Effects of a new sigma ligand, JO 1784, on cysteamine ulcers and duodenal alkaline secretion in rats

Sigma (σ) receptors as potential therapeutic targets to mitigate psychostimulant effects

Many psychostimulants, including cocaine and methamphetamine, interact with sigma (σ) receptors at physiologically relevant concentrations. The potential therapeutic relevance of this interaction is underscored by the ability to selectively target σ receptors to mitigate many behavioral and physiological effects of psychostimulants in animal and cell-based model systems. This chapter begins with an overview of these enigmatic proteins. Provocative preclinical data showing that σ ligands modulate an array of cocaine and methamphetamine effects are summarized, along with emerging areas of research. Together, the literature suggests targeting of σ receptors as an innovative option for combating undesired actions of psychostimulants through both neuronal and glial mechanisms.

Altered expression level of Sigma1 receptor gene in human colorectal cancer

Nonopioid Sigma1 receptor (Sig1R) influences numerous metabolism functions including regulation of ion channels, reaction on stress and response to growth signals. Due to this influence, Sigma1 receptor ligands show anti-proliferative and cytotoxic action on tumor cells. Additionally its increased level is observed in some types of tumors. Colorectal cancer is one of the most common cancers worldwide and its clinical development is well described. The aim of the study was evaluation of Sigma1 receptor mRNA expression level in human colorectal cancer and colorectal cancer liver metastases at different stages of tumor development. The mRNA was isolated from 30 patients: 18 with colorectal cancer (CRC) and 12 with colorectal cancer liver metastases (CRCLM). The cDNA of Sig1R gene was amplified by polymerase chain reaction using specific primers. The level of Sig1R mRNA expression was determined by measurement of optical density. Sig1R expression level was increased in CRC and CRCLM. The highest level of Sig1R mRNA was observed in UICC stage III. We also showed significant interactions of UICC stage and tumor localization with Sig1R expression level. There were no interactions between UICC stage and age of patients, although we observed significantly decreased level of Sig1R mRNA in older patients. Clinical advancement stage, localization of tumor and age of patients seems to be an important factors influencing Sigma1 receptor expression level. It is probably due to double nature of Sig1R action - in certain conditions it could act pro- or antiapoptotic. This action might depend on Sig1R activity resulting from its expression level.

2,3-Dimercaptopropanol, a thiol chelator, alleviates gastroduodenal ulcers in rats

Earlier studies have implicated reactive oxygen species and transitional metals in the pathogenesis of gastric lesions. In this study, we have evaluated the effect of 2,3-dimercaptopropanol (DMP), a thiol compound and metal chelator, on chemically induced gastroduodenal ulcers in rats. Acid secretion studies were undertaken using pylorus-ligated rats pretreated with DMP (3-100 mg/kg, i.p.). The effect of orally administered DMP on cysteamine-induced duodenal ulcers and ethanol-induced gastric ulcers was also tested. The level of nonprotein sulfhydryls (NP-SH) and gastric wall mucus was measured in the glandular stomach of rats treated with ethanol. None of the dose of DMP affected the volume or acidity of gastric secretion. Low doses of DMP (3 and 10 mg/kg) significantly reduced cysteamine-induced duodenal ulcers, whereas the high doses (30 and 100 mg/kg) were ineffective in this model. All the doses of DMP significantly and dose dependently attenuated ethanol-induced gastric lesions. The adverse effects of ethanol on gastric wall mucus and NP-SH were significantly and dose dependently reversed by DMP. In conclusion, the protective effects of DMP appear to be independent of gastric acid secretion and may be associated with counteracting the oxidative stress by replenishing glutathione and reducing the pool of transition metals.

