Nitric oxide modulates pepsinogen secretion induced by calcium-mediated agonist in guinea pig gastric chief cells

Importance of Ca(2+) in gastric epithelial restitution-new views revealed by real-time in vivo measurements

It has been a few decades since Ca(2+) was identified as one of the important factors that can accelerate gastric wound repair as well as contribute to epithelial homeostasis and regulation of gastric secretions. The mechanistic basis has remained largely unexplored in vivo because it was not possible to track in real time either intracellular Ca(2+) mobilization or wound repair in living tissues. Recent advances in technology, such as combining high resolution light microscopy and genetically encoded Ca(2+) reporters in mice, now allow the monitoring of Ca(2+) mobilization during gastric epithelial cell restitution. Ca(2+) is a ubiquitous second messenger that influences numerous cellular processes, including gastric acid/bicarbonate secretion, mucus secretion, and cell migration. We have demonstrated that cytosolic Ca(2+) mobilization within the restituting gastric epithelial cells is a central signal driving small wound repair. However, extracellular Ca(2+) is also mobilized in the juxtamucosal luminal space above a wound, and evidence suggests extracellular Ca(2+) is a third messenger that also promotes gastric epithelial restitution. Interplay between intracellular and extracellular Ca(2+) is necessary for efficient gastric epithelial restitution.

Low Levels of Pepsinogen I and Pepsinogen I/II Ratio are Valuable Serologic Markers for Predicting Extensive Gastric Corpus Atrophy in Patients Undergoing Endoscopic Mucosectomy

BACKGROUND/AIMS

The levels of pepsinogen (PG) I and the PGI/II ratio are useful serologic markers for chronic atrophic gastritis. This study evaluated the performance and clinical implications of these markers in patients undergoing endoscopic mucosectomy.

METHODS

We enrolled 142 consecutive patients with early gastric tumors and Helicobacter pylori infection who were eligible for mucosectomy. Chronic gastritis and atrophy were assessed using four defined biopsy procedures. Serum PGs were measured by an enzyme immunoassay. Optimal diagnostic cut-offs and performance were determined using receiver operating characteristic curves.

RESULTS

The PGI level and the PGI/II ratio decreased with corpus-dominant gastritis and as atrophy advanced toward the corpus greater curvature (GC). For the presence of corpus GC atrophy, the areas under the PGI and PGI/II-ratio curves were 0.82 and 0.77, respectively. The optimal cut-off levels were 59.3µg/L for PGI (sensitivity, 83.3%; specificity, 78.4%) and 3.6µg/L for PGI/II ratio (sensitivity, 70.0%; specificity, 78.4%). Using these serologic cut-off levels, we found that the frequency of corpus tumor location differed significantly (32.9% vs 11.1% for PGI <59.3 and ≥59.3µg/L, respectively; and 31.1% vs 14.8% for PGI/II ratio <3.5 and ≥3.5, respectively; p<0.05).

CONCLUSIONS

A low PGI level and PGI/II ratio are valuable serologic markers for predicting corpus GC atrophy, and have clinical implications with respect to the corpus location of tumors in mucosectomy patients.

Dual role of nitric oxide in gastric hypersecretion in the distended stomach: inhibition of acid secretion and stimulation of pepsinongen secretion

AIMS

We investigate the role of nitric oxide (NO) in the hypersecretion of acid and pepsinogen induced by stomach distension.

MAIN METHOD

The rat stomach was distended by instillation of saline through an acute fistula under urethane anesthesia.

KEY FINDINGS

Both secretions of acid and pepsinogen were increased by the distension depending on the volume of saline introduced, and responses were attenuated by bilateral cervical vagotomy or prior administration of atropine. N(G)-nitro-l-arginine methyl ester (L-NAME) had a dual effect on these responses, causing an increase in the acid response and a decrease in the pepsin response, both in an l-arginine-sensitive manner. Distension of the stomach increased the luminal NO release; this response was suppressed by vagotomy and L-NAME. Intragastric application of FK409, a NO donor, dose-dependently increased pepsinogen secretion while decreasing acid secretion in the stomach without distension. However, serosal application of both FK409 and 8-bromo-guanosine cyclic 3', 5'-monophosphate (8-Br-cGMP) stimulated the secretion of pepsinogen in isolated mouse stomachs in vitro. The stimulatory effect of FK409 on pepsinogen secretion was totally abolished by LY83583, a guanylate cyclase inhibitor.

