N/OFQ Peptide Research Articles

Effects of Stress Exposure to Pain Perception in Pre-Clinical Studies: Focus on the Nociceptin/Orphanin FQ-NOP Receptor System.

Exposure to physical and psychological stress modulates pain transmission in a dual manner. Stress-induced analgesia (SIA) refers to the reduction in pain sensitivity that can occur in response to acute stress. On the contrary, chronic stress exposure may lead to a phenomenon named stress-induced hyperalgesia (SIH). SIH is a clinically relevant phenomenon since it has been well documented that physical and psychological stress exacerbates pain in patients with several chronic pain syndromes, including migraine. The availability of animal models of SIA and SIH is of high importance for understanding the biological mechanisms leading to these phenomena and for the identification of pharmacological targets useful to alleviate the burden of stress-exacerbated chronic pain. Among these targets, the nociceptin/orphanin FQ (N/OFQ)-N/OFQ peptide (NOP) receptor system has been identified as a key modulator of both pain transmission and stress susceptibility. This review describes first the experimental approaches to induce SIA and SIH in rodents. The second part of the manuscript summarizes the scientific evidence that suggests the N/OFQ-NOP receptor system as a player in the stress-pain interaction and candidates NOP antagonists as useful drugs to mitigate the detrimental effects of stress exposure on pain perception.

The Nociceptin/Orphanin FQ peptide receptor antagonist, SB-612111, improves cerebral blood flow in a rat model of traumatic brain injury.

Traumatic brain injury (TBI) affects more than 2.5 million people in the U.S. each year and is the leading cause of death and disability in children and adults ages 1 to 44. Approximately 90% of TBI cases are classified as mild but may still lead to acute detrimental effects such as impaired cerebral blood flow (CBF) that result in prolonged impacts on brain function and quality of life in up to 15% of patients. We previously reported that nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor antagonism reversed mild blast TBI-induced vestibulomotor deficits and prevented hypoxia. To explore mechanisms by which the NOP receptor-N/OFQ pathway modulates hypoxia and other TBI sequelae, the ability of the NOP antagonist, SB-612111 (SB), to reverse TBI-induced CBF and associated injury marker changes were tested in this study. Male Wistar rats randomly received sham craniotomy or craniotomy + TBI via controlled cortical impact. Injury severity was assessed after 1h (modified neurological severity score (mNSS). Changes in CBF were assessed 2h post-injury above the exposed cortex using laser speckle contrast imaging in response to the direct application of increasing concentrations of vehicle or SB (1, 10, and 100µM) to the brain surface. TBI increased mNSS scores compared to baseline and confirmed mild TBI (mTBI) severity. CBF was significantly impaired on the ipsilateral side of the brain following mTBI, compared to contralateral side and to sham rats. SB dose-dependently improved CBF on the ipsilateral side after mTBI compared to SB effects on the respective ipsilateral side of sham rats but had no effect on contralateral CBF or in uninjured rats. N/OFQ levels increased in the cerebral spinal fluid (CSF) following mTBI, which correlated with the percent decrease in ipsilateral CBF. TBI also activated ERK and cofilin within 3h post-TBI; ERK activation correlated with increased CSF N/OFQ. In conclusion, this study reveals a significant contribution of the N/OFQ-NOP receptor system to TBI-induced dysregulation of cerebral vasculature and suggests that the NOP receptor should be considered as a potential therapeutic target for TBI.

Recovery from Traumatic Brain Injury Is Nociceptin/Orphanin FQ Peptide Receptor Genotype-, Sex-, and Injury Severity-Dependent.

