Clinical-pathological study of levodopa complications

Effect of Levodopa on Heat Hypersensitivity and Complex Motor Parkinsonism

OBJECTIVES

The aim of the study is to report a case with heat intolerance, complex motor fluctuations, and parkinsonism.

MATERIALS AND METHODS

A male with onset of heat intolerance at the age of 46 years developed left upper limb tremor at the age of 58 years. He was diagnosed with Parkinson disease at the age of 62 years and presented to Movement Disorders Clinic Saskatchewan at the age of 65 years. He reported motor response fluctuations, including WO and dyskinesias. There was no history of dizziness on standing, bladder, or sexual dysfunction. We recorded an asymptomatic drop of orthostatic blood pressure. He reported loss of smell sensation for 5 years and REM behavior disorder characterized by talking in his sleep. He was assessed at the age of 65 years over the course of a day with 4 video recordings of his evolving findings and symptoms with his informed consent.

RESULTS

Initial assessment after levodopa was withheld more than 14 hours revealed him to be 'off' with severe dystonic neck flexion and with bradykinesia and rigidity in the limbs. He was anhidrotic, felt hot, and needed a wet towel over his neck. Over the course of 4 hours, he turns "on" with improvement in heat intolerance, neck hypertonicity, and parkinsonian findings and develops evolving dyskinetic movements before turning "off" again. His overall clinical picture was most consistent with multiple system atrophy.

CONCLUSIONS

Heat intolerance can precede onset of motor symptoms of parkinsonism by several years and supports a diagnosis of multiple system atrophy. To our knowledge, this is the first documented case of improvement in heat intolerance with levodopa.

A meta-analysis identifies factors predicting the future development of freezing of gait in Parkinson's disease

Freezing of gait (FOG) is a debilitating problem that is common among many, but not all, people with Parkinson's disease (PD). Numerous attempts have been made at treating FOG to reduce its negative impact on fall risk, functional independence, and health-related quality of life. However, optimal treatment remains elusive. Observational studies have recently investigated factors that differ among patients with PD who later develop FOG, compared to those who do not. With prediction and prevention in mind, we conducted a systematic review and meta-analysis of publications through 31.12.2022 to identify risk factors. Studies were included if they used a cohort design, included patients with PD without FOG at baseline, data on possible FOG predictors were measured at baseline, and incident FOG was assessed at follow-up. 1068 original papers were identified, 38 met a-priori criteria, and 35 studies were included in the meta-analysis (n = 8973; mean follow-up: 4.1 ± 2.7 years). Factors significantly associated with a risk of incident FOG included: higher age at onset of PD, greater severity of motor symptoms, depression, anxiety, poorer cognitive status, and use of levodopa and COMT inhibitors. Most results were robust in four subgroup analyses. These findings indicate that changes associated with FOG incidence can be detected in a subset of patients with PD, sometimes as long as 12 years before FOG manifests, supporting the possibility of predicting FOG incidence. Intriguingly, some of these factors may be modifiable, suggesting that steps can be taken to lower the risk and possibly even prevent the future development of FOG.

Comparative motor effectiveness of non-invasive brain stimulation techniques in patients with Parkinson's disease: A network meta-analysis

BACKGROUND

Although noninvasive brain stimulation (NIBS) techniques are an effective alternative treatment option, their relative effects in patients with Parkinson's disease (PD) remain undefined. Here, we aimed to compare motor efficacy of the NIBS techniques in PD.

METHODS

We carried out an electronic search in PubMed, Embase, Cochrane Library, CINAHL, PEDro and PsycINFO (accessed via Ovid) for articles published until August 2022. The treatment efficacy of motor function was quantified by the Unified Parkinson's disease rating scale part III.

RESULTS

28 randomized controlled trials with parallel group were included in the analysis, enrolling 1057 patients. In the "on" state, high-frequency repetitive transcranial magnetic stimulation (HFrTMS) conferred better short-term and long-term efficacy compared to transcranial direct current stimulation. Surface under the cumulative ranking curve rank showed that HFrTMS combined with transcranial direct current stimulation and low-frequency TMS ranked first among PD in improving motor function. In the "off" state, there were no significant differences in most of the treatments, but surface under the cumulative ranking curve rank showed that continuous theta burst stimulation and low-frequency TMS had the highest short- and long-term effect in improving motor function.

CONCLUSION

HFrTMS is an effective intervention in improving motor function. Besides, its combination with another NIBS technique produces better therapeutic effects in the "on" state.

Levodopa-Induced Dyskinesias in Parkinson's Disease: An Overview on Pathophysiology, Clinical Manifestations, Therapy Management Strategies and Future Directions

Since its first introduction, levodopa has become the cornerstone for the treatment of Parkinson's disease and remains the leading therapeutic choice for motor control therapy so far. Unfortunately, the subsequent appearance of abnormal involuntary movements, known as dyskinesias, is a frequent drawback. Despite the deep knowledge of this complication, in terms of clinical phenomenology and the temporal relationship during a levodopa regimen, less is clear about the pathophysiological mechanisms underpinning it. As the disease progresses, specific oscillatory activities of both motor cortical and basal ganglia neurons and variation in levodopa metabolism, in terms of the dopamine receptor stimulation pattern and turnover rate, underlie dyskinesia onset. This review aims to provide a global overview on levodopa-induced dyskinesias, focusing on pathophysiology, clinical manifestations, therapy management strategies and future directions.

