Synergistic antidyskinetic effects of topiramate and amantadine in animal models of Parkinson's disease

Altered Amantadine Effects after Repetitive Treatment for l-dopa-induced Involuntary Movements in a Rat Model of Parkinson's Disease

BACKGROUND

l-3,4-dihydroxyphenylalanine (l-dopa) is the most effective drug for Parkinson's disease (PD); however, most PD patients develop motor fluctuations including wearing-off and l-dopa-induced dyskinesia (LID). Amantadine is beneficial for improving the motor symptoms, reducing "off" time, and ameliorating LID, although its long-term efficacy remains unknown.

OBJECTIVES

To investigate the effects of amantadine on PD and LID using a rat model with repetitive drug treatment.

METHOD

We utilized 6-hydroxydopamine injections to develop a hemiparkinsonian rat model. The rats were assigned to four groups: five rats received l-dopa and benserazide for 31 days, six rats received l-dopa and benserazide plus amantadine for 31 days, five rats received l-dopa and benserazide for 15 days followed by l-dopa and benserazide plus amantadine for 16 days, and five rats received l-dopa and benserazide plus amantadine for 15 days followed by l-dopa and benserazide treatment for 16 days. We evaluated the l-dopa-induced abnormal involuntary movements on treatment days 1, 7, 14, 16, 22, and 29. Subsequently, immunohistochemistry for drebrin was performed.

RESULTS

l-dopa-induced abnormal movements were reduced on the first day of amantadine treatment, and these effects disappeared with repetitive treatment. In contrast, the extension of l-dopa "on" time was observed after repetitive amantadine treatment. All groups showed enlarged drebrin immunoreactive dots in the dopamine-denervated striatum, indicating that amantadine did not prevent priming effects of repetitive l-dopa treatment.

CONCLUSION

Anti-LID effect of amantadine diminished after repetitive treatment, and the effect of amantadine on wearing-off emerged after repetitive treatment in a hemiparkinsonian rat model. Fluctuations in amantadine effects should be considered when using it in clinical settings.

An Update on Nondopaminergic Treatments for Motor and Non-motor Symptoms of Parkinson's Disease

Nondopaminergic neurotransmitters such as adenosine, norepinephrine, serotonin, glutamate, and acetylcholine are all involved in Parkinson's disease (PD) and promote its symptoms. Therefore, nondopaminergic receptors are key targets for developing novel preparations for the management of motor and non-motor symptoms in PD, without the potential adverse events of dopamine replacement therapy. We reviewed English-written articles and ongoing clinical trials of nondopaminergic treatments for PD patients till 2014 to summarize the recent findings on nondopaminergic preparations for the treatment of PD patients. The most promising research area of nondopaminergic targets is to reduce motor complications caused by traditional dopamine replacement therapy, including motor fluctuations and levodopa-induced dyskinesia. Istradefylline, Safinamide, and Zonisamide were licensed for the management of motor fluctuations in PD patients, while novel serotonergic and glutamatergic agents to improve motor fluctuations are still under research. Sustained- release agents of Amantadine were approved for treating levodopa induced dyskinesia (LID), and serotonin 5HT1B receptor agonist also showed clinical benefits to LID. Nondopaminergic targets were also being explored for the treatment of non-motor symptoms of PD. Pimavanserin was approved globally for the management of hallucinations and delusions related to PD psychosis. Istradefylline revealed beneficial effect on daytime sleepiness, apathy, depression, and lower urinary tract symptoms in PD subjects. Droxidopa may benefit orthostatic hypotension in PD patients. Safinamide and Zonisamide also showed clinical efficacy on certain non-motor symptoms of PD patients. Nondopaminergic drugs are not expected to replace dopaminergic strategies, but further development of these drugs may lead to new approaches with positive clinical implications.

Dyskinesia and Parkinson's disease: animal model, drug targets, and agents in preclinical testing

INTRODUCTION

Parkinson's disease (PD) is the second most common neurodegenerative disease after Alzheimer's disease. PD patients exhibit a classic spectrum of motor symptoms, arising when dopamine neurons in the substantia nigra pars compacta are reduced by 60%. The dopamine precursor L-DOPA represents the most effective therapy for improving PD motor dysfunctions, thus far available. Unfortunately, long-term treatment with L-DOPA is associated with the development of severe side effects, resulting in abnormal involuntary movements termed levodopa-induced dyskinesia (LID). Amantadine is the only drug currently approved for the treatment of LID indicating that LID management is still an unmet need in PD and encouraging the search for novel anti-dyskinetic drugs or the assessment of combined therapies with different molecular targets.

AREAS COVERED

This review provides an overview of the main preclinical models used to study LID and of the latest preclinical evidence on experimental and clinically available pharmacological approaches targeting non-dopaminergic systems.

EXPERT OPINION

LIDs are supported by complex molecular and neurobiological mechanisms that are still being studied today. This complexity suggests the need of developing personalized pharmacological approach to obtain an effective amelioration of LID condition and improve the quality of life of PD patients.