Traumatic brain injury (TBI) is a leading cause of death and disability in the United States, and survivors often experience mental and physical health consequences that reduce quality of life. We previously reported that blockade of the nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor reduced tissue damage markers produced by blast TBI. The goal of this study was to determine the extent to which N/OFQ and NOP receptor levels change following mild (mTBI) and moderate TBI (modTBI) and whether the absence of the NOP receptor attenuates TBI-induced sequelae. Male and female NOP receptor knockout (KO) or wild-type (WT) rats received craniotomy-only (sham) or craniotomy plus mTBI, or modTBI impact to the left cerebral hemisphere. Neurologic and vestibulomotor deficits and nociceptive hyperalgesia and allodynia found in WT male and female rats following mTBI and modTBI were greatly reduced or absent in NOP receptor KO rats. NOP receptor levels increased in brain tissue from injured males but remained unchanged in females. Neurofilament light chain (NF-L) and glial fibrillary acidic protein (GFAP) expression were reduced in NOP receptor KO rats compared with WT following TBI. Levels of N/OFQ in injured brain tissue correlated with neurobehavioral outcomes and GFAP in WT males, but not with KO male or WT and KO female rats. This study reveals a significant contribution of the N/OFQ-NOP receptor system to TBI-induced deficits and suggests that the NOP receptor should be regarded as a potential therapeutic target for TBI. SIGNIFICANCE STATEMENT: This study revealed that nociceptin/orphanin FQ peptide (NOP) receptor knockout animals experienced fewer traumatic brain injury (TBI)-induced deficits than their wild-type counterparts in a sex- and injury severity-dependent manner, suggesting that NOP receptor antagonists may be a potential therapy for TBI.

Nociceptin Receptor-Related Agonists as Safe and Non-addictive Analgesics.

As clinical use of currently available opioid analgesics is often impeded by dose-limiting adverse effects, such as abuse liability and respiratory depression, new approaches have been pursued to develop safe, effective, and non-addictive pain medications. After the identification of the nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor more than 25 years ago, NOP receptor-related agonists have emerged as a promising target for developing novel and effective opioids that modulate the analgesic and addictive properties of mu-opioid peptide (MOP) receptor agonists. In this review, we highlight the effects of the NOP receptor-related agonists compared with those of MOP receptor agonists in experimental rodent and more translational non-human primate (NHP) models and the development status of key NOP receptor-related agonists as potential safe and non-addictive analgesics. Several lines of evidence demonstrated that peptidic and non-peptidic NOP receptor agonists produce potent analgesic effects by intrathecal delivery in NHPs. Moreover, mixed NOP/MOP receptor partial agonists (e.g., BU08028, BU10038, and AT-121) display potent analgesic effects when administered intrathecally or systemically, without eliciting adverse effects, such as respiratory depression, itch behavior, and signs of abuse liability. More importantly, cebranopadol, a mixed NOP/opioid receptor agonist with full efficacy at NOP and MOP receptors, produces robust analgesic efficacy with reduced adverse effects, conferring promising outcomes in clinical studies. A balanced coactivation of NOP and MOP receptors is a strategy that warrants further exploration and refinement for the development of novel analgesics with a safer and effective profile.

Formulation of Solid Lipid Nanoparticles Loaded with Nociceptin/Orphanin FQ (N/OFQ) and Characterization in a Murine Model of Airway Hyperresponsiveness

Asthma is characterized by chronic inflammation and a variable degree of airway hyperresponsiveness (AHR). Our previous papers documented a role for Nociceptin/Orphanin FQ (N/OFQ) and its receptor N/OFQ peptide (NOP) in AHR. Therefore, the aim of this study was to improve the bioavailability of N/OFQ by developing solid lipid nanoparticles (SLNs). N/OFQ-loaded SLNs were prepared by the Quasi Emulsion Solvent Diffusion (QESD) technique and then characterized. Brown Norway rats were sensitized to ovalbumin (OVA) and treated with an intratracheal administration of saline solution or N/OFQ-SLN. Then, 24 h after the last challenge, functional histological and molecular evaluations were performed. SLNs showed a mean diameter of 233 ± 0.03 nm, a polydispersity index (PDI) value around 0.28 ± 0.02 and a drug release percentage of 84.3. The in vitro release of N/OFQ from SLNs showed that the release of the peptide starts already after two hours of incubation. Animals receiving N/OFQ-SLN showed a significative decrease in allergen-induced AHR compared to the control group. These results showed the positive effects of N/OFQ-SLNs on the inflammatory process and on the mechanical properties of the airways, suggesting that the innovative nanotechnological approach may be therapeutically beneficial for asthmatic patients.

