Glutamatergic mechanisms in l-DOPA-induced dyskinesia and therapeutic implications

4'-fluorocannabidiol associated with capsazepine restrains L-DOPA-induced dyskinesia in hemiparkinsonian mice: Contribution of anti-inflammatory and anti-glutamatergic mechanisms

We tested the efficacy of 4'-fluorocannabidiol (4'-F-CBD), a semisynthetic cannabidiol derivative, and HU-910, a cannabinoid receptor 2 (CB2) agonist in resolving l-DOPA-induced dyskinesia (LID). Specifically, we were interested in studying whether these compounds could restrain striatal inflammatory responses and rescue glutamatergic disturbances characteristic of the dyskinetic state. C57BL/6 mice were rendered hemiparkinsonian by unilateral striatal lesioning with 6-OHDA. Abnormal involuntary movements were then induced by repeated i.p. injections of l-DOPA + benserazide. After LID was installed, the effects of a 3-day treatment with 4'-F-CBD or HU-910 in combination or not with the TRPV1 antagonist capsazepine (CPZ) or CB2 agonists HU-308 and JWH015 were assessed. Immunostaining was conducted to investigate the impacts of 4'-F-CBD and HU-910 (with CPZ) on inflammation and glutamatergic synapses. Our results showed that the combination of 4'-F-CBD + CPZ, but not when administered alone, decreased LID. Neither HU-910 alone nor HU-910+CPZ were effective. The CB2 agonists HU-308 and JWH015 were also ineffective in decreasing LID. Both combination treatments efficiently reduced microglial and astrocyte activation in the dorsal striatum of dyskinetic mice. However, only 4'-F-CBD + CPZ normalized the density of glutamate vesicular transporter-1 (vGluT1) puncta colocalized with the postsynaptic density marker PSD95. These findings suggest that 4'-F-CBD + CPZ normalizes dysregulated cortico-striatal glutamatergic inputs, which could be involved in their anti-dyskinetic effects. Although it is not possible to rule out the involvement of anti-inflammatory mechanisms, the decrease in striatal neuroinflammation markers by 4'-F-CBD and HU-910 without an associated reduction in LID indicates that they are insufficient per se to prevent LID manifestations.

Suppression of presynaptic corticostriatal glutamate activity attenuates L-dopa-induced dyskinesia in 6-OHDA-lesioned Parkinson's disease mice

A common adverse effect of Parkinson's disease (PD) treatment is L-dopa-induced dyskinesia (LID). This condition results from both dopamine (DA)-dependent and DA-independent mechanisms, as glutamate inputs from corticostriatal projection neurons impact DA-responsive medium spiny neurons in the striatum to cause the dyskinetic behaviors. In this study, we explored whether suppression of presynaptic corticostriatal glutamate inputs might affect the behavioral and biochemical outcomes associated with LID. We first established an animal model in which 6-hydroxydopamine (6-OHDA)-lesioned mice were treated daily with L-dopa (10 mg/kg, i.p.) for 2 weeks; these mice developed stereotypical abnormal involuntary movements (AIMs). When the mice were pretreated with the NMDA antagonist, amantadine, we observed suppression of AIMs and reductions of phosphorylated ERK1/2 and NR2B in the striatum. We then took an optogenetic approach to manipulate glutamatergic activity. Slc17a6 (vGluT2)-Cre mice were injected with pAAV5-Ef1a-DIO-eNpHR3.0-mCherry and received optic fiber implants in either the M1 motor cortex or dorsolateral striatum. Optogenetic inactivation at either optic fiber implant location could successfully reduce the intensity of AIMs after 6-OHDA lesioning and L-dopa treatment. Both optical manipulation strategies also suppressed phospho-ERK1/2 and phospho-NR2B signals in the striatum. Finally, we performed intrastriatal injections of LDN 212320 in the dyskenesic mice to enhance expression of glutamate uptake transporter GLT-1. Sixteen hours after the LDN 212320 treatment, L-dopa-induced AIMs were reduced along with the levels of striatal phospho-ERK1/2 and phospho-NR2B. Together, our results affirm a critical role of corticostriatal glutamate neurons in LID and strongly suggest that diminishing synaptic glutamate, either by suppression of neuronal activity or by upregulation of GLT-1, could be an effective approach for managing LID.