Glutamate modulation for the treatment of levodopa induced dyskinesia: a brief review of the drugs tested in the clinic

Levodopa is the standard treatment for Parkinson's disease, but its use is marred by the emergence of dyskinesia, for which treatment options remain limited. Here, we review the glutamatergic modulators that were assessed for their antidyskinetic potential in clinical trials, including N-methyl-D-aspartate (NMDA) antagonists, agonists at the glycine-binding site on NMDA receptors, metabotropic glutamate (mGlu) 4 agonists, mGlu₅ antagonists, α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) antagonists and glutamate release inhibitors. Several agents that were investigated are not selective for their targets, raising uncertainty about the extent to which glutamatergic modulation contributed to their effects. Except for amantadine, the use of glutamatergic modulators for the treatment of dyskinesia in Parkinson's disease remains largely investigational, with promising results obtained with mGlu₅ negative allosteric modulation.

Effect of the glycine transporter 1 inhibitor ALX-5407 on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset

Dyskinesia and psychosis are complications encountered in advanced Parkinson's disease (PD) following long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA). Disturbances in the glutamatergic system have been associated with both dyskinesia and psychosis, making glutamatergic modulation a potential therapeutic approach for these. Treatments thus far have sought to dampen glutamatergic transmission, for example through blockade of N-methyl-D-aspartate (NMDA) receptors or modulation of metabotropic glutamate receptors 5. In contrast, activation of the glycine-binding site on NMDA receptors is required for their physiological response. Here, we investigated whether indirectly enhancing glutamatergic transmission through inhibition of glycine re-uptake would be efficacious in diminishing both dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six marmosets were rendered parkinsonian by MPTP injection. Following repeated administration of L-DOPA to induce dyskinesia and PLBs, they underwent acute challenges of the glycine transporter 1 (GlyT₁) inhibitor ALX-5407 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA, after which the severity of dyskinesia, PLBs and parkinsonian disability was evaluated. In combination with L-DOPA, ALX-5407 0.1 and 1 mg/kg significantly reduced the severity of dyskinesia, by 51% and 41% (both P < 0.001), when compared to vehicle. ALX-5407 0.01, 0.1 and 1 mg/kg also decreased the severity of global PLBs, by 25%, 51% and 38% (all P < 0.001), when compared to vehicle. The benefits on dyskinesia and PLBs were achieved without compromising the therapeutic effect of L-DOPA on parkinsonism. Our results suggest that GlyT₁ inhibition may be a novel strategy to attenuate dyskinesia and PLBs in PD, without interfering with L-DOPA anti-parkinsonian action.

Amantadine in the treatment of Parkinson's disease and other movement disorders

The efficacy of amantadine in the symptomatic treatment of patients with Parkinson's disease, discovered serendipitously more than 50 years ago, has stood the test of time and the drug is still commonly used by neurologists today. Its pharmacological actions are unique in combining dopaminergic and glutamatergic properties, which account for its dual effect on parkinsonian signs and symptoms and levodopa-induced dyskinesias. Furthermore, amantadine has additional and less well-defined pharmacological effects, including on anticholinergic and serotonergic activity. Evidence from randomised controlled trials over the past 5 years has confirmed the efficacy of amantadine to treat levodopa-induced dyskinesias in patients with Parkinson's disease, and clinical studies have also provided support for its potential to reduce motor fluctuations. Other uses of amantadine, such as in the treatment of drug-induced parkinsonism, atypical parkinsonism, Huntington's disease, or tardive dyskinesia, lack a strong evidence base. Future trials should examine its role in the management of motor and non-motor symptoms in patients with early Parkinson's disease and those with other movement disorders.

Additive effects of mGluR2 positive allosteric modulation, mGluR2 orthosteric stimulation and 5-HT2AR antagonism on dyskinesia and psychosis-like behaviours in the MPTP-lesioned marmoset

PURPOSE

Antagonising serotonin (5-HT) type 2A receptors (5-HT_2AR) is an effective strategy to alleviate both dyskinesia and psychosis in Parkinson's disease (PD). We have recently shown that activation of metabotropic glutamate 2 receptors (mGluR₂), via either orthosteric stimulation or positive allosteric modulation, enhances the anti-dyskinetic and anti-psychotic effects of 5-HT_2AR antagonism. Here, we investigated if greater therapeutic efficacy would be achieved by combining 5-HT_2AR antagonism with concurrent mGluR₂ orthosteric stimulation and mGluR₂ positive allosteric modulation.

METHODS

Five 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned marmosets exhibiting dyskinesia and psychosis-like behaviours (PLBs) were administered L-3,4-dihydroxyphenylalanine (L-DOPA) in combination with vehicle or the 5-HT_2AR antagonist EMD-281,014. EMD-281,014 was itself administered alone or with the mGluR₂ orthosteric agonist (OA) LY-354,740, the mGluR₂ positive allosteric modulator (PAM) LY-487,379 and combination thereof, after which the severity of dyskinesia, PLBs and parkinsonism was rated.

RESULTS

EMD-281,014 reduced dyskinesia and PLBs by up to 47% and 40%, respectively (both P < 0.001). The addition of LY-354,740, LY-487,379 and LY-354,740/LY-487,379 decreased dyskinesia by 56%, 65% and 77%, while PLBs were diminished by 55%, 63% and 71% (all P < 0.001). All treatment combinations provided anti-dyskinetic and anti-psychotic benefits significantly greater than those conferred by EMD-281,014 alone (all P < 0.05). The combination of EMD-281,014/LY-354,740/LY-487,379 resulted in anti-dyskinetic and anti-psychotic effects significantly greater than those conferred by EMD-281,014 with either LY-354,740 or LY-487,379 (both P < 0.05). No deleterious effects on L-DOPA anti-parkinsonian action were observed.