SIGNIFICANCE

Distension of the stomach increases both acid and pepsinogen secretion through a vagal-cholinergic pathway in addition to the luminal release of NO, and NO affects these responses in opposite ways, suppressing the acid response while enhancing the pepsin response, both mediated by a guanylate cyclase/cGMP pathway.

mGluR1 in the fundic glands of rat stomach

l-glutamate not only confers cognitive discrimination for umami taste in the oral cavity, but also conveys sensory information to vagal afferent fibers in the gastric mucosa. We used RT-PCR, western blotting, and immunohistochemistry to demonstrate that mGluR1 is located in glandular stomach. Double staining revealed that mGluR1 is found at the apical membrane of chief cells and possibly in parietal cells. Moreover, a diet with 1% l-glutamate induced changes in the expression of pepsinogen C mRNA in stomach mucosa. These data suggest that mGluR1 is involved in the gastric phase regulation of protein digestion.

Luminal amino acid sensing in the rat gastric mucosa

Recent advancements in molecular biology in the field of taste perception in the oral cavity have raised the possibility for ingested nutrients to be "tasted" in the upper gastrointestinal tract. The purpose of this study was to identify the existence of a nutrient-sensing system by the vagus in the rat stomach. Afferent fibers of the gastric branch increased their firing rate solely with the intragastric application of the amino acid glutamate. Other amino acids failed to have the same effect. This response to glutamate was blocked by the depletion of serotonin (5-HT) and inhibition of serotonin receptor(3) (5-HT(3)) or nitric oxide (NO) synthase enzyme. Luminal perfusion with the local anesthesia lidocaine abolished the glutamate-evoked afferent activation. The afferent response was also mimicked by luminal perfusion with a NO donor, sodium nitroprusside. In addition, the NO donor-induced afferent activation was abolished by 5-HT(3) blockade as well. Altogether, these results strongly suggest the existence of a sensing system for glutamate in the rat gastric mucosa. Thus luminal glutamate would enhance the electrophysiological firing rate of afferent fibers from the vagus nerve of the stomach through the production of mucosal bioactive substances such as NO and 5-HT. Assuming there is a universal coexistence of free glutamate with dietary protein, a glutamate-sensing system in the stomach could contribute to the gastric phase of protein digestion.

PAR-2 modulates pepsinogen secretion from gastric-isolated chief cells

In the present study, we investigated whether activation of protease-activated receptor type 2 (PAR-2) with SLIGRL (SL)NH2, a short mimetic agonistic peptide, directly stimulates pepsinogen secretion from gastric-isolated, pepsinogen-secreting (chief) cells. Immunostaining of gastric-dispersed chief cells with a specific anti-PAR-2 antibody demonstrated expression of PAR-2 receptors on membrane and cytoplasm. SL-NH2 and trypsin potently stimulated pepsinogen secretion (EC50 = 0.3 nM) and caused Ca2+ mobilization (EC50 = 0.6 nM). In contrast to SL-NH2, the scramble peptide LSIGRL-NH2 failed to stimulate pepsinogen release. Exposure to SL-NH2 also resulted in ERK1/2 phosphorylation and activation. Exposure of chief cells to phosphotyrosine kinase inhibitors and 2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one, a selective MEK inhibitor, significantly reduced secretion induced by SL-NH2. Pepsinogen secretion induced by SL-NH2 was desensitized by pretreating the cells with the mimetic peptide and trypsin, and exposure to SL-NH2 abrogates pepsinogen secretion induced by carbachol and CCK-8, but not secretion induced by secretin and vasointestinal peptide. Exposure to Arg-Pro-Lys-Pro-Gln-Gln-Phe-Phe-Gly-Leu-Met-NH2 (substance P) but not to calcitonin gene-related peptide increased pepsinogen release. The neurokinin-1 receptor antagonist, N-acetyl-l-tryptophan 3,5-bis(trifluoromethyl)benzyl ester, inhibited substance P-stimulated pepsinogen secretion, whereas it did not affect secretion induced by SL-NH2. Collectively, these data indicate that PAR-2 is expressed on gastric chief cells and that its activation causes a Ca2+-ERK-dependent stimulation of pepsinogen secretion.

