Post- versus presynaptic plasticity in L-DOPA-induced dyskinesia

Effects of genetic knockdown of the serotonin transporter on established L-DOPA-induced dyskinesia and gene expression in hemiparkinsonian rats

Parkinson's disease (PD) is a neurodegenerative disorder typified by the loss of dopamine (DA) neurons in the substantia nigra pars compacta (SNpc) leading to motor symptoms including resting tremor, rigidity, akinesia, and postural instability. DA replacement therapy with levodopa (L-DOPA) remains the gold-standard treatment for the motor symptoms of PD. Unfortunately, chronic use of L-DOPA leads to the development of side effects known as L-DOPA-induced dyskinesia (LID). The mechanisms underlying LID are multifaceted, but accumulating research has strongly implicated maladaptive neuroplasticity within the raphe-striatal serotonin (5-HT) circuit. The 5-HT transporter (SERT) has emerged as an intriguing therapeutic target as it is upregulated in the brains of dyskinetic patients and animal models of LID, and pharmacological blockade of SERT alters L-DOPA's effects. Therefore, the current study employed an interventional genetic knockdown of SERT (SERT-KD) to investigate its role in LID expression and LID-associated transcription factors. To do so, hemiparkinsonian, stably dyskinetic rats (N = 68) received adeno-associated virus 9 (AAV9) expressing either a short-hairpin RNA against SERT (SERT-shRNA) or a scrambled control shRNA (SCR-shRNA) after which LID reinstatement and motor performance were assayed over 2 weeks. Dorsal raphe and striatal tissue were collected for the expression analyses of known parkinsonian and LID-associated genes. Results demonstrated that SERT-KD significantly and durably reduced LID and L-DOPA-induced striatal cFOS mRNA without altering L-DOPA efficacy. Such findings point to SERT-mediated adaptations as a 5-HT mechanism by which L-DOPA exerts its actions and therapeutic target for LID.

Phosphodiesterase inhibition and Gucy2C activation enhance tyrosine hydroxylase Ser40 phosphorylation and improve 6-hydroxydopamine-induced motor deficits

BACKGROUND

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the nigrostriatal pathway, leading to dopamine deficiency and motor impairments. Current treatments, such as L-DOPA, provide symptomatic relief but result in off-target effects and diminished efficacy over time. This study explores an alternative approach by investigating the activation of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Specifically, we explore the effects of phosphodiesterase (PDE) inhibition and guanylate cyclase-C (GUCY2C) activation on tyrosine hydroxylase Ser40 phosphorylation and their impact on motor behavior in a 6-hydroxydopamine (6-OHDA) Parkinson's disease model.

RESULTS

Our findings demonstrate that increasing cyclic nucleotide levels through PDE inhibition and GUCY2C activation significantly enhances tyrosine hydroxylase Ser40 phosphorylation. In a Pitx3-deficient mouse model, which mimics the loss of dopaminergic neurons seen in Parkinson's disease, Ser40 phosphorylation remained manipulable despite reduced tyrosine hydroxylase protein levels. Moreover, we observed no evidence of tyrosine hydroxylase degradation due to Ser40 phosphorylation, challenging previous reports. Furthermore, both PDE inhibition and GUCY2C activation resulted in improved motor behavior in the 6-OHDA Parkinson's disease mouse model, highlighting the potential therapeutic benefits of these approaches.

CONCLUSIONS

This study underscores the therapeutic potential of enhancing tyrosine hydroxylase Ser40 phosphorylation to improve motor function in Parkinson's disease. Both PDE inhibition and GUCY2C activation represent promising non-invasive strategies to modulate endogenous dopamine biosynthesis and address motor deficits. These findings suggest that targeting cyclic nucleotide pathways could lead to novel therapeutic approaches, either as standalone treatments or in combination with existing therapies like L-DOPA, aiming to provide more durable symptom relief and potentially mitigate neurodegeneration in Parkinson's disease.

Natural Product-Inspired Dopamine Receptor Ligands

Due to their evolutionary bias as ligands for biologically relevant drug targets, natural products offer a unique opportunity as lead compounds in drug discovery. Given the involvement of dopamine receptors in various physiological and behavioral functions, they are linked to numerous diseases and disorders such as Parkinson's disease, schizophrenia, and substance use disorders. Consequently, ligands targeting dopamine receptors hold considerable therapeutic and investigative promise. As this perspective will highlight, dopamine receptor targeting natural products play a pivotal role as scaffolds with unique and beneficial pharmacological properties, allowing for natural product-inspired drug design and lead optimization. As such, dopamine receptor targeting natural products still have untapped potential to aid in the treatment of disorders and diseases related to central nervous system (CNS) and peripheral nervous system (PNS) dysfunction.

The chronic use of serotonin norepinephrine reuptake inhibitors facilitates dyskinesia priming in early Parkinson's disease

BACKGROUND

Parkinson's disease (PD) patients are frequently exposed to antidepressant medications (ADMs). Norepinephrine (NE) and serotonin (5HT) systems have a role in levodopa-induced dyskinesias (LID) pathophysiology.

METHODS

We performed a longitudinal analysis on the PPMI cohort including drug-naïve PD patients, who are progressively exposed to dopamine replacement therapies (DRTs) to test the effect of ADM exposure on LID development by the 4th year of follow-up.

RESULTS

LID prevalence (according to MDS UPDRS score 4.1 ≥ 1) was 16% (42/251); these patients were more likely women (p = 0.01), had higher motor (p < 0.001) and depression scores (p = 0.01) and lower putaminal DAT binding ratio (p = 0.01). LID were associated with the exposure time to L-DOPA (2.2 ± 1.07 vs 2.6 ± 0.9, p = 0.02) and to the exposure to ADMs, in particular to SNRI (4.8% vs 21.4%, p < 0.001). The latter persisted after correcting for significant covariates (e.g., disease duration, cognitive status, motor impairment, depression, dopaminergic denervation). A similar difference in LID prevalence in PD patients exposed vs non-exposed to SNRI was observed on matched data by the real-world TriNetX repository (22% vs 13%, p < 0.001).

DISCUSSION

This study supports the presence of an effect of SNRI on LID priming in patients with early PD. Independent prospective cohort studies are warranted to further verify such association.

Targeting Striatal Glutamate and Phosphodiesterases to Control L-DOPA-Induced Dyskinesia

A large body of work during the past several decades has been focused on therapeutic strategies to control L-DOPA-induced dyskinesias (LIDs), common motor complications of long-term L-DOPA therapy in Parkinson's disease (PD). Yet, LIDs remain a clinical challenge for the management of patients with advanced disease. Glutamatergic dysregulation of striatal projection neurons (SPNs) appears to be a key contributor to altered motor responses to L-DOPA. Targeting striatal hyperactivity at the glutamatergic neurotransmission level led to significant preclinical and clinical trials of a variety of antiglutamatergic agents. In fact, the only FDA-approved treatment for LIDs is amantadine, a drug with NMDAR antagonistic actions. Still, novel agents with improved pharmacological profiles are needed for LID therapy. Recently other therapeutic targets to reduce dysregulated SPN activity at the signal transduction level have emerged. In particular, mechanisms regulating the levels of cyclic nucleotides play a major role in the transduction of dopamine signals in SPNs. The phosphodiesterases (PDEs), a large family of enzymes that degrade cyclic nucleotides in a specific manner, are of special interest. We will review the research for antiglutamatergic and PDE inhibition strategies in view of the future development of novel LID therapies.

