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Natale CA, Christie MJ, Aubrey KR. Spinal glycinergic currents are reduced in a rat model of neuropathic pain following partial nerve ligation but not chronic constriction injury. J Neurophysiol 2023; 129:333-341. [PMID: 36541621 DOI: 10.1152/jn.00451.2022] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
Animal models have consistently indicated that central sensitization and the development of chronic neuropathic pain are linked to changes to inhibitory signaling in the dorsal horn of the spinal cord. However, replication of data investigating the cellular mechanisms that underlie these changes remains a challenge and there is still a lack of understanding about what aspects of spinal inhibitory transmission most strongly contribute to the disease. Here, we compared the effect of two different sciatic nerve injuries commonly used to generate rodent models of neuropathic pain on spinal glycinergic signaling. Using whole cell patch-clamp electrophysiology in spinal slices, we recorded from neurons in the lamina II of the dorsal horn and evoked inhibitory postsynaptic currents with a stimulator in lamina III, where glycinergic cell bodies are concentrated. We found that glycine inputs onto radial neurons were reduced following partial nerve ligation (PNL) of the sciatic nerve, consistent with a previous report. However, this finding was not replicated in animals that underwent chronic constriction injury (CCI) to the same nerve region. To limit the between-experiment variability, we kept the rat species, sex, and age consistent and had a single investigator carry out the surgeries. These data show that PNL and CCI cause divergent spinal signaling outcomes in the cord and add to the body of evidence suggesting that treatments for neuropathic pain should be triaged according to nerve injury or cellular dysfunction rather than the symptoms of the disease.NEW & NOTEWORTHY Neuropathic pain models are used in preclinical research to investigate the mechanisms underlying allodynia, a common symptom of neuropathic pain, and to test, develop, and validate therapies for persistent pain. We demonstrate that a glycinergic dysfunction is consistently associated with partial nerve ligation but not the chronic constriction injury model. This suggests that the cellular effects produced by each injury are distinct and that data from different neuropathic pain models should be considered separately.
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Affiliation(s)
- Claudia A Natale
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales, Australia
| | - Macdonald J Christie
- School of Medical Sciences, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales, Australia
| | - Karin R Aubrey
- Pain Management Research, Kolling Institute, Royal North Shore Hospital, St Leonards, New South Wales, Australia.,Northern Clinical School, Faculty of Medicine and Health, University of Sydney, Camperdown, New South Wales, Australia
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2
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Wilson BS, Peiser-Oliver J, Gillis A, Evans S, Alamein C, Mostyn SN, Shimmon S, Rawling T, Christie MJ, Vandenberg RJ, Mohammadi SA. Peripheral administration of selective GlyT2 inhibitor, oleoyl-D-lysine, reverses chronic neuropathic pain but not acute or inflammatory pain in mice. J Pharmacol Exp Ther 2022; 382:246-255. [PMID: 35779948 DOI: 10.1124/jpet.122.001265] [Citation(s) in RCA: 2] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2022] [Accepted: 06/13/2022] [Indexed: 11/22/2022] Open
Abstract
Aberrations in spinal glycinergic signalling are a feature of pain chronification. Normalising these changes by inhibiting glycine transporter-2 (GlyT2) is a promising treatment strategy. However, existing GlyT2 inhibitors e.g. ORG25543 are limited by narrow therapeutic windows and severe dose-limiting side effects such as convulsions, and are therefore poor candidates for clinical development. Here, intraperitoneally administered oleoyl-D-lysine, a lipid-based GlyT2 inhibitor, was characterised in mouse models of acute (hotplate), inflammatory (CFA) and chronic neuropathic (CCI) pain. Side effects were also assessed on a numerical rating score, convulsions score, for motor incoordination (rotarod) and for respiratory depression (whole body plethysmography). Oleoyl-D-lysine produced near complete anti-allodynia for chronic neuropathic pain but no anti-allodynia/analgesia in inflammatory or acute pain. No side effects were seen at the peak analgesic dose, 30 mg/kg. Mild side effects were observed at the highest dose, 100 mg/kg, on the numerical rating score, but no convulsions. These results contrasted markedly with ORG25543, which reached less than 50% reduction in allodynia score only at the lethal/near-lethal dose of 50 mg/kg. At this dose, ORG25543 caused maximal side effects on the numerical rating score and severe convulsions. Oleoyl-D-lysine (30 mg/kg) did not cause any respiratory depression, a problematic side effect of opiates. These results show the safe and effective reversal of neuropathic pain in mice by oleoyl-D-lysine and provide evidence for a distinct role of glycine in chronic pain over acute or short-term pain conditions. Significance Statement Partially inhibiting GlyT2 can alleviate chronic pain by restoring lost glycinergic function. Novel lipid-based GlyT2 inhibitor, ol-D-lys, is safe and effective in alleviating neuropathic pain, but not inflammatory or acute pain. Clinical application of GlyT2 inhibitors may be better suited to chronic neuropathic pain over other pain aetiologies.
