Continuous dopaminergic stimulation: Is it the answer to the motor complications of Levodopa?

An Individualized Multi-Modal Approach for Detection of Medication "Off" Episodes in Parkinson's Disease via Wearable Sensors

The primary treatment for Parkinson's disease (PD) is supplementation of levodopa (L-dopa). With disease progression, people may experience motor and non-motor fluctuations, whereby the PD symptoms return before the next dose of medication. Paradoxically, in order to prevent wearing-off, one must take the next dose while still feeling well, as the upcoming off episodes can be unpredictable. Waiting until feeling wearing-off and then taking the next dose of medication is a sub-optimal strategy, as the medication can take up to an hour to be absorbed. Ultimately, early detection of wearing-off before people are consciously aware would be ideal. Towards this goal, we examined whether or not a wearable sensor recording autonomic nervous system (ANS) activity could be used to predict wearing-off in people on L-dopa. We had PD subjects on L-dopa record a diary of their on/off status over 24 hours while wearing a wearable sensor (E4 wristband^®) that recorded ANS dynamics, including electrodermal activity (EDA), heart rate (HR), blood volume pulse (BVP), and skin temperature (TEMP). A joint empirical mode decomposition (EMD) / regression analysis was used to predict wearing-off (WO) time. When we used individually specific models assessed with cross-validation, we obtained > 90% correlation between the original OFF state logged by the patients and the reconstructed signal. However, a pooled model using the same combination of ASR measures across subjects was not statistically significant. This proof-of-principle study suggests that ANS dynamics can be used to assess the on/off phenomenon in people with PD taking L-dopa, but must be individually calibrated. More work is required to determine if individual wearing-off detection can take place before people become consciously aware of it.

Effect of pH on Iontophoretic Transport of Pramipexole Dihydrochloride across Human Epidermal Membrane

PURPOSE

Drugs with higher molecular charges generally show higher flux enhancement when electromigration is the main mechanism in transdermal iontophoresis. This study evaluated the effect of decreasing the formulation pH to increase the positive charges of pramipexole dihydrochloride (PXCl) on its iontophoretic transport across skin.

METHODS

In vitro transdermal iontophoresis of PXCl in buffer solution isotonized with either sodium chloride or mannitol were performed in a pH range of 3.0-7.0. Experiments of iontophoresis under symmetric condition with respect to donor and receiver pH and passive transport of the drugs after pretreatment with iontophoresis were conducted to investigate the transport mechanism involved.

RESULTS

Iontophoretic permeation of PXCl was pH-dependent in drug solution isotonized with mannitol. The iontophoretic flux of PXCl with valence z = +2 at pH 3.0 was half of that of PXCl with z = +1 at pH 7.0. The results suggest that the decrease in PXCl delivery at higher valence at pH 3 was mainly due to pH-dependent selectivity of PX ion permeation across the skin and not electroosmosis.

CONCLUSIONS

Skin permselectivity is a significant factor for iontophoretic transport of PXCl, and reducing formulation pH to increase the positive charges on PX ions did not enhance PXCl delivery.

Improving the Delivery of Levodopa in Parkinson's Disease: A Review of Approved and Emerging Therapies

Levodopa is the most effective drug for the treatment of Parkinson's disease, but its use as an oral medication is complicated by its erratic absorption, extensive metabolism and short plasma half-life. On long-term use and with disease progression, there is a high incidence of motor and non-motor complications, which remain a major clinical and research challenge. It is widely accepted that levodopa needs to be administered using formulations that result in good and consistent bioavailability and the physiologically relevant and continuous formation of dopamine in the brain to maximise its efficacy while avoiding and reversing 'wearing off' and dyskinesia. However, the physicochemical properties of levodopa along with its pharmacokinetic and pharmacodynamic profile make it difficult to deliver the drug in a manner that fulfils these criteria. In this review, we examine the problems associated with the administration of levodopa in Parkinson's disease and how the use of novel technologies and delivery devices is leading to a more consistent and sustained levodopa delivery with the aim of controlling motor function as well as non-motor symptoms.