Metabotropic Glutamate Receptor 4 (mGlu4) Positive Allosteric Modulators Lack Efficacy in Rat and Marmoset Models of L-DOPA-Induced Dyskinesia

Background

Increased activity across corticostriatal glutamatergic synapses may contribute to L-DOPA-induced dyskinesia in Parkinson's disease. Given the weak efficacy and side-effect profile of amantadine, alternative strategies to reduce glutamate transmission are being investigated. Metabotropic glutamate receptor 4 (mGlu4) is a promising target since its activation would reduce glutamate release.

Objective

We hypothesized that two mGlu4 positive allosteric modulators, Lu AF21934 ((1 S,2 R)-N1-(3,4-dichlorophenyl)cyclohexane-1,2-dicarboxamide) and ADX88178 (5-Methyl-N-(4-methylpyrimidin-2-yl)-4-(1H-pyrazol-4-yl)thiazol-2-amine), would provide relief in rat and primate models of L-DOPA-induced dyskinesia.

Methods

The ability of Lu AF21934 or ADX88178 to reverse pre-established dyskinesia was examined in L-DOPA-primed 6-hydroxydopamine-lesioned rats expressing abnormal involuntary movements (AIMs) or in 1-methyl-4-phenyl,1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets expressing L-DOPA-induced dyskinesia. Additionally, the ability of Lu AF21934 to prevent the development of de novo L-DOPA-induced AIMs was explored in the 6-hydroxydopamine-lesioned rats.

Results

Neither Lu AF21934 (10 or 30 mg/kg p.o.) nor ADX88178 (10 or 30 mg/kg p.o.) reduced pre-established AIMs in 6-hydroxydopamine-lesioned rats. Similarly, in L-DOPA-primed common marmosets, no reduction in established dyskinesia was observed with Lu AF21934 (3 or 10 mg/kg p.o.). Conversely, amantadine significantly reduced (>40%) the expression of dyskinesia in both models. Lu AF21934 also failed to suppress the development of AIMs in 6-hydroxydopamine-lesioned rats.

Conclusions

This study found no benefit of mGlu4 positive allosteric modulators in tackling L-DOPA-induced dyskinesia. These findings are concordant with the recent failure of foliglurax in phase II clinical trials supporting the predictive validity of these pre-clinical dyskinesia models, while raising further doubt on the anti-dyskinetic potential of mGlu4 positive allosteric modulators.

ONO-2506 Can Delay Levodopa-induced Dyskinesia in the Early Stage

BACKGROUND

Levodopa-induced dyskinesia (LID) is a common motor complication of levodopa (L-DOPA) treatment for Parkinson's disease (PD). In recent years, the role of astrocytes in LID has increasingly attracted attention.

OBJECTIVE

To explore the effect of an astrocyte regulator (ONO-2506) on LID in a rat model and the potential underlying physiological mechanism.

METHODS

Unilateral LID rat models, established by administering 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle through stereotactic injection, were injected with ONO-2506 or saline into the striatum through brain catheterization and were administered L-DOPA to induce LID. Through a series of behavioral experiments, LID performance was observed. Relevant indicators were assessed through biochemical experiments.

RESULTS

In the LID model of 6-OHDA rats, ONO-2506 significantly delayed the development and reduced the degree of abnormal involuntary movement in the early stage of L-DOPA treatment and increased glial fibrillary acidic protein and glutamate transporter 1 (GLT-1) expression in the striatum compared to saline. However, there was no significant difference in the improvement in motor function between the ONO-2506 and saline groups.

CONCLUSIONS

ONO-2506 delays the emergence of L-DOPA-induced abnormal involuntary movements in the early stage of L-DOPA administration, without affecting the anti-PD effect of L-DOPA. The delaying effect of ONO-2506 on LID may be linked to the increased expression of GLT-1 in the rat striatum. Interventions targeting astrocytes and glutamate transporters are potential therapeutic strategies to delay the development of LID.

