tract. In the present study, we examined the action of CSS on pacemaker potentials in cultured ICCs from the mouse small intestine in vitro and on GI motility in vivo. We used the electrophysiological methods to measure the pacemaker potentials in ICCs. GI motility was investigated by measuring intestinal transit rates (ITR). CSS inhibited the pacemaker potentials in a dose-dependent manner. The capsazepine did not block the effect of CSS. However, the effects of CSS were blocked by glibenclamide. In addition, N^G-nitro-L-arginine methyl ester (L-NAME) also blocked the CSS-induced effects. Pretreatment with SQ-22536 or with KT-5720 did not suppress the effects of CSS; however, pretreatment with ODQ or KT-5823 did. Furthermore, CSS significantly suppressed murine ITR enhancement by neostigmine in vivo. These results suggest that CSS exerts inhibitory effects on the pacemaker potentials of ICCs via nitric oxide (NO)/cGMP and ATP-sensitive K⁺ channel dependent and transient receptor potential vanilloid 1 (TRPV1) channel independent pathways. Accordingly, CSS could provide the basis for the development of new treatments for GI motility dysfunction.

Potential Antiulcer Agents From Plants: A Comprehensive Review

Background:

Peptic ulcer is a deep gastrointestinal erosion disorder that involves the entire mucosal thickness and can even penetrate the muscular mucosa. Nowadays, several plants and compounds derived from it have been screened for their antiulcer activity. In the last few years, there has been an exponential growth in the field of herbal medicine. This field has gained popularity in both developing and developed countries because of their natural origin and less side effects.

Objective:

This review aims to provide a comprehensive summary of currently available knowledge of medicinal plants and phytoconstituents reported for their anti-ulcer properties.

Methods:

The worldwide accepted database like SCOPUS, PUBMED, SCIELO, NISCAIR, ScienceDirect, Springerlink, Web of Science, Wiley, SciFinder and Google Scholar were used to retrieve available published literature.

Results:

A comprehensive review of the present paper is an attempt to list the plants with antiulcer activity. The review narrates the dire need to explore potential chemical moieties that exert an antiulcer effect, from unexploited traditional plants. Furthermore, the present study reveals the intense requirement to exploit the exact mechanism through which either the plant extracts or their active constituents exhibit their antiulcer properties.

Conclusion:

This article is the compilation of the plants and its constituents reported for the treatment of peptic ulcers. The Comprehensive data will surely attract the number of investigators to initiate further research that might lead to the drugs for the treatment of ulcers. As sufficient scientific data is not available on plants, most of the herbals cannot be recommended for the treatment of diseases. This can be achieved by research on pure chemical structures derived from plants or to prepare new lead compounds with proven beneficial preclinical in vitro and in vivo effects. However, a lot remains to be done in further investigations for the better status of medicinal plants.

The Role of Transient Receptor Potential Vanilloid 1 in Common Diseases of the Digestive Tract and the Cardiovascular and Respiratory System

Transient receptor potential vanilloid subtype 1 (TRPV1), a member of the transient receptor potential vanilloid (TRPV) channel family, is a nonselective cation channel that is widely expressed in sensory nerve fibers and nonneuronal cells, including certain vascular endothelial cells and smooth muscle cells. The activation of TRPV1 may be involved in the regulation of various physiological functions, such as the release of inflammatory mediators in the body, gastrointestinal motility function, and temperature regulation. In recent years, a large number of studies have revealed that TRPV1 plays an important role in the physiological and pathological conditions of the digestive system, cardiovascular system, and respiratory system, but there is no systematic report on TRPV1. The objective of this review is to explain the function and effects of TRPV1 on specific diseases, such as irritable bowel syndrome, hypertension, and asthma, and to further investigate the intrinsic relationship between the expression and function of TRPV1 in those diseases to find new therapeutic targets for the cure of related diseases.

Molecular Changes in Diabetic Wound Healing following Administration of Vitamin D and Ginger Supplements: Biochemical and Molecular Experimental Study

BACKGROUND

Circulating micro-RNAs are differentially expressed in various tissues and could be considered as potential regulatory biomarkers for T2DM and related complications, such as chronic wounds.

AIM

In the current study, we investigated whether ginger extract enriched with [6]-gingerol-fractions either alone or in combination with vitamin D accelerates diabetic wound healing and explores underlying molecular changes in the expression of miRNA and their predicted role in diabetic wound healing.

METHODS

Diabetic wounded mice were treated with [6]-gingerol-fractions (GF) (25 mg/kg of body weight) either alone or in combination with vitamin D (100 ng/kg per day) for two weeks. Circulating miRNA profile, fibrogenesis markers, hydroxyproline (HPX), fibronectin (FN), and collagen deposition, diabetic control variables, FBS, HbA1c, C-peptide, and insulin, and wound closure rate and histomorphometric analyses were, respectively, measured at days 3, 6, 9, and 15 by RT-PCR and immunoassay analysis.

RESULTS

Treatment of diabetic wounds with GF and vitamin D showed significant improvement in wound healing as measured by higher expression levels of HPX, FN, collagen, accelerated wound closure, complete epithelialization, and scar formation in short periods (11-13 days, (P < 0.01). On a molecular level, three circulating miRNAs, miR-155, miR-146a, and miR-15a, were identified in diabetic and nondiabetic skin wounds by PCR analysis. Lower expression in miR-155 levels and higher expression of miR-146a and miR-15a levels were observed in diabetic skin wounds following treatment with gingerols fractions and vitamin D for 15 days. The data showed that miRNAs, miR-146a, miR-155, and miR-15a, correlated positively with the expression levels of HPX, FN, and collagen and negatively with FBS, HbA1c, C-peptide, and insulin in diabetic wounds following treatment with GF and /or vitamin D, respectively.

CONCLUSION

Treatment with gingerols fractions (GF) and vitamin D for two weeks significantly improves delayed diabetic wound healing. The data showed that vitamin D and gingerol activate vascularization, fibrin deposition (HPX, FN, and collagen), and myofibroblasts in such manner to synthesize new tissues and help in the scar formation. Accordingly, three miRNAs, miR-155, miR-146a, and miR-15, as molecular targets, were identified and significantly evaluated in wound healing process. It showed significant association with fibrin deposition, vascularization, and reepithelialization process following treatment with GF and vitamin D. It proposed having anti-inflammatory action and promoting new tissue formation via vascularization process during the wound healing. Therefore, it is very interesting to consider miRNAs as molecular targets for evaluating the efficiency of nondrug therapy in the regulation of wound healing process.