Update on the Management of Parkinson's Disease for General Neurologists

Management of Parkinson's disease (PD) is complicated due to its progressive nature, the individual patient heterogeneity, and the wide range of signs, symptoms, and daily activities that are increasingly affected over its course. The last 10–15 years have seen great progress in the identification, evaluation, and management of PD, particularly in the advanced stages. Highly specialized information can be found in the scientific literature, but updates do not always reach general neurologists in a practical and useful way, potentially creating gaps in knowledge of PD between them and neurologists subspecialized in movement disorders, resulting in several unmet patient needs. However, general neurologists remain instrumental in diagnosis and routine management of PD. This review provides updated practical information to identify problems and resolve common issues, particularly when the advanced stage is suspected. Some tips are provided for efficient communication with the members of a healthcare team specialized in movement disorders, in order to find support at any stage of the disease in a given patient, and especially for a well-timed decision on referral.

Dyskinesia in multiple system atrophy and progressive supranuclear palsy

In the differential diagnosis of Parkinson syndromes, the response to L-Dopa is an essential criterion for the diagnosis of idiopathic Parkinson's syndrome (IPS), and the presence of L-Dopa-induced dyskinesia (LID) is considered a supportive criterion. This implies that in the presence of LID an atypical Parkinson-syndrome (APS) is unlikely. However, dyskinesia, and in particular LID, can also be present in APS such as MSA and PSP, although less frequently, and with varying clinical appearance. We conclude that whilst presence of dyskinesia provides support for a diagnosis of IPD, they do not allow reliable differentiation from APS.

The effect of continuous levodopa treatment during the afternoon hours

OBJECTIVE

The aim of this retrospective study was to investigate whether patients with Parkinson's disease, who are treated with levodopa-carbidopa intestinal gel (LCIG), clinically worsen during the afternoon hours and if so, to evaluate whether this occurs in all LCIG-treated patients or in a subgroup of patients.

METHODS

Three published studies were identified and included in the analysis. All studies provided individual response data assessed on the treatment response scale (TRS), and patients were treated with continuous LCIG. Ninety-eight patients from the three studies fulfilled the criteria. t tests were performed to find differences on the TRS values between the morning and the afternoon hours, linear mixed effect models were fitted on the afternoon hours' evaluations to find trends of wearing-off, and patients were classified into three TRS categories (meaningful increase in TRS, meaningful decrease in TRS, non-meaningful increase or decrease).

RESULTS

In all three studies, significant statistical differences were found between the morning TRS values and the afternoon TRS values (P-value <=0.001 in all studies). The linear mixed effect models had significant negative coefficients for time in two studies, and 48 out of 98 patients (49%) showed a meaningful decrease in TRS during the afternoon hours.

CONCLUSION

The results from all studies were consistent, both in the proportion of patients in the three groups and in the value of TRS decrease in the afternoon hours. Based on these findings, there seems to be a group of patients with predictable "off" behavior in the later parts of the day.

Chemical management of levodopa-induced dyskinesia in Parkinson's disease patients

INTRODUCTION

Levodopa-induced dyskinesias (LID) appears in more than 50% of Parkinson's disease patients after 5 years of treatment and clinicians always have to ensure that there is a balance between the beneficial effect of the treatment and the potential complications.

AREAS COVERED

In this review, the authors discuss the treatment of LID. Treatment can be divided into strategies for preventing their occurrence, modification of dopaminergic therapy, and providing more continuous dopaminergic stimulation as well as the use of nondopaminergic drugs.

