Carla Petrella

Peripheral anti-nociceptive effect of nociceptin/orphanin FQ in inflammation and stress-induced colonic hyperalgesia in rats

ABSTRACT Nociceptin/orphanin FQ (N/OFQ) and its NOP receptors are present in the central nervous system and in the periphery playing important roles in the modulation of gastrointestinal functions and pain. The aim of this study was to investigate the role of central and peripheral N/OFQ–NOP receptor system in the nociceptive response to colorectal distension (CRD) in basal condition and in two models of gut hypersensitivity triggered by both inflammation and stress. Male Wistar rats were tested in basal and in post‐inflammatory conditions, i.e., 5 days after IC TNBS instillation (80 mg/Kg) and received N/OFQ (2 nmol/Kg IP), UFP‐101 (a selective NOP receptor antagonist, 10 nmol/Kg IP), N/OFQ+UFP‐101, N/OFQ (0.5 nmol/rat ICV) or vehicle. Female rats were tested in basal and after partial restraint stress receiving the same pharmacological treatment. CRD was performed using barostat and abdominal contractions were recorded by electromyography. In basal condition, N/OFQ, ICV and IP injected, did not modify basal visceral sensitivity. Both in TNBS and stress‐induced hyperalgesia, IP but not ICV injection of N/OFQ significantly decreased the number of abdominal contractions. Peripheral injection of UFP‐101 antagonized N/OFQ effect. Moreover, in post‐inflammatory colitis, UFP‐101, injected alone, exacerbated visceral hyperalgesia to CRD compared with vehicle. These findings indicate that in rats, N/OFQ, only peripherally injected, reduces visceral hypersensitivity triggered by inflammation or stress without affecting basal sensitivity. N/OFQ visceral anti‐hyperalgesic effect involves peripheral NOP receptors. In a post‐inflammatory, but not in an acute stress colitis model, N/OFQergic system is endogenously activated.

Evidence of Central and Peripheral Sensitization in a Rat Model of Narcotic Bowel-Like Syndrome

BACKGROUND & AIMS Narcotic bowel syndrome (NBS) is a subset of opioid bowel dysfunctions that results from prolonged treatment with narcotics and is characterized by chronic abdominal pain. NBS is under-recognized and its molecular mechanisms are unknown. We aimed to (1) develop a rat model of NBS and (2) to investigate its peripheral and central neurobiological mechanisms. METHODS Male Wistar rats were given a slow-release emulsion that did or did not contain morphine (10 mg/kg) for 8 days. Visceral sensitivity to colorectal distension (CRD) was evaluated during and after multiple administrations of morphine or vehicle (controls). The effects of minocycline (a microglia inhibitor), nor-binaltorphimine (a kappa-opioid antagonist), and doxantrazole (a mast-cell inhibitor) were observed on morphine-induced visceral hyperalgesia. Levels of OX-42, P-p38 mitogen-activated protein kinase, rat mast cell protease II, and protein gene product 9.5 were assessed at different spinal segments (lumbar 6 to sacral 1) or colonic mucosa by immunohistochemistry. RESULTS On day 8 of morphine administration, rats developed visceral hyperalgesia to CRD (incipient response) that lasted for 8 more days (delayed response). Minocycline reduced the incipient morphine-induced hypersensitivity response to CRD whereas nor-binaltorphimine and doxantrazole antagonized the delayed hyperalgesia. Levels of OX-42 and P-p38 increased in the spinal sections, whereas rat mast cell protease II and protein gene product 9.5 increased in the colonic mucosa of rats that were given morphine compared with controls. CONCLUSIONS We developed a rat model of narcotic bowel-like syndrome and showed that spinal microglia activation mediates the development of morphine-induced visceral hyperalgesia; peripheral neuroimmune activation and spinal dynorphin release represent an important mechanism in the delayed and long-lasting morphine-induced colonic hypersensitivity response to CRD.

Gastrointestinal effects of intracerebroventricularly injected nociceptin/orphaninFQ in rats.