Activation of mGlu2/3 receptors in the striatum alleviates L-DOPA-induced dyskinesia and inhibits abnormal postsynaptic molecular expression

Group II metabotropic glutamate receptors (mGlu2/3 receptors) have been regarded as promising candidates for the treatment of L-DOPA-induced dyskinesia (LID); however, confirmation is still lacking. As the hub of the basal ganglia circuit, the striatum plays a critical role in action control. Supersensitive responsiveness of glutamatergic corticostriatal input may be the key mechanism for the development of LID. In this study, we first examined the potency of LY354740 (12 mg/kg, i.p.) in modulating glutamate and dopamine release in lesioned striatum of stable LID rats. Then, we injected LY354740 (20nmoL or 40nmoL in 4 μL of sterile 0.9 % saline) directly into the lesioned striatum to verify its ability to reduce or attenuate L-DOPA-induced abnormal involuntary movements. In experiment conducted in established LID rats, after continuous injection for 4 days, we found that LY354740 significantly reduced the expression of dyskinesia. In another experiment conducted in parkinsonism rat models, we found that LY354740 attenuated the development of LID with an inverted-U dose-response curve. The role of LY354740 in modulating striatal expressions of LID-related molecular changes was also assessed after these behavioral experiments. We found that LY354740 significantly inhibited abnormal expressions of p-Fyn/p-NMDA/p-ERK1/2/p-HistoneH3/ΔFosB, which is in line with its ability to alleviate abnormal involuntary movements in both LID expression and induction phase. Our study indicates that activation of striatal mGlu2/3 receptors can attenuate the development of dyskinesia in parkinsonism rats and provide some functional improvements in LID rats by inhibiting LID-related molecular changes.

Serotonin 5-HT1A receptors and their interactions with adenosine A2A receptors in Parkinson's disease and dyskinesia

The dopamine neuronal loss that characterizes Parkinson's Disease (PD) is associated to changes in neurotransmitters, such as serotonin and adenosine, which contribute to the symptomatology of PD and to the onset of dyskinetic movements associated to levodopa treatment. The present review describes the role played by serotonin 5-HT_1A receptors and the adenosine A_2A receptors on dyskinetic movements induced by chronic levodopa in PD. The focus is on preclinical and clinical results showing the interaction between serotonin 5-HT_1A receptors and other receptors such as 5-HT_1B receptors and adenosine A_2A receptors. 5-HT_1A/1B receptor agonists and A_2A receptor antagonists, administered in combination, contrast dyskinetic movements induced by chronic levodopa without impairing motor behaviour, suggesting that this drug combination might be a useful therapeutic approach for counteracting the PD motor deficits and dyskinesia associated with chronic levodopa treatment. This article is part of the Special Issue on "The receptor-receptor interaction as a new target for therapy".

Characterizing the relationship between L-DOPA-induced-dyskinesia and psychosis-like behaviors in a bilateral rat model of Parkinson's disease

Parkinson's disease associated psychosis (PDAP) is a prevalent non-motor symptom (NMS) that significantly erodes patients' and caregivers' quality of life yet remains vastly understudied. One potential source of PDAP in late-stage Parkinson's disease (PD) is the common dopamine (DA) replacement therapy for motor symptoms, Levodopa (L-DOPA). Given the high incidence of L-DOPA-induced dyskinesia (LID) in later phases of PD, this study sought to characterize the relationship between PDAP and LID in a bilateral medial forebrain bundle 6-hydroxydopamine hydrobromide (6-OHDA) lesion rat model. To assess PDAP in this model, prepulse inhibition (PPI), a well-validated assay of sensorimotor gating, was employed. First, we tested whether a bilateral lesion alone or after chronic L-DOPA treatment was sufficient to induce PPI dysfunction. Rats were also monitored for LID development, using the abnormal involuntary movements (AIMs) test, to examine PPI and LID associations. In experiment 2, Vilazodone (VZD), a serotonin transporter (SERT) blocker and 1A receptor (5-HT_1A) partial agonist was administered to test its potential efficacy in reducing LID and PPI dysfunction. Once testing was complete, tissue was collected for high performance liquid chromatography (HPLC) to examine the monoamine levels in motor and non-motor circuits. Results indicate that bilateral DA lesions produced motor deficits and that chronic L-DOPA induced moderate AIMs; importantly, rats that developed more severe AIMs were more likely to display sensorimotor gating dysfunction. In addition, VZD treatment dose-dependently reduced L-DOPA-induced AIMs without impairing L-DOPA efficacy, although VZD's effects on PPI were limited. Altogether, this project established the bilateral 6-OHDA lesion model accurately portrayed LID and PDAP-like behaviors, uncovered their potential relationship, and finally, demonstrated the utility of VZD for reducing LID.

Doxycycline attenuates l-DOPA-induced dyskinesia through an anti-inflammatory effect in a hemiparkinsonian mouse model

The pharmacological manipulation of neuroinflammation appears to be a promising strategy to alleviate l-DOPA-induced dyskinesia (LID) in Parkinson's disease (PD). Doxycycline (Doxy), a semisynthetic brain-penetrant tetracycline antibiotic having interesting anti-inflammatory properties, we addressed the possibility that this compound could resolve LID in l-DOPA-treated C57BL/6 mice presenting either moderate or intermediate lesions of the mesostriatal dopaminergic pathway generated by intrastriatal injections of 6-OHDA. Doxy, when given subcutaneously before l-DOPA at doses of 20 mg kg-1 and 40 mg kg-1, led to significant LID reduction in mice with moderate and intermediate dopaminergic lesions, respectively. Importantly, Doxy did not reduce locomotor activity improved by l-DOPA. To address the molecular mechanism of Doxy, we sacrificed mice with mild lesions 1) to perform the immunodetection of tyrosine hydroxylase (TH) and Fos-B and 2) to evaluate a panel of inflammation markers in the striatum, such as cyclooxygenase-2 and its downstream product Prostaglandin E2 along with the cytokines TNF-α, IL-1β and IL-6. TH-immunodetection revealed that vehicle and Doxy-treated mice had similar striatal lesions, excluding that LID improvement by Doxy could result from neurorestorative effects. Importantly, LID inhibition by Doxy was associated with decreased Fos-B and COX-2 expression and reduced levels of PGE2, TNF-α, and IL-1β in the dorsolateral striatum of dyskinetic mice. We conclude 1) that Doxy has the potential to prevent LID regardless of the intensity of dopaminergic lesioning and 2) that the anti-inflammatory effects of Doxy probably account for LID attenuation. Overall, the present results further indicate that Doxy might represent an attractive and alternative treatment for LID in PD.

Low skull bone density is associated with poor motor prognosis in women with Parkinson’s disease

Parkinson’s disease (PD) and osteoporosis are degenerative diseases that have shared pathomechanisms. To investigate the associations of skull bone density with nigrostriatal dopaminergic degeneration and longitudinal motor prognosis in female patients with PD. We analyzed the data of 260 drug-naïve female PD patients aged ≥50 years old who were followed-up for ≥3 years after their first visit to the clinic with baseline dopamine transporter (DAT) imaging. We measured skull bone density as a surrogate marker for systemic bone loss by calculating the Hounsfield unit (HU) in computed tomography scans. A Cox proportional hazard model was built to compare the rates of levodopa-induced dyskinesia (LID) or wearing-off according to skull HU. Longitudinal changes in levodopa-equivalent dose (LED) during a 3-year follow-up were assessed using a linear mixed model. A lower skull HU was associated with lower baseline DAT availability in striatal subregions; however, this relationship was not significant after adjusting for age, disease duration, body mass index, and white matter hyperintensities. After adjusting for confounding factors, a lower skull HU was significantly associated with an increased risk of LID development (hazard ratio = 1.660 per 1 standard deviation decrease, p = 0.007) and wearing-off (hazard ratio = 1.613, p = 0.016) in younger (&lt;67 years) but not in older patients. Furthermore, a lower skull HU was associated with a steeper increase in LED during follow-up in younger patients only (β = –21.99, p &lt; 0.001). This study suggests that baseline skull bone density would be closely linked to motor prognosis in drug naïve women with PD.

Nanomedicine in the Face of Parkinson's Disease: From Drug Delivery Systems to Nanozymes

The complexity and overall burden of Parkinson's disease (PD) require new pharmacological approaches to counteract the symptomatology while reducing the progressive neurodegeneration of affected dopaminergic neurons. Since the pathophysiological signature of PD is characterized by the loss of physiological levels of dopamine (DA) and the misfolding and aggregation of the alpha-synuclein (α-syn) protein, new proposals seek to restore the lost DA and inhibit the progressive damage derived from pathological α-syn and its impact in terms of oxidative stress. In this line, nanomedicine (the medical application of nanotechnology) has achieved significant advances in the development of nanocarriers capable of transporting and delivering basal state DA in a controlled manner in the tissues of interest, as well as highly selective catalytic nanostructures with enzyme-like properties for the elimination of reactive oxygen species (responsible for oxidative stress) and the proteolysis of misfolded proteins. Although some of these proposals remain in their early stages, the deepening of our knowledge concerning the pathological processes of PD and the advances in nanomedicine could endow for the development of potential treatments for this still incurable condition. Therefore, in this paper, we offer: (i) a brief summary of the most recent findings concerning the physiology of motor regulation and (ii) the molecular neuropathological processes associated with PD, together with (iii) a recapitulation of the current progress in controlled DA release by nanocarriers and (iv) the design of nanozymes, catalytic nanostructures with oxidoreductase-, chaperon, and protease-like properties. Finally, we conclude by describing the prospects and knowledge gaps to overcome and consider as research into nanotherapies for PD continues, especially when clinical translations take place.