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Affiliation(s)
| | | | | | | | | | | | | | | | | | | | - Sarasa A Mohammadi
- Discipline of Pharmacology, Sydney Pharmacy School, The University of Sydney, Australia
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Inhibition of Glycine Re-Uptake: A Potential Approach for Treating Pain by Augmenting Glycine-Mediated Spinal Neurotransmission and Blunting Central Nociceptive Signaling. Biomolecules 2021; 11:biom11060864. [PMID: 34200954 PMCID: PMC8230656 DOI: 10.3390/biom11060864] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/24/2021] [Revised: 06/07/2021] [Accepted: 06/08/2021] [Indexed: 12/23/2022] Open
Abstract
Among the myriad of cellular and molecular processes identified as contributing to pathological pain, disinhibition of spinal cord nociceptive signaling to higher cortical centers plays a critical role. Importantly, evidence suggests that impaired glycinergic neurotransmission develops in the dorsal horn of the spinal cord in inflammatory and neuropathic pain models and is a key maladaptive mechanism causing mechanical hyperalgesia and allodynia. Thus, it has been hypothesized that pharmacological agents capable of augmenting glycinergic tone within the dorsal horn may be able to blunt or block aberrant nociceptor signaling to the brain and serve as a novel class of analgesics for various pathological pain states. Indeed, drugs that enhance dysfunctional glycinergic transmission, and in particular inhibitors of the glycine transporters (GlyT1 and GlyT2), are generating widespread interest as a potential class of novel analgesics. The GlyTs are Na+/Cl−-dependent transporters of the solute carrier 6 (SLC6) family and it has been proposed that the inhibition of them presents a possible mechanism by which to increase spinal extracellular glycine concentrations and enhance GlyR-mediated inhibitory neurotransmission in the dorsal horn. Various inhibitors of both GlyT1 and GlyT2 have demonstrated broad analgesic efficacy in several preclinical models of acute and chronic pain, providing promise for the approach to deliver a first-in-class non-opioid analgesic with a mechanism of action differentiated from current standard of care. This review will highlight the therapeutic potential of GlyT inhibitors as a novel class of analgesics, present recent advances reported for the field, and discuss the key challenges associated with the development of a GlyT inhibitor into a safe and effective agent to treat pain.
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Pharmacological Evidence on Augmented Antiallodynia Following Systemic Co-Treatment with GlyT-1 and GlyT-2 Inhibitors in Rat Neuropathic Pain Model. Int J Mol Sci 2021; 22:ijms22052479. [PMID: 33804568 PMCID: PMC7957511 DOI: 10.3390/ijms22052479] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2020] [Revised: 02/19/2021] [Accepted: 02/25/2021] [Indexed: 12/16/2022] Open
Abstract
The limited effect of current medications on neuropathic pain (NP) has initiated large efforts to develop effective treatments. Animal studies showed that glycine transporter (GlyT) inhibitors are promising analgesics in NP, though concerns regarding adverse effects were raised. We aimed to study NFPS and Org-25543, GlyT-1 and GlyT-2 inhibitors, respectively and their combination in rat mononeuropathic pain evoked by partial sciatic nerve ligation. Cerebrospinal fluid (CSF) glycine content was also determined by capillary electrophoresis. Subcutaneous (s.c.) 4 mg/kg NFPS or Org-25543 showed analgesia following acute administration (30-60 min). Small doses of each compound failed to produce antiallodynia up to 180 min after the acute administration. However, NFPS (1 mg/kg) produced antiallodynia after four days of treatment. Co-treatment with subanalgesic doses of NFPS (1 mg/kg) and Org-25543 (2 mg/kg) produced analgesia at 60 min and thereafter meanwhile increased significantly the CSF glycine content. This combination alleviated NP without affecting motor function. Test compounds failed to activate G-proteins in spinal cord. To the best of our knowledge for the first time we demonstrated augmented analgesia by combining GlyT-1 and 2 inhibitors. Increased CSF glycine content supports involvement of glycinergic system. Combining selective GlyT inhibitors or developing non-selective GlyT inhibitors might have therapeutic value in NP.