Rabphilin-3A as a Novel Target to Reverse α-synuclein-induced Synaptic Loss in Parkinson's Disease

Toxic aggregates of α-synuclein (αsyn) are considered key drivers of Parkinson's disease (PD) pathology. In early PD, αsyn induces synaptic dysfunction also modulating the glutamatergic neurotransmission. However, a more detailed understanding of the molecular mechanisms underlying αsyn-triggered synaptic failure is required to design novel therapeutic interventions. Here, we described the role of Rabphilin-3A (Rph3A) as novel target to counteract αsyn-induced synaptic loss in PD. Rph3A is a synaptic protein interacting with αsyn and involved in stabilizing dendritic spines and in promoting the synaptic retention of NMDA-type glutamate receptors. We found that in vivo intrastriatal injection of αsyn-preformed fibrils in mice induces the early loss of striatal synapses associated with decreased synaptic levels of Rph3A and impaired Rph3A/NMDA receptors interaction. Modulating Rph3A striatal expression or interfering with the Rph3A/αsyn complex with a small molecule prevented dendritic spine loss and rescued associated early motor defects in αsyn-injected mice. Notably, the same experimental approaches prevented αsyn-induced synaptic loss in vitro in primary hippocampal neurons. Overall, these findings indicate that approaches aimed at restoring Rph3A synaptic functions can slow down the early synaptic detrimental effects of αsyn aggregates in PD.

Protein-protein interactions at the NMDA receptor complex: From synaptic retention to synaptonuclear protein messengers

N-methyl-d-aspartate receptors (NMDARs) are glutamate-gated ion channels that support essential functions throughout the brain. NMDARs are tetramers composed of the GluN1 subunit in complex with GluN2- and GluN3-type regulatory subunits, resulting in the formation of various receptor subtypes throughout the central nervous system (CNS), characterised by different kinetics, biophysical and pharmacological properties, and the abilities to interact with specific partners at dendritic spines. NMDARs are expressed at high levels, are widely distributed throughout the brain, and are involved in several physiological and pathological conditions. Here, we will focus on the GluN2A- and GluN2B-containing NMDARs found at excitatory synapses and their interactions with plasticity-relevant proteins, such as the postsynaptic density family of membrane-associated guanylate kinases (PSD-MAGUKs), Ca²⁺/calmodulin-dependent kinase II (CaMKII) and synaptonuclear protein messengers. The dynamic interactions between NMDAR subunits and various proteins regulating synaptic receptor retention and synaptonuclear signalling mediated by protein messengers suggest that the NMDAR serves as a key molecular player that coordinates synaptic activity and cell-wide events that require gene transcription. Importantly, protein-protein interactions at the NMDAR complex can also contribute to synaptic dysfunction in several brain disorders. Therefore, the modulation of the molecular composition of the NMDAR complex might represent a novel pharmacological approach for the treatment of certain disease states.

A novel phosphodiesterase 1 inhibitor reverses L-dopa-induced dyskinesia, but not motivation deficits, in monkeys

The enzyme phosphodiesterase 1 (PDE1) is highly expressed in the striatum and cortex. However, its role in corticostriatal function has not been fully investigated. The present study was aimed at evaluating the therapeutic potential of PDE1 inhibitors in treating motivation deficits and 3,4-dihydroxy-L-phenylalanine (L-dopa)-induced dyskinesia, which are pathological conditions of the corticostriatal system. We used a novel PDE1 inhibitor 3-ethyl-2-{[trans-4-(methoxymethyl)cyclohexyl]oxy}-7-(tetrahydro-2H-pyran-4-yl)-imidazo[5,1-f][1,2,4]triazin-4(3H)-one (DSR-143136), which was identified in our drug discovery program. Motivation in monkeys was measured using a progressive ratio task. L-Dopa-induced dyskinesia and disability scores were measured in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated monkeys. DSR-143136 had a high selectivity for PDE1 over other PDE families and 67 other biologic targets. A dopamine D₁ receptor antagonist SCH-39166 at 0.01, 0.03 and 0.1 mg/kg potently decreased motivation in monkeys. However, DSR-143136 at 0.3 and 3 mg/kg did not affect motivation deficits induced by low-dose SCH-39166 (0.01 mg/kg). On the other hand, DSR-143136 at 3 mg/kg potently decreased L-dopa-induced dyskinesia in the Parkinsonian monkey model. Importantly, this antidyskinesic efficacy was NOT accompanied by detrimental effects on motor function. Further, this compound decreased on-time with marked or severe dyskinesia, without affecting on-time itself. These findings suggest that PDE1 inhibitor could be a therapeutic candidate for treating L-dopa-induced dyskinesia in Parkinson's disease, but not for motivation deficits.

