Clinical pattern and risk factors for dyskinesias following fetal nigral transplantation in Parkinson's disease: A double blind video-based analysis

A video-atlas of levodopa-induced dyskinesia in Parkinson's disease: terminology matters

Dyskinesia is a common complication of long-term levodopa therapy in patients with Parkinson's disease (PD), which often worsens the quality of life. It is usually dose-dependent and emerges possibly due to pulsatile stimulation of dopamine receptors. Delineating the pattern of dyskinesia is crucial for determining the most effective therapeutic approach, a task that often presents challenges for numerous neurologists. This article comprehensively describes various patterns of dyskinesia in PD patients and features video demonstration of some of the common forms of dyskinesia. We have used a real case scenario as an example to lead the discussion on the phenomenology, distinguishing features, and management of various types of dyskinesia. A comprehensive literature search was conducted in PubMed using "dyskinesia" as a keyword. The prototype case with videos highlights the differentiating features of dyskinesia along with the treatment strategies. A wide range of descriptive rubrics have been used for certain dyskinesia which are described in detail in this article. The newer types of dyskinesia associated with continuous dopaminergic stimulation in patients with advanced PD and their implications have been described. As there are distinct ways of managing various types of dyskinesia, understanding the phenomenology and chronology of dyskinesia is vital for the optimal management of dyskinetic PD patients. We suggest that dyskinesia should be classified broadly into peak-dose dyskinesia (PDD), biphasic dyskinesia (BD), and OFF-period dystonia. The occurrence of low-dose dyskinesia and complex dyskinesia of continuous dopaminergic treatments should be known to specialists and will require additional studies.

Transfection of the BDNF Gene in the Surviving Dopamine Neurons in Conjunction with Continuous Administration of Pramipexole Restores Normal Motor Behavior in a Bilateral Rat Model of Parkinson's Disease

In Parkinson's disease (PD), progressive degeneration of nigrostriatal innervation leads to atrophy and loss of dendritic spines of striatal medium spiny neurons (MSNs). The loss disrupts corticostriatal transmission, impairs motor behavior, and produces nonmotor symptoms. Nigral neurons express brain-derived neurotropic factor (BDNF) and dopamine D3 receptors, both protecting the dopamine neurons and the spines of MSNs. To restore motor and nonmotor symptoms to normality, we assessed a combined therapy in a bilateral rat Parkinson's model, with only 30% of surviving neurons. The preferential D3 agonist pramipexole (PPX) was infused for four ½ months via mini-osmotic pumps and one month after PPX initiation; the BDNF-gene was transfected into the surviving nigral cells using the nonviral transfection NTS-polyplex vector. Overexpression of the BDNF-gene associated with continuous PPX infusion restored motor coordination, balance, normal gait, and working memory. Recovery was also related to the restoration of the average number of dendritic spines of the striatal projection neurons and the number of TH-positive neurons of the substantia nigra and ventral tegmental area. These positive results could pave the way for further clinical research into this promising therapy.

Positive and negative cell therapy in randomized control trials for central nervous system diseases

Neurorestorative cell therapies have been tested to treat patients with nervous system diseases for over 20 years. Now it is still hard to answer which kinds of cells can really play a role on improving these patients' quality of life. Non-randomized clinical trials or studies could not provide strong evidences in answering this critical question. In this review, we summarized randomized clinical trials of cell therapies for central nervous diseases, such as stroke, spinal cord injury, cerebral palsy (CP), Parkinson's disease (PD), multiple sclerosis (MS), brain trauma, amyotrophic lateral sclerosis (ALS), etc. Most kinds of cell therapies demonstrated negative results for stoke, brain trauma and amyotrophic lateral sclerosis. A few kinds of cell therapies showed neurorestorative effects in this level of evidence-based medicine, such as olfactory ensheating cells for chronic ischemic stroke. Some kinds of cells showed positive or negative effects from different teams in the same or different diseases. We analyzed the possible failed reasons of negative results and the cellular bio-propriety basis of positive results. Based on therapeutic results of randomized control trials and reasonable analysis, we recommend: (1) to further conduct trials for successful cell therapies with positive results to increase neurorestorative effects; (2) to avoid in repeating failed cell therapies with negative results in same diseases because it is nonsense for them to be done with similar treatment methods, such as cell dosage, transplanting way, time of window, etc. Furthermore, we strongly suggest not to do non-randomized clinical trials for cells that had shown negative results in randomized clinical trials.

Cell-therapy for Parkinson's disease: a systematic review and meta-analysis

BACKGROUND

Cell-based strategies focusing on replacement or protection of dopaminergic neurons have been considered as a potential approach to treat Parkinson's disease (PD) for decades. However, despite promising preclinical results, clinical trials on cell-therapy for PD reported mixed outcomes and a thorough synthesis of these findings is lacking. We performed a systematic review and meta-analysis to evaluate cell-therapy for PD patients.

METHODS

We systematically identified all clinical trials investigating cell- or tissue-based therapies for PD published before July 2023. Out of those, studies reporting transplantation of homogenous cells (containing one cell type) were included in meta-analysis. The mean difference or standardized mean difference in quantitative neurological scale scores before and after cell-therapy was analyzed to evaluate treatment effects.

