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

A comprehensive review on calcitonin gene-related peptide in the management of gastrointestinal disorders

The prevalence of gastrointestinal disorders caused by alcohol, Helicobacter pylori, non-steroidal anti-inflammatory drugs, chronic stress and sedentary lifestyle is on the rise. Calcitonin gene-related peptide (CGRP), a 37-amino acid neuropeptide, has emerged as a protective factor against various gastrointestinal issues. Despite its known benefits, the dual role of CGRP in gastrointestinal damage remains unclear. Discovered 30 years ago through alternative RNA processing of the calcitonin gene, CGRP is known to be a potent vasodilator involved in crucial defensive mechanisms for both physiological and pathological conditions. Promising evidences from preclinical research have attracted the interest of scientists for the exploration of CGRP as a therapeutic neuropeptide. Numerous evidences suggest that this neuropeptide is secreted by the neurons under the influence of endogenous as well as exogenous stimuli. CGRP repairs the gastric mucosal barrier and maintain mucosal integrity by suppressing NF-κB activation, thereby reducing tumour necrosis factor-alpha expression. In addition, recent studies suggest that CGRP modulates immune responses and enhances epithelial cell proliferation, further contributing to its cytoprotective effects. Consequently, CGRP and the CGRP secretagogues represent promising novel targets for clinical applications. This review aims to elucidate the role of CGRP and CGRP secretagogues in the management of gastrointestinal disorders, highlighting its potential as a therapeutic agent in the context of evidence-based modern gastroenterology.

Forced degradation of lafutidine and characterization of its non-volatile and volatile degradation products using LC-MS/TOF, LC-MSn and HS-GC-MS

The study involved establishment of the intrinsic degradation behaviour of lafutidine under hydrolytic, oxidative and photolytic conditions.

New satiety hormone nesfatin-1 protects gastric mucosa against stress-induced injury: mechanistic roles of prostaglandins, nitric oxide, sensory nerves and vanilloid receptors

Nesfatin-1 belongs to a family of anorexigenic peptides, which are responsible for satiety and are identified in the neurons and endocrine cells within the gut. These peptides have been implicated in the control of food intake; however, very little is known concerning its contribution to gastric secretion and gastric mucosal integrity. In this study the effects of nesfatin-1 on gastric secretion and gastric lesions induced in rats by 3.5h of water immersion and restraint stress (WRS) were determined. Exogenous nesfatin-1 (5-40μg/kg i.p.) significantly decreased gastric acid secretion and attenuated gastric lesions induced by WRS, and this was accompanied by a significant rise in plasma NUCB2/nefatin-1 levels, the gastric mucosal blood flow (GBF), luminal NO concentration, generation of PGE2 in the gastric mucosa, an overexpression of mRNA for NUBC2 and cNOS, as well as a suppression of iNOS and proinflammatory cytokine IL-1β and TNF-α mRNAs. Nesfatin-1-induced protection was attenuated by suppression of COX-1 and COX-2 activity, the inhibition of NOS with L-NNA, the deactivation of afferent nerves with neurotoxic doses of capsaicin, and the pretreatment with capsazepine to inhibit vanilloid VR1 receptors. This study shows for the first time that nesfatin-1 exerts a potent protective action in the stomach of rats exposed to WRS and these effects depend upon decrease in gastric secretion, hyperemia mediated by COX-PG and NOS-NO systems, the activation of vagal and sensory nerves and vanilloid receptors.

Afferent signalling from the acid-challenged rat stomach is inhibited and gastric acid elimination is enhanced by lafutidine

BACKGROUND

Lafutidine is a histamine H2 receptor antagonist, the gastroprotective effect of which is related to its antisecretory activity and its ability to activate a sensory neuron-dependent mechanism of defence. The present study investigated whether intragastric administration of lafutidine (10 and 30 mg/kg) modifies vagal afferent signalling, mucosal injury, intragastric acidity and gastric emptying after gastric acid challenge.

METHODS

Adult rats were treated with vehicle, lafutidine (10 - 30 mg/kg) or cimetidine (10 mg/kg), and 30 min later their stomachs were exposed to exogenous HCl (0.25 M). During the period of 2 h post-HCl, intragastric pH, gastric volume, gastric acidity and extent of macroscopic gastric mucosal injury were determined and the activation of neurons in the brainstem was visualized by c-Fos immunocytochemistry.

RESULTS

Gastric acid challenge enhanced the expression of c-Fos in the nucleus tractus solitarii but caused only minimal damage to the gastric mucosa. Lafutidine reduced the HCl-evoked expression of c-Fos in the NTS and elevated the intragastric pH following intragastric administration of excess HCl. Further analysis showed that the gastroprotective effect of lafutidine against excess acid was delayed and went in parallel with facilitation of gastric emptying, measured indirectly via gastric volume changes, and a reduction of gastric acidity. The H2 receptor antagonist cimetidine had similar but weaker effects.