EXPERT OPINION

Amantadine is currently considered the most effective drug for the treatment of LID. Several compounds developed to target adenosine, adrenergic, glutamatergic, and serotonergic receptors have shown to significantly decrease dyskinesias in animal models. However, despite promising preclinical results, translation to clinical practice remains challenging and majority of these compounds failed to decrease LID in randomized controlled trials with moderate-to-advanced parkinsonian patients. Despite promising results with nondopaminergic drugs, treatment of dyskinesias is still challenging and largely due to their side effects. Future research should focus on developing treatments that can provide continuous dopaminergic delivery throughout the day in a noninvasive manner. Studies on the impact of the early administration of long-acting formulations of levo-3,4-dihydroxy-phenylalanine on dyskinesias are also necessary.

Epigenetic Effects Induced by Methamphetamine and Methamphetamine-Dependent Oxidative Stress

Methamphetamine is a widely abused drug, which possesses neurotoxic activity and powerful addictive effects. Understanding methamphetamine toxicity is key beyond the field of drug abuse since it allows getting an insight into the molecular mechanisms which operate in a variety of neuropsychiatric disorders. In fact, key alterations produced by methamphetamine involve dopamine neurotransmission in a way, which is reminiscent of spontaneous neurodegeneration and psychiatric schizophrenia. Thus, understanding the molecular mechanisms operated by methamphetamine represents a wide window to understand both the addicted brain and a variety of neuropsychiatric disorders. This overlapping, which is already present when looking at the molecular and cellular events promoted immediately after methamphetamine intake, becomes impressive when plastic changes induced in the brain of methamphetamine-addicted patients are considered. Thus, the present manuscript is an attempt to encompass all the molecular events starting at the presynaptic dopamine terminals to reach the nucleus of postsynaptic neurons to explain how specific neurotransmitters and signaling cascades produce persistent genetic modifications, which shift neuronal phenotype and induce behavioral alterations. A special emphasis is posed on disclosing those early and delayed molecular events, which translate an altered neurotransmitter function into epigenetic events, which are derived from the translation of postsynaptic noncanonical signaling into altered gene regulation. All epigenetic effects are considered in light of their persistent changes induced in the postsynaptic neurons including sensitization and desensitization, priming, and shift of neuronal phenotype.

Preparation and evaluation of rotigotine-loaded implant for the treatment of Parkinson's disease and its evolution study

Purpose

To develop rotigotine-loaded implants (RI) to achieve continuous release of rotigotine for long duration for the treatment of Parkinson’s disease (PD).

Methods

RI was prepared by hot-melt extrusion method using poly (lactide-co-glycolide) (PLGA) as the matrix. In vitro drug release was optimized by drug loading, melting temperature during preparing process and additives. The surface and internal morphology of RI was imaged by SEM. The in vivo release profile of RI was investigated on rat.

Results

RI prepared with PLGA 7525 5A showed sustained release of 40 days while suffering a lag phase, which was significantly shortened by blending 5050 2A and mannitol in the matrix. RI prepared by 7525 5A/5050 2A/mannitol = 55:10:5 (rotigotine 30%) showed a 40-day sustained release in vivo with no lag phase. The drug release from RI was also affected by drug loading and melting temperature probably due to the drug state existed in the implant. The evolution of implants during release process was correlated well with the drug release kinetics.

Conclusion

RI could achieve sustained drug release for 40 days which could supply an alternative of continuous dopaminergic stimulation (CDS) for the treatment of PD.

Impact of Pharmacotherapy on Quality of Life in Patients with Parkinson's Disease