Circuit Mechanisms of L-DOPA-Induced Dyskinesia (LID)

L-DOPA is the criterion standard of treatment for Parkinson disease. Although it alleviates some of the Parkinsonian symptoms, long-term treatment induces L-DOPA–induced dyskinesia (LID). Several theoretical models including the firing rate model, the firing pattern model, and the ensemble model are proposed to explain the mechanisms of LID. The “firing rate model” proposes that decreasing the mean firing rates of the output nuclei of basal ganglia (BG) including the globus pallidus internal segment and substantia nigra reticulata, along the BG pathways, induces dyskinesia. The “firing pattern model” claimed that abnormal firing pattern of a single unit activity and local field potentials may disturb the information processing in the BG, resulting in dyskinesia. The “ensemble model” described that dyskinesia symptoms might represent a distributed impairment involving many brain regions, but the number of activated neurons in the striatum correlated most strongly with dyskinesia severity. Extensive evidence for circuit mechanisms in driving LID symptoms has also been presented. LID is a multisystem disease that affects wide areas of the brain. Brain regions including the striatum, the pallidal–subthalamic network, the motor cortex, the thalamus, and the cerebellum are all involved in the pathophysiology of LID. In addition, although both amantadine and deep brain stimulation help reduce LID, these approaches have complications that limit their wide use, and a novel antidyskinetic drug is strongly needed; these require us to understand the circuit mechanism of LID more deeply.

The Rodent Models of Dyskinesia and Their Behavioral Assessment

Dyskinesia, a major motor complication resulting from dopamine replacement treatment, manifests as involuntary hyperkinetic or dystonic movements. This condition poses a challenge to the treatment of Parkinson's disease. So far, several behavioral models based on rodent with dyskinesia have been established. These models have provided an important platform for evaluating the curative effect of drugs at the preclinical research level over the past two decades. However, there are differences in the modeling and behavioral testing procedures among various laboratories that adversely affect the rat and mouse models as credible experimental tools in this field. This article systematically reviews the history, the pros and cons, and the controversies surrounding rodent models of dyskinesia as well as their behavioral assessment protocols. A summary of factors that influence the behavioral assessment in the rodent dyskinesia models is also presented, including the degree of dopamine denervation, stereotaxic lesion sites, drug regimen, monitoring styles, priming effect, and individual and strain differences. Besides, recent breakthroughs like the genetic mouse models and the bilateral intoxication models for dyskinesia are also discussed.

Evidence for Sprouting of Dopamine and Serotonin Axons in the Pallidum of Parkinsonian Monkeys

This light and electron microscopie immunohistochemical quantitative study aimed at determining the state of the dopamine (DA) and serotonin (5-HT) innervations of the internal (GPi) and external (GPe) segments of the pallidum in cynomolgus monkeys (Macaca fascicularis) rendered parkinsonian by systemic injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). In contrast to the prominent DA denervation of striatum, the GPi in MPTP monkeys was found to be markedly enriched in DA (TH+) axon varicosities. The posterior sensorimotor region of this major output structure of the basal ganglia was about 8 times more intensely innervated in MPTP monkeys (0.71 ± 0.08 × 10⁶ TH+ axon varicosities/mm³) than in controls (0.09 ± 0.01 × 10⁶). MPTP intoxication also induced a two-fold increase in the density of 5-HT (SERT+) axon varicosities in both GPe and GPi. This augmentation was particularly pronounced anteriorly in the so-called associative and limbic pallidal territories. The total length of the labeled pallidal axons was also significantly increased in MPTP monkeys compared to controls, but the number of DA and 5-HT axon varicosities per axon length unit remained the same in the two groups, indicating that the DA and 5-HT pallidal hyperinnervations seen in MPTP monkeys result from axon sprouting rather than from the appearance of newly formed axon varicosities on non-growing axons. At the ultrastructural level, pallidal TH+ and SERT+ axons were morphologically similar in MPTP and controls, and their synaptic incidence was very low suggesting a volumic mode of transmission. Altogether, our data reveal a significant sprouting of DA and 5-HT pallidal afferents in parkinsonian monkeys, the functional significance of which remains to be determined. We suggest that the marked DA hyperinnervation of the GPi represents a neuroadaptive change designed to normalize pallidal firing patterns associated with the delayed appearance of motor symptoms, whereas the 5-HT hyperinnervation might be involved in the early expression of non-motor symptoms in Parkinson's disease.

Dopamine transporter imaging predicts motor responsiveness to levodopa challenge in patients with Parkinson's disease: A pilot study of DATSCAN for subthalamic deep brain stimulation

Imaging studies are necessary prior to subthalamic deep brain stimulation (STN-DBS). Dopamine transporter (DAT) imaging is a powerful tool for visualizing dopamine terminals in the striatum, but its usefulness in STN-DBS is unclear. Here, we retrospectively investigated the relationship between motor symptoms and the specific binding ratio (SBR) on DAT imaging in patients with Parkinson's disease (PD). We included 23 consecutive patients (9 female; 14 male) who were evaluated for DBS eligibility between October 2013 and October 2014 and subsequently received bilateral STN-DBS. Correlation and simple regression analyses were performed on SBR values and clinical parameters before and after surgery. SBR value was negatively correlated with Unified Parkinson's Disease Rating Scale (UPDRS) motor score in the "ON" state before surgery (r_s=-0.637, p=0.001) and positively correlated with the reduction of the levodopa equivalent daily dose by surgery (r=0.422, p=0.045). A simple regression analysis revealed that SBR value was positively correlated with UPDRS motor score improvement after levodopa challenge before surgery (p=0.001, R²=0.423). DAT imaging may be useful in STN-DBS candidate selection and the identification of the therapeutic mechanism of STN-DBS in patients with advanced PD and motor symptom fluctuations.