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Imam MZ, Kuo A, Nicholson JR, Corradini L, Smith MT. Assessment of the anti-allodynic efficacy of a glycine transporter 2 inhibitor relative to pregabalin and duloxetine in a rat model of prostate cancer-induced bone pain. Pharmacol Rep 2020; 72:1418-1425. [PMID: 32715433 DOI: 10.1007/s43440-020-00145-8] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Revised: 07/16/2020] [Accepted: 07/18/2020] [Indexed: 12/12/2022]
Abstract
BACKGROUND The pathobiology of prostate cancer-induced bone pain (PCIBP) is underpinned by both inflammatory and neuropathic components. Here, we used a rat model of PCIBP to assess the analgesic efficacy of a glycine transporter 2 (GlyT2) inhibitor (N-(6-((1,3-dihydroxypropan-2-yl)amino)-2-(dimethylamino)pyridin-3-yl)-3,5-dimethoxy-4-(4-(trifluoromethyl)phenoxy) benzamide) relative to two clinically available adjuvant drugs that are recommended for the relief of neuropathic pain, viz, pregabalin and duloxetine. METHODS PCIBP was induced in male Wistar Han rats following intra-tibial injection (ITI) of rat prostate cancer (AT3B) cells into the left tibia. Sham-rats received an ITI of heat-killed AT3B cells. PCIBP rats with fully developed mechanical allodynia in the ipsilateral hindpaws as assessed using von Frey filaments, received single oral (p.o.) bolus doses of the GlyT2 inhibitor (3-30 mg/kg), pregabalin (3-100 mg/kg), duloxetine (3-100 mg/kg), or vehicle. Baseline paw withdrawal thresholds (PWTs) were determined in the ipsilateral (injured side) and contralateral hindpaws immediately prior to dosing and at scheduled times for 3 h post dosing in individual animals. RESULTS Single oral bolus doses of the GlyT2 inhibitor (3-30 mg/kg) evoked partial pain relief at the doses tested in the ipsilateral hindpaws of PCIBP rats without any discernible behavioural side effects. By contrast, single oral bolus doses of pregabalin at 10-100 mg/kg evoked dose-dependent and complete alleviation of mechanical allodynia. By comparison, single oral bolus doses of duloxetine at doses up to 100 mg/kg lacked efficacy. CONCLUSION Oral administration of this GlyT2 inhibitor evoked partial pain relief in PCIBP rats and did not evoke central nervous system side effects in contrast to GlyT2 inhibitors reported by others.
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Affiliation(s)
- Mohammad Zafar Imam
- Centre for Integrated Preclinical Drug Development, School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, Brisbane, QLD, Australia
| | - Andy Kuo
- Centre for Integrated Preclinical Drug Development, School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, Brisbane, QLD, Australia
| | | | - Laura Corradini
- Boehringer Ingelheim Pharma GmbH and Co. KG, Biberach, Germany
| | - Maree T Smith
- Centre for Integrated Preclinical Drug Development, School of Biomedical Sciences, Faculty of Medicine, The University of Queensland, Brisbane, QLD, Australia.
