Levodopa-induced dyskinesias

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.

TC-8831, a nicotinic acetylcholine receptor agonist, reduces L-DOPA-induced dyskinesia in the MPTP macaque

Long-term L-DOPA treatment for Parkinson's disease (PD) is limited by motor complications, particularly L-DOPA-induced dyskinesia (LID). A therapy with the ability to ameliorate LID without reducing anti-parkinsonian benefit would be of great value. We assessed the ability of TC-8831, an agonist at nicotinic acetylcholine receptors (nAChR) containing α6β2/α4β2 subunit combinations, to provide such benefits in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine- (MPTP) lesioned macaques with established LID. Animals were treated orally for consecutive 14-day periods with twice-daily vehicle (weeks 1-2) or TC-8831 (0.03, 0.1 or 0.3 mg/kg, weeks 3-8). L-DOPA was also administered, once-daily, (weeks 1-12, median-dose 30 mg/kg, p.o.). For the following two-weeks (weeks 9-10), TC-8831 was washed out, while once-daily L-DOPA treatment was maintained. The effects of once-daily amantadine (3 mg/kg, p.o.) were then assessed over weeks 11-12. LID, parkinsonism, duration and quality of ON-time were assessed weekly by a neurologist blinded to treatment. TC-8831 reduced the duration of 'bad' ON-time (ON-time with disabling dyskinesia) by up to 62% and decreased LID severity (median score 18 cf. 34 (vehicle), 0.1 mg/kg, 1-3 h period). TC-8831 also significantly reduced choreiform and dystonic dyskinesia (median scores 6 and 31 cf. 19 and 31 respectively (vehicle), both 0.03 mg/kg, 1-3 h). At no time did TC-8831 treatment result in a reduction in anti-parkinsonian benefit of L-DOPA. By comparison, amantadine also significantly reduced dyskinesia and decreased 'bad' ON-time (up to 61%) but at the expense of total ON-time (reduced by up to 23%). TC-8831 displayed robust anti-dyskinetic actions and improved the quality of ON-time evoked by L-DOPA without any reduction in anti-parkinsonian benefit.

Chronic treatment with MPEP, an mGlu5 receptor antagonist, normalizes basal ganglia glutamate neurotransmission in L-DOPA-treated parkinsonian monkeys

Metabotropic glutamate 5 (mGlu5) receptor antagonists reduce L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias (LID) in Parkinson's disease (PD). The aim of this study was to investigate the long-term effect of the prototypal mGlu5 receptor antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) on glutamate receptors known to be involved in the development of LID in the de novo chronic treatment of monkeys lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). MPTP monkeys were treated for one month with L-DOPA and developed dyskinesias while those treated with L-DOPA and MPEP (10 mg/kg) developed significantly less. Normal control and saline-treated MPTP monkeys were also included. All MPTP monkeys were extensively and similarly denervated. The basal ganglia [(3)H]ABP688 specific binding (mGlu5 receptors) was elevated in L-DOPA-treated MPTP monkeys compared to controls but not in those treated with L-DOPA and MPEP; dyskinesia scores of these monkeys correlated positively with their [(3)H]ABP688 specific binding. Striatal density (B(max)) of [(3)H]ABP688 specific binding increased in L-DOPA-treated MPTP monkeys compared to other groups and affinity (Kd) remained unchanged. Striatal mGlu5 receptor mRNA remained unchanged following treatments. Elevated basal ganglia specific binding of [(3)H]Ro 25-6981 (NMDA NR1/NR2B receptors), [(3)H]Ro 48-8587 (AMPA receptors) but not [(3)H]CGP-39653 (NMDA NR1/NR2A receptors) was observed only in L-DOPA-treated MPTP monkeys; dyskinesias scores correlated with binding. By contrast, basal ganglia [(3)H]LY341495 specific binding (mGlu2/3 receptors) decreased in L-DOPA-treated MPTP monkeys compared to controls, saline and L-DOPA + MPEP treated MPTP monkeys; dyskinesias scores correlated negatively with this binding. Hence, chronic MPEP treatment reduces the development of LID and is associated with a normalization of glutamate neurotransmission.

Simultaneous determination of levodopa and carbidopa from fava bean, green peas and green beans by high performance liquid gas chromatography

INTRODUCTION

According to many studies, sprouted fava beans are a rich source of levo-dihydroxy phenylalanine (L-dopa) the precursor of dopamine, and they are now being investigated for use in the management of Parkinson's disease. The addition of Carbidopa (C-dopa) can reduce the daily use of the L-dopa dosage requirements and it can also reduce the side effects which are associated with the L-dopa administration.

MATERIAL AND METHODS

The present research was conducted to find the levo-dihydroxy phenylalanine (L-dopa) and Carbidopa (C-dopa) in fava beans, green peas and green beans by High Performance Gas Chromatography (HPLC). Carbidopa (C-dopa) is a peripheral decarboxylase inhibitor. As a substitution therapy, it used in combination to treat Parkinson's disease.

