Activation of the nociceptin/orphanin-FQ receptor promotes NREM sleep and EEG slow wave activity.

Sleep/wake control involves several neurotransmitter and neuromodulatory systems yet the coordination of the behavioral and physiological processes underlying sleep is incompletely understood. Previous studies have suggested that activation of the Nociceptin/orphanin FQ (N/OFQ) receptor (NOPR) reduces locomotor activity and produces a sedation-like effect in rodents. In the present study, we systematically evaluated the efficacy of two NOPR agonists, Ro64-6198 and SR16835, on sleep/wake in rats, mice, and Cynomolgus macaques. We found a profound, dose-related increase in non-Rapid Eye Movement (NREM) sleep and electroencephalogram (EEG) slow wave activity (SWA) and suppression of Rapid Eye Movement sleep (REM) sleep in all three species. At the highest dose tested in rats, the increase in NREM sleep and EEG SWA was accompanied by a prolonged inhibition of REM sleep, hypothermia, and reduced locomotor activity. However, even at the highest dose tested, rats were immediately arousable upon sensory stimulation, suggesting sleep rather than an anesthetic state. NOPR agonism also resulted in increased expression of c-Fos in the anterodorsal preoptic and parastrial nuclei, two GABAergic nuclei that are highly interconnected with brain regions involved in physiological regulation. These results suggest that the N/OFQ-NOPR system may have a previously unrecognized role in sleep/wake control and potential promise as a therapeutic target for the treatment of insomnia.

Rare GPR37L1 Variants Reveal Potential Association between GPR37L1 and Disorders of Anxiety and Migraine.

GPR37L1 is an orphan receptor that couples through heterotrimeric G-proteins to regulate physiological functions. Since its role in humans is not fully defined, we used an unbiased computational approach to assess the clinical significance of rare G-protein-coupled receptor 37-like 1 (GPR37L1) genetic variants found among 51,289 whole-exome sequences from the DiscovEHR cohort. Rare GPR37L1 coding variants were binned according to predicted pathogenicity and analyzed by sequence kernel association testing to reveal significant associations with disease diagnostic codes for epilepsy and migraine, among others. Since associations do not prove causality, rare GPR37L1 variants were functionally analyzed in SK-N-MC cells to evaluate potential signaling differences and pathogenicity. Notably, receptor variants exhibited varying abilities to reduce cAMP levels, activate mitogen-activated protein kinase (MAPK) signaling, and/or upregulate receptor expression in response to the agonist prosaptide (TX14(A)), as compared with the wild-type receptor. In addition to signaling changes, knock-out (KO) of GPR37L1 or expression of certain rare variants altered cellular cholesterol levels, which were also acutely regulated by administration of the agonist TX14(A) via activation of the MAPK pathway. Finally, to simulate the impact of rare nonsense variants found in the large patient cohort, a KO mouse line lacking Gpr37l1 was generated. Although KO animals did not recapitulate an acute migraine phenotype, the loss of this receptor produced sex-specific changes in anxiety-related disorders often seen in chronic migraineurs. Collectively, these observations define the existence of rare GPR37L1 variants associated with neuropsychiatric conditions in the human population and identify the signaling changes contributing to pathological processes.

Potent and selective NOP receptor activation reduces cocaine self-administration in rats by lowering hedonic set point.

Developing new medications for the treatment of cocaine dependence continues to be a research priority. Compelling evidence indicates that mixed opioid receptor agonists, particularly bifunctional compounds that target nociceptin/orphanin FQ peptide (NOP) and mu opioid receptors, may be useful for the treatment of cocaine addiction. Here, we verify that potent and selective pharmacological activation of NOP receptors is sufficient to reduce relevant facets of cocaine addiction in animal models. Accordingly, we determined whether systemic injections of the small molecule AT-312 (0, 1, 3 mg/kg) could reduce operant cocaine self-administration, motivation for cocaine, and vulnerability to cocaine relapse in rats. Results indicate that a potent and selective NOP receptor agonist was equally efficacious in reducing the number of cocaine infusions in short (1-hour), as well as long (6-hour) access sessions. When tested on an economic-demand reinforcement schedule, AT-312 reduced Q0 , the parameter that describes the amount of drug consumed at zero price, while leaving the parameter α, a measure of motivation for drug consumption, unaltered. Furthermore, AT-312 successfully reduced conditioned reinstatement of cocaine seeking. In contrast, the NOP receptor agonist did not modify food self-administration. Blockade of the NOP receptor with the antagonist SB-612111 prevented the effect of AT-312 in decreasing cocaine-reinforced responding under a 2-hour fixed ratio 1 schedule, suggesting a NOP receptor-mediated mechanism. This work demonstrates that potent and selective activation of NOP receptors is sufficient to decrease cocaine taking and seeking behaviors in rats.

NOP Receptor Antagonists Decrease Alcohol Drinking in the Dark in C57BL/6J Mice.

BACKGROUND: The nociceptin/orphanin FQ opioid peptide (NOP) receptor and its endogenous ligand N/OFQ have been implicated in the regulation of drug and alcohol use disorders (AUD). In particular, evidence demonstrated that NOP receptor activation blocks reinforcing and motivating effects of alcohol across a range of behavioral measures, including alcohol intake, conditioned place preference, and vulnerability to relapse. METHODS: Here, we show the effects of pharmacological activation and inhibition of NOP receptors on binge-like alcohol consumption, as measured by the "drinking in the dark" (DID) model in C57BL/6J mice. RESULTS: We found that 2 potent and selective NOP agonists AT-202 (0, 0.3, 1, 3 mg/kg) and AT-312 (0, 0.3, 1 mg/kg) did not affect binge alcohol drinking at doses that do not affect locomotor activity. AT-202 also failed to alter DID behavior when administered to mice previously exposed to chronic alcohol treatment with an alcohol-containing liquid diet. Conversely, treatment with either the high affinity NOP receptor antagonist SB-612111 (0, 3, 10, 30 mg/kg) or the selective antagonist LY2817412 (0, 3, 10, 30 mg/kg) decreased binge drinking. SB-612111 was effective at all doses examined, and LY2817412 was effective at 30 mg/kg. Consistently, NOP receptor knockout mice consumed less alcohol compared to wild type. SB-612111 reduced DID and increased sucrose consumption at doses that do not appear to affect locomotor activity. However, the high dose of SB-612111 (30 mg/kg) reduced alcohol intake but failed to inhibit preference in a 2-bottle choice DID model that can assess moderate alcohol intake. CONCLUSIONS: The present results suggest that NOP receptor inhibition rather than activation may represent a valuable approach for treatment of AUD characterized by excessive alcohol consumption such as binge drinking.

BU10038 as a safe opioid analgesic with fewer side-effects after systemic and intrathecal administration in primates.

BACKGROUND: The marked increase in mis-use of prescription opioids has greatly affected our society. One potential solution is to develop improved analgesics which have agonist action at both mu opioid peptide (MOP) and nociceptin/orphanin FQ peptide (NOP) receptors. BU10038 is a recently identified bifunctional MOP/NOP partial agonist. The aim of this study was to determine the functional profile of systemic or spinal delivery of BU10038 in primates after acute and chronic administration. METHODS: A series of behavioural and physiological assays have been established specifically to reflect the therapeutic (analgesia) and side-effects (abuse potential, respiratory depression, itch, physical dependence, and tolerance) of opioid analgesics in rhesus monkeys. RESULTS: After systemic administration, BU10038 (0.001-0.01 mg kg-1) dose-dependently produced long-lasting antinociceptive and antihypersensitive effects. Unlike the MOP agonist oxycodone, BU10038 lacked reinforcing effects (i.e. little or no abuse liability), and BU10038 did not compromise the physiological functions of primates including respiration, cardiovascular activities, and body temperature at antinociceptive doses and a 10-30-fold higher dose (0.01-0.1 mg kg-1). After intrathecal administration, BU10038 (3 µg) exerted morphine-comparable antinociception and antihypersensitivity without itch scratching responses. Unlike morphine, BU10038 did not cause the development of physical dependence and tolerance after repeated and chronic administration. CONCLUSIONS: These in vivo findings demonstrate the translational potential of bifunctional MOP/NOP receptor agonists such as BU10038 as a safe, non-addictive analgesic with fewer side-effects in primates. This study strongly supports that bifunctional MOP/NOP agonists may provide improved analgesics and an alternative solution for the ongoing prescription opioid crisis.