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de Bartolomeis A, Manchia M, Marmo F, Vellucci L, Iasevoli F, Barone A. Glycine Signaling in the Framework of Dopamine-Glutamate Interaction and Postsynaptic Density. Implications for Treatment-Resistant Schizophrenia. Front Psychiatry 2020; 11:369. [PMID: 32477178 PMCID: PMC7240307 DOI: 10.3389/fpsyt.2020.00369] [Citation(s) in RCA: 21] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/22/2020] [Accepted: 04/14/2020] [Indexed: 12/14/2022] Open
Abstract
Treatment-resistant schizophrenia (TRS) or suboptimal response to antipsychotics affects almost 30% of schizophrenia (SCZ) patients, and it is a relevant clinical issue with significant impact on the functional outcome and on the global burden of disease. Among putative novel treatments, glycine-centered therapeutics (i.e. sarcosine, glycine itself, D-Serine, and bitopertin) have been proposed, based on a strong preclinical rationale with, however, mixed clinical results. Therefore, a better appraisal of glycine interaction with the other major players of SCZ pathophysiology and specifically in the framework of dopamine - glutamate interactions is warranted. New methodological approaches at cutting edge of technology and drug discovery have been applied to study the role of glycine in glutamate signaling, both at presynaptic and post-synaptic level and have been instrumental for unveiling the role of glycine in dopamine-glutamate interaction. Glycine is a non-essential amino acid that plays a critical role in both inhibitory and excitatory neurotransmission. In caudal areas of central nervous system (CNS), such as spinal cord and brainstem, glycine acts as a powerful inhibitory neurotransmitter through binding to its receptor, i.e. the Glycine Receptor (GlyR). However, glycine also works as a co-agonist of the N-Methyl-D-Aspartate receptor (NMDAR) in excitatory glutamatergic neurotransmission. Glycine concentration in the synaptic cleft is finely tuned by glycine transporters, i.e. GlyT1 and GlyT2, that regulate the neurotransmitter's reuptake, with the first considered a highly potential target for psychosis therapy. Reciprocal regulation of dopamine and glycine in forebrain, glycine modulation of glutamate, glycine signaling interaction with postsynaptic density proteins at glutamatergic synapse, and human genetics of glycinergic pathways in SCZ are tackled in order to highlight the exploitation of this neurotransmitters and related molecules in SCZ and TRS.
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Affiliation(s)
- Andrea de Bartolomeis
- Laboratory of Molecular Psychiatry and Translational Psychiatry, Unit of Treatment Resistant Psychosis, Section of Psychiatry, Department of Neuroscience, Reproductive Science and Odontostomatology, University School of Medicine of Napoli Federico II, Naples, Italy
| | - Mirko Manchia
- Section of Psychiatry, Department of Medical Science and Public Health, University of Cagliari, Cagliari, Italy.,Department of Pharmacology, Dalhousie University, Halifax, NS, Canada
| | - Federica Marmo
- Laboratory of Molecular Psychiatry and Translational Psychiatry, Unit of Treatment Resistant Psychosis, Section of Psychiatry, Department of Neuroscience, Reproductive Science and Odontostomatology, University School of Medicine of Napoli Federico II, Naples, Italy
| | - Licia Vellucci
- Laboratory of Molecular Psychiatry and Translational Psychiatry, Unit of Treatment Resistant Psychosis, Section of Psychiatry, Department of Neuroscience, Reproductive Science and Odontostomatology, University School of Medicine of Napoli Federico II, Naples, Italy
| | - Felice Iasevoli
- Laboratory of Molecular Psychiatry and Translational Psychiatry, Unit of Treatment Resistant Psychosis, Section of Psychiatry, Department of Neuroscience, Reproductive Science and Odontostomatology, University School of Medicine of Napoli Federico II, Naples, Italy
| | - Annarita Barone
- Laboratory of Molecular Psychiatry and Translational Psychiatry, Unit of Treatment Resistant Psychosis, Section of Psychiatry, Department of Neuroscience, Reproductive Science and Odontostomatology, University School of Medicine of Napoli Federico II, Naples, Italy
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7
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Al-Khrasani M, Mohammadzadeh A, Balogh M, Király K, Barsi S, Hajnal B, Köles L, Zádori ZS, Harsing LG. Glycine transporter inhibitors: A new avenue for managing neuropathic pain. Brain Res Bull 2019; 152:143-158. [PMID: 31302238 DOI: 10.1016/j.brainresbull.2019.07.008] [Citation(s) in RCA: 26] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/21/2019] [Revised: 06/27/2019] [Accepted: 07/08/2019] [Indexed: 12/12/2022]
