Drug selection and timing of initiation of treatment in early Parkinson's disease

Overcoming Methodological Challenges for Advancing Stem Cell Therapies in Parkinson's Disease

The quest for new and improved therapies for Parkinson's disease (PD) remains of paramount importance, despite previous trial failures. There is a current debate regarding the potential of stem cell research as a therapeutic approach for PD. The studies of dopaminergic fetal stem cells for PD treatment, their design, and the results of the initial surgical placebo-controlled trials were reviewed in this study. Some of the fundamental methodological challenges and possible strategies to resolve them were proposed. In this article, we argue that the most important impact lies in the proof-of-principle demonstrated by clinical trials for cell replacement strategies in reconstructing the human brain. While some researchers argue that the considerable technical challenges associated with cell therapies for PD warrant the discontinuation of further development using stem cells, we believe that the opposing viewpoints are instrumental in identifying a series of methodological misunderstandings. Here, we propose to expose key challenges to ensure the advancement of the field and unlock the potential of stem cell therapies in PD treatment. Overall, this review underscores the need for further research and innovation to overcome the hurdles in realizing the potential of stem cell-based therapies for PD.

The dilemma between milestones of progression versus clinical scales in Parkinson's disease

There are significant challenges in accurately documenting the progression of Parkinson's disease (PD). The disease course is highly heterogeneous, there are no validated biomarkers, and we are reliant on repeated clinical measures to assess disease state over time. Yet, the ability to chart disease progression accurately is vital in both observational and interventional study designs, where reliable measures are critical to determine whether an outcome has been met. In this chapter, we first discuss the natural history of PD, including the spectrum of clinical presentation and expected developments through the course of the disease. We then explore in detail the current strategies for measuring disease progression, which can be broadly divided into: (i) the use of quantitative clinical scales; and (ii) determination of the onset time of key milestones. We discuss the strengths and limitations of these approaches for use in clinical trials, with a particular focus on disease modification trials. The selection of outcome measures for a particular study will depend on multiple factors, but trial duration is an important determinant. Milestones are reached over a course of years rather than months, and hence clinical scales with sensitivity to change are needed for short-term studies. However, milestones represent important markers of disease stage which are not confounded by symptomatic therapies and are of critical relevance to the patient. Prolonged but low intensity follow-up beyond a limited period of treatment with a putative disease-modifying agent may allow milestones to be incorporated into evaluation of efficacy in a practical and cost-effective way.

Glial cell line-derived neurotrophic factors (GFLs) and small molecules targeting RET receptor for the treatment of pain and Parkinson's disease

Rearranged during transfection (RET), in complex with glial cell line-derived (GDNF) family receptor alpha (GFRα), is the canonical signaling receptor for GDNF family ligands (GFLs) expressed in both central and peripheral parts of the nervous system and also in non-neuronal tissues. RET-dependent signaling elicited by GFLs has an important role in the development, maintenance and survival of dopamine and sensory neurons. Both Parkinson's disease and neuropathic pain are devastating disorders without an available cure, and at the moment are only treated symptomatically. GFLs have been studied extensively in animal models of Parkinson's disease and neuropathic pain with remarkable outcomes. However, clinical trials with recombinant or viral vector-encoded GFL proteins have produced inconclusive results. GFL proteins are not drug-like; they have poor pharmacokinetic properties and activate multiple receptors. Targeting RET and/or GFRα with small molecules may resolve the problems associated with using GFLs as drugs and can result in the development of therapeutics for disease-modifying treatments against Parkinson's disease and neuropathic pain.

Sex-Dependent Improvement in Survival of Parkinson's Disease Patients

Background

Advances in the treatment of Parkinson's disease (PD) and changes in general life expectancy may have improved survival in patients with PD.

Objective

The objective of this study was to investigate recent trends in PD mortality.

Methods

In total, 1521 patients with PD in local and national registries were followed for 11 years (2006-2016) from diagnosis until exit date or death, and the causes of death were recorded.

Results

The survival of men with PD improved during the follow-up period, but no change was observed in women (2-year postdiagnosis survival in men, 79.0%-86.3%, P = 0.03; 2-year postdiagnosis survival in women, 82.8%-87.5%, P = 0.42). Pneumonia was the most common immediate cause of death.

Discussion

The survival of men with PD has improved in Finland without a similar change in women. Because changes in treatment likely affect both sexes similarly, the results may reflect the decreasing sex gap in life expectancy. This phenomenon will likely increase the already high male-to-female prevalence ratio of PD.

Long-term safety and efficacy of adjunctive rasagiline in levodopa-treated Japanese patients with Parkinson's disease

Rasagiline is a monoamine oxidase type-B inhibitor in development in Japan for Parkinson’s disease (PD). This open-label study evaluated the long-term safety and efficacy of rasagiline in Japanese patients with PD receiving levodopa. Patients were aged 30–79 years and had wearing-off or weakened effect. Patients received rasagiline 1 mg/day for 52 weeks. The primary objective was to evaluate safety. Secondary endpoints included MDS-UPDRS Part II and Part III total scores (ON-state) and change from baseline in mean daily OFF-time. An additional endpoint was the Parkinson’s Disease Questionnaire-39 (PDQ-39) Summary Index (SI) score. In total, 222 patients were enrolled; 52.3% had wearing-off phenomena. Treatment-emergent adverse events (TEAEs) were mostly mild or moderate and occurred in 83.3% of patients; 63.1% had drug-related TEAEs; and 21.2% had TEAEs resulting in discontinuation. Fall (16.7%), nasopharyngitis (14.0%), and dyskinesia (10.8%) were the most frequent TEAEs. Serious TEAEs were reported in 17.6% of patients, and led to discontinuation in 9.5%. At week 52 (last-observation-carried forward), the mean change from baseline in MDS-UPDRS Part III total score (ON-state) was − 7.6; the mean change from baseline in daily OFF-time was − 0.89 h in patients with wearing-off phenomena at the start of the run-in period. The mean change from baseline in PDQ-39 SI was − 0.64. No major safety issues were observed during this 52-week trial of rasagiline as an adjunct to levodopa in Japanese patients. Mean changes in MDS-UPDRS scores and daily OFF-time suggested that adjunctive rasagiline treatment with levodopa was efficacious, with efficacy maintained for at least 52 weeks.

Therapeutic strategies in the early stages of Parkinson's disease: a cross-sectional evaluation of 15 years' experience with a large cohort of Romanian patients

INTRODUCTION

In patients older than 70 years there is no valid alternative to progressively introduced substitution therapy. The antiparkinsonian drugs introduced in the last decade to treat Parkinson's disease, especially in its early phases, promised a comparable efficacy in reducing symptoms to levodopa. In younger patients and/or patients with mild symptoms we hoped to delay the motor complications by postponing the start of levodopa therapy. While these assumptions may not be true for all patients, probably the most important current challenge is the optimal starting moment of levodopa therapy. The aim of the study was to analyze the therapeutical choices during the early phase of Parkinson's disease in the Neurological Departments of Târgu Mures¸ County Hospital.

MATERIALS AND METHODS

We examined data obtained from hospitalized Parkinson's disease patients during a 15-year period. According to the duration of the disease we split the patients into two groups, patients with Parkinson's disease for less than or equal to 5 years and patients with disease duration longer than 5 years, and then analyzed only the former group.

RESULTS

During the examined period, 2,379 patients with Parkinson's disease were hospitalized, and 1,237 patients had a disease duration shorter than 5 years. In this group, 18 patients had monoamine oxidase inhibitor monotherapy. Also, 665 patients received dopamine agonists, in 120 cases as monotherapy and in 83 patients associated with monoamine oxidase inhibitors. In 521 patients we found only levodopa treatment. A further 481 patients received combined therapy (levodopa with dopamine agonists and/or monoamine oxidase inhibitors).

CONCLUSION

Treatment strategies for the early stages of Parkinson's disease in our group were comparable to results from other studies. However, the authors feel that neurologists should use levodopa-sparing drugs with greater courage. Furthermore, if the clinical context is appropriate, physicians should combine substitution therapy with other antiparkinsonian drugs in order to reduce levodopa doses.

A Randomized Double-Blind Placebo-Controlled Phase III Trial of Selegiline Monotherapy for Early Parkinson Disease

Background

In Japan, selegiline has been approved for combination therapy with levodopa for Parkinson disease (PD). We conducted a trial of selegiline monotherapy for early PD.

Methods

In this 12-week controlled phase III trial, a total of 292 subjects were randomized to receive placebo (n = 146) (full analysis set 140) or selegiline (n = 146) (full analysis set 139). The primary outcome measure was the change in the Unified Parkinson Disease Rating Scale part I + II + III total score from baseline to the final visit. Other secondary measures and a safety profile were evaluated.

Results

Selegiline monotherapy reduced the primary outcome measure by −6.26 ± 7.86 compared with the placebo −3.14 ± 6.98 (mean ± SD, P = 0.0005 by analysis of covariance). There was no significant difference in the number of adverse events between the 2 groups (P > 0.05).

Conclusions

Selegiline monotherapy reduced the total Unified Parkinson Disease Rating Scale part I + II + III score and was well tolerated in Japanese patients with early PD.

α-Synuclein stimulation of monoamine oxidase-B and legumain protease mediates the pathology of Parkinson's disease

Dopaminergic neurodegeneration in Parkinson's disease (PD) is associated with abnormal dopamine metabolism by MAO-B (monoamine oxidase-B) and intracellular α-Synuclein (α-Syn) aggregates, called the Lewy body. However, the molecular relationship between α-Syn and MAO-B remains unclear. Here, we show that α-Syn directly binds to MAO-B and stimulates its enzymatic activity, which triggers AEP (asparagine endopeptidase; legumain) activation and subsequent α-Syn cleavage at N103, leading to dopaminergic neurodegeneration. Interestingly, the dopamine metabolite, DOPAL, strongly activates AEP, and the N103 fragment of α-Syn binds and activates MAO-B. Accordingly, overexpression of AEP in SNCA transgenic mice elicits α-Syn N103 cleavage and accelerates PD pathogenesis, and inhibition of MAO-B by Rasagiline diminishes α-Syn-mediated PD pathology and motor dysfunction. Moreover, virally mediated expression of α-Syn N103 induces PD pathogenesis in wild-type, but not MAO-B-null mice. Our findings thus support that AEP-mediated cleavage of α-Syn at N103 is required for the association and activation of MAO-B, mediating PD pathogenesis.

Early versus delayed initiation of pharmacotherapy in Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease and pathologically is characterised by a progressive loss of dopaminergic cells of the nigrostriatal pathway. Clinically, PD is mainly defined by the presence of the motor symptoms of bradykinesia, rigidity, rest tremor and postural instability, but non-motor symptoms such as depression, dementia and autonomic disturbances are recognised as integral parts of the disease. Although pharmacotherapy for PD was introduced almost 50 years ago, and has improved significantly over the intervening period, the timing of initiation of treatment in newly diagnosed PD remains controversial. While some physicians favour an early start of pharmacotherapy at or soon after diagnosis, others prefer to delay pharmacological treatment until a certain degree of disability has developed. This article aims to discuss the advantages and disadvantages of both strategies by exploring their effects on symptoms, disease progression and quality of life. Although the data on putative disease-modifying effects of early pharmacological intervention in PD are still inconclusive, we believe that the most important indication for an early initiation of anti-parkinsonian treatment should be to maintain the quality of life of PD patients and to secure their socioeconomic status as long as possible.

Contributions of signaling by dopamine neurons in dorsal striatum to cognitive behaviors corresponding to those observed in Parkinson's disease

Although the cardinal features of Parkinson's disease (PD) are motor symptoms, PD also causes cognitive deficits including cognitive flexibility and working memory, which are strongly associated with prefrontal cortex (PFC) functions. Yet, early stage PD is not characterized by pathology in the PFC but by a loss of dopaminergic (DA) projections from the substantia nigra to the dorsal striatum. Moreover, the degree to which PD symptoms can be ascribed to the loss of DA alone or to the loss of DA neurons is unknown. We addressed these issues by comparing mouse models of either chronic DA depletion or loss of DA projections to the dorsal striatum. We achieved equal levels of striatal DA reduction in both models which ranged from mild (~25%) to moderate (~60%). Both models displayed DA concentration-dependent reductions of motor function as well as mild deficits of cognitive flexibility and working memory. Interestingly, whereas both motor function and cognitive flexibility were more severely impaired after mild ablation of DA neurons as compared to mild loss of DA alone, both models had equal deficits after moderate loss of DA. Our results confirm contributions of nigro-striatal dopamine signaling to cognitive behaviors that are affected in early stage PD. Furthermore, our findings suggest that the phenotype after ablation of DA neurons accrues from factors beyond the mere loss of DA.

