Non-dopaminergic treatments in development for Parkinson's disease

Antagonism of kappa opioid receptors accelerates the development of L-DOPA-induced dyskinesia in a preclinical model of moderate dopamine depletion

Levels of the opioid peptide dynorphin, an endogenous ligand selective for kappa-opioid receptors (KORs), its mRNA and pro-peptide precursors are differentially dysregulated in Parkinson's disease (PD) and following the development of l-DOPA-induced dyskinesia (LID). It remains unclear whether these alterations contribute to the pathophysiological mechanisms underlying PD motor impairment and the subsequent development of LID, or whether they are part of compensatory mechanisms. We sought to investigate nor-BNI, a KOR antagonist, 1) in the dopamine (DA)-depleted PD state, 2) during the development phase of LID, and 3) via measuring of tonic levels of striatal DA. While nor-BNI (3 mg/kg; s.c.) did not lead to functional restoration in the DA-depleted state, it affected the dose-dependent development of abnormal voluntary movements (AIMs) in response to escalating doses of l-DOPA in a rat PD model with a moderate striatal 6-hydroxdopamine (6-OHDA) lesion. We tested five escalating doses of l-DOPA (6, 12, 24, 48, 72 mg/kg; i.p.), and nor-BNI significantly increased the development of AIMs at the 12 and 24 mg/kg l-DOPA doses. However, after reaching the 72 mg/kg l-DOPA, AIMs were not significantly different between control and nor-BNI groups. In summary, while blocking KORs significantly increased the rate of development of LID induced by chronic, escalating doses of l-DOPA in a moderate-lesioned rat PD model, it did not contribute further once the overall severity of LID was established. While we observed an increase of tonic DA levels in the moderately lesioned dorsolateral striatum, there was no tonic DA change following administration of nor-BNI.

Predictability of inter-regional cerebral perfusion similarity on dopamine responsiveness and the moderation role of cognition in PD patients

BACKGROUND

Large heterogeneity can be found in dopamine responsiveness of patients with Parkinson's disease (PD). Instantly and objectively understanding dopamine responsiveness of patients may help clinical practice.

PURPOSE

This PD study explored the predictability of off-state inter-regional cerebral blood flow (CBF) perfusion similarity on patient's dopamine responsiveness and tested whether the predictive power could be moderated by patient's cognitive status.

MATERIALS AND METHOD

The PD cohort with 192 patients (containing off state and on state (PD-off and PD-on)) and the normal control (NC) cohort with 92 subjects were included. The intra-individual CBF relative variation networks were constructed and compared between PD-off and PD-on, PD-off and NC to identify the alterations caused by dopamine depletion. Based on that, regression analysis of off-state inter-regional CBF perfusion similarity on patient's dopamine responsiveness was performed. Finally, moderation analysis was conducted to test the moderation role of cognition on the regression model.

RESULTS

In the PD-off cohort, a total of 82 edges in the network were identified that affected by dopamine depletion. Off-state inter-regional CBF perfusion similarity was found that had a significant influence on patient's dopamine responsiveness. Cognitive status was validated that positively moderated the relationship between off-state inter-regional CBF perfusion similarity and dopamine responsiveness.

CONCLUSION

Dopamine responsiveness of PD patient could be predicted by off-state inter-regional CBF perfusion similarity. Patient's cognitive status might have a positive moderation effect on his/her dopamine responsiveness.

Antagonism of kappa opioid receptors accelerates the development of L-DOPA-induced dyskinesia in a preclinical model of moderate dopamine depletion

Levels of the opioid peptide dynorphin, an endogenous ligand selective for kappa-opioid receptors (KORs), its mRNA and pro-peptide precursors are differentially dysregulated in Parkinson disease (PD) and following the development of L-DOPA-induced dyskinesia (LID). It remains unclear, whether these alterations contribute to the pathophysiological mechanisms underlying PD motor impairment and the subsequent development of LID, or whether they are part of compensatory mechanisms. We sought to investigate nor-BNI, a KOR antagonist, 1) in the dopamine (DA)-depleted PD state, 2) during the development phase of LID, and 3) with measuring tonic levels of striatal DA. Nor-BNI (3 mg/kg; s.c.) did not lead to functional restoration in the DA-depleted state, but a change in the dose-dependent development of abnormal voluntary movements (AIMs) in response to escalating doses of L-DOPA in a rat PD model with a moderate striatal 6-hydroxydopamine (6-OHDA) lesion. We tested five escalating doses of L-DOPA (6, 12, 24, 48, 72 mg/kg; i.p.), and nor-BNI significantly increased the development of AIMs at the 12 and 24 mg/kg L-DOPA doses. However, after dosing with 72 mg/kg L-DOPA, AIMs were not significantly different between control and nor-BNI groups. In summary, while blocking KORs significantly increased the rate of development of LID induced by chronic, escalating doses of L-DOPA in a moderate-lesioned rat PD model, it did not contribute further once the overall severity of LID was established. While we saw an increase of tonic DA levels in the moderately lesioned dorsolateral striatum, there was no tonic DA change following administration of nor-BNI.

Therapeutic Approaches to Non-Motor Symptoms of Parkinson's Disease: A Current Update on Preclinical Evidence

Despite being classified as a movement disorder, Parkinson's disease (PD) is characterized by a wide range of non-motor symptoms that significantly affect the patients' quality of life. However, clear evidence-based therapy recommendations for non-motor symptoms of PD are uncommon. Animal models of PD have previously been shown to be useful for advancing the knowledge and treatment of motor symptoms. However, these models may provide insight into and assess therapies for non-motor symptoms in PD. This paper highlights non-motor symptoms in preclinical models of PD and the current position regarding preclinical therapeutic approaches for these non-motor symptoms. This information may be relevant for designing future preclinical investigations of therapies for nonmotor symptoms in PD.

