Treatment options for Parkinson's disease

A neoteric annotation on the advances in combination therapy for Parkinson's disease: nanocarrier-based combination approach and future anticipation. Part I: exploring theoretical insights and pharmacological advances

INTRODUCTION

Parkinson's disease (PD) is a neurological condition defined by a substantial reduction in dopamine-containing cells in the substantia nigra. Levodopa (L-Dopa) is considered the gold standard in treatment. Recent research has clearly shown that resistance to existing therapies can develop. Moreover, the involvement of multiple pathways in the nigrostriatal dopaminergic neuronal loss suggests that modifying the treatment strategy could effectively reduce this degeneration.

AREAS COVERED

This review summarizes the key concerns with treating PD patients and the combinations, aimed at effectively managing PD. Part I focuses on the clinical diagnosis at every stage of the disease as well as the pharmacological treatment strategies that are applied throughout its course. It methodically elucidates the potency of multifactorial interventions in attenuating the disease trajectory, substantiating the rationale for co-administration of dual or multiple therapeutic agents. Significant emphasis is laid on evidence-based pharmacological combinations for PD management.

EXPERT OPINION

By utilizing multiple drugs in a combination fashion, this approach can leverage the additive or synergistic effects of these agents, amplify the spectrum of treatment, and curtail the risk of side effects by reducing the dose of each drug, demonstrating significantly greater efficacy.

Methanolic Extract of Boswellia serrata Gum Protects the Nigral Dopaminergic Neurons from Rotenone-Induced Neurotoxicity

Boswellia serrata gum is a natural product that showed beneficial effects on neurodegenerative diseases in recent studies. In this study, we investigated the effects of Boswellia serrata resin on rotenone-induced dopaminergic neurotoxicity. Firstly, we attempted to see if the resin can induce AMP-activated protein kinase (AMPK) signaling pathway which has been known to have broad neuroprotective effects. Boswellia increased AMPK phosphorylation and reduced phosphorylation of mammalian target of rapamycin (p-mTOR) and α-synuclein (p-α-synuclein) in the striatum while increased the expression level of Beclin1, a marker for autophagy and brain-derived neurotrophic factor. Next, we examined the neuroprotective effects of the Boswellia extract in the rotenone-injected mice. The results showed that Boswellia evidently attenuated the loss of the nigrostriatal dopaminergic neurons and microglial activation caused by rotenone. Moreover, Boswellia ameliorated rotenone-induced decrease in the striatal dopamine and impairment in motor function. Accumulation of α-synuclein meditated by rotenone was significantly ameliorated by Boswellia. Also, we showed that β-boswellic acid, the active constituents of Boswellia serrata gum, induced AMPK phosphorylation and attenuated α-synuclein phosphorylation in SHSY5 cells. These results suggest that Boswellia protected the dopaminergic neurons from rotenone neurotoxicity via activation of the AMPK pathway which might be associated with attenuation of α-synuclein aggregation and neuroinflammation. Further investigations are warranted to identify specific molecules in Boswellia which are responsible for the neuroprotection.

Protection of dopaminergic neurons in hemiparkinsonian monkeys by flavouring ingredient glyceryl tribenzoate

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and this study underlines the significance of a small molecule glyceryl tribenzoate (GTB), a FDA approved food additive, in preventing parkinsonian pathologies in MPTP-induced animal models. The study conducted in MPTP-induced mice demonstrated dose-dependent protection of nigral tyrosine hydroxylase (TH) and striatal dopamine level by GTB oral treatment and the optimum dose was found to be 50 mg/kg/d. In the next phase, the study was carried out in MPTP-injected hemiparkinsonian monkeys, which recapitulate better clinical parkinsonian syndromes. GTB inhibited MPTP-driven induction of glial inflammation, which was evidenced by reduced level of GTP-p21Ras and phospho-p65 in SN of monkeys. It led to decreased expression of inflammatory markers such as IL-1β and iNOS. Simultaneously, GTB oral treatment protected nigral TH cells, striatal dopamine, and improved motor behaviour of hemiparkinsonian monkeys. Presence of sodium benzoate, a GTB metabolite and a FDA-approved drug for urea cycle disorders and glycine encephalopathy, in the brain suggests that the neuroprotective effect imparted by GTB might be mediated by sodium benzoate. Although the mechanism of action of GTB is poorly understood, the study sheds light on the therapeutic possibility of a food additive GTB in PD.

Soybean isoflavones protect SH-SY5Y neurons from atrazine-induced toxicity by activating mitophagy through stimulation of the BEX2/BNIP3/NIX pathway

Atrazine (ATR) is a widely used herbicide that can induce the degeneration of dopaminergic (DAergic) neurons in the substantia nigra, resulting in a Parkinson's disease-like syndrome. Despite the high risk of environmental exposure, few studies have investigated strategies for the prevention of ATR neurotoxicity. Our previous studies demonstrated that ATR can impair mitochondrial function, leading to metabolic failure. Cells maintain mitochondrial quality through selective autophagic elimination, termed mitophagy. Soybean isoflavones (SI) possess multiple beneficial bioactivities, including preservation of mitochondria function, so it was hypothesized that SI can protect neurons against ATR toxicity by promoting mitophagy. Pretreatment of SH-SY5Y neurons with SI prevented ATR-induced metabolic failure and cytotoxicity as assessed by intracellular ATP, Na+-K+-ATPase activity, mitochondrial membrane potential, and cell viability assays. The neuroprotective efficacy of SI was superior to the major individual components genistein, daidzein, and glycitein. Ultrastructural analyses revealed that ATR induced mitochondrial damage, while SI promoted the sequestration of damaged mitochondria into autophagic vesicles. Soybean isoflavones also induced mitophagy as evidenced by upregulated expression of BNIP3/NIX, BEX2, and LC3-II, while co-treatment with the mitophagy inhibitor Mdivi-1 blocked SI-mediated neuroprotection and prevented SI from reversing ATR-induced BEX2 downregulation. Furthermore, BEX2 knockdown inhibited SI-induced activation of the BNIP3/NIX pathway, mitophagy, and neuroprotection. These findings suggest that SI protects against ATR-induced mitochondrial dysfunction and neurotoxicity by activating the BEX2/BNIP3/NIX pathway.