CONCLUSION

Our results suggest that combining 5-HT_2AR antagonism with mGluR₂ activation results in greater reduction of L-DOPA-induced dyskinesia and PD psychosis. They also indicate that further additive effect can be achieved when a mGluR₂ OA and a mGluR₂ PAM are combined with a 5-HT_2AR antagonist than when a mGluR₂ OA or a mGluR₂ PAM are added to a 5-HT_2AR antagonist.

Selective blockade of the 5-HT3 receptor acutely alleviates dyskinesia and psychosis in the parkinsonian marmoset

In Parkinson's disease (PD), management of L-3,4-dihydroxyphenylalanine (l-DOPA)-related complications, such as l-DOPA induced dyskinesia and psychosis, remains inadequate, which poses a significant burden on the quality of life of patients. We have shown, in the hemi-parkinsonian rat model of PD, that the selective serotonin type 3 (5-HT₃) receptor antagonists ondansetron and granisetron decreased the severity of established dyskinesia, and ondansetron even attenuated the development of dyskinesia. Here, we seek to confirm these favourable data on dyskinesia and to explore the effect of ondansetron on the severity of psychosis-like behaviours (PLBs) in the gold standard model of PD, the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned non-human primate. We first determined the pharmacokinetic profile of ondansetron in the marmoset. Subsequently, six MPTP-lesioned marmosets were administered l-DOPA chronically until they exhibited stable and reproducible dyskinesia and PLBs upon each administration of l-DOPA. On behavioural assessment days, ondansetron (0.01, 0.1 and 1 mg/kg) or vehicle was administered in conjunction with l-DOPA, and the severity of dyskinesia, PLBs and parkinsonism was evaluated. Ondansetron 0.1 mg/kg alleviated global dyskinesia severity by 73% (P < 0.0001) and decreased duration of on-time with disabling dyskinesia by 88% (P = 0.0491). Ondansetron 0.1 mg/kg reduced the severity of global PLBs by 80% (P < 0.0001) and suppressed on-time with disabling PLBs (P = 0.0213). Ondansetron enhanced the anti-parkinsonian action of l-DOPA, reducing global parkinsonism by 53% compared to l-DOPA (P = 0.0004). These results suggest that selective blockade of the 5-HT₃ receptor with ondansetron may be an effective approach to alleviate l-DOPA-related complications.

Non-Dopaminergic Treatments for Motor Control in Parkinson's Disease: An Update

Glutamatergic, noradrenergic, serotonergic, and cholinergic systems play a critical role in the basal ganglia circuitry. Targeting these non-dopaminergic receptors remains a focus of ongoing research to improve Parkinson's disease (PD) motor symptoms, without the potential side effects of dopamine replacement therapy. This review updates advancements in non-dopaminergic treatments for motor control in PD since 2013. To date, no non-dopaminergic selective drug has shown significant long-term efficacy as monotherapy in PD. The largest area of development in non-dopaminergic targets has been for motor complications of dopamine replacement therapy (motor fluctuations and dyskinesia). For treatment of motor fluctuations, safinamide, zonisamide, and istradefylline are currently approved, and novel glutamatergic and serotonergic drugs are in development. Long-acting formulations of amantadine are approved for treating dyskinesia. Several non-dopaminergic drugs have failed to show anti-dyskinetic efficacy, while some are still in development. Non-dopaminergic targets are also being pursued to treat specific motor symptoms of PD. For example, CX-8998 (a calcium channel modulator) is being evaluated for PD tremor and rivastigmine may improve gait dysfunction in PD. Drug repurposing continues to be a key strategy for non-dopaminergic targets in PD, but the field needs to increase discovery and availability of such drugs.

Receptor Ligands as Helping Hands to L-DOPA in the Treatment of Parkinson's Disease

Levodopa (LD) is the most effective drug in the treatment of Parkinson’s disease (PD). However, although it represents the “gold standard” of PD therapy, LD can cause side effects, including gastrointestinal and cardiovascular symptoms as well as transient elevated liver enzyme levels. Moreover, LD therapy leads to LD-induced dyskinesia (LID), a disabling motor complication that represents a major challenge for the clinical neurologist. Due to the many limitations associated with LD therapeutic use, other dopaminergic and non-dopaminergic drugs are being developed to optimize the treatment response. This review focuses on recent investigations about non-dopaminergic central nervous system (CNS) receptor ligands that have been identified to have therapeutic potential for the treatment of motor and non-motor symptoms of PD. In a different way, such agents may contribute to extending LD response and/or ameliorate LD-induced side effects.