Review of the pharmacological and clinical profile of rimcazole

Rimcazole is a carbazole derivative that acts in part as a sigma receptor antagonist. Wellcome Research Laboratories introduced this compound during the 1980s when it was hypothesized to be a novel antipsychotic with an improved side effect profile. However, subsequent clinical trials demonstrated that rimcazole lacked efficacy in schizophrenic patients and it is now primarily used as an experimental tool. In addition to its actions as a sigma receptor antagonist, rimcazole also has high affinity for dopamine transporters, and in recent years it has served as a lead compound for the development of novel dopamine transporter ligands. Although rimcazole cannot be considered a selective ligand for sigma receptors, the recent development of other selective agonists and antagonists for sigma receptors have aided in clarifying the involvement of these receptors in the actions of rimcazole. Many of the physiological and behavioral effects of rimcazole can in fact be ascribed to its action as a sigma receptor antagonist, although there are exceptions. Rimcazole is likely to have a continued role in elucidating sigma receptor function in either in vitro or in vivo systems where sigma receptor-mediated effects can be studied independently of the influence of dopamine and serotonin transporters.

Inhibition of prostaglandin-induced intestinal secretion by igmesine in healthy volunteers

BACKGROUND & AIMS

Igmesine, a final sigma ligand, has been shown to inhibit intestinal secretion and diarrhea in animal models. The purpose of this study was to measure the inhibitory effect of igmesine on basal and prostaglandin E2 (PGE2)-induced jejunal secretion in normal volunteers.

METHODS

Jejunal absorption of water and electrolytes was measured with a three-lumen open-segment perfusion method in 16 volunteers. A double-blind crossover study was performed involving intraluminal infusion of PGE2 after oral administration of placebo or igmesine at two doses.

RESULTS

PGE2 induced net secretion of water and electrolytes (P < 0.01 vs. basal conditions). The effect of PGE2 on water and electrolytes was not changed by 25 mg of igmesine but was suppressed by 200 mg of igmesine. This effect lasted at least 3 hours after a single oral dose. Igmesine at a dose of 200 mg also produced a significant decrease in basal rates of water and electrolyte absorption.

CONCLUSIONS

Igmesine, a final sigma ligand, inhibits PGE2-induced intestinal secretion in normal humans. Evaluating the drug in chronic diarrheas may be of interest.

Role of dopamine and other stimuli of mucosal bicarbonate secretion in duodenal protection

Duodenal mucosal secretion of bicarbonate is one main mechanism in the protection of this epithelium against luminal acid. The duodenal secretagogue vasoactive intestinal polypeptide, at doses not affecting mucosal blood flow, protects against acid-induced morphological changes. Some sigma receptor ligands, which increase the duodenal alkaline secretion, prevent duodenal but not gastric mucosal ulceration. Dopamine D-1 receptor agonists and the peripherally acting catechol-O-methyl-transferase (COMT) inhibitor nitecapone stimulate the bicarbonate secretion in the rat and a similar increase in secretion has been observed in human volunteers. COMT inhibitors decrease tissue degradation of catecholamines, including dopamine. The D-2 agonist bromocriptine, in contrast, decreases the secretion. These results, indicating that the bicarbonate secretion is stimulated via peripheral dopamine D-1 receptors, are supported by the finding that dopamine D-1 (but not D-2) agonists increase the production of cyclic AMP in isolated duodenal enterocytes. The increase in mucosal alkaline secretion may contribute to the previously observed ulceroprotective actions of dopaminergic compounds.

Binding properties of KB-5492, a novel anti-ulcer agent, at sigma receptors in porcine gastric fundic mucosa

We examined the effects of KB-5492, 4-methoxyphenyl 4-(3,4,5-trimethoxybenzyl)-1-piperazine acetate monofumarate monohydrate, a novel anti-ulcer agent and a selective sigma receptor ligand, on specific [3H](+)-N-allyl-normetazocine (SKF 10,047) and [3H]1,3-di(2-tolyl)guanidine (DTG) binding in porcine gastric fundic mucosa. KB-5492 inhibited specific [3H](+)-SKF 10,047 binding in a competitive manner and specific [3H]DTG binding in a non-competitive manner. The Ki value of KB-5492 on specific [3H]DTG binding (Ki = 4.6 microM) was 8.4-fold higher than that on specific [3H](+)-SKF 10,047 binding (Ki = 0.55 microM). Computer-assisted analysis of the displacement curve of KB-5492 for specific [3H]DTG binding indicated the best fit for a two-site model rather than a one-site model, but not for specific [3H](+)-SKF 10,047 binding. Anti-ulcer agents such as omeprazole, cetraxate, cimetidine, sofalcone, sucralfate, teprenone and troxipide had weak or little effect on specific [3H](+)-SKF 10,047 and [3H]DTG binding at a concentration of 100 microM, except that omeprazole exhibited a low affinity for specific [3H](+)-SKF 10,047 binding. These findings suggest that KB-5492 is a unique anti-ulcer agent which binds to sigma receptors in porcine gastric fundic mucosa.