Discovery of levodopa-induced dyskinesia-associated genes using genomic studies in patients and Drosophila behavioral analyses

Although levodopa is the most effective medication for Parkinson’s disease, long-term levodopa treatment is largely compromised due to late motor complications, including levodopa-induced dyskinesia (LID). However, the genetic basis of LID pathogenesis has not been fully understood. Here, we discover genes pathogenic for LID using Drosophila genetics and behavioral analyses combined with genome-wide association studies on 578 patients clinically diagnosed with LID. Similar to the therapeutic effect of levodopa in patients, acute levodopa treatments restore the motor defect of Parkinson’s disease model flies, while prolonged treatments cause LID-related symptoms, such as increased yawing, freezing and abrupt acceleration of locomotion. These symptoms require dopamine 1-like receptor 1 and are induced by neuronal overexpression of the receptor. Among genes selected from our analyses in the patient genome, neuronal knockdown of adenylyl cyclase 2 suppresses the levodopa-induced phenotypes and the receptor overexpression-induced symptoms in Drosophila. Together, our study provides genetic insights for LID pathogenesis through the D1-like receptor-adenylyl cyclase 2 signaling axis.

A combined research approach using GWAS on Parkinson's disease patients and a Drosophila model of L-DOPA-induced dyskinesia (LID) reveals that LID is linked to ADCY2 signaling.

Long-term effects of safinamide adjunct therapy on levodopa-induced dyskinesia in Parkinson's disease: post-hoc analysis of a Japanese phase III study

This post-hoc analysis investigated the long-term effects of safinamide on the course of dyskinesia and efficacy outcomes using data from a phase III, open-label 52-week study of safinamide 50 or 100 mg/day in Japanese patients with Parkinson’s disease (PD) with wearing-off. Patients (N = 194) were grouped using the UPDRS Part IV item 32: with and without pre-existing dyskinesia (pre-D subgroup; item 32 > 0 at baseline [n = 81], without pre-D subgroup; item 32 = 0 at baseline [n = 113]). ON-time with troublesome dyskinesia (ON-TD) increased significantly from baseline to Week 4 in the pre-D subgroup (+ 0.25 ± 0.11 h [mean ± SE], p = 0.0355) but gradually decreased up to Week 52 (change from baseline: − 0.08 ± 0.17 h, p = 0.6224); ON-TD did not change significantly in the Without pre-D subgroup. UPDRS Part IV item 32 score increased significantly at Week 52 compared with baseline in the Without pre-D subgroup, but no UPDRS Part IV dyskinesia related-domains changed in the pre-D subgroup. Both subgroups improved in ON-time without TD, UPDRS Part III, and Part II [OFF-phase] scores. The cumulative incidence of new or worsening dyskinesia (adverse drug reaction) at Week 52 was 32.5 and 5.0% in the pre-D and Without pre-D subgroups, respectively. This study suggested that safinamide led to short-term increasing dyskinesia but may be not associated with marked dyskinesia at 1-year follow-up in patients with pre-existing dyskinesia, and that it improved motor symptoms regardless of the presence or absence of dyskinesia at baseline. Further studies are warranted to investigate this association in more details.

Trial registration: JapicCTI-153057 (Registered: 2015/11/02).

Contracted thalamic shape is associated with early development of levodopa-induced dyskinesia in Parkinson's disease

Levodopa-induced dyskinesia (LID), a long-term motor complication in Parkinson’s disease (PD), is attributable to both presynaptic and postsynaptic mechanisms. However, no studies have evaluated the baseline structural changes associated with LID at a subcortical level in PD. A total of 116 right-handed PD patients were recruited and based on the LID latency of 5 years, we classified patients into those vulnerable to LID (PD-vLID, n = 49) and those resistant to LID (PD-rLID, n = 67). After adjusting for covariates including dopamine transporter (DAT) availability of the posterior putamen, we compared the subcortical shape between the groups and investigated its association with the onset of LID. The PD-vLID group had lower DAT availability in the posterior putamen, higher parkinsonian motor deficits, and faster increment in levodopa equivalent dose than the PD-rLID group. The PD-vLID group had significant inward deformation in the right thalamus compared to the PD-rLID group. Inward deformation in the thalamus was associated with an earlier onset of LID at baseline. This study suggests that independent of presynaptic dopamine depletion, the thalamus is a major neural substrate for LID and that a contracted thalamic shape at baseline is closely associated with an early development of LID.

White matter connectivity networks predict levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND

Although levodopa-induced dyskinesia-relevant white matter change has been evaluated, it is uncertain whether these changes may reflect the underlying predisposing conditions leading to the development of levodopa-induced dyskinesia.

OBJECTIVE

To elucidate the role of white matter connectivity networks in the development of levodopa-induced dyskinesia in drug-naïve Parkinson's disease.

METHODS

We recruited 30 patients who developed levodopa-induced dyskinesia within 5 years from MRI acquisition (vulnerable-group), 47 patients who had not developed levodopa-induced dyskinesia within 5 years (resistant-group), and 28 controls. We performed comparative analyses of whole-brain white matter integrity and connectivity using tract-based spatial and network- and degree-based statistics. We evaluated the predictability of levodopa-induced dyskinesia development and relationship with its latency, using the average connectivity strength as a predictor in Cox- and linear-regression, respectively.

RESULTS

Mean-diffusivity was lower mainly at the left frontal region in the vulnerable-group compared to the resistant-group. Network-based statistics identified a subnetwork consisting of the bilateral fronto-striato-pallido-thalamic and lateral parietal regions (subnetwork A) and degree-based statistics identified four subnetworks (hub-subnetwork) consisting of edges centered on the left superior frontal gyrus, left putamen, left insular, or left precentral gyrus, where the vulnerable-group had stronger connectivity compared to the resistant-group. Stronger connectivity within the subnetwork A and hub-subnetwork centered on the left superior frontal gyrus was a predictor of levodopa-induced dyskinesia development independent of known risk factors and had an inverse relationship with its latency.

CONCLUSIONS

Our data suggest that white matter connectivity subnetworks within corticostriatal regions play a pivotal role in the development of levodopa-induced dyskinesia.

Cabergoline, a long-acting dopamine agonist, attenuates L-dopa-induced dyskinesia without L-dopa sparing in a rat model of Parkinson's disease

Intermittent administration of L-dopa in Parkinson's disease is associated with L-dopa-induced dyskinesia (LID). Long-acting dopamine agonists may reduce the risk of LID by continuous dopaminergic stimulation. We examined the LID-like behavior, preprodynorphin messenger ribonucleic acid (mRNA) expression in the striatum (a neurochemical LID hallmark), and the volume of the entopeduncular nucleus (a pathological LID hallmark) in Parkinson's disease rat models that were treated with L-dopa and cabergoline. Cabergoline co-treatment with L-dopa reduced LID, striatal preprodynorphin mRNA expression, and hypertrophy of the entopeduncular nucleus, indicating that cabergoline has an anti-LID effect independent of the L-dopa-sparing effect.

[Relevance of COMT inhibitors in the treatment of motor fluctuations]

Catechol O‑methyltransferase (COMT) inhibitors have been established in the treatment of Parkinson's disease for more than 20 years. They are considered the medication of choice for treating motor fluctuations. The available COMT inhibitors, entacapone, opicapone and tolcapone, differ pharmacokinetically in terms of their half-lives with implications for the dose frequency, in their indication requirements and in their spectrum of side effects, including diarrhea and yellow discoloration of urine. Many patients with motor fluctuations are currently not treated with COMT inhibitors and are, therefore, unlikely to receive individually optimized drug treatment. This manuscript summarizes the results of a working group including several Parkinson's disease experts, in which the value of COMT inhibitors was critically discussed.