Abstract
Interneurons operating with glycine neurotransmitter are involved in the regulation of pain transmission in the dorsal horn of the spinal cord. In addition to interneurons, glycine release also occurs from glial cells neighboring glutamatergic synapses in the spinal cord. Neuronal and glial release of glycine is controlled by glycine transporters (GlyTs). Inhibitors of the two isoforms of GlyTs, the astrocytic type-1 (GlyT-1) and the neuronal type-2 (GlyT-2), decrease pain sensation evoked by injuries of peripheral sensory neurons or inflammation. The function of dorsal horn glycinergic interneurons has been suggested to be reduced in neuropathic pain, which can be reversed by GlyT-2 inhibitors (Org-25543, ALX1393). Several lines of evidence also support that peripheral nerve damage or inflammation may shift glutamatergic neurochemical transmission from N-methyl-D aspartate (NMDA) NR1/NR2A receptor- to NR1/NR2B receptor-mediated events (subunit switch). This pathological overactivation of NR1/NR2B receptors can be reduced by GlyT-1 inhibitors (NFPS, Org-25935), which decrease excessive glycine release from astroglial cells or by selective antagonists of NR2B subunits (ifenprodil, Ro 25-6981). Although several experiments suggest that GlyT inhibitors may represent a novel strategy in the control of neuropathic pain, proving this concept in human beings is hampered by lack of clinically applicable GlyT inhibitors. We also suggest that drugs inhibiting both GlyT-1 and GlyT-2 non-selectively and reversibly, may favorably target neuropathic pain. In this paper we overview inhibitors of the two isoforms of GlyTs as well as the effects of these drugs in experimental models of neuropathic pain. In addition, the possible mechanisms of action of the GlyT inhibitors, i.e. how they affect the neurochemical and pain transmission in the spinal cord, are also discussed. The growing evidence for the possible therapeutic intervention of neuropathic pain by GlyT inhibitors further urges development of drugable compounds, which may beneficially restore impaired pain transmission in various neuropathic conditions.
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Affiliation(s)
- Mahmoud Al-Khrasani
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary.
| | - Amir Mohammadzadeh
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - Mihály Balogh
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - Kornél Király
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - Szilvia Barsi
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - Benjamin Hajnal
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - László Köles
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - Zoltán S Zádori
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
| | - Laszlo G Harsing
- Department of Pharmacology and Pharmacotherapy, Faculty of Medicine, Semmelweis University, Nagyvarad ter 4, P.O. Box 370, H-1445 Budapest, Hungary
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8
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Fratev F, Miranda-Arango M, Lopez AB, Padilla E, Sirimulla S. Discovery of GlyT2 Inhibitors Using Structure-Based Pharmacophore Screening and Selectivity Studies by FEP+ Calculations. ACS Med Chem Lett 2019; 10:904-910. [PMID: 31223446 PMCID: PMC6580377 DOI: 10.1021/acsmedchemlett.9b00003] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2019] [Accepted: 05/21/2019] [Indexed: 12/23/2022] Open
Abstract
In recent years, mammalian Glycine transporter 2 (GlyT2) has emerged as a promising target for the development of compounds against chronic pain states. In our current work, we discovered a new set of promising hits that inhibit the glycine transporter at nano- and micromolar activity and have excellent selectivity over GlyT1 (as shown by in vitro studies) using a newly designed virtual screening (VS) protocol that combines a structure-based pharmacophore and docking screens with a success rate of 75%. Furthermore, the free energy perturbation calculations and molecular dynamics (MD) studies revealed the GlyT2 amino acid residues critical for the binding and selectivity of both Glycine and our Hit1 compound. The FEP+ results well-matched with the available literature mutational data proving the quality of the generated GlyT2 structure. On the basis of these results, we propose that our hit compounds may lead to new chronic pain agents to address unmet and challenging clinical needs.