Functional Selectivity Does Not Predict Antinociceptive/Locomotor Impairing Potencies of NOP Receptor Agonists

Nociceptin/orphanin FQ controls several functions, including pain transmission, via stimulation of the N/OFQ peptide (NOP) receptor. Here we tested the hypothesis that NOP biased agonism may be instrumental for identifying innovative analgesics. In vitro experiments were performed with the dynamic mass redistribution label free assay and the NOP non-peptide agonists Ro 65-6570, AT-403 and MCOPPB. In vivo studies were performed in wild type and β-arrestin 2 knockout mice using the formalin, rotarod and locomotor activity tests. In vitro all compounds mimicked the effects of N/OFQ behaving as potent NOP full agonists. In vivo Ro 65-6570 demonstrated a slightly higher therapeutic index (antinociceptive vs. motor impairment effects) in knockout mice. However, all NOP agonists displayed very similar therapeutic index in normal mice despite significant differences in G protein biased agonism. In conclusion the different ability of inducing G protein vs. β-arrestin 2 recruitment of a NOP agonist cannot be applied to predict its antinociceptive vs. motor impairment properties.

Therapeutic potentials of safe opioid analgesics targeting nociceptin/orphanin FQ peptide receptor

After the identification of nociceptin/orphanin FQ (N/OFQ) peptide (NOP) and its cognate receptor, the unique functional profiles of the N/OFQ-NOP receptor system have been uncovered. NOP receptors are distributed in the key regions that regulate pain and reward processing in the central nervous system. In non-human primates (NHPs), activation of the NOP receptor causes antinociception and anti-hypersensitivity via spinal and supraspinal effects. Moreover, activation of the NOP receptor attenuates dopaminergic transmission and potentiates mu-opioid peptide (MOP) receptor-mediated analgesia. Here, we highlight the functional profiles of bifunctional NOP and MOP receptor agonists based on their promising effects for the treatment of pain and drug abuse. Bifunctional NOP/MOP receptor "partial" agonists, such as AT-121, BU08028, and BU10038, exert potent analgesic effects without MOP receptor-related side effects such as abuse liability, respiratory depression, physical dependence, and itching in NHPs. These novel NOP/MOP receptor agonists reduce rewarding and the reinforcing effects of abused drugs. Furthermore, a mixed NOP/opioid receptor "full" agonist, cebranopadol, is undergoing several clinical trials, and the therapeutic advantage of the coactivation of NOP and MOP receptors has also been confirmed in humans. Therefore, this class of drugs that coactivate NOP and MOP receptors proposes a wide therapeutic range with fewer side effects, indicating a greater potential for the development of novel safer opioid analgesics.

Exacerbated Headache-Related Pain in the Single Prolonged Stress Preclinical Model of Post-traumatic Stress Disorder

Chronic headache pain is one of the most commonly reported comorbid pain conditions with post-traumatic stress disorder (PTSD) patients and resistant to effective treatment, yet no combined preclinical model of the two disorders has been reported. Here, we used a modified chronic headache pain model to investigate the contribution of single prolonged stress (SPS) model of PTSD with sodium nitroprusside (SNP)-induced hyperalgesia. Injection of SNP (2 mg/kg, i.p.) occurred every other day from day 7 to day 15 after initiation of SPS in rats. Paw withdrawal threshold (PWT) to von Frey stimuli and tail flick latencies (TFL) dramatically decreased as early as 7 days after SPS and lasted until at least day 21. Basal PWT and TFL also significantly decreased during the SNP treatment period. The lower nociceptive thresholds recovered in 6 days following the final SNP injection in SNP group, but not in SPS + SNP group. Elevated nociceptin/OFQ (N/OFQ) levels observed in cerebrospinal fluid of SPS rats were even higher in SPS + SNP group. Glial fibrillary acidic protein (GFAP) and N/OFQ peptide (NOP) receptor mRNA expression increased in dorsal root ganglia (DRG) 21 days after SPS exposure; mRNA increases in the SPS/SNP group was more pronounced than SPS or SNP alone. GFAP protein expression was upregulated in trigeminal ganglia by SPS. Our results indicate that traumatic stress exaggerated chronic SNP-induced nociceptive hypersensitivity, and that N/OFQ and activated satellite glia cells may play an important role in the interaction between both conditions.

