Doxycