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Hoare SRJ, Tewson PH, Sachdev S, Connor M, Hughes TE, Quinn AM. Quantifying the Kinetics of Signaling and Arrestin Recruitment by Nervous System G-Protein Coupled Receptors. Front Cell Neurosci 2022; 15:814547. [PMID: 35110998 PMCID: PMC8801586 DOI: 10.3389/fncel.2021.814547] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2021] [Accepted: 12/17/2021] [Indexed: 11/13/2022] Open
Abstract
Neurons integrate inputs over different time and space scales. Fast excitatory synapses at boutons (ms and μm), and slow modulation over entire dendritic arbors (seconds and mm) are all ultimately combined to produce behavior. Understanding the timing of signaling events mediated by G-protein-coupled receptors is necessary to elucidate the mechanism of action of therapeutics targeting the nervous system. Measuring signaling kinetics in live cells has been transformed by the adoption of fluorescent biosensors and dyes that convert biological signals into optical signals that are conveniently recorded by microscopic imaging or by fluorescence plate readers. Quantifying the timing of signaling has now become routine with the application of equations in familiar curve fitting software to estimate the rates of signaling from the waveform. Here we describe examples of the application of these methods, including (1) Kinetic analysis of opioid signaling dynamics and partial agonism measured using cAMP and arrestin biosensors; (2) Quantifying the signaling activity of illicit synthetic cannabinoid receptor agonists measured using a fluorescent membrane potential dye; (3) Demonstration of multiplicity of arrestin functions from analysis of biosensor waveforms and quantification of the rates of these processes. These examples show how temporal analysis provides additional dimensions to enhance the understanding of GPCR signaling and therapeutic mechanisms in the nervous system.
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Affiliation(s)
- Sam R. J. Hoare
- Pharmechanics LLC, Owego, NY, United States
- *Correspondence: Sam R. J. Hoare
| | | | - Shivani Sachdev
- Department of Biomedical Sciences, Macquarie University, Sydney, NSW, Australia
| | - Mark Connor
- Department of Biomedical Sciences, Macquarie University, Sydney, NSW, Australia
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Zhao Y, Joshi AA, Aldrich JV, Murray TF. Quantification of kappa opioid receptor ligand potency, efficacy and desensitization using a real-time membrane potential assay. Biomed Pharmacother 2021; 143:112173. [PMID: 34536757 PMCID: PMC8516733 DOI: 10.1016/j.biopha.2021.112173] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Revised: 09/02/2021] [Accepted: 09/05/2021] [Indexed: 10/25/2022] Open
Abstract
We explored the utility of the real-time FLIPR Membrane Potential (FMP) assay as a method to assess kappa opioid receptor (KOR)-induced hyperpolarization. The FMP Blue dye was used to measure fluorescent signals reflecting changes in membrane potential in KOR expressing CHO (CHO-KOR) cells. Treatment of CHO-KOR cells with kappa agonists U50,488 or dynorphin [Dyn (1-13)NH2] produced rapid and concentration-dependent decreases in FMP Blue fluorescence reflecting membrane hyperpolarization. Both the nonselective opioid antagonist naloxone and the κ-selective antagonists nor-binaltorphimine (nor-BNI) and zyklophin produced rightward shifts in the U50,488 concentration-response curves, consistent with competitive antagonism of the KOR mediated response. The decrease in fluorescent emission produced by U50,488 was blocked by overnight pertussis toxin pretreatment, indicating the requirement for PTX-sensitive G proteins in the KOR mediated response. We directly compared the potency of U50,488 and Dyn (1-13)NH2 in the FMP and [35S]GTPγS binding assays, and found that both were approximately 10 times more potent in the cellular fluorescence assay. The maximum responses of both U50,488 and Dyn (1-13)NH2 declined following repeated additions, reflecting receptor desensitization. We assessed the efficacy and potency of structurally distinct KOR small molecule and peptide ligands. The FMP assay reliably detected both partial agonists and stereoselectivity. Using KOR-selective peptides with varying efficacies, we found that the FMP assay allowed high throughput quantification of peptide efficacy. These data demonstrate that the FMP assay is a sensitive method for assessing κ-opioid receptor induced hyperpolarization, and represents a useful approach for quantification of potency, efficacy and desensitization of KOR ligands.
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Affiliation(s)
- Yuanzi Zhao
- Department of Pharmacology and Neuroscience, School of Medicine, Creighton University, Omaha, NE, USA
| | - Anand A Joshi
- Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, USA.
| | - Jane V Aldrich
- Department of Medicinal Chemistry, University of Kansas, Lawrence, KS, USA; Department of Medicinal Chemistry, University of Florida, Gainesville, FL, USA
| | - Thomas F Murray
- Department of Pharmacology and Neuroscience, School of Medicine, Creighton University, Omaha, NE, USA
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Lu JJ, Polgar WE, Mann A, Dasgupta P, Schulz S, Zaveri NT. Differential In Vitro Pharmacological Profiles of Structurally Diverse Nociceptin Receptor Agonists in Activating G Protein and Beta-Arrestin Signaling at the Human Nociceptin Opioid Receptor. Mol Pharmacol 2021; 100:7-18. [PMID: 33958480 DOI: 10.1124/molpharm.120.000076] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Accepted: 03/26/2021] [Indexed: 11/22/2022] Open
Abstract
Agonists at the nociceptin opioid peptide receptor (NOP) are under investigation as therapeutics for nonaddicting analgesia, opioid use disorder, Parkinson's disease, and other indications. NOP full and partial agonists have both been of interest, particularly since NOP partial agonists show a reduced propensity for behavioral disruption than NOP full agonists. Here, we investigated the in vitro pharmacological properties of chemically diverse NOP receptor agonists in assays measuring functional activation of the NOP receptor such as guanosine 5'-O-[gamma-thio]triphosphate (GTPγS) binding, cAMP inhibition, G protein-coupled inwardly rectifying potassium (GIRK) channel activation, phosphorylation, β-arrestin recruitment and receptor internalization. When normalized to the efficacy of the natural agonist nociceptin/orphanin FQ (N/OFQ), we found that different functional assays that measure intrinsic activity produce inconsistent levels of agonist efficacy, particularly for ligands that were partial agonists. Agonist efficacy obtained in the GTPγS assay tended to be lower than that in the cAMP and GIRK assays. These structurally diverse NOP agonists also showed differential receptor phosphorylation profiles at the phosphosites we examined and induced varying levels of receptor internalization. Interestingly, although the rank order for β-arrestin recruitment by these NOP agonists was consistent with their ability to induce receptor internalization, their phosphorylation signatures at the time point we investigated were not indicative of the levels of β-arrestin recruitment or internalization induced by these agonists. It is possible that other phosphorylation sites, yet to be identified, drive the recruitment of NOP receptor ensembles and subsequent receptor trafficking by some nonpeptide NOP agonists. These findings potentially help understand NOP agonist pharmacology in the context of ligand-activated receptor trafficking. SIGNIFICANCE STATEMENT: Chemically diverse agonist ligands at the nociceptin opioid receptor G protein-coupled receptor showed differential efficacy for activating downstream events after receptor binding, in a suite of functional assays measuring guanosine 5'-O-[gamma-thio]triphosphate binding, cAMP inhibition, G protein-coupled inwardly rectifying protein channel activation, β-arrestin recruitment, receptor internalization and receptor phosphorylation. These analyses provide a context for understanding nociceptin opioid peptide receptor (NOP) agonist pharmacology driven by ligand-induced differential NOP receptor signaling.
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Affiliation(s)
- James J Lu
- Astraea Therapeutics, Mountain View, California (J.J.L., W.E.P., N.T.Z.); and Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany (A.M., P.D., S.S.)
| | - Willma E Polgar
- Astraea Therapeutics, Mountain View, California (J.J.L., W.E.P., N.T.Z.); and Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany (A.M., P.D., S.S.)
| | - Anika Mann
- Astraea Therapeutics, Mountain View, California (J.J.L., W.E.P., N.T.Z.); and Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany (A.M., P.D., S.S.)
| | - Pooja Dasgupta
- Astraea Therapeutics, Mountain View, California (J.J.L., W.E.P., N.T.Z.); and Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany (A.M., P.D., S.S.)
| | - Stefan Schulz
- Astraea Therapeutics, Mountain View, California (J.J.L., W.E.P., N.T.Z.); and Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany (A.M., P.D., S.S.)
| | - Nurulain T Zaveri
- Astraea Therapeutics, Mountain View, California (J.J.L., W.E.P., N.T.Z.); and Institute of Pharmacology and Toxicology, Jena University Hospital, Friedrich Schiller University Jena, Jena, Germany (A.M., P.D., S.S.)
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4
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Sachdev S, Banister SD, Santiago M, Bladen C, Kassiou M, Connor M. Differential activation of G protein-mediated signaling by synthetic cannabinoid receptor agonists. Pharmacol Res Perspect 2020; 8:e00566. [PMID: 32101383 PMCID: PMC7043210 DOI: 10.1002/prp2.566] [Citation(s) in RCA: 12] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2019] [Revised: 01/23/2020] [Accepted: 01/27/2020] [Indexed: 12/19/2022] Open
Abstract
Synthetic cannabinoid receptor agonists (SCRAs) are new psychoactive substances associated with acute intoxication and even death. However, the molecular mechanisms through which SCRAs may exert their toxic effects remain unclear-including the potential differential activation of G protein subtypes by cannabinoid receptor type 1 (CB1), a major target of SCRA. We measured CB1-mediated activation of Gαs and Gαi/o proteins by SCRAs by examining stimulation (pertussis toxin, PTX treated) as well as inhibition (non-PTX treated) of forskolin (FSK)-induced cyclic adenosine monophosphate (cAMP) accumulation in human embryonic kidney (HEK) cells stably expressing CB1. Real-time measurements of stimulation and inhibition of cAMP levels were made using a BRET biosensor. We found that the maximum concentration of SCRAs tested (10 µmol L-1 ), increased cAMP levels 12%-45% above that produced by FSK alone, while the phytocannabinoid THC did not significantly alter cAMP levels in PTX-treated HEK-CB1 cells. All SCRAs had greater potency to inhibit FSK-induced cAMP levels than to stimulate cAMP levels. The rank order of potencies for SCRA stimulation of cAMP (Gαs ) was PB-22 > 5F-MDMB-PICA > JWH-018 ≈ AB-FUBINACA > XLR-11. By contrast, the potency of SCRAs for inhibition of cAMP (Gαi/o ) was 5F-MDMB-PICA > AB-FUBINACA > PB-22 > JWH-018 > XLR-11. The different rank order of potency and EMax of the SCRAs to stimulate Gαs -like signaling compared to Gαi/o signaling suggests differences in G protein preference between SCRAs. Understanding the apparent differences among these drugs may contribute to unravelling their complex effects in humans.
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Affiliation(s)
- Shivani Sachdev
- Department of Biomedical SciencesMacquarie UniversitySydneyNSWAustralia
| | - Samuel D. Banister
- The Lambert Initiative for Cannabinoid Therapeutics, Brain and Mind CentreThe University of SydneySydneyNSWAustralia
- School of ChemistryThe University of SydneySydneyNSWAustralia
| | - Marina Santiago
- Department of Biomedical SciencesMacquarie UniversitySydneyNSWAustralia
| | - Chris Bladen
- Department of Biomedical SciencesMacquarie UniversitySydneyNSWAustralia
| | - Michael Kassiou
- School of ChemistryThe University of SydneySydneyNSWAustralia
| | - Mark Connor
- Department of Biomedical SciencesMacquarie UniversitySydneyNSWAustralia
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Abstract
This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, United States.
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Redmond WJ, Cawston EE, Grimsey NL, Stuart J, Edington AR, Glass M, Connor M. Identification of N-arachidonoyl dopamine as a highly biased ligand at cannabinoid CB1 receptors. Br J Pharmacol 2016; 173:115-27. [PMID: 26398720 PMCID: PMC4813372 DOI: 10.1111/bph.13341] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/09/2014] [Revised: 09/13/2015] [Accepted: 09/17/2015] [Indexed: 12/25/2022] Open
Abstract
BACKGROUND AND PURPOSE N-arachidonyl dopamine (NADA) has been identified as a putative endocannabinoid, but there is little information about which signalling pathways it activates. The purpose of this study was to identify the signalling pathways activated by NADA in vitro. EXPERIMENTAL APPROACH Human or rat cannabinoid CB1 receptors were expressed in AtT20, CHO or HEK 293 cells. NADA displacement of radiolabelled cannabinoids, and CB1 receptor mediated activation of K channels or ERK phosphorylation, release of intracellular calcium ([Ca]i ) and modulation of adenylyl cyclase were measured in addition to NADA effects on CB1 receptor trafficking. KEY RESULTS At concentrations up to 30 μM, NADA failed to activate any signalling pathways via CB1 receptors, with the exception of mobilization of [Ca]i . The elevations of [Ca]i were insensitive to pertussis toxin, and reduced or abolished by blockers of Gq /11 -dependent processes including U73122, thapsigargin and a peptide antagonist of Gq /11 activation. Prolonged NADA incubation produced modest loss of cell surface CB1 receptors. The prototypical cannabinoid agonist CP55940 signalled as expected in all assays. CONCLUSIONS AND IMPLICATIONS NADA is an ineffective agonist at most canonical cannabinoid receptor signalling pathways, but did promote mobilization of [Ca]i via Gq -dependent processes and some CB1 receptor trafficking. This signalling profile is distinct from that of any known cannabinoid, and suggests that NADA may have a unique spectrum of effects in vivo. Our results also indicate that it may be possible to identify highly biased CB1 receptor ligands displaying a subset of the pharmacological or therapeutic effects usually attributed to CB1 ligands.
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Affiliation(s)
- William J. Redmond
- Department of Biomedical Sciences, Faculty of Medicine and Health SciencesMacquarie UniversityNSW2109Australia
| | - Erin E. Cawston
- Department of Pharmacology and Clinical Pharmacology, and Centre for Brain ResearchUniversity of AucklandAucklandNew Zealand
| | - Natasha L. Grimsey
- Department of Pharmacology and Clinical Pharmacology, and Centre for Brain ResearchUniversity of AucklandAucklandNew Zealand
| | - Jordyn Stuart
- Department of Biomedical Sciences, Faculty of Medicine and Health SciencesMacquarie UniversityNSW2109Australia
| | - Amelia R. Edington
- Department of Biomedical Sciences, Faculty of Medicine and Health SciencesMacquarie UniversityNSW2109Australia
| | - Michelle Glass
- Department of Pharmacology and Clinical Pharmacology, and Centre for Brain ResearchUniversity of AucklandAucklandNew Zealand
| | - Mark Connor
- Department of Biomedical Sciences, Faculty of Medicine and Health SciencesMacquarie UniversityNSW2109Australia
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Jorgensen WT, Gulliver DW, Werry EL, Reekie T, Connor M, Kassiou M. Flexible analogues of WAY-267,464: Synthesis and pharmacology at the human oxytocin and vasopressin 1a receptors. Eur J Med Chem 2015; 108:730-740. [PMID: 26741855 DOI: 10.1016/j.ejmech.2015.11.050] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2015] [Revised: 11/30/2015] [Accepted: 11/30/2015] [Indexed: 12/31/2022]
Abstract
A previously identified, non-peptidic oxytocin (OT) receptor agonist WAY-267,464 (1) and nine novel derivatives (3, 4a-7a, 4b-7b) were synthesised and evaluated in vitro with the aim of systematically exploring hydrogen bonding interactions and ligand flexibility. All analogues were subjected to competition radioligand binding assays at human oxytocin (OT) and arginine vasopressin 1a (V1a) receptors. Physiological activity was determined using whole cell IP1 accumulation assays. Under these conditions, WAY-267,464 had higher affinity for the V1a receptor compared to the OT receptor (8.5x more selective) with poor functional selectivity (2x selective for OT receptor agonism over V1a receptor antagonism). Methylation of the resorcinol moiety (3) reversed the OT receptor pharmacological profile, removing agonist activity and inducing antagonist activity, without altering V1a receptor pharmacology. All flexible tethered derivatives removed OT receptor affinity and activity resulting in the generation of highly selective V1a receptor ligands.
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Affiliation(s)
| | - Damien W Gulliver
- School of Medical Sciences (Pharmacology), Bosch Institute, The University of Sydney, Sydney, NSW 2006, Australia
| | - Eryn L Werry
- Faculty of Health Sciences, The University of Sydney, Sydney, NSW 2006, Australia
| | - Tristan Reekie
- School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia
| | - Mark Connor
- Department of Biomedical Sciences, Faculty of Medicine and Health Sciences, Macquarie University, NSW 2109, Australia
| | - Michael Kassiou
- School of Chemistry, The University of Sydney, Sydney, NSW 2006, Australia; Faculty of Health Sciences, The University of Sydney, Sydney, NSW 2006, Australia.
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Fluorescence-based, high-throughput assays for μ-opioid receptor activation using a membrane potential-sensitive dye. Methods Mol Biol 2015; 1230:177-85. [PMID: 25293325 DOI: 10.1007/978-1-4939-1708-2_14] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/24/2022]
Abstract
The development of new and improved opioid analgesics requires high-throughput screening (HTS) methods to identify potential therapeutics from large libraries of lead compounds. Here we describe two simple, real-time fluorescence-based assays of μ-opioid receptor activation that may be scaled up for HTS. In AtT-20 cells expressing the μ-opioid receptor (MOPr), opioids activate endogenous G protein gated inwardly rectifying K channels (GIRK channels), leading to membrane hyperpolarization. In Chinese hamster ovary cells expressing MOPr, adenylyl cyclase activation via forskolin results in membrane hyperpolarization, which is inhibited by opioids. Changes in membrane potential can be measured using a proprietary membrane potential-sensitive dye. In contrast to many HTS methods currently available, these assays reflect naturalistic coupling of the receptor to effector molecules.
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Knapman A, Santiago M, Connor M. Buprenorphine signalling is compromised at the N40D polymorphism of the human μ opioid receptor in vitro. Br J Pharmacol 2015; 171:4273-88. [PMID: 24846673 DOI: 10.1111/bph.12785] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2014] [Revised: 05/02/2014] [Accepted: 05/03/2014] [Indexed: 12/11/2022] Open
Abstract
BACKGROUND AND PURPOSE There is significant variation in individual response to opioid drugs, which may result in inappropriate opioid therapy. Polymorphisms of the μ opioid receptor (MOP receptor) may contribute to individual variation in opioid response by affecting receptor function, and the effect may be ligand-specific. We sought to determine functional differences in MOP receptor signalling at several signalling pathways using a range of structurally distinct opioid ligands in cells expressing wild-type MOP receptors (MOPr-WT) and the commonly occurring MOP receptor variant, N40D. EXPERIMENTAL APPROACH MOPr-WT and MOPr-N40D were stably expressed in CHO cells and in AtT-20 cells. Assays of AC inhibition and ERK1/2 phosphorylation were performed on CHO cells, and assays of K activation were performed on AtT-20 cells. Signalling profiles for each ligand were compared between variants. KEY RESULTS Buprenorphine efficacy was reduced by over 50% at MOPr-N40D for AC inhibition and ERK1/2 phosphorylation. Buprenorphine potency was reduced threefold at MOPr-N40D for K channel activation. Pentazocine efficacy was reduced by 50% for G-protein-gated inwardly rectifying K channel activation at MOPr-N40D. No other differences were observed for any other ligands tested. CONCLUSIONS AND IMPLICATIONS The N40D variant is present in 10-50% of the population. Buprenorphine is a commonly prescribed opioid analgesic, and many individuals do not respond to buprenorphine therapy. This study demonstrates that buprenorphine signalling to several effectors via the N40D variant of MOP receptors is impaired, and this may have important consequences in a clinical setting for individuals carrying the N40D allele.
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Affiliation(s)
- Alisa Knapman
- Australian School of Advanced Medicine, Macquarie University, Sydney, NSW, Australia
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10
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Knapman A, Santiago M, Connor M. A6V polymorphism of the human μ-opioid receptor decreases signalling of morphine and endogenous opioids in vitro. Br J Pharmacol 2015; 172:2258-72. [PMID: 25521224 DOI: 10.1111/bph.13047] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2014] [Revised: 11/11/2014] [Accepted: 12/09/2014] [Indexed: 11/28/2022] Open
Abstract
BACKGROUND AND PURPOSE Polymorphisms of the μ opioid receptor (MOPr) may contribute to the variation in responses to opioid drugs in clinical and unregulated situations. The A6V variant of MOPr (MOPr-A6V) is present in up to 20% of individuals in some populations, and may be associated with heightened susceptibility to drug abuse. There are no functional studies examining the acute signalling of MOPr-A6V in vitro, so we investigated potential functional differences between MOPr and MOPr-A6V at several signalling pathways using structurally distinct opioid ligands. EXPERIMENTAL APPROACH CHO and AtT-20 cells stably expressing MOPr and MOPr-A6V were used. AC inhibition and ERK1/2 phosphorylation were assayed in CHO cells; K channel activation was assayed in AtT-20 cells. KEY RESULTS Buprenorphine did not inhibit AC or stimulate ERK1/2 phosphorylation in CHO cells expressing MOPr-A6V, but buprenorphine activation of K channels in AtT-20 cells was preserved. [D-Ala2, N-MePhe4, Gly-ol]-enkephalin, morphine and β-endorphin inhibition of AC was significantly reduced via MOPr-A6V, as was signalling of all opioids to ERK1/2. However, there was little effect of the A6V variant on K channel activation. CONCLUSIONS AND IMPLICATIONS Signalling to AC and ERK via the mutant MOPr-A6V was decreased for many opioids, including the clinically significant drugs morphine, buprenorphine and fentanyl, as well endogenous opioids. The MOPr-A6V variant is common and this compromised signalling may affect individual responses to opioid therapy, while the possible disruption of the endogenous opioid system may contribute to susceptibility to substance abuse.
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Affiliation(s)
- Alisa Knapman
- Australian School of Advanced Medicine, Macquarie University, Sydney, NSW, Australia
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Khroyan TV, Wu J, Polgar WE, Cami-Kobeci G, Fotaki N, Husbands SM, Toll L. BU08073 a buprenorphine analogue with partial agonist activity at μ-receptors in vitro but long-lasting opioid antagonist activity in vivo in mice. Br J Pharmacol 2014; 172:668-80. [PMID: 24903063 DOI: 10.1111/bph.12796] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2013] [Revised: 05/22/2014] [Accepted: 05/25/2014] [Indexed: 01/06/2023] Open
Abstract
BACKGROUND AND PURPOSE Buprenorphine is a potent analgesic with high affinity at μ, δ and κ and moderate affinity at nociceptin opioid (NOP) receptors. Nevertheless, NOP receptor activation modulates the in vivo activity of buprenorphine. Structure activity studies were conducted to design buprenorphine analogues with high affinity at each of these receptors and to characterize them in in vitro and in vivo assays. EXPERIMENTAL APPROACH Compounds were tested for binding affinity and functional activity using [(35) S]GTPγS binding at each receptor and a whole-cell fluorescent assay at μ receptors. BU08073 was evaluated for antinociceptive agonist and antagonist activity and for its effects on anxiety in mice. KEY RESULTS BU08073 bound with high affinity to all opioid receptors. It had virtually no efficacy at δ, κ and NOP receptors, whereas at μ receptors, BU08073 has similar efficacy as buprenorphine in both functional assays. Alone, BU08073 has anxiogenic activity and produces very little antinociception. However, BU08073 blocks morphine and U50,488-mediated antinociception. This blockade was not evident at 1 h post-treatment, but is present at 6 h and remains for up to 3-6 days. CONCLUSIONS AND IMPLICATIONS These studies provide structural requirements for synthesis of 'universal' opioid ligands. BU08073 had high affinity for all the opioid receptors, with moderate efficacy at μ receptors and reduced efficacy at NOP receptors, a profile suggesting potential analgesic activity. However, in vivo, BU08073 had long-lasting antagonist activity, indicating that its pharmacokinetics determined both the time course of its effects and what receptor-mediated effects were observed. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.
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12
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Knapman A, Connor M. Cellular signalling of non-synonymous single-nucleotide polymorphisms of the human μ-opioid receptor (OPRM1). Br J Pharmacol 2014; 172:349-63. [PMID: 24527749 DOI: 10.1111/bph.12644] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2013] [Revised: 01/21/2014] [Accepted: 02/07/2014] [Indexed: 12/15/2022] Open
Abstract
UNLABELLED There is significant variability in individual responses to opioid drugs, which is likely to have a significant genetic component. A number of non-synonymous single-nucleotide polymorphisms (SNPs) in the coding regions of the μ-opioid receptor gene (OPRM1) have been postulated to contribute to this variability. Although many studies have investigated the clinical influences of these μ-opioid receptor variants, the outcomes are reported in the context of thousands of other genes and environmental factors, and we are no closer to being able to predict individual response to opioids based on genotype. Investigation of how μ-opioid receptor SNPs affect their expression, coupling to second messengers, desensitization and regulation is necessary to understand how subtle changes in receptor structure can impact individual responses to opioids. To date, the few functional studies that have investigated the consequences of SNPs on the signalling profile of the μ-opioid receptor in vitro have shown that the common N40D variant has altered functional responses to some opioids, while other, rarer, variants display altered signalling or agonist-dependent regulation. Here, we review the data available on the effects of μ-opioid receptor polymorphisms on receptor function, expression and regulation in vitro, and discuss the limitations of the studies to date. Whether or not μ-opioid receptor SNPs contribute to individual variability in opioid responses remains an open question, in large part because we have relatively little good data about how the amino acid changes affect μ-opioid receptor function. LINKED ARTICLES This article is part of a themed section on Opioids: New Pathways to Functional Selectivity. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2015.172.issue-2.
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Affiliation(s)
- Alisa Knapman
- Australian School of Advanced Medicine, Macquarie University, Sydney, NSW, Australia
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