Modulation of gastric acid secretion by cannabinoids in rats

The current study aimed to evaluate the role of cannabinoid receptors in the regulation of gastric acid secretion and oxidative stress in gastric mucosa. To fulfill this aim, gastric acid secretion stimulated with histamine (5 mg/kg, subcutaneous [SC]), 2-deoxy- d-glucose (D-G) (200 mg/kg, intravenous) or -carbachol (4 μg/kg, SC) in the 4-hour pylorus-ligated rats. The CB1R agonist ( N-arachidonoyl dopamine, 1 mg/kg, SC) inhibited gastric acid secretion stimulated by D-G and carbachol but not in histamine, reduced pepsin content, and increased mucin secretion. Furthermore, it decreased malondialdehyde (MDA) and nitric oxide (NO) contents with an increase in glutathione (GSH) and paraoxonase 1 (PON-1). Meanwhile, CB2R antagonist (AM630, 1 mg/kg, SC) inhibited gastric acid secretion stimulated by D-G and reduced MDA and NO contents with an increase in GSH and PON-1. Meanwhile, CB1R antagonist rimonabant or CB2R agonist GW 405833 had no effect on stimulated gastric acid secretion. Therefore, both CB1R agonist and CB2R antagonist may exert antisecretory and antioxidant potential in the stomach.

[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.

Effect of intragastric administration of capsaicin on gastric mucosal barrier in rats

AIM: To explore the effect of different doses of capsaicin (CAP) given for different durations on gastric mucosal barrier, liver and kidney histopathology, blood tests, and blood biochemistry in rats.

METHODS: Two hundred and forty SD rats were randomly divided into either an experimental group or a control group (group D). The experimental group was further divided into subgroups, which were given 0.1 mg/(kg•d) (group A), 1.0 mg/(kg•d) (group B), or 5.0 mg/(kg•d) CAP (group C) for 1 d, 7 d, 14 d or 28 d. Blood tests and blood biochemistry were measured. Gastric mucosa barrier and liver and kidney histopathology were assessed.

RESULTS: The status of rats in each group was good. The weight of all rats increased, and the weight of rats in group C increased relatively slowly, although there was no significant difference compared with group D. Rats of all groups had smooth gastric mucosa and had no erosion or bleeding. Guth score was 0 points for all rats. HE staining analysis showed that Masude score had no statistical differences among all groups (P > 0.05). Routine blood tests, AST, ALT and crea showed no statistical difference among each group. Serum CHOL and TG in groups B and C significantly decreased compared with group D. Liver and kidney histopathology was not affected in all groups.

CONCLUSION: Intragastric administration of low dose capsaicin had no significant impact on gastric mucosa barrier, liver and kidney histopathology, routine blood tests, AST, ALT and crea.

Neuronal nitric oxide synthase-derived nitric oxide is involved in gastric mucosal hyperemic response to capsaicin in rats

BACKGROUND AND AIMS

Activation of transient receptor potential vanilloid type 1 (TRPV1) by capsaicin leads to gastric hyperemic response through capsaicin-sensitive sensory nerves and nitric oxide (NO). The aim of the present study is to examine which isoform of nitric oxide synthase (NOS)/NO is involved in the hyperemic response to capsaicin in the rat stomach.

METHODS

Gastric mucosal blood flow (GMBF) was measured by laser Doppler flowmetry in rats. The localizations of TRPV1 and neuronal NOS (nNOS) in the rat gastric mucosa were detected by immunohistochemical staining.

RESULTS

The nNOS inhibitor N(5)-[imino(propylamino)methyl]-L-ornithine substantially reduced GMBF during capsaicin application, whereas the endothelial NOS (eNOS) inhibitor N(5)-(1-iminomethyl)-L-ornithine did not affect the effect of capsaicin during the application. The nonselective NOS inhibitor N(G)-nitro-L-arginine methyl ester apparently inhibited the capsaicin-induced GMBF, while the inducible NOS inhibitor 1400W did not affect GMBF response to capsaicin. The immunohistochemical studies revealed nerve fibers coexpressing TRPV1 and nNOS around blood vessels in the gastric submucosa.

CONCLUSION

We demonstrated for the first time that nNOS/NO is involved in gastric hyperemic responses to capsaicin.

Differential changes in Substance P, VIP as well as neprilysin levels in patients with gastritis or ulcer

The protective effect of capsaicin-sensitive sensory nerve (CSSN) activation was recently demonstrated in human gastric mucosa. We here examined changes in neuropeptides, specifically Substance P (SP), calcitonin-gene related peptide (CGRP) and vasoactive intestinal peptide (VIP) in patients with chronic gastritis or ulcer. Furthermore changes in neprilysin levels, which hydrolyse these neuropeptides, were determined. Gastric biopsies were obtained from both lesion- and normal-appearing mucosa of 57 patients. The presence of H. pylori infection was verified with rapid urease assay. Neuronal and non-neuronal levels of SP, VIP, CGRP and neprilysin activity were determined in freshly frozen biopsies. Immunohistochemical localization of neprilysin was performed in 30 paraffin embedded specimens. We here found that neuronal SP levels decreased significantly in normally appearing mucosa of patients with gastritis while levels of non-neuronal SP increased in diseased areas of gastritis and ulcer. The presence of H. pylori led to further decreases of SP levels. The content of VIP in both disease-involved and uninvolved mucosa, and expression of neprilysin, markedly decreased in patients with gastritis or ulcer. Since VIP, as well as SP fragments, formed following hydrolysis with neprilysin is recognized to have gastroprotective effects, decreased levels of VIP, SP and neprilysin may predispose to cellular damage.