Nociceptin/orphanin FQ/(N/OFQ), a novel heptadecapeptide recently isolated from porcine and rat brain, is the endogenous ligand of the N/OFQ peptide receptor (NOP, previously known as ORL-1). In this study we examined the effects of intracerebroventricularly (icv) injected N/OFQ on gastric emptying, gastrointestinal transit, colonic propulsion and gastric acid secretion in rats. N/OFQ (0.01-10 nmol/rat) significantly delayed gastric emptying of a phenol red meal, inhibited transit of a non-absorbable charcoal marker through the small intestine and increased the mean colonic bead expulsion time. These N/OFQ-motor effects were abolished by the NOP receptor selective antagonist [NPhe(1)]N/OFQ(1-13)-NH(2) (50 nmol/rat), but were unaltered by the classical opioid receptor antagonist, naloxone (9.2 micromol/kg). Icv injected N/OFQ (10 nmol/rat) decreased gastric acid secretion in 2-h pylorus ligated rats in a naloxone sensitive manner. [NPhe(1)]N/OFQ(1-13)-NH(2) (100 nmol/rat) icv administered alone stimulated gastric acid secretion. These results indicate that N/OFQ activates via NOP receptor stimulation a central inhibitory pathway modulating gastrointestinal propulsive activity and gastric acid secretion in rats.

Central and peripheral role of the nociceptin/orphaninFQ system on normal and disturbed colonic motor function and faecal pellet output in the rat

Abstract  In this study, seeking further information on the role of the nociceptin/orphanin FQ (N/OFQ)‐ergic system in normal and disturbed colonic motor function in rats, we compared the colonic effects of UFP‐112, a novel highly potent agonist, with those of N/OFQ. When injected intracerebroventricularly (i.c.v.) and intraperitoneally (i.p.), UFP‐112 and N/OFQ increased bead expulsion time in a statistically significant and dose‐related manner and reduced the percentage of rats with castor oil‐induced diarrhoea. UFP‐112 showed greater efficacy, higher potency and longer‐lasting inhibitory effects than N/OFQ, and pretreatment with UFP‐101, a selective antagonist, blocked the N/OFQ analogue‐induced responses in both tests. When injected i.c.v., UFP‐112 and N/OFQ inhibited corticotrophin releasing factor‐ and restrain stress‐stimulated faecal pellet excretion significantly and in a dose‐related manner. Conversely, when injected peripherally both peptides significantly inhibited colonic propulsive motility but did so in a non‐dose‐related manner. In conclusion, these findings indicate that, in the rat, the central and peripheral N/OFQ systems have an inhibitory role in modulating distal colonic propulsive motility under physiological and pathological conditions. UFP‐112 therefore promises to be a useful pharmacological tool for investigating the role of the N/OFQ system in motor functions in the distal colonic tract under physiological and pathological conditions.

The effects of [Arg14, Lys15] nociceptin/orphanin FQ, a highly potent agonist of the NOP receptor, on in vitro and in vivo gastrointestinal functions

Nociceptin/orphanin FQ (N/OFQ) administered into the lateral left cerebral ventricle of rats has been reported to inhibit in vivo gut motor and secretory functions. Recently, a novel N/OFQ analog, [Arg14, Lys15] N/OFQ, was synthesized and demonstrated to behave as a highly potent agonist at the human recombinant N/OFQ peptide (NOP) receptors and to produce long-lasting effects in vivo in mice compared with the natural ligand N/OFQ. In the present study, the pharmacological profile of [Arg14, Lys15] N/OFQ was further evaluated and compared with that of N/OFQ in vitro on guinea pig exocrine pancreas and in vivo on gastric emptying, colonic propulsion and gastric acid secretion in rats. [Arg14, Lys15] N/OFQ and N/OFQ significantly decreased the KCl-evoked amylase secretion from isolated pancreatic lobules of the guinea pig. In in vivo experiments, [Arg14, Lys15] N/OFQ mimicked the effects of N/OFQ, inducing, after intracerebroventricular injection, a delay (up to 70%) in the gastric emptying of a phenol red meal, an increase (about 40 times) of the mean bead colonic expulsion time and a decrease (up to 90%) of gastric acid secretion in water loaded rats after 90 min pylorus ligature. In all these assays, [Arg14, Lys15] N/OFQ was more effective than N/OFQ, and its effective doses were at least 10-fold lower than N/OFQ effective doses. The highly selective NOP receptor antagonist, UFP-101, decreased the efficacy of [Arg14, Lys15] N/OFQ in in vitro and in vivo assays above reported. These findings: (a) show that pancreatic NOP receptors mediate an in vitro inhibitory effect on stimulated guinea pig amylase secretion; (b) confirm that the stimulation of central NOP receptors exerts an inhibitory control on gastric emptying, colonic motility and gastric secretion in rats and (c) put in evidence that [Arg14, Lys15] N/OFQ, being more potent and effective than the natural ligand N/OFQ, represents a new pharmacological tool for the study of the physiological and pharmacological roles mediated by the N/OFQ-NOP receptor system.

Involvement of cannabinoid CB1- and CB2-receptors in the modulation of exocrine pancreatic secretion.