Quality of life (QoL) is a patient-reported outcome frequently included in Parkinson's disease (PD) clinical trials as a secondary or tertiary endpoint. However, QoL is an important variable that reflects the impact of disease and treatment from the patients' perspective. In a chronic, neurodegenerative disease such as PD, with a wide range of complex symptoms, QoL provides valuable and comprehensive information on the patients' health status. This narrative review aims to evaluate the effect of specific PD treatments currently in use on patients' QoL measured with the Parkinson's Disease Questionnaire, 39-item (PDQ-39) or 8-item (PDQ-8) version. A quantification of this effect is provided by calculation of the relative change and effect size. These two parameters allow an intuitive standardized approach to the importance of change based on its magnitude. Some high-quality studies (Level I) were found for levodopa (immediate- or extended-release formulations), levodopa with added-on catechol-O-methyltransferase (COMT) inhibitors, levodopa/carbidopa gel for intestinal infusion, some dopamine agonists (ropinirole, cabergoline, pergolide), and the monoamine oxidase B (MAO-B) inhibitor safinamide. As a whole, these studies found a beneficial effect of variable magnitude, weak to moderate, on patients' QoL. Studies with a lower level of evidence or not providing enough data to estimate relative change and effect size, including those for the apomorphine subcutaneous pump, also reported improvement of QoL, but the evidence was insufficient to confirm the effect. More high-quality studies focused on QoL are needed to determine the real impact of PD drug treatments for this important outcome.

Pharmacological strategies for the management of levodopa-induced dyskinesia in patients with Parkinson's disease

L-Dopa-induced dyskinesias (LID) are the most common adverse effects of long-term dopaminergic therapy in Parkinson's disease (PD). However, the exact mechanisms underlying dyskinesia are still unclear. For a long time, nigrostriatal degeneration and pulsatile stimulation of striatal postsynaptic receptors have been highlighted as the key factors for the development of LID. In recent years, PD models have revealed a wide range of non-dopaminergic neurotransmitter systems involved in pre- and postsynaptic changes and thereby contributing to the pathophysiology of LID. In the current review, we focus on therapeutic LID targets, mainly based on agents acting on dopaminergic, glutamatergic, serotoninergic, adrenergic, and cholinergic systems. Despite a large number of clinical trials, currently only amantadine and, to a lesser extent, clozapine are being used as effective strategies in the treatment of LID in clinical settings. Thus, in the second part of the article, we review the placebo-controlled trials on LID treatment in order to disentangle the changing scenario of drug development. Promising results include the extension of L-dopa action without inducing LID of the novel monoamine oxidase B- and glutamate-release inhibitor safinamide; however, this had no obvious effect on existing LID. Others, like the metabotropic glutamate-receptor antagonist AFQ056, showed promising results in some of the studies; however, confirmation is still lacking. Thus, to date, strategies of continuous dopaminergic stimulation seem the most promising to prevent or ameliorate LID. The success of future therapeutic strategies once moderate to severe LID occur will depend on the translation from preclinical experimental models into clinical practice in a bidirectional process.

MRI brain findings in ephedrone encephalopathy associated with manganese abuse: Single-center perspective

BACKGROUND

Manganese (Mn) is a well-known toxic agent causing symptoms of parkinsonism in employees of certain branches of industry. Home production of a psychostimulant ephedrone (methcathinone), involving the use of potassium permanganate, became a new cause of intoxications in Poland.

CASE REPORT

This article presents clinical symptoms, initial brain MRI findings and characteristics of changes observed in follow-up examinations in 4 patients with manganese intoxication associated with intravenous administration of ephedrone. All patients in our case series presented symptoms of parkinsonism. T1-WI MRI revealed high intensity signal in globi pallidi in all patients; hyperintense lesions in midbrain were observed in three patients, while lesions located in cerebellar hemispheres and pituitary gland in just one patient. The reduction of signal intensity in the affected brain structures was observed in follow-up studies, with no significant improvement in clinical symptoms.

CONCLUSIONS

Brain MRI is helpful in the assessment of distribution as well as dynamics of changes in ephedrone encephalopathy. Regression of signal intensity changes visible in brain MRI is not associated with clinical condition improvement. Although brain MRI findings are not characteristic for ephedrone encephalopathy, they may contribute to diagnosing this condition.