Transient receptor potential (TRP) channels as drug targets for diseases of the digestive system

Approximately 20 of the 30 mammalian transient receptor potential (TRP) channel subunits are expressed by specific neurons and cells within the alimentary canal. They subserve important roles in taste, chemesthesis, mechanosensation, pain and hyperalgesia and contribute to the regulation of gastrointestinal motility, absorptive and secretory processes, blood flow, and mucosal homeostasis. In a cellular perspective, TRP channels operate either as primary detectors of chemical and physical stimuli, as secondary transducers of ionotropic or metabotropic receptors, or as ion transport channels. The polymodal sensory function of TRPA1, TRPM5, TRPM8, TRPP2, TRPV1, TRPV3 and TRPV4 enables the digestive system to survey its physical and chemical environment, which is relevant to all processes of digestion. TRPV5 and TRPV6 as well as TRPM6 and TRPM7 contribute to the absorption of Ca²⁺ and Mg²⁺, respectively. TRPM7 participates in intestinal pacemaker activity, and TRPC4 transduces muscarinic acetylcholine receptor activation to smooth muscle contraction. Changes in TRP channel expression or function are associated with a variety of diseases/disorders of the digestive system, notably gastro-esophageal reflux disease, inflammatory bowel disease, pain and hyperalgesia in heartburn, functional dyspepsia and irritable bowel syndrome, cholera, hypomagnesemia with secondary hypocalcemia, infantile hypertrophic pyloric stenosis, esophageal, gastrointestinal and pancreatic cancer, and polycystic liver disease. These implications identify TRP channels as promising drug targets for the management of a number of gastrointestinal pathologies. As a result, major efforts are put into the development of selective TRP channel agonists and antagonists and the assessment of their therapeutic potential.

TRP channels in neurogastroenterology: opportunities for therapeutic intervention

The members of the superfamily of transient receptor potential (TRP) cation channels are involved in a plethora of cellular functions. During the last decade, a vast amount of evidence is accumulating that attributes an important role to these cation channels in different regulatory aspects of the alimentary tract. In this review we discuss the expression patterns and roles of TRP channels in the regulation of gastrointestinal motility, enteric nervous system signalling and visceral sensation, and provide our perspectives on pharmacological targeting of TRPs as a strategy to treat various gastrointestinal disorders. We found that the current knowledge about the role of some members of the TRP superfamily in neurogastroenterology is rather limited, whereas the function of other TRP channels, especially of those implicated in smooth muscle cell contractility (TRPC4, TRPC6), visceral sensitivity and hypersensitivity (TRPV1, TRPV4, TRPA1), tends to be well established. Compared with expression data, mechanistic information about TRP channels in intestinal pacemaking (TRPC4, TRPC6, TRPM7), enteric nervous system signalling (TRPCs) and enteroendocrine cells (TRPM5) is lacking. It is clear that several different TRP channels play important roles in the cellular apparatus that controls gastrointestinal function. They are involved in the regulation of gastrointestinal motility and absorption, visceral sensation and visceral hypersensitivity. TRP channels can be considered as interesting targets to tackle digestive diseases, motility disorders and visceral pain. At present, TRPV1 antagonists are under development for the treatment of heartburn and visceral hypersensitivity, but interference with other TRP channels is also tempting. However, their role in gastrointestinal pathophysiology first needs to be further elucidated.

Characterization of the mechanisms involved in the gastric antisecretory effect of TLQP-21, a vgf-derived peptide, in rats

TLQP-21, a vgf-derived peptide modulates gastric emptying and prevents ethanol-induced gastric lesions in rats. However, it remains to be studied whether or not TLQP-21 affects gastric acid secretion. In this study, we evaluated the effects of central (0.8-8 nmol/rat) or peripheral (48-240 nmol/kg, intraperitoneally) TLQP-21 administration on gastric acid secretion in pylorus-ligated rats. The mechanisms involved in such activity were also examined. Central TLQP-21 injection significantly reduced gastric acid volume and dose-dependently inhibited total acid output (ED(50) = 2.71 nmol), while peripheral TLQP-21 administration had no effect. The TLQP-21 antisecretory activity was prevented by cysteamine (300 mg/kg, subcutaneously), a depletor of somatostatin, by indomethacin (0.25 mg/rat, intracerebroventricularly), a non-selective cyclooxygenase inhibitor, and by functional ablation of sensory nerves by capsaicin. We conclude that TLQP-21 could be considered a new member of the large group of regulatory peptides affecting gastric acid secretion. The central inhibitory effect of TLQP-21 on gastric acid secretion is mediated by endogenous somatostatin and prostaglandins and requires the integrity of sensory nerve fibres.

Distribution of transient receptor potential vanilloid 1 channel-expressing nerve fibers in mouse rectal and colonic enteric nervous system: relationship to peptidergic and nitrergic neurons

In the gut, transient receptor potential vanilloid (TRPV) 1 activation leads to release of neurotransmitters such as neuropeptides and nitric oxide. However, the distribution of TRPV1 nerve fibers and neurotransmitters released form sensory nerve endings in the enteric nervous system are currently not well understood. The present study investigated the immunohistochemical distribution of TRPV1 channels, sensory neuropeptides, and nitric oxide and their co-localization in mouse large intestine. Numerous TRPV1 and calcitonin gene-related peptide (CGRP) immunoreactivities were detected, mainly in the mucosa, submucosal layer, and myenteric plexus. Abundant substance P (SP), neurokinin A (NKA), and neuronal nitric oxide synthase (nNOS)-immunoreactivity were revealed in muscle layers. Motor function studies of circular and longitudinal muscles found that contractile responses to capsaicin in the rectum were most sensitive among the rectum, and distal, transverse, and proximal colon. Double labeling studies were carried out in horizontal sections of mouse rectum. TRPV1/protein gene product (PGP)9.5 double labeled axons were observed, but PGP9.5 and neuronal nuclear protein immunopositive cell bodies did not express TRPV1 immunoreactivity in the myenteric plexus. In the mucosa, submucosal layer, deep muscular plexus, circular muscle, myenteric plexus and longitudinal muscle layer, TRPV1 nerve fibers were found to contain CGRP, SP and nNOS. SP and NKA were almost entirely colocalized at the axons and cell bodies in all layers. Double labeling with c-Kit revealed that TRPV1 nerve fibers localized adjacent to the interstitial cells of Cajal (ICC). These results suggest that the TRPV1-expressing nerve and its neurotransmitters regulate various functions of the large intestine.