Socially Assistive Robots for Parkinson's Disease: Needs, Attitudes and Specific Applications as Identified by Healthcare Professionals

To explore how socially assistive robots (SARs) may assist the specific needs of individuals with Parkinson's disease (IwPD), we conducted three focus groups with 12 clinicians who treat IwPD. We present a thematic analysis of their perceptions of the needs of the patients, and their own expectations, perceived advantages, disadvantages and concerns regarding the use of SARs for IwPD. Clinicians were positive towards using SARs for IwPD, if used in the patient's home, for motor, communication, emotional, and cognitive needs, especially for practice and for help with activities of daily living. They were concerned that a SAR might be used to replace clinicians’ work, and stressed it should only augment the clinicians’ work. They thought a SAR may relieve some of the burden experienced by informal caregivers, and identified specific applications for SARs for PD. We asked 18 stakeholders (nine IwPD, nine family members) to rate their level of agreement with the clinicians’ statements. The greatest divergence between their views and those of the clinicians was on the topic of using a SAR as a companion, or as a feeding assistant, to which they objected. This work may be used as a basis for future studies designing SARs for IwPD.

Eye tracking identifies biomarkers in α-synucleinopathies versus progressive supranuclear palsy

OBJECTIVES

This study (1) describes and compares saccade and pupil abnormalities in patients with manifest alpha-synucleinopathies (αSYN: Parkinson's disease (PD), Multiple System Atrophy (MSA)) and a tauopathy (progressive supranuclear palsy (PSP)); (2) determines whether patients with rapid-eye-movement sleep behaviour disorder (RBD), a prodromal stage of αSYN, already have abnormal responses that may indicate a risk for developing PD or MSA.

METHODS

Ninety (46 RBD, 27 PD, 17 MSA) patients with an αSYN, 10 PSP patients, and 132 healthy age-matched controls (CTRL) were examined with a 10-min video-based eye-tracking task (Free Viewing). Participants were free to look anywhere on the screen while saccade and pupil behaviours were measured.

RESULTS

PD, MSA, and PSP spent more time fixating the centre of the screen than CTRL. All patient groups made fewer macro-saccades (> 2◦ amplitude) with smaller amplitude than CTRL. Saccade frequency was greater in RBD than in other patients. Following clip change, saccades were temporarily suppressed, then rebounded at a slower pace than CTRL in all patient groups. RBD had distinct, although discrete saccade abnormalities that were more marked in PD, MSA, and even more in PSP. The vertical saccade rate was reduced in all patients and decreased most in PSP. Clip changes produced large increases or decreases in screen luminance requiring pupil constriction or dilation, respectively. PSP elicited smaller pupil constriction/dilation responses than CTRL, while MSA elicited the opposite.

CONCLUSION

RBD patients already have discrete but less pronounced saccade abnormalities than PD and MSA patients. Vertical gaze palsy and altered pupil control differentiate PSP from αSYN.

Newly Approved and Investigational Drugs for Motor Symptom Control in Parkinson's Disease

Motor symptoms are a core feature of Parkinson's disease (PD) and cause a significant burden on patients' quality of life. Oral levodopa is still the most effective treatment, however, the motor benefits are countered by inherent pharmacologic limitations of the drug. Additionally, with disease progression, chronic levodopa leads to the appearance of motor complications including motor fluctuations and dyskinesia. Furthermore, several motor abnormalities of posture, balance, and gait may become less responsive to levodopa. With these unmet needs and our evolving understanding of the neuroanatomic and pathophysiologic underpinnings of PD, several advances have been made in defining new therapies for motor symptoms. These include newer levodopa formulations and drug delivery systems, refinements in adjunctive medications, and non-dopaminergic treatment strategies. Although some are in early stages of development, these novel treatments potentially widen the available options for the management of motor symptoms allowing clinicians to provide an individually tailored care for PD patients. Here, we review the existing and emerging interventions for PD with focus on newly approved and investigational drugs for motor symptoms, motor fluctuations, dyskinesia, and balance and gait dysfunction.

Wearable Electrochemical Sensors in Parkinson's Disease

Parkinson’s disease (PD) is a neurodegenerative disorder associated with widespread aggregation of α-synuclein and dopaminergic neuronal loss in the substantia nigra pars compacta. As a result, striatal dopaminergic denervation leads to functional changes in the cortico-basal-ganglia-thalamo-cortical loop, which in turn cause most of the parkinsonian signs and symptoms. Despite tremendous advances in the field in the last two decades, the overall management (i.e., diagnosis and follow-up) of patients with PD remains largely based on clinical procedures. Accordingly, a relevant advance in the field would require the development of innovative biomarkers for PD. Recently, the development of miniaturized electrochemical sensors has opened new opportunities in the clinical management of PD thanks to wearable devices able to detect specific biological molecules from various body fluids. We here first summarize the main wearable electrochemical technologies currently available and their possible use as medical devices. Then, we critically discuss the possible strengths and weaknesses of wearable electrochemical devices in the management of chronic diseases including PD. Finally, we speculate about possible future applications of wearable electrochemical sensors in PD, such as the attractive opportunity for personalized closed-loop therapeutic approaches.

Acrolein scavenger dimercaprol offers neuroprotection in an animal model of Parkinson's disease: implication of acrolein and TRPA1

BACKGROUND

The mechanisms underlying lesions of dopaminergic (DA) neurons, an essential pathology of Parkinson's disease (PD), are largely unknown, although oxidative stress is recognized as a key factor. We have previously shown that the pro-oxidative aldehyde acrolein is a critical factor in PD pathology, and that acrolein scavenger hydralazine can reduce the elevated acrolein, mitigate DA neuron death, and alleviate motor deficits in a 6-hydroxydopamine (6-OHDA) rat model. As such, we hypothesize that a structurally distinct acrolein scavenger, dimercaprol (DP), can also offer neuroprotection and behavioral benefits.

METHODS

DP was used to lower the elevated levels of acrolein in the basal ganglia of 6-OHDA rats. The acrolein levels and related pathologies were measured by immunohistochemistry. Locomotor and behavioral effects of 6-OHDA injections and DP treatment were examined using the open field test and rotarod test. Pain was assessed using mechanical allodynia, cold hypersensitivity, and plantar tests. Finally, the effects of DP were assessed in vitro on SK-N-SH dopaminergic cells exposed to acrolein.

RESULTS

DP reduced acrolein and reversed the upregulation of pain-sensing transient receptor potential ankyrin 1 (TRPA1) channels in the substantia nigra, striatum, and cortex. DP also mitigated both motor and sensory deficits typical of PD. In addition, DP lowered acrolein and protected DA-like cells in vitro. Acrolein's ability to upregulate TRPA1 was also verified in vitro using cell lines.

CONCLUSIONS

These results further elucidated the acrolein-mediated pathogenesis and reinforced the critical role of acrolein in PD while providing strong arguments for anti-acrolein treatments as a novel and feasible strategy to combat neurodegeneration in PD. Considering the extensive involvement of acrolein in various nervous system illnesses and beyond, anti-acrolein strategies may have wide applications and broad impacts on human health.

Association of the Non-Motor Burden with Patterns of Striatal Dopamine Loss in de novo Parkinson's Disease

BACKGROUND

Striatal dopamine deficits play a key role in the pathogenesis of Parkinson's disease (PD), and several non-motor symptoms (NMSs) have a dopaminergic component.

OBJECTIVE

To investigate the association between early NMS burden and the patterns of striatal dopamine depletion in patients with de novo PD.

METHODS

We consecutively recruited 255 patients with drug-naïve early-stage PD who underwent 18F-FP-CIT PET scans. The NMS burden of each patient was assessed using the NMS Questionnaire (NMSQuest), and patients were divided into the mild NMS burden (PDNMS-mild) (NMSQuest score <6; n = 91) and severe NMS burden groups (PDNMS-severe) (NMSQuest score >9; n = 90). We compared the striatal dopamine transporter (DAT) activity between the groups.

RESULTS

Patients in the PDNMS-severe group had more severe parkinsonian motor signs than those in the PDNMS-mild group, despite comparable DAT activity in the posterior putamen. DAT activity was more severely depleted in the PDNMS-severe group in the caudate and anterior putamen compared to that in the PDMNS-mild group. The inter-sub-regional ratio of the associative/limbic striatum to the sensorimotor striatum was lower in the PDNMS-severe group, although this value itself lacked fair accuracy for distinguishing between the patients with different NMS burdens.

CONCLUSION

This study demonstrated that PD patients with severe NMS burden exhibited severe motor deficits and relatively diffuse dopamine depletion throughout the striatum. These findings suggest that the level of NMS burden could be associated with distinct patterns of striatal dopamine depletion, which could possibly indicate the overall pathological burden in PD.

PT320, Sustained-Release Exendin-4, Mitigates L-DOPA-Induced Dyskinesia in a Rat 6-Hydroxydopamine Model of Parkinson's Disease

Background

We previously demonstrated that subcutaneous administration of PT320, a sustained-release (SR) form of exendin-4, resulted in the long-term maintenance of steady-state exenatide (exendin-4) plasma and target levels in 6-hydroxydopamine (6-OHDA)-pretreated animals. Additionally, pre- or post-treatment with PT320 mitigated the early stage of 6-OHDA-induced dopaminergic neurodegeneration. The purpose of this study was to evaluate the effect of PT320 on L-3,4-dihydroxyphenylalanine (L-DOPA)-induced abnormal involuntary movements (AIMs) in the rat 6-OHDA model of Parkinson’s disease.

Methods

Adult male Sprague–Dawley rats were unilaterally lesioned in the right medial forebrain bundle by 6-OHDA. L-DOPA and benserazide were given daily for 22 days, starting from 4 weeks after lesioning. PT320 was co-administered weekly for 3 weeks. AIM was evaluated on days 1, 16, and 22 after initiating L-DOPA/benserazide + PT320 treatment. Brain tissues were subsequently collected for HPLC measurements of dopamine (DA) and metabolite concentrations.

Results

L-DOPA/benserazide increased AIMs of limbs and axial as well as the sum of all dyskinesia scores (ALO) over 3 weeks. PT320 significantly reduced the AIM scores of limbs, orolingual, and ALO. Although PT320 did not alter DA levels in the lesioned striatum, PT320 significantly attenuated 6-OHDA-enhanced DA turnover.

Conclusion

PT320 attenuates L-DOPA/benserazide-induced dyskinesia in a 6-OHDA rat model of PD and warrants clinical evaluation to mitigate Parkinson’s disease in humans.

Managing autonomic dysfunction in Parkinson's disease: a review of emerging drugs

Introduction: Autonomic dysfunction is an integral part of Parkinson disease (PD) complex and can be seen both in early and advanced stages. There is a paucity of medicines available to manage autonomic dysfunction in PD and this adds to the considerable morbidity associated with the illness.Areas covered: The pathophysiology and the available therapeutic options of autonomic dysfunction seen in PD are discussed in detail. The potential targets for novel regimens are reviewed and the available literature on the drugs emerging in management of autonomic dysfunction in PD is highlighted.Expert opinion: In the current scenario, there are several drugs that can be tried for constipation viz stool laxatives, prucalopride, prokinetic agents and a high fiber diet. Bladder dysfunction has been treated with β-agonists and with mirabegron, a selective β-3 agonist, the anticholinergic side effects are minimized, and the drug has been found to be effective. Orthostatic hypotension is managed with midodrine while droxidopa is a new drug with promising efficacy. Botulinum toxin works best for management of sialorrhea, but repeated injections are needed.

Pharmacologic Treatment of Motor Symptoms Associated with Parkinson Disease

The cardinal motor features of Parkinson disease (PD) are driven by striatal dopamine deficiency. Pharmacologic dopamine substitution is the mainstay of drug treatment of PD. Levodopa is still the most efficacious drug to treat PD motor symptoms. MAO-B inhibitors and dopamine agonists are useful options. The main limitation of levodopa is the development of motor response fluctuations and drug-induced dyskinesias. Adjunct MAO-B and COMT inhibitors as well as dopamine agonists and continuous infusions of levodopa intestinal gel or subcutaneous apomorphine are efficacious in reducing motor fluctuations and amantadine is the only drug with established efficacy in reducing dyskinesias.

Clonidine modulates the activity of the subthalamic-supplementary motor loop: evidence from a pharmacological study combining deep brain stimulation and electroencephalography recordings in Parkinsonian patients

Clonidine is an anti-hypertensive medication which acts as an alpha-adrenergic receptor agonist. As the noradrenergic system is likely to support cognitive functions including attention and executive control, other clinical uses of clonidine have recently gained popularity for the treatment of neuropsychiatric disorders like attention-deficit hyperactivity disorder or Tourette syndrome, but the mechanism of action is still unclear. Here, we test the hypothesis that the noradrenergic system regulates the activity of subthalamo-motor cortical loops, and that this influence can be modulated by clonidine. We used pharmacological manipulation of clonidine in a placebo-controlled study in combination with subthalamic nucleus-deep brain stimulation (STN-DBS) in 16 Parkinson's disease patients performing a reaction time task requiring to refrain from reacting (proactive inhibition). We recorded electroencephalographical activity of the whole cortex, and applied spectral analyses directly at the source level after advanced blind source separation. We found only one cortical source localized to the supplementary motor area (SMA) that supported an interaction of pharmacological and subthalamic stimulation. Under placebo, STN-DBS reduced proactive alpha power in the SMA, a marker of local inhibitory activity. This effect was associated with the speeding-up of movement initiation. Clonidine substantially increased proactive alpha power from the SMA source, and canceled out the benefits of STN-DBS on movement initiation. These results provide the first direct neural evidence in humans that the tonic inhibitory activity of the subthalamocortical loops underlying the control of movement initiation is coupled to the noradrenergic system, and that this activity can be targeted by pharmacological agents acting on alpha-adrenergic receptors.

Functional imaging studies of Impulse Control Disorders in Parkinson's disease need a stronger neurocognitive footing

Impulse control disorders (ICDs) in Parkinson's disease (PD) are associated with dopaminergic dysfunction and treatment, but have no satisfactory therapeutic solution. While studies assessing the neurofunctional bases of ICDs are important for advancing our understanding and management of ICDs, they remain sparse and inconsistent. Based on a systematic analysis of the neuroimaging literature, the present review pinpoints various abnormalities beyond the mesocorticolimbic circuit that supports reward processing, suggesting possible dysfunction at the sensorimotor, executive and affective levels. We advocate that: 1) Future studies should use more sophisticated psychological models and behavioral designs that take into account the potentially multifaceted aspect of ICDs; this would allow a more accurate assessment of the underlying neurocognitive processes, which are not all dependent on the dopaminergic system. 2) Future neuroimaging studies should rely more strongly on task-based, event-related analyses to disentangle the various mechanisms that can be dysfunctional in ICDs. We believe these guidelines constitute a prerequisite towards distinguishing causes, correlates and individual susceptibility factors of PD patients with ICDs.

PBF509, an Adenosine A2A Receptor Antagonist With Efficacy in Rodent Models of Movement Disorders

Adenosine A_2A receptor (A_2AR) antagonists have emerged as complementary non-dopaminergic drugs to alleviate Parkinson's disease (PD) symptomatology. Here, we characterize a novel non-xhantine non-furan A_2AR antagonist, PBF509, as a potential pro-dopaminergic drug for PD management. First, PBF509 was shown to be a highly potent ligand at the human A_2AR, since it antagonized A_2AR agonist-mediated cAMP accumulation and impedance responses with K_B values of 72.8 ± 17.4 and 8.2 ± 4.2 nM, respectively. Notably, these results validated our new A_2AR-based label-free assay as a robust and sensitive approach to characterize A_2AR ligands. Next, we evaluated the efficacy of PBF509 reversing motor impairments in several rat models of movement disorders, including catalepsy, tremor, and hemiparkinsonism. Thus, PBF509 (orally) antagonized haloperidol-mediated catalepsy, reduced pilocarpine-induced tremulous jaw movements and potentiated the number of contralateral rotations induced by L-3,4-dihydroxyphenylalanine (L-DOPA) in unilaterally 6-OHDA-lesioned rats. Moreover, PBF509 (3 mg/kg) inhibited L-DOPA-induced dyskinesia (LID), showing not only its efficacy on reversing parkinsonian motor impairments but also acting as antidyskinetic agent. Overall, here we describe a new orally selective A_2AR antagonist with potential utility for PD treatment, and for some of the side effects associated to the current pharmacotherapy (i.e., dyskinesia).

The combination of the opioid glycopeptide MMP-2200 and a NMDA receptor antagonist reduced l-DOPA-induced dyskinesia and MMP-2200 by itself reduced dopamine receptor 2-like agonist-induced dyskinesia

Dopamine (DA)-replacement therapy utilizing l-DOPA is the gold standard symptomatic treatment for Parkinson's disease (PD). A critical complication of this therapy is the development of l-DOPA-induced dyskinesia (LID). The endogenous opioid peptides, including enkephalins and dynorphin, are co-transmitters of dopaminergic, GABAergic, and glutamatergic transmission in the direct and indirect striatal output pathways disrupted in PD, and alterations in expression levels of these peptides and their precursors have been implicated in LID genesis and expression. We have previously shown that the opioid glycopeptide drug MMP-2200 (a.k.a. Lactomorphin), a glycosylated derivative of Leu-enkephalin mediates potent behavioral effects in two rodent models of striatal DA depletion. In this study, the mixed mu-delta agonist MMP-2200 was investigated in standard preclinical rodent models of PD and of LID to evaluate its effects on abnormal involuntary movements (AIMs). MMP-2200 showed antiparkinsonian activity, while increasing l-DOPA-induced limb, axial, and oral (LAO) AIMs by ∼10%, and had no effect on dopamine receptor 1 (D1R)-induced LAO AIMs. In contrast, it markedly reduced dopamine receptor 2 (D2R)-like-induced LAO AIMs. The locomotor AIMs were reduced by MMP-2200 in all three conditions. The N-methyl-d-aspartate receptor (NMDAR) antagonist MK-801 has previously been shown to be anti-dyskinetic, but only at doses that induce parkinsonism. When MMP-2200 was co-administered with MK-801, MK-801-induced pro-parkinsonian activity was suppressed, while a robust anti-dyskinetic effect remained. In summary, the opioid glycopeptide MMP-2200 reduced AIMs induced by a D2R-like agonist, and MMP-2200 modified the effect of MK-801 to result in a potent reduction of l-DOPA-induced AIMs without induction of parkinsonism.

Remote control of movement disorders using a photoactive adenosine A2A receptor antagonist

G protein-coupled adenosine receptors are promising therapeutic targets for a wide range of neuropathological conditions, including Parkinson's disease (PD). However, the ubiquity of adenosine receptors and the ultimate lack of selectivity of certain adenosine-based drugs have frequently diminished their therapeutic use. Photopharmacology is a novel approach that allows the spatiotemporal control of receptor function, thus circumventing some of these limitations. Here, we aimed to develop a light-sensitive caged adenosine A_2A receptor (A_2AR) antagonist to photocontrol movement disorders. We synthesized MRS7145 by blocking with coumarin the 5-amino position of the selective A_2AR antagonist SCH442416, which could be photoreleased upon violet light illumination (405 nm). First, the light-dependent pharmacological profile of MRS7145 was determined in A_2AR-expressing cells. Upon photoactivation, MRS7145 precluded A_2AR ligand binding and agonist-induced cAMP accumulation. Next, the ability of MRS7145 to block A_2AR in a light-dependent manner was assessed in vivo. To this end, A_2AR antagonist-mediated locomotor activity potentiation was evaluated in brain (striatum) fiber-optic implanted mice. Upon irradiation (405 nm) of the dorsal striatum, MRS7145 induced significant hyperlocomotion and counteracted haloperidol-induced catalepsy and pilocarpine-induced tremor. Finally, its efficacy in reversing motor impairment was evaluated in a PD animal model, namely the hemiparkinsonian 6-hydroxydopamine (6-OHDA)-lesioned mouse. Photo-activated MRS7145 was able to potentiate the number of contralateral rotations induced by L-3,4-dihydroxyphenylalanine (l-DOPA). Overall, MRS7145 is a new light-operated A_2AR antagonist with potential utility to manage movement disorders, including PD.

Autophagy, its mechanisms and regulation: Implications in neurodegenerative diseases

Autophagy is a major regulatory cellular mechanism which gives the cell an ability to cope with some of the destructive events that normally occur within a metabolically living cell. This is done by maintaining the cellular homeostasis, clearance of damaged organelles and proteins and recycling necessary molecules like amino acids and fatty acids. There is a wide array of factors that influence autophagy in the state of health and disease. Disruption of these mechanisms may not only give rise to several autophagy-related disease, but also it can occur as the result of intracellular changes induced during disease pathogenesis causing exacerbation of the disease. Our knowledge is increasing regarding the role of autophagy and its mechanisms in the pathogenesis of various neurodegenerative diseases such as multiple sclerosis, Parkinson's disease, Alzheimer's disease, Huntington's disease and Amyotrophic lateral sclerosis. Indeed, getting to know about the pathways of autophagy and its regulation can provide the basis for designing therapeutic interventions. In the present paper, we review the pathways of autophagy, its regulation and the possible autophagy-targeting interventions for the treatment of neurodegenerative disorders.

Antiparkinsonian Efficacy of Guanosine in Rodent Models of Movement Disorder

Guanosine (GUO) is a guanine-based purine nucleoside with important trophic functions and promising neuroprotective properties. Although the neuroprotective effects of GUO have been corroborated in cellular models of Parkinson’s disease (PD), its efficacy as an antiparkinsonian agent has not been fully explored in PD animal models. Accordingly, we evaluated the effectiveness of GUO in reversing motor impairments in several rodent movement disorder models, including catalepsy, tremor, and hemiparkinsonism. Our results showed that orally administered GUO antagonized reserpine-mediated catalepsy, reduced reserpine-induced tremulous jaw movements, and potentiated the number of contralateral rotations induced by L-3,4-dihydroxyphenylalanine in unilaterally 6-hydroxidopamine-lesioned rats. In addition, at 5 and 7.5 mg/kg, GUO inhibited L-DOPA-induced dyskinesia in rats chronically treated with a pro-dopaminergic agent. Overall, we describe the therapeutic potential of GUO, which may be effective not only for reversing parkinsonian motor impairments but also for reducing dyskinesia induced by treatment for PD.

Nonmotor Effects of Conventional and Transdermal Dopaminergic Therapies in Parkinson's Disease

Nonmotor symptoms (NMS) are an integral component of Parkinson's disease (PD). Because the burden and range of NMS are key determinants of quality of life for patients and caregivers, their management is a crucial issue in clinical practice. Although a range of NMS have a dopaminergic pathophysiological basis, this fact is underrecognized, and thus, they are often regarded as dopamine unresponsive symptoms. However, substantial evidence indicates that many NMS respond to oral and transdermal dopaminergic therapies. In contrast, certain NMS are exacerbated or even precipitated by dopaminergic drugs and these unwanted effects may be seriously dangerous. Therefore, a dopaminergic strategy for NMS should be based on a consideration of the benefits vs the risks in individual patients with PD.

Non-human primate models of PD to test novel therapies

Non-human primate (NHP) models of Parkinson disease show many similarities with the human disease. They are very useful to test novel pharmacotherapies as reviewed here. The various NHP models of this disease are described with their characteristics including the macaque, the marmoset, and the squirrel monkey models. Lesion-induced and genetic models are described. There is no drug to slow, delay, stop, or cure Parkinson disease; available treatments are symptomatic. The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-Dopa) still remains the gold standard symptomatic treatment of Parkinson. However, involuntary movements termed L-Dopa-induced dyskinesias appear in most patients after chronic treatment and may become disabling. Dyskinesias are very difficult to manage and there is only amantadine approved providing only a modest benefit. In this respect, NHP models have been useful to seek new drug targets, since they reproduce motor complications observed in parkinsonian patients. Therapies to treat motor symptoms in NHP models are reviewed with a discussion of their translational value to humans. Disease-modifying treatments tested in NHP are reviewed as well as surgical treatments. Many biochemical changes in the brain of post-mortem Parkinson disease patients with dyskinesias are reviewed and compare well with those observed in NHP models. Non-motor symptoms can be categorized into psychiatric, autonomic, and sensory symptoms. These symptoms are present in most parkinsonian patients and are already installed many years before the pre-motor phase of the disease. The translational usefulness of NHP models of Parkinson is discussed for non-motor symptoms.