NOP-Related Mechanisms in Pain and Analgesia.

Since the discovery of the NOP receptor and N/OFQ as the endogenous ligand, evidence has appeared demonstrating the involvement of this receptor system in pain. This was not surprising for members of the opioid receptor and peptide families, particularly since both the receptor and N/OFQ are highly expressed in brain regions involved in pain, spinal cord, and dorsal root ganglia. What has been surprising is the complicated picture that has emerged from 25 years of research. The original finding that N/OFQ decreased tail flick and hotplate latency, when administered i.c.v., led to the hypothesis that NOP receptor antagonists could have analgesic activity without abuse liability. However, as data accumulated, it became clear that not only the potency but the activity per se was different when N/OFQ or small molecule NOP agonists were administered in the brain versus the spinal cord and it also depended upon the pain assay used. When administered systemically, NOP receptor agonists are generally ineffective in attenuating heat pain but are antinociceptive in an acute inflammatory pain model. Most antagonists administered systemically have no antinociceptive activity of their own, even though selective peptide NOP antagonists have potent antinociceptive activity when administered i.c.v. Chronic pain models provide different results as well, as small molecule NOP receptor agonists have potent anti-allodynic and anti-hyperalgesic activity after systemic administration. A considerable number of electrophysiological and anatomical experiments, in particular with NOP-eGFP mice, have been conducted in an attempt to explain the complicated profile resulting from NOP receptor modulation, to examine receptor plasticity, and to elucidate mechanisms by which selective NOP agonists, bifunctional NOP/mu agonists, or NOP receptor antagonists modulate acute and chronic pain.

Nociceptin/Orphanin FQ Receptor Structure, Signaling, Ligands, Functions, and Interactions with Opioid Systems.

The NOP receptor (nociceptin/orphanin FQ opioid peptide receptor) is the most recently discovered member of the opioid receptor family and, together with its endogenous ligand, N/OFQ, make up the fourth members of the opioid receptor and opioid peptide family. Because of its more recent discovery, an understanding of the cellular and behavioral actions induced by NOP receptor activation are less well developed than for the other members of the opioid receptor family. All of these factors are important because NOP receptor activation has a clear modulatory role on mu opioid receptor-mediated actions and thereby affects opioid analgesia, tolerance development, and reward. In addition to opioid modulatory actions, NOP receptor activation has important effects on motor function and other physiologic processes. This review discusses how NOP pharmacology intersects, contrasts, and interacts with the mu opioid receptor in terms of tertiary structure and mechanism of receptor activation; location of receptors in the central nervous system; mechanisms of desensitization and downregulation; cellular actions; intracellular signal transduction pathways; and behavioral actions with respect to analgesia, tolerance, dependence, and reward. This is followed by a discussion of the agonists and antagonists that have most contributed to our current knowledge. Because NOP receptors are highly expressed in brain and spinal cord and NOP receptor activation sometimes synergizes with mu receptor-mediated actions and sometimes opposes them, an understanding of NOP receptor pharmacology in the context of these interactions with the opioid receptors will be crucial to the development of novel therapeutics that engage the NOP receptor.

Knock-In Mice with NOP-eGFP Receptors Identify Receptor Cellular and Regional Localization.