Receptor binding profiles of KB-5492, a novel anti-ulcer agent, at sigma receptors in guinea-pig brain

We studied the receptor binding profile of 4-methoxyphenyl 4-(3,4,5-trimethoxybenzyl)-1-piperazine acetate monofumarate monohydrate (KB-5492), a novel anti-ulcer agent, for the sigma receptor in guinea-pig brain membranes. KB-5492 selectively inhibited specific [3H]1,3-di(2-tolyl)guanidine (DTG) binding to the sigma receptor (IC50 = 3.15 microM) with a pseudo-Hill coefficient of 0.33. Computer-assisted analysis revealed that KB-5492 bound to high- and low-affinity sites. Although KB-5492 had weak affinity for alpha 2-adrenoceptors at 10 microM, it was almost inactive at a concentration of 10 microM in 33 other binding assays for receptors, second messenger systems and ion channels. sigma Receptor ligands such as haloperidol, DTG, (+)-3-(3-hydroxyphenol)-N-(1-propyl)piperidine (3-PPP), rimcazole and (-)-3-PPP inhibited specific [3H]DTG binding and their IC50 values were 0.003, 0.044, 0.33, 0.67 and 1.03 microM, respectively. On the other hand, various anti-ulcer agents such as cetraxate, cimetidine, omeprazole, sofalcone, sucralfate, teprenone and troxipide could hardly displace specific [3H]DTG binding at 100 microM. Scatchard-Rosenthal analysis indicated that [3H]DTG bound to a single site, and KD and Bmax values for [3H]DTG were 87.3 nM and 679.3 fmol/mg protein, respectively. KB-5492 significantly decreased the Bmax value, but did not affect the KD value. In contrast, haloperidol and DTG significantly increased the KD values, but did not affect the Kmax values. These findings indicate that KB-5492 selectively bound to the [3H]DTG-labeled sigma receptor and that other anti-ulcer agents had little affinity for the sigma receptor.(ABSTRACT TRUNCATED AT 250 WORDS)

4-Methoxyphenyl 4-(3,4,5-trimethoxybenzyl)-1-piperazineacetate monofumarate monohydrate (KB-5492), a new anti-ulcer agent with a selective affinity for the sigma receptor, prevents cysteamine-induced duodenal ulcers in rats by a mechanism different from that of cimetidine

Both KB-5492, a new anti-ulcer agent, and cimetidine, administered orally at 25-200 mg/kg, dose-dependently prevented cysteamine (400 mg/kg, s.c.)-induced duodenal ulcers in rats with ED50 values of 63 and 40 mg/kg, respectively. Anti-ulcer doses of cimetidine, but not KB-5492, inhibited gastric acid hypersecretion induced by cysteamine (400 mg/kg, s.c.). In contrast, anti-ulcer doses of KB-5492, but not cimetidine, increased duodenal HCO3- secretion in normal anesthetized rats. These findings suggest that KB-5492 prevents cysteamine-induced duodenal ulcers by stimulating duodenal HCO3- secretion, whereas cimetidine does so by inhibiting cysteamine-induced gastric acid hypersecretion.