Biased Agonism at Nociceptin/Orphanin FQ Receptors: A Structure Activity Study on N/OFQ(1-13)-NH2.

Nociceptin/orphanin FQ (N/OFQ) controls different biological functions via selective stimulation of the N/OFQ peptide (NOP) receptor. The pleiotropic actions of N/OFQ may limit the development of NOP ligands as innovative drugs in different therapeutic areas. The pharmacological concept of functional selectivity (aka biased agonism) might be useful for amplifying beneficial actions and/or counteracting side effects. Thus, molecules with large bias factors toward G protein or β arrestin are required for investigating the translational value of NOP biased modulation. Herein, the biased behavior of a heterogeneous library of NOP-targeting peptide derivatives was evaluated in vitro with the aim to provide possible insights into the structural determinants that govern the selective activation of G protein versus β-arrestin. Our results demonstrate that lipidation of N/OFQ(1–13)-NH2 is a useful strategy for obtaining G protein biased agonists for the NOP receptor.

Therapeutic potentials of NOP and MOP receptor coactivation for the treatment of pain and opioid abuse.

Following the identification of the nociceptin/orphanin FQ (N/OFQ) peptide (NOP) as an endogenous ligand for the NOP receptor, ample evidence has revealed unique functional profiles of the N/OFQ-NOP receptor system. NOP receptors are expressed in key neural substrates involved in pain and reward modulation. In nonhuman primates (NHPs), NOP receptor activation effectively exerts antinociception and anti-hypersensitivity at the spinal and supraspinal levels. Moreover, NOP receptor activation inhibits dopaminergic transmission and synergistically enhances mu-opioid peptide (MOP) receptor-mediated analgesia. In this article, we have discussed the functional profiles of ligands with dual NOP and MOP receptor agonist activities and highlight their optimal functional efficacy for pain relief and drug abuse treatment. Through coactivation of NOP and MOP receptors, bifunctional NOP/MOP receptor "partial" agonists (e.g., AT-121, BU08028, and BU10038) reveal a wider therapeutic window with fewer side effects. These newly developed ligands potently induce antinociception without MOP receptor agonist-associated side effects such as abuse potential, respiratory depression, itching sensation, and physical dependence. In addition, in both rodent and NHP models, bifunctional NOP/MOP receptor agonists can attenuate reward processing and/or the reinforcing effects of opioids and other abused drugs. While a mixed NOP/opioid receptor "full" agonist cebranopadol is undergoing clinical trials, bifunctional NOP/MOP "partial" agonists exhibit promising therapeutic profiles in translational NHP models for the treatment of pain and opioid abuse. This class of drugs demonstrates the therapeutic advantage of NOP and MOP receptor coactivation, indicating a greater potential for future development.

NOP Receptor Signaling Cascades.

The nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor is a G protein-coupled receptor with wide distribution throughout the peripheral and central nervous system. Similar to other opioid receptors, NOP receptors couple to intracellular second messengers and regulatory proteins to affect biological systems. In this chapter, we review the current literature for NOP signaling cascades including their role as classic GPCRs, the investigation of their kinase and arrestin signaling pathways, and the importance of examining biased signaling to critically evaluate the therapeutic potential of novel NOP agonists.

Nociceptin/Orphanin Fq in inflammation and remodeling of the small airways in experimental model of airway hyperresponsiveness.