Bipolar spectrum disorders in neurologic disorders

Psychiatric symptoms frequently predate or complicate neurological disorders, such as neurodegenerative diseases. Symptoms of bipolar spectrum disorders (BSD), like mood, behavioral, and psychotic alterations, are known to occur - individually or as a syndromic cluster - in Parkinson's disease and in the behavioral variant of frontotemporal dementia (FTD). Nonetheless, due to shared pathophysiological mechanisms, or genetic predisposition, several other neurological disorders show significant, yet neglected, clinical and biological overlaps with BSD like neuroinflammation, ion channel dysfunctions, neurotransmission imbalance, or neurodegeneration. BSD pathophysiology is still largely unclear, but large-scale network dysfunctions are known to participate in the onset of mood disorders and psychotic symptoms. Thus, functional alterations can unleash BSD symptoms years before the evidence of an organic disease of the central nervous system. The aim of our narrative review was to illustrate the numerous intersections between BSD and neurological disorders from a clinical-biological point of view and the underlying predisposing factors, to guide future diagnostic and therapeutical research in the field.

Role of 5-HT1A Receptor in Vilazodone-Mediated Suppression of L-DOPA-Induced Dyskinesia and Increased Responsiveness to Cortical Input in Striatal Medium Spiny Neurons in an Animal Model of Parkinson's Disease

L-DOPA therapy in Parkinson’s disease (PD) is limited due to emerging L-DOPA-induced dyskinesia. Research has identified abnormal dopamine release from serotonergic (5-HT) terminals contributing to this dyskinesia. Selective serotonin reuptake inhibitors (SSRIs) or 5-HT receptor (5-HTr) agonists can regulate 5-HT activity and attenuate dyskinesia, but they often also produce a loss of the antiparkinsonian efficacy of L-DOPA. We investigated vilazodone, a novel multimodal 5-HT agent with SSRI and 5-HTr_1A partial agonist properties, for its potential to reduce dyskinesia without interfering with the prokinetic effects of L-DOPA, and underlying mechanisms. We assessed vilazodone effects on L-DOPA-induced dyskinesia (abnormal involuntary movements, AIMs) and aberrant responsiveness to corticostriatal drive in striatal medium spiny neurons (MSNs) measured with in vivo single-unit extracellular recordings, in the 6-OHDA rat model of PD. Vilazodone (10 mg/kg) suppressed all subtypes (axial, limb, orolingual) of AIMs induced by L-DOPA (5 mg/kg) and the increase in MSN responsiveness to cortical stimulation (shorter spike onset latency). Both the antidyskinetic effects and reversal in MSN excitability by vilazodone were inhibited by the 5-HTr_1A antagonist WAY-100635, demonstrating a critical role for 5-HTr_1A in these vilazodone actions. Our results indicate that vilazodone may serve as an adjunct therapeutic for reducing dyskinesia in patients with PD.

Antiparkinsonian Effects of a Metabotropic Glutamate Receptor 4 Agonist in MPTP-Treated Marmosets

BACKGROUND

Increased firing across glutamatergic synapses may contribute to both the motor dysfunction and L-DOPA-induced dyskinesia seen in Parkinson's disease. Given their ability to reduce glutamate release, activation of group III metabotropic glutamate receptors such as metabotropic glutamate receptor 4 may prove effective against both motor dysfunction and dyskinesia in Parkinson's disease.

OBJECTIVE

We hypothesised that activation of metabotropic glutamate receptor 4 by an orthosteric agonist ((2S)-2-amino-4-(hydroxy(hydroxy(4-hydroxy-3-methoxy-5-nitrophenyl)methyl)phosphoryl)butanoic acid, LSP1-2111) would produce antiparkinsonian activity and reduce expression of dyskinesia in a 1-methyl-4-phenyl,1,2,3,6-tetrahydropyridine (MPTP)-treated marmoset model of Parkinson's disease.

METHODS

Common marmosets were previously treated with MPTP and pre-primed with L-DOPA for up to 28 days to express dyskinesia. LSP1-2111 (1, 3, or 6 mg/kg s.c.) or vehicle (0.9% saline s.c.) were administered immediately prior to L-DOPA (8 mg/kg + benserazide (10 mg/kg) p.o.) or vehicle (10% sucrose p.o.). Locomotor activity was measured in automated test cages and animals were scored for dyskinesia and disability.

RESULTS

As expected, L-DOPA reversed motor disability and induced moderate dyskinesia. By contrast, LSP1-2111 alone significantly reduced the motor disability without any accompanying expression of dyskinesia. When administered in combination with L-DOPA, LSP1-2111 did not significantly reduce the severity of L-DOPA-induced dyskinesia.

CONCLUSION

Systemic administration of LSP1-2111 reduces motor disability without causing dyskinesia in MPTP-treated marmosets, supporting a role for metabotropic glutamate receptor 4 orthosteric agonists as promising monotherapy for PD. Conversely, this study found no evidence to support their use as antidyskinetic agents within the dose range tested.

New insights into pathogenesis of l-DOPA-induced dyskinesia

Parkinson's disease (PD) is a progressive and self-propelling neurodegenerative disorder, which is characterized by motor symptoms, such as rigidity, tremor, slowness of movement and problems with gait. These symptoms become worse over time. To date, Dopamine (DA) replacement therapy with 3, 4-dihydroxy-l-phenylalanine (L-DOPA) is still the most effective pharmacotherapy for motor symptoms of PD. Unfortunately, motor fluctuations consisting of wearing-off effect actions and dyskinesia tend to occur in a few years of starting l-DOPA. Currently, l-DOPA-induced dyskinesia (LID) is troublesome and the pathogenesis of LID requires further investigation. Importantly, a new intervention for LID is imminent. Thus, this review mainly summarized the clinical features, risk factors and pathogenesis of LID to provide updatefor the development of therapeutic targets and new approaches for the treatment of LID.

Imaging SERT Availability in a Rat Model of L-DOPA-Induced Dyskinesia

PURPOSE

The development of L-DOPA-induced dyskinesia (LID) is one of the most severe side effects of chronic L-DOPA treatment in Parkinson's disease patients. [¹¹C]DASB positron emission tomography (PET) provides a prominent tool to visualize and quantify serotonin transporter (SERT) pathology in vivo in patients and in animal models. To evaluate the effect of chronic L-DOPA treatment on SERT availability in an animal model of LID, we performed a longitudinal PET study.

PROCEDURES

Rats received a unilateral 6-hydroxydopamine (6-OHDA) lesion, and striatal and extrastriatal SERT expression levels were studied with [¹¹C]DASB, a marker of SERT availability, before and after daily treatment with L-DOPA. Dyskinesias were evaluated at different time points over a period of 21 days.

RESULTS

[¹¹C]DASB binding was found to be decreased after 6-OHDA lesions in the striatum, cortex, and hippocampus 5 weeks after 6-OHDA injection in the lesioned hemisphere of the rat brain. Chronic L-DOPA priming resulted in a relative preservation of SERT availability in the lesioned and healthy hemisphere compared to baseline measurements.

CONCLUSIONS

Our longitudinal PET data support a preservation of SERT availability after the induction of L-DOPA-induced dyskinesia, which is in line with previous reports in dyskinetic PD patients.

Mechanisms of Antiparkinsonian Anticholinergic Therapy Revisited

Before the advent of L-DOPA, the gold standard symptomatic therapy for Parkinson's disease (PD), anticholinergic drugs (muscarinic receptor antagonists) were the preferred antiparkinsonian therapy, but their unwanted side effects associated with impaired extrastriatal cholinergic function limited their clinical utility. Since most patients treated with L-DOPA also develop unwanted side effects such as L-DOPA-induced dyskinesia (LID), better therapies are needed. Recent studies in animal models demonstrate that optogenetic and chemogenetic manipulation of striatal cholinergic interneurons (SCIN), the main source of striatal acetylcholine, modulate parkinsonism and LID, suggesting that restoring SCIN function might serve as a therapeutic option that avoids extrastriatal anticholinergics' side effects. However, it is still unclear how the altered SCIN activity in PD and LID affects the striatal circuit, whereas the mechanisms of action of anticholinergic drugs are still not fully understood. Recent animal model studies showing that SCINs undergo profound changes in their tonic discharge pattern after chronic L-DOPA administration call for a reexamination of classical views of how SCINs contribute to PD symptoms and LID. Here, we review the recent advances on the circuit implications of aberrant striatal cholinergic signaling in PD and LID in an effort to provide a comprehensive framework to understand the effects of anticholinergic drugs and with the aim of shedding light into future perspectives of cholinergic circuit-based therapies.