RESULT

We obtained L-dopa and C-dopa from fava beans which were in the fresh and dry sprouted form, whose concentrations were 1.4,1.5 and 2.6,2.4 mg/ml respectively. The maximal stimulation of the L-DOPA content was seen on day 8 for the fava beans, which was 100% higher than that of the control level.

CONCLUSION

The results of this study indicate that faba beans are a good source of natural L-dopa and C-dopa. The quantification of this capacity according to the stage and the plant part could be suitable for applications in the food industry and in plant medicine. The consumption of fava beans can increase the levels of L-dopa and C-dopa in the blood, with a marked improvement in the motor performance of the patients with parkinson disease, without any side effects.

The effects of BMY-14802 against L-DOPA- and dopamine agonist-induced dyskinesia in the hemiparkinsonian rat

RATIONALE

L-DOPA continues to be the primary treatment for patients with Parkinson's disease; however, the benefits of long-term treatment are often accompanied by debilitating side effects known as dyskinesias. In recent years, several 5-HT1A receptor agonists have been found to reduce dyskinesia in clinical and experimental models of PD. The purported sigma-1 antagonist, BMY-14802 has been previously demonstrated to reduce L-DOPA induced dyskinesia in a 5-HT1A receptor dependent manner.

OBJECTIVE

In the present study, we extend these findings by examining the anti-dyskinetic potential of BMY-14802 against L-DOPA, the D1 receptor agonist SKF81297 and the D2 receptor agonist, quinpirole, in the hemi-parkinsonian rat model. In addition, the receptor specificity of BMY-14802's effects was evaluated using WAY-100635, a 5-HT1A receptor antagonist.

RESULTS

Results confirmed the dose-dependent (20 > 10 > 5 mg/kg) anti-dyskinetic effects of BMY-14802 against L-DOPA with preservation of anti-parkinsonian efficacy at 10 mg/kg. BMY-14802 at 10 and 20 mg/kg also reduced dyskinesia induced by both D1 and D2 receptor agonists. Additionally, BMY-14802's anti-dyskinetic effects against L-DOPA, but not SKF81297 or quinpirole, were reversed by WAY-100635 (0.5 mg/kg).

CONCLUSION

Collectively, these findings demonstrate that BMY-14802 provides anti-dyskinetic relief against L-DOPA and direct DA agonist in a preclinical model of PD, acting via multiple receptor systems and supports the utility of such compounds for the improved treatment of PD.

Safinamide: a novel anti-Parkinsonian drug with multiple actions

SUMMARY Parkinson’s disease is the second most common neurodegenerative disease associated with motor symptoms, such as resting tremor, rigidity, bradykinesia and postural instability. Levodopa, dopamine agonists, MAO-B inhibitors and COMTs form the mainstay of treatment. However, advanced disease is associated with motor complications, especially dyskinesias, that limit dopaminergic replacement therapy. Safinamide is a novel anti-Parkinsonian drug with actions such as MAO-B and glutamate receptor inhibition, and sodium and calcium channel blockade. Safinamide has been shown to be effective as an adjunct to dopamine agonists and levodopa. The possible antidyskinetic and neuroprotective properties add to the usefulness of the drug; it is also a potential anticonvulsant drug.

Do tardive dyskinesia and L-dopa induced dyskinesia share common genetic risk factors? An exploratory study

Tardive dyskinesia (TD) in schizophrenia patients treated with antipsychotic medications and L-dopa induced dyskinesia (LID) among Parkinson's disease (PD) affected individuals share similar clinical features. Both conditions are induced by chronic exposure to drugs that target dopaminergic receptors (antagonists in TD and agonists in LID) and cause pulsatile and nonphysiological stimulation of these receptors. We hypothesized that the two motor adverse effects partially share genetic risk factors such that certain genetic variants exert a pleiotropic effect, influencing susceptibility to TD as well as to LID. In this pilot study, we focused on 21 TD-associated SNPs, previously reported in TD genome-wide association studies or in candidate gene studies. By applying logistic regression and controlling for relevant clinical risk factors, we studied the association of the SNPs with LID vulnerability in two independent pharmacogenetic samples. We included a Jewish Israeli sample of 203 PD patients treated with L-dopa for a minimum of 3 years and evaluated the existence or absence of LID (LID+ = 128; LID- = 75). An Italian sample was composed of early LID developers (within the first 3 years of treatment, N = 187) contrasted with non-early LID developers (after 7 years or more of treatment, N = 203). None of the studied SNPs were significantly associated with LID susceptibility in the two samples. Therefore, we were unable to obtain proof of concept for our initial hypothesis of an overlapping contribution of genetic risk factors to TD and LID. Further studies in larger samples are required to reach definitive conclusions.