Capsaicin inhibits the spontaneous pacemaker activity in interstitial cells of cajal from the small intestine of mouse

Background/Aims

Capsaicin (8-methyl-N-vanillyl-6-ninenamide), a compound found in hot peppers, has been reported to have different physiological actions on different cell types. Not much work has been done about the effect of capsaicin on the function of interstitial cells of Cajal (ICC). In the present study, we examined the action of external application of capsaicin on pacemaker activity in the cultured ICC from the small intestine of mouse.

Methods

We investigated the effect of capsaicin on pacemaker currents in cultured ICC from the small intestine of mouse using a whole cell patch-clamp technique and Ca²⁺-imaging analysis.

Results

When capsaicin was applied externally to the pacemaker generating ICC, it completely inhibited the pacemaker potential under current-clamp mode (I = 0) and the pacemaker current under voltage-clamp mode at a -70 mV of holding potentials. The effect of capsaicin on pacemaker activity in ICC was shown dose dependently. The effect of capsaicin was not through the transient receptor potential of the vanilloid type 1 (TRPV1) channel as capsazepine did not block the effect of capsaicin. L-NAME, an inhibitor of nitric oxide synthase, also did not block the capsaicin-induced effects. When the action of capsaicin was examined in the intracellular calcium oscillation, it completely abolished the calcium oscillation.

Conclusions

These results prove that the capsaicin has the inhibitory effects on the ICC which is carried out neither through TRPV channel nor the nitric oxide production. Intracellular Ca²⁺ was also an important target for actions of capsaicin on ICC.

TRPV1: a target for next generation analgesics

Transient Receptor Potential Vanilloid 1 (TRPV1) is a Ca²⁺ permeant non-selective cation channel expressed in a subpopulation of primary afferent neurons. TRPV1 is activated by physical and chemical stimuli. It is critical for the detection of nociceptive and thermal inflammatory pain as revealed by the deletion of the TRPV1 gene. TRPV1 is distributed in the peripheral and central terminals of the sensory neurons and plays a role in initiating action potentials at the nerve terminals and modulating neurotransmitter release at the first sensory synapse, respectively. Distribution of TRPV1 in the nerve terminals innervating blood vessels and in parts of the CNS that are not subjected to temperature range that is required to activate TRPV1 suggests a role beyond a noxious thermal sensor. Presently, TRPV1 is being considered as a target for analgesics through evaluation of different antagonists. Here, we will discuss the distribution and the functions of TRPV1, potential use of its agonists and antagonists as analgesics and highlight the functions that are not related to nociceptive transmission that might lead to adverse effects.

The vanilloid receptor TRPV1: role in cardiovascular and gastrointestinal protection

It has been shown that the transient receptor potential channel vanilloid type 1 (TRPV1) is able to sense a vast range of stimuli and exerts multiple functions under physiological or pathophysiological conditions. TRPV1 not only plays a fundamental role in pain signaling but also involves in many other physiological or pathophysiological functions including the beneficial effects on cardiovascular and gastrointestinal function. It has been found that TRPV1 could be activated by endogenous ligands such as anandamide, N-arachidonoyl dopamine and N-oleoyldopamine or by exogenous agonists such as capsaicin and rutaecarpine. Since capsaicin-sensitive sensory nerves (rich in TRPV1) are densely distributed in the cardiovascular and gastrointestinal system, activation of TRPV1 either by endogenous ligands or by exogenous agonists has been repeatedly reported to exert hypotensive effects or protective effects against cardiac or gastrointestinal injury through stimulating the synthesis and release of multiple neurotransmitters such as calcitonin gene-related peptide and substance P. Therefore, TRPV1 is not only a prime target for the pharmacological control of pain but also a useful target for drug development to treat various diseases including cardiovascular and gastrointestinal diseases. However, considering the contribution of TRPV1 to the development of inflammation in the gastrointestinal tract, the potential side effects of TRPV1 agonist cannot be neglected while in seeking and developing the novel TRPV1 agonists.

Localization of TRPV1 and contractile effect of capsaicin in mouse large intestine: high abundance and sensitivity in rectum and distal colon

We investigated immunohistochemical differences in the distribution of TRPV1 channels and the contractile effects of capsaicin on smooth muscle in the mouse rectum and distal, transverse, and proximal colon. In the immunohistochemical study, TRPV1 immunoreactivity was found in the mucosa, submucosal, and muscle layers and myenteric plexus. Large numbers of TRPV1-immunoreactive axons were observed in the rectum and distal colon. In contrast, TRPV1-positive axons were sparsely distributed in the transverse and proximal colon. The density of TRPV1-immunoreactive axons in the rectum and distal colon was much higher than those in the transverse and proximal colon. Axons double labeled with TRPV1 and protein gene product (PGP) 9.5 were detected in the myenteric plexus, but PGP 9.5-immunoreactive cell bodies did not colocalize with TRPV1. In motor function studies, capsaicin induced a fast transient contraction, followed by a large long-lasting contraction in the rectum and distal colon, whereas in the transverse and proximal colon only the transient contraction was observed. The capsaicin-induced transient contraction from the proximal colon to the rectum was moderately inhibited by an NK1 or NK2 receptor antagonist. The capsaicin-induced long-lasting contraction in the rectum and distal colon was markedly inhibited by an NK2 antagonist, but not by an NK1 antagonist. The present results suggest that TRPV1 channels located on the rectum and distal colon play a major role in the motor function in the large intestine.

The effect and mechanism of action of capsaicin on gastric acid output

BACKGROUND

Capsaicin has beneficial pharmacological properties, such as the ability to improve appetite and digestion. However, capsaicin has been reported to suppress gastric acid output, but to increase secretion; no consensus as to its effects on gastric acid output has been reached, and the underlying mechanisms remain to be elucidated.

METHODS

Rat gastric lumen was perfused with capsaicin. Basal acid output and gastric acid secretion stimulated by vagal nerve activation and bethanecol, a muscarinic receptor agonist, were measured. After intravenous infusion of calcitonin gene-related peptide (CGRP), the measurements were repeated. The secretion of gastrin, somatostatin, and histamine was measured in isolated vascularly perfused rat stomach after vagal nerve and bethanecol stimulation, and under the influence of capsaicin.