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Affiliation(s)
- Filip Fratev
- Department
of Pharmaceutical Sciences, School of Pharmacy, The University of Texas at El Paso, El Paso, Texas 79968, United States
- Micar21 Ltd., Persenk 34B, 1407 Sofia, Bulgaria
| | - Manuel Miranda-Arango
- Department
of Biological Sciences, The University of
Texas at El Paso, 500 West University Avenue, El Paso, Texas 79902, United States
| | - Ashley Bryan Lopez
- Department
of Biological Sciences, The University of
Texas at El Paso, 500 West University Avenue, El Paso, Texas 79902, United States
| | - Elvia Padilla
- Department
of Biological Sciences, The University of
Texas at El Paso, 500 West University Avenue, El Paso, Texas 79902, United States
| | - Suman Sirimulla
- Department
of Pharmaceutical Sciences, School of Pharmacy, The University of Texas at El Paso, El Paso, Texas 79968, United States
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9
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Mostyn SN, Rawling T, Mohammadi S, Shimmon S, Frangos ZJ, Sarker S, Yousuf A, Vetter I, Ryan RM, Christie MJ, Vandenberg RJ. Development of an N-Acyl Amino Acid That Selectively Inhibits the Glycine Transporter 2 To Produce Analgesia in a Rat Model of Chronic Pain. J Med Chem 2019; 62:2466-2484. [PMID: 30714733 DOI: 10.1021/acs.jmedchem.8b01775] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Inhibitors that target the glycine transporter 2, GlyT2, show promise as analgesics, but may be limited by their toxicity through complete or irreversible binding. Acyl-glycine inhibitors, however, are selective for GlyT2 and have been shown to provide analgesia in animal models of pain with minimal side effects, but are comparatively weak GlyT2 inhibitors. Here, we modify the simple acyl-glycine by synthesizing lipid analogues with a range of amino acid head groups in both l- and d-configurations, to produce nanomolar affinity, selective GlyT2 inhibitors. The potent inhibitor oleoyl-d-lysine (33) is also resistant to degradation in both human and rat plasma and liver microsomes, and is rapidly absorbed following an intraperitoneal injection to rats and readily crosses the blood-brain barrier. We demonstrate that 33 provides greater analgesia at lower doses, and does not possess the severe side effects of the very slowly reversible GlyT2 inhibitor, ORG25543 (2).
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Affiliation(s)
- Shannon N Mostyn
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Tristan Rawling
- School of Mathematical and Physical Sciences, Faculty of Science , The University of Technology Sydney , Sydney , NSW 2007 , Australia
| | - Sarasa Mohammadi
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Susan Shimmon
- School of Mathematical and Physical Sciences, Faculty of Science , The University of Technology Sydney , Sydney , NSW 2007 , Australia
| | - Zachary J Frangos
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Subhodeep Sarker
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Arsalan Yousuf
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Irina Vetter
- Institute for Molecular Bioscience & School of Pharmacy , The University of Queensland , Brisbane , Qld 4072 , Australia
| | - Renae M Ryan
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Macdonald J Christie
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
| | - Robert J Vandenberg
- Discipline of Pharmacology, School of Medical Sciences , University of Sydney , Sydney , NSW 2006 , Australia
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10
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Zeilhofer HU, Acuña MA, Gingras J, Yévenes GE. Glycine receptors and glycine transporters: targets for novel analgesics? Cell Mol Life Sci 2018; 75:447-465. [PMID: 28791431 PMCID: PMC11105467 DOI: 10.1007/s00018-017-2622-x] [Citation(s) in RCA: 49] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2017] [Revised: 07/14/2017] [Accepted: 08/04/2017] [Indexed: 01/29/2023]
Abstract
Glycinergic neurotransmission has long been known for its role in spinal motor control. During the last two decades, additional functions have become increasingly recognized-among them is a critical contribution to spinal pain processing. Studies in rodent pain models provide proof-of-concept evidence that enhancing inhibitory glycinergic neurotransmission reduces chronic pain symptoms. Apparent strategies for pharmacological intervention include positive allosteric modulators of glycine receptors and modulators or inhibitors of the glial and neuronal glycine transporters GlyT1 and GlyT2. These prospects have led to drug discovery efforts in academia and in industry aiming at compounds that target glycinergic neurotransmission with high specificity. Available data show promising analgesic efficacy. Less is currently known about potential unwanted effects but the presence of glycinergic innervation in CNS areas outside the nociceptive system prompts for a careful evaluation not only of motor function, but also of potential respiratory impairment and addictive properties.