Neuroimaging over the course of Parkinson's disease: from early detection of the at-risk patient to improving pharmacotherapy of later-stage disease

Brain imaging of striatal dopamine terminal degeneration serves an important role in the clinical management of Parkinson's disease (PD). Imaging biomarkers for interrogating dopaminergic systems are used for clarifying diagnosis when only subtle motor symptoms are present. However, motor dysfunction is not the earliest symptom of PD. There is increasing interest in identifying premotor PD patients, particularly because potential disease-modifying therapies are developed and the clinical imperative becomes early and accurate diagnosis. On the other end of the spectrum of the disease course, during later stages of PD, significant clinical challenges like levo-dopa-induced dyskinesias and medication on-off phenomenon become more prevalent. In this instance, better understanding of altered PD motor pathways suggests the potential utility of novel treatments targeting neuronal systems that are impacted by degenerating dopamine neurons and chronic dopamine replacement treatment. Molecular neuroimaging serves unique roles in both very early PD and later-stage disease, in the former, potentially pushing back the time of diagnosis, and in the latter, elucidating pathology relevant to new drug development.

Striatal molecular signature of subchronic subthalamic nucleus high frequency stimulation in parkinsonian rat

This study addresses the molecular mechanisms underlying the action of subthalamic nucleus high frequency stimulation (STN-HFS) in the treatment of Parkinson's disease and its interaction with levodopa (L-DOPA), focusing on the striatum. Striatal gene expression profile was assessed in rats with nigral dopamine neuron lesion, either treated or not, using agilent microarrays and qPCR verification. The treatments consisted in anti-akinetic STN-HFS (5 days), chronic L-DOPA treatment inducing dyskinesia (LIDs) or the combination of the two treatments that exacerbated LIDs. STN-HFS modulated 71 striatal genes. The main biological processes associated with the differentially expressed gene products include regulation of growth, of apoptosis and of synaptic transmission, and extracellular region is a major cellular component implicated. In particular, several of these genes have been shown to support survival or differentiation of striatal or of dopaminergic neurons. These results indicate that STN HFS may induce widespread anatomo-functional rearrangements in the striatum and create a molecular environment favorable for neuroprotection and neuroplasticity. STN-HFS and L-DOPA treatment share very few common gene regulation features indicating that the molecular substrates underlying their striatal action are mostly different; among the common effects is the down-regulation of Adrb1, which encodes the adrenergic beta-1-receptor, supporting a major role of this receptor in Parkinson's disease. In addition to genes already reported to be associated with LIDs (preprodynorphin, thyrotropin-releasing hormone, metabotropic glutamate receptor 4, cannabinoid receptor 1), the comparison between DOPA and DOPA/HFS identifies immunity-related genes as potential players in L-DOPA side effects.

Levodopa-induced dyskinesia is strongly associated with resonant cortical oscillations

The standard pharmacological treatment for Parkinson's disease using the dopamine precursor levodopa is unfortunately limited by gradual development of disabling involuntary movements for which the underlying causes are poorly understood. Here we show that levodopa-induced dyskinesia in hemiparkinsonian rats is strongly associated with pronounced 80 Hz local field potential oscillations in the primary motor cortex following levodopa treatment. When this oscillation is interrupted by application of a dopamine antagonist onto the cortical surface the dyskinetic symptoms disappear. The finding that abnormal cortical oscillations are a key pathophysiological mechanism calls for a revision of the prevailing hypothesis that links levodopa-induced dyskinesia to an altered sensitivity to dopamine only in the striatum. Apart from having important implications for the treatment of Parkinson's disease, the discovered pathophysiological mechanism may also play a role in several other psychiatric and neurological conditions involving cortical dysfunction.

Parallel dopamine D1 receptor activity dependence of l-Dopa-induced normal movement and dyskinesia in mice

l-3,4-Dihydroxyphenylalanine (l-Dopa)-induced dyskinesia (LID) in Parkinson's disease (PD) is a major clinical problem. The prevailing view is that in PD patients and animal PD models dyskinesia develops after repeated l-dopa use or priming, independent of l-dopa's anti-PD therapeutic effect that occurs immediately. Here we show that in mice with severe and consistent dopamine (DA) loss in the dorsal striatum, rendered by transcription factor Pitx3 null mutation, the very first injection of l-dopa or D1-like agonist SKF81297 induced both normal ambulatory and dyskinetic movements. Furthermore, the robust stimulating effects on normal and dyskinetic movements had an identical time course and parallel dose-response curves. In contrast, D2-like agonist ropinirole stimulated normal and dyskinetic movements relatively modestly. These results demonstrate that severe DA loss in the dorsal striatum sets the stage for dyskinesia to occur on the first exposure to l-dopa or a D1 agonist without any priming. These results also indicate that l-dopa stimulated both normal and dyskinetic movements primarily via D1 receptor activation and that proper D1 agonism is potentially an efficacious therapy for PD motor deficits.