RESULTS

The systematic literature search revealed 106 articles. Eleven studies reporting data from 11 independent trials (210 patients) were eligible for meta-analysis. Disease severity and motor function evaluation indicated beneficial effects of homogenous cell-therapy in the 'off' state at 3-, 6-, 12-, or 24-month follow-ups, and for motor function even after 36 months. Most of the patients were levodopa responders (61.6-100% in different follow-ups). Cell-therapy was also effective in improving the daily living activities in the 'off' state of PD patients. Cells from diverse sources were used and multiple transplantation modes were applied. Autografts did not improve functional outcomes, while allografts exhibited beneficial effects. Encouragingly, both transplantation into basal ganglia and to areas outside the basal ganglia were effective to reduce disease severity. Some trials reported adverse events potentially related to the surgical procedure. One confirmed and four possible cases of graft-induced dyskinesia were reported in two trials included in this meta-analysis.

CONCLUSIONS

This meta-analysis provides preliminary evidence for the beneficial effects of homogenous cell-therapy for PD, potentially to the levodopa responders. Allogeneic cells were superior to autologous cells, and the effective transplantation sites are not limited to the basal ganglia. PROSPERO registration number: CRD42022369760.

Neural Cells for Neurodegenerative Diseases in Clinical Trials

Neurodegenerative diseases (ND) are an entire spectrum of clinical conditions that affect the central and peripheral nervous system. There is no cure currently, with treatment focusing mainly on slowing down progression or symptomatic relief. Cellular therapies with various cell types from different sources are being conducted as clinical trials for several ND diseases. They include neural, mesenchymal and hemopoietic stem cells, and neural cells derived from embryonic stem cells and induced pluripotent stem cells. In this review, we present the list of cellular therapies for ND comprising 33 trials that used neural stem progenitors, 8 that used differentiated neural cells ,and 109 trials that involved non-neural cells in the 7 ND. Encouraging results have been shown in a few early-phase clinical trials that require further investigations in a randomized setting. However, such definitive trials may not be possible given the relative cost of the trials, and in the setting of rare diseases.

Clinical results of neurorestorative cell therapies and therapeutic indications according to cellular bio-proprieties

Cell therapies have been explored to treat patients with nervous diseases for over 20 years. Even though most kinds of cell therapies demonstrated neurorestorative effects in non-randomized clinical trials; the effects of the majority type cells could not be confirmed by randomized controlled trials. In this review, clinical therapeutic results of neurorestorative cell therapies according to cellular bio-proprieties or cellular functions were introduced. Currently it was demonstrated from analysis of this review that some indications of cell therapies were not appropriate, they might be reasons why their neurorestorative effects could not be proved by multicenter, randomized, double blind, placebo-controlled clinical trials. Theoretically if one kind of cell therapy has neurorestorative effects according to its cellular bio-proprieties, it should have appropriate indications. The cell therapies with special bio-properties is promising if the indication selections are appropriate, such as olfactory ensheathing cells for chronic ischemic stroke, and their neurorestorative effects can be confirmed by higher level clinical trials of evidence-based medicine.

Defining the unknowns for cell therapies in Parkinson's disease

First-in-human clinical trials have commenced to test the safety and efficacy of cell therapies for people with Parkinson's disease (PD). Proof of concept that this neural repair strategy is efficacious is based on decades of preclinical studies and clinical trials using primary foetal cells, as well as a significant literature exploring more novel stem cell-derived products. Although several measures of efficacy have been explored, including the successful in vitro differentiation of stem cells to dopamine neurons and consistent alleviation of motor dysfunction in rodent models, many unknowns still remain regarding the long-term clinical implications of this treatment strategy. Here, we consider some of these outstanding questions, including our understanding of the interaction between anti-Parkinsonian medication and the neural transplant, the impact of the cell therapy on cognitive or neuropsychiatric symptoms of PD, the role of neuroinflammation in the therapeutic process and the development of graft-induced dyskinesias. We identify questions that are currently pertinent to the field that require further exploration, and pave the way for a more holistic understanding of this neural repair strategy for treatment of PD.

Optimizing maturity and dose of iPSC-derived dopamine progenitor cell therapy for Parkinson's disease

In pursuit of treating Parkinson’s disease with cell replacement therapy, differentiated induced pluripotent stem cells (iPSC) are an ideal source of midbrain dopaminergic (mDA) cells. We previously established a protocol for differentiating iPSC-derived post-mitotic mDA neurons capable of reversing 6-hydroxydopamine-induced hemiparkinsonism in rats. In the present study, we transitioned the iPSC starting material and defined an adapted differentiation protocol for further translation into a clinical cell transplantation therapy. We examined the effects of cellular maturity on survival and efficacy of the transplants by engrafting mDA progenitors (cryopreserved at 17 days of differentiation, D17), immature neurons (D24), and post-mitotic neurons (D37) into immunocompromised hemiparkinsonian rats. We found that D17 progenitors were markedly superior to immature D24 or mature D37 neurons in terms of survival, fiber outgrowth and effects on motor deficits. Intranigral engraftment to the ventral midbrain demonstrated that D17 cells had a greater capacity than D24 cells to innervate over long distance to forebrain structures, including the striatum. When D17 cells were assessed across a wide dose range (7,500-450,000 injected cells per striatum), there was a clear dose response with regards to numbers of surviving neurons, innervation, and functional recovery. Importantly, although these grafts were derived from iPSCs, we did not observe teratoma formation or significant outgrowth of other cells in any animal. These data support the concept that human iPSC-derived D17 mDA progenitors are suitable for clinical development with the aim of transplantation trials in patients with Parkinson’s disease.

Spontaneous Graft-Induced Dyskinesias Are Independent of 5-HT Neurons and Levodopa Priming in a Model of Parkinson's Disease

BACKGROUND

The risk of graft-induced dyskinesias (GIDs) presents a major challenge in progressing cell transplantation as a therapy for Parkinson's disease. Current theories implicate the presence of grafted serotonin neurons, hotspots of dopamine release, neuroinflammation and established levodopa-induced dyskinesia.

OBJECTIVE

To elucidate the mechanisms of GIDs.

METHODS

Neonatally desensitized, dopamine denervated rats received intrastriatal grafts of human embryonic stem cells (hESCs) differentiated into either ventral midbrain dopaminergic progenitor (vmDA) (n = 15) or ventral forebrain cells (n = 14).

RESULTS

Of the eight rats with surviving grafts, two vmDA rats developed chronic spontaneous GIDs, which were observed at 30 weeks post-transplantation. GIDs were inhibited by D2 -like receptor antagonists and not affected by 5-HT1A/1B/5-HT6 agonists/antagonists. Grafts in GID rats showed more microglial activation and lacked serotonin neurons.

CONCLUSIONS

These findings argue against current thinking that rats do not develop spontaneous GID and that serotonin neurons are causative, rather indicating that GID can be induced in rats by hESC-derived dopamine grafts and, critically, can occur independently of both previous levodopa exposure and grafted serotonin neurons. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Levodopa-induced dyskinesia: a historical review of Parkinson's disease, dopamine, and modern advancements in research and treatment

Over the past two decades, animal models of Parkinson's disease (PD) have helped to determine the plausible underlying mechanism of levo-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia following L-DOPA treatment. However, our understanding of the mechanisms related to this phenomenon remains incomplete. The purpose of this manuscript is to provide a comprehensive review of treatment protocols used for assessing the occurrence of L-DOPA-induced dyskinesia, L-DOPA absorption, distribution, drug/food interaction, and discuss current strategies and future directions. This review offers a historical perspective using L-DOPA in animal models of PD and the occurrence of L-DOPA-induced dyskinesia.

Regenerative medicine for neurological diseases-will regenerative neurosurgery deliver?

Regenerative medicine aspires to transform the future practice of medicine by providing curative, rather than palliative, treatments. Healing the central nervous system (CNS) remains among regenerative medicine's most highly prized but formidable challenges. "Regenerative neurosurgery" provides access to the CNS or its surrounding structures to preserve or restore neurological function. Pioneering efforts over the past three decades have introduced cells, neurotrophins, and genes with putative regenerative capacity into the CNS to combat neurodegenerative, ischemic, and traumatic diseases. In this review we critically evaluate the rationale, paradigms, and translational progress of regenerative neurosurgery, harnessing access to the CNS to protect, rejuvenate, or replace cell types otherwise irreversibly compromised by neurological disease. We discuss the evidence surrounding fetal, somatic, and pluripotent stem cell derived implants to replace endogenous neuronal and glial cell types and provide trophic support. Neurotrophin based strategies via infusions and gene therapy highlight the motivation to preserve neuronal circuits, the complex fidelity of which cannot be readily recreated. We specifically highlight ongoing translational efforts in Parkinson's disease, amyotrophic lateral sclerosis, stroke, and spinal cord injury, using these to illustrate the principles, challenges, and opportunities of regenerative neurosurgery. Risks of associated procedures and novel neurosurgical trials are discussed, together with the ethical challenges they pose. After decades of efforts to develop and refine necessary tools and methodologies, regenerative neurosurgery is well positioned to advance treatments for refractory neurological diseases. Strategic multidisciplinary efforts will be critical to harness complementary technologies and maximize mechanistic feedback, accelerating iterative progress toward cures for neurological diseases.

Persistent dyskinesias in patients with fetal tissue transplantation for Parkinson disease

Cell transplants are being developed for patients with Parkinson disease (PD) who have insufficient benefit with standard medical treatment. We describe the clinical features of five patients who developed persistent dyskinesias after fetal dopaminergic tissue transplantation. All had levodopa-induced dyskinesias preoperatively. We implanted fetal mesencephalic dopaminergic tissue into the putamina bilaterally in 34 patients with advanced PD. They were not immunosuppressed. Five of 34 patients (15%) developed troublesome choreic or dystonic dyskinesias that persisted despite lowering or discontinuing medications. Attempts to treat the involuntary movements with amantadine, clozapine, anticholinergics, dopamine depletors and other medicines had limited success. Metyrosine eliminated dyskinesias but led to the parkinsonian “off” state. Increasing the dose of levodopa worsened the dyskinesias. Three patients required placement of pallidal stimulators, bilaterally in two and unilaterally in one patient who had only contralateral dyskinesias. The two with the bilateral stimulators had improvement in dyskinesias. The patient with the unilateral pallidal stimulator had a substantial reduction of the dyskinesias, but attempts to treat residual “off” symptoms with levodopa were limited by worsening dyskinesias. Although the number of patients developing these persistent dyskinesias was small, these five patients had dramatic improvement after transplant. As a group, they had milder Parkinson signs at baseline and improved to the point of having minimal parkinsonism, with reduction or elimination of levodopa therapy prior to developing persistent dyskinesias. These involuntary movements establish the principle that fetal dopaminergic tissue transplants can mimic the effects of levodopa, not only in reducing bradykinesia, but also in provoking dyskinesias.

Serotonergic imaging in Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by the progressive degeneration of monoaminergic central pathways such as the serotonergic. The degeneration of serotonergic signaling in striatal and extrastriatal brain regions is an early feature of PD and is associated with several motor and non-motor complications of the disease. Molecular imaging techniques with Positron Emission Tomography (PET) have greatly contributed to the investigation of biological changes in vivo and to the understanding of the extent of serotonergic pathology in patients or individuals at risk for PD. Such discoveries provide with opportunities for the identification of new targets that can be used for the development of novel disease-modifying drugs or symptomatic treatments. Future studies of imaging serotonergic molecular targets will better clarify the importance of serotonergic pathology in PD, including progression of pathology, target-identification for pharmacotherapy, and relevance to endogenous synaptic serotonin levels. In this article, we review the current status and understanding of serotonergic imaging in PD.