Serotonin System Implication in l-DOPA-Induced Dyskinesia: From Animal Models to Clinical Investigations

In the recent years, the serotonin system has emerged as a key player in the induction of l-DOPA-induced dyskinesia (LID) in animal models of Parkinson's disease. In fact, serotonin neurons possess the enzymatic machinery able to convert exogenous l-DOPA to dopamine (DA), and mediate its vesicular storage and release. However, serotonin neurons lack a feedback control mechanism able to regulate synaptic DA levels. While in a situation of partial DA depletion spared DA terminals can buffer DA released from serotonin neurons, the progression of DA neuron degeneration impairs this protective mechanism, causing swings in synaptic DA levels and pulsatile stimulation of post-synaptic DA receptors. In line with this view, removal of serotonin neurons by selective toxin, or pharmacological silencing of their activity, produced complete suppression of LID in animal models of Parkinson's disease. In this article, we will revise the experimental evidence pointing to the important role of serotonin neurons in dyskinesia, and we will discuss the clinical implications.

Role of movement in long-term basal ganglia changes: implications for abnormal motor responses

Abnormal involuntary movements (AIMs) and dyskinesias elicited by drugs that stimulate dopamine receptors in the basal ganglia are a major issue in the management of Parkinson’s disease (PD). Preclinical studies in dopamine-denervated animals have contributed to the modeling of these abnormal movements, but the precise neurochemical and functional mechanisms underlying these untoward effects are still elusive. It has recently been suggested that the performance of movement may itself promote the later emergence of drug-induced motor complications, by favoring the generation of aberrant motor memories in the dopamine-denervated basal ganglia. Our recent results from hemiparkinsonian rats subjected to the priming model of dopaminergic stimulation are in agreement with this. These results demonstrate that early performance of movement is crucial for the manifestation of sensitized rotational behavior, indicative of an abnormal motor response, and neurochemical modifications in selected striatal neurons following a dopaminergic challenge. Building on this evidence, this paper discusses the possible role of movement performance in drug-induced motor complications, with a look at the implications for PD management.

Drug-induced dyskinesia in Parkinson's disease. Should success in clinical management be a function of improvement of motor repertoire rather than amplitude of dyskinesia?

BACKGROUND

Dyskinesia, a major complication in the treatment of Parkinson's disease (PD), can require prolonged monitoring and complex medical management.

DISCUSSION

The current paper proposes a new way to view the management of dyskinesia in an integrated fashion. We suggest that dyskinesia be considered as a factor in a signal-to-noise ratio (SNR) equation where the signal is the voluntary movement and the noise is PD symptomatology, including dyskinesia. The goal of clinicians should be to ensure a high SNR in order to maintain or enhance the motor repertoire of patients. To understand why such an approach would be beneficial, we first review mechanisms of dyskinesia, as well as their impact on the quality of life of patients and on the health-care system. Theoretical and practical bases for the SNR approach are then discussed.

SUMMARY

Clinicians should not only consider the level of motor symptomatology when assessing the efficacy of their treatment strategy, but also breadth of the motor repertoire available to patients.

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.

Dopamine-induced nonmotor symptoms of Parkinson's disease

Nonmotor symptoms of Parkinson's disease (PD) may emerge secondary to the underlying pathogenesis of the disease, while others are recognized side effects of treatment. Inevitably, there is an overlap as the disease advances and patients require higher dosages and more complex medical regimens. The non-motor symptoms that emerge secondary to dopaminergic therapy encompass several domains, including neuropsychiatric, autonomic, and sleep. These are detailed in the paper. Neuropsychiatric complications include hallucinations and psychosis. In addition, compulsive behaviors, such as pathological gambling, hypersexuality, shopping, binge eating, and punding, have been shown to have a clear association with dopaminergic medications. Dopamine dysregulation syndrome (DDS) is a compulsive behavior that is typically viewed through the lens of addiction, with patients needing escalating dosages of dopamine replacement therapy. Treatment side effects on the autonomic system include nausea, orthostatic hypotension, and constipation. Sleep disturbances include fragmented sleep, nighttime sleep problems, daytime sleepiness, and sleep attacks. Recognizing the non-motor symptoms that can arise specifically from dopamine therapy is useful to help optimize treatment regimens for this complex disease.