CONCLUSION

These observations indicate that lafutidine inhibits the vagal afferent signalling of a gastric acid insult, which may reflect an inhibitory action on acid-induced gastric pain. The ability of lafutidine to decrease intragastric acidity following exposure to excess HCl cannot be explained by its antisecretory activity but appears to reflect dilution and/or emptying of the acid load into the duodenum. This profile of actions emphasizes the notion that H2 receptor antagonists can protect the gastric mucosa from acid injury independently of their ability to suppress gastric acid secretion.

Therapeutic potential of 1-methylnicotinamide against acute gastric lesions induced by stress: role of endogenous prostacyclin and sensory nerves

1-Methylnicotinamide (MNA) is one of the major derivatives of nicotinamide, which was recently shown to exhibit antithrombotic and antiinflammatory actions. However, it is not yet known whether MNA affects gastric mucosal defense. The effects of exogenous MNA were studied on gastric secretion and gastric lesions induced in rats by 3.5 h of water immersion and water restraint stress (WRS) or in rats administered 75% ethanol. MNA [6.25-100 mg/kg intragastrically (i.g.)] led to a dose-dependent rise in the plasma MNA level, inhibited gastric acid secretion, and attenuated these gastric lesions induced by WRS or ethanol. The gastroprotective effect of MNA was accompanied by an increase in the gastric mucosal blood flow and plasma calcitonin gene-related peptide (CGRP) levels, the preservation of prostacyclin (PGI(2)) generation (measured as 6-keto-PGF1alpha), and an overexpression of mRNAs for cyclooxygenase (COX)-2 and CGRP in the gastric mucosa. R-3-(4-Fluoro-phenyl)-2-[5-(4-fluoro-phenyl)-benzofuran-2-ylmethoxycarbonylamino]-propionic acid (RO 324479), which is the selective antagonist of IP/PGI(2) receptors, reversed the effects of MNA on gastric lesions and GBF. MNA-induced gastroprotection was attenuated by suppression of COX-1 [5-(4-chlorophenyl)-1-(4-methoxyphenyl)-3-(trifluoromethyl)-1H-pyrazole; SC-560] and COX-2 [4-(4-methylsulfonylphenyl)-3-phenyl-5H-furan-2-one; rofecoxib] activity, capsaicin denervation, and by the pretreatment with CGRP(8-37) or capsazepine. Addition of exogenous PGI(2) or CGRP restored the MNA-induced gastroprotection in rats treated with COX-1 and COX-2 inhibitors or in those with capsaicin denervation. WRS enhanced MDA content while decreasing superoxide dismutase (SOD) activity in the gastric mucosa, but pretreatment with MNA reversed these changes. MNA exerts potent gastroprotection against WRS damage via mechanisms involving cooperative action of PGI(2) and CGRP in preservation of microvascular flow, antioxidizing enzyme SOD activity, and reduction in lipid peroxidation.

Gastroprotective action of orexin-A against stress-induced gastric damage is mediated by endogenous prostaglandins, sensory afferent neuropeptides and nitric oxide

Orexin-A, identified in the neurons and endocrine cells in the gut, has been implicated in control of food intake and sleep behavior but little is known about its influence on gastric secretion and mucosal integrity. The effects of orexin-A on gastric secretion and gastric lesions induced in rats by 3.5 h of water immersion and restraint stress (WRS) or 75% ethanol were determined. Orexin-A (5-80 microg/kg i.p.) increased gastric acid secretion and attenuated gastric lesions induced by WRS and this was accompanied by the significant rise in plasma orexin-A, CGRP and gastrin levels, the gastric mucosal blood flow (GBF), luminal NO concentration and an increase in mRNA for CGRP and overexpression of COX-2 protein and the generation of PGE(2) in the gastric mucosa. Orexin-A-induced protection was abolished by selective OX-1 receptor antagonist, vagotomy and attenuated by suppression of COX-1 and COX-2, deactivation of afferent nerves with neurotoxic dose of capsaicin, pretreatment with CCK(2)/gastrin antagonist, CGRP(8-37) or capsazepine and by inhibition of NOS with L-NNA. This study shows for the first time that orexin-A exerts a potent protective action on the stomach of rats exposed to non-topical ulcerogens such as WRS or topical noxious agents such as ethanol and these effects depend upon hyperemia mediated by COX-PG and NOS-NO systems, activation of vagal nerves and sensory neuropeptides such as CGRP released from sensory nerves probably triggered by an increase in gastric acid secretion induced by this peptide.

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.