Interactions Between the Serotonergic and Other Neurotransmitter Systems in the Basal Ganglia: Role in Parkinson's Disease and Adverse Effects of L-DOPA

Parkinson's disease (PD) is characterized by the progressive loss of dopaminergic neurons in the substantia nigra. However, other non-dopaminergic neuronal systems such as the serotonergic system are also involved. Serotonergic dysfunction is associated with non-motor symptoms and complications, including anxiety, depression, dementia, and sleep disturbances. This pathology reduces patient quality of life. Interaction between the serotonergic and other neurotransmitters systems such as dopamine, noradrenaline, glutamate, and GABA controls the activity of striatal neurons and are particularly interesting for understanding the pathophysiology of PD. Moreover, serotonergic dysfunction also causes motor symptoms. Interestingly, serotonergic neurons play an important role in the effects of L-DOPA in advanced PD stages. Serotonergic terminals can convert L-DOPA to dopamine, which mediates dopamine release as a "false" transmitter. The lack of any autoregulatory feedback control in serotonergic neurons to regulate L-DOPA-derived dopamine release contributes to the appearance of L-DOPA-induced dyskinesia (LID). This mechanism may also be involved in the development of graft-induced dyskinesias (GID), possibly due to the inclusion of serotonin neurons in the grafted tissue. Consistent with this, the administration of serotonergic agonists suppressed LID. In this review article, we summarize the interactions between the serotonergic and other systems. We also discuss the role of the serotonergic system in LID and if therapeutic approaches specifically targeting this system may constitute an effective strategy in PD.

Temporal evolution of microglia and α-synuclein accumulation following foetal grafting in Parkinson's disease

We observed Lewy pathology in healthy embryonic dopamine neurons implanted into the striatum of patients with advanced Parkinson's disease. In the present study we examined the temporal relationship between the presence of inflammation with activated microglia and the emergence of α-synuclein pathology. Inflammation with activated microglia was observed in all grafts and at all time points examined between 18 months and 16 years as determined by both CD45 and TMEM119 staining. In contrast, α-synuclein was not detected at 18 months, only diffuse monomeric α-synuclein staining was observed at 4 years, and α-synuclein aggregates were not observed until 14-16 years after transplantation. Thus, there is evidence of inflammation and microglial activation in graft deposits long before the accumulation of α-synuclein pathology in implanted dopamine neurons. These observations raise the possibility that microglial activation contributes to the development of α-synuclein pathology, and supports the concept that microglia play an integral role in the propagation and spread of α-synuclein pathology.

L-DOPA for Parkinson's disease-a bittersweet pill

3,4-dihydroxy-L-phenylalanine (L-DOPA) is the gold standard treatment for Parkinson's disease. It has earned that title through its highly effective treatment of some of the motor symptoms in the early stages of the disease but it is a far from perfect drug. The inevitable long-term treatment that comes with this chronic neurodegenerative condition raises the risk significantly of the development of motor fluctuations including disabling L-DOPA-induced dyskinesia. Being unsurpassed as a therapy means that understanding the mechanisms of dyskinesia priming and induction is vital to the search for therapies to treat these side effects and allow optimal use of L-DOPA. However, L-DOPA use may also have consequences (positive or negative) for the development of other interventions, such as cell transplantation, which are designed to treat or repair the ailing brain. This review looks at the issues around the use of L-DOPA with a focus on its potential impact on advanced reparative interventions.

Cell reprogramming approaches in gene- and cell-based therapies for Parkinson's disease

Degeneration of dopamine (DA) neurons in the substantia nigra pars compacta is the pathological hallmark of Parkinson's disease (PD). In PD multiple pathogenic mechanisms initiate and drive this neurodegenerative process, making the development of effective treatments challenging. To date, PD patients are primarily treated with dopaminergic drugs able to temporarily enhance DA levels, therefore relieving motor symptoms. However, the drawbacks of these therapies including the inability to alter disease progression are constantly supporting the search for alternative treatment approaches. Over the past years efforts have been put into the development of new therapeutic strategies based on the delivery of therapeutic genes using viral vectors or transplantation of DA neurons for cell-based DA replacement. Here, past achievements and recent advances in gene- and cell-based therapies for PD are outlined. We discuss how current gene and cell therapy strategies hold great promise for the treatment of PD and how the use of stem cells and recent developments in cellular reprogramming could contribute to open a new avenue in PD therapy.

Recent advances in lineage differentiation from stem cells: hurdles and opportunities?

Pluripotent stem cells have the property of long-term self-renewal and the potential to give rise to descendants of the three germ layers and hence all mature cells in the human body. Therefore, they hold the promise of offering insight not only into human development but also for human disease modeling and regenerative medicine. However, the generation of mature differentiated cells that closely resemble their in vivo counterparts remains challenging. Recent advances in single-cell transcriptomics and computational modeling of gene regulatory networks are revealing a better understanding of lineage commitment and are driving modern genome editing approaches. Additional modification of the chemical microenvironment, as well as the use of bioengineering tools to recreate the cellular, extracellular matrix, and physical characteristics of the niche wherein progenitors and mature cells reside, is now being used to further improve the maturation and functionality of stem cell progeny.