Soybean isoflavones prevent atrazine-induced neurodegenerative damage by inducing autophagy

Atrazine (ATR) is a widely used herbicide with documented dopaminergic (DAergic) neurotoxicity that can lead to a Parkinson's disease (PD)-like motor syndrome. However, there have been few studies on preventative interventions. The aim of the present study was to investigate the neuroprotective efficacy of soybean isoflavones (SI) and associated molecular mechanisms in a rat model of ATR-induced DAergic toxicity. Male Sprague-Dawley rats (6 weeks old) received daily intraperitoneal injection of SI (10, 50, or 100 mg/kg) or vehicle followed 1 h later by oral gavage of ATR (50 mg/kg) for 45 consecutive days. Open field and grip-strength tests indicated no differences in motor function among treatment groups. Alternatively, histopathology revealed neuronal damage in the striatum of rats receiving vehicle plus ATR that was ameliorated by SI pretreatment. SI attenuate ATR-induced oxidative stress (indicated by MDA accumulation and GSH depletion) and inflammatory damage (as evidenced by TNF-α and IL-6 elevation) in the substantia nigra. ATR increased expression of the pro-apoptotic factor Bax and reduced expression levels of the DA synthesis enzyme tyrosine hydroxylase (TH) and the anti-apoptotic factor Bcl-2 in the substantia nigra and striatum. All of these effects were reversed by SI pretreatment, suggesting that SI can inhibit ATR-induced apoptosis of DAergic neurons. ATR also inhibited autophagy in the substantial nigra as evidenced by LC3-II and Beclin-1 downregulation and increased expression of p62, whereas SI pretreatment reversed these effects, indicating autophagy induction. Furthermore, ATR increased the expression of mTOR and reduced the expression of phosphorylated S6 (p-S6) and BEX2 in the substantia nigra. Collectively, these findings suggest that SI can prevent ATR-mediated degeneration of DAergic neurons by inducing autophagy through an mTOR-dependent signaling pathway.

Baicalein enhances the effect of low dose Levodopa on the gait deficits and protects dopaminergic neurons in experimental Parkinsonism

Parkinson's Disease (PD) is the second most common neurodegenerative disease with the clinical characteristics of gait deficits. The classical symptomatic treatment for PD is Levodopa (L-DOPA) which brings a plethora of side effects and dosage problems in a prolonged drug regimen. Baicalein is a flavonoid extracted from Scutellaria baicalensis Georgi with the properties of neuroprotection. In this study, we investigated the ameliorative effect of baicalein with low dose L-DOPA (25 mg/kg) on the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induced Parkinsonism. The gait variability was assessed by a computer-assisted gait analysis system Catwalk. The results showed that MPTP challenged mice had significant gait deficits on dynamic paw function and posture stability. L-DOPA reversed the MPTP induced gait deficits and the effect was positively dose-dependent. The combined treatment of baicalein and under threshold dose of L-DOPA significantly improved gait functions, compared with exclusive low dose L-DOPA treatment, and the effect was comparable with high dose L-DOPA treatment. The histological assessment demonstrated that the Tyrosine hydroxylase expression increased in all the baicalein stratified groups, which suggest baicalein might have the neuroprotective effect to retain the dopaminergic neurons or enhance the dopaminergic neuron regeneration after MPTP injection. This neuroprotection probably depended on altering the inflammatory response and resisting the apoptosis through the underlying mechanism investigation. Our study provides experimental evidence that the combination of L-DOPA and baicalein might be a potential treatment for Parkinson's disease. The synergistic interaction of baicalein and L-dopa treatment might reduce the side-effect of the normal to high dose L-DOPA used today.

Lead-Induced Atypical Parkinsonism in Rats: Behavioral, Electrophysiological, and Neurochemical Evidence for a Role of Noradrenaline Depletion

Background: Lead neurotoxicity is a major health problem known as a risk factor for neurodegenerative diseases, including the manifestation of parkinsonism-like disorder. While lead is known to preferentially accumulate in basal ganglia, the mechanisms underlying behavioral disorders remain unknown. Here, we investigated the neurophysiological and biochemical correlates of motor deficits induced by sub-chronic injections of lead.

Methods: Sprague Dawely rats were exposed to sub-chronic injections of lead (10 mg/kg, i.p.) or to a single i.p. injection of 50 mg/kg N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine hydrochloride (DSP-4), a drug known to induce selective depletion of noradrenaline. Rats were submitted to a battery of behavioral tests, including the open field for locomotor activity and rotarod for motor coordination. Electrophysiological recordings were carried out in three major basal ganglia nuclei, the subthalamic nucleus (STN), globus pallidus (GP), and substantia nigra pars reticulata (SNr). At the end of experiments, post-mortem tissue level of the three monoamines (dopamine, noradrenaline, and serotonin) and their metabolites has been determined using HPLC.