Stimulatory effects of nitric oxide donors on histamine release in isolated rat gastric mucosal cells

We previously reported stimulatory effects of endogenous and exogenous nitric oxide (NO) on gastric acid secretion. In the present study, we investigated effects of NO donors on release of histamine, which is related to acid secretion, in isolated rat gastric mucosal cells. NO donors such as (+/-)-(E)-4-methyl-2-[(E)-hydroxyimino]-5-nitro-6-methoxy-3-hexanamide (NOR 1) and sodium nitroprusside significantly augmented the histamine release. It was inhibited by 2-(4-carboxyphenyl)-4,4,5,5,-tetramethylimidazoline-1-oxyl-3-amide (carboxy-PTIO), a NO scavenger, and 6-(phenylamino)-5,8-quinolinedione (LY83583), a soluble guanylate cyclase inhibitor. Dibutyryl cyclic GMP also stimulated histamine release. These results suggest that NO donors act on cyclic GMP pathway in isolated gastric mucosal cells, resulting in facilitation of histamine release. NO may stimulate gastric acid secretion through histamine release from the histamine-containing cells, possibly enterochromaffin-like cells.

Nitric oxide regulates the release of somatostatin from cultured gastric rabbit primary D-cells

BACKGROUND & AIMS

Neuronal nitric oxide synthase (nNOS) is present in gastric D-cells. Mucosal somatostatin is diminished in H. pylori gastritis, where production of nitric oxide (NO) is increased. Therefore, we investigated the role of NO in D-cell function and the effects of prolonged exposure of D-cells to NO.

METHODS

Rabbit gastric D-cells were cultured. Somatostatin-14 was measured after 2 hours to examine the effects of arginine, nitric oxide sythase (NOS) inhibitors, and NO donors. Some cells were preincubated with a slow releasing NO donor for 12 hours. Results are expressed as percentage of total cell content. Nitrate content was measured by chemiluminescent assay.

RESULTS

L-arginine increased somatostatin-14 release in the presence of CCK8 from 4.4% +/- 0.5% to 6.4% +/- 0.4% (P < 0.02), and this was accompanied by NO release from 27 +/- 7 micromol/L to 86 +/- 12 micromol/L (P = 0.001). D-arginine and L-lysine had no effect. NOS inhibitors LNNA, SMT, and 7NI significantly attenuated the stimulatory response to L-arginine. NO donors sodium nitroprusside (SNP), 1 mmol/L, and S-nitroso-N-acetyl-D-L-penicillamine, 0.1 mmol/L, significantly increased basal and cholecystokinin-8 (CCK8) stimulated somatostatin release. Oxyhemoglobin attenuated the effect of SNP but not of L-arginine. Neither cyclic guanosine monophosphate nor guanylate cyclase were involved in the response to NO. However, inhibition of adenosine diphosphate (ADP) ribosyltransferase significantly decreased the response to L-arginine. Preincubation for 12 hours with 150 micromol/L (Z)-1-[(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate; IP3, inositol triphosphate decreased the 2-hour cellular response to CCK8 and SNP.

CONCLUSIONS

NO regulates rabbit D-cells. Acute exposure stimulates somatostatin mediated by ADP ribosylation, whereas long-term exposure reduces cellular responses to stimuli. The latter pathway may be responsible for the suppression of somatostatin in H. pylori gastritis.

Helicobacter pylori infection increases serum nitrate and nitrite more prominently than serum pepsinogens

BACKGROUND

Helicobacter pylori infection causes chronic gastritis and results in increased serum concentrations of pepsinogens I and II as well as gastrin, while the ratio of pepsinogen I to II (I : II) is decreased. Inducible nitric oxide synthase (iNOS) is induced in H. pylori-associated gastritis and may modulate inflammation. However serum nitrate and nitrite (NOx) concentrations in patients with H. pylori-induced chronic gastritis have not been reported. We examined differences in serum NOx between H. pylori-negative and positive volunteers relative to differences in pepsinogens and gastrin.

MATERIALS AND METHODS

Sera from 80 healthy asymptomatic volunteers younger than 36 years were analyzed for anti-H. pylori antibody, NOx, gastrin and pepsinogens.