The nociceptin/orphanin FQ (NOP) receptor, the fourth member of the opioid receptor family, is involved in many processes common to the opioid receptors including pain and drug abuse. To better characterize receptor location and trafficking, knock-in mice were created by inserting the gene encoding enhanced green fluorescent protein (eGFP) into the NOP receptor gene (Oprl1) and producing mice expressing a functional NOP-eGFP C-terminal fusion in place of the native NOP receptor. The NOP-eGFP receptor was present in brain of homozygous knock-in animals in concentrations somewhat higher than in wild-type mice and was functional when tested for stimulation of [(35)S]GTPγS binding in vitro and in patch-clamp electrophysiology in dorsal root ganglia (DRG) neurons and hippocampal slices. Inhibition of morphine analgesia was equivalent when tested in knock-in and wild-type mice. Imaging revealed detailed neuroanatomy in brain, spinal cord, and DRG and was generally consistent with in vitro autoradiographic imaging of receptor location. Multicolor immunohistochemistry identified cells coexpressing various spinal cord and DRG cellular markers, as well as coexpression with µ-opioid receptors in DRG and brain regions. Both in tissue slices and primary cultures, the NOP-eGFP receptors appear throughout the cell body and in processes. These knock-in mice have NOP receptors that function both in vitro and in vivo and appear to be an exceptional tool to study receptor neuroanatomy and correlate with NOP receptor function. SIGNIFICANCE STATEMENT: The NOP receptor, the fourth member of the opioid receptor family, is involved in pain, drug abuse, and a number of other CNS processes. The regional and cellular distribution has been difficult to determine due to lack of validated antibodies for immunohistochemical analysis. To provide a new tool for the investigation of receptor localization, we have produced knock-in mice with a fluorescent-tagged NOP receptor in place of the native NOP receptor. These knock-in mice have NOP receptors that function both in vitro and in vivo and have provided a detailed characterization of NOP receptors in brain, spinal cord, and DRG neurons. They appear to be an exceptional tool to study receptor neuroanatomy and correlate with NOP receptor function.

Tyrosine 308 is necessary for ligand-directed Gs protein-biased signaling of ß2-adrenoceptor.

Interaction of a given G protein-coupled receptor to multiple different G proteins is a widespread phenomenon. For instance, ß2-adrenoceptor (ß2-AR) couples dually to Gs and Gi proteins. Previous studies have shown that cAMP-dependent protein kinase (PKA)-mediated phosphorylation of ß2-AR causes a switch in receptor coupling from Gs to Gi. More recent studies have demonstrated that phosphorylation of ß2-AR by G protein-coupled receptor kinases, particularly GRK2, markedly enhances the Gi coupling. We have previously shown that although most ß2-AR agonists cause both Gs and Gi activation, (R,R')-fenoterol preferentially activates ß2-AR-Gs signaling. However, the structural basis for this functional selectivity remains elusive. Here, using docking simulation and site-directed mutagenesis, we defined Tyr-308 as the key amino acid residue on ß2-AR essential for Gs-biased signaling. Following stimulation with a ß2-AR-Gs-biased agonist (R,R')-4'-aminofenoterol, the Gi disruptor pertussis toxin produced no effects on the receptor-mediated ERK phosphorylation in HEK293 cells nor on the contractile response in cardiomyocytes expressing the wild-type ß2-AR. Interestingly, Y308F substitution on ß2-AR enabled (R,R')-4'-aminofenoterol to activate Gi and to produce these responses in a pertussis toxin-sensitive manner without altering ß2-AR phosphorylation by PKA or G protein-coupled receptor kinases. These results indicate that, in addition to the phosphorylation status, the intrinsic structural feature of ß2-AR plays a crucial role in the receptor coupling selectivity to G proteins. We conclude that specific interactions between the ligand and the Tyr-308 residue of ß2-AR stabilize receptor conformations favoring the receptor-Gs protein coupling and subsequently result in Gs-biased agonism.

Comparative molecular field analysis of fenoterol derivatives interacting with an agonist-stabilized form of the ß2-adrenergic receptor.

The ß2-adrenergic receptor (ß2-AR) agonist [(3)H]-(R,R')-methoxyfenoterol was employed as the marker ligand in displacement studies measuring the binding affinities (Ki values) of the stereoisomers of a series of 4'-methoxyfenoterol analogs in which the length of the alkyl substituent at α' position was varied from 0 to 3 carbon atoms. The binding affinities of the compounds were additionally determined using the inverse agonist [(3)H]-CGP-12177 as the marker ligand and the ability of the compounds to stimulate cAMP accumulation, measured as EC50 values, were determined in HEK293 cells expressing the ß2-AR. The data indicate that the highest binding affinities and functional activities were produced by methyl and ethyl substituents at the α' position. The results also indicate that the Ki values obtained using [(3)H]-(R,R')-methoxyfenoterol as the marker ligand modeled the EC50 values obtained from cAMP stimulation better than the data obtained using [(3)H]-CGP-12177 as the marker ligand. The data from this study was combined with data from previous studies and processed using the Comparative Molecular Field Analysis approach to produce a CoMFA model reflecting the binding to the ß2-AR conformation probed by [(3)H]-(R,R')-4'-methoxyfenoterol. The CoMFA model of the agonist-stabilized ß2-AR suggests that the binding of the fenoterol analogs to an agonist-stabilized conformation of the ß2-AR is governed to a greater extend by steric effects than binding to the [(3)H]-CGP-12177-stabilized conformation(s) in which electrostatic interactions play a more predominate role.