RESULTS

Capsaicin administration had no effect on basal gastric acid output, but inhibited acid secretion resulting from vagal stimulation. Capsaicin had no effect on acid secretion resulting from stimulation with bethanecol. Administration of high-dose CGRP inhibited basal acid output and gastric acid secretion from both vagal nerve and bethanecol stimulation. Low-dose CGRP inhibited gastric acid secretion because of vagal stimulation, but had no effect on basal secretion or acid secretion following stimulation with bethanecol. Capsaicin administration inhibited the stimulated gastrin and histamine secretion and reversed the suppression of somatostatin secretion mediated by vagal stimulation. However, capsaicin had no effect on stimulated gastrin secretion, suppression of somatostatin secretion, or stimulated histamine secretion because of bethanecol.

CONCLUSIONS

Capsaicin inhibited gastric acid output, and the mechanism underlying this effect appears to involve vagal nerve inactivation.

Effect of repeated, long term capsaicin ingestion on intestinal chemo- and mechanosensation in healthy volunteers

Repeated ingestion of capsaicin over a prolonged period reduces symptoms in functional dyspepsia, but initially induces upper abdominal symptoms. Sensitizing chemonociception might be the cause for this initial effect of capsaicin. The aim was to evaluate the effect of prolonged capsaicin ingestion on duodenal chemo- and mechanonociception. Healthy subjects ingested capsules containing either 0.25 mg capsaicin tid (n = 8) or placebo (n = 8) for 28 days. Before (day 0) and after (day 29) capsule ingestion the duodenum was distended with a balloon and perfused with a capsaicin solution. Mechanically and chemically induced sensation was evaluated by a graded questionnaire. Aggregate perception scores were calculated. Perception scores during balloon distensions with 12 and 18 mmHg were significantly lower after 4 weeks capsaicin when compared to baseline (P < 0.05). Balloon volumes to induce first sensation (63 +/- 14 mL (day 0) vs 92 +/- 22 mL (day 29); P < 0.05) and discomfort (101 +/- 12 mL vs 137 +/- 22 mL; P = 0.05) where significantly higher after 4 weeks capsaicin application; balloon pressures to induce sensations were not significantly different. Intraluminal capsaicin application induced first sensation after 3.4 +/- 1.5 min (day 0) and 7.5 +/- 4.6 min (day 29) (P < 0.05) and discomfort after 15.9 +/- 9.8 min and 22.4 +/- 7.3 min (P < 0.05). The quality of perception was not altered by repeated capsaicin ingestion. In the placebo group, mechano- and chemonociception remained unaltered at day 29. Four weeks ingestion of capsaicin desensitized both chemonociceptive and mechanonociceptive pathways in healthy volunteers. Symptom reduction after prolonged treatment with capsaicin in dyspeptic patients might be attributed to a dual desensitizing effect of capsaicin on chemonociceptors and mechanonociceptors.

A combination of curcumin and ginger extract improves abrasion wound healing in corticosteroid-impaired hairless rat skin

Hairless rats were topically treated with a combination of 10% curcumin and 3% ginger extract (or with each agent alone) for a 21-day period. Following this, the rats were treated topically with Temovate (corticosteroid) for an additional 15 days. At the end of the treatment period, superficial abrasion wounds were induced in the treated skin. Abrasion wounds healed more slowly in the skin of Temovate-treated rats than in skin of control animals. Healing was more rapid in skin of rats that had been pretreated with either curcumin or ginger extract alone or with the combination of curcumin-ginger extract (along with Temovate) than in the skin of rats treated with Temovate and vehicle alone. Skin samples were obtained at the time of wound closure. Collagen production was increased and matrix metalloproteinase-9 production was decreased in the recently healed skin from rats treated with the botanical preparation relative to rats treated with Temovate plus vehicle. In none of the rats was there any indication of skin irritation during the treatment phase or during wounding and repair. Taken together, these data suggest that a combination of curcumin and ginger extract might provide a novel approach to improving structure and function in skin and, concomitantly, reducing formation of nonhealing wounds in "at-risk" skin.

The effects of capsaicin on gastrin secretion in isolated human antral glands: before and after ingestion of red chilli

BACKGROUND

Capsaicin is known to have regulatory effects on gastrointestinal functions via the vanilloid receptor (VR1). We reported previously that endocrine-like cells in the human antrum express VR1.

AIM

To identify VR1-expressing endocrine-like cells in human antral glands and to examine whether stimulation with capsaicin causes release of gastrin, somatostatin, and serotonin. Further, to investigate the effects of a chilli-rich diet.

METHODS

Gastroscopic biopsies were received from 11 volunteers. Seven of the 11 subjects agreed to donor gastric biopsies a second time after a 3-week chilli-rich diet containing 1.4-4.2 mg capsaicin/day. VR1-immunoreactive cells were identified by double-staining immunohistochemistry against gastrin, somatostatin, and serotonin. For the stimulation studies, we used an in vitro method where antral glands in suspension were stimulated with 0.01 mM capsaicin and physiological buffer was added to the control vials. The concentrations of secreted hormones were detected and calculated with radioimmunoassay (RIA). Results The light microscopic examination revealed that VR1 was localized in gastrin cells. The secretory studies showed an increase in release of gastrin and somatostatin compared to the control vials (P = 0.003; P = 0.013). Capsaicin-stimulation caused a consistent raise of the gastrin concentrations in the gland preparations from all subjects. A chilli-rich diet had an inhibitory effect on gastrin release upon stimulation compared to the results that were obtained before the start of the diet.

CONCLUSION

This study shows that capsaicin stimulates gastrin secretion from isolated human antral glands, and that a chilli-rich diet decreases this secretion.