Daily consumption of methylene blue reduces attentional deficits and dopamine reduction in a 6-OHDA model of Parkinson's disease

Recently, alternative drug therapies for Parkinson's disease (PD) have been investigated as there are many shortcomings of traditional dopamine-based therapies including difficulties in treating cognitive and attentional dysfunction. A promising therapeutic avenue is to target mitochondrial dysfunction and oxidative stress in PD. One option might be the use of methylene blue (MB), an antioxidant and metabolic enhancer. MB has been shown to improve cognitive function in both intact rodents and rodent disease models. Therefore, we investigated whether MB might treat attentional deficits in a rat model of PD induced by 6-hydroxydopamine (6-OHDA). MB also has neuroprotective capabilities against neurotoxic insult, so we also assessed the ability of MB to provide neuroprotection in our PD model. The results show that MB could preserve some dopamine neurons in the substantia nigra par compacta when 6-OHDA was infused into the medial forebrain bundle. This neuroprotection did not yield a significant behavioral improvement when motor functions were measured. However, MB significantly improved attentional performance in the five-choice task designed to measure selective and sustained attention. In conclusion, MB might be useful in improving some attentional function and preserving dopaminergic cells in this model. Future work should continue to study and optimize the abilities of MB for the treatment of PD.

Clinical efficacy of istradefylline versus rTMS on Parkinson's disease in a randomized clinical trial

OBJECTIVE

To compare the efficacy of istradefylline (20 mg/day, 40 mg/day) and repetitive transcranial magnetic stimulation (rTMS) (1 Hz, 10 Hz) as an adjunct therapy to levodopa in the treatment of Parkinson's disease (PD).

METHODS

A total of 132 PD patients from China were randomly assigned to receive 20 mg/day istradefylline plus sham-rTMS (Group I), 40 mg/day istradefylline plus sham-rTMS (Group II), placebo plus 1 Hz rTMS (Group III) and placebo plus 10 Hz rTMS (Group IV) for 12 weeks. Unified Parkinson's Disease Rating Scale (UPDRS) part III score was the primary outcome. Clinical Global Impression-Global Improvement (CGI-I) was the secondary outcome. The change in daily off time in Groups I and II was also recorded.

RESULTS

After 12 weeks of treatment, the changes in UPDRS part III score were -6.05, -6.39, -5.91 and -6.46 for Groups I, II, III and IV, respectively, and the difference was not significant. The difference in CGI-I among the four groups was not significant. The daily off time was reduced by -1.43 hours in Group I and -1.62 hours in Group II. No severe adverse events occurred among the four groups.

CONCLUSION

These results indicate that, as augmentation agents to levodopa in the treatment of PD, istradefylline and rTMS had comparable efficacy and tolerability.

Normal substantia nigra patients treated with levodopa - Clinical, therapeutic and pathological observations

BACKGROUND

Definite diagnosis of idiopathic Parkinson's disease is based on histological findings of marked substantia nigra neuronal loss and Lewy body inclusions. Almost all cases with clinical diagnosis of idiopathic Parkinson's disease are treated with levodopa. Because there is no biological marker for the diagnosis, erroneous clinical diagnosis and treatment of such cases with levodopa are well known. There is very limited literature on levodopa treated cases that had normal substantia nigra at autopsy.

METHODS

Patients seen at Movement Disorders Clinic Saskatchewan are offered autopsy at no cost to the family/estate of the patient. Autopsy studies are performed by certified neuropathologists. Notation on the status of substantia nigra is made in every autopsied case.

RESULTS

Between 1968 and 2014, 21 cases treated with levodopa had normal substantia nigra at autopsy. Eleven patients continued levodopa until death and 9 received the drug for four years or longer. No objective motor symptom benefit, dyskinesia or motor response fluctuations on levodopa were observed in any case. The most common final diagnosis was essential tremor.

CONCLUSION

Individuals with normal substantia nigra do not benefit from levodopa and do not manifest motor response fluctuations or dyskinesia. Long-term use of levodopa is not toxic to normal human substantia nigra.

Contribution of brain serotonin subtype 1B receptors in levodopa-induced motor complications

L-DOPA-induced dyskinesias (LID) are abnormal involuntary movements limiting the chronic use of L-DOPA, the main pharmacological treatment of Parkinson's disease. Serotonin receptors are implicated in the development of LID and modulation of basal ganglia 5-HT1B receptors is a potential therapeutic alternative in Parkinson's disease. In the present study, we used receptor-binding autoradiography of the 5-HT1B-selective radioligand [3H]GR125743 to investigate possible contributions of changes in ligand binding of this receptor in LID in post-mortem brain specimens from Parkinson's disease patients (n=14) and control subjects (n=11), and from 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned monkeys treated with saline (n=5), L-DOPA (n=4) or L-DOPA+2-methyl-6-(phenylethynyl)pyridine (MPEP) (n=5), and control monkeys (n=4). MPEP is the prototypal metabotropic glutamate 5 (mGlu5) receptor antagonist and has been shown to reduce the development of LID in these monkeys in a chronic treatment of one month. [3H]GR125743 specific binding to striatal and pallidal 5-HT1B receptors respectively were only increased in L-DOPA-treated MPTP monkeys (dyskinetic monkeys) as compared to controls, saline and L-DOPA+MPEP MPTP monkeys; dyskinesias scores correlated positively with this binding. Parkinson's disease patients with motor complications (L-DOPA-induced dyskinesias and wearing-off) had higher [3H]GR125743 specific binding compared to those without motor complications and controls in the basal ganglia. Reduction of motor complications was associated with normal striatal 5-HT1B receptors, suggesting the potential of this receptor for the management of motor complications in Parkinson's disease.

Early-onset vs. Late-onset Parkinson's disease: A Clinical-pathological Study

BACKGROUND

Several studies have compared early-onset Parkinson disease (EOPD) and late-onset Parkinson disease (LOPD) but most are not based on autopsy confirmed cases.