Epigenetics in Parkinson's and Alzheimer's diseases

Neurodegenerative disorders, such as Parkinson's and Alzheimer's disease, are highly complex, due to their multifactorial origin, not only depending on genetic but also on environmental factors. Several genetic risk factors have already been associated with both the diseases, however, the precise way through which the environment contributes to neurodegeneration is still unclear.Recently, epigenetic mechanisms, such as DNA methylation, chromatin remodeling or miRNAs, which may induce alterations in genes expression, have started to be implicated in both AD and PD. Epigenetic modulation is present since pre-natal stages and throughout lifetime, and depends on lifestyle conditions and environmental exposures, and consequently could represent the missing link between risk factors and the development of sporadic disorders. This chapter will discusses the role of epigenetics in AD and PD.

Higher iron in the red nucleus marks Parkinson's dyskinesia

Dopamine cell loss and increased iron in the substantia nigra (SN) characterize Parkinson's disease (PD), with cerebellar involvement increasingly recognized, particularly in motor compensation and levodopa-induced dyskinesia (LID) development. Because the red nucleus (RN) mediates cerebellar circuitry, we hypothesized that RN iron changes might reflect cerebellum-related compensation, and/or the intrinsic capacity for LID development. We acquired high resolution magnetic resonance images from 23 control and 38 PD subjects (12 with PD and history of LID [PD+DYS]) and 26 with PD and no history of LID (PD-DYS). Iron content was estimated from bilateral RN and SN transverse relaxation rates (R2*). PD subjects overall displayed higher R2* values in both the SN and RN. RN R2* values correlated with off-drug Unified Parkinson's Disease Rating Scale-motor scores, but not disease duration or drug dosage. RN R2* values were significantly higher in PD+DYS compared with control and PD-DYS subjects; control and PD-DYS subjects did not differ. The association of higher RN iron content with PD-related dyskinesia suggests increased iron content is involved in, or reflects, greater cerebellar compensatory capacity and thus increased likelihood of LID development.

Management of pain in Parkinson's disease

Pain is a common symptom in Parkinson's disease (PD) and accounts for substantial morbidity in up to 80 % of patients. Despite contributing to disease-related discomfort and disability, pain in PD frequently goes underacknowledged and undertreated in clinical practice. Although the exact underlying neurophysiology is unclear, there is increasing understanding of the role of the basal ganglia in somatosensory processing, as well as involvement of additional brainstem structures and non-dopaminergic pathways; appreciation of these mechanisms has implications for treatment strategies. Categorizing painful symptoms based on their clinical description into musculoskeletal, dystonic, radicular-peripheral neuropathic and central pain categories provides a useful framework for management. Importantly, these symptoms should be evaluated in relation to motor symptoms and dopaminergic therapy. A multi-disciplinary approach is recommended as follows: physical therapy, liaison with pain management and consultations to rheumatological, orthopaedic and neurosurgical services should be considered.

Thermodynamic parameters of electrochemical oxidation of L-DOPA: experimental and theoretical studies

Electrode potential and thermodynamic parameters of the electrochemical reaction of L-DOPA in aqueous solution are obtained experimentally by cyclic voltammetry method and also calculated theoretically using accurate ab initio calculations (G3MP2//B3LYP) along with the available solvation model of CPCM. The pH dependence of the redox activity of L-DOPA in aqueous solution at temperatures in the range of 10-30 °C was used for the experimental determination of the standard reduction potential, changes of entropy, enthalpy, and Gibbs free energy for the studied reaction. The experimental formal redox potential of the two-proton-two-electron reduction process was obtained to be 0.745 V versus standard hydrogen electrode (SHE). The theoretical and experimental values (0.728 and 0.745 V) for the standard electrode potential of L-DOPA are in agreement with each other. The difference between the peak potential of the L-DOPA and the products, which are produced by chemical reactions, has been measured experimentally and also calculated theoretically. There is also an agreement between experimental and theoretical potential difference. Also in this work, the changes of thermodynamic functions of solvation are calculated from the differences between the solution-phase experimental values and the gas-phase theoretical values.

Conserved role of dopamine in the modulation of behavior

Dopamine is an ancient signaling molecule. It is responsible for maintaining the adaptability of behavioral outputs and is found across taxa. The following is a summary of the role of dopamine and the mechanisms of its function and dysfunction. We discuss our recent findings on dopaminergic control of behaviors in C. elegans and discuss its potential implications for work in the fields of C. elegans and Parkinson research.