An update on the management of juvenile and young-onset Parkinson’s disease

Early-onset Parkinson’s disease (PD) denotes onset of the disease below the age of 40 years. Patients tend to have a slower disease progression, an increased rate of dystonia, an increased rate of dyskinesias in response to L-3,4-dihydroxyphenylalanine and a lower rate of dementia compared with those in late-onset PD. Early-onset PD patients may experience more social and psychosocial conflict compared with late-onset patients and these factors would contribute to greater impairment of quality of life. Unemployment due to disability or early retirement may be causes for these conflicts. We have to take these factors into account whenever we institute drug therapy in early-onset PD. There is no randomized controlled study on early-onset PD; however, we may make a reasonable decision by considering the data on PD in general and clinical characteristics of early-onset patients. The management of motor and non-motor symptoms of early-onset PD patients is reviewed here.

Monoamine oxidase B inhibitors for the treatment of Parkinson's disease: a review of symptomatic and potential disease-modifying effects

Parkinson's disease is a disorder characterized pathologically by progressive neurodegeneration of the dopaminergic cells of the nigrostriatal pathway. Although the resulting dopamine deficiency is the cause of the typical motor features of Parkinson's disease (bradykinesia, rigidity, tremor), additional non-motor symptoms appear at various timepoints and are the result of non-dopamine nerve degeneration. Monoamine oxidase B (MAO-B) inhibitors are used in the symptomatic treatment of Parkinson's disease as they increase synaptic dopamine by blocking its degradation. Two MAO-B inhibitors, selegiline and rasagiline, are currently licensed in Europe and North America for the symptomatic improvement of early Parkinson's disease and to reduce off-time in patients with more advanced Parkinson's disease and motor fluctuations related to levodopa. A third MAO-B inhibitor (safinamide), which also combines additional non-dopaminergic properties of potential benefit to Parkinson's disease, is currently under development in phase III clinical trials as adjuvant therapy to either a dopamine agonist or levodopa. MAO-B inhibitors have also been studied extensively for possible neuroprotective or disease-modifying actions. There is considerable laboratory evidence that MAO-B inhibitors do exert some neuroprotective properties, at least in the Parkinson's disease models currently available. However, these models have significant limitations and caution is required in assuming that such results may easily be extrapolated to clinical trials. Rasagiline 1 mg/day has been shown to provide improved motor control in terms of Unified Parkinson's Disease Rating Scale (UPDRS) score at 18 months in those patients with early disease who began the drug 9 months before a second group. There are a number of possible explanations for this effect that may include a disease-modifying action; however, the US FDA recently declined an application for the licence of rasagiline to be extended to cover disease modification.

Pramipexole for the treatment of early Parkinson's disease

Pramipexole is a nonergolinic dopamine agonist, with high affinity for the D2 subfamily of dopamine receptors. Pramipexole is efficacious for the symptomatic treatment of early Parkinson's Disease (PD) and its early use, before that of levodopa can delay the emergence of levodopa-related motor complication. Dosage should be increased gradually from a starting dose of 0.375 mg/day up to a maximum of 4.5 mg/day in equally divided doses taken three times per day with pramipexole immediate-release or equivalent daily dosages once-daily with pramipexole extended-release. Pramipexole can also improve depressive symptoms and possibly health-related quality of life in PD. Nonetheless, its use is not devoid of tolerability problems. While peripheral adverse drug reactions, such as nausea, vomiting or orthostatic hypotension, can be effectively treated and usually pose few problems to most patients, neuropsychiatric events can seriously limit the use of pramipexole in some cases. Indeed, excessive daytime somnolence, impulse-control disorders, hallucinations or delusions can severely affect patients, causing important personal or social handicap. Patients should be informed about the risk of such neuropsychiatric complications and their presence should be actively detected at each consultation. More effort will have to be put into further studying the risk-benefit ratio of pramipexole and other dopamine agonists in the treatment of early PD.