METHODS

We compared clinical and pharmacological profiles, time to reach irreversible Hoehn and Yahr (H&Y) Stage 3 and levodopa motor complications in autopsy confirmed EOPD and LOPD cases.

RESULTS

At first clinic visit EOPD cases were younger but had longer disease duration and they died at a younger age (all p<0.0001). Anti-Parkinsonian drug use, including levodopa, was significantly delayed in EOPD. Lifetime use of amantadine (p<0.05) and dopamine agonists (p<0.01) were higher in EOPD. While lifetime use of levodopa was similar in the two groups, levodopa was used for a significantly longer period by EOPD (p< 0.0001). EOPD had a higher cumulative incidence of dyskinesias (p<0.01), wearing-off (p<0.01), and on-off (p<0.01). However, the time to dyskinesia onset was similar in the two groups. The threshold to wearing-off was much longer in EOPD (p<0.01). H&Y stage profile at first visit was similar in the two groups. The duration from disease onset to reach irreversible H&Y stage 3 was significantly longer in EOPD.

CONCLUSIONS

Our observations indicate that progression of PD is slower in EOPD and suggest that the pre-clinical interval in this group is longer. These findings can be used for case selection for drug trials and studies of the pathogenesis of PD.

Zonisamide improves wearing-off in Parkinson's disease: A randomized, double-blind study

BACKGROUND

Previously, we reported 50 mg/d zonisamide improved wearing-off without increasing dyskinesia in patients with Parkinson's disease (PD).

METHODS

To determine the efficacy of zonisamide for treatment of "off" time in PD patients, we conducted a multicenter, randomized, double-blind, parallel-group, placebo-controlled study in Japan. Patients with PD and wearing-off received placebo for 4 weeks and then were treated for 12 weeks with zonisamide 25 or 50 mg/d or placebo, in addition to their previous therapy. The primary endpoint was the change from baseline in daily "off" time as determined by patients' diaries at the final assessment. Secondary endpoints included changes from baseline in the total scores of the Unified Parkinson's Disease Rating Scale Parts I, II, III, and IV, the dyskinesia duration, and PDQ-39 score.

RESULTS

Of 422 patients enrolled, 389 (131 for placebo, 130 for zonisamide 25 mg, and 128 for zonisamide 50 mg) were randomized, and 354 (120, 119, and 115, respectively) completed the study. The "off" time significantly reduced by 0.719 ± 0.179 h for zonisamide, 50 mg compared with placebo (0.011 ± 0.173 h, P = 0.005). Although the incidence of somnolence was higher for zonisamide (3.1% for zonisamide 25 mg, 6.3% for zonisamide 50 mg) than for placebo (2.3%), the incidences of the other adverse events, including dyskinesia or hallucination, for both zonisamide treatments were comparable to those for placebo.

CONCLUSION

The study provides evidence that confirms the efficacy of zonisamide 50 mg/d for reduction in "off" time in PD patients with wearing-off phenomena.

Saskatchewan movement disorders program

We review the Saskatchewan Movement Disorders Program, which started in 1968 and has had the dual goals of patient care and research. The clinics are structured to collect research-worthy data including videos, longitudinal follow-up, and autopsy studies of patients seen in the clinics. At every clinic visit, the patient is evaluated by one or both authors. A total of 25% to 30% of the deceased come to autopsy. Frozen half-brain and formalin-fixed remnants from autopsy are preserved in our laboratories. Patients not seen in our clinic are not included in research, which makes it different from brain banks. So far, 515 cases have come to autopsy. So far, there have been 17 collaborating scientific teams from Canada, the United States, Europe, and Japan. The collaborators are not charged for access to our resources. This program offers a unique opportunity to study multiple aspects of movement disorder patients seen in clinical practice.

Protection of MPTP-induced neuroinflammation and neurodegeneration by rotigotine-loaded microspheres

AIMS

The aim of the study is to evaluate the neuroprotective effects of continuous dopaminergic stimulation (CDS) by rotigotine-loaded microspheres (RoMS) in a mouse model of MPTP-induced Parkinson's disease (PD) and to elucidate the potential mechanism underlying these effects.

MAIN METHODS

Male C57BL/6 mice were treated either intramuscularly once with RoMS or twice daily for two weeks with rotigotine, and from the 9th day, MPTP (30 mg/kg, i.p.) was injected for the last 5 days. Following treatment, Parkinsonism scores were calculated and oxidative stress-related indicators in the striatum were performed. Neuroinflammatory cytokines, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6) were detected in the striatum. Expression of apoptosis-related proteins B-cell leukemia/lymphoma 2 (Bcl-2) and Bcl-2-associated X protein (BAX) was measured in the striatum by Western blot. Nigral tyrosine hydroxylase (TH)-positive neurons and microglial cell markers, i.e., ionized calcium binding adaptor molecule-1 (Iba-1) and neuronal synaptosomes, were quantified to assess the neuroprotective efficacy of RoMS.

KEY FINDINGS

The administration of rotigotine significantly improved the Parkinsonism score, protected dopaminergic neurons with antioxidants, reduced microglial cell activation and the release of neuroinflammatory cytokines, and balanced the expression of Bcl-2 and Bax in MPTP-treated mice. Interestingly, the neuroprotective properties of rotigotine were remarkably amplified by CDS treatment with RoMS.

SIGNIFICANCE

These results suggest that CDS therapy can play a neuroprotective role in an MPTP mouse model. Neuroprotective disease-modifying therapy may have the potential benefits of early treatment by normalizing compensatory mechanisms and may also help to delay dyskinesia in the later stages of PD.