It is widely recognized that airway inflammation and remodeling play a key role not only in the central airway but also small airway pathology during asthma. Nociceptin/Orphanin FQ (N/OFQ), an endogenous peptide, and its receptor N/OFQ peptide (NOP) are involved in airway hyperresponsiveness (AHR). We studied a murine model of AHR in order to understand the role of N/OFQ in the inflammation and remodeling of the small airways. Balb/c mice were sensitized to ovalbumin (OVA). At days 0 and 7 (pre‐OVA sensitization) or from day 21 to 23 (post‐OVA sensitization), the mice were treated intraperitoneally with N/OFQ or saline solution. After the last OVA challenge, all OVA‐sensitized mice were aerosol‐challenged with 1% OVA in PBS for 48 h, and then euthanized. Small airway compliance (sCaw) was measured and lung samples were collected for histological and molecular evaluations such as perimeter and diameter of small airway, total wall area, airway smooth muscle (ASM) thickness and number of alveolar attachments. Both pre‐ and post‐OVA sensitization N/OFQ treatments induced: (1) increases in sCaw; (2) reduction of the bronchial wall thickness; (3) attenuation of the hyperplastic phase of airway smooth muscle mass; and (4) protection against loss of alveolar attachments compared with saline solution treatments. These results suggest that N/OFQ protects against inflammation, and mechanical damage and remodeling of small airways caused by OVA sensitization, suggesting a new potential therapeutic target for asthma.

Possible Involvement of Beta-Adrenergic Receptors on Nociceptin/Orphanin FQ Induced Food Consumption in Male Rats

Background: The nociceptin/orphanin FQ (N/OFQ) peptide is the endogenous ligand for the N/OFQ peptide (NOP) receptor. Beta adrenergic receptors and N/OFQ are involved in the regulation of food intake through central and peripheral mechanisms. Objectives: The aim of this study was to determine the possible interaction between beta adrenergic and N/OFQ receptors on food consumption in male rats. N/OFQ agonists have been shown to increase food intake in mammals and birds. Beta adrenergic receptors physiologically inhibit food intake in mammals. Methods: In this experimental study were used male rats (250-300 g). In first two experiments, rats received intraperitoneal injections of isoproterenol (0, 0.5, 1 and 2 mg/kg) and Nociceptin agonist 64 - 6198 (0, 1, 2 and 4 mg/kg) respectively. In third experiment 64 - 6198 (4 mg/kg) and (2 mg/kg) isoproterenol were injected. In experiments 4 effects of isoproterenol (0.5 mg/kg) and Nociceptin antagonist (8 mg/kg) on food consumption was investigated. Latency time to feeding was examined in experiment 5. The data were statistically analyzed using One-way ANOVA and Tukey test. Results: Latency time to feeding increased and decreased by isoproterenol and nociceptin/orphanin, respectively. Administration of N/OFQ increased cumulative food intake in rats (P < 0.05). The i.p. injection of isoproterenol decreased food intake and also the hyperphagic effect of N/OFQ agonist is inhibited by isoproterenol, whereas sub-anorectic doses of isoproterenol and N/OFQ antagonist synergistically attenuated cumulative feed consumption when combined (P < 0.01). Conclusions: On the basis of these findings, it can be concluded that isoproterenol may decrease food intake in rats by reduction in the N/OFQ content.

Exacerbated Headache‐Related Pain in the Single Prolonged Stress Model of Post‐traumatic Stress Disorder