Gastrointestinal Dysfunctions in Parkinson's Disease: Symptoms and Treatments

A diagnosis of Parkinson's disease is classically established after the manifestation of motor symptoms such as rigidity, bradykinesia, and tremor. However, a growing body of evidence supports the hypothesis that nonmotor symptoms, especially gastrointestinal dysfunctions, could be considered as early biomarkers since they are ubiquitously found among confirmed patients and occur much earlier than their motor manifestations. According to Braak's hypothesis, the disease is postulated to originate in the intestine and then spread to the brain via the vagus nerve, a phenomenon that would involve other neuronal types than the well-established dopaminergic population. It has therefore been proposed that peripheral nondopaminergic impairments might precede the alteration of dopaminergic neurons in the central nervous system and, ultimately, the emergence of motor symptoms. Considering the growing interest in the gut-brain axis in Parkinson's disease, this review aims at providing a comprehensive picture of the multiple gastrointestinal features of the disease, along with the therapeutic approaches used to reduce their burden. Moreover, we highlight the importance of gastrointestinal symptoms with respect to the patients' responses towards medical treatments and discuss the various possible adverse interactions that can potentially occur, which are still poorly understood.

How to make a midbrain dopaminergic neuron

Midbrain dopaminergic (mDA) neuron development has been an intense area of research during recent years. This is due in part to a growing interest in regenerative medicine and the hope that treatment for diseases affecting mDA neurons, such as Parkinson's disease (PD), might be facilitated by a better understanding of how these neurons are specified, differentiated and maintained in vivo. This knowledge might help to instruct efforts to generate mDA neurons in vitro, which holds promise not only for cell replacement therapy, but also for disease modeling and drug discovery. In this Primer, we will focus on recent developments in understanding the molecular mechanisms that regulate the development of mDA neurons in vivo, and how they have been used to generate human mDA neurons in vitro from pluripotent stem cells or from somatic cells via direct reprogramming. Current challenges and future avenues in the development of a regenerative medicine for PD will be identified and discussed.

Social intentions in Parkinson's disease patients: A kinematic study

Dysfunction of the dopaminergic system leads to motor, cognitive and motivational symptoms in brain disorders such as Parkinson's disease (PD). Moreover, the dopaminergic system plays an important role in social interactions. The dopaminergic input to the basal ganglia (BG) thought to integrate social cues during the planning and execution of voluntary movements remains, however, largely unexplored. Since PD provides a model to assess this function in humans, our study aimed to investigate the effects of social intentions on actions in non-demented PDpatients receiving dopamine replacement therapy (Levodopa = l-Dopa) and in neurologically healthy control participants. Patients' ability to modulate motor patterning depending on the intention motivating the action to be performed was evaluated both in "on" (with l-Dopa) and "off" (without l-Dopa) states. Participants were instructed to reach for and to grasp an object; they were then told to hand it to another person (social condition) or to place it on a concave frame (individual condition). A 'passive-observer' condition, which was similar to the 'individual' condition except for the presence of an onlooker who simply observed the scene, was also assessed to exclude the possibility that differences might be due to the presence of another person. Movement kinematics were recorded using a three-dimensional motion analysis system. Study results demonstrated that the controls and the PD patients in an 'on' state adopted different kinematic patterning for the 'social' and the 'individual' conditions; the PD patients in the 'off' state, instead, were unable to kinematically differentiate between the two conditions. These results suggest that l-Dopa treatment has positive effects on translating social intentions into specific motor patterns in PD patients.

Treatment of the later stages of Parkinson's disease - pharmacological approaches now and in the future

The problems associated with the pharmacological treatment of the later stages of Parkinson's disease (PD) remain those seen over many years. These centre on a loss of drug effect ('wearing off') with disease progression, the occurrence of dyskinesia, notably with L-dopa use and the appearance of non-motor symptoms that are largely refractory to dopaminergic medication. Treatment strategies in late PD have been dominated by the use of drug combinations and the subtle manipulation of drug dosage. However, change is occurring as the understanding of the basis of motor complications and fluctuations and non-motor symptoms improves. New pharmacological options are expanding with the advent of longer acting versions of existing dopaminergic drugs, new drug delivery systems and the introduction of non-dopaminergic agents able to manipulate motor function both within the basal ganglia and in other brain regions. Non-dopaminergic agents are also being investigated for the treatment of dyskinesia and for the relief of non-motor symptoms. However, while therapy continues to improve, the treatment of late stage PD remains problematic with non-motor symptoms dominating the unmet need in this patient group.

Unprecedented therapeutic potential with a combination of A2A/NR2B receptor antagonists as observed in the 6-OHDA lesioned rat model of Parkinson's disease

In Parkinson's disease, the long-term use of dopamine replacing agents is associated with the development of motor complications; therefore, there is a need for non-dopaminergic drugs. This study evaluated the potential therapeutic impact of six different NR2B and A2A receptor antagonists given either alone or in combination in unilateral 6-OHDA-lesioned rats without (monotherapy) or with (add-on therapy) the co-administration of L-Dopa: Sch-58261+ Merck 22; Sch-58261+Co-101244; Preladenant + Merck 22; Preladenant + Radiprodil; Tozadenant + Radiprodil; Istradefylline + Co-101244. Animals given monotherapy were assessed on distance traveled and rearing, whereas those given add-on therapy were assessed on contralateral rotations. Three-way mixed ANOVA were conducted to assess the main effect of each drug separately and to determine whether any interaction between two drugs was additive or synergistic. Additional post hoc analyses were conducted to compare the effect of the combination with the effect of the drugs alone. Motor activity improved significantly and was sustained for longer when the drugs were given in combination than when administered separately at the same dose. Similarly, when tested as add-on treatment to L-Dopa, the combinations resulted in higher levels of contralateral rotation in comparison to the single drugs. Of special interest, the activity observed with some combinations could not be described by a simplistic additive effect and involved more subtle synergistic pharmacological interactions. The combined administration of A2A/NR2B-receptor antagonists improved motor behaviour in 6-OHDA rats. Given the proven translatability of this model such a combination may be expected to be effective in improving motor symptoms in patients.