The serotonergic system in Parkinson's patients with dyskinesia: evidence from imaging studies

The purpose of review is to review the current status of positron emission tomography (PET) molecular imaging of serotonergic system in Parkinson’s patients who experience levodopa-induced (LIDs) and graft-induced dyskinesias (GIDs). PET imaging studies have shown that Parkinson’s disease is characterized by progressive loss of dopaminergic and serotonergic neurons. Parkinson’s patients who experienced LIDs and GIDs have an aberrant spreading of serotonergic terminals, which lead to an increased serotonergic/dopaminergic terminals ratio within the putamen. Serotonergic terminals convert exogenous levodopa into dopamine in a non-physiological manner and release an abnormal amount of dopamine without an auto-regulatory feedback. This results in higher swings in synaptic levels of dopamine, which leads to the development of LIDs and GIDs. The modulation of serotonergic terminals with 5-HT_1A and 5-HT_1B receptors agonists partially reduced these motor complications. In vivo PET studies confirmed that abnormal spreading of serotonergic terminals within the putamen has a pivotal role in the development of LIDs and GIDs. However, glutamatergic, adenosinergic, opioid systems, and phosphodiesterases 10A may also play a role in the development of these motor complications. An integrative multimodal imaging approach combining PET and MRI imaging techniques is needed to fully understand the mechanisms underlying the development of LIDs and GIDs.

Restorative Strategies in Movement Disorders: the Contribution of Imaging

Purpose of Review

The purpose of this review was to review the imaging, particularly positron emission tomography (PET), findings in neurorestoration studies in movement disorders, with specific focus on neural transplantation in Parkinson’s disease (PD) and Huntington’s disease (HD).

Recent Findings

PET findings in PD transplantation studies have shown that graft survival as reflected by increases in dopaminergic PET markers does not necessarily correlate with clinical improvement. PD patients with more denervated ventral striatum and more imbalanced serotonin-to-dopamine ratio in the grafted neurons tended to have worse outcome. In HD transplantation studies, variable graft survival and clinical responses may be related to host inflammatory/immune responses to the grafts.

Summary

Information gleaned from imaging findings in previous neural transplantation studies has been used to refine study protocol and patient selection in future trials. This includes identifying suitable candidates for transplantation using imaging markers, employing multiple and/or novel PET tracers to better assess graft functions and inflammatory responses to grafts.

Striatal activation by optogenetics induces dyskinesias in the 6-hydroxydopamine rat model of Parkinson disease

BACKGROUND

Long-term levodopa (l-dopa) treatment is associated with the development of l-dopa-induced dyskinesias in the majority of patients with Parkinson disease (PD). The etiopathogonesis and mechanisms underlying l-dopa-induced dyskinesias are not well understood.

METHODS

We used striatal optogenetic stimulation to induce dyskinesias in a hemiparkinsonian model of PD in rats. Striatal dopamine depletion was induced unilaterally by 6-hydroxydopamine injection into the medial forebrain bundle. For the optogenetic manipulation, we injected adeno-associated virus particles expressing channelrhodopsin to stimulate striatal medium spiny neurons with a laser source.

RESULTS

Simultaneous optical activation of medium spiny neurons of the direct and indirect striatal pathways in the 6-hydroxydopamine lesion but l-dopa naïve rats induced involuntary movements similar to l-dopa-induced dyskinesias, labeled here as optodyskinesias. Noticeably, optodyskinesias were facilitated by l-dopa in animals that did not respond initially to the laser stimulation. In general, optodyskinesias lasted while the laser stimulus was applied, but in some instances remained ongoing for a few seconds after the laser was off. Postmortem tissue analysis revealed increased FosB expression, a molecular marker of l-dopa-induced dyskinesias, primarily in medium spiny neurons of the direct pathway in the dopamine-depleted hemisphere.

CONCLUSION

Selective optogenetic activation of the dorsolateral striatum elicits dyskinesias in the 6-hydroxydopamine rat model of PD. This effect was associated with a preferential activation of the direct striato-nigral pathway. These results potentially open new avenues in the understanding of mechanisms involved in l-dopa-induced dyskinesias. © 2017 International Parkinson and Movement Disorder Society.

Robust graft survival and normalized dopaminergic innervation do not obligate recovery in a Parkinson disease patient

OBJECTIVE

The main goal of dopamine cell replacement therapy in Parkinson disease (PD) is to provide clinical benefit mediated by graft survival with nigrostriatal reinnervation. We report a dichotomy between graft structure and clinical function in a patient dying 16 years following fetal nigral grafting.

METHODS

A 55-year-old levodopa-responsive woman with PD received bilateral putaminal fetal mesencephalic grafts as part of an NIH-sponsored double-blind sham-controlled trial. The patient never experienced clinical benefit, and her course was complicated by the development of graft-related dyskinesias. Fluorodopa positron emission tomography demonstrated significant increases postgrafting bilaterally. She experienced worsening of parkinsonism with severe dyskinesias, and underwent subthalamic nucleus deep brain stimulation 8 years after grafting. She died 16 years after transplantation.

RESULTS

Postmortem analyses confirmed the diagnosis of PD and demonstrated >300,000 tyrosine hydroxylase (TH)-positive grafted cells per side with normalized striatal TH-immunoreactive fiber innervation and bidirectional synaptic connectivity. Twenty-seven percent and 17% of grafted neurons were serine 129-phosphorylated α-synuclein positive in the left and right putamen, respectively.

INTERPRETATION

These findings represent the largest number of surviving dopamine neurons and the densest and most widespread graft-mediated striatal dopamine reinnervation following a transplant procedure reported to date. Despite this, clinical recovery was not observed. Furthermore, the grafts were associated with a form of dyskinesias that resembled diphasic dyskinesia and persisted in the off-medication state. We hypothesize that the grafted cells produced a low level of dopamine sufficient to cause a levodopa-independent continuous form of diphasic dyskinesias, but insufficient to provide an antiparkinsonian benefit. ANN NEUROL 2017;81:46-57.