Results: Lead intoxication significantly impaired exploratory and locomotor activity as well as motor coordination. It resulted in a significant reduction in the level of noradrenaline in the cortex and dopamine and its metabolites, DOPAC, and HVA, in the striatum. The tissue level of serotonin and its metabolite 5-HIAA was not affected in the two structures. Similarly, DSP-4, which induced a selective depletion of noradrenaline, significantly decreased exploratory, and locomotor activity as well as motor coordination. L-DOPA treatment did not improve motor deficits induced by lead and DSP-4 in the two animal groups. Electrophysiological recordings showed that both lead and DSP-4 did not change the firing rate but resulted in a switch from the regular normal firing to irregular and bursty discharge patterns of STN neurons. Neither lead nor DSP-4 treatments changed the firing rate and the pattern of GP and SNr neurons.

Conclusions: Our findings provide evidence that lead represents a risk factor for inducing parkinsonism-like deficits. As the motor deficits induced by lead were not improved by L-DOPA, we suggest that the deficits may be due to the depletion of noradrenaline and the parallel disorganization of STN neuronal activity.

Nimodipine, an L-type calcium channel blocker attenuates mitochondrial dysfunctions to protect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

Parkinson's disease (PD), the most common progressive neurodegenerative movement disorder, results from loss of dopaminergic neurons of substantia nigra pars compacta. These neurons exhibit Cav1.3 channel-dependent pacemaking activity. Epidemiological studies suggest reduced risk for PD in population under long-term antihypertensive therapy with L-type calcium channel antagonists. These prompted us to investigate nimodipine, an L-type calcium channel blocker for neuroprotective effect in cellular and animal models of PD. Nimodipine (0.1-10 μM) significantly attenuated 1-methyl-4-phenyl pyridinium ion-induced loss in mitochondrial morphology, mitochondrial membrane potential and increases in intracellular calcium levels in SH-SY5Y neuroblastoma cell line as measured respectively employing Mitotracker green staining, TMRM, and Fura-2 fluorescence, but only a feeble neuroprotective effect was observed in MTT assay. Nimodipine dose-dependently reduced 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonian syndromes (akinesia and catalepsy) and loss in swimming ability in Balb/c mice. It attenuated MPTP-induced loss of dopaminergic tyrosine hydroxylase positive neurons in substantia nigra, improved mitochondrial oxygen consumption and inhibited reactive oxygen species production in the striatal mitochondria measured using dichlorodihydrofluorescein fluorescence, but failed to block striatal dopamine depletion. These results point to an involvement of L-type calcium channels in MPTP-induced dopaminergic neuronal death in experimental parkinsonism and more importantly provide evidences for nimodipine to improve mitochondrial integrity and function.

Pathophysiology of L-dopa-induced motor and non-motor complications in Parkinson's disease

Involuntary movements, or dyskinesia, represent a debilitating complication of levodopa (L-dopa) therapy for Parkinson's disease (PD). L-dopa-induced dyskinesia (LID) are ultimately experienced by the vast majority of patients. In addition, psychiatric conditions often manifested as compulsive behaviours, are emerging as a serious problem in the management of L-dopa therapy. The present review attempts to provide an overview of our current understanding of dyskinesia and other L-dopa-induced dysfunctions, a field that dramatically evolved in the past twenty years. In view of the extensive literature on LID, there appeared a critical need to re-frame the concepts, to highlight the most suitable models, to review the central nervous system (CNS) circuitry that may be involved, and to propose a pathophysiological framework was timely and necessary. An updated review to clarify our understanding of LID and other L-dopa-related side effects was therefore timely and necessary. This review should help in the development of novel therapeutic strategies aimed at preventing the generation of dyskinetic symptoms.

Melatonin enhances L-DOPA therapeutic effects, helps to reduce its dose, and protects dopaminergic neurons in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced Parkinsonism in mice

L-3,4-dihydroxyphenylalanine (L-DOPA) reduces symptoms of Parkinson's disease (PD), but suffers from serious side effects on long-term use. Melatonin (10-30 mg/kg, 6 doses at 10 hr intervals) was investigated to potentiate L-DOPA therapeutic effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced parkinsonism in mice. Striatal tyrosine hydroxylase (TH) immunoreactivity, TH, and phosphorylated ser 40 TH (p-TH) protein levels were assayed on 7th day. Nigral TH-positive neurons stereology was conducted on serial sections 2.8 mm from bregma rostrally to 3.74 mm caudally. MPTP caused 39% and 58% decrease, respectively, in striatal fibers and TH protein levels, but 2.5-fold increase in p-TH levels. About 35% TH neurons were lost between 360 and 600 μm from 940 μm of the entire nigra analyzed, but no neurons were lost between 250 μm rostrally and 220 μm caudally. When L-DOPA in small doses (5-8 mg/kg) failed to affect MPTP-induced akinesia or catalepsy, co-administration of melatonin with L-DOPA attenuated these behaviors. Melatonin administration significantly attenuated MPTP-induced loss in striatal TH fibers (82%), TH (62%) and p-TH protein (100%) levels, and nigral neurons (87-100%). Melatonin failed to attenuate MPTP-induced striatal dopamine depletion. L-DOPA administration (5 mg/kg, once 40 min prior to sacrifice, p.o.) in MPTP- and melatonin-treated mice caused significant increase in striatal dopamine (31%), as compared to L-DOPA and MPTP-treated mice. This was equivalent to 8 mg/kg L-DOPA administration in parkinsonian mouse. Therefore, prolonged, effective use of L-DOPA in PD with lesser side effects could be achieved by treating with 60% lower doses of L-DOPA along with melatonin.

CNB-001 a novel curcumin derivative, guards dopamine neurons in MPTP model of Parkinson's disease

Copious experimental and postmortem studies have shown that oxidative stress mediated degeneration of nigrostriatal dopaminergic neurons underlies Parkinson's disease (PD) pathology. CNB-001, a novel pyrazole derivative of curcumin, has recently been reported to possess various neuroprotective properties. This study was designed to investigate the neuroprotective mechanism of CNB-001 in a subacute 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) rodent model of PD. Administration of MPTP (30 mg/kg for four consecutive days) exacerbated oxidative stress and motor impairment and reduced tyrosine hydroxylase (TH), dopamine transporter, and vesicular monoamine transporter 2 (VMAT2) expressions. Moreover, MPTP induced ultrastructural changes such as distorted cristae and mitochondrial enlargement in substantia nigra and striatum region. Pretreatment with CNB-001 (24 mg/kg) not only ameliorated behavioral anomalies but also synergistically enhanced monoamine transporter expressions and cosseted mitochondria by virtue of its antioxidant action. These findings support the neuroprotective property of CNB-001 which may have strong therapeutic potential for treatment of PD.

Melatonin synergizes with low doses of L-DOPA to improve dendritic spine density in the mouse striatum in experimental Parkinsonism

The dopamine precursor, L-3,4-dihydroxyphenylalanine (L-DOPA), is the preferred drug for Parkinson's disease, but long-term treatment results in the drug-induced dyskinesias and other side effects. This study was undertaken to examine whether melatonin could potentiate low dose L-DOPA effects in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced experimental parkinsonism. Mice were treated with the parkinsonian neurotoxin, MPTP, and different doses of melatonin and low doses of L-DOPA. Behavior, striatal histology, and dopamine metabolism were evaluated on the 7th day. MPTP-induced striatal dopamine loss was not modified by melatonin administration (10-30 mg/kg; i.p. at 10-hr intervals, 6 times; or at 2-hr intervals, by day). However, low doses of L-DOPA (5 mg/kg, by oral gavage) administered alone or along with melatonin (10 mg/kg, i.p.) twice everyday for 2 days, 10 hr apart, after two doses of MPTP significantly attenuated striatal dopamine loss and provided improvements in both catalepsy and akinesia. Additionally, Golgi-impregnated striatal sections showed preservation of the medium spiny neurons, which have been damaged in MPTP-treated mouse. The results demonstrated that melatonin, but not L-DOPA, restored spine density and spine morphology of medium spiny neurons in the striatum and suggest that melatonin could be an ideal adjuvant to L-DOPA therapy in Parkinson's disease, and by the use of this neurohormone, it is possible to bring down the therapeutic doses of L-DOPA.

Theaflavin, a black tea polyphenol, protects nigral dopaminergic neurons against chronic MPTP/probenecid induced Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative disorder, characterized by loss of dopominergic neurons in substantia nigra pars compacta, and can be experimentally induced by the neurotoxin 1-methyl-4-phenyl-1, 2, 3, 6-tetrahydropyridine (MPTP). Chronic administration of MPTP/probenecid (MPTP/p) leads to oxidative stress, induction of apoptosis, and loss of dopominergic neurons which results in motor impairments. Epidemiological studies have shown an inverse relationship between tea consumption and susceptibility to PD. Theaflavin is a black tea polyphenol, which possess a wide variety of pharmacological properties including potent anti oxidative, anti apoptotic and anti inflammatory effects. The current study is aimed to assess the effect of theaflavin against MPTP/p induced neurodegenaration in C57BL/6 mice. We found that the theaflavin attenuates MPTP/p induced apoptosis and neurodegeneration as evidenced by increased expression of nigral tyrosine hydroxylase (TH), dopamine transporter (DAT) and reduced apoptotic markers such as caspase-3, 8, 9 accompanied by normalized behavioral characterization. This may be due to anti oxidative and anti apoptotic activity and these data indicate that theaflavin may provide a valuable therapeutic strategy for the treatment of progressive neurodegenerative diseases such as PD.

Relationship between neuropsychological outcome and DBS surgical trajectory and electrode location

BACKGROUND

The outcome literature of subthalamic nuclei (STN) deep brain stimulation (DBS) suggests that cognitive declines are commonly reported following surgery. We hypothesized that differences in electrode position and surgical trajectory may lead to a differential neuropsychological outcome.

METHODS

We conducted a standardized evaluation of the location of the DBS electrode tip and the active electrodes, the surgical trajectory through which they were placed, and their relation to neuropsychological change scores (mental status, verbal memory, verbal fluency, and psychological measures) in 17 bilateral STN DBS patients using 6 months post-surgical magnetic resonance imaging data.

RESULTS

Declines in mental status scores were related to electrodes that were more posterior-laterally placed within the frontal quadrant in either hemisphere or those located superiorally in the left hemisphere. Electrodes that were closer to the approximated STN and more superiorally located in the left hemisphere were associated with verbal learning declines at 6 months following surgery. In the right hemisphere, the electrodes that were located more in the lateral direction were related to verbal short-term memory declines; while for verbal long-term memory declines were found for electrodes located more posterior-laterally in the left hemisphere. Declines in verbal fluency scores were more variable with associations found between change scores and electrodes in the lateral and superior directions in the left hemisphere and those electrodes closer to the approximated STN and more superiorally and posteriorally located in the right hemisphere. In contrast, semantic fluency declines were only related to right hemisphere electrodes located more superiorally. Declines in mood were related to those electrodes located further away from the approximated STN, particularly those located more inferiorally and laterally in the left hemisphere. Anxiety change scores were not associated with the location of the electrodes.

CONCLUSIONS

The results provide preliminary evidence that 6 months following bilateral STN DBS cognitive and emotional changes may be related to the surgical trajectory and electrode placement.

Contribution of the striatum to the effects of 5-HT1A receptor stimulation in L-DOPA-treated hemiparkinsonian rats

Clinical and experimental studies implicate the use of serotonin (5-HT)1A receptor agonists for the reduction of L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID). Although raphe nuclei likely play a role in these antidyskinetic effects, an unexplored population of striatal 5-HT1A receptors (5-HT1AR) may also contribute. To better characterize this mechanism, L-DOPA-primed hemiparkinsonian rats received the 5-HT1AR agonist +/-8-OH-DPAT (0, 0.1, 1.0 mg/kg, i.p.) with or without cotreatment with the 5-HT1AR antagonist WAY100635 (0.5 mg/kg, i.p.) 5 min after L-DOPA, after which abnormal involuntary movements (AIMs), rotations, and forelimb akinesia were quantified. To establish the effects of 5-HT1AR stimulation on L-DOPA-induced c-fos and preprodynorphin (PPD) mRNA within the dopamine-depleted striatum, immunohistochemistry and real-time reverse transcription polymerase chain reaction, respectively, were used. Finally, to determine the contribution of striatal 5-HT1AR to these effects, L-DOPA-primed hemiparkinsonian rats received bilateral intrastriatal microinfusions of +/-8-OH-DPAT (0, 5, or 10 microg/side), WAY100635 (5 microg/side), or both (10 microg + 5 microg/side) 5 min after L-DOPA, after which AIMs and rotations were examined. Systemic +/-8-OH-DPAT dose- and receptor-dependently attenuated L-DOPA-mediated AIMs and improved forelimb akinesia. Striatal c-fos immunoreactivity and PPD mRNA ipsilateral to the lesion were strongly induced by L-DOPA, while +/-8-OH-DPAT suppressed these effects. Finally, intrastriatal infusions of +/-8-OH-DPAT reduced AIMs while coinfusion of WAY100635 reversed its antidyskinetic effect. Collectively, these results support the hypothesis that the cellular and behavioral properties of 5-HT1AR agonists are conveyed in part via a population of functional 5-HT1AR within the striatum.

Proline-directed phosphorylation of the dopamine transporter N-terminal domain

Phosphorylation of the dopamine transporter (DAT) on N-terminal serines and unidentified threonines occurs concomitantly with protein kinase C (PKC)- and substrate-induced alterations in transporter activity, subcellular distribution, and dopamine efflux, but the residues phosphorylated and identities of protein kinases and phosphatases involved are not known. As one approach to investigating these issues, we recombinantly expressed the N-terminal tail of rat DAT (NDAT) and examined its phosphorylation and dephosphorylation properties in vitro. We found that NDAT could be phosphorylated to significant levels by PKCalpha, PKA, PKG, and CaMKII, which catalyzed serine phosphorylation, and ERK1, JNK, and p38, which catalyzed threonine phosphorylation. We identified Thr53, present in a membrane proximal proline-directed kinase motif as the NDAT site phosphorylated in vitro by ERK1, JNK and p38, and confirmed by peptide mapping and mutagenesis that Thr53 is phosphorylated in vivo. Dephosphorylation studies showed that protein phosphatase 1 catalyzed near-complete in vitro dephosphorylation of PKCalpha-phosphorylated NDAT, similar to its in vivo and in vitro effects on native DAT. These findings demonstrate the ability of multiple enzymes to directly recognize the DAT N-terminal domain and for kinases to act at multiple distinct sites. The strong correspondence between NDAT and rDAT phosphorylation characteristics suggests the potential for the enzymes that are active on NDAT in vitro to act on DAT in vivo and indicates the usefulness of NDAT for guiding future DAT phosphorylation analyses.

Quantitative study of salivary secretion in Parkinson's disease

We examined basal and reflex salivary flow rate and composition in 46 patients with Parkinson's disease (PD), both in off and on conditions, compared to 13 age-matched controls without underlying disease or treatment affecting autonomic function. Whole saliva was collected 12 hours after withdrawal of dopaminergic drugs and at the peak of levodopa-induced motor improvement. Twenty-three of the 46 PD patients had received domperidone a week before the study. Basal salivary flow rate was significantly lower in PD patients in the off state compared to controls (P<0.005). Levodopa increased salivary flow rate (P<0.05) both in the domperidone-pretreated and untreated groups. Citric acid stimulated salivary flow rate in both the off and on states in PD patients. This effect was higher in the domperidone-pretreated patients. Salivary concentration of sodium, chloride, and amylase was higher in PD patients than in controls and was not affected by levodopa or domperidone treatment. Levodopa stimulates both basal and reflex salivary flow rate in PD. The mechanism appears to be central, as the effect is not blocked by domperidone. Domperidone may have a peripheral effect that potentiates reflex salivary secretion. Salivary composition is abnormal in PD and is not affected by levodopa treatment.

MDMA and fenfluramine reduce L-DOPA-induced dyskinesia via indirect 5-HT1A receptor stimulation

Chronic L-3,4-dihydroxyphenylalanine (L-DOPA) pharmacotherapy in Parkinson's disease is often accompanied by the development of abnormal and excessive movements known as dyskinesia. Clinical and experimental studies indicate that indirect serotonin agonists can suppress dyskinesia without affecting the efficacy of L-DOPA. While the mechanism by which these effects occur is not clear, recent research suggests that serotonin 5-HT1A receptors may play a pivotal role. To test this, male Sprague-Dawley rats with unilateral 6-hydroxydopamine medial forebrain bundle lesions received 1 week of daily treatment with L-DOPA (12 mg/kg, i.p.) plus benserazide (15 mg/kg, i.p.). Beginning on the 8th day of treatment and every 3rd or 4th day thereafter, rats were pretreated with vehicle (0.9% NaCl), the serotonin and dopamine releaser 3,4-methylenedioxymethamphetamine (MDMA; 0.25 or 2.5 mg/kg, i.p.) or the serotonin releaser fenfluramine (FEN; 0.25 or 2.5 mg/kg, i.p.) 5 min prior to L-DOPA, after which abnormal involuntary movements (AIMs) and rotations were quantified every 20th minute for 2 h. Pretreatment with 2.5 mg/kg of either MDMA or FEN reduced AIMs. To determine the contribution of the 5-HT1A receptor to these effects, another group of L-DOPA-primed 6-hydroxydopamine-lesioned rats were pretreated with the 5-HT1A antagonist WAY100635 (0.5 mg/kg, i.p.), MDMA + WAY100635 (2.5 + 0.5 mg/kg, i.p.) or FEN + WAY100635 (2.5 + 0.5 mg/kg, i.p.) 5 min prior to L-DOPA and subsequent AIMs and rotation tests. The antidyskinetic effects of MDMA and FEN were reversed by cotreatment with WAY100635. These results suggest that 5-HT-augmenting compounds such as MDMA and FEN probably convey antidyskinetic properties in part via stimulation of 5-HT1A receptors.

Electrophysiological characterization of substantia nigra dopaminergic neurons in partially lesioned rats: Effects of subthalamotomy and levodopa treatment

Progressive degeneration of dopaminergic neurons in the substantia nigra pars compacta is the main histopathological characteristic of Parkinson's disease. We studied the electrophysiological characteristics of the spontaneous activity of substantia nigra pars compacta dopaminergic neurons in rats with a partial, unilateral, 6-hydroxydopamine lesion of the nigrostriatal pathway. In addition, the effects of subthalamotomy and prolonged levodopa treatment on the activity of dopaminergic neurons were investigated. As a result of the lesion ( approximately 50% neuronal loss), the number of spontaneously active neurons was significantly reduced. Basal firing rate, burst firing and responsiveness to intravenously administered apomorphine remained unchanged. In contrast, the variation coefficient, a measure of interspike interval regularity, was significantly increased. Ibotenic acid (10 microg) lesion of the ipsilateral subthalamic nucleus in lesioned rats did not modify the electrophysiological parameters. However, prolonged levodopa treatment (100 mg/kg/day + benserazide 25 mg/kg/day, 14 days) reversed the irregularity observed in cells from lesioned rats, while it induced an irregular firing pattern in cells from intact rats. Our results using an experimental model of moderate Parkinson's disease indicate that surviving substantia nigra pars compacta dopaminergic neurons fire irregularly. In this model, subthalamotomy does not modify the firing pattern while levodopa treatment efficiently restores normal firing of SNpc neurons and does not appear to be toxic to them.

Cannabinoids provide neuroprotection against 6-hydroxydopamine toxicity in vivo and in vitro: relevance to Parkinson's disease

Cannabinoids have been reported to provide neuroprotection in acute and chronic neurodegeneration. In this study, we examined whether they are also effective against the toxicity caused by 6-hydroxydopamine, both in vivo and in vitro, which may be relevant to Parkinson's disease (PD). First, we evaluated whether the administration of cannabinoids in vivo reduces the neurodegeneration produced by a unilateral injection of 6-hydroxydopamine into the medial forebrain bundle. As expected, 2 weeks after the application of this toxin, a significant depletion of dopamine contents and a reduction of tyrosine hydroxylase activity in the lesioned striatum were noted, and were accompanied by a reduction in tyrosine hydroxylase-mRNA levels in the substantia nigra. None of these events occurred in the contralateral structures. Daily administration of delta9-tetrahydrocannabinol (delta9-THC) during these 2 weeks produced a significant waning in the magnitude of these reductions, whereas it failed to affect dopaminergic parameters in the contralateral structures. This effect of delta9-THC appeared to be irreversible since interruption of the daily administration of this cannabinoid after the 2-week period did not lead to the re-initiation of the 6-hydroxydopamine-induced neurodegeneration. In addition, the fact that the same neuroprotective effect was also produced by cannabidiol (CBD), another plant-derived cannabinoid with negligible affinity for cannabinoid CB1 receptors, suggests that the antioxidant properties of both compounds, which are cannabinoid receptor-independent, might be involved in these in vivo effects, although an alternative might be that the neuroprotection exerted by both compounds might be due to their anti-inflammatory potential. As a second objective, we examined whether cannabinoids also provide neuroprotection against the in vitro toxicity of 6-hydroxydopamine. We found that the non-selective cannabinoid agonist HU-210 increased cell survival in cultures of mouse cerebellar granule cells exposed to this toxin. However, this effect was significantly lesser when the cannabinoid was directly added to neuronal cultures than when these cultures were exposed to conditioned medium obtained from mixed glial cell cultures treated with HU-210, suggesting that the cannabinoid exerted its major protective effect by regulating glial influence to neurons. In summary, our results support the view of a potential neuroprotective action of cannabinoids against the in vivo and in vitro toxicity of 6-hydroxydopamine, which might be relevant for PD. Our data indicated that these neuroprotective effects might be due, among others, to the antioxidant properties of certain plant-derived cannabinoids, or exerted through the capability of cannabinoid agonists to modulate glial function, or produced by a combination of both mechanisms.

FDG PET in the differential diagnosis of parkinsonian disorders

The differential diagnosis of parkinsonian disorders can be challenging, especially early in the disease course. PET imaging with [(18)F]-fluorodeoxyglucose (FDG) has been used to identify characteristic patterns of regional glucose metabolism in patient cohorts with idiopathic Parkinson's disease (PD), as well as variant forms of parkinsonism such as multiple system atrophy (MSA), progressive supranuclear palsy (PSP), and corticobasal degeneration (CBGD). In this study, we assessed the utility of FDG PET in the differential diagnosis of individual patients with clinical parkinsonism. 135 parkinsonian patients were referred for FDG PET to determine whether their diagnosis could be made accurately based upon their scans. Imaging-based diagnosis was obtained by visual assessment of the individual scans and also by computer-assisted interpretation. The results were compared with 2-year follow-up clinical assessments made by independent movement disorders specialists who were blinded to the original PET findings. We found that blinded computer assessment agreed with clinical diagnosis in 92.4% of all subjects (97.7% early PD, 91.6% late PD, 96% MSA, 85% PSP, 90.1% CBGD, 86.5% healthy control subjects). Concordance of visual inspection with clinical diagnosis was achieved in 85.4% of the patients scanned (88.4% early PD, 97.2% late PD, 76% MSA, 60% PSP, 90.9% CBGD, 90.9% healthy control subjects). This study demonstrates that FDG PET performed at the time of initial referral for parkinsonism accurately predicted the clinical diagnosis of individual patients made at subsequent follow-up. Computer-assisted methodologies may be particularly helpful in situations where experienced readers of FDG PET images are not readily available.

Levodopa Infusion Therapy in Parkinson Disease

Orally administered levodopa, in combination with a decarboxylase inhibitor, is the gold standard therapy for Parkinson disease (PD). The problems in management of motor fluctuations in the advanced stages of the disorder are due to the close relationship between plasma levodopa levels and availability of dopamine at striatal receptor sites. The fluctuating levodopa concentrations are mainly explained by the fact that levodopa absorption only occurs in the proximal small intestine. The patient's motor function thus depends on gastric emptying, which is erratic and may even be delayed in PD. Oral therapy with sustained-release formulations and COMT inhibitors have not solved the problems satisfactorily. Therefore, infusions of levodopa by intravenous and enteral (duodenal/jejunal) routes of administration have been studied. In this review of the literature on clinically relevant levodopa infusion studies, it is shown that improvements regarding fluctuations in both plasma levodopa levels and motor performance have been repeatedly reported. The results acquired so far suggest that levodopa infusion is a safe and efficacious therapy. Recent drug delivery development and long-term studies have shown that infusion is a clinically feasible alternative to treat advanced PD.

Effect of the D3 dopamine receptor partial agonist BP897 [N-[4-(4-(2-methoxyphenyl)piperazinyl)butyl]-2-naphthamide] on L-3,4-dihydroxyphenylalanine-induced dyskinesias and parkinsonism in squirrel monkeys

Although l-3,4-dihydroxyphenylalanine (L-dopa) is one of the most effective therapies for Parkinson's disease, continued treatment may result in excessive involuntary movements known as L-dopa-induced dyskinesias (LIDs). Because LIDs can become dose-limiting, there is great interest in finding ways to ameliorate or prevent this troubling side effect of L-dopa therapy. It was recently reported that the D3 receptor partial agonist BP897 [N-[4-(4-(2-methoxyphenyl)piperazinyl)butyl]-2-naphthamide] reduces LIDs without diminishing antiparkinsonian effects of L-dopa in macaques. In the present study, we tested the effects of BP897 on LIDs in squirrel monkeys, a nonhuman primate particularly prone to dyskinesias. Parkinsonism was induced using 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine. Animals were then gavaged with L-dopa/carbidopa (7.5 or 15 mg/kg/dose) without and with BP897. The effects of BP897 treatment were evaluated on several components of LIDs, including time course, peak dyskinesias, and area under the curve (AUC), a measure that encompasses both peak and duration of the response. Analyses of the time course and overall dyskinetic response (AUC) showed that BP897 significantly reduced LIDs but at the expense of the antiparkinsonian effect of L-dopa. BP897 had no significant effect on peak dyskinesias. Correlation studies showed that beneficial effects of BP897 on dyskinesias were linked to a decline in the antiparkinsonian action of L-dopa. Analyses of a subgroup of animals with mild/moderate parkinsonism yielded comparable results. Thus, in squirrel monkeys in contrast to macaques, BP897 fails to exert an antidyskinetic effect without diminishing the antiparkinsonian effects of L-dopa. These results suggest that BP897 may be less effective than originally anticipated for treating LIDs in Parkinson's disease.