Scaling and coordination deficits during dynamic object manipulation in Parkinson's disease

The ability to reach for and dynamically manipulate objects in a dexterous fashion requires scaling and coordination of arm, hand, and fingertip forces during reach and grasp components of this behavior. The neural substrates underlying dynamic object manipulation are not well understood. Insight into the role of basal ganglia-thalamocortical circuits in object manipulation can come from the study of patients with Parkinson's disease (PD). We hypothesized that scaling and coordination aspects of motor control are differentially affected by this disorder. We asked 20 PD patients and 23 age-matched control subjects to reach for, grasp, and lift virtual objects along prescribed paths. The movements were subdivided into two types, intensive (scaling) and coordinative, by detecting their underlying self-similarity. PD patients off medication were significantly impaired relative to control subjects for both aspects of movement. Intensive deficits, reduced peak speed and aperture, were seen during the reach. Coordinative deficits were observed during the reach, namely, the relative position along the trajectory at which peak speed and aperture were achieved, and during the lift, when objects tilted with respect to the gravitational axis. These results suggest that basal ganglia-thalamocortical circuits may play an important role in fine motor coordination. Dopaminergic therapy significantly improved intensive but not coordinative aspects of movements. These findings are consistent with a framework in which tonic levels of dopamine in the dorsal striatum encode the energetic cost of a movement, thereby improving intensive or scaling aspects of movement. However, repletion of brain dopamine levels does not restore finely coordinated movement.

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.

AMPA receptor inhibitors for the treatment of epilepsy: the role of perampanel

α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors in the postsynaptic membrane are involved in fast excitatory signaling in the brain and their activation may lead to the firing of action potentials. Talampanel and perampanel were the first noncompetitive AMPA receptor antagonists to be tested as add-on drugs in patients with refractory partial seizures, and were found to be effective in improving seizure control. Due to an unfavorable kinetic and tolerability profile, talampanel clinical development in the field of epilepsy was discontinued early while perampanel has been recently approved in Europe and the USA as adjunctive therapy for adults with partial seizures with or without secondary generalization. The recommended perampanel starting dose is 2 mg/day once daily, which can be increased up to the recommended maintenance dose of 4-8 mg/day. Increments should be of 2 mg/day and based on clinical response and tolerability. Titration should be performed at 1-week intervals or at lower speed and a 12-mg daily dose should be considered after careful evaluation. To date, no serious and/or idiosyncratic adverse effects have been associated with this agent. Most frequently reported adverse effects are dizziness, ataxia, aggression, irritability, vertigo, somnolence, fatigue, headache and gait disturbance. Weight increase is the only non-neurological adverse effects associated with perampanel.

Alterations of NMDA receptor binding in various brain regions among 6-hydroxydopamine-induced Parkinsonian rats

The N-methyl-d-aspartate (NMDA) system closely interacts with the dopaminergic system and is strongly implicated in the pathophysiological mechanisms and therapeutic paradigms of Parkinson's disease. This study aims to systematically investigate the changes of NMDA receptors in a wide range of brain structures 3 weeks after unilateral medial forebrain bundle lesion by 6-hydroxydopamine (6-OHDA). NMDA receptor distributions and alterations in the post-mortem rat brain were detected by [(3)H] MK-801 binding autoradiography. In the 6-OHDA-induced Parkinsonian rat model, nigrostriatal dopaminergic neuron loss significantly mediated the decreased [(3)H] MK-801 binding, predominantly in the hippocampus (-22.4%, p < 0.001), caudate putamen (-14.1%, p < 0.01), accumbens nucleus (-13.8%, p < 0.05), cingulate cortex (-13.4%, p < 0.001), posteromedial cortical amygdala (-14.5%, p < 0.01) and piriform cortex (-9%, p < 0.05) compared to the controls, while there was a profound reduction of tyrosine hydroxylase (TH) immunohistochemistry in the substantia nigra pars compacta. Alterations in [(3)H] MK-801 in the specific brain regions related to cognitive functions may indicate that cognitive dysfunctions caused by 6-OHDA lesion were via the NMDA system. The downregulation of NMDA receptor binding in the present study provides indirect evidence for plasticity in the NMDA system in the rat brain. The present study improves our understanding of the critical roles of the NMDA receptors in treating neurodegenerative disorders, and implicates NMDA receptors as a novel therapeutic target in the treatment of Parkinson's disease.

Cyperi Rhizoma inhibits the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced reduction in nigrostriatal dopaminergenic neurons in estrogen-deprived mice

ETHNOPHARMACOLOGICAL RELEVANCE

Cyperi Rhizoma has commonly been used for the treatment of gynecological and neuropsychiatric disorders in traditional medicine. The aim of this study was to evaluate the estrogenic properties and neuroprotective effects of Cyperi Rhizoma under estrogen-deprived condition in female mice.

MATERIALS AND METHODS

To determine the estrogen-like effect of Cyperi Rhizoma extract (CRE), we measured luciferase expression after transfection of a promoter construct containing an estrogen response element (ERE) and treatment of CRE. To evaluate the neuroprotective effect of CRE, we measured striatal dopamine, movement ability, tyrosine hydroxylase (TH) immunoreactivity, and apoptosis-related protein expression levels after treatment of CRE either with or without 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) in ovariectomized female mice.