Post‐traumatic stress disorder (PTSD) frequently shares co‐morbidity with chronic pain and negatively impacts the course of treatment for both disorders. Single‐prolonged stress (SPS), an established animal model for PTSD, models many of the symptoms of PTSD reported in humans including exaggerated negative feedback of the HPA axis, hypocortisolism, enhanced fear and anxiety responses and cognitive impairment. We and others reported that SPS induces long‐lasting mechanical and thermal allodynia and visceral and inflammatory hypersensitivity. Chronic headache pain is one of the most commonly reported co‐morbid pain conditions by PTSD patients and one of the most resistant to effective treatment, yet this has never been modeled in an animal model of PTSD. We modified the chronic headache pain model recently developed by Pradhan and colleagues (2014) to investigate the contribution of SPS to sodium nitroprusside (SNP)‐induced hyperalgesia. SPS and control Sprague Dawley rats were randomly divided into SNP or vehicle‐treated groups. SNP (2 mg/kg, i.p.) was injected every second day from day 7 to 15 after initiation of SPS. Rat paw withdrawal threshold (PWT) to von Frey stimuli and tail flick latencies (TFL) dramatically decreased as early as 7 days after SPS and lasted until at least day 21. Basal PWT and TFL, as assessed prior to each SNP administration, also significantly decreased during the SNP treatment period. The lower pain thresholds recovered 7 days following the final SNP injection in SNP group, but not in SPS/SNP group. Nociceptin/orphanin FQ (N/OFQ) plays an important role in maintenance of hyperalgesia and allodynia following SPS. Elevated N/OFQ levels observed in cerebrospinal fluid (CSF) of SPS rats were even higher in CSF of the SPS/SNP group. Real‐time PCR revealed that glial fibrillary acidic protein (GFAP) and N/OFQ peptide (NOP) receptor mRNA expression increased in dorsal root ganglia (DRG) 21 days after SPS exposure; mRNA increases in the SPS/SNP group was more pronounced than SPS or SNP alone. PreproN/OFQ mRNA expression decreased in both SPS and SPS/SNP rats compared to control, but no difference was observed between the two groups. SNP treatment alone did not alter GFAP, NOP receptor or N/OFQ mRNA levels in DRG. Significant interaction between SNP and SPS was noted following immunoblot analysis of TNF alpha protein expression in DRG and NOP receptor expression in trigeminal ganglia. Our results indicate that chronic SNP‐induced nociceptive hypersensitivity (headache pain) is exaggerated in rats exposed to PTSD, and that N/OFQ may play an important role in the interaction between SPS and SNP.The animal protocol was approved by the OUHSC IACUC committee; studies conformed to the FASEB Statement of Principles for the use of animals in research and education.Support or Funding InformationUniversity of Oklahoma Health Sciences Center Vice President for Research and Presbyterian Health Foundation Bridge Grant Programs.

Discovery of small-molecule nonpeptide antagonists of nociceptin/orphanin FQ receptor: The studies of design, synthesis, and structure–activity relationships for (4-arylpiperidine substituted-methyl)-[bicyclic (hetero)cycloalkanobenzene] derivatives

Nociceptin/orphanin FQ (N/OFQ) and N/OFQ peptide (NOP) receptor are expressed and distributed in various regions such as central nervous system (CNS), peripheral nervous system, immune system, and peripheral tissues. N/OFQ and NOP receptor have important roles on a variety of physiological, pathophysiological, regulatory, and dysregulatory mechanisms in the living body. Both activation and blockade of NOP receptor function have displayed clinical potential of NOP receptor agonists and antagonists for the treatment of various diseases or pathophysiological conditions, respectively. Potent and selective NOP receptor agonists/antagonists are also useful tools to investigate the various mechanisms mediated by NOP receptor–N/OFQ system. As the present study, a series of (4-arylpiperidine substituted-methyl)-[bicyclic (hetero)cycloalkanobenzene] analogs was designed, synthesized, and biologically evaluated in vitro to seek and identify potent and selective, small-molecules of nonpeptide NOP receptor antagonists, which resulted in the discovery of novel potent small-molecule 15 with high human NOP receptor selectivity over human μ receptor. The structure–activity relationship (SAR) of the potency and selectivity, structure–metabolic stability relationship (SMR), and SAR of hERG (human ether-a-go-go related gene) potassium ion channel binding affinity for the analogs in the present studies in vitro provided or suggested significant and/or useful structural determinants and insights for the respective purposes. The superior profiles of compound 15 are discussed with a viewpoint of multisite interactions between ligand and NOP receptor, together with the results of previous NOP receptor agonist/antagonist studies.