MPEP, an mGlu5 receptor antagonist, reduces the development of L-DOPA-induced motor complications in de novo parkinsonian monkeys: biochemical correlates

L-3,4-Dihydroxyphenylalanine (l-DOPA), the gold standard therapy for Parkinson disease (PD), is associated with motor fluctuations and dyskinesias. This study sought to prevent the development of l-DOPA-induced dyskinesias (LID) with the metabotropic glutamate receptor type 5 (mGlu5 receptor) antagonist 2-methyl-6-(phenylethynyl)pyridine (MPEP) in the de novo treatment of monkeys lesioned with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a PD model. MPTP-lesioned monkeys were treated once daily for one month with either l-DOPA or l-DOPA + MPEP (10 mg/kg). MPEP (administered 15 min before l-DOPA) plasma concentrations were elevated during all the l-DOPA motor activation and did not accumulate during a month. The antiparkinsonian effect was maintained throughout the treatment period in MPTP-lesioned monkeys treated with l-DOPA + MPEP, while the duration of this effect decreased over time in MPTP-lesioned monkeys treated with l-DOPA alone, suggesting wearing-off. Over the month-long treatment, the mean dyskinesia score increased in l-DOPA-treated monkeys; interestingly, this increase was reduced by overall 72% in the l-DOPA + MPEP group. Mean dyskinesia scores of monkeys correlated inversely with plasma MPEP concentrations. Normal control and saline-treated MPTP-lesioned monkeys were also included for biochemical analyses. All MPTP-lesioned monkeys were extensively and similarly denervated. [(3)H]ABP688 specific binding to mGlu5 receptors increased in the putamen of l-DOPA-treated monkeys compared to control, saline or l-DOPA + MPEP-treated monkeys. Mean dyskinesia scores of MPTP-lesioned monkeys correlated positively with [(3)H]ABP688 specific binding in the putamen. This study showed a beneficial chronic antidyskinetic effect of MPEP in de novol-DOPA-treated MPTP-lesioned monkeys, supporting the therapeutic use of mGlu5 receptor antagonists in PD to prevent LID. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Clinical aspects and management of levodopa-induced dyskinesia

In Parkinson's disease, one of the most troublesome dilemmas is the treatment of levodopa-induced dyskinesia. After a few years, chronic treatment with levodopa is associated with the development of dyskinesias. Strategies to delay or to reduce dyskinesias are based on the change of levodopa dosing or the early use of dopamine agonists. Dopamine agonists with different pharmacological profile are available. Our paper was aimed to analyse the clinical impact and the management of dyskinesias with dopamine agonists.

Group III and subtype 4 metabotropic glutamate receptor agonists: discovery and pathophysiological applications in Parkinson's disease

Restoring the balance between excitatory and inhibitory circuits in the basal ganglia, following the loss of dopaminergic (DA) neurons of the substantia nigra pars compacta, represents a major challenge to treat patients affected by Parkinson's disease (PD). The imbalanced situation in favor of excitation in the disease state may also accelerate excitotoxic processes, thereby representing a potential target for neuroprotective therapies. Reducing the excitatory action of glutamate, the major excitatory neurotransmitter in the basal ganglia, should lead to symptomatic improvement for PD patients and may promote the survival of DA neurons. Recent studies have focused on the modulatory action of metabotropic glutamate (mGlu) receptors on neurodegenerative diseases including PD. Group III mGlu receptors, including subtypes 4, 7 and 8, are largely expressed in the basal ganglia. Recent studies highlight the use of selective mGlu4 receptor positive allosteric modulators (PAMs) for the treatment of PD. Here we review the effects of newly-designed group-III orthosteric agonists on neuroprotection, neurorestoration and reduction of l-DOPA induced dyskinesia in animal models of PD. The combination of orthosteric mGlu4 receptor selective agonists with PAMs may open new avenues for the symptomatic treatment of PD. This article is part of a Special Issue entitled 'Metabotropic Glutamate Receptors'.

Impact of L-DOPA treatment on regional cerebral blood flow and metabolism in the basal ganglia in a rat model of Parkinson's disease