Neuropsychiatric Behaviors in the MPTP Marmoset Model of Parkinson’s Disease

Objectives:

Neuropsychiatric symptoms are increasingly recognised as a significant problem in patients with Parkinson's disease (PD). These symptoms may be due to ‘sensitisation’ following repeated levodopa treatment or a direct effect of dopamine on the disease state. The levodopa-treated MPTP-lesioned marmoset was used as a model of neuropsychiatric symptoms in PD patients. Here we compare the time course of levodopa-induced motor fluctuations and neuropsychiatric-like behaviors to determine the relationship between duration of treatment and onset of symptoms.

Methods:

Marmosets were administered 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (2.0 mg/kg s.c.) for five days, resulting in stable parkinsonism. Levodopa (15 mg/kg and benserazide, 3.75 mg/kg) p.o. b.i.d. was administered for 30 days. Animals were evaluated for parkinsonian disability, dyskinesia and on-time (motor fluctuations) and neuropsychiatric-like behaviors on Day 0 (prior to levodopa) and on Days 1, 7, 13, 27 and 30 of treatment using post hoc DVD analysis by a trained rater, blind to the treatment day.

Results:

The neuropsychiatric-like behavior rating scale demonstrated high interrater reliability between three trained raters of differing professional backgrounds. As anticipated, animals exhibited a progressive increase in levodopa-induced motor fluctuations, dyskinesia and wearing-off, that correlated with the duration of levodopa therapy. In contrast, levodopa-induced neuropsychiatric-like behaviors were present on Day 1 of levodopa treatment and their severity did not correlate with duration of treatment.

Conclusions:

The data suggest that neuropsychiatric disorders in PD are more likely an interaction between levodopa and the disease state than a consequence of sensitisation to repeated dopaminergic therapy.

Parkinson’s disease management strategies

Parkinson's disease (PD) treatment strategies should consider each patient individually. Drug therapy is the mainstay of treatment. An average 62-year-old male first diagnosed with PD will likely live for 20 years and treatment should be geared for long-term control of symptoms and quality of life. Of the currently available drugs, none are neurotoxic to the human substantia nigra and none are neuroprotective. As PD is a progressive disorder, all drugs have adverse effects and reduced efficacy with time. PD patients need regular follow-ups to make necessary medication adjustments. There is no perfect treatment. The authors have discussed their treatment methods and the reasoning behind it. Depending on the patient's age, the predominant symptoms and quality of life, treatment is individualized. In an average patient the least potent drugs, such as anticholinergics or amantadine, are administered first adding a dopamine agonist later on. Levodopa (LD) remains the most useful drug for PD and is reserved for later stages of disease. The objective is to keep the patient at Hoehn and Yahr Stage 2.0 or lower level of disability (bilateral findings with preserved postural reflexes) during off-stage and to avoid adverse effects. There is no long-term difference between standard preparations and control release formulations of LD/carbidopa or LD/benserazide. In older subjects, the first choice is LD. In patients who cannot be managed medically, surgical treatment is an option in selected patients (nondemented, <70 years old, previous good LD response). The surgical treatment of choice is currently subthalamic nucleus deep-brain stimulation. Physiotherapy, occupational therapy and speech therapy are valuable in advanced PD cases.

Functional neuroimaging in Parkinson's disease

The use of functional imaging in neurodegenerative diseases has increased in recent years, with applications in research into the underlying pathophysiology, aiding in diagnosis, or evaluating new treatments. In Parkinson's disease (PD), these imaging methods have expanded our understanding of the disease beyond dopaminergic deficits. Moreover, functional imaging methods have described alterations in functional networks relating not only to the motor symptoms, but also to many nonmotor features of PD, such as cognitive dysfunction. From a clinical viewpoint, functional imaging methods can assist in monitoring disease progression, such as in the context of clinical trials, and holds the potential to aid in early diagnosis of PD and differentiation from other parkinsonian disorders.

Adenosine A2A receptor antagonist istradefylline reduces daily OFF time in Parkinson's disease

BACKGROUND

We evaluated the efficacy and safety of istradefylline, a selective adenosine A2A receptor antagonist administered as adjunctive treatment to levodopa for 12 weeks in a double-blind manner in Parkinson's disease patients with motor complications in Japan.

METHODS

A total of 373 subjects were randomized to receive placebo (n=126), istradefylline 20 mg/day (n=123), or istradefylline 40 mg/day (n=124). The primary efficacy variable was the change in daily OFF time. Other secondary variables were also evaluated.

RESULTS

The change in daily OFF time was significantly reduced in the istradefylline 20 mg/day (-0.99 hours, P=.003) and istradefylline 40 mg/day (-0.96 hours, P=.003) groups compared with the placebo group (-0.23 hours). The most common adverse event was dyskinesia (placebo, 4.0%; istradefylline 20 mg/day, 13.0%; istradefylline 40 mg/day, 12.1%).

CONCLUSIONS

Istradefylline reduced daily OFF time and was well tolerated in Japanese PD patients with motor complications on levodopa treatment.

Dysfunction of dopamine homeostasis: clues in the hunt for novel Parkinson's disease therapies

Parkinson's disease is the second most common neurodegenerative disorder and, at present, has no cure. Both environmental and genetic factors have been implicated in the etiology of the disease; however, the pathogenic pathways leading to neuronal degeneration are still unclear. Parkinson's disease is characterized by the preferential death of a subset of neurons in the mesencephalon that use dopamine as neurotransmitter for synaptic communication. Dopamine is a highly reactive molecule that can lead to cytotoxicity if not properly stored and metabolized. Targeting any of the pathways that tightly control this neurotransmitter holds great therapeutic expectations. In this article we present a comprehensive overview of the cellular pathways that control dopamine fate and discuss potential therapeutic approaches to counteract or slow Parkinson's disease onset and progression.