Nociceptin/Orphanin FQ Inhibits the Survival and Axon Growth of Midbrain Dopaminergic Neurons Through a p38-MAPK Dependent Mechanism.

Nociceptin/orphanin FQ (N/OFQ) is an opioid-like neuropeptide that binds and signals through a G-protein-coupled receptor called the N/OFQ peptide (NOP) receptor. N/OFQ and the NOP receptor are expressed in the midbrain and have been implicated in the pathogenesis of Parkinson's disease (PD). Genetic removal of the N/OFQ precursor partially protects midbrain dopaminergic neurons from 1-methyl-4-phenylpyridine-induced toxicity, suggesting that endogenous N/OFQ may be detrimental to dopaminergic neurons. However, whether N/OFQ directly affects the survival and growth of dopaminergic neurons is unknown. Here, we show that N/OFQ has a detrimental effect on the survival of dopaminergic neurons and the growth of their axons in primary cultures of the E14 rat ventral mesencephalon. N/OFQ potentiates the effects of the neurotoxins 6-hydroxydopamine and 1-methyl-4-phenylpyridinium through p38-MAPK signalling. We also show that like α-synuclein, there is a significant reduction in N/OFQ messenger RNA (mRNA) expression in the midbrain of patients with Parkinson's disease. These results demonstrate for the first time that N/OFQ is detrimental to the survival and growth of dopaminergic neurons and that its expression is altered in the midbrain of patients with Parkinson's disease.

A Selective Nociceptin Receptor Antagonist to Treat Depression: Evidence from Preclinical and Clinical Studies.

Nociceptin/Orphanin FQ (N/OFQ) is an endogenous ligand of the N/OFQ peptide (NOP) receptor, which is a G protein-coupled receptor in brain regions associated with mood disorders. We used a novel, potent, and selective orally bioavailable antagonist, LY2940094, to test the hypothesis that blockade of NOP receptors would induce antidepressant effects. In this study we demonstrate that targeting NOP receptors with LY2940094 translates to antidepressant-like effects in rodent models and, importantly, to antidepressant efficacy in patients with major depressive disorder (MDD). The proof-of-concept study (POC) was an 8-week, double-blind, placebo-controlled trial that evaluated LY2940094 as a novel oral medication for the treatment of patients with MDD. Once daily oral dosing of LY2940094 at 40 mg for 8 weeks vs placebo provided some evidence for an antidepressant effect based on the change from baseline to week 8 in the GRID-Hamilton Depression Rating Scale-17 item total score, although the predefined POC efficacy criterion (probability of LY2940094 being better than placebo⩾88%) was not met (82.9%). LY2940094 also had an early effect on the processing of emotional stimuli at Week 1 as shown by an increased recognition of positive relative to negative facial expressions in an emotional test battery. LY2940094 was safe and well tolerated. Overall, these are the first human data providing evidence that the blockade of NOP receptor signaling represents a promising strategy for the treatment of MDD.

Intrathecal administration of nociceptin/orphanin FQ receptor agonists in rats: A strategy to relieve chemotherapy-induced neuropathic hypersensitivity

Oxaliplatin and paclitaxel are considered central components in the treatment of colorectal and breast cancer, respectively. The development of neuropathy during chronic treatment represents the major dose-limiting side effect that leads to discontinuation or interruption of therapies. The management of neuropathy is a challenge to individuate innovative therapeutic strategies based on new targets and correct routes of administration. We evaluated the hypersensitivity reliever effect of different opioid receptor agonists in rat models of oxaliplatin and paclitaxel-induced neuropathy. Compounds were spinally infused by intrathecal catheter. In oxaliplatin-treated rats, 0.3nmol morphine induced the reversion of the mechanical hypersensitivity (Paw-pressure test), nociceptin/orphanin FQ (N/OFQ; 0.3–3nmol) significantly increased the pain threshold without reaching the values of the control animals. The N/OFQ peptide (NOP) receptor full agonist UFP-112 reverted pain threshold alterations at lower dosage (0.1nmol) vs morphine and N/OFQ, the partial agonist UFP-113 (0.1–1nmol) was similar to N/OFQ. The higher efficacy of morphine vs N/OFQ was highlighted also in paclitaxel-treated rats. The mechanical hypersensitivity was fully reverted by 0.1nmol UFP-112 and UFP-113. In conclusion, intrathecal μ opioid peptide (MOP) and NOP receptor agonists relieved chemotherapy-induced neuropathic pain. The synthetic peptides showed valuable potency and efficacy suggesting the NOP system as an exploitable target.