The role of the cannabinoid system in the regulation of exocrine pancreatic secretion was investigated by studying the effects of the synthetic CB1- and CB2-receptors agonist, WIN55,212, on amylase secretion in isolated lobules and acini of guinea pig and rat, and the expression of CB-receptors in rat pancreatic tissue by immuno-chemistry and Western-blot analysis in both basal and cerulein (CK)-induced pancreatitis condition. In pancreatic lobules of guinea pig and rat, WIN55,212 significantly inhibited amylase release stimulated by KCl depolarization through inhibition of presynaptic acetylcholine release, but did not modify basal, carbachol- or CK-stimulated amylase secretion. The effect of WIN55,212 was significantly reduced by pre-treatment with selective CB1- and CB2-receptor antagonists. The antagonists, when given alone, did not affect the KCl-evoked response. Conversely, WIN55,212 was unable to affect basal and CK- or carbachol-stimulated amylase release from pancreatic acini of guinea pig and rat. Immunofluorescent staining of rat pancreatic tissues showed that CB1- and CB2-receptors are expressed in lobules and in acinar cells and their presence in acinar cells was also shown by Western-blot analysis. After CK-induced pancreatitis, the expression of CB1-receptors in acinar cells was not changed, whilst a down-regulation of CB2-receptors was observed. In conclusion, the present study shows that WIN55,212 inhibits amylase release from guinea pig and rat pancreatic lobules and, for the first time, that cannabinoid receptors are expressed in lobules of the rat pancreas, suggesting an inhibitory presynaptic role of this receptor system. Finally, in rat pancreatic acinar cells, CB1- and CB2-receptors, expressed both in basal conditions and after CK-induced pancreatitis but inactive on amylase secretion, have an unknown role both in physiological and pathological conditions.

The gastric effects of UFP-112, a new nociceptin/orphanin receptor agonist, in physiological and pathological conditions

Nociceptin/orphanin FQ (N/OFQ), the endogenous NOP receptor ligand, centrally modulates gastric motor and secretory functions and prevents ethanol-induced gastric lesions in rats. A recently synthesized N/OFQ analog, [(pF)Phe(4)Aib(7)Arg(14)Lys(15)]N/OFQ-NH(2) (UFP-112), acts as a highly potent and selective peptide agonist for NOP receptors and produces longer-lasting in vitro and in vivo effects in mice than the natural ligand N/OFQ. In this study, we evaluated the effects of centrally (intracerebroventricularly/icv) and peripherally (intraperitoneally/ip) injected UFP-112 on gastric emptying and gastric acid secretion, and on the development of gastric mucosal lesions induced by 50% ethanol in the rat. When injected icv, it dose-dependently delayed gastric emptying of a phenol red meal (by up to 70%), decreased gastric secretion in water-loaded rats after 90 pylorus ligature, and reduced ethanol-induced gastric lesions (by up to 87%). In all three assays, UFP-112 was more effective than N/OFQ. The highly selective NOP receptor antagonist, UFP-101, decreased the efficacy of UFP-112, thus confirming that central NOP receptors mediate inhibitory control on these functional and pathological conditions in rats. Ip injected N/OFQ and UFP-112 induced non-dose-related gastric hypersecretory and antiulcer effects, which UFP-101 partially abolished. Ip N/OFQ appeared equiactive but about 30-100 times less potent than ip UFP-112 in stimulating gastric acid secretion and preventing lesion formation. When ip injected, both UFP-112 and N/OFQ left gastric emptying in rats unchanged, suggesting that peripheral NOP receptors have a role in mediating gastric hypersecretory and antiulcer effects but are not involved in regulating gastric motility. In addition, the inhibitory effects induced by this novel NOP receptor agonist lasted longer than those induced by N/OFQ. In conclusion, UFP-112 is a promising new pharmacological tool for studying the functional roles of the central and peripheral N/OFQ receptor system.

Association of TrkA and APP Is Promoted by NGF and Reduced by Cell Death-Promoting Agents

The amyloid precursor protein (APP) interacts with the tropomyosin receptor kinase A (TrkA) in normal rat, mouse, and human brain tissue but not in Alzheimer’s disease (AD) brain tissue. However, it has not been reported whether the two proteins interact directly, and if so, which domains are involved. Clarifying these points will increase our understanding of the role and regulation of the TrkA/APP interaction in normal brain functioning as well as in AD. Here we addressed these questions using bimolecular fluorescence complementation (BiFC) and the proximity ligation assay (PLA). We demonstrated that exogenously expressed APP and TrkA associate through their juxtamembrane/transmembrane domains, to form a complex that localizes mainly to the plasma membrane, endoplasmic reticulum (ER) and Golgi. Formation of the complex was inhibited by p75NTR, ShcC and Mint-2. Importantly, we demonstrated that the association between endogenous APP and TrkA in primary septal neurons were modified by NGF, or by drugs that either inhibit ER-to-Golgi transport or perturb microtubules and microfilaments. Interestingly, several agents that induce cell death [amyloid β (Aβ)-peptide, staurosporine and rapamycin], albeit via different mechanisms, all caused dissociation of APP/TrkA complexes and increased production of C-terminal fragment (β-CTF) APP fragment. These findings open new perspectives for investigating the interplay between these proteins during neurodegeneration and AD.