Effects of Aging on Levo-Dihydroxyphenylalanine- Induced Dyskinesia in a Rat Model of Parkinson's Disease

Background

It remains unclear why patients with young-onset Parkinson's disease more often develop levo-dihydroxyphenylalanine (L-dopa)-induced dyskinesia (LID) and have a more severe form than patients with old-onset Parkinson's disease. Previous studies using animal models have failed to show young-onset Parkinson's disease enhances LID.

Objectives

To evaluate the association of age at dopaminergic denervation (onset age) and initiation of L-dopa treatment (treatment age) with LID development in model rats.

Methods

We established rat models of young- and old-lesioned Parkinson's disease (6-hydroxydopamine lesions at 10 and 88 weeks of age, respectively). Dopaminergic denervation was confirmed by the rotational behavior test using apomorphine. Rats in the young-lesioned group were allocated to either L-dopa treatment at a young or old age, or saline treatment. Rats in the old-lesioned group were allocated to either L-dopa treatment or saline group. We evaluated L-dopa-induced abnormal involuntary movements during the 14-day treatment period. We also examined preprodynorphin mRNA expression in the striatum (a neurochemical hallmark of LID) and the volume of the medial globus pallidus (a pathological hallmark of LID).

Results

LID-like behavior was enhanced in L-dopa-treated young-lesioned rats compared with L-dopa-treated old-lesioned rats. Preprodynorphin mRNA expression was higher in L-dopa-treated young-lesioned rats than in in L-dopa-treated old-lesioned rats. The volume of the medial globus pallidus was greater in L-dopa-treated young-lesioned rats than in L-dopa-treated old-lesioned rats. Treatment age did not affect LID-like behavior or the degree of medial globus pallidus hypertrophy in the young-lesioned model.

Conclusion

Both dopaminergic denervation and L-dopa initiation at a young age contributed to the development of LID; however, the former may be a more important factor.

Beneficial effects of dipeptidyl peptidase-4 inhibitors in diabetic Parkinson's disease

Dipeptidyl peptidase 4 (DPP4) inhibitors are widely used hypoglycaemic agents and improve glucose metabolism by enhancing the bioavailability of active glucagon-like peptide-1. In this study, we hypothesized that treatment with DPP4 inhibitors may have beneficial effects on nigrostriatal dopamine and longitudinal motor performance in diabetic patients with Parkinson's disease. We classified 697 drug naive patients with de novo Parkinson's disease who had undergone dopamine transporter imaging into three groups according to a prior diagnosis of diabetes and use of DPP4 inhibitors: diabetic patients with Parkinson's disease being treated with (n = 54) or without DPP4 inhibitors (n = 85), and non-diabetic patients with Parkinson's disease (n = 558). Diabetic patients with Parkinson's disease being treated with DPP4 inhibitors had a higher baseline dopamine transporter availability in the anterior (2.56 ± 0.74 versus 2.10 ± 0.50; P = 0.016), posterior (1.83 ± 0.69 versus 1.40 ± 0.50; P < 0.001), and ventral putamina (1.72 ± 0.58 versus 1.35 ± 0.37; P = 0.001) than that in diabetic patients with Parkinson's disease without DPP4 inhibitors. Additionally, diabetic patients with Parkinson's disease being treated with DPP4 inhibitors had higher dopamine transporter availability in the posterior putamen than that in non-diabetic patients with Parkinson's disease (1.83 ± 0.69 versus 1.43 ± 0.59; P < 0.001). After adjusting for age, sex, disease duration, and vascular risk factors, linear regression models showed that a prior treatment of DPP4 inhibitors remained independently and significantly associated with dopamine transporter availability in the anterior (β = -0.186, P = 0.012; β = -0.207, P = 0.003), posterior (β = -0.336, P < 0.001; β = -0.286, P < 0.001), and ventral putamina (β = -0.204, P = 0.005; β = -0.250, P < 0.001). A linear mixed model revealed that the diabetic group with Parkinson's disease being treated with DPP4 inhibitors had a slower longitudinal increase in levodopa-equivalent dose than the other groups (P = 0.003). Survival analyses showed that the rate of levodopa-induced dyskinesia was significantly lower in the diabetic group with a prior treatment with DPP4 inhibitors than the diabetic group without DPP4 inhibitors (hazard ratio = 0.194, P = 0.037). These findings suggest that DPP4 inhibitors may confer beneficial effects on the baseline nigrostriatal dopamine degeneration and long-term motor outcomes in diabetic patients with Parkinson's disease and may extend its role into non-diabetic patients with Parkinson's disease.

Abnormal Cortico-Basal Ganglia Neurotransmission in a Mouse Model of l-DOPA-Induced Dyskinesia

l-3,4-dihydroxyphenylalanine (l-DOPA) is an effective treatment for Parkinson's disease (PD); however, long-term treatment induces l-DOPA-induced dyskinesia (LID). To elucidate its pathophysiology, we developed a mouse model of LID by daily administration of l-DOPA to PD male ICR mice treated with 6-hydroxydopamine (6-OHDA), and recorded the spontaneous and cortically evoked neuronal activity in the external segment of the globus pallidus (GPe) and substantia nigra pars reticulata (SNr), the connecting and output nuclei of the basal ganglia, respectively, in awake conditions. Spontaneous firing rates of GPe neurons were decreased in the dyskinesia-off state (≥24 h after l-DOPA injection) and increased in the dyskinesia-on state (20-100 min after l-DOPA injection while showing dyskinesia), while those of SNr neurons showed no significant changes. GPe and SNr neurons showed bursting activity and low-frequency oscillation in the PD, dyskinesia-off, and dyskinesia-on states. In the GPe, cortically evoked late excitation was increased in the PD and dyskinesia-off states but decreased in the dyskinesia-on state. In the SNr, cortically evoked inhibition was largely suppressed, and monophasic excitation became dominant in the PD state. Chronic l-DOPA treatment partially recovered inhibition and suppressed late excitation in the dyskinesia-off state. In the dyskinesia-on state, inhibition was further enhanced, and late excitation was largely suppressed. Cortically evoked inhibition and late excitation in the SNr are mediated by the cortico-striato-SNr direct and cortico-striato-GPe-subthalamo-SNr indirect pathways, respectively. Thus, in the dyskinesia-on state, signals through the direct pathway that release movements are enhanced, while signals through the indirect pathway that stop movements are suppressed, underlying LID.SIGNIFICANCE STATEMENT Parkinson's disease (PD) is caused by progressive loss of midbrain dopaminergic neurons, characterized by tremor, rigidity, and akinesia, and estimated to affect around six million people world-wide. Dopamine replacement therapy is the gold standard for PD treatment; however, control of symptoms using l-3,4-dihydroxyphenylalanine (l-DOPA) becomes difficult over time because of abnormal involuntary movements (AIMs) known as l-DOPA-induced dyskinesia (LID), one of the major issues for advanced PD. Our electrophysiological data suggest that dynamic changes in the basal ganglia circuitry underlie LID; signals through the direct pathway that release movements are enhanced, while signals through the indirect pathway that stop movements are suppressed. These results will provide the rationale for the development of more effective treatments for LID.