RESULTS

In H. pylori antibody-positive subjects serum NOx concentrations were higher than in negative subjects (p < .005). In H. pylori-negative subjects, NOx correlated with pepsinogen II (r = .405, p < .05). In subjects with low pepsinogen I or II, NOx was higher in H. pylori-positive than negative subjects (p < .001). In subjects with high pepsinogen I : II (6 or higher), serum NOx was higher in H. pylori-positive than in negative subjects.

CONCLUSIONS

H. pylori-induced gastritis increases serum NOx concentrations more prominently than those of pepsinogen. In H. pylori-negative subjects, serum correlates with serum pepsinogen II.

Stimulatory effects of nitric oxide donors on gastric acid secretion in isolated mouse stomach

We previously reported on the stimulatory role of endogenous nitric oxide (NO) in gastric acid secretion. In the present study, we investigated the effects of NO donors on acid secretion in isolated mouse stomach. Nitroprusside (100 microM(-1) x mM) inhibited the gastric acid secretion induced by histamine (500 microM) in a concentration-dependent manner. In addition, nitroprusside abolished the acid secretion induced by bethanechol (100 microM) and by electrical stimulation (10 Hz) of the vagus nerve. On the other hand, nitroprusside, 75 microM, which did not affect the acid secretion induced by histamine, itself elicited an increase in acid secretion. The acid secretion induced by 75 microM nitroprusside was inhibited by 10 microM famotidine, a histamine H2 receptor antagonist. These results suggest that NO donors at high doses act on gastric parietal cells, resulting in inhibition of the stimulated acid secretion, and, at lower doses, facilitate histamine release from histamine-containing cells, leading to the increased acid secretion.

Neuronal nitric oxide synthase: expression in rat parietal cells

Nitric oxide synthases (NOS) are enzymes that catalyze the generation of nitric oxide (NO) from L-arginine and require nicotinamide adenine dinucleotide phosphate (NADPH) as a cofactor. At least three isoforms of NOS have been identified: neuronal NOS (nNOS or NOS I), inducible NOS (iNOS or NOS II), and endothelial NOS (eNOS or NOS II). Recent studies implicate NO in the regulation of gastric acid secretion. The aim of the present study was to localize the cellular distribution and characterize the isoform of NOS present in oxyntic mucosa. Oxyntic mucosal segments from rat stomach were stained by the NADPH-diaphorase reaction and with isoform-specific NOS antibodies. The expression of NOS in isolated, highly enriched (>98%) rat parietal cells was examined by immunohistochemistry, Western blot analysis, and RT-PCR. In oxyntic mucosa, histochemical staining revealed NADPH-diaphorase and nNOS immunoreactivity in cells in the midportion of the glands, which were identified as parietal cells in hematoxylin and eosin-stained step sections. In isolated parietal cells, decisive evidence for nNOS expression was obtained by specific immunohistochemistry, Western blotting, and RT-PCR. Cloning and sequence analysis of the PCR product confirmed it to be nNOS (100% identity). Expression of nNOS in parietal cells suggests that endogenous NO, acting as an intracellular signaling molecule, may participate in the regulation of gastric acid secretion.

IL-1 beta converting enzyme is a target for nitric oxide-releasing aspirin: new insights in the antiinflammatory mechanism of nitric oxide-releasing nonsteroidal antiinflammatory drugs

Caspase-1, the IL-1beta converting enzyme (ICE), is required for intracellular processing/maturation of IL-1beta and IL-18. NO releasing nonsteroidal antiinflammatory drugs (NSAIDs) are a new class of NSAID derivatives that spare the gastric mucosa. Here, we tested the hypothesis that NCX-4016, a NO-aspirin derivative, inhibits proinflammatory cytokine release from endotoxin (LPS)-challenged monocytes. Our results demonstrated that exposing LPS-stimulated human monocytes to NCX-4016 resulted in a 40-80% inhibition of IL-1beta, IL-8, IL-12, IL-18, IFN-gamma, and TNF-alpha release with an EC(50) of 10-20 microM for IL-1beta and IL-18. Incubating LPS-primed monocytes with NCX-4016 resulted in intracellular NO formation as assessed by measuring nitrite/nitrate, intracellular cGMP concentration, and intracellular NO formation. Exposing LPS-stimulated monocytes to aspirin or celecoxib caused a 90% inhibition of prostaglandin E(2) generation but had no effect on cytokine release. NCX-4016, similar to the NO donor S-nitroso-N-acetyl-D-L-penicillamine, inhibited caspase-1 activity with an EC(50) of approximately 20 microM. The inhibition of caspase-1 by NCX-4016 was reversible by the addition of DTT, which is consistent with S-nitrosylation as the mechanism of caspase-1 inhibition. NCX-4016, but not aspirin, prevented ICE activation as measured by assessing the release of ICE p20 subunit. IL-18 immunoneutralization resulted in a 60-80% reduction of IL-1beta, IL-8, IFN-gamma, and TNF-alpha release from LPS-stimulated monocytes. Taken together, these data indicate that incubating human monocytes with NCX-4016 causes intracellular NO formation and suppresses IL-1beta and IL-18 processing by inhibiting caspase-1 activity. Caspase-1 inhibition is a new, cycloxygenase-independent antiinflammatory mechanism of NO-aspirin.