Contributive Role of TNF-α to L-DOPA-Induced Dyskinesia in a Unilateral 6-OHDA Lesion Model of Parkinson's Disease

Our present objective was to better characterize the mechanisms that regulate striatal neuroinflammation in mice developing L-DOPA-induced dyskinesia (LID). For that, we used 6-hydroxydopamine (6-OHDA)-lesioned mice rendered dyskinetic by repeated intraperitoneal injections of 3,4-dihydroxyphenyl-L-alanine (L-DOPA) and quantified ensuing neuroinflammatory changes in the dopamine-denervated dorsal striatum. LID development was associated with a prominent astrocytic response, and a more moderate microglial cell reaction restricted to this striatal area. The glial response was associated with elevations in two pro-inflammatory cytokines, tumor necrosis factor-α (TNF-α) and interleukin-1β. Treatment with the phytocannabinoid cannabidiol and the transient receptor potential vanilloid-1 (TRPV-1) channel antagonist capsazepine diminished LID intensity and decreased TNF-α levels without impacting other inflammation markers. To possibly reproduce the neuroinflammatory component of LID, we exposed astrocyte and microglial cells in culture to candidate molecules that might operate as inflammatory cues during LID development, i.e., L-DOPA, dopamine, or glutamate. Neither L-DOPA nor dopamine produced an inflammatory response in glial cell cultures. However, glutamate enhanced TNF-α secretion and GFAP expression in astrocyte cultures and promoted Iba-1 expression in microglial cultures. Of interest, the antidyskinetic treatment with cannabidiol + capsazepine reduced TNF-α release in glutamate-activated astrocytes. TNF-α, on its own, promoted the synaptic release of glutamate in cortical neuronal cultures, whereas cannabidiol + capsazepine prevented this effect. Therefore, we may assume that the release of TNF-α by glutamate-activated astrocytes may contribute to LID by exacerbating corticostriatal glutamatergic inputs excitability and maintaining astrocytes in an activated state through a self-reinforcing mechanism.

New Evidence on the Role of D-Aspartate Metabolism in Regulating Brain and Endocrine System Physiology: From Preclinical Observations to Clinical Applications

The endogenous amino acids serine and aspartate occur at high concentrations in free D-form in mammalian organs, including the central nervous system and endocrine glands. D-serine (D-Ser) is largely localized in the forebrain structures throughout pre and postnatal life. Pharmacologically, D-Ser plays a functional role by acting as an endogenous coagonist at N-methyl-D-aspartate receptors (NMDARs). Less is known about the role of free D-aspartate (D-Asp) in mammals. Notably, D-Asp has a specific temporal pattern of occurrence. In fact, free D-Asp is abundant during prenatal life and decreases greatly after birth in concomitance with the postnatal onset of D-Asp oxidase expression, which is the only enzyme known to control endogenous levels of this molecule. Conversely, in the endocrine system, D-Asp concentrations enhance after birth during its functional development, thereby suggesting an involvement of the amino acid in the regulation of hormone biosynthesis. The substantial binding affinity for the NMDAR glutamate site has led us to investigate the in vivo implications of D-Asp on NMDAR-mediated responses. Herein we review the physiological function of free D-Asp and of its metabolizing enzyme in regulating the functions of the brain and of the neuroendocrine system based on recent genetic and pharmacological human and animal studies.

New insights on the influence of free d-aspartate metabolism in the mammalian brain during prenatal and postnatal life

Free d-aspartate is abundant in the mammalian embryonic brain. However, following the postnatal onset of the catabolic d-aspartate oxidase (DDO) activity, cerebral d-aspartate levels drastically decrease, remaining constantly low throughout life. d-Aspartate stimulates both glutamatergic NMDA receptors (NMDARs) and metabotropic Glu5 receptors. In rodents, short-term d-aspartate exposure increases spine density and synaptic plasticity, and improves cognition. Conversely, persistently high d-Asp levels produce NMDAR-dependent neurotoxic effects, leading to precocious neuroinflammation and cell death. These pieces of evidence highlight the dichotomous impact of d-aspartate signaling on NMDAR-dependent processes and, in turn, unveil a neuroprotective role for DDO in preventing the detrimental effects of excessive d-aspartate stimulation during aging. Here, we will focus on the in vivo influence of altered d-aspartate metabolism on the modulation of glutamatergic functions and its involvement in translational studies. Finally, preliminary data on the role of embryonic d-aspartate in the mouse brain will also be reviewed.