Adaptive HNE-Nrf2-HO-1 pathway against oxidative stress is associated with acute gastric mucosal lesions

Disturbance of the microcirculation and generation of reactive oxygen species are crucial in producing acute gastric mucosal lesions (AGML). To understand the protective mechanism against mucosal injury and oxidative stress in the stomach, we investigated sequential expression and localization of a product of lipid peroxidation and a chemical mediator of the oxidative response array, 4-hydroxynonenal (HNE), transcriptional factor, NF-E2-related factor (Nrf2), and the inducible heme oxygenase (HO-1) in the injured stomach. AGML was produced by intragastric administration of 0.6 N HCl in male rats. Expression and localization of HNE, Nrf2, and HO-1 were investigated by Western blotting, immunohistochemistry, real-time RT-PCR, and in situ hybridization histochemistry. Mucosal lesions and expression of HNE and HO-1 were assessed by prior treatment with the PGI2 analog beraprast or after sensory denervation by pretreatment with capsaicin. Mucosal lesions were assessed by prior treatment with a HO-1 inhibitor, zinc protoporphyrin (ZnPP). After AGML, increased generation of HNE was observed in the injured mucosa and the surrounding submucosa, followed by nuclear translocation of Nrf2 and upregulation of HO-1 in the macrophages located in the margin of the injured mucosa and in the submucosa. Pretreatment with beraprost attenuated AGML and downregulated the expression of HNE and HO-1, while sensory denervation aggravated AGML and upregulated the expression of HNE and HO-1. Pretreatment with ZnPP also aggravated AGML. The sequential HNE-Nrf2-HO-1 pathway in the gastric mucosal cells and the macrophages is involved in an adaptive mechanism against oxidative stress after AGML.

Immunohistochemical localization of transient receptor potential vanilloid subtype 1 in the trachea of ovalbumin-sensitized Guinea pigs

BACKGROUND

We previously found many transient receptor potential vanilloid receptor subtype 1 (TRPV1) axons in the tracheal smooth muscle and epithelium of the guinea pig airway. One report indicates that the number of TRPV1 axons is significantly increased in patients with cough variant asthma.

AIM

To determine whether the distribution of TRPV1 in the airways is altered in guinea pigs with an allergic phenotype.

METHODS

Ten guinea pigs were assigned to 2 groups in a double-blind study. Five animals were sensitized with ovalbumin and the other 5 underwent sham sensitization. Cryopreserved sections (30 microm) of tracheal tissues removed from each animal were stained with polyclonal serum rabbit anti-TRPV1 antibody (1:30,000) and examined by confocal microscopy.

RESULTS

Axons immunoreactive to TRPV1 localized to fine axons within the epithelium and around areas of smooth muscle, were more densely stained and frequent in the ovalbumin than in the sham group.

CONCLUSION

The number of TRPV1-immunoreactive axons in the trachea increases under allergic inflammatory conditions.

Role of visceral afferent neurons in mucosal inflammation and defense

The maintenance of gastrointestinal (GI) mucosal integrity depends on the rapid alarm of protective mechanisms in the face of pending injury. Two populations of extrinsic primary afferent neurons, vagal and spinal, subserve this goal through different mechanisms. These sensory neurons react to GI insults by triggering protective autonomic reflexes including the so-called cholinergic anti-inflammatory reflex. Spinal afferents, in addition, can initiate protective tissue reactions at the site of assault through release of calcitonin gene-related peptide (CGRP) from their peripheral endings. The protective responses triggered by sensory neurons comprise alterations in GI blood flow, secretion, and motility as well as modifications of immune function. This article focuses on significant advances that during the past couple of years have been made in identifying molecular nocisensors on afferent neurons and in dissecting the signaling mechanisms whereby afferent neurons govern inflammatory processes in the gut.

Contractile effect of TRPA1 receptor agonists in the isolated mouse intestine

TRPA1 is a member of the transient receptor potential (TRP) channel family expressed in sensory neurons. The present study focused on the effects of TRPA1 activation on contractile responses in isolated mouse intestine preparations. The jejunum, ileum, and proximal and distal colon were surgically isolated from male ddY mice. Intestinal motility was recorded as changes in isotonic tension. TRPA1, TRPM8, and TRPV1 expressions were examined by reverse transcription-polymerase chain reaction (RT-PCR). A TRPA1 agonist allyl isothiocyanate (AITC) dose-dependently induced contractions in the proximal and distal colon, whereas in the jejunum and ileum, even 100 muM AITC caused very little contraction. Likewise, a TRPA1 and TRPM8 agonist icilin, a TRPA1 agonist allicin, and a TRPV1 agonist capsaicin induced contractions in the colon. However, a TRPM8 agonist menthol induced long-lasting relaxation in the colon. Repeated exposure to AITC produced desensitization of its own contraction in the colon. Moreover, contractions induced by AITC generate cross-desensitization with icilin and capsaicin. Tetrodotoxin completely abolished AITC-induced contractions in the colon, whereas atropine significantly attenuated AITC-induced contractions in the distal colon, but not in the proximal colon. Menthol-induced relaxation in the colon was not inhibited by tetrodotoxin and atropine. RT-PCR analysis revealed the expression of TRPA1 and TRPV1, but not TRPM8, throughout the mouse intestine. These results suggest that TRPA1, but not TRPM8, are functionally expressed in the enteric nervous system throughout the mouse intestine on neurons that may also co-express TRPV1, yet the contractile responses to TRPA1 activation differ depending on their location along the intestine.

A curcumin-based 1-week triple therapy for eradication of Helicobacter pylori infection: something to learn from failure?

BACKGROUND

Curcumin is the principal element of turmeric powder extracted from the root of Curcuma longa. Studies on curcumin have demonstrated some anti-Helicobacter pylori activity as well as immunomodulating properties. N-acetylcysteine and lactoferrin with their respective mucolytic and antibacterial activities might also be effective in H. pylori eradication therapy.

AIM

To determine if a 7-day non-antibiotic therapy comprised of curcumin, lactoferrin, N-acetylcysteine, and pantoprazole was effective for eradication of H. pylori infection and reduction of gastric inflammation, assessed by serum pepsinogens and relief of symptoms.

SUBJECTS AND METHODS

Twenty-five consecutive H. pylori-positive patients (12 males, mean age 50 +/- 12 years, range 31-76) with functional dyspepsia were enrolled. Patients were administered for 7 days curcumin 30 mg b.i.d., bovine lactoferrin 100 mg b.i.d., N-acetylcysteine 600 mg b.i.d., and pantoprazole 20 mg b.i.d. H. pylori status and upper gastrointestinal symptoms were assessed by (13)C-urea breath test and a scale of upper gastrointestinal symptoms intensity (absent, mild, moderate, and severe), as well as a blood test for serum pepsinogens (sPGI, sPGII), gastrin-17 (G-17), and anti-H. pylori IgG (IgG-Hp) at baseline (T0) and after 2 months (T1).