Expression of neuronal nitric oxide synthase in several cell types of the rat gastric epithelium

The aim of this study was to identify which cell types of the rat gastric epithelium express neuronal nitric oxide synthase (nNOS) because the results of the previous studies have been very divergent regarding this point. By the combination of immunohistochemical (IHC) and in situ hybridization (ISH) techniques, we detected expression of nNOS in chief and mucosecretory cells of the gastric epithelium. Moreover, some gastric endocrine cells were immunoreactive for nNOS, although they could not be distinguished in sections treated with ISH techniques. The strongest signal for all antibodies in IHC techniques was obtained when microwave (MW) heating was performed before the IHC procedure. Our results indicate that in the gastric epithelium a variety of cell types are able to produce NO. The NO produced by the different cell types (chief, mucous, and endocrine) may form a complex network of paracrine communication with an important role in gastric physiology.

Pepsinogens: physiology, pharmacology pathophysiology and exercise

Human gastric mucosa contains aspartic proteinases that can be separated electrophoretically on the basis of their physical properties into two major groups: Pepsinogen I (PGA, PGI); and Pepsinogen II (PGC, PGII). Pepsinogens consist of a single polypeptide chain with molecular weight of approximately 42,000 Da. Pepsinogens are mainly synthesized and secreted by the gastric chief cells of the human stomach before being converted into the proteolytic enzyme pepsin, which is crucial for the digestive processes in the stomach. Pepsinogen synthesis and secretion are regulated by positive and negative feed-back mechanisms. In the resting state pepsinogens are stored in granules, which inhibit further synthesis. After appropriate physiological or external chemical stimuli, pepsinogens are secreted in the stomach lumen where hydrochloric acid, secreted by the parietal cells, converts them into the corresponding active enzyme pepsins. The stimulus-secreting coupling mechanisms of pepsinogens appear to include at least two major pathways: one involving cAMP as a mediator, the other involving modification of intracellular Ca(2+)concentration. Physiological or external chemical stimuli acting through the intracellular metabolic adenyl cyclase are more effective in inducing ' de novo ' pepsinogen synthesis than those acting through intracellular Ca(2+). The activation of protein kinase C (PK-C) would appear to be involved in regulatory processes. The measurement of pepsinogens A and C in the serum is considered to be one of the non-invasive biochemical markers for monitoring peptic secretion and obtaining information on the gastric mucosa status of healthy subjects. Recently, pepsinogen measurements have been used as an effective biochemical method for evaluating and monitoring patients with gastrointestinal diseases and for checking the effects of drug treatment. The level of PGA in the serum is always high in normal gastritis, while in atrophic gastritis it is always low. In both cases the PGC level in the serum is high. In most gastrointestinal pathologies the ratio between the PGA/PGC decreases. Various reports concerning hormone and/or enzyme modification as well as gastrointestinal distress in the case of long distance exercise have been reported. It has been suggested that the origin of the gastrointestinal distress experienced by long distance runners is a transient ischaemia of the gastric mucosa; it is also suggested that a hypobaric-hypoxic environment could contribute to induce gastric mucosa necrosis. Interrelation between gastrointestinal distress, hypobaric-hypoxic environment and modifications of PGA and PGC, gastrin and cortisol was evaluated in 13 athletes after a marathon performed at 4300 m. Gastrointestinal symptoms occurred in approximately 40% of the athletes. After the race the athletes showed a significant increase of gastrin and cortisol, while the ratio between PGA/PGC decreased. No relationship was observed between gastrointestinal symptoms and hormonal changes after the race. A control group of five subjects, who had been exposed to the same environmental conditions, showed no gastrointestinal or hormonal alteration. Conversely, control subjects presented a significant decrease of cortisol related to the circadian rhythm. The same incidence of gastrointestinal symptoms at high altitude and at sea level and the absence of pathological alteration of PGA and PGC in the serum of the athletes indicates that running a marathon and living for 6 days at 4300 m does not induce gastric mucosa necrosis. Cortisol and gastrin alteration observed in the athletes at this altitude would seem to be related to an activation of the mesopontine and forebrain structures involved in the behavioural and metabolic integration of the autonomic control and arousal and psychophysical-exercise stress. 2000 Academic Press@p$hr