Synthesis and Characterization of Fluorine-18-Labeled N-(4-Chloro-3-((fluoromethyl-d2)thio)phenyl)picolinamide for Imaging of mGluR4 in Brain

We have synthesized and characterized [18F]-N-(4-chloro-3-((fluoromethyl-d2)thio)phenyl)-picolinamide ([18F]15) as a potential ligand for the positron emission tomography (PET) imaging of mGluR4 in the brain. Radioligand [18F]15 displays central nervous system drug-like properties, including mGluR4 affinity, potent mGluR4 PAM activity, and selectivity against other mGluRs, as well as sufficient metabolic stability. Radiosynthesis was carried out in two steps. The radiochemical yield of [18F]15 was 11.6 ± 2.9% (n = 7, decay corrected) with a purity of 99% and a molar activity of 84.1 ± 11.8 GBq/μmol. Ex vivo biodistribution studies showed reversible binding of [18F]15 in all investigated tissues including the brain, liver, heart, lungs, and kidneys. PET imaging studies in male Sprague Dawley rats showed that [18F]15 accumulates in the brain regions known to express mGluR4. Pretreatment with the unlabeled mGluR4 PAM compounds 13 (methylthio analogue) and 15 showed significant dose-dependent blocking effects. These results suggest that [18F]15 is a promising radioligand for PET imaging mGluR4 in the brain.

Intrastriatal Memantine Infusion Dampens Levodopa-Induced Dyskinesia and Motor Deficits in a Mouse Model of Hemiparkinsonism

Although the administration of dopamine precursor levodopa remains as the mainstay for the treatment of Parkinson's disease, long-term exposure to levodopa often causes a disabling complication, referred to as levodopa-induced dyskinesias. Therefore, the development of new therapeutic interventions to dampen levodopa-induced dyskinesias and parkinsonian motor deficits is needed in the treatment of Parkinson's disease. Intracerebral brain infusion has the merit of being able to specifically deliver any drug into any brain part. By using an intracerebral infusion system equipped with implantable, programmable, and refillable pumps, we show herein that continuous intrastriatal administration of memantine (MMT), which is a non-competitive N-methyl-D-aspartate receptor antagonist, attenuates levodopa-induced dyskinesias and parkinsonian signs in 6-hydroxydopamine-lesioned hemiparkinsonian mice that received daily levodopa treatment. Corroborating the general thought that overactivation of the striatal N-methyl-D-aspartate receptor function might generate levodopa-induced dyskinesias and parkinsonism, our results suggest that a continuous intrastriatal MMT infusion can be beneficial for the management of Parkinson's disease with levodopa-induced dyskinesias. Our study also provides indications for the prototypic use of pharmacological deep-brain modulation through intracerebral infusion systems for treating medically intractable movement disorders.

From medications to surgery: advances in the treatment of motor complications in Parkinson's disease

Motor complications are responsible for the large burden of disability and poor quality of life in Parkinson’s disease (PD). The pulsatile nature of stimulation with oral dopaminergic therapies due to relatively short pharmacokinetic profiles and dysfunctional gastrointestinal absorption have been attributed to the development of PD motor complications. In this review, we will provide an overview of the pharmacologic and surgical therapies currently available and under investigation for the treatment of motor fluctuations and dyskinesia.

Dystonia and levodopa-induced dyskinesias in Parkinson's disease: Is there a connection?

Dystonia and levodopa-induced dyskinesia (LID) are both hyperkinetic movement disorders. Dystonia arises most often spontaneously, although it may be seen after stroke, injury, or as a result of genetic causes. LID is associated with Parkinson's disease (PD), emerging as a consequence of chronic therapy with levodopa, and may be either dystonic or choreiform. LID and dystonia share important phenomenological properties and mechanisms. Both LID and dystonia are generated by an integrated circuit involving the cortex, basal ganglia, thalamus and cerebellum. They also share dysregulation of striatal cholinergic signaling and abnormalities of striatal synaptic plasticity. The long duration nature of both LID and dystonia suggests that there may be underlying epigenetic dysregulation as a proximate cause. While both may improve after interventions such as deep brain stimulation (DBS), neither currently has a satisfactory medical therapy, and many people are disabled by the symptoms of dystonia and LID. Further study of the fundamental mechanisms connecting these two disorders may lead to novel approaches to treatment or prevention.