Strategies for Parkinson’s disease care: prevention and management of motor fluctuations

SUMMARY Parkinson’s disease (PD) is characterized clinically by the hallmark motor signs of bradykinesia, rest tremor and rigidity. Current pharmacological management goals include control of motor symptoms as well as prevention and management of motor complications including motor fluctuations and dyskinesias. While the use of levodopa revolutionized the pharmacological management of PD, multiple other agents and strategies have emerged with many demonstrable, albeit sometimes controversial, advantages to a ‘levodopa’ only approach. Despite these developments, the progressive nature of PD requires vigilance and creativity from clinicians as both motor and nonmotor complications grow in number and severity over time.

Seniors with Parkinson's disease: initial medical treatment

Parkinson's disease most often presents after age 60, and patients in this age group are best managed with levodopa therapy as the primary treatment modality. Unlike young-onset parkinsonism (onset <age 40), this older age group is much less prone to subsequent development of levodopa responsive instability (dyskinesias, fluctuations). When these problems do occur in seniors, they usually can be managed by medication adjustments. The treatment goal is to keep patients active and engaged; levodopa dosage should be guided by the patients' responses and not arbitrarily limited to low doses, which may compromise patients' lives.

Lithium fails to protect dopaminergic neurons in the 6-OHDA model of Parkinson's disease

Lithium has been used for the treatment of bipolar mood disorder and is shown to have neuroprotective properties. Since lithium inhibits the activity of glycogen synthase kinase 3 (GSK3) which is implicated in various human diseases, particularly neurodegenerative diseases, the therapeutic potential of lithium receives great attention. Parkinson's disease (PD) is the second most common neurodegenerative disease, characterized by the pathological loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc). Intranigral injection of the catecholaminergic neurotoxin 6-hydroxydopamine (6-OHDA) causes selective and progressive degeneration of dopaminergic neurons in SNpc, and is a commonly used animal model of PD. The current study was designated to determine whether lithium is effective in alleviating 6-OHDA-induced neurodegeneration in the SNpc of rats. We demonstrated that chronic subcutaneous administration of lithium inhibited GSK3 activity in the SNpc, which was evident by an increase in phosphorylation of GSK3β at serine 9, cyclin D1 expression, and a decrease in tau phosphorylation. 6-OHDA did not affect GSK3 activity in the SNpc. Moreover, lithium was unable to alleviate 6-OHDA-induced degeneration of SNpc dopaminergic neurons. The results suggest that GSK3 is minimally involved in the neurodegeneration in the rat 6-OHDA model of PD.

Mitochondrial abnormalities in the putamen in Parkinson's disease dyskinesia

Prolonged treatment of Parkinson's disease (PD) with levodopa leads to disabling side effects collectively referred to as 'dyskinesias'. We hypothesized that bioenergetic function in the putamen might play a crucial role in the development of dyskinesias. To test this hypothesis, we used post mortem samples of the human putamen and applied real time-PCR approaches and gene expression microarrays. We found that mitochondrial DNA (mtDNA) levels are decreased in patients who have developed dyskinesias, and mtDNA damage is concomitantly increased. These pathologies were not observed in PD subjects without signs of dyskinesias. The group of nuclear mRNA transcripts coding for the proteins of the mitochondrial electron transfer chain was decreased in patients with dyskinesias to a larger extent than in patients who had not developed dyskinesias. To examine whether dopamine fluctuations affect mtDNA levels in dopaminoceptive neurons, rat striatal neurons in culture were repeatedly exposed to levodopa, dopamine or their metabolites. MtDNA levels were reduced after treatment with dopamine, but not after treatment with dopamine metabolites. Levodopa led to an increase in mtDNA levels. We conclude that mitochondrial susceptibility in the putamen plays a role in the development of dyskinesias.