Cell Therapy for Parkinson's Disease: A Translational Approach to Assess the Role of Local and Systemic Immunosuppression

Neural transplantation is a promising therapeutic approach for neurodegenerative diseases; however, many patients receiving intracerebral fetal allografts exhibit signs of immunization to donor antigens that could compromise the graft. In this context, we intracerebrally transplanted mesencephalic pig xenografts into primates to identify a suitable strategy to enable long-term cell survival, maturation, and differentiation. Parkinsonian primates received WT or CTLA4-Ig transgenic porcine xenografts and different durations of peripheral immunosuppression to test whether systemic plus graft-mediated local immunosuppression might avoid rejection. A striking recovery of spontaneous locomotion was observed in primates receiving systemic plus local immunosuppression for 6 mo. Recovery was associated with restoration of dopaminergic activity detected both by positron emission tomography imaging and histological examination. Local infiltration by T cells and CD80/86+ microglial cells expressing indoleamine 2,3-dioxigenase were observed only in CTLA4-Ig recipients. Results suggest that in this primate neurotransplantation model, peripheral immunosuppression is indispensable to achieve the long-term survival of porcine neuronal xenografts that is required to study the beneficial immunomodulatory effect of local blockade of T cell costimulation.

Striatal Plasticity in L-DOPA- and Graft-Induced Dyskinesia; The Common Link?

One of the major symptoms of the neurodegenerative condition Parkinson's disease (PD) is a slowness or loss of voluntary movement, yet frustratingly therapeutic strategies designed to restore movement can result in the development of excessive abnormal movements known as dyskinesia. These dyskinesias commonly develop as a result of pharmacotherapy in the form of L-DOPA administration, but have also been identified following deep brain stimulation (DBS) and intrastriatal cell transplantation. In the case of L-DOPA these movements can be treatment limiting, and whilst they are not long lasting or troubling following DBS, recognition of their development had a near devastating effect on the field of cell transplantation for PD.Understanding the relationship between these therapeutic approaches and the development of dyskinesia may improve our ability to restore function without disabling side effects. Interestingly, despite the fact that dopaminergic cell transplantation repairs many of the changes induced by the disease process and through L-DOPA treatment, there appears to be a relationship between the two. In rodent models of the disease, the severity of dyskinesia induced by L-DOPA prior to the transplantation procedure correlated with post-transplantation, graft-induced dyskinesia. A review of clinical data also suggested that the worse preoperational dyskinesia causes worsened graft-induced dyskinesia (GID). Understanding how these aberrant behaviors come about has been of keen interest to open up these therapeutic options more widely and one major underlying theory is the effects of these approaches on the plasticity of synapses within the basal ganglia. This review uniquely brings together developments in understanding the role of striatal synaptic plasticity in both L-DOPA and GID to guide and stimulate further investigations on the important striatal plasticity.

Foetal Cell Transplantation for Parkinson's Disease: Focus on Graft-Induced Dyskinesia

Transplantation of dopamine- (DA-) rich foetal ventral mesencephalic cells emerged as a promising therapy for Parkinson's disease (PD), as it allowed significant improvement of motor symptoms in several PD patients in open-label studies. However, double-blind clinical trials have been largely disappointing. The general agreement in the field is that the lack of standardization of tissue collection and preparation, together with the absence of postsurgical immunosuppression, played a key role in the failure of these studies. Moreover, a further complication that emerged in previous studies is the appearance of the so-called graft-induced dyskinesia (GID), in a subset of grafted patients, which resembles dyskinesia induced by L-DOPA but in the absence of medication. Preclinical evidence pointed to the serotonin neurons as possible players in the appearance of GID. In agreement, clinical investigations have shown that grafted tissue may contain a large number of serotonin neurons, in the order of half of the DA cells; moreover, the serotonin 5-HT1A receptor agonist buspirone has been found to produce significant dampening of GID in grafted patients. In this paper, we will review the recent preclinical and clinical studies focusing on cell transplantation for PD and on the mechanisms underlying GID.

Molecular imaging of levodopa-induced dyskinesias

Levodopa-induced dyskinesias (LIDs) occur in the majority of patients with Parkinson's disease (PD) following years of levodopa treatment. The pathophysiology underlying LIDs in PD is poorly understood, and current treatments generate only minor benefits for the patients. Studies with positron emission tomography (PET) molecular imaging have demonstrated that in advanced PD patients, levodopa administration induces sharp increases in striatal dopamine levels, which correlate with LIDs severity. Fluctuations in striatal dopamine levels could be the result of the attenuated buffering ability in the dopaminergically denervated striatum. Lines of evidence from PET studies indicate that serotonergic terminals could also be responsible for the development of LIDs in PD by aberrantly processing exogenous levodopa and by releasing dopamine in a dysregulated manner from the serotonergic terminals. Additionally, other downstream mechanisms involving glutamatergic, cannabinoid, opioid, cholinergic, adenosinergic, and noradrenergic systems may contribute in the development of LIDs. In this article, we review the findings from preclinical, clinical, and molecular imaging studies, which have contributed to our understanding the pathophysiology of LIDs in PD.

The potential of alternate sources of cells for neural grafting in Parkinson's and Huntington's disease

Cell-based therapies for Parkinson's and Huntington's disease have provided mixed clinical outcomes and one of the reasons underlying this is the use of primary fetal tissue as the source of grafted cells. An alternate source of cells, such as stem cells, could overcome many of the issues associated with primary fetal tissue and would help bring forward cell replacement therapy as a reliable and effective treatment for these two neurodegenerative disorders. This review will discuss which stem cells are likely to go to clinic in the next generation of cells, based on trials for Parkinson's and Huntington's disease.