Functional and anatomical analyses of active spinal circuits in a mouse model of chronic pain.

ABSTRACT: Decades of efforts in elucidating pain mechanisms, including pharmacological, neuroanatomical, and physiological studies have provided insights into how nociceptive information transmits from the periphery to the brain and the locations receiving nociceptive signals. However, little is known about which specific stimulus-dependent activated neurons, amongst heterogeneous neural environments, discriminatively evoke the cognate pain behavior. We here shed light on the population of neurons in the spinal cord activated by a painful stimulus to identify chronic pain-dependent activated neuronal subsets using Fos2A-iCreER (TRAP2) mice. We have found a large number of neurons activated by a normally nonpainful stimulus in the spinal cord of spinal nerve-ligated mice, compared with sham. Neuronal activation was observed in laminae I and II outer under heat hyperalgesia. A large number of neurons in laminae II inner were activated in both mechanical allodynia and heat hyperalgesia conditions, while mechanical allodynia tends to be the only stimulus that activates cells at lamina II inner dorsal region. Neuroanatomical analyses using spinal cell markers identified a large number of spinal inhibitory neurons that are recruited by both mechanical allodynia and heat hyperalgesia. Of interest, spinal neurons expressing calretinin, calbindin, and parvalbumin were activated differently with distinct pain modalities (ie, mechanical allodynia vs heat hyperalgesia). Chemogenetic inhibition of those activated neurons significantly and specifically reduced the response to the pain stimulus associated with the stimulus modality originally given to the animals. These findings support the idea that spinal neuronal ensembles underlying nociceptive transmission undergo dynamic changes to regulate selective pain responses.

Synthesis of α3ß4 Nicotinic Acetylcholine Receptor Modulators Derived from Aristoquinoline That Reduce Reinstatement of Cocaine-Seeking Behavior.

Growing evidence suggests that inhibition of the α3ß4 nicotinic acetylcholine receptor (nAChR) represents a promising therapeutic strategy to treat cocaine use disorder. Recently, aristoquinoline (1), an alkaloid from Aristotelia chilensis, was identified as an α3ß4-selective nAChR inhibitor. Here, we prepared 22 derivatives of 1 and evaluated their ability to inhibit the α3ß4 nAChR. These studies revealed structure-activity trends and several compounds with increased potency compared to 1 with few off-target liabilities. Additional mechanistic studies indicated that these compounds inhibit the α3ß4 nAChR noncompetitively, but do not act as channel blockers, suggesting they are negative allosteric modulators. Finally, using a cocaine-primed reinstatement paradigm, we demonstrated that 1 significantly attenuates drug-seeking behavior in an animal model of cocaine relapse. The results from these studies further support a role for the α3ß4 nAChR in the addictive properties of cocaine and highlight the possible utility of aristoquinoline derivatives in treating cocaine use disorder.

Physical presence of nor-binaltorphimine in mouse brain over 21 days after a single administration corresponds to its long-lasting antagonistic effect on κ-opioid receptors.