Large increases in regional cerebral blood flow (rCBF) have been measured in patients with Parkinson's disease (PD) following the administration of L-DOPA, but the underlying mechanisms have remained unknown. In this study, rats with unilateral 6-hydroxydopamine (6-OHDA) lesions were used to compare patterns of rCBF and regional cerebral glucose utilisation (rCGU) in chronically L-DOPA-treated subjects following a final injection of L-DOPA or saline. The same animal model was used to the leakage of a blood-brain barrier (BBB) tracer molecule at 60 min vs. 24h following the last L-DOPA injection of a chronic treatment. All the parameters under investigation were examined with brain autoradiography following intravenous injections of specific radiotracers in awake animals ([14C]-iodoantipyrine for rCBF, [14C]-2-deoxyglucose for rCGU, and [14C]-α-aminoisobutyric acid for BBB leakage). Significant changes in rCBF and rCGU on the side ipsilateral to the 6-OHDA lesion relative to the non-lesioned side were seen at 60 min ("ON") but not 24h ("OFF") following L-DOPA administration. These changes were not seen in sham-operated rats. In the output nuclei of the basal ganglia (the entopeduncular nucleus and the substantia nigra pars reticulata) both rCBF and rCGU were elevated both in acutely L-DOPA-treated rats and chronically L-DOPA-treated rats displaying dyskinesia, but did not change significantly in chronically L-DOPA-treated non-dyskinetic cases. Acutely and chronically L-DOPA-treated rats with dyskinesia exhibited increases in rCBF "ON L-DOPA" also in the motor cortex, the striatum, and the globus pallidus, but the corresponding changes in rCGU did not show the same direction, magnitude, and/or relative group differences. The uptake of a BBB tracer (studied in the striatum and the substantia nigra reticulata in chronically L-DOPA treated rats) was significantly higher ON vs. OFF L-DOPA. The present results are the first to show that the administration of L-DOPA is followed by transient and robust increases in rCBF in the dopamine-denervated basal ganglia. This effect occurs already upon acute L-DOPA treatment and persists upon repeated drug administration in animals that develop dyskinesia. Increases in rCBF ON L-DOPA are not necessarily accompanied by enhanced glucose utilisation in the affected regions, pointing to altered mechanisms of neurovascular coupling. Finally, our results show that increases in rCBF ON L-DOPA may be accompanied by BBB hyperpermeability in the most affected regions.

Facing the unique challenges of dyskinesias in Parkinson’s disease

Dyskinesia is among the most challenging complications of levodopa and dopaminergic drug therapy in advanced Parkinson’s disease. This symptom has a negative impact on the quality of life of patients with Parkinson’s disease and is hard to manage. Current advances in our understanding of the diverse phenomenology and complicated pathophysiology of dyskinesia have led to a number of novel strategies aimed at better control of this complication. Further insight has been gained from focusing on the characteristics of the rating scale used for assessment of dyskinesia and from the inherent susceptibility of dyskinesia to placebo effect. Here, we will briefly review the phenomenology, pathophysiology and the treatment of dyskinesia in Parkinson’s disease.

Prospects for cannabinoid therapies in basal ganglia disorders

Cannabinoids are promising medicines to slow down disease progression in neurodegenerative disorders including Parkinson's disease (PD) and Huntington's disease (HD), two of the most important disorders affecting the basal ganglia. Two pharmacological profiles have been proposed for cannabinoids being effective in these disorders. On the one hand, cannabinoids like Δ(9) -tetrahydrocannabinol or cannabidiol protect nigral or striatal neurons in experimental models of both disorders, in which oxidative injury is a prominent cytotoxic mechanism. This effect could be exerted, at least in part, through mechanisms independent of CB(1) and CB(2) receptors and involving the control of endogenous antioxidant defences. On the other hand, the activation of CB(2) receptors leads to a slower progression of neurodegeneration in both disorders. This effect would be exerted by limiting the toxicity of microglial cells for neurons and, in particular, by reducing the generation of proinflammatory factors. It is important to mention that CB(2) receptors have been identified in the healthy brain, mainly in glial elements and, to a lesser extent, in certain subpopulations of neurons, and that they are dramatically up-regulated in response to damaging stimuli, which supports the idea that the cannabinoid system behaves as an endogenous neuroprotective system. This CB(2) receptor up-regulation has been found in many neurodegenerative disorders including HD and PD, which supports the beneficial effects found for CB(2) receptor agonists in both disorders. In conclusion, the evidence reported so far supports that those cannabinoids having antioxidant properties and/or capability to activate CB(2) receptors may represent promising therapeutic agents in HD and PD, thus deserving a prompt clinical evaluation.

New pharmacological avenues for the treatment of L-DOPA-induced dyskinesias in Parkinson's disease: targeting glutamate and adenosine receptors

INTRODUCTION

Parkinson's disease (PD) therapy is still centered on the use of L-3,4-dihydroxyphenylalanine (L-DOPA), which is hampered by numerous side effects, including abnormal involuntary movements known as L-DOPA-induced dyskinesias (LIDs). LIDs are the result of pre- and postsynaptic changes at the corticostriatal level, induced by chronic and pulsatile stimulation of striatal dopaminergic receptors. These changes impact on synaptic plasticity and involve also selected, nondopaminergic receptors expressed by striatal projection neurons.

AREAS COVERED

Among nondopaminergic receptors, glutamate receptors - NMDA and mGluR5 subtypes in particular - and adenosine A(2A) receptors are those most likely involved in LIDs. The aim of the present review is to summarize results of studies undertaken with specific antagonists of these receptors, first conducted in animal models of LIDs, which in selected cases have been translated into clinical trials.

EXPERT OPINION

Selected antagonists of glutamate and adenosine receptors have been proposed as anti-dyskinetic agents. Promising results have been obtained in preclinical investigations and in initial clinical trials, but long-term safety, tolerability and efficacy studies in patients are still required. The current development of novel antagonists, including tools able to act on receptor mosaics, may provide innovative tools for LIDs management in the next future.