RESULTS

Three of 25 patients (12%) were cured of H. pylori infection. A significant decrease in the overall severity of symptoms (T0: 6, interquartile range [IQR]: 4.5-8; T1: 2, IQR: 2-3; p < or = .001), and sPGII (T0: 16 microg/L, IQR: 13-22; T1: 10 microg/L, IQR: 8-16; p < or = .001) and sPGI (T0: 82 microg/L, IQR: 67-97; T1: 74 microg/L, IQR: 62-94; p = .02) levels were observed after 2 months of the treatment. IgG and G-17 values did not significantly decrease after 2 months.

CONCLUSIONS

This novel therapy was not effective for H. pylori eradication. However, despite the bacterium persistence, significant improvement of dyspeptic symptoms and reduction of serologic signs of gastric inflammation were observed after 2 months at the end of the 7-day treatment schedule.

The vanilloid receptor TRPV1: 10 years from channel cloning to antagonist proof-of-concept

The clinical use of TRPV1 (transient receptor potential vanilloid subfamily, member 1; also known as VR1) antagonists is based on the concept that endogenous agonists acting on TRPV1 might provide a major contribution to certain pain conditions. Indeed, a number of small-molecule TRPV1 antagonists are already undergoing Phase I/II clinical trials for the indications of chronic inflammatory pain and migraine. Moreover, animal models suggest a therapeutic value for TRPV1 antagonists in the treatment of other types of pain, including pain from cancer. We argue that TRPV1 antagonists alone or in conjunction with other analgesics will improve the quality of life of people with migraine, chronic intractable pain secondary to cancer, AIDS or diabetes. Moreover, emerging data indicate that TRPV1 antagonists could also be useful in treating disorders other than pain, such as urinary urge incontinence, chronic cough and irritable bowel syndrome. The lack of effective drugs for treating many of these conditions highlights the need for further investigation into the therapeutic potential of TRPV1 antagonists.

Gastrocardiac afferent convergence in upper thoracic spinal neurons: a central mechanism of postprandial angina pectoris

The aim of this study was to examine whether gastric afferent information converged onto upper thoracic spinal neurons that received noxious cardiac input. Extracellular potentials of single upper thoracic (T3) spinal neurons were recorded in pentobarbital-anesthetized, paralyzed, ventilated male rats. Gastric distension (GD) (20, 40, 60 mm Hg, 20 seconds) was produced by air inflation of a latex balloon surgically placed in the stomach. A catheter was placed in the pericardial sac to administer bradykinin solution (10 microg/mL, 0.2 mL, 1 minute) as a noxious cardiac stimulus. Noxious GD (> or =40 mm Hg) altered activity of 26 of 31 (84%) spinal neurons receiving cardiac input. Twenty-two (85%) gastrocardiac convergent neurons were excited, and 1 neuron was inhibited by both intrapericardial bradykinin and GD; the remainder exhibited biphasic response patterns. Twenty-three of 26 (88%) gastrocardiac neurons also received convergent somatic input from the chest, triceps, and upper back areas. Bilateral cervical vagotomy did not significantly affect excitatory responses to GD in 5 of 5 neurons tested. Spinal transection at the C1 segment after vagotomy did not affect excitatory responses to GD in 3 of 4 neurons but abolished the GD response in 1 neuron. These data showed that a gastric stimulus excited T3 spinal neurons with noxious cardiac input primarily by way of intraspinal ascending pathways.

PERSPECTIVE

Convergence of gastric afferent input onto upper thoracic spinal neurons receiving noxious cardiac input that was observed in the present study may provide a spinal mechanism that explains stomach-heart cross-organ communication, such as postprandial triggering and worsening of angina pectoris in patients with coronary artery disease.

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.

Inhibition of neutrophil activation by lafutidine, an H2-receptor antagonist, through enhancement of sensory neuron activation contributes to the reduction of stress-induced gastric mucosal injury in rats

Sensory neuron activation reduces water-immersion restraint stress (WIR)-induced gastric mucosal injury by inhibiting neutrophil activation through increase in endothelial production of prostacyclin. This study was designed to examine whether lafutidine, which is an H(2)-receptor antagonist and activates sensory neurons, inhibits neutrophil activation, thereby reducing WIR-induced gastric mucosal injury. Lafutidine enhanced WIR-induced increases in gastric tissue levels of calcitonin gene-related peptide (CGRP) and 6-keto-PGF(1alpha), a stable metabolite of prostacyclin, whereas famotidine, another H(2)-receptor antagonist, did not. Such lafutidine-induced increases in gastric tissue levels of 6-keto-PGF(1alpha) were reversed by pretreatment with capsazepine, an inhibitor of sensory neuron activation, CGRP(8-37), a CGRP antagonist, and indomethacin. Lafutidine inhibited acid-induced exacerbation of gastric mucosal injury in animals subjected to WIR by inhibiting neutrophil activation, whereas famotidine did not. Lafutidine synergistically increased CGRP release from isolated rat dorsal root ganglion neurons in the presence of anandamide, but famotidine did not. These observations suggest that lafutidine might reduce WIR-induced gastric mucosal injury not only by inhibiting acid secretion but also by inhibiting neutrophil activation through enhancement of sensory neuron activation.

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.

Review article: duodenal bicarbonate - mucosal protection, luminal chemosensing and acid-base balance

The duodenum serves as a buffer zone between the stomach and the jejunum. Over a length of only 25 cm, large volumes of strong acid secreted by the stomach must be converted to the neutral-alkaline chyme of the hindgut lumen, generating large volumes of CO(2). The duodenal mucosa consists of epithelial cells connected by low-resistance tight junctions, forming a leaky epithelial barrier. Despite this permeability, the epithelial cells, under intense stress from luminal mineral acid and highly elevated Pco(2), maintain normal functioning. Bicarbonate ion uniquely protects the duodenal epithelial cells from acid-related injury. The specific protective mechanisms likely involve luminal bicarbonate secretion, intracellular pH buffering and interstitial buffering. Furthermore, the duodenum plays an active role in foregut acid-base homeostasis, absorbing large amounts of H(+) and CO(2). We have studied mucosal protection and acid-base balance using live-animal fluorescence ratio microimaging and by performing H(+) and CO(2) balance studies on duodenal perfusates. On the basis of these data, we have formulated novel hypotheses with regard to mucosal protection.