Apoptosis in rat gastric antrum: evidence that regulation by food intake depends on nitric oxide synthase

The turnover of the epithelium of the gastrointestinal tract is regulated by a balance between cell multiplication and cell loss. We examined the effects of starvation on apoptosis in endocrine and other epithelial cells of rat antropyloric mucosa. Apoptosis was determined by the TUNEL reaction combined with immunocytochemical staining for gastrin and somatostatin. Apoptotic cell morphology was determined by bisbenzimide staining for DNA. Both gastrin and somatostatin cells showed a significantly lower apoptotic index than the general epithelium. This agrees with the longer turnover kinetics of gastric endocrine cells. On starvation, the apoptotic index of the general epithelium and of the gastrin but not of the somatostatin, cells increased significantly. This was prevented by the nitric oxide synthase (NOS) inhibitor L-NAME but not by its inactive stereoisomer D-NAME. Immunoreactive neuronal NOS was present in somatostatin cells, in nonendocrine cells predominating in the surface and pit epithelium, and in rare nerve fibers. Endothelial cell NOS was present in vessels, whereas the inducible isoform was barely detectable. Thus, endogenous NOS isoforms participate in regulating antropyloric epithelial apoptosis during starvation. The close paracrine relation between somatostatin cells and gastrin cells suggests that the former regulates apoptosis of the latter through release of NO.

CCK1 and CCK2 receptors regulate gastric pepsinogen secretion

The present study investigated (1) the pharmacological profile of cholecystokinin (CCK) receptor subtypes involved in the regulation of gastric pepsinogen secretion, (2) the influence of gastric acidity on peptic responses induced by CCK-8-sulfate (CCK-8S) or gastrin-I; and (3) the mechanisms accounting for the effects of CCK-like peptides on pepsinogen secretion. In anaesthetized rats, i.v. injection of CCK-8S or gastrin-I increased both pepsinogen and acid secretion. The pepsigogue effect of CCK-8S was higher than that of gastrin-I, whereas acid hypersecretion after CCK-8S was lower than that induced by gastrin-I. Peptic output following CCK-8S was partly blocked by i.v. injection of the CCK1 receptor antagonist, devazepide (-75.3%), or the CCK2 receptor antagonist, L-365,260 [3R(+)-N-(2,3-dihydro-1-methyl-2-oxo-5-phenyl-1H-1,4-benzodiazepine-3 yl)-N'-(3-methyl-phenyl)urea; -27.9%], but was fully prevented by combined administration of devazepide and L-365,260. The gastric acid hypersecretory effect of CCK-8S was enhanced by devazepide (+84.5%) and blocked by L-365,260. In contrast, the gastric secretory actions of gastrin-I were insensitive to devazepide, but abolished by L-365,260. Excitatory effects of CCK-8S and gastrin-I were not modified by vagotomy or atropine, whereas cimetidine or alpha-fluoromethylhistidine (irreversible blocker of histidine decarboxylase) partly prevented acid hypersecretion induced by both peptides without affecting their pepsigogue effects. After pretreatment with omeprazole, both CCK-8S and gastrin-I failed to stimulate acid secretion, while they increased pepsinogen output. In rats with gastric perfusion of acid solutions, CCK-8S or gastrin-I increased peptic output in a pH-independent manner either with or without pretreatment with omeprazole. Ablation of capsaicin-sensitive sensory nerves as well as application of lidocaine to the gastric mucosa failed to modify the excitatory effects of CCK-8S or gastrin-I on pepsinogen and acid secretion. Blockade of the nitric oxide (NO) synthase pathway by N(G)-nitro-L-arginine-methyl ester prevented the pepsigogue actions of both CCK-8S and gastrin-I (-61.8% and -71.7%, respectively), without affecting the concomitant increase in acid output. In addition, both these peptides significantly increased the release of NO breakdown products into the gastric lumen. The present results suggest that: (1) both CCK1 and CCK2 receptors mediate the peptic secretory responses induced by CCK-like peptides; (2) the excitatory inputs of CCK-8S and gastrin-I to chief cells are not driven through acid-dependent mechanisms or capsaicin-sensitive afferent sensory nerves; and (3) under in vivo conditions, the stimulant actions of CCK-like peptides on pepsinogen secretion are mediated, at least in part, by an increase in NO generation.