Pharmacological interactions between adenosine A2A receptor antagonists and different neurotransmitter systems

While Parkinson's disease (PD) is traditionally characterized by dopaminergic neuron degeneration, several neurotransmitters and neuromodulators besides dopamine are also involved in the onset and progression of the disease and its symptoms. The other principal neurotransmitters/neuromodulators known to control basal ganglia functions and, in particular, motor functions, are GABA, glutamate, serotonin (5-HT), noradrenaline, acetylcholine, adenosine and endocannabinoids. Among these, adenosine is the most relevant, acting through its adenosine A_2A receptor. Work in experimental models of PD has established the effects of A_2A receptor antagonists, including the alleviation of disrupted dopamine functions and improved efficacy of dopamine replacement therapy. Moreover, positive interactions between A_2A receptor antagonists and both D₂ and D₁ receptor agonists have been described in vitro at the receptor-receptor level or in more complex in vivo models of PD, respectively. In addition, the interactions between A_2A receptor antagonists and glutamate ionotropic GluN_2B-containing N-Methyl-d-aspartic acid receptors, or metabotropic glutamate (mGlu) receptors, including both mGlu₅ receptor inhibitors and mGlu₄ receptor activators, have been reported in both in vitro and in vivo animal models of PD, as have positive interactions between A_2A and endocannabinoid CB₁ receptor antagonists. At the same time, a combination of A_2A receptor antagonists and 5-HT_1A-5-HT_1B receptor agonists have been described to modulate the expression of dyskinesia induced by chronic dopamine replacement therapy.

The Multimodal Serotonergic Agent Vilazodone Inhibits L-DOPA-Induced Gene Regulation in Striatal Projection Neurons and Associated Dyskinesia in an Animal Model of Parkinson's Disease

Levodopa (L-DOPA) treatment in Parkinson's disease is limited by the emergence of L-DOPA-induced dyskinesia. Such dyskinesia is associated with aberrant gene regulation in neurons of the striatum, which is caused by abnormal dopamine release from serotonin terminals. Previous work showed that modulating the striatal serotonin innervation with selective serotonin reuptake inhibitors (SSRIs) or 5-HT1A receptor agonists could attenuate L-DOPA-induced dyskinesia. We investigated the effects of a novel serotonergic agent, vilazodone, which combines SSRI and 5-HT1A partial agonist properties, on L-DOPA-induced behavior and gene regulation in the striatum in an animal model of Parkinson's disease. After unilateral dopamine depletion by 6-hydroxydopamine (6-OHDA), rats received repeated L-DOPA treatment (5 mg/kg) alone or in combination with vilazodone (10 mg/kg) for 3 weeks. Gene regulation was then mapped throughout the striatum using in situ hybridization histochemistry. Vilazodone suppressed the development of L-DOPA-induced dyskinesia and turning behavior but did not interfere with the prokinetic effects of L-DOPA (forelimb stepping). L-DOPA treatment drastically increased the expression of dynorphin (direct pathway), 5-HT1B, and zif268 mRNA in the striatum ipsilateral to the lesion. These effects were inhibited by vilazodone. In contrast, vilazodone had no effect on enkephalin expression (indirect pathway) or on gene expression in the intact striatum. Thus, vilazodone inhibited L-DOPA-induced gene regulation selectively in the direct pathway of the dopamine-depleted striatum, molecular changes that are considered critical for L-DOPA-induced dyskinesia. These findings position vilazodone, an approved antidepressant, as a potential adjunct medication for the treatment of L-DOPA-induced motor side effects.

Genomic Analysis Identifies New Loci Associated With Motor Complications in Parkinson's Disease

Background: Parkinson's disease (PD) is a common neurodegenerative disorder, characterized by a clinical symptomatology involving both motor and non-motor symptoms. Motor complications associated with long-term dopaminergic treatment include motor fluctuations and levodopa-induced dyskinesia (LID), which may have a major impact on the quality of life. The clinical features and onset time of motor complications in the disease course are heterogeneous, and the etiology remains unknown. Objective: We aimed to identify genomic variants associated with the development of motor fluctuations and LID at 5 years after the onset of PD. Methods: Genomic data were obtained using Affymetrix Axiom KORV1.1 array, including an imputation genome-wide association study (GWAS) grid and other GWAS loci; functional variants of the non-synonymous exome; pharmacogenetic variants; variants in genes involved in absorption, distribution, metabolism, and excretion of drugs; and expression quantitative trait loci in 741 patients with PD. Results: FAM129B single-nucleotide polymorphism (SNP) rs10760490 was nominally associated with the occurrence of motor fluctuations at 5 years after the onset of PD [odds ratio (OR) = 2.9, 95% confidence interval (CI) = 1.8-4.8, P = 6.5 × 10^-6]. GALNT14 SNP rs144125291 was significantly associated with the occurrence of LID (OR = 5.5, 95% CI = 2.9-10.3, P = 7.88 × 10^-9) and was still significant after Bonferroni correction. Several other genetic variants were associated with the occurrence of motor fluctuations or LID, but the associations were not significant after Bonferroni correction. Conclusion: This study identified new loci associated with the occurrence of motor fluctuations and LID at 5 years after the onset of PD. However, further studies are needed to confirm our findings.

GABA storage and release in the medial globus pallidus in L-DOPA-induced dyskinesia priming

Levo-dihydroxyphenylalanine (L-DOPA) is the most effective treatment for Parkinson's disease; however, most patients develop uncontrollable abnormal involuntary movements known as L-DOPA-induced dyskinesia. L-DOPA-induced dyskinesia can be reduced by pallidotomy of the medial globus pallidus or pallidal deep brain stimulation, suggesting that the medial globus pallidus plays a significant role in the development of L-DOPA-induced dyskinesia. In the present study, the pathological changes of the medial globus pallidus in L-DOPA-induced dyskinesia were studied in rat models of Parkinson's disease (unilateral 6-hydroxydopamine lesioning) and L-DOPA-induced dyskinesia (L-DOPA injection in Parkinson's disease-model rats twice daily for 2 weeks, confirmed by display of dyskinesia-like abnormal involuntary movements). L-DOPA-induced dyskinesia-model rats displayed medial globus pallidus hypertrophy, enlarged axon terminals surrounding the dendrites of medial globus pallidus neurons, and increased density of synaptic vesicles in enlarged axon terminals on the lesioned side. Synaptic terminal enlargement reversed after discontinuation of L-DOPA. Histological studies revealed the enlarged synaptic terminals were those of GABAergic striatal (direct pathway) neurons. A single injection of L-DOPA enhanced GABA release in the medial globus pallidus on the lesioned side in L-DOPA-induced dyskinesia-model rats compared to Parkinson's disease-model rats. In addition, microinjection of muscimol, a GABA_A receptor agonist, into the medial globus pallidus on the lesioned side of Parkinson's disease-model rats induced dyskinesia-like abnormal involuntary movements. Microinjection of bicuculline, a GABA_A receptor antagonist, into the medial globus pallidus on the lesioned side alleviated L-DOPA-induced dyskinesia in Parkinson's disease-model rats that had received L-DOPA prior to the microinjection. These results indicate that priming for L-DOPA-induced dyskinesia comprises excessive GABA storage in axon terminals of the direct pathway and that expression of L-DOPA-induced dyskinesia is associated with enhanced GABA release into the medial globus pallidus after L-DOPA dosing and the resultant excessive stimulation of GABA_A receptors.

White matter hyperintensities and risk of levodopa-induced dyskinesia in Parkinson's disease

Objective

To investigate whether the burden of white matter hyperintensities (WMHs) is associated with the risk of developing levodopa‐induced dyskinesia (LID) in Parkinson’s disease (PD).

Methods

According to the Clinical Research Center for Dementia of South Korea WMH visual rating scale, 336 patients with drug‐naïve early stage PD (follow‐up >3 years) were divided into two groups of PD with minimal WMHs (PD‐WMH–; n = 227) and moderate‐to‐severe WMHs (PD‐WMH+; n = 109). The Cox regression model was used to estimate the hazard ratio for the development of LID in the PD‐WMH + group compared with the PD‐WMH– group, while adjusting for age at PD onset, sex, striatal dopamine depletion, and PD medication dose. Additionally, we assessed the effects of WMH burden rated by the Scheltens scale and regional WMH distribution on the development of LID.

Results

Patients in the PD‐WMH + group were older and had more severe parkinsonian motor signs despite comparable striatal dopamine transporter availability than those in the PD‐WMH– group. Patients in the PD‐WMH + group had a higher risk of developing LID (hazard ratio, 2.66; P < 0.001) than those in the PD‐WMH– group after adjustment for other confounding factors. A greater WMH burden was associated with earlier occurrence of LID (hazard ratio, 1.04; P = 0.001), although the effects of WMHs on LID development did not exhibit region‐specific patterns.