Modulatory effects and afferent pathways of gastric electrical stimulation on rat thoracic spinal neurons receiving input from the stomach

Gastric electrical stimulation (GES) has been suggested as a potential therapy for patients with obesity or gastric motility disorders. The aim of this study was to investigate the spinal mechanism of GES effects on gastric functions. Extracellular potentials of single spinal (T9-T10) neurons were recorded in pentobarbital anesthetized, paralyzed, ventilated male rats (n=19). Gastric distension (GD) was produced by air inflation of a balloon. One pair of platinum electrodes (1.0-1.5cm apart) was sutured onto the serosal surface of the lesser curvature of the stomach. GES with four sets of parameters was applied for 1min: GES-A (6mA, 0.3ms, 40Hz, 2s on, 3s off), GES-B (6mA, 0.3ms, 14Hz, 0.1s on, 5s off), GES-C (6mA, 3ms, 40Hz, 2s on, 3s off), GES-D (6mA, 200ms, 12pulses/min). 62/158 (39%) spinal neurons responded to GD (20, 40, 60mmHg, 20s. Most GD-responsive neurons (n=43) had excitatory responses; the remainder had inhibitory (n=12) or biphasic responses (n=7). GES-A, -B, -C and -D affected activity of 12/33 (36%), 4/31 (13%), 22/29 (76%) and 13/30 (43%) GD-responsive neurons, respectively. Bilateral cervical vagotomy did not significantly alter mean excitatory neuronal responses to GD (n=5) or GES (n=6). Resiniferatoxin (2.0microg/kg, i.v.), an ultrapotent agonist of vanilloid receptor-1, abolished excitatory responses to GD and GES in 4/4 neurons recorded in vagotomized rats. The results suggested that GES mainly had an excitatory effect on T9-T10 spinal neurons with gastric inputs; neuronal responses to GES were strengthened with stimulation at an increased pulse width and/or number of pulses. The modulatory effect of GES involved thoracic spinal (sympathetic) afferent fibers containing vanilloid receptor-1.

The TRPV1 receptor and nociception

The capsaicin receptor TRPV1 is an emerging target for the treatment of pain with a unique expression profile in peripheral nociceptors and the ability to show polymodal activation, TRPV1 is an important integrator of responses to inflammatory mediators. Sensitization of TRPV1 during chronic pain is believed to contribute to the transduction of noxious signaling for normally innocuous stimuli and consequently the search for novel TRPV1 therapeutics is intense. The current understanding of the physiological role the receptor, as well as the potential therapeutic utility and emerging liabilities of TRPV1 modulators are discussed.

Effect of repeated capsaicin ingestion on intestinal chemosensation and mechanosensation

BACKGROUND

Ingestion of capsaicin reduces symptoms in functional dyspepsia but induces upper abdominal symptoms initially.

AIMS

To evaluate the effects of one week of oral dosing with capsaicin on mechanonociception and chemonociception.

METHODS

Healthy subjects ingested capsules containing 0.5 mg capsaicin t.d.s (n = 8) or placebo (n = 5) for 7 days. Before (day 0) and after (day 8) capsule ingestion the jejunum was distended with a balloon and perfused with a capsaicin solution. A graded questionnaire evaluated distension- and capsaicin-induced sensation, aggregate perception scores were calculated.

RESULTS

Infusion of capsaicin induced sensations similar to distension. In subjects receiving capsaicin capsules, mean +/- S.E.M. perception scores at 24 mL distension volumes were 4.7 +/- 1.2 (day 0) and 3.2 +/- 1.3 (day 8, N.S.). Distension with 40 mL induced perception scores of 10.3 +/- 1.0 vs. 8.2 +/- 1.0 (P < 0.05). During capsaicin perfusion, first sensation was reported after 13.2 +/- 1.9 min (day 0) and 8.1 +/- 0.8 min (day 8, N.S.), discomfort thresholds after 44.1 +/- 6.0 and 31.2 +/- 5.7 min (P < 0.05). In the placebo group, mechano- and chemonociception remained unaltered on days 0 and 8.

CONCLUSIONS

One week of ingestion of capsaicin sensitized chemonociceptors, while sensitivity of mechanonociceptors for distension decreased. Painful sensations during the first week of treatment with capsaicin can be attributed to a sensitizing effect of capsaicin on vanilloid receptors.

Carbonic anhydrases and mucosal vanilloid receptors help mediate the hyperemic response to luminal CO2 in rat duodenum

BACKGROUND & AIMS

The duodenal mucosa is exposed to PCO(2) >200 mm Hg due to the luminal mixture of gastric acid with secreted bicarbonate, which augments mucosal protective mechanisms. We examined the hyperemic response to elevated luminal PCO(2) in the duodenum of anesthetized rats luminally exposed to high CO(2) saline to help elucidate luminal acid-sensing mechanisms.

METHODS

Blood flow was measured by laser Doppler, and intracellular pH of epithelial cells by measured by ratio microimaging. The permeant carbonic anhydrase (CA) inhibitor methazolamide, relatively impermeant CA inhibitor benzolamide, vanilloid receptor antagonist capsazepine, or sodium-hydrogen exchanger 1 (NHE-1) inhibitor dimethyl amiloride were perfused with or without the high CO(2) solution.

RESULTS

The high CO(2) solution increased duodenal blood flow, which was abolished by pretreatment with methazolamide or capsazepine or by dimethyl amiloride coperfusion. Sensory denervation with capsaicin also abolished the CO(2) effects. Benzolamide dose-dependently inhibited CO(2)-induced hyperemia and at 100 nmol/L inhibited CO(2)-induced intracellular acidification. The membrane-bound CA isoforms IV, IX, XII, and XIV and cytosolic CA II and the vanilloid receptor 1 (TRPV1) were expressed in duodenum and stomach. Dorsal root ganglion and nodose ganglion expressed all isoforms except for CA IX.

CONCLUSIONS

The duodenal hyperemic response to luminal CO(2) is dependent on cytosolic and membrane-bound CA isoforms, NHE-1, and TRPV1. CO(2)-induced intracellular acidification was inhibited by selective extracellular CA inhibition, suggesting that CO(2) diffusion across the epithelial apical membrane is mediated by extracellular CA. NHE-1 activation preceding TRPV1 stimulation suggests that luminal CO(2) is sensed as H(+) in the subepithelium.

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.