Gastrointestinal safety of nitric oxide-derived aspirin is related to inhibition of ICE-like cysteine proteases in rats

BACKGROUND & AIMS

Caspases, a class of cysteine proteases, modulate apoptosis. Nitric oxide (NO)-releasing nonsteroidal anti-inflammatory drugs (NSAIDs) are a new class of NSAID derivatives with reduced gastrointestinal toxicity. The aim of this study was to investigate whether cysteine endoproteases are involved in the pathogenesis of NSAID gastropathy and are target for NO-aspirin (NCX-4016).

METHODS

Rats were treated orally with aspirin or equimolar doses of NCX-4016. Caspase activities were measured by fluorometric assay. Apoptosis was quantified by an enzyme-linked immunosorbent assay for histone-associated DNA, DNA ladder on agarose gel, and terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling assay. A primary culture of gastric chief cells was used to investigate whether NCX-4016 modulates guanosine 3',5'-cyclic monophosphate (cGMP)-dependent pathways.

RESULTS

Short- and long-term (7 days) aspirin administration resulted in a time- and dose-dependent gastric injury that was associated with apoptosis and caspase up-regulation. Z-VAD.FMK, a pancaspase inhibitor, and NO donors protected from acute damage induced by aspirin. NCX-4016 spared the gastric mucosa and caused caspase inactivation by S-nitrosylation. Inhibition of tumor necrosis factor (TNF)-alpha release or activity by TAPI-2 or anti-TNF-alpha receptor monoclonal antibodies protected against mucosal damage and caspase activation. NCX-4016 protected gastric chief cells from toxicity induced by TNF-alpha by activating cGMP-dependent pathways.

CONCLUSIONS

Aspirin administration leads to a TNF-alpha-dependent activation of gastric caspases. NO-aspirin spares the gastric mucosa and inhibits caspase activity through cGMP-dependent and -independent pathways.

Nitric oxide-releasing NSAIDs inhibit interleukin-1beta converting enzyme-like cysteine proteases and protect endothelial cells from apoptosis induced by TNFalpha

BACKGROUND

Nitric oxide (NO)-releasing NSAIDs are a new class of NSAID derivatives with markedly reduced gastrointestinal toxicity. Although it has been demonstrated that NO-NSAIDs spare gastric mucosal blood flow, molecular determinants involved in this effect are unknown.

AIM

To investigate the effect of aspirin, naproxen and flurbiprofen, and their NO-derivatives, on gastric apoptosis and endothelial cell damage induced by tumour necrosis factor-alpha (TNFalpha). In other systems, TNFalpha-induced apoptosis is mediated by caspases, a growing family of cysteine proteases similar to the IL-1beta converting enzyme (ICE), and so we have investigated whether NO-NSAIDs modulate ICE-like endopeptidases.

METHODS

Rats were treated orally with aspirin, naproxen and flurbiprofen, or their NO-releasing derivatives in equimolar doses, and were killed 3 h later to assess mucosal damage and caspase activity. Endothelial cells (HUVECs) were obtained from human umbilical cord by enzymatic digestion. Caspase 1 and 3 activities were measured by a fluorimetric assay using selective peptides as substrates and inhibitors. Apoptosis was quantified by ELISA specific for histone-associated DNA fragments and by the terminal transferase nick-end translation method (TUNEL).