Cell based therapies in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disorder after Alzheimer’s disease. It is characterized by bradykinesia, hypokinesia/ akinesia, rigidity, tremor, and postural instability, caused by dopaminergic (DA) striatal denervation. The prevalence of PD increases from 50 years of age with steep rise after age 60 years. Current treatment of PD relies heavily on replacing lost dopamine either with its precursor L-dopa or dopamine agonists (ropinirole, pramipexole, bromocriptine, lisuride etc). Other pharmacological measures like catechol-O-methyltrasferase (COMT) inhibitors like entacopone, telcapone and monoamine oxidase B (MAO-B) inhibitors like selegiline and rasagiline are also useful, while L-dopa remains the gold standard in the treatment of PD. Emerging therapies are focusing on cell based therapeutics derived from various sources.

Dyskinesias in Parkinson's disease: views from positron emission tomography studies

Levodopa-induced dyskinesias (LIDs) and graft-induced dyskinesias (GIDs) are serious and common complications of Parkinson's disease (PD) management following chronic treatment with levodopa or intrastriatal transplantation with dopamine-rich foetal ventral mesencephalic tissue, respectively. Positron emission tomography (PET) molecular imaging provides a powerful in vivo tool that has been employed over the past 20 years for the elucidation of mechanisms underlying the development of LIDs and GIDs in PD patients. PET used together with radioligands tagging molecular targets has allowed the functional investigation of several systems in the brain including the dopaminergic, serotonergic, glutamatergic, opioid, endocannabinoid, noradrenergic and cholinergic systems. In this article the role of PET imaging in unveiling pathophysiological mechanisms underlying the development of LIDs and GIDs in PD patients is reviewed.

Clinical features, pathophysiology, and treatment of levodopa-induced dyskinesias in Parkinson's disease

Dyskinetic disorders are characterized by excess of motor activity that may interfere with normal movement control. In patients with Parkinson's disease, the chronic levodopa treatment induces dyskinetic movements known as levodopa-induced dyskinesias (LID). This paper analyzed the pathophysiology, clinical manifestations, pharmacological treatments, and surgical procedures to treat hyperkinetic disorders. Surgery is currently the only treatment available for Parkinson's disease that may improve both parkinsonian motor syndrome and LID. However, this paper shows the different mechanisms involved are not well understood.

α-Synuclein and neuronal cell death

Parkinson’s disease (PD) is a progressive neurodegenerative disorder affecting ∼1 % of people over the age of 65. Neuropathological hallmarks of PD are prominent loss of dopaminergic (DA) neurons in the substantia nigra and formation of intraneuronal protein inclusions termed Lewy bodies, composed mainly of α-synuclein (αSyn). Missense mutations in αSyn gene giving rise to production of degradation-resistant mutant proteins or multiplication of wild-type αSyn gene allele can cause rare inherited forms of PD. Therefore, the existence of abnormally high amount of αSyn protein is considered responsible for the DA neuronal death in PD. Normally, αSyn protein localizes to presynaptic terminals of neuronal cells, regulating the neurotransmitter release through the modulation of assembly of soluble N-ethylmaleimide-sensitive factor attachment protein receptor complex. On the other hand, of note, pathological examinations on the recipient patients of fetal nigral transplants provided a prion-like cell-to-cell transmission hypothesis for abnormal αSyn. The extracellular αSyn fibrils can internalize to the cells and enhance intracellular formation of protein inclusions, thereby reducing cell viability. These findings suggest that effective removal of abnormal species of αSyn in the extracellular space as well as intracellular compartments can be of therapeutic relevance. In this review, we will focus on αSyn-triggered neuronal cell death and provide possible disease-modifying therapies targeting abnormally accumulating αSyn.

Stem cells and regenerative therapies for Parkinson's disease

Currently the mainstay of Parkinson's disease (PD) therapy is the pharmacological replacement of the loss of the dopaminergic nigrostriatal pathway using drugs such as dopamine agonists and levodopa. Whilst these drugs effectively ameliorate some of the motor features of PD, they do not improve many of the nonmotor features that arise secondary to pathology outside of this system, nor do they slow the progressive neurodegeneration that is a characteristic of the disease. Regenerative therapies for PD seek to fill this therapeutic gap, with cell transplantation being the most explored approach to date. A number of different cell sources have been used in this therapeutic approach, but to date, the most successful has been the use of fetal ventral mesencephalic (VM) tissue that contains within it the developing nigral dopaminergic cells. Cell transplantation for PD was pioneered in the 1980-1990s, with several successful open-label trials of fetal VM transplantation in patients with relatively advanced PD. Whilst these findings were not replicated in two subsequent double-blind sham-surgery controlled trials, there were reasons to explain this outside of the one drawn at the time that these therapies are ineffective. Indeed all these studies have provided evidence that following the transplantation of fetal VM tissue, dopaminergic cells can survive long term, produce dopamine, and bring about clinical improvements in younger patients over many years. The use of fetal tissue, irrespective of its true efficacy, will never become a widely available therapy for PD for a host of practical and ethical reasons, and thus much work has been put in recently to exploring the utility of stem cells as a source of nigral dopaminergic neurons. In this respect, the advent of embryonic stem cell and induced pluripotent cells has heralded a new era in cell therapy for PD, and several groups have now demonstrated that these cells can form dopaminergic neurons which improve functional deficits in animal models of PD. Whilst encouraging, problems with respect to the immunogenicity and tumorigenicity of these cells means that they will need to be used in the clinic cautiously. Other regenerative therapies in PD have been tried over the years and include the use of trophic factors. This has primarily involved glial cell line-derived neurotrophic factor (GDNF) and again has produced mixed clinical effects, and in order to try and resolve this, a new trial of intraputamenal GDNF is now being planned. In addition, a new trial for platelet derived growth factor as a treatment for PD has just completed recruitment, and PYM50028 (Cogane) an oral agent shown in animal models to reduce the effects of MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) lesioning by the induction of growth factors is currently under investigation in a multicentre Phase II trial. Overall, there are a number of promising new regenerative therapies being developed and tested in PD, although the true long-term efficacy of any of these in large numbers of patients is still not known.