In the mouse 55°C warm-water tail-withdrawal assay, a single administration of nor-binaltorphimine (nor-BNI; 10 mg/kg i.p.) antagonized κ-opioid receptor (KOR) agonist-induced antinociception up to 14 days, whereas naloxone (10 mg/kg i.p.)-mediated antagonism lasted less than 1 day. In saturation binding experiments, mouse brain membranes isolated and washed 1 or 7 (but not 14) days after nor-BNI administration demonstrated a significant time-dependent decrease in maximal KOR agonist [(3)H]U69,593 binding. To determine whether brain concentrations of nor-BNI were sufficient to explain the antagonism of KOR-mediated antinociception, mouse blood and perfused brain were harvested at time points ranging from 30 minutes to 21 days after a single administration and analyzed for the presence of nor-BNI using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS). Nor-BNI was detected in the perfused brain homogenate up to 21 days after administration (30 nmol i.c.v. or 10 mg/kg i.p.). Subsequent experiments in which nor-BNI was administered at doses estimated from the amounts detected in the brain homogenates isolated from pretreated mice over time demonstrated significant antagonism of U50,488 antinociception in a manner consistent with the magnitude of observed KOR antagonism. The dose (1.4 nmol) approximating the lowest amount of nor-BNI detected in brain on day 14 did not antagonize U50,488-induced antinociception, consistent with the absence of U50,488 antagonism observed in vivo at this time point after pretreatment. Overall, the physical presence of nor-BNI in the mouse brain paralleled its in vivo pharmacological profile, suggesting physicochemical and pharmacokinetic properties of nor-BNI may contribute to the prolonged KOR antagonism.

Peptides derived from the prohormone proNPQ/spexin are potent central modulators of cardiovascular and renal function and nociception.

Computational methods have led two groups to predict the endogenous presence of a highly conserved, amidated, 14-aa neuropeptide called either spexin or NPQ. NPQ/spexin is part of a larger prohormone that contains 3 sets of RR residues, suggesting that it could yield more than one bioactive peptide; however, no in vivo activity has been demonstrated for any peptide processed from this precursor. Here we demonstrate biological activity for two peptides present within proNPQ/spexin. NPQ/spexin (NWTPQAMLYLKGAQ-NH(2)) and NPQ 53-70 (FISDQSRRKDLSDRPLPE) have differing renal and cardiovascular effects when administered intracerebroventricularly or intravenously into rats. Intracerebroventricular injection of NPQ/spexin produced a 13 ± 2 mmHg increase in mean arterial pressure, a 38 ± 8 bpm decrease in heart rate, and a profound decrease in urine flow rate. Intracerebroventricular administration of NPQ 53-70 produced a 26 ± 9 bpm decrease in heart rate with no change in mean arterial pressure, and a marked increase in urine flow rate. Intraventricular NPQ/spexin and NPQ 53-70 also produced antinociceptive activity in the warm water tail withdrawal assay in mice (ED(50)<30 and 10 nmol for NPQ/spexin and NPQ 53-70, respectively). We conclude that newly identified peptides derived from the NPQ/spexin precursor contribute to CNS-mediated control of arterial blood pressure and salt and water balance and modulate nociceptive responses.

Designing bifunctional NOP receptor-mu opioid receptor ligands from NOP receptor-selective scaffolds. Part I.

The nociceptin receptor (NOP) and its endogenous agonist, nociceptin/orphanin FQ (N/OFQ), members of the opioid receptor and peptide families respectively, modulate the pharmacological effects of classical opioids, particularly opioid-induced reward and nociception. We hypothesized that compounds containing both NOP and opioid receptor activity in a single molecule may have useful pharmacological profiles as non-addicting analgesics or as drug abuse medications. We report here our forays into the structure-activity relationships for discovering 'bifunctional' NOP-mu opioid receptor (MOP) ligands, starting from our NOP-selective scaffolds. This initial SAR suggests pharmacophoric elements that may be modified to modulate/increase opioid affinity, while maintaining high affinity for the NOP receptor, to result in potent bifunctional small-molecule NOP/MOP ligands.

Oxidative folding and preparation of α-conotoxins for use in high-throughput structure-activity relationship studies.