Repurposing drugs to treat l-DOPA-induced dyskinesia in Parkinson's disease

In this review, we discuss the opportunity for repurposing drugs for use in l-DOPA-induced dyskinesia (LID) in Parkinson's disease. LID is a particularly suitable indication for drug repurposing given its pharmacological diversity, translatability of animal-models, availability of Phase II proof-of-concept (PoC) methodologies and the indication-specific regulatory environment. A compound fit for repurposing is defined as one with appropriate human safety-data as well as animal safety, toxicology and pharmacokinetic data as found in an Investigational New Drug (IND) package for another indication. We first focus on how such repurposing candidates can be identified and then discuss development strategies that might progress such a candidate towards a Phase II clinical PoC. We discuss traditional means for identifying repurposing candidates and contrast these with newer approaches, especially focussing on the use of computational and artificial intelligence (AI) platforms. We discuss strategies that can be categorised broadly as: in vivo phenotypic screening in a hypothesis-free manner; in vivo phenotypic screening based on analogy to a related disorder; hypothesis-driven evaluation of candidates in vivo and in silico screening with a hypothesis-agnostic component to the selection. To highlight the power of AI approaches, we describe a case study using IBM Watson where a training set of compounds, with demonstrated ability to reduce LID, were employed to identify novel repurposing candidates. Using the approaches discussed, many diverse candidates for repurposing in LID, originally envisaged for other indications, will be described that have already been evaluated for efficacy in non-human primate models of LID and/or clinically. This article is part of the Special Issue entitled 'Drug Repurposing: old molecules, new ways to fast track drug discovery and development for CNS disorders'.

Current Nondopaminergic Therapeutic Options for Motor Symptoms of Parkinson's Disease

Objective:

The aim of this study was to summarize recent studies on nondopaminergic options for the treatment of motor symptoms in Parkinson's disease (PD).

Data Sources:

Papers in English published in PubMed, Cochrane, and Ovid Nursing databases between January 1988 and November 2016 were searched using the following keywords: PD, nondopaminergic therapy, adenosine, glutamatergic, adrenergic, serotoninergic, histaminic, and iron chelator. We also reviewed the ongoing clinical trials in the website of clinicaltrials.gov.

Study Selection:

Articles related to the nondopaminergic treatment of motor symptoms in PD were selected for this review.

Results:

PD is conventionally treated with dopamine replacement strategies, which are effective in the early stages of PD. Long-term use of levodopa could result in motor complications. Recent studies revealed that nondopaminergic systems such as adenosine, glutamatergic, adrenergic, serotoninergic, histaminic, and iron chelator pathways could include potential therapeutic targets for motor symptoms, including motor fluctuations, levodopa-induced dyskinesia, and gait disorders. Some nondopaminergic drugs, such as istradefylline and amantadine, are currently used clinically, while most such drugs are in preclinical testing stages. Transitioning of these agents into clinically beneficial strategies requires reliable evaluation since several agents have failed to show consistent results despite positive findings at the preclinical level.

Conclusions:

Targeting nondopaminergic transmission could improve some motor symptoms in PD, especially the discomfort of dyskinesia. Although nondopaminergic treatments show great potential in PD treatment as an adjunct therapy to levodopa, further investigation is required to ensure their success.

Efficacy and safety of amantadine for the treatment of L-DOPA-induced dyskinesia

L-DOPA induced dyskinesias (LIDs) may affect up to 40% of Parkinson's disease (PD) and impact negatively health-related quality of life. Amantadine has demonstrated significant antidyskinetic effects in animal PD models and in randomized double-blind placebo-controlled trials (RCTs) in patients with PD. These effects are thought to be related to the blockade of NMDA receptors modulating cortico-striatal glutamatergic-dopaminergic interactions involved in the genesis of LIDs. There are three pharmaceutical forms of amantadine currently available in the market: an oral immediate-release (IR) formulation, which is widely available; an extended-release (ER) formulation (ADS-5102) which has been recently developed and approved by the FDA; and an intravenous infusion (IV) solution, which is not commonly used in clinical practice. RCTs with amantadine IR or ER, involving more than 650 patients have shown consistent and long-lasting reductions in LIDs. Interestingly, ADS-5102 not only reduced LIDs, but also reduced significantly at the same time the duration of daily OFF-time, a unique finding compared with other antiparkinsonian medications that usually reduce time spent OFF at the cost of worsening of LIDs. Amantadine IR might also have possible effects on other PD symptoms such as apathy or fatigue. The most common adverse reactions with amantadine are constipation, cardiovascular dysfunction including QT prolongation, orthostatic hypotension and edema, neuropsychiatric symptoms such as hallucinations, confusion and delirium, nausea and livedo reticularis. Corneal degeneration is rare but critical. In summary, amantadine immediate and extended-release are effective and safe for the treatment of LIDs.

Levodopa treatment and dendritic spine pathology

Parkinson's disease (PD) is a neurodegenerative disorder associated with the progressive loss of nigrostriatal dopaminergic neurons. Levodopa is the most effective treatment for the motor symptoms of PD. However, chronic oral levodopa treatment can lead to various motor and nonmotor complications because of nonphysiological pulsatile dopaminergic stimulation in the brain. Examinations of autopsy cases with PD have revealed a decreased number of dendritic spines of striatal neurons. Animal models of PD have revealed altered density and morphology of dendritic spines of neurons in various brain regions after dopaminergic denervation or dopaminergic denervation plus levodopa treatment, indicating altered synaptic transmission. Recent studies using rodent models have reported dendritic spine head enlargement in the caudate‐putamen, nucleus accumbens, primary motor cortex, and prefrontal cortex in cases where chronic levodopa treatment following dopaminergic denervation induced dyskinesia‐like abnormal involuntary movement. Hypertrophy of spines results from insertion of alpha‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid receptors into the postsynaptic membrane. Such spine enlargement indicates hypersensitivity of the synapse to excitatory inputs and is compatible with a lack of depotentiation, which is an electrophysiological hallmark of levodopa‐induced dyskinesia found in the corticostriatal synapses of dyskinetic animals and the motor cortex of dyskinetic PD patients. This synaptic plasticity may be one of the mechanisms underlying the priming of levodopa‐induced complications such as levodopa‐induced dyskinesia and dopamine dysregulation syndrome. Drugs that could potentially prevent spine enlargement, such as calcium channel blockers, N‐methyl‐D‐aspartate receptor antagonists, alpha‐amino‐2,3‐dihydro‐5‐methyl‐3‐oxo‐4‐isoxazolepropanoic acid receptor antagonists, and metabotropic glutamate receptor antagonists, are candidates for treatment of levodopa‐induced complications in PD. © 2017 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.

Nondopaminergic treatments for Parkinson's disease: current and future prospects

Parkinson's disease is primarily caused by dysfunction of dopaminergic neurons, however, nondopaminergic (ND) systems are also involved. ND targets are potentially useful to reduce doses of levodopa or to treat nonlevodopa-responsive symptoms. Recent studies have investigated the role of ND drugs for motor and nonmotor symptoms. Adenosine A2A receptor antagonists, mixed inhibitors of sodium/calcium channels and monoamine oxidase-B have recently been found to improve motor fluctuations. N-methyl-d-aspartate receptor antagonists and serotonin 5HT1B receptor agonists demonstrated benefit in levodopa-induced dyskinesia. Conversely, studies using antiepileptic drugs and adrenoreceptor antagonist had conflicting results. Moreover, metabotropic glutamate receptor antagonists also failed to improve symptoms. The current review summarizes the most recent findings on ND drugs over the last 2 years.

α7 nicotinic receptor agonists reduce levodopa-induced dyskinesias with severe nigrostriatal damage

BACKGROUND

ABT-126 is a novel, safe, and well-tolerated α7 nicotinic receptor agonist in a Phase 2 Alzheimer's disease study. We tested the antidyskinetic effect of ABT-126 in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-treated squirrel monkeys with moderate and more severe nigrostriatal damage.

METHODS

Monkeys (n = 21, set 1) were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine 1-2×. When parkinsonian, they were gavaged with levodopa (10 mg/kg)/carbidopa (2.5 mg/kg) twice daily and dyskinesias rated. They were then given nicotine in drinking water (n = 5), or treated with vehicle (n = 6) or ABT-126 (n = 10) twice daily orally 30 min before levodopa. Set 1 was then re-lesioned 1 to 2 times for a total of 3 to 4 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine injections. The antidyskinetic effect of ABT-126, nicotine, and the β2* nicotinic receptor agonist ABT-894 was re-assessed. Another group of monkeys (n = 23, set 2) were lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine only 1× to 2×. They were treated with levodopa/carbidopa, administered the α7 agonist ABT-107 (n = 6), ABT-894 (n = 6), nicotine (n = 5), or vehicle (n = 6) and dyskinesias evaluated. All monkeys were euthanized and the dopamine transporter measured.

RESULTS

With moderate nigrostriatal damage (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine 1×-2×), ABT-126 dose-dependently decreased dyskinesias (∼60%), with similar results seen with ABT-894 (∼60%) or nicotine (∼60%). With more severe damage (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine 3-4×), ABT-126 and nicotine reduced dyskinesias, but ABT-894 did not. The dopamine transporter was 41% and 8.9% of control, with moderate and severe nigrostriatal damage, respectively. No drug modified parkinsonism.

CONCLUSION

The novel α7 nicotinic receptor drug ABT-126 reduced dyskinesias in monkeys with both moderate and severe nigrostriatal damage. ABT-126 may be useful to reduce dyskinesias in both early- and later-stage Parkinson's disease.

Dyskinesias and impulse control disorders in Parkinson's disease: From pathogenesis to potential therapeutic approaches

Dopaminergic treatment in Parkinson's disease (PD) reduces the severity of motor symptoms of the disease. However, its chronic use is associated with disabling motor and behavioral side effects, among which levodopa-induced dyskinesias (LID) and impulse control disorders (ICD) are the most common. The underlying mechanisms and pathological substrate of these dopaminergic complications are not fully understood. Recently, the refinement of imaging techniques and the study of the genetics and molecular bases of LID and ICD indicate that, although different, they could share some features. In addition, animal models of parkinsonism with LID have provided important knowledge about mechanisms underlying such complications. In contrast, animal models of parkinsonism and abnormal impulsivity, although useful regarding some aspects of human ICD, do not fully resemble the clinical phenotype of ICD in patients with PD, and until now have provided limited information. Studies on animal models of addiction could complement the previous models and provide some insights into the background of these behavioral complications given that ICD are regarded as behavioral addictions. Here we review the most relevant advances in relation to imaging, genetics, biochemistry and pharmacological interventions to treat LID and ICD in patients with PD and in animal models with a view to better understand the overlapping and unique maladaptations to dopaminergic therapy that are associated with LID and ICD.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Glutamatergic pathways as a target for the treatment of dyskinesias in Parkinson's disease

PD (Parkinson's disease) is characterized by some typical motor features that are caused by striatal dopamine depletion and respond well to dopamine-replacement therapy with L-dopa. Unfortunately, the majority of PD patients treated with L-dopa develop abnormal involuntary movements (dyskinesias) within a few years. The mechanisms underlying the development of LIDs (L-dopa-induced dyskinesias) involve, on one hand, a presynaptic dysregulation of dopamine release and clearance and, on the other hand, an abnormal postsynaptic response to dopamine in the brain. There is a large amount of evidence that these dopamine-dependent mechanisms are modulated by glutamatergic pathways and glutamate receptors. The present article summarizes the pathophysiological role of glutamatergic pathways in LID and reviews pre-clinical and clinical results obtained using pharmacological modulators of different classes and subtypes of glutamate receptors to treat parkinsonian dyskinesias.

Targeting glutamatergic synapses in Parkinson's disease

Parkinson's disease (PD) is characterized by progressive degeneration of dopaminergic neurons of the substantia nigra and dramatic motor and cognitive impairments. The current knowledge indicates that the strength of glutamatergic signals from the cortex to the striatum is regulated during the progression of the disease. The efficacy of ionotropic glutamate receptors to modulate synaptic transmission in the striatum indicates that modulation of the activity of these receptors may represent a key target to rescue the altered neurotransmission in PD. Preclinical and clinical studies suggest that agents targeting ionotropic glutamate receptors may ameliorate the motor symptoms of PD as well as to reduce the onset of levodopa-induced dyskinetic motor behaviour.

Advances in non-dopaminergic treatments for Parkinson's disease

Since the 1960's treatments for Parkinson's disease (PD) have traditionally been directed to restore or replace dopamine, with L-Dopa being the gold standard. However, chronic L-Dopa use is associated with debilitating dyskinesias, limiting its effectiveness. This has resulted in extensive efforts to develop new therapies that work in ways other than restoring or replacing dopamine. Here we describe newly emerging non-dopaminergic therapeutic strategies for PD, including drugs targeting adenosine, glutamate, adrenergic, and serotonin receptors, as well as GLP-1 agonists, calcium channel blockers, iron chelators, anti-inflammatories, neurotrophic factors, and gene therapies. We provide a detailed account of their success in animal models and their translation to human clinical trials. We then consider how advances in understanding the mechanisms of PD, genetics, the possibility that PD may consist of multiple disease states, understanding of the etiology of PD in non-dopaminergic regions as well as advances in clinical trial design will be essential for ongoing advances. We conclude that despite the challenges ahead, patients have much cause for optimism that novel therapeutics that offer better disease management and/or which slow disease progression are inevitable.

Role for the nicotinic cholinergic system in movement disorders; therapeutic implications

A large body of evidence using experimental animal models shows that the nicotinic cholinergic system is involved in the control of movement under physiological conditions. This work raised the question whether dysregulation of this system may contribute to motor dysfunction and whether drugs targeting nicotinic acetylcholine receptors (nAChRs) may be of therapeutic benefit in movement disorders. Accumulating preclinical studies now show that drugs acting at nAChRs improve drug-induced dyskinesias. The general nAChR agonist nicotine, as well as several nAChR agonists (varenicline, ABT-089 and ABT-894), reduces l-dopa-induced abnormal involuntary movements or dyskinesias up to 60% in parkinsonian nonhuman primates and rodents. These dyskinesias are potentially debilitating abnormal involuntary movements that arise as a complication of l-dopa therapy for Parkinson's disease. In addition, nicotine and varenicline decrease antipsychotic-induced abnormal involuntary movements in rodent models of tardive dyskinesia. Antipsychotic-induced dyskinesias frequently arise as a side effect of chronic drug treatment for schizophrenia, psychosis and other psychiatric disorders. Preclinical and clinical studies also show that the nAChR agonist varenicline improves balance and coordination in various ataxias. Lastly, nicotine has been reported to attenuate the dyskinetic symptoms of Tourette's disorder. Several nAChR subtypes appear to be involved in these beneficial effects of nicotine and nAChR drugs including α4β2*, α6β2* and α7 nAChRs (the asterisk indicates the possible presence of other subunits in the receptor). Overall, the above findings, coupled with nicotine's neuroprotective effects, suggest that nAChR drugs have potential for future drug development for movement disorders.

Differential effects of the NMDA receptor antagonist MK-801 on dopamine receptor D1- and D2-induced abnormal involuntary movements in a preclinical model

Dopamine-replacement therapy with l-DOPA is still the gold standard treatment for Parkinson's disease (PD). One drawback is the common development of l-DOPA-induced dyskinesia (LID) in patients, which can be as disabling as the disease itself. There is no satisfactory adjunct therapy available. Glutamatergic transmission in the basal ganglia circuitry has been shown to be an important player in the development of LID. The N-methyl-d-aspartate (NMDA) receptor antagonist MK-801 has previously been shown to reduce l-DOPA-induced abnormal involuntary movements (AIMs) in a rat preclinical model but only at concentrations that worsen parkinsonism. We investigated the contribution of the direct and indirect striatofugal pathways to these effects. In the direct pathway, dopamine D1 receptors (D1R) are expressed, whereas in the indirect pathway, dopamine D2 receptors (D2R) are expressed. We used the 6-hydroxydopamine-lesioned hemi-parkinsonian rat model initially primed with l-DOPA to induce dyskinesia. When the rats were then primed and probed with the D1R agonist SKF81297, co-injection of MK-801 worsened the D1R-induced limb, axial, and orolingual (LAO) AIMs by 18% (predominantly dystonic axial AIMs) but did not aggravate parkinsonian hypokinesia as reflected by a surrogate measure of ipsiversive rotations in this model. In contrast, when the rats were then primed and probed with the D2R agonist quinpirole, co-injection of MK-801 reduced D2R-induced LAO AIMs by 89% while inducing ipsiversive rotations. The data show that only inhibition of the indirect striatopallidal pathway is sufficient for the full anti-dyskinetic/pro-parkinsonian effects of the NMDA receptor antagonist MK-801, and that MK-801 modestly worsens dyskinesias that are due to activation of the direct striatonigral pathway alone. This differential activation of the glutamatergic systems in D1R- and D2R-mediated responses is relevant to current therapy for PD which generally includes a mixture of dopamine agonists and l-DOPA.

NMDA antagonists as Parkinson’s disease therapy: disseminating the evidence

SUMMARY Oral levodopa is the current baseline therapy in the management of Parkinson’s disease, but nonmotor complications and therapy-related dyskinesias pose an important challenge for clinicians. Glutamate receptors have been implicated in the neurodegenerative process of Parkinson’s disease and also in the development of levodopa-induced dyskinesias. This article discusses the role of NMDA receptors in Parkinson’s disease and their modulation as a possible therapeutic approach.

Randomized clinical trial of topiramate for levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND

The antiepileptic drug topiramate reduces levodopa-induced dyskinesia without exacerbating parkinsonism in animal models. We report a randomized, double-blind, placebo-controlled crossover trial in patients with Parkinson's disease and levodopa-induced dyskinesia.

METHODS

Fifteen patients with Parkinson's disease and stable levodopa-induced dyskinesia were enrolled into the study, of whom 13 were randomized to topiramate or placebo. The study medication was titrated to 100 mg/day over four weeks, and assessments were carried out after a further two weeks. Dyskinesia severity assessed by a blinded rater from video recordings was the primary outcome measure.

RESULTS

Seven patients (mean age 58.9 ± 12.8 years) completed the study. Patients taking topiramate vs. placebo showed a significant increase in dyskinesia severity compared to baseline (Wilcoxon signed rank test, P = 0.043). Five patients withdrew from the study whilst taking topiramate due to adverse effects.

CONCLUSIONS

Topiramate tended to worsen dyskinesia in patients with Parkinson's disease, and was poorly tolerated.

IRC-082451, a novel multitargeting molecule, reduces L-DOPA-induced dyskinesias in MPTP Parkinsonian primates

The development of dyskinesias following chronic L-DOPA replacement therapy remains a major problem in the long-term treatment of Parkinson's disease. This study aimed at evaluating the effect of IRC-082451 (base of BN82451), a novel multitargeting hybrid molecule, on L-DOPA-induced dyskinesias (LIDs) and hypolocomotor activity in a non-human primate model of PD. IRC-082451 displays multiple properties: it inhibits neuronal excitotoxicity (sodium channel blocker), oxidative stress (antioxidant) and neuroinflammation (cyclooxygenase inhibitor) and is endowed with mitochondrial protective properties. Animals received daily MPTP injections until stably parkinsonian. A daily treatment with increasing doses of L-DOPA was administered to parkinsonian primates until the appearance of dyskinesias. Then, different treatment regimens and doses of IRC-082451 were tested and compared to the benchmark molecule amantadine. Primates were regularly filmed and videos were analyzed with specialized software. A novel approach combining the analysis of dyskinesias and locomotor activity was used to determine efficacy. This analysis yielded the quantification of the total distance travelled and the incidence of dyskinesias in 7 different body parts. A dose-dependent efficacy of IRC-082451 against dyskinesias was observed. The 5 mg/kg dose was best at attenuating the severity of fully established LIDs. Its effect was significantly different from that of amantadine since it increased spontaneous locomotor activity while reducing LIDs. This dose was effective both acutely and in a 5-day sub-chronic treatment. Moreover, positron emission tomography scans using radiolabelled dopamine demonstrated that there was no direct interference between treatment with IRC-082451 and dopamine metabolism in the brain. Finally, post-mortem analysis indicated that this reduction in dyskinesias was associated with changes in cFOS, FosB and ARC mRNA expression levels in the putamen. The data demonstrates the antidyskinetic efficacy of IRC-082451 in a primate model of PD with motor complications and opens the way to the clinical application of this treatment for the management of LIDs.

Intrastriatal injections of KN-93 ameliorates levodopa-induced dyskinesia in a rat model of Parkinson's disease

BACKGROUND

Levodopa remains the most effective drug for the treatment of Parkinson's disease (PD). However, long-term levodopa treatment is associated with the emergence of levodopa-induced dyskinesia (LID), which has hampered its use for PD treatment. The mechanisms of LID are only partially understood. A previous study showed that KN-93, a Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) inhibitor, could be used to ameliorate LID in rats. However, the precise mechanisms by which KN-93 acts as an antidyskinetic are not fully understood.

METHODS

In the present study, a rat model of PD was induced by 6-hydroxydopamine (OHDA) injections. Then, the successfully lesioned rats were intrastriatally administered with a different dose of KN-93 (1 μg, 2 μg, or 5 μg) prior to levodopa treatment. Abnormal involuntary movements (AIMs) scores and apomorphine-induced rotations were measured in PD rats. Phosphorylated levels of GluR1 at Serine-845 (pGluR1S845) levels were determined by western blot. Arc and Penk levels were measured by real-time polymerase chain reaction (PCR).

RESULTS

We found that both 2 μg and 5 μg KN-93 treatment lowered AIMs scores in levodopa priming PD rats without affecting the antiparkinsonian effect of levodopa. In agreement with behavioral analysis, KN-93 treatment (2 μg) reduced pGluR1S845 levels in PD rats. Moreover, KN-93 treatment (2 μg) reduced the expression of Gad1 and Nur77 in PD rats.

CONCLUSION

These data indicated that intrastriatal injections of KN-93 were beneficial in reducing the expression of LID by lowering the expression of pGluR1S845 via suppressing the activation of CaMKII in PD rats. Decreased expression of pGluR1S845 further reduced the expression of Gad1 and Nur77 in PD rats.

Levodopa/benserazide microspheres reduced levodopa-induced dyskinesia by downregulating phosphorylated GluR1 expression in 6-OHDA-lesioned rats

Background

Levodopa is the gold standard in the treatment of Parkinson’s disease (PD). However, long-term levodopa replacement therapy is accompanied by abnormal involuntary movements (AIMs), known as levodopa-induced dyskinesia (LID). Until now, the precise mechanisms of LID were only partially understood. Previous studies have shown that continuous dopamine stimulation was helpful in reducing the expression of LID. In addition to dopamine D1 receptor, glutamatergic receptors such as α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor also contribute to the expression of LID. The current authors have previously reported that levodopa/benserazide-loaded microspheres could ameliorate the expression of LID by reducing the protein kinase A signaling pathway in dyskinetic rats. However, whether AMPA receptor is involved in the mechanism by which levodopa/benserazide-loaded microspheres ameliorate the expression of LID in dyskinetic rats was unknown.

Methods

In the present study, as reported previously, levodopa and benserazide were loaded by poly(lactic-co-glycolic acid) microspheres, which can release levodopa and benserazide in a sustained manner. 6-Hydroxydopamine was injected into the right medial forebrain bundle to produce a rat model of PD. Then valid PD rats were treated with levodopa plus benserazide for 3 weeks to induce a rat model of LID. Dyskinetic rats were treated with levodopa/beserazide-loaded microspheres containing levodopa (6 mg/kg) plus benserazide (15 mg/kg) or same dose of levodopa plus benserazide. Abnormal involuntary movements were measured in rats on days 1, 5, 10, 15, and 20 during the treatment. The levels of GluR1 at serine-831 (pGluR1S831) and serine-845 (pGluR1S845) were determined by Western blot. Arc and proenkephalin (Penk) levels were measured by real-time polymerase chain reaction.

Results

Three-week levodopa plus benserazide treatment induced dyskinesia in PD rats. Levodopa/benserazide-loaded microsphere-treated dyskinetic rats showed lower AIM scores than levodopa plus benserazide-treated dyskinetic rats. Microsphere treatment downregulated the phosphrylated levels of pGluR1S831 and pGluR1S845 in the striatum of dyskinetic rats. In addition, microsphere treatment reduced the levels of Arc and Penk.

Conclusion

These data indicated that levodopa/benserazide-loaded microspheres could be used to ameliorate the expression of LID by reducing the expression of pGluR1S831 and pGluR1S845 as well as Arc and Penk.

The role of the subthalamic nucleus in L-DOPA induced dyskinesia in 6-hydroxydopamine lesioned rats

L-DOPA is the most effective treatment for Parkinson's disease (PD), but prolonged use leads to disabling motor complications including dyskinesia. Strong evidence supports a role of the subthalamic nucleus (STN) in the pathophysiology of PD whereas its role in dyskinesia is a matter of controversy. Here, we investigated the involvement of STN in dyskinesia, using single-unit extracellular recording, behavioural and molecular approaches in hemi-parkinsonian rats rendered dyskinetic by chronic L-DOPA administration. Our results show that chronic L-DOPA treatment does not modify the abnormal STN activity induced by the 6-hydroxydopamine lesion of the nigrostriatal pathway in this model. Likewise, we observed a loss of STN responsiveness to a single L-DOPA dose both in lesioned and sham animals that received daily L-DOPA treatment. We did not find any correlation between the abnormal involuntary movement (AIM) scores and the electrophysiological parameters of STN neurons recorded 24 h or 20–120 min after the last L-DOPA injection, except for the axial subscores. Nonetheless, unilateral chemical ablation of the STN with ibotenic acid resulted in a reduction in global AIM scores and peak-severity of dyskinesia. In addition, STN lesion decreased the anti-dyskinetogenic effect of buspirone in a reciprocal manner. Striatal protein expression was altered in dyskinetic animals with increases in ΔFosB, phosphoDARPP-32, dopamine receptor (DR) D3 and DRD2/DRD1 ratio. The STN lesion attenuated the striatal molecular changes and normalized the DRD2/DRD1 ratio. Taken together, our results show that the STN plays a role, if modest, in the physiopathology of dyskinesias.