RESULTS

CRE significantly induced the luciferase expression driven by an ERE in PC12 cells, a dopaminergic cell line, in a dose-dependent manner. In mice, MPTP significantly decreased the levels of dopamine in the striatum and behavior performance; in contrast, both CRE and 17β-estradiol benzoate (EB) recovered these parameters to normal levels. CRE and EB treatment also recovered TH immunopositive fibers and cells, respectively, from MPTP toxicity. Additionally, MPTP significantly down-regulated Bcl-2 expression in the mitochondria of dopaminergic cells in the SN, followed by an increase in Bax expression, cytochrome C translocation to the cytosol, and cleaved-caspase-3 expression, whereas these were inhibited by CRE or EB treatment.

CONCLUSIONS

These findings provide the first evidence that CRE has estrogen-like and neuroprotective effects on dopaminergic neurons in estrogen-deprived mice treated with MPTP-toxin.

The development of the rotigotine transdermal patch: a historical perspective

The rotigotine transdermal system is a dopamine receptor agonist delivered over a 24-hour period. It is approved for the treatment of idiopathic Parkinson's disease (PD). This article reviews the development of the rotigotine transdermal system, including rotigotine's receptor profile, steady-state pharmacokinetics, and metabolism. Preclinical studies of rotigotine in animal models of PD and proof-of-concept studies in patients with PD are reviewed. These preclinical and clinical studies established this system as an effective method for providing continuous rotigotine delivery across the skin providing the basis for continued clinical development of rotigotine for the treatment of early and advanced PD.

The effects of fast-off-D2 receptor antagonism on L-DOPA-induced dyskinesia and psychosis in parkinsonian macaques

3,4-Dihydroxyphenylalanine (L-DOPA) treatment of Parkinson's disease (PD) is compromised by motor side effects, such as dyskinesia and non-motor problems, including psychosis. Because of the marked reduction in brain dopamine in PD and the resultant dopamine D2 receptor supersensitivity, it is impossible to use standard potent dopamine D2 receptor antagonists such as haloperidol to alleviate side effects without compromising the anti-parkinsonian benefits of L-DOPA. Haloperidol antagonizes D2 receptors with high affinity and slowly dissociates from D2 receptors (50% dissociation at 38min). We hypothesized that a rapidly dissociating D2 antagonist might allow some functional dopaminergic transmission and thus have a profile, with respect to reduction of dyskinesia and anti-parkinsonian effects, that was more useful therapeutically. The present study tested the principle of using a fast-off-D2 drug, CLR151 (50% dissociation at 23s) to modify L-DOPA actions in cynomolgus macaques with MPTP-parkinsonism. CLR151 (100mg/kg p.o.) reduced L-DOPA-induced dyskinesia and activity in the parkinsonian macaque by 86% and 52% respectively during peak action. CLR151 (100mg/kg) also reduced psychosis-like behaviour (i.e. reduced apparent visual hallucinations by 78%). Nevertheless, this dose of CLR151 significantly reduced the duration of anti-parkinsonian action of L-DOPA, ON-time (by 90%), and increased parkinsonian disability (by 57%). These data suggest that fast-off-D2 dopamine receptor antagonists, with D2-off-rate values close to those for CLR151, are unlikely to be useful in the treatment of dyskinesia and psychosis in PD. However, fast-off-D2 drugs could provide benefit if new congeners would have an even faster dissociation rate. Such drugs are now becoming available.

Pramipexole reduces phosphorylation of α-synuclein at serine-129

α-Synuclein is a central component of the pathogenesis of Parkinson’s disease (PD). Phosphorylation at serine-129 represents an important post-translational modification and constitutes the major form of the protein in Lewy bodies. Several kinases have been implicated in the phosphorylation of α-synuclein. The targeting of kinase pathways as a potential to influence the pathogenesis of PD is an important focus of attention, given that mutations of specific kinases (LRRK2 and PINK1) are causes of familial PD. Pramipexole (PPX) is a dopamine agonist developed for the symptomatic relief of PD. Several in vitro and in vivo laboratory studies have demonstrated that PPX exerts neuroprotective properties in model systems of relevance to PD. The present study demonstrates that PPX inhibits the phosphorylation of α-synuclein and that this is independent of dopamine receptor activation. PPX blocks the increase in phosphorylated α-synuclein induced by inhibition of the ubiquitin proteasomal system. The phosphorylation of α-synuclein occurs in part at least through casein kinase 2, and PPX in turn reduces the phosphorylation of this enzyme, thereby inhibiting its activity. Thus, PPX decreases the phosphorylation of α-synuclein, and this mechanism may contribute to its protective properties in PD models.

The adverse event profile of perampanel: meta-analysis of randomized controlled trials

BACKGROUND AND PURPOSE

To identify adverse events (AEs) significantly associated with perampanel treatment in double-blind clinical studies (RCTs). Serious AEs, study withdrawals due to AEs and dose-effect responses of individual AEs were also investigated.

METHODS

All placebo controlled, double-blind RCTs investigating therapeutic effects of oral perampanel were searched. AEs were assessed for their association with perampanel after exclusion of synonyms, rare AEs and non-assessable AEs. Risk difference (RD) was used to evaluate the association of any AE (99% confidence intervals) and withdrawals or serious AEs (95% confidence intervals) with perampanel.

RESULTS

Nine RCTs (five in pharmacoresistant epilepsy and four in Parkinson's disease) were included in our study. Almost 4000 patients had been recruited, 2627 of whom were randomized to perampanel and treated with drug doses of 0.5 mg/day (n = 68), 1 mg/day (n = 65), 2 mg/day (n = 753), 4 mg/day (n = 1017), 8 mg/day (n = 431) or 12 mg/day (n = 293). Serious AEs were not significantly associated with perampanel treatment. The experimental drug was significantly associated with an increased risk of AE-related study withdrawals at 4 mg/day [RD (95% confidence interval) 0.03 (0.00, 0.06)] and 12 mg/day [RD (95% confidence interval) 0.13 (0.07, 0.18)]. Of 15 identified AEs, five (dizziness, ataxia, somnolence, irritability and weight increase) were found to be significantly associated with perampanel and one (seizure worsening) was significantly associated with placebo.

CONCLUSIONS

Vestibulocerebellar AEs (dizziness, ataxia), sedative effects (somnolence), irritability and weight increase were significantly associated with perampanel treatment.