Measuring the rate of progression of Parkinson's disease over a 5-year period with beta-CIT SPECT

Recent imaging studies suggest a rapid degeneration of the dopaminergic system in early Parkinson's disease (PD), followed by a slowing of the degenerative process in advanced disease. In the present study, a group of early-stage PD patients underwent three sequential [123I]beta-CIT SPECT studies to assess the decline of striatal dopamine transporter binding over a 5-year period. Twenty-one of a cohort of 24 early PD patients who participated in an earlier longitudinal beta-CIT SPECT imaging study [Mov Disord 2002;17:45-53] were included. Scan intervals were 26 +/- 11 months (scan 1-2) and 38 +/- 15 months (scan 2-3), respectively. The relative annual rate of decline of striatal beta-CIT binding from age-expected normal values at the time of Scan 1 was used as primary outcome variable. The relative annual decline of striatal binding from Scan 1 to Scan 2 (4.5 +/- 4.6%) and from Scan 2 to Scan 3 (3.0 +/- 3.0%) was not significantly different. The non-significant difference in progression rate was due mainly to the rapid early decline of striatal binding in 1 patient who subsequently developed a severe dysexecutive dementia syndrome. These data are not suggestive of substantial change in the course of dopaminergic degeneration in PD within the first 5 to 7 years after symptom onset.

PITX2 is required for normal development of neurons in the mouse subthalamic nucleus and midbrain

Pitx2, a homeodomain transcription factor, is essential for normal development of the pituitary gland, craniofacial region, eyes, heart, abdominal viscera, and limbs. Complete loss of Pitx2 in mice (Pitx2(-/-)) results in embryonic lethality by approximately e15 due to cardiac defects, whereas embryos with partial loss of function (Pitx2(neo/-) or Pitx2(neo/neo)) survive until later in development (e17-e19). Pitx2 is expressed in discrete populations of postmitotic neurons in the mouse brain, but its role in mammalian central nervous system (CNS) development is not known. We undertook an analysis of Pitx2-deficient embryos to determine whether loss of Pitx2 affects CNS development. The CNS is normal in hypomorphic e16.5 Pitx2(neo/-) and e18.5 Pitx2(neo/neo) embryos, with no evidence of midline or other defects. Midgestation (e10.5) Pitx2(-/-) embryos have normally formed neural tube structures and cerebral vesicles, whereas older (e14.5) Pitx2(-/-) embryos exhibit loss of gene expression and axonal projections in the subthalamic nucleus (a group of cells in the ventrolateral thalamus) and in the developing superior colliculus of dorsal midbrain. Our results suggest a role for Pitx2 in regulating regionally specific terminal neuronal differentiation in the developing ventrolateral thalamus and midbrain.

Stroke and neurodegenerative disorders. 4. neurodegenerative disorders11No commercial party having a direct financial interest in the results of the research supporting this article has or will confer a benefit upon the authors(s) or upon any organization with which the author(s) is/are associated

This self-directed learning module highlights diagnosis, treatment, and rehabilitation issues in patients with neurodegenerative disorders, including multiple sclerosis (MS), Parkinson's disease, and amyotrophic lateral sclerosis (ALS). It is part of the study guide on stroke and neurodegenerative disorders in the Self-Directed Physiatric Education Program for practitioners and trainees in physical medicine and rehabilitation. This article specifically focuses on the differential diagnosis, diagnostic evaluation, medical management, and rehabilitation issues in MS. Similarly, the differential diagnosis treatment and rehabilitation in Parkinson's disease is discussed. Electrodiagnosis, pharmacologic treatment, and rehabilitation options for ALS are also discussed.

OVERALL ARTICLE OBJECTIVES

To review the differential diagnosis, evaluation, medical treatment, and rehabilitation management of patients with MS, Parkinson's disease, and ALS.

The dopamine transporter constitutively internalizes and recycles in a protein kinase C-regulated manner in stably transfected PC12 cell lines

The dopamine transporter (DAT) removes dopamine from the extracellular milieu and is potently inhibited by number of psychoactive drugs, including cocaine, amphetamines, and methylphenidate (Ritalin). Multiple lines of evidence demonstrate that protein kinase C (PKC) down-regulates dopamine transport, primarily by redistributing DAT from the plasma membrane to endosomal compartments, although the mechanisms facilitating transporter sequestration are not defined. Here, we demonstrate that DAT constitutively internalizes and recycles in rat pheochromocytoma (PC12) cells. Temperature blockades demonstrated basal internalization and reliance on recycling to maintain DAT cell surface levels. In contrast, recycling blockade with bafilomycin A1 significantly decreased transferrin receptor (TfR) surface expression but had no effect on DAT surface levels, suggesting that DAT and TfR traffic via distinct endosomal mechanisms. Kinetic analyses reveal robust constitutive DAT cycling to and from the plasma membrane, independent of transporter expression levels. In contrast, phorbol ester-mediated PKC activation accelerated DAT endocytosis and attenuated transporter recycling in a manner sensitive to DAT expression levels. These data demonstrate constitutive DAT trafficking and that PKC-mediated DAT sequestration is achieved by a combination of accelerated internalization and reduced recycling. Additionally, the differential sensitivity to expression level exhibited by constitutive and regulated DAT trafficking suggests that these two processes are mediated by independent cellular mechanisms.