Understanding and prevention of "therapy-" induced dyskinesias

L-dopa is the most effective, currently available treatment for Parkinson's disease (PD), but it leads to the development of involuntary movements known as L-dopa-induced dyskinesia (LID) in the majority of patients after long-term use. Both gene and cell therapy approaches are the subject of multiple ongoing studies as potential ways of relieving symptoms of PD without the complication of dyskinesia. However, the spectre of dyskinesia in the absence of L-dopa, the so-called "off-phase" or graft-induced dyskinesia (GID), remains a major obstacle particularly in the further development of cell therapy in PD, but it is also a concern for proponents of gene therapy approaches. LID results from nonphysiological dopamine release, supersensitivity of dopamine receptors, and consequent abnormal signalling through mechanisms of synaptic plasticity. Restoration of physiological circuitry within the basal ganglia loops is ultimately the aim of all cell and gene therapy approaches but each using distinctive strategies and accompanied by risks of exacerbation of LID or development of "off-phase"/GID. In this paper we discuss the details of what is understood regarding the development of dyskinesias with relevance to cell and gene therapy and potential strategies to minimize their occurrence.

The immunological challenges of cell transplantation for the treatment of Parkinson's disease

Dopaminergic cell transplantation is an experimental therapy for Parkinson's disease (PD). It has many potential theoretical advantages over current treatment strategies such as providing continuous local dopaminergic replenishment, eliminating motor fluctuations and medication-induced dyskinesias, slowing down disease progression or even reversing disease pathology in the host. Recent studies also show that dopaminergic cell transplants provide long-term neuromodulation in the basal ganglia that simulates the combined effects of oral dopaminergic therapy and surgical therapies like deep brain stimulation, the contemporary therapeutic approach to advanced PD. However, dopaminergic cell transplantation in PD as not been optimized and current experimental techniques have many drawbacks. In published experiments to date of attempted dopaminergic grafting in PD, the major challenges are unacceptable graft-induced dyskinesias or failure of such grafts to exceed the benefits afforded by sham surgery. A deleterious host immune response to the transplant has been implicated as a major putative cause for these adverse outcomes. This article focuses on recent advances in understanding the immunology of the transplantation in PD and possible methods to overcome adverse events such that we could translate cell replacement strategies into viable clinical treatments in the future.

Co-transplantation of macaque autologous Schwann cells and human embryonic nerve stem cells in treatment of macaque Parkinson's disease

OBJECTIVE

To investigate the therapeutic effects of co-transplantation with Schwann cells (SCs) and human embryonic nerve stem cells (NSCs) on macaque Parkinson's disease (PD).

METHODS

Macaque autologous SCs and human embryonic NSCs were adopted for the treatment of macaque PD.

RESULTS

Six months after transplantation, positron emission computerized tomography showed that (18)F-FP-β-CIT was significantly concentrated in the injured striatum in the co-transplanted group. Immunohistochemical staining of transplanted area tissue showed migration of tyroxine hydroxylase positive cells from the transplant area to the surrounding area was significantly increased in the co-transplanted group.

CONCLUSIONS

Co-transplantation of SCs and NSCs could effectively cure PD in macaques. SCs harvested from the autologous peripheral nerves can avoid rejection and the ethics problems, so it is expected to be applied clinically.

Anatomy of Graft-induced Dyskinesias: Circuit Remodeling in the Parkinsonian Striatum

The goal of researchers and clinicians interested in re-instituting cell based therapies for PD is to develop an effective and safe surgical approach to replace dopamine (DA) in individuals suffering from Parkinson's disease (PD). Worldwide clinical trials involving transplantation of embryonic DA neurons into individuals with PD have been discontinued because of the often devastating post-surgical side-effect known as graft-induced dyskinesia (GID). There have been many review articles published in recent years on this subject. There has been a tendency to promote single factors in the cause of GID. In this review, we contrast the pros and cons of multiple factors that have been suggested from clinical and/or preclinical observations, as well as novel factors not yet studied that may be involved with GID. It is our intention to provide a platform that might be instrumental in examining how individual factors that correlate with GID and/or striatal pathology might interact to give rise to dysfunctional circuit remodeling and aberrant motor output.

Multiple system atrophy: current and future approaches to management

Multiple system atrophy (MSA) is a rare neurodegenerative disorder without any effective treatment in slowing or stopping disease progression. It is characterized by poor levodopa responsive Parkinsonism, cerebellar ataxia, pyramidal signs and autonomic failure in any combination. Current therapeutic strategies are primarily based on dopamine replacement and improvement of autonomic failure. However, symptomatic management remains disappointing and no curative treatment is yet available. Recent experimental evidence has confirmed the key role of alpha-synuclein aggregation in the pathogenesis of MSA. Referring to this hypothesis, transgenic and toxic animal models have been developed to assess candidate drugs for MSA. The standardization of diagnosis criteria and assessment procedures will allow large multicentre clinical trials to be conducted. In this article we review the available symptomatic treatment, recent results of studies investigating potential neuroprotective drugs, and future approaches for the management in MSA.