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.

Transcriptional alterations under continuous or pulsatile dopaminergic treatment in dyskinetic rats

Continuous dopaminergic treatment is considered to prevent or delay the occurrence of dyskinesia in patients with Parkinson's disease (PD). Rotigotine is a non-ergolinic D(3) > D(2) > D(1) dopamine-receptor agonist for the treatment of PD using a transdermal delivery system providing stable plasma levels. We aimed to investigate the differential influence on gene expression of pulsatile L: -DOPA or rotigotine versus a continuous rotigotine treatment. The gene expression profile within the nigro-striatal system of unilateral 6-hydroxydopamine-lesioned rats was assessed in order to differentiate potential changes in gene expression following the various treatment using Affymetrix microarrays and quantitative RT-PCR. The expression of 15 genes in the substantia nigra and of 11 genes in the striatum was altered under pulsatile treatments inducing dyskinetic motor response, but was unchanged under continuous rotigotine treatment that did not cause dyskinetic motor response. The route of administration of a dopaminergic drug is important for the induction or prevention of motor abnormalities and adaptive gene expressions. The decline of neurotrophin-3 expression under pulsatile administration was considered of particular importance.

From the MPTP-treated primate to the treatment of motor complications in Parkinson's disease

The MPTP-treated primate has proved to be a highly predictive model of the effects of dopaminergic drugs in the symptomatic treatment of Parkinson's disease (PD) and for the avoidance of motor complications. Using MPTP-treated primates, new dopaminergic therapies have been devised alongside novel treatment strategies and novel routes of administration while providing knowledge on how to use dopaminergic drugs in a manner that avoids the onset of motor complications. The use of MPTP-treated primates led to the concept of continuous dopaminergic stimulation (CDS) and the early introduction of dopamine receptor agonists as monotherapy for PD for the prevention of dyskinesia. However, CDS does not explain the differences in dyskinesia induction that exist between L-dopa and dopamine receptor agonists, and a more rationale approach to therapy involves continuous drug delivery (CDD). CDD has been explored in the MPTP-treated primate and this review focuses on some of the evidence showing that the delivery of dopaminergic drugs in PD is key to the avoidance of dyskinesia while maintaining therapeutic efficacy. Other types of motor complication, such as "wearing off" and "on-off" remain to be explored in MPTP-treated primates and the model has yet to be used to examine non-motor components of PD. Despite having been employed for almost 25 years, the MPTP-treated primate has many potential uses in the future that will further improve the treatment of PD.

The duration of the motor response to apomorphine boluses is conditioned by the length of a prior infusion in Parkinson's disease

"Pulsatile" administration of levodopa has been invocated a relevant factor for motor fluctuations in Parkinson's disease (PD). We studied dopaminergic sensitivity to apomorphine in 10 parkinsonian patients with motor fluctuations. Patients were tested as follows: the minimal effective dose of apomorphine (MED-1) was administered in the morning to induce an on response. Fifteen minutes after this motor response had disappeared, an apomorphine infusion was initiated and maintained to ensure on periods of three different durations on different days. Infusion lasted for approximately 30, 60 and 90 minutes. Subsequently, the infusion was stopped, and after 15 minutes in the off state, a second bolus of apomorphine (MED-2) was given. The mean infusion doses were 49.2 +/- 5.4, 108.4 +/- 10.3, and 150 +/- 8.2 mg. These elicited on periods of 48.2 +/- 4.1, 110 +/- 4.5, and 195 +/- 3.8 minutes. The MED-2 elicited on responses with a duration of 30 +/- 4.5, 18.4 +/- 3.2, and 11.2 +/- 4.1 minutes. The duration of the on response induced by the apomorphine infusions correlated inversely (P < 0.01) with the on induced by the MED-2 of apomorphine. Our findings indicate that a continuous dopaminergic stimulus may induce pharmacodynamic changes associated with tolerance in PD patients.