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Affiliation(s)
- Hanns Ulrich Zeilhofer
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland.
- Institute of Pharmaceutical Sciences, Swiss Federal Institute of Technology (ETH) Zürich, Vladimir-Prelog-Weg 1-5/10, 8093, Zurich, Switzerland.
| | - Mario A Acuña
- Institute of Pharmacology and Toxicology, University of Zurich, Winterthurerstrasse 190, 8057, Zurich, Switzerland
| | | | - Gonzalo E Yévenes
- Department of Physiology, University of Concepción, Concepción, Chile
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11
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Cioffi CL. Modulation of Glycine-Mediated Spinal Neurotransmission for the Treatment of Chronic Pain. J Med Chem 2017; 61:2652-2679. [PMID: 28876062 DOI: 10.1021/acs.jmedchem.7b00956] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
Chronic pain constitutes a significant and expanding worldwide health crisis. Currently available analgesics poorly serve individuals suffering from chronic pain, and new therapeutic agents that are more effective, safer, and devoid of abuse liabilities are desperately needed. Among the myriad of cellular and molecular processes contributing to chronic pain, spinal disinhibition of pain signaling to higher cortical centers plays a critical role. Accumulating evidence shows that glycinergic inhibitory neurotransmission in the spinal cord dorsal horn gates nociceptive signaling, is essential in maintaining physiological pain sensitivity, and is diminished in pathological pain states. Thus, it is hypothesized that agents capable of enhancing glycinergic tone within the dorsal horn could obtund nociceptor signaling to the brain and serve as analgesics for persistent pain. This Perspective highlights the potential that pharmacotherapies capable of increasing inhibitory spinal glycinergic neurotransmission hold in providing new and transformative analgesic therapies for the treatment of chronic pain.
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Affiliation(s)
- Christopher L Cioffi
- Departments of Basic and Clinical Sciences and Pharmaceutical Sciences , Albany College of Pharmacy and Health Sciences , 106 New Scotland Avenue , Albany , New York 12208 United States
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12
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Glycinergic transmission: glycine transporter GlyT2 in neuronal pathologies. Neuronal Signal 2016; 1:NS20160009. [PMID: 32714574 PMCID: PMC7377260 DOI: 10.1042/ns20160009] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/14/2016] [Revised: 11/04/2016] [Accepted: 11/09/2016] [Indexed: 11/17/2022] Open
Abstract
Glycinergic neurons are major contributors to the regulation of neuronal excitability, mainly in caudal areas of the nervous system. These neurons control fluxes of sensory information between the periphery and the CNS and diverse motor activities like locomotion, respiration or vocalization. The phenotype of a glycinergic neuron is determined by the expression of at least two proteins: GlyT2, a plasma membrane transporter of glycine, and VIAAT, a vesicular transporter shared by glycine and GABA. In this article, we review recent advances in understanding the role of GlyT2 in the pathophysiology of inhibitory glycinergic neurotransmission. GlyT2 mutations are associated to decreased glycinergic function that results in a rare movement disease termed hyperekplexia (HPX) or startle disease. In addition, glycinergic neurons control pain transmission in the dorsal spinal cord and their function is reduced in chronic pain states. A moderate inhibition of GlyT2 may potentiate glycinergic inhibition and constitutes an attractive target for pharmacological intervention against these devastating conditions.
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Glycine transporter2 inhibitors: Getting the balance right. Neurochem Int 2015; 98:89-93. [PMID: 26723543 DOI: 10.1016/j.neuint.2015.12.007] [Citation(s) in RCA: 18] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2015] [Revised: 11/13/2015] [Accepted: 12/18/2015] [Indexed: 12/28/2022]
Abstract
Neurotransmitter transporters are targets for a wide range of therapeutically useful drugs. This is because they have the capacity to selectively manipulate the dynamics of neurotransmitter concentrations and thereby enhance or diminish signalling through particular brain pathways. High affinity glycine transporters (GlyTs) regulate extracellular concentrations of glycine and provide novel therapeutic targets for neurological disorders.
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