Catechol-O-methyltransferase Val158Met and the risk of dyskinesias in Parkinson's disease

BACKGROUND

The A-allele of the catechol-O-methyltransferase (COMT) Val158Met polymorphism is associated with decreased enzymatic activity and higher dopamine availability.

METHODS

We studied 219 patients with PD who were free of dyskinesias at baseline and underwent thorough annual examinations.

RESULTS

The A-allele of the COMT Val158Met polymorphism was related to an increased risk of developing dyskinesias during follow-up, in a dose-dependent manner (adjusted hazard ratios for the AG and AA genotypes [compared to GG]: 2.09 [95% confidence interval (CI), 1.07-4.06] and 2.81 [CI, 1.43-5.54], respectively).

CONCLUSIONS

This finding suggests that genetic factors may affect susceptibility to dyskinesias in PD.

Retigabine, a K(V)7 (KCNQ) potassium channel opener, attenuates L-DOPA-induced dyskinesias in 6-OHDA-lesioned rats

L-DOPA-induced dyskinesias (LID) represent a severe complication of long-time pharmacotherapy in Parkinson's disease that necessitates novel therapeutics. The acute and chronic effects of K(V)7.2-7.5 channel openers (retigabine, flupirtine) on the severity of LID and parkinsonian signs were examined in comparison to the glutamate receptor antagonist amantadine (positive control) in a rat model of LID. Acute treatment with retigabine (2.5, 5 mg/kg i.p.) and flupirtine (5, 10 mg/kg i.p.) significantly reduced the severity of abnormal involuntary movements (AIM) to a comparable extent as amantadine (20, 40 mg/kg s.c.), but flupirtine delayed the disappearance of AIM. Chronic treatment with retigabine (daily 5 mg/kg i.p. over 19 days combined with l-DOPA 10 mg i.p.) did not prevent or delay the development of LID, but reduced the severity of AIM, while antidyskinetic effects of amantadine (40 mg/kg i.p.) were restricted to the first day of treatment. Retigabine caused sedation and ataxia which declined during the chronic treatment, but did not reduce the antiparkinsonian effects of l-DOPA in these experiments. Acute co-injections of retigabine (5 mg) together with l-DOPA (10 mg/kg) neither reduced the motor performance in the rotarod test nor exerted negative effects on the antiparkinsonian efficacy of l-DOPA in the block and stepping test. Nevertheless, the sedative effects of retigabine may limit its therapeutic potential for the treatment of LID. The present data indicate that K(V)7 channels deserve attention in the research of the pathophysiology of dyskinesias. This article is part of a Special Issue entitled 'Post-Traumatic Stress Disorder'.

L-DOPA-Induced Dyskinesia and Abnormal Signaling in Striatal Medium Spiny Neurons: Focus on Dopamine D1 Receptor-Mediated Transmission

Dyskinesia is a serious motor complication caused by prolonged administration of l-DOPA to patients affected by Parkinson's disease. Accumulating evidence indicates that l-DOPA-induced dyskinesia (LID) is primarily caused by the development of sensitized dopamine D1 receptor (D1R) transmission in the medium spiny neurons (MSNs) of the striatum. This phenomenon, combined with chronic administration of l-DOPA, leads to persistent and intermittent hyper-activation of the cAMP signaling cascade. Activation of cAMP signaling results in increased activity of the cAMP-dependent protein kinase (PKA) and of the dopamine- and cAMP-dependent phosphoprotein of 32 kDa (DARPP-32), which regulate several downstream effector targets implicated in the control of the excitability of striatal MSNs. Dyskinesia is also accompanied by augmented activity of the extracellular signal-regulated kinases (ERK) and the mammalian target of rapamycin complex 1 (mTORC1), which are involved in the control of transcriptional and translational efficiency. Pharmacological or genetic interventions aimed at reducing abnormal signal transduction at the level of these various intracellular cascades have been shown to attenuate LID in different animal models. For instance, LID is reduced in mice deficient for DARPP-32, or following inhibition of PKA. Blockade of ERK obtained genetically or using specific inhibitors is also able to attenuate dyskinetic behavior in rodents and non-human primates. Finally, administration of rapamycin, a drug which blocks mTORC1, results in a strong reduction of LID. This review focuses on the abnormalities in signaling affecting the D1R-expressing MSNs and on their potential relevance for the design of novel anti-dyskinetic therapies.

The serotonergic system in Parkinson's disease

Although the cardinal manifestations of Parkinson's disease (PD) are attributed to a decline in dopamine levels in the striatum, a breadth of non-motor features and treatment-related complications in which the serotonergic system plays a pivotal role are increasingly recognised. Serotonin (5-HT)-mediated neurotransmission is altered in PD and the roles of the different 5-HT receptor subtypes in disease manifestations have been investigated. The aims of this article are to summarise and discuss all published preclinical and clinical studies that have investigated the serotonergic system in PD and related animal models, in order to recapitulate the state of the current knowledge and to identify areas that need further research and understanding.