Optimising levodopa therapy

Levodopa is still recognised to be the "gold standard" symptomatic treatment for Parkinson's disease. After 4-5 years however, its clinical efficacy declines and patients may experience the so-called "long-term levodopa syndrome", which represents the clinical counterpart of the changes of pharmacodynamic response to the drug. Long duration response (LDR) is substituted by the short duration response (SDR), which is responsible for the fluctuations of the clinical response. Strategies aimed at maintaining the clinical benefits for as long as possible and postponing the occurrence of motor complications as late as possible have been at the centre of scientific debates in recent years. We are still far from optimal use of the drug in the different stages or the disease, both regarding mode of administration and dose adjustment to individual needs.

Molecular mechanisms of L-DOPA-induced dyskinesia

L-DOPA (L-3,4-dihydroxyphenylalanine) remains the most effective drug for the treatment of Parkinson's disease. However, chronic use causes dyskinesia, a complex motor phenomenon that consists of two components: the execution of involuntary movements in response to drug administration, and the 'priming' phenomenon that underlies these movements' establishment and persistence. A reinterpretation of recent data suggests that priming for dyskinesia results from nigral denervation and the loss of striatal dopamine input, which alters glutamatergic synaptic connectivity in the striatum. The subsequent response of the abnormal basal ganglia to dopaminergic drugs determines the manner and timing of dyskinesia expression. The combination of nigral denervation and drug treatment establishes inappropriate signalling between the motor cortex and the striatum, leading to persistent dyskinesia.

Pharmacokinetics and pharmacodynamics of levodopa

The pharmacokinetics and pharmacodynamics of levodopa are dominated by two features: the short plasma half-life of the drug and the portion of the antiparkinsonian response that parallels the plasma levodopa levels, the so-called short-duration response. These features are the basis of motor fluctuations that complicate long-term therapy with levodopa. Motor fluctuations will predictably improve with measures that prolong the elevations of plasma levodopa or prolong the efficacy of dopamine synthesized from exogenous levodopa. Because dyskinesia is closely linked to the short-duration response and conceivably part of the short-duration response, it is less clear that dyskinesia will be improved by therapeutic strategies that reduce motor fluctuations.

Functional organization of the basal ganglia: therapeutic implications for Parkinson's disease

The basal ganglia (BG) are a highly organized network, where different parts are activated for specific functions and circumstances. The BG are involved in movement control, as well as associative learning, planning, working memory, and emotion. We concentrate on the "motor circuit" because it is the best understood anatomically and physiologically, and because Parkinson's disease is mainly thought to be a movement disorder. Normal function of the BG requires fine tuning of neuronal excitability within each nucleus to determine the exact degree of movement facilitation or inhibition at any given moment. This is mediated by the complex organization of the striatum, where the excitability of medium spiny neurons is controlled by several pre- and postsynaptic mechanisms as well as interneuron activity, and secured by several recurrent or internal BG circuits. The motor circuit of the BG has two entry points, the striatum and the subthalamic nucleus (STN), and an output, the globus pallidus pars interna (GPi), which connects to the cortex via the motor thalamus. Neuronal afferents coding for a given movement or task project to the BG by two different systems: (1) Direct disynaptic projections to the GPi via the striatum and STN. (2) Indirect trisynaptic projections to the GPi via the globus pallidus pars externa (GPe). Corticostriatal afferents primarily act to inhibit medium spiny neurons in the "indirect circuit" and facilitate neurons in the "direct circuit." The GPe is in a pivotal position to regulate the motor output of the BG. Dopamine finely tunes striatal input as well as neuronal striatal activity, and modulates GPe, GPi, and STN activity. Dopaminergic depletion in Parkinson's disease disrupts the corticostriatal balance leading to increased activity the indirect circuit and reduced activity in the direct circuit. The precise chain of events leading to increased STN activity is not completely understood, but impaired dopaminergic regulation of the GPe, GPi, and STN may be involved. The parkinsonian state is characterized by disruption of the internal balance of the BG leading to hyperactivity in the two main entry points of the network (striatum and STN) and excessive inhibitory output from the GPi. Replacement therapy with standard levodopa creates a further imbalance, producing an abnormal pattern of neuronal discharge and synchronization of neuronal firing that sustain the "off" and "on with dyskinesia" states. The effect of levodopa is robust but short-lasting and converts the parkinsonian BG into a highly unstable system, where pharmacological and compensatory effects act in opposing directions. This creates a scenario that substantially departs from the normal physiological state of the BG.