PTEN deletion enhances survival, neurite outgrowth and function of dopamine neuron grafts to MitoPark mice

Clinical trials in Parkinson’s disease have shown that transplants of embryonic mesencephalic dopamine neurons form new functional connections within the host striatum, but the therapeutic benefits have been highly variable. One obstacle has been poor survival and integration of grafted dopamine neurons. Activation of Akt, a serine/threonine kinase that promotes cell survival and growth, increases the ability of neurons to survive after injury and to regenerate lost neuronal connections. Because the lipid phosphatase, phosphatase and tensin homolog (PTEN) inhibits Akt, we generated a mouse with conditional knock-out of PTEN in dopamine neurons, leading to constitutive expression of Akt in these neurons. Ventral mesencephalic tissue from dopamine phosphatase and tensin homologue knock-out or control animals was then transplanted bilaterally into the dopamine depleted striata of MitoPark mice that express a parkinsonian phenotype because of severe respiratory chain dysfunction in dopamine neurons. After transplantation into MitoPark mice, PTEN-deficient dopamine neurons were less susceptible to cell death, and exhibited a more extensive pattern of fibre outgrowth compared to control grafts. Voltammetric measurements demonstrated that dopamine release and reuptake were significantly increased in the striata of animals receiving dopamine PTEN knock-out transplants. These animals also displayed enhanced spontaneous and drug-induced locomotor activity, relative to control transplanted MitoPark mice. Our results suggest that disinhibition of the Akt-signalling pathway may provide a valuable strategy to enhance survival, function and integration of grafted dopamine neurons within the host striatum and, more generally, to improve survival and integration of different forms of neural grafts.

Preparation of rotigotine-loaded microspheres and their combination use with L-DOPA to modify dyskinesias in 6-OHDA-lesioned rats

PURPOSE

To prepare rotigotine loaded microspheres (RoMS) to achieve continuous dopaminergic stimulation (CDS) for the treatment of Parkinson's disease (PD) and investigate both the therapeutic benefit and inducibility of AIMs of administration of RoMS combination with L-DOPA in 6-OHDA-leisioned rats.

METHODS

Rotigotine was encapsulated into poly(lactic-co-glycolic acid) (PLGA) microspheres by an oil-in-water emulsion solvent evaporation technique. In vitro characteristics and in vivo pharmacokinetics of RoMS either in rat blood or brain (by microdialysis) were investigated. Contraversive rotations and AIMs were observed to investigate the therapeutic benefit and the propensity to induce dyskinesia of RoMS or RoMS combination with L-DOPA in 6-OHDA-lesioned rats.

RESULTS

RoMS displayed continuous-release characteristics of rotigotine in animals and exhibited a steady efficacy lasted for 2 weeks in 6-OHDA-lesioned rats. No significant difference of the therapeutic benefit between the treatment of RoMS and pulsatile L-DOPA combination and mono L-DOPA was found. While the dyskinesia was significantly decreased with the treatment of RoMS and pulsatile L-DOPA combination compared to mono L-DOPA.

CONCLUSIONS

RoMS could supply an alternative of CDS for the treatment of PD and the study indicates a potential advantage of RoMS for the treatment of mild and advanced PD patient in combination with L-DOPA.

Exendin-4 treatment enhances L-DOPA evoked release of striatal dopamine and decreases dyskinetic movements in the 6-hydoxydopamine lesioned rat

OBJECTIVES

To determine whether the glucagon-like 1 peptide analogue exendin-4 (EX-4) augments the neurochemical effects of a single L-DOPA treatment and whether EX-4 can decrease L-DOPA induced dyskinesias (LIDS).

METHODS

Rats were lesioned with 6-hydroxydopamine (6-OHDA) and 7 days later given EX-4 for 7 days. The following day, rats were given L-DOPA and extracellular dopamine was measured. The animals were then killed to determine tissue dopamine. To study LIDS, EX-4 and/or L-DOPA were co-administered daily, 7 days after 6-OHDA. LIDS were determined on Days 2, 4, 8, 12 and 16 prior to neurochemical assessment.

KEY FINDINGS

EX-4 reduced 6-OHDA induced damage. Acute effects of L-DOPA were potentiated by EX-4 in lesioned rats. Treatments with EX-4 caused a progressive reduction in LIDS.

CONCLUSIONS

EX-4 treatment potentiates the effects of a single dose of L-DOPA. This augmentation indicates that lower L-DOPA doses might be used to the same effect in patients. The reduction in LIDS suggests that co-treatment with EX-4 could allow the use of L-DOPA with fewer side-effects and possibly therefore allow earlier introduction of L-DOPA in the clinic.

L-DOPA is incorporated into brain proteins of patients treated for Parkinson's disease, inducing toxicity in human neuroblastoma cells in vitro

Levodopa (L-DOPA), a close structural analogue of the protein amino acid L-tyrosine, can substitute for L-tyrosine in protein synthesis and be mistakenly incorporated into newly synthesised proteins in vitro. We show that L-DOPA-containing proteins are present in the brain in L-DOPA-treated Parkinson's disease patients and accumulate in specific brain regions. In vitro studies demonstrate that substitution of L-tyrosine residues in proteins with L-DOPA causes protein misfolding and promotes protein aggregation in SH-SY5Y neuroblastoma cells resulting in the appearance of autofluorescent bodies. We show that the presence of L-DOPA-containing proteins causes profound changes in mitochondria and stimulates the formation of autophagic vacuoles in cells. Unlike L-DOPA, which is toxic to cells through its ability to generate radicals, proteins containing incorporated L-DOPA are toxic to SH-SY5Y cells by a mechanism independent of oxidative stress and resistant to antioxidants. These data suggest that the accumulation of L-DOPA-containing proteins in vulnerable cells might negatively impact on cell function.