Protective effect of Zhen-Wu-Tang (ZWT) through keeping DA stable and VMAT 2/DAT mRNA in balance in rats with striatal lesions induced by MPTP

ETHNOPHARMACOLOGICAL RELEVANCE

Zhen-Wu-Tang (ZWT), the modified formulation of a classical Chinese prescription from "Treaties on Febrile Disease", was clinically employed to treat Parkinson's disease.

AIM OF THE STUDY

To investigate the neuroprotective effect of ZWT on intra-striatum injection of MPTP-induced Parkinson's disease in rats.

MATERIALS AND METHODS

The effect of ZWT on the behavioral changes (open-field test, Ladder walking, spontaneous alternation in Y maze), the dopamine transmitter systems of substantia nigra, striatum and frontal cortex of rats by HPLC-ECD, mRNA expression of tyrosine hydroxylase (TH), dopamine transporter (DAT) and vesicular monoamine transporter 2 (VMAT 2) of the above three brain regions was investigated.

RESULTS

This study showed that ZWT not only ameliorated the behavior induced by the administration of MPTP in striatum, but also increased DA in the brain, prevented the decreasing of TH and balanced the ratio of VMAT 2/DAT in mRNA level.

CONCLUSIONS

These results suggest that ZWT possesses neuroprotective and anti-parkinsonism properties.

AFQ056 treatment of levodopa-induced dyskinesias: results of 2 randomized controlled trials

Study objectives were to assess the efficacy, safety, and tolerability of AFQ056 in Parkinson's disease patients with levodopa-induced dyskinesia. Two randomized, double-blind, placebo-controlled, parallel-group, in-patient studies for Parkinson's disease patients with moderate to severe levodopa-induced dyskinesia (study 1) and severe levodopa-induced dyskinesia (study 2) on stable dopaminergic therapy were performed. Patients received 25-150 mg AFQ056 or placebo twice daily for 16 days (both studies). Study 2 included a 4-day down-titration. Primary outcomes were the Lang-Fahn Activities of Daily Living Dyskinesia Scale (study 1), the modified Abnormal Involuntary Movement Scale (study 2), and the Unified Parkinson's Disease Rating Scale-part III (both studies). Secondary outcomes included the Unified Parkinson's Disease Rating Scale-part IV items 32-33. The primary analysis was change from baseline to day 16 on all outcomes. Treatment differences were assessed. Fifteen patients were randomized to AFQ056 and 16 to placebo in study 1; 14 patients were randomized to each group in study 2. AFQ056-treated patients showed significant improvements in dyskinesias on day 16 versus placebo (eg, Lang-Fahn Activities of Daily Living Dyskinesia Scale, P = .021 [study 1]; modified Abnormal Involuntary Movement Scale, P = .032 [study 2]). No significant changes were seen from baseline on day 16 on the Unified Parkinson's Disease Rating Scale-part III in either study. Adverse events were reported in both studies, including dizziness. Serious adverse events (most commonly worsening of dyskinesias, apparently associated with stopping treatment) were reported by 4 AFQ056-treated patients in study 1, and 3 patients (2 AFQ056-treated patient and 1 in the placebo group) in study 2. AFQ056 showed a clinically relevant and significant antidyskinetic effect without changing the antiparkinsonian effects of dopaminergic therapy. © 2011 Movement Disorder Society.

Regional changes in type 1 cannabinoid receptor availability in Parkinson's disease in vivo

The type 1 cannabinoid receptor (CB1) is a crucial modulator of synaptic transmission in brain and has been proposed as a potential therapeutic target in Parkinson's disease (PD), especially for treatment of levodopa-induced dyskinesias (LID). Our aim was to measure CB1 levels in brains of PD patients in vivo and to investigate the relation between CB1 availability and LID. We studied 12 healthy controls and 29 PD patients (9 drug-naïve patients with early PD, 10 patients with advanced PD and LID, and 10 patients with advanced PD without LID). PD patients were examined using the Unified Parkinson's Disease Rating Scale (UPDRS) and the modified Abnormal Involuntary Movement Scale (mAIMS). All subjects underwent positron emission tomography (PET) with the CB1-selective radioligand [(18)F] MK-9470 and magnetic resonance imaging (MRI). PD patients showed an absolute decrease in CB1 availability in the substantia nigra. By contrast, CB1 availability was relatively increased in nigrostriatal, mesolimbic, and mesocortical dopaminergic projection areas. CB1 availability did not differ significantly between advanced PD patients with and without LID. Within the group of PD patients with LID, there was no significant correlation between CB1 availability and LID severity. These data demonstrate regional changes in CB1 availability in PD in vivo, but do not support a role for dysregulation of CB1 levels in the pathogenesis of LID.