Interpretation

The present study demonstrates that the burden of WMHs is associated with occurrence of LID in patients with PD, suggesting comorbid WMHs as a risk factor for LID.

Dyskinesia matters

Levodopa-induced dyskinesia (LID) represents a significant source of discomfort for people with Parkinson's disease (PD). It negatively affects quality of life, it is associated with both motor and nonmotor fluctuations, and it brings an increased risk of disability, balance problems, and falls. Although the prevalence of severe LID appears to be lower than in previous eras (likely owing to a more conservative use of oral levodopa), we have not yet found a way to prevent the development of this complication. Advanced surgical therapies, such as deep brain stimulation, ameliorate LID, but only a minority of PD patients qualify for these interventions. Although some have argued that PD patients would rather be ON with dyskinesia than OFF, the deeper truth is that patients would very much prefer to be ON without dyskinesia. As researchers and clinicians, we should aspire to make that goal a reality. To this end, translational research on LID is to be encouraged and persistently pursued. © 2019 International Parkinson and Movement Disorder Society.

From protocol to product: ventral midbrain dopaminergic neuron differentiation for the treatment of Parkinson's disease

Current cell therapy product limitations include the need for in-depth product understanding to ensure product potency, safety and purity. New technologies require development and validation to address issues of production scale-up to meet clinical need; assays are required for process control, validation and release. Prior to clinical realization, an understanding of production processes is required to implement process changes that are essential for process control. Identification of key parameters forms the basis of process tolerances, allowing for validated, adaptive manufacturing processes. This enables greater process control and yield while withstanding regulatory scrutiny. This report summaries key milestones in specifically for ventral midbrain dopaminergic neuroprogenitor differentiation and key translational considerations and recommendations to enable successful, robust and reproducible current cell therapy product-manufacturing.

Cerebellar connectivity in Parkinson's disease with levodopa-induced dyskinesia

OBJECTIVE

The precise pathogenesis or neural correlates underlying levodopa-induced dyskinesia (LID) remains poorly understood. There is growing evidence of the involvement of the cerebellum in Parkinson's disease (PD). The present study evaluated the role of motor cerebellar connectivity in determining vulnerability to LID.

METHODS

We enrolled 25 de novo patients with PD who developed LID within 5 years of levodopa treatment, 26 propensity score-matched PD patients who had not developed LID, and 24 age- and sex-matched healthy controls. We performed a comparative analysis of resting-state functional connectivity (FC) between the motor cerebellum and whole brain between the groups.

RESULTS

The patients with PD had increased FC bewteen the motor cerebellum and posterior cortical and cerebellar regions, while no gray matter regions had decreased FC with the motor cerebellum compared to the control participant. The patients with PD who were vulnerable to the development of LID had a significantly higher FC between the motor cerebellum lobule VIIIb and the left inferior frontal gyrus than those who were resistant to LID development. The connectivity of the motor cerebellum and left inferior frontal gyrus was negatively correlated with the latency from PD onset to the occurrence of LID.

INTERPRETATION

Increased FC between the motor cerebellum and left inferior frontal gyrus in de novo patients with PD could be an important determinant of vulnerability to LID.

Cardinal Motor Features of Parkinson's Disease Coexist with Peak-Dose Choreic-Type Drug-Induced Dyskinesia

Background:

Clinical and anecdotal observations propose that patients with Parkinson’s disease (PD) may show drug-induced dyskinesia (DID) concomitantly with cardinal motor features. However, the extent of the concomitant presence of DID and cardinal features remains to be determined.

Objectives:

This cross-sectional study measured peak-dose choreic-type DID in a quantitative manner in patients diagnosed with PD, and determined whether symptoms such as tremor, bradykinesia, rigidity, postural instability or freezing of gait (FoG) were still detectable in these patients.

Methods:

89 patients diagnosed with PD were recruited and assessed using a combination of quantitative measures using inertial measurement units to capture DID, tremor, bradykinesia, and FoG. Clinical evaluations were also used to assess rigidity and postural instability. Motor symptoms of PD were assessed 3 times during the testing period, and a series of activities of daily living were repeated twice, in between clinical tests, during which the level of DID was quantified. Peak-dose was identified as the period during which patients had the highest levels of DID. Levels of tremor, rigidity, bradykinesia, postural instability, and FoG were used to determine the percentage of patients showing these motor symptoms simultaneously with DID.

Results:

72.4% of patients tested presented with measurable DID during the experiment. Rest, postural and kinetic tremor (12.7% , 38.1% , and 15.9% respectively), bradykinesia (28.6% ), rigidity (55.6% ), postural instability (71.4% ) and FoG (9.5% ) were detected simultaneously with DID.

Conclusions:

PD symptomatology remains present in patients showing peak-dose choreic-type DID, illustrating the challenge facing physicians when trying to avoid dyskinesia while attempting to alleviate motor symptoms.

L-DOPA-Induced Motor Impairment and Overexpression of Corticostriatal Synaptic Components Are Improved by the mGluR5 Antagonist MPEP in 6-OHDA-Lesioned Rats

Levodopa (L-DOPA) is still the most effective drug for the treatment of Parkinson's disease (PD). However, the long-term therapy often triggers L-DOPA-induced dyskinesia (LID). Metabotropic glutamate receptor type 5 (mGluR5) is abundant in the basal ganglia, and its inhibition is thought to modulate postsynaptic excitatory synaptic transmission and glutamate hyperactivity in PD and LID. In this report, we examined the effects of mGluR5-specific antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) on LID and synaptic components in the PD model rat. We found the selective mGluR5 antagonist MPEP attenuated abnormal involuntary movements, prolonged the duration of rotational response, reversed the decrease of left forepaw adjusting steps, and reduced overexpression of striatal mGluR5 in the LID rats. Moreover, our results showed much thicker postsynaptic densities, narrower synapse cleft, as well as the increased ratio of perforated synapses induced by L-DOPA treatment, while coadministration of L-DOPA and MPEP reversed these postsynaptic effects. Finally, MPEP reduced overexpression of the two postsynaptic proteins (PSD-95 and SAP102) induced by L-DOPA treatment. Hence, these results provide evidence that aberrant neural plasticity at corticostriatal synapses in the striatum is closely correlated with the occurrence of LID, and targeted inhibition of mGluR5 by MPEP alleviates LID in the PD rat model.

Pathophysiological clues to therapeutic applications of glutamate mGlu5 receptor antagonists in levodopa-induced dyskinesia

Levodopa remains to be the mainstay for treatment of Parkinson disease (PD). Long-term levodopa treatment bears a risk for developing levodopa-induced dyskinesia (LID). LID significantly overshadows patients' quality of life and therapeutic efficacy of levodopa. Pre- and post-synaptic changes in dopamine secretion and signaling, along with altered glutamate receptor expression and glutamatergic signaling in striatal neurons, and the resulting disinhibition-like changes in the corticostriatal circuitry, lead to aberrant activity of motor cortex and formation of LID. Research has highlighted the role of group I metabotropic glutamate receptors especially the metabotropic glutamate receptor 5 (mGlu5) in formation of LID through potentiating of ionotropic glutamate NMDA receptors and dopamine D₁/D₅ receptors in direct pathway. Accordingly, MTEP and MPEP were the first mGlu5 receptor antagonists which were shown to attenuate LID in animal models through suppression of downstream signaling cascades involving mitogen-activated protein kinase (MAPK) and FosB/delta FosB activation, as well as modulation of prodynorphinegic, preproenkephalinergic, and GABA-ergic neurotransmission systems. Beneficial effects of other mGlu5 receptor antagonists such as AFQ056/mavoglurant and ADX48621/dipraglurant in amelioration of LID has been shown not only in animal models but also in clinical trials. Considering the presence of mGlu receptor dysregulation in rapid eye movement (REM) sleep behavior disorder and depression, which are prodromal signs of PD, along with the neuroprotective effects of mGlu receptor antagonists, and their cognitive benefits, potential effectiveness of mGlu receptor antagonists in early prevention of PD remains to be investigated.