The pharmacokinetics and pharmacological effect of (S)-5-OH-DPAT following controlled delivery with transdermal iontophoresis

The pharmacokinetic (PK) and pharmacodynamic (PD) properties of the active (S)-enantiomer of the potent dopamine (DA) agonist 5-hydroxy-2-(N,N,-di-n-propylamino)tetralin (5-OH-DPAT) were investigated in a novel anesthetized animal model. First, the relationship between current density, in vivo transport, and plasma profile was characterized. Second, the effect of the anesthetic mixture, transdermal iontophoresis, and blood sampling on the striatal DA release (PD end point) was investigated. Third, the PK-PD relationship following transdermal iontophoresis was investigated during a controlled reversible pharmacological response. Given that striatal DA levels are unaltered during experimental procedures, this rat model can be used to investigate the PK-PD relationship. The in vivo flux was linearly correlated with the current density, indicating that drug delivery can be titrated by the current density. Following transdermal iontophoresis and intravenous infusion, a strong reversible effect was observed. Compartmental modeling showed that the relationship between plasma concentration and biomarker response is best characterized by an effect compartment, rather than an indirect response model. In addition, covariate analysis suggested that the delivery rate can affect the PD efficiency. Finally, PK-PD analysis revealed that steady delivery rates are translated into continuous dopaminergic stimulation. This can be of benefit for reducing side effects in the symptomatic treatment of Parkinson's disease with 5-OH-DPAT.

l-Dopa-induced dyskinesia-clinical presentation, genetics, and treatment

Levodopa-induced dyskinesia (LID) has been recognized since the introduction of levodopa for the management of Parkinson's disease (PD) and continues to be one of the most clinically challenging factors in long-term management of patients with PD. Most patients develop LID within 10 years of PD onset and the cause has been attributed to various factors including disease demographics, pharmacological, and possibly genetic causes. The clinical pattern of LID varies and shows intra and inter-patient variability and has been classified based upon phenomenology and relation to timing of levodopa. The potential armamentarium to address and manage LID has significantly increased in the last decade. This chapter addresses the current understanding of various clinical aspects and available therapeutics for LID.

Metabotropic glutamate receptor type 5 in levodopa-induced motor complications

Metabotropic glutamate receptors type 5 (mGluR5) are implicated in regulation of synaptic plasticity and learning, and were the focus of our investigation in human Parkinson's disease (PD) patients with dyskinesias and wearing-off, and in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) monkeys with dyskinesias. Using the selective mGluR5 ligand [(3)H]ABP688 autoradiography, we measured mGluR5 in brain slices from 11 normal and 14 PD patients and from MPTP monkeys, in relation to motor complications (dyskinesias and wearing-off) associated with treatment with l-dopa. In 16 monkeys with a bilateral MPTP lesion and four controls, [(3)H]ABP688 specific binding was elevated in the striatum of dyskinetic l-dopa-treated MPTP monkeys but not in MPTP monkeys without dyskinesias compared to controls. PD patients with motor complications (either dyskinesias or wearing-off) had higher [(3)H]ABP688 specific binding compared to those without motor complications and controls in putamen, external and internal globus pallidus. Elevated glutamatergic transmission as measured with increased mGluR5 specific binding was associated with motor complications and its antagonism could be targeted for their treatment.

Metabotropic glutamate receptor II in the brains of Parkinsonian patients

Modulation of basal ganglia group II metabotropic glutamate receptors (mGluR2/3) is a potential therapeutic alternative to levodopa in Parkinson disease (PD). We used receptor-binding autoradiography of the mGluR2/3-selective radioligand [H]LY341495 in postmortem brain specimens from PD patients (n = 14) and controls (n=11) to investigate possible contributions of changes in ligand binding of this receptor to levodopa-associated motor complications experienced premortem in PD patients. The PD patients included those with and without histories of dyskinesias and those with and without "wearing off," which is defined as a reduced period of benefit from levodopa. Specific binding of [H]LY341495 to mGluR2/3 in the basal ganglia was higher in the caudate nucleus than the putamen and lower by approximately half in the external and internal globus pallidus (GPi) in controls. [H]LY341495-specific binding was reduced in the caudate and GPi in patients without wearing-off (-22% caudate, -30% GPi), compared with controls and with patients who had experienced wearing-off; there were no differences among PD patients with or without dyskinesias. These data suggest that an adaptive downregulation of mGluR2/3 in PD patients without wearing-off may compensate for increased glutamate. They indicate a key role for mGluR2/3 in control of movement and the potential for mGluR2/3-targeted drugs in the management of wearing-off fluctuations in PD.

How do you treat motor complications in Parkinson's disease: Medicine, surgery, or both?

The motor complications associated with levodopa therapy, namely, fluctuations in motor response and dyskinesias, occur in the majority of Parkinson's disease patients. These complications can impair a patient's quality of life and even cause pronounced disability. "Off" states that result in freezing of gait and falling are disabling for many patients. Dyskinesias most commonly occur at peak dose and typically alternate with the wearing-off state. Once these problems appear, they usually persist, and the physician needs to make continual adjustments in medications to minimize these problems. Medical treatments should be attempted before treatments such as deep brain stimulation are considered because of the potential adverse effects that are associated with surgery. The timing of surgery, however, is also important because younger patients and less advanced patients tend to have a better outcome. There is thus a need for experienced and knowledgeable physicians and surgeons who are able to handle these motor complications. This review discusses available medications and surgical approaches, and their outcomes.

Current approaches to the treatment of Parkinson's disease

Enormous progress has been made in the treatment of Parkinson's disease (PD). As a result of advances in experimental therapeutics, many promising therapies for PD are emerging. Levodopa remains the most potent drug for controlling PD symptoms, yet is associated with significant complications such as the "wearing off" effect, levodopa-induced dyskinesias and other motor complications. Catechol-o-methyl-transferase inhibitors, dopamine agonists and nondopaminergic therapy are alternative modalities in the management of PD and may be used concomitantly with levodopa or one another. The neurosurgical treatment, focusing on deep brain stimulation, is reviewed briefly. Although this review has attempted to highlight the most recent advances in the treatment of PD, it is important to note that new treatments are not necessarily better than the established conventional therapy and that the treatment options must be individualized and tailored to the needs of each individual patient.