The levels of the NMDA receptor co-agonist D-serine are reduced in the substantia nigra of MPTP-lesioned macaques and in the cerebrospinal fluid of Parkinson's disease patients

Dysfunction of NMDA receptor (NMDAR)-mediated transmission is supposed to contribute to the motor and non-motor symptoms of Parkinson’s Disease (PD), and to L-DOPA-induced dyskinesia. Besides the main agonist L-glutamate, two other amino acids in the atypical D-configuration, D-serine and D-aspartate, activate NMDARs. In the present work, we investigated the effect of dopamine depletion on D-amino acids metabolism in the brain of MPTP-lesioned Macaca mulatta, and in the serum and cerebrospinal fluid of PD patients. We found that MPTP treatment increases D-aspartate and D-serine in the monkey putamen while L-DOPA rescues both D-amino acids levels. Conversely, dopaminergic denervation is associated with selective D-serine reduction in the substantia nigra. Such decrease suggests that the beneficial effect of D-serine adjuvant therapy previously reported in PD patients may derive from the normalization of endogenous D-serine levels and consequent improvement of nigrostriatal hypoglutamatergic transmission at glycine binding site. We also found reduced D-serine concentration in the cerebrospinal fluid of L-DOPA-free PD patients. These results further confirm the existence of deep interaction between dopaminergic and glutamatergic neurotransmission in PD and disclose a possible direct influence of D-amino acids variations in the changes of NMDAR transmission occurring under dopamine denervation and L-DOPA therapy.

Therapeutic strategies for Parkinson disease: beyond dopaminergic drugs

Existing therapeutic strategies for managing Parkinson disease (PD), which focus on addressing the loss of dopamine and dopaminergic function linked with degeneration of dopaminergic neurons, are limited by side effects and lack of long-term efficacy. In recent decades, research into PD pathophysiology and pharmacology has focused on understanding and tackling the neurodegenerative processes and symptomology of PD. In this Review, we discuss the challenges associated with the development of novel therapies for PD, highlighting emerging agents that aim to target cell death, as well as new targets offering a symptomatic approach to managing features and progression of the disease.

An mGlu4-Positive Allosteric Modulator Alleviates Parkinsonism in Primates

BACKGROUND

Levodopa remains the gold-standard treatment for PD. However, it becomes less effective as the disease progresses and produces debilitating side effects, such as motor fluctuations and l-dopa-induced dyskinesia. Modulation of metabotropic glutamate receptor 4 represents a promising antiparkinsonian approach in combination with l-dopa, but it has not been demonstrated in primates.

OBJECTIVE

We studied whether a novel positive allosteric modulator of the metabotropic glutamate receptor 4, PXT002331 (foliglurax), could reduce parkinsonism in primate models.

METHODS

We assessed the therapeutic potential of PXT002331 in three models of MPTP-induced parkinsonism in macaques. These models represent three different stages of disease evolution: early stage and advanced stage with and without l-dopa-induced dyskinesia.

RESULTS

As an adjunct to l-dopa, PXT002331 induced a robust and dose-dependent reversal of parkinsonian motor symptoms in macaques, including bradykinesia, tremor, posture, and mobility. Moreover, PXT002331 strongly decreased dyskinesia severity, thus having therapeutic efficacy on both parkinsonian motor impairment and l-dopa-induced dyskinesia. PXT002331 brain penetration was also assessed using PET imaging in macaques, and pharmacodynamic analyses support target engagement in the therapeutic effects of PXT002331.

CONCLUSIONS

This work provides a demonstration that a positive allosteric modulator of metabotropic glutamate receptor 4 can alleviate the motor symptoms of PD and the motor complications induced by l-dopa in primates. PXT002331 is the first compound of its class to enter phase IIa clinical trials. © 2018 International Parkinson and Movement Disorder Society.