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.

Intermittent Dopaminergic stimulation causes behavioral sensitization in the addicted brain and parkinsonism

The gold standard therapy for Parkinson's disease (PD) consists in chronic administration of pulses of the dopamine (DA) precursor l-dihydroxyphenylalanine (l-DOPA). Although the main brain area which is DA-deficient is the dorsal striatum (more the putamen than the caudate nucleus), other DA-innervated brain regions (i.e., the ventral striatum and other limbic areas) are affected by systemic administration of l-DOPA. While such a therapy produces an increase in synaptic and nonsynaptic DA, which replace the neurotransmitter deficiency, peaks of extracellular DA in the course of disease progression produce abnormal involuntary movements related to behavioral sensitization. Methamphetamine (METH), a widely abused drug, is known to produce behavioral sensitization, related to DA release (more in the ventral than dorsal striatum as well as other limbic regions). The present review discusses the overlapping between these treatments, based on pulses of DA stimulation with an emphasis on the class of DA receptors; signal transduction pathways; rearranged expression of neurotransmitters, cotransmitters, and their receptors coupled with ultrastructural changes. In fact, all these levels of synaptic plasticity show a surprising homology following these treatments, posing the mechanisms of behavioral sensitization during DA-replacement therapy in PD very close to the neurobiological mechanisms operating during METH abuse. In line with this view is the growing evidence of addictive behaviors in PD patients during the course of DA-replacement therapy.

Ropinirole 24-hour prolonged release and ropinirole immediate release in early Parkinson's disease: a randomized, double-blind, non-inferiority crossover study

OBJECTIVE

This study compares once-daily ropinirole 24-h prolonged release and three-times-daily ropinirole immediate release in patients with early Parkinson's disease.

METHODS

This multicentre, double-blind, non-inferiority crossover study involved 161 patients randomized to one of four formulation sequences: (1) immediate release-immediate release-prolonged release; (2) immediate release-prolonged release-prolonged release; (3) prolonged release-prolonged release-immediate release; (4) prolonged release-immediate release-immediate release. During a 12-week dose-titration period, ropinirole immediate release was titrated according to the approved labelling; titration of ropinirole 24-h prolonged release started at a higher dose and was more rapid. Patients then entered three consecutive, flexible-dose, 8-week maintenance periods. At the end of the first maintenance period, half of the patients in each formulation group switched to the same or closest dose of the alternative formulation; remaining patients switched at the end of the second maintenance period.

RESULTS

At the end of titration, before the first dose switch, there were substantial reductions in mean Unified Parkinson's Disease Rating Scale (UPDRS) motor scores. During maintenance periods, both groups showed similar efficacy on the UPDRS motor score. Overall mean (standard error) change from period baseline was -0.1 (0.28) for ropinirole 24-h prolonged release, and 0.6 (0.30) for ropinirole immediate release (adjusted mean treatment difference -0.7; 95% confidence interval [CI]: -1.51, 0.10; p = 0.0842). The upper limit of the 95% CI was less than the predefined threshold of 3 points for non-inferiority. Ropinirole 24-h prolonged release was well-tolerated when titrated more rapidly than ropinirole immediate release; overnight switching between formulations was also well-tolerated. Study limitations included complexity of the non-inferiority study design and the forced dose-titration schedule.

CONCLUSION

Ropinirole 24-h prolonged release was effective and well-tolerated in patients with early Parkinson's disease.