α-Conotoxins are peptide neurotoxins that selectively inhibit various subtypes of nicotinic acetylcholine receptors. They are important research tools for studying numerous pharmacological disorders, with profound potential for developing drug leads for treating pain, tobacco addiction, and other conditions. They are characterized by the presence of two disulfide bonds connected in a globular arrangement, which stabilizes a bioactive helical conformation. Despite extensive structure-activity relationship studies that have produced α-conotoxin analogs with increased potency and selectivity towards specific nicotinic acetylcholine receptor subtypes, the efficient production of diversity-oriented α-conotoxin combinatorial libraries has been limited by inefficient folding and purification procedures. We have investigated the optimized conditions for the reliable folding of α-conotoxins using simplified oxidation procedures for use in the accelerated production of synthetic combinatorial libraries of α-conotoxins. To this end, the effect of co-solvent, redox reagents, pH, and temperature on the proportion of disulfide bond isomers was determined for α-conotoxins exhibiting commonly known Cys loop spacing frameworks. In addition, we have developed high-throughput 'semi-purification' methods for the quick and efficient parallel preparation of α-conotoxin libraries for use in accelerated structure-activity relationship studies. Our simplified procedures represent an effective strategy for the preparation of large arrays of correctly folded α-conotoxin analogs and permit the rapid identification of active hits directly from high-throughput pharmacological screening assays.

Preclinical effects of cannabidiol in an experimental model of migraine.

ABSTRACT: Migraine is a disabling disorder characterized by recurrent headaches, accompanied by abnormal sensory sensitivity and anxiety. Despite extensive historical use of cannabis in headache disorders, there is limited research on the nonpsychoactive cannabidiol (CBD) for migraine and there is no scientific evidence to prove that CBD is an effective treatment. The effects of CBD are examined here using a calcitonin gene-related peptide (CGRP)-induced migraine model that provides measures of cephalic allodynia, spontaneous pain, altered light sensitivity (photophobia), and anxiety-like behavior in C57BL/6J mice. A single administration of CGRP induced facial hypersensitivity in both female and male mice. Repeated CGRP treatment produced progressively decreased levels in basal thresholds of allodynia in females, but not in males. A single CBD administration protected both females and males from periorbital allodynia induced by a single CGRP injection. Repeated CBD administration prevented increased levels of basal allodynia induced by repeated CGRP treatment in female mice and did not lead to responses consistent with migraine headache as occurs with triptans. Cannabidiol, injected after CGRP, reversed CGRP-evoked allodynia. Cannabidiol also reduced spontaneous pain traits induced by CGRP administration in female mice. Finally, CBD blocked CGRP-induced anxiety in male mice, but failed in providing protection from CGRP-induced photophobia in females. These results demonstrate the efficacy of CBD in preventing episodic and chronic migraine-like states with reduced risk of causing medication overuse headache. Cannabidiol also shows potential as an abortive agent for treating migraine attacks and headache-related conditions such as spontaneous pain and anxiety.

A novel G protein-biased agonist at the µ opioid receptor induces substantial receptor desensitisation through G protein-coupled receptor kinase.

BACKGROUND AND PURPOSE: G protein-biased µ opioid receptor agonists have the potential to induce less receptor desensitisation and tolerance than balanced opioids. Here, we investigated if the cyclic endomorphin analogue Tyr-c[D-Lys-Phe-Tyr-Gly] (Compound 1) is a G protein-biased µ agonist and characterised its ability to induce rapid receptor desensitisation in mammalian neurones. EXPERIMENTAL APPROACH: The signalling and trafficking properties of opioids were characterised using bioluminescence resonance energy transfer assays, enzyme-linked immunosorbent assay and phosphosite-specific immunoblotting in human embryonic kidney 293 cells. Desensitisation of opioid-induced currents were studied in rat locus coeruleus neurones using whole-cell patch-clamp electrophysiology. The mechanism of Compound 1-induced µ receptor desensitisation was probed using kinase inhibitors. KEY RESULTS: Compound 1 has similar intrinsic activity for G protein signalling as morphine. As predicted for a G protein-biased µ agonist, Compound 1 induced minimal agonist-induced internalisation and phosphorylation at intracellular µ receptor serine/threonine residues known to be involved in G protein-coupled receptor kinase (GRK)-mediated desensitisation. However, Compound 1 induced robust rapid µ receptor desensitisation in locus coeruleus neurons, to a greater degree than morphine. The extent of Compound 1-induced desensitisation was unaffected by activation or inhibition of protein kinase C (PKC) but was significantly reduced by inhibition of GRK. CONCLUSION AND IMPLICATIONS: Compound 1 is a novel G protein-biased µ agonist that induces substantial rapid receptor desensitisation in mammalian neurons. Surprisingly, Compound 1-induced desensitisation was demonstrated to be GRK dependent despite its G protein bias. Our findings refute the assumption that G protein-biased agonists will evade receptor desensitisation and tolerance. LINKED ARTICLES: This article is part of a themed issue on Advances in Opioid Pharmacology at the Time of the Opioid Epidemic. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v180.7/issuetoc.