Ratings of L-DOPA-induced dyskinesia in the unilateral 6-OHDA lesion model of Parkinson's disease in rats and mice

This unit provides detailed protocols for establishing rodent models of L-DOPA-induced dyskinesia. The 6-hydroxydopamine (6-OHDA) lesion procedure is described in more detail for mice than for rats since the lesioning procedure in rats has been described extensively in previous work and is less difficult to perform. Unlike primate models, rodent models of L-DOPA-induced dyskinesia are relatively simple and fast to set up, thus being affordable to most laboratories. These models allow for studying the dyskinetic complications of L-DOPA treatment on large groups of animals under strictly controlled experimental conditions. Along with information and structured protocols for the practical execution of the test, this unit provides a detailed description of the rating scale and the phenomenology of rodent abnormal involuntary movements, and suggestions for beginners.

Altered behavioural and neurochemical profile of L-DOPA following deuterium substitutions in the molecule

In Parkinson's disease patients, a prolonged half-life of dopamine formed from L-DOPA may reduce the risk of developing L-DOPA-induced side-effects. Deuterium substitutions in the L-DOPA molecule are expected to yield dopamine with an altered half-life because C-D bonds are more stable than C-H bonds. Therefore we tested, in the rat, the neurochemical and behavioral effects of different types of L-DOPA with deuterium substitutions at the alpha-carbon and/or the beta-carbon. By means of microdialysis, we found that L-DOPA with 3 deuterium substitutions (D3-L-DOPA) enhanced dopamine output in the striatum more effectively than L-DOPA and all the other deuterium variants. Moreover, D3-L-DOPA produced a more pronounced stimulation of locomotor activity in reserpinized rats compared to conventional L-DOPA. In contrast beta,beta-D2-L-DOPA was less effective than L-DOPA in raising striatal dopamine levels and was ineffective at restoring locomotor activity in reserpinized rats. These results demonstrate that the introduction of deuterium at different positions in the L-DOPA molecule dramatically changes its behavioral and neurochemical profile and suggest that L-DOPA treatment of Parkinson's disease may be improved in this way.

The management approaches to dyskinesia vary from country to country

Many Parkinson's disease (PD) patients treated with levodopa develop motor fluctuations and/or dyskinesia. This large, retrospective study was conducted to compare the prevalence and treatment of dyskinesia in PD patients in seven countries. A total of 380 physicians were interviewed and completed patient record forms retrospectively for their last 5 patients with dyskinesia (total 1,900). The overall prevalence of dyskinesia in PD patients was 34%, but the rate varied from 24 to 51% according to geographical location. This study showed that 51.0% of Japanese physicians and 50.6% of UK physicians were dissatisfied with current treatment strategies for dyskinesia. Regardless of geographical location, physicians were dissatisfied with the current treatment strategies for dyskinesia.

Levodopa-induced dyskinesias

Levodopa-induced dyskinesias (LID) are common and difficult to treat. This review focuses on three issues related to LID: clinical features, classification and rating, pathophysiology and pathogenesis, and management. The three primary clinical syndromes are OFF-period dystonia, peak-dose dyskinesia, and diphasic dyskinesia. Several other forms also occur, making the evaluation and choice of treatment complicated. A core component of the pathophysiology of LID is overactivity of the direct striatal output pathway. This pathway provides a direct GABAergic connection by which the striatum inhibits the output regions of the basal ganglia, i.e., the internal globus pallidus and the substantia nigra pars reticulata. Altering dopaminergic dosing and timing can abate dyskinesias, but usually impact the control of parkinsonism. Putative therapies to reduce the problem of dyskinesias could focus on the glutamatergic, GABAergic, alpha2 adrenergic, serotonergic (5HT1A, 5HT2A), opioid, histamine H3, adenosine A2A receptors, the monoamine transport or cannabinoid CB1 receptors systems. The only currently available drug with an evidence-based recommendation on efficacy for dyskinesia is amantadine. Therapy goals include the prevention of dyskinesia and treatment of dyskinesias that are troublesome clinically. New rating measures to assess severity and disability related to dyskinesia are in the process of development and clinimetric testing.

Role of adenosine A2A receptors in parkinsonian motor impairment and l-DOPA-induced motor complications

Adenosine A2A receptors have a unique cellular and regional distribution in the basal ganglia, being particularly concentrated in areas richly innervated by dopamine such as the caudate-putamen and the globus pallidus. Adenosine A2A receptors are selectively located on striatopallidal neurons and are capable of forming functional heteromeric complexes with dopamine D2 and metabotropic glutamate mGlu5 receptors. Based on the unique cellular and regional distribution of this receptor and in line with data showing that A2A receptor antagonists improve motor symptoms in animal models of Parkinson's disease (PD) and in initial clinical trials, A2A receptor antagonists have emerged as an attractive non-dopaminergic target to improve the motor deficits that characterize PD. Experimental data have also shown that A2A receptor antagonists do not induce neuroplasticity phenomena that complicate long-term dopaminergic treatments. The present review provides an updated summary of results reported in the literature concerning the biochemical characteristics and basal ganglia distribution of A2A receptors. We subsequently aim to examine the effects of adenosine A2A antagonists in rodent and primate models of PD and of l-DOPA-induced dyskinesia. Finally, concluding remarks are made on post-mortem human brains and on the translation of adenosine A2A receptor antagonists in the treatment of PD.