Protective and worsening peripheral nociceptin/orphanin FQ receptor-mediated effect in a rat model of experimental colitis.

Nociceptin/orphanin FQ (N/OFQ) and nociceptin orphanin peptide (NOP) receptors represent an endogenous system modulating gastrointestinal functions and inflammation. We investigated the peripheral effect of N/OFQ and of UFP-101, the NOP antagonist, in a model of colitis induced by TNBS (2,4,6 trinitrobenzenesulphonic acid; 60mg/kg). Male rats received two intraperitoneal injections per day of N/OFQ, UFP-101 or saline for 3 days after colitis induction. Four days after TNBS, animals were sacrificed and colonic histological damage, myeloperoxidase (MPO) activity and cytokine (IL-1β and IL-10) levels were evaluated. N/OFQ plasmatic levels were assessed by radioimmunoassay. TNBS increased all the inflammatory variables considered. In colitic rats, N/OFQ (0.02 and 0.2nmol/kg) improved microscopic damage, MPO activity and decreased IL-1β levels in comparison with TNBS group, whereas at the highest dose (20nmol/kg) the peptide worsened colitis. UFP-101 at the dose of 1nmol/kg, without pharmacological activity, antagonised the protective effect of N/OFQ (0.2nmol/kg) on colitis, but at a dose level of 3 and 10nmol/kg worsened inflammation, revealing the endogenous N/OFQergic system protective role. N/OFQ plasmatic levels were not modified in TNBS-treated rats compared with controls, whereas they were reduced in rats treated with the doses of UFP-101 aggravating colitis. In conclusion, peripheral low doses of N/OFQ have a beneficial effect on colonic inflammation in rats. In contrast, N/OFQ at a dose 100-1000-fold higher than those that protect worsens colitis, probably through different mechanisms. The peripheral N/OFQergic system can represent a new field of investigation in some intestinal inflammatory conditions.

Cannabinoid agonist WIN55,212 in vitro inhibits interleukin‐6 (IL‐6) and monocyte chemo‐attractant protein‐1 (MCP‐1) release by rat pancreatic acini and in vivo induces dual effects on the course of acute pancreatitis

Background  Cannabinoids (CBs) evoke their effects by activating the cannabinoid receptor subtypes CB1‐r and CB2‐r and exert anti‐inflammatory effects altering chemokine and cytokine expression. Various cytokines and chemokines are produced and released by rodent pancreatic acini in acute pancreatitis. Although CB1‐r and CB2‐r expressed in rat exocrine pancreatic acinar cells do not modulate digestive enzyme release, whether they modulate inflammatory mediators remains unclear. We investigated the CB‐r system role on exocrine pancreas in unstimulated conditions and during acute pancreatitis. Methods We evaluated in vitro and in vivo changes induced by WIN55,212 on the inflammatory variables amylasemia, pancreatic edema and morphology, and on acinar release and content of the cytokine interleukin‐6 (IL‐6) and chemokine monocyte chemo‐attractant protein‐1 (MCP‐1) in untreated rats and rats with caerulein (CK)‐induced pancreatitis. Key Results In the in vitro experiments, WIN55,212 (10−6 mol L−1) inhibited IL‐6 and MCP‐1 release from acinar cells of unstimulated rats and after CK‐induced pancreatitis. In vivo, when rats were pretreated with WIN55,212 (2 mg kg−1, intraperitoneally) before experimentally‐induced pancreatitis, serum amylase, pancreatic edema and IL‐6 and MCP‐1 acinar content diminished and pancreatic morphology improved. Conversely, when rats with experimentally‐induced pancreatitis were post‐treated with WIN55,212, pancreatitis worsened. Conclusions & Inferences These findings provide new evidence showing that the pancreatic CB1‐r/CB2‐r system modulates pro‐inflammatory factor levels in rat exocrine pancreatic acinar cells. The dual, time‐dependent WIN55,212‐induced changes in the development and course of acute pancreatitis support the idea that the role of the endogenous CB receptor system differs according to the local inflammatory status.