Effects of KB-5492, a new anti-ulcer agent with a selective affinity for the sigma-receptor, on aspirin-induced disruption of the rat gastric mucosal barrier

The effect of KB-5492, a new anti-ulcer agent with a selective affinity for the sigma-receptor, on aspirin-induced disruption of the gastric mucosal barrier was studied in rats. Intragastric instillation of aspirin at 200 mg/kg rapidly decreased the gastric transmucosal potential difference (PD) in anesthetized rats. The PD recovered gradually following the removal of aspirin from the instillation solution. Aspirin, administered orally at 200 mg/kg, also reduced the amount of gastric covering mucus and induced a decrease in gastric H+ concentration and an increase in gastric Na+ concentration in pylorus-ligated rats. KB-5492, administered intraduodenally at 200 mg/kg, significantly prevented the aspirin-induced decrease in PD and accelerated the recovery of PD. In addition, KB-5492 at 200 mg/kg significantly prevented the reduction of gastric covering mucus, the decrease in gastric H+ concentration and the increase in gastric Na+ concentration induced by aspirin. These effects were similar to those of 0.01 mg/kg of 16,16-dimethyl prostaglandin E2 (dmPGE2). Teprenone at 200 mg/kg did not show any effect except for the inhibitory effects on the changes in gastric H+ and Na+ concentration. In the histological study, marked reduction of PAS-positive epithelial mucus and the exfoliation of surface epithelial cells were observed in the gastric mucosa exposed to aspirin. KB-5492 and dmPGE2 almost completely prevented the former, whereas both drugs prevented the latter incompletely. These findings indicate that KB-5492 protects the gastric mucosal barrier against the disruption by aspirin, which may be mainly exerted by retention of the gastric covering mucus.

Effects of KB-5492, a new anti-ulcer agent, on ethanol- and acidified aspirin-induced gastric mucosal damage in vivo and in vitro

The effects of KB-5492, a new anti-ulcer agent with selective affinity for the sigma receptor, on ethanol- and acidified aspirin-induced gastric mucosal damage were studied in vivo and in vitro and compared with those of 16,16-dimethyl prostaglandin E2 (dmPGE2). In the in vivo study, KB-5492 (200 mg/kg, p.o.) as well as dmPGE2 (0.01 mg/kg, p.o.) significantly prevented the acute macroscopic lesions in rat gastric mucosa induced by oral administration of either absolute ethanol or 80 mM aspirin in 150 mM HCl. The light microscopic examination revealed that KB-5492 almost completely prevented the deep mucosal lesions induced by these necrotizing agents. KB-5492 also prevented the exfoliation of surface epithelial cells, but its preventive effect was incomplete. In the in vitro study, gastric epithelial cells, isolated from the rat stomach, were cultured for 6 days until they reached confluency. Subsequently, 51Cr was incorporated into the cells. Both 10 mM aspirin (at pH 5.0) and 12.5% ethanol (at pH 7.4) induced damage to the cells and markedly increased 51Cr release from the cells. KB-5492 at 0.3 and 1 mM and dmPGE2 at 0.3 and 1 microM significantly, but not completely, prevented both the aspirin- and ethanol-induced increases in 51Cr release from the cells. These findings indicate that KB-5492 as well as dmPGE2 may exert a direct but limited protective effect on the surface epithelial cells in vivo.

Neuropeptide Y and sigma receptor agonists act through a common pathway to stimulate duodenal alkaline secretion in rats

Neuropeptide Y (NPY) has been shown to mimic the effects of some sigma receptor agonists in the brain and to possess the same proabsorptive effect as these agonists in the isolated mouse jejunum. The aim of present study was to investigate the effect of NPY on duodenal alkaline secretion in the rat and to define its mode of action. NPY (0.01 to 3 micrograms/kg i.v.) induced a dose-related increase in duodenal bicarbonate secretion, the maximal effect being obtained at 1 micrograms/kg. This response was significantly inhibited by the i.v. administration of haloperidol, BMY 14802, devazepide, hexamethonium, tetrodotoxin and by bilateral truncal vagotomy, but not by SCH 23390, sulpiride, prazosin or atropine, whereas i.c.v. devazepide had no effect. This pharmacological profile is identical to that reported for sigma receptor agonists. The results suggest that NPY and sigma ligands act through a common pathway to stimulate duodenal alkaline secretion in the rat.