Rare GPR37L1 variants reveal potential roles in anxiety and migraine disorders.

GPR37L1 is an orphan receptor that couples through heterotrimeric G-proteins to regulate physiological functions. Since its role in humans is not fully defined, we used an unbiased computational approach to assess the clinical significance of rare GPR37L1 genetic variants found among 51,289 whole exome sequences from the DiscovEHR cohort. Briefly, rare GPR37L1 coding variants were binned according to predicted pathogenicity, and analyzed by Sequence Kernel Association testing to reveal significant associations with disease diagnostic codes for epilepsy and migraine, among others. Since associations do not prove causality, rare GPR37L1 variants were then functionally analyzed in SK-N-MC cells to evaluate potential signaling differences and pathogenicity. Notably, receptor variants exhibited varying abilities to reduce cAMP levels, activate MAPK signaling, and/or upregulate receptor expression in response to the agonist prosaptide (TX14(A)), as compared to the wild-type receptor. In addition to signaling changes, knockout of GPR37L1 or expression of certain rare variants altered cellular cholesterol levels, which were also acutely regulated by administration of the agonist TX14(A) via activation of the MAPK pathway. Finally, to simulate the impact of rare nonsense variants found in the large patient cohort, a knockout (KO) mouse line lacking Gpr37L1 was generated, revealing loss of this receptor produced sex-specific changes implicated in migraine-related disorders. Collectively, these observations define the existence of rare GPR37L1 variants in the human population that are associated with neuropsychiatric conditions and identify the underlying signaling changes that are implicated in the in vivo actions of this receptor in pathological processes leading to anxiety and migraine. SIGNIFICANCE STATEMENT: G-protein coupled receptors (GPCRs) represent a diverse group of membrane receptors that contribute to a wide range of diseases and serve as effective drug targets. However, a number of these receptors have no identified ligands or functions, i.e., orphan receptors. Over the past decade, advances have been made, but there is a need for identifying new strategies to reveal their roles in health and disease. Our results highlight the utility of rare variant analyses of orphan receptors for identifying human disease associations, coupled with functional analyses in relevant cellular and animal systems, to ultimately reveal their roles as novel drug targets for treatment of neurological disorders that lack wide-spread efficacy.

Thermodynamics and docking of agonists to the ß(2)-adrenoceptor determined using [(3)H](R,R')-4-methoxyfenoterol as the marker ligand.

G protein-coupled receptors (GPCRs) are integral membrane proteins that change conformation after ligand binding so that they can transduce signals from an extracellular ligand to a variety of intracellular components. The detailed interaction of a molecule with a G protein-coupled receptor is a complicated process that is influenced by the receptor conformation, thermodynamics, and ligand conformation and stereoisomeric configuration. To better understand the molecular interactions of fenoterol analogs with the ß(2)-adrenergic receptor, we developed a new agonist radioligand for binding assays. [(3)H](R,R')-methoxyfenoterol was used to probe the binding affinity for a series of fenoterol stereoisomers and derivatives. The results suggest that the radioligand binds with high affinity to an agonist conformation of the receptor, which represents approximately 25% of the total ß(2)-adrenoceptor (AR) population as determined with the antagonist [(3)H]CGP-12177. The ß(2)-AR agonists tested in this study have considerably higher affinity for the agonist conformation of the receptor, and K(i) values determined for fenoterol analogs model much better the cAMP activity of the ß(2)-AR elicited by these ligands. The thermodynamics of binding are also different when interacting with an agonist conformation, being purely entropy-driven for each fenoterol isomer, rather than a mixture of entropy and enthalpy when the fenoterol isomers binding was determined using [(3)H]CGP-12177. Finally, computational modeling identified the molecular interactions involved in agonist binding and allow for the prediction of additional novel ß(2)-AR agonists. The study underlines the possibility of using defined radioligand structure to probe a specific conformation of such shape-shifting system as the ß(2)-adrenoceptor.