RESULTS

In vivo NSAID administration caused a time-dependent increase in gastric mucosal damage and caspase activity. NCX-4016, NO-naproxen and NO-flurbiprofen did not cause any mucosal damage and prevented cysteine protease activation. NSAIDs and NO-NSAIDs stimulated TNFalpha release. Exposure to TNFalpha resulted in a time- and concentration-dependent HUVEC apoptosis, an effect that was prevented by pretreating the cells with NCX-4016, NO-naproxen, NO-flurbiprofen, SNP or Z-VAD.FMK, a pan-caspase inhibitor. The activation of ICE-like cysteine proteases was required to mediate TNFalpha-induced apoptosis of HUVECs. Exogenous NO donors inhibited TNFalpha-induced cysteine protease activation. Inhibition of caspase activity was due to S-nitrosylation of ICE/CPP32-like proteases. NO-NSAIDs prevented IL-1beta release from endotoxin-stimulated macrophages.

CONCLUSIONS

NO-releasing NSAIDs are a new class of non-peptide caspase inhibitors. Inhibition of ICE-like cysteine proteases prevents endothelial cell damage induced by pro-inflammatory agents and might contribute to the gastro-protective effects of NO-NSAIDs.

NSAIDs upregulate beta 2-integrin expression on human neutrophils through a calcium-dependent pathway

BACKGROUND

Margination of circulating neutrophils (PMN) into the gastric microcirculation is an early and critical event in the pathogenesis of non-steroidal antinflammatory drug (NSAID)-induced gastropathy. This effect is mediated through the upregulation of beta 2 integrins on the PMN surface.

AIMS

To investigate whether indomethacin modulates: (1) Mac-1 expression; (2) Ca2+ mobilization ([Ca2+]i), protein kinase C and nitric oxide accumulation; and (3) mitogen-associated protein kinase phosphorylation in human PMN.

METHODS

Human PMN were isolated by centrifugation through a double Ficoll gradient. [Ca2+]i was measured in PMN loaded with fura-2 and Mac-1 expression by flow cytometry.

RESULTS

Indomethacin caused a concentration- and time-dependent upregulation of CD11b and CD18 expression and PMN adhesion to endothelial cells. Maximal upregulation of Mac-1 expression (40-50%) occurred after a 30-min incubation with 0.1mM indomethacin. The effect was prevented by removing the Ca2+. Ionomycin and thapsigargin caused a 7-10-fold increase in [Ca2+]i and a 2-4-fold increase in Mac-1 expression. Indomethacin induced a concentration-dependent phosphorylation of a 41-kDa mitogen-associated protein kinase. Tyrosine kinase inhibitors prevented the effect of indomethacin on Mac-1 expression and Ca2+ mobilization. Indomethacin and ionomycin increased superoxide generation, myeloperoxidase secretion and PMN adherence to endothelial cells and stimulated nitric oxide production. Indomethacin-induced Mac-1 upregulation was prevented by a nitric oxide synthase inhibitor.

CONCLUSIONS

Indomethacin-induced upregulation of Mac-1 is mediated by changes in [Ca2+]i and nitric oxide. Phosphorylation of the 41-kDa mitogen-associated protein isoform is a previously unreported target of NSAID action. These effects might help to explain the ability of indomethacin to cause gastric neutrophil margination.

Oxides, onions, and other matters gastrointestinal--1996--a perspective

A selection of landmark articles for a given year in any subject risks being somewhat subjective, and subjectivity is best avoided in scientific endeavor. However, the very nature of such a selection process invites judgment. Like most judges, I, too, claim to avoid conscious bias, but no one who has ever graced the bench can claim that at the subconscious level personal bias has never crept into a decision. Similarly, deep down in the vault of my subconscious, I love a maverick. That perhaps explains why so many articles that challenge long-held beliefs have especially found favor. Among them are those that question the strength of the association of Helicobacter pylori with gastric cancer, the usefulness of surveillance endoscopy in patients with Barrett's esophagus, a randomized trial that casts doubt on the preeminence of laparoscopic cholecystectomy, and a metaanalysis that concludes that corticosteroids may not be nearly as good for alcoholic hepatitis as we were once told. I have tried to resist the temptation to be too laudatory of technologic advancement, unless the benefit to the patient of such technology has been defined clearly. Thus, of all of the new technologies (endoscopic retrograde choledochopancreatography is no longer a new technology), only endoscopic ultrasonography finds a place. Articles that assess preventive strategies and are in the realm of epidemiology have received mention. All in all, 1996 was not a spectacular year for major therapeutic advances. In contrast, some notable advances have been made in the laboratory, and perhaps the most important has to do with the role of nitric oxide both in the regulation of normal function and in the genesis of disease.