Remnants of Cardinal Symptoms of Parkinson's Disease, Not Dyskinesia, Are Problematic for Dyskinetic Patients Performing Activities of Daily Living

Introduction: The impact of levodopa-induced dyskinesia (LID) on the daily lives of patients with Parkinson's disease (PD) remains to be determined. Furthermore, evidence suggests that cardinal motor symptoms of PD may coexist with LID, but their impact on activities of daily living (ADL) relative to LID is not known. This cross-sectional study aimed at determining the effect of LID and cardinal motor symptoms of PD on ADL in patients who were experiencing peak-dose choreic-type LID.

Method: One hundred and twenty-one patients diagnosed with PD known to experience choreic-type LID were recruited for the study. Patients were asked to perform a set of ADL. Levels of LID, tremor, bradykinesia, and freezing of gait (FoG) were measured using 17 inertial sensors design to capture full body movements, while rigidity, and postural instability were assessed using clinical evaluations. Cognition was also assessed using the mini-mental state examination. Success criteria were set for each ADL using the time needed to perform the task and errors measured in 69 age-gender-matched healthy controls. Binary logistic regressions were used to identify symptoms influencing success or failure for each activity. Receiver operating characteristic curves were computed on each significant symptom, and Youden indexes were calculated to determine the critical level of symptomatology at which the performance significantly changed.

Results: Results show that 97.7% of patients who presented with LID during the experiment also presented with at least one cardinal motor symptom. On average, patients took more time and did more errors during ADL. Multivariate analyses revealed that for the great majority of ADL, LID were not associated with worsening of performance; however, postural instability, tremor, rigidity, and cognitive decline significantly decreased the odds of success.

Conclusions: Residual symptoms of PD, such as tremor, rigidity, and postural instability still present at peak-dose were more problematic than LID in the performance of ADL for patients experiencing slight-to-moderate LID. We also found that cognitive decline was associated with decreased performance in certain tasks. Therefore, a strategy using lower doses of medication to manage LID may be counterproductive since it would not address most of these symptoms already present in patients.

Does Late Levodopa Administration Delay the Development of Dyskinesia in Patients with De Novo Parkinson's Disease?

BACKGROUND

It remains controversial whether late levodopa administration is a reasonable approach to reducing the risk of levodopa-induced dyskinesia in Parkinson's disease.

OBJECTIVE

This study aimed to investigate the effects of levodopa sparing on the development of levodopa-induced dyskinesia.

METHODS

We retrospectively reviewed medical records for patients with de novo Parkinson's disease who visited the Yonsei Parkinson Center between April 2009 and June 2015 and received at least 2 years of treatment. Among 657 patients with drug-naïve Parkinson's disease who met the study criteria, 90 were initially treated with dopamine agonists (levodopa-sparing group; levodopa supplementation after 2.15 years). Another 90 patients who were initially treated with levodopa (levodopa group) were matched to the 90 patients for age, sex, follow-up duration, Parkinson's disease duration, Unified Parkinson's Disease Rating Scale Part III scores, and baseline dopamine transporter availability in the posterior putamen. The effects of levodopa sparing on dyskinesia development were assessed with Kaplan-Meier estimates and a stratified Cox regression model adjusted for age of onset, sex, dopamine transporter availability, and daily levodopa dose per weight.

RESULTS

The levodopa-sparing group had a comparable age of onset (54.80 ± 7.36 years) to the levodopa group (56.53 ± 6.16 years). The Kaplan-Meier analysis revealed that the risk of levodopa-induced dyskinesia after treatment initiation was similar between the groups. Once the levodopa-sparing group started levodopa supplementation, they had a higher risk of developing levodopa-induced dyskinesia. However, a stratified Cox regression model indicated that hazard ratios for levodopa sparing to levodopa-induced dyskinesia development were 0.138 (95% confidence interval 0.024-0.785) after treatment initiation and 0.438 (95% confidence interval 0.105-1.832) after levodopa initiation.

CONCLUSION

Late levodopa administration was associated with a low risk of dyskinesia after adjusting for confounding effects and may be a reasonable strategy for prolonging the levodopa-induced dyskinesia-free period in Parkinson's disease.

An mGlu4-Positive Allosteric Modulator Alleviates Parkinsonism in Primates

BACKGROUND

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

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Opioidergic Modulation of Striatal Circuits, Implications in Parkinson's Disease and Levodopa Induced Dyskinesia

The functional organization of the dorsal striatum is complex, due to the diversity of neural inputs that converge in this structure and its subdivision into direct and indirect output pathways, striosomes and matrix compartments. Among the neurotransmitters that regulate the activity of striatal projection neurons (SPNs), opioid neuropeptides (enkephalin and dynorphin) play a neuromodulatory role in synaptic transmission and plasticity and affect striatal-based behaviors in both normal brain function and pathological states, including Parkinson's disease (PD). We review recent findings on the cell-type-specific effects of opioidergic neurotransmission in the dorsal striatum, focusing on the maladaptive synaptic neuroadaptations that occur in PD and levodopa-induced dyskinesia. Understanding the plethora of molecular and synaptic mechanisms underpinning the opioid-mediated modulation of striatal circuits is critical for the development of pharmacological treatments that can alleviate motor dysfunctions and hyperkinetic responses to dopaminergic stimulant drugs.

mGlu4 allosteric modulation for treating Parkinson's disease

2017 is the 200th anniversary of the first published description of Parkinson's disease (PD). Fifty years ago, the clinical benefit of levodopa was first documented, representing the most important advance in the treatment of PD so far. Among the novel targets identified in the last decade, positive allosteric modulators (PAM) of mGlu₄ receptors show great promise, with the potential to change the paradigm of the PD treatment approach. mGlu₄ PAMs have shown consistent efficacy in various preclinical models of PD, and entered clinical trials for the first time in 2017. This review synthesizes the rationale for mGlu₄ PAM development for PD and progress to date, reporting the key achievements from preclinical studies to the first-in-class compound assessment in man.

Molecular basis of dopamine replacement therapy and its side effects in Parkinson's disease

There is currently no cure for Parkinson's disease. The symptomatic therapeutic strategy essentially relies on dopamine replacement whose efficacy was demonstrated more than 50 years ago following the introduction of the dopamine precursor, levodopa. The spectacular antiparkinsonian effect of levodopa is, however, balanced by major limitations including the occurrence of motor complications related to its particular pharmacokinetic and pharmacodynamic properties. Other therapeutic strategies have thus been developed to overcome these problems such as the use of dopamine receptor agonists, dopamine metabolism inhibitors and non-dopaminergic drugs. Here we review the pharmacology and molecular mechanisms of dopamine replacement therapy in Parkinson's disease, both at the presynaptic and postsynaptic levels. The perspectives in terms of novel drug development and prediction of drug response for a more personalised medicine will be discussed.

Role of adenosine A2A receptors in motor control: relevance to Parkinson's disease and dyskinesia

Adenosine is an endogenous purine nucleoside that regulates several physiological functions, at the central and peripheral levels. Besides, adenosine has emerged as a major player in the regulation of motor behavior. In fact, adenosine receptors of the A_2A subtype are highly enriched in the caudate-putamen, which is richly innervated by dopamine. Moreover, several studies in experimental animals have consistently demonstrated that the pharmacological antagonism of A_2A receptors has a facilitatory influence on motor behavior. Taken together, these findings have envisaged A_2A receptors as a promising target for symptomatic therapies aimed at ameliorating motor deficits. Accordingly, A_2A receptor antagonists have been extensively studied as new agents for the treatment of Parkinson's disease (PD), the epitome of motor disorders. In this review, we provide an overview of the effects that adenosine A_2A receptor antagonists elicit in rodent and primate experimental models of PD, with regard to the counteraction of motor deficits as well as to manifestation of dyskinesia and motor fluctuations. Moreover, we briefly present the results of clinical trials of A_2A receptor antagonists in PD patients experiencing motor fluctuations, with particular regard to dyskinesia. Finally, we discuss the interaction between A_2A receptor antagonists and serotonin receptor agonists, since combined administration of these drugs has recently emerged as a new potential therapeutic strategy in the treatment of dyskinesia.