Supraspinal actions of nociceptin/orphanin FQ, morphine and substance P in regulating pain and itch in non-human primates.

Nociceptin/orphanin FQ (N/OFQ) peptide (NOP) receptor agonists display a promising analgesic profile in preclinical studies. However, supraspinal N/OFQ produced hyperalgesia in rodents and such effects have not been addressed in primates. Thus, the aim of this study was to investigate the effects of centrally administered ligands on regulating pain and itch in non-human primates. In particular, nociceptive thresholds affected by intracisternal N/OFQ were compared with those of morphine and substance P, known to provide analgesia and mediate hyperalgesia, respectively, in humans. Intrathecal catheters were installed to allow intracisternal and lumbar intrathecal administration in awake and unanaesthetized rhesus monkeys. Nociceptive responses were measured using the warm water tail-withdrawal assay. Itch scratching responses were scored from videotapes recording behavioural activities of monkeys in their home cages. Antagonist studies were conducted to validate the receptor mechanisms underlying intracisternally elicited behavioural responses. Intracisternal morphine (100 nmol) elicited more head scratches than those after intrathecal morphine. Distinct dermatomal scratching locations between the two routes suggest a corresponding activation of supraspinal and spinal μ receptors. Unlike intracisternal substance P, which induced hyperalgesia, intracisternal N/OFQ (100 nmol) produced antinociceptive effects mediated by NOP receptors. Neither peptide increased scratching responses. Taken together, these results demonstrated differential actions of ligands in the primate supraspinal region in regulating pain and itch. This study not only improves scientific understanding of the N/OFQ-NOP receptor system in pain processing but also supports the therapeutic potential of NOP-related ligands as analgesics.

Acute and subchronic antinociceptive effects of nociceptin/orphanin FQ receptor agonists infused by intrathecal route in rats

Severe pain occurs in the context of many diseases and conditions and is a leading cause of disability. Nociceptin/orphanin FQ (N/OFQ) is the endogenous ligand of the N/OFQ peptide (NOP) receptor. This peptidergic system controls pain transmission and in particular spinally administered N/OFQ has robust antinociceptive properties.The aim of this study was to investigate the spinal antinociceptive properties of NOP peptide agonists after acute and subchronic treatment in rats. Doses unable to alter motor coordination were selected. UFP-112 (full NOP agonist) and UFP-113 (partial NOP agonist) were administered intrathecally (i.t.) by spinal catheterization. Acute injection of UFP-112 induced antinociceptive response at lower dosages (0.03–1nmol i.t.) compared to morphine and similar to N/OFQ. UFP-113 was effective in a 0.001–1nmol i.t. dose range. The antinociceptive effects of NOP ligands were no longer evident in rats knockout for the NOP gene, while those of morphine were maintained. The continuous spinal infusion (by osmotic pumps) of 0.1nmol/h UFP-112 and UFP-113 showed antinociceptive action comparable to 1–3nmol/h morphine or N/OFQ. The antinociceptive effect of morphine progressively decreased and was no longer significant after 6 days of treatment. Similar results were obtained with N/OFQ, UFP-112, and UFP-113. The acute i.t. injection of morphine in animals tolerant to N/OFQ and UFP-112 evoked analgesic effects. Neither morphine nor N/OFQ induced antinociceptive effects in morphine- and UFP-113-tolerant rats. In conclusion this study highlights the analgesic efficacy and potency of UFP-112 and UFP-113 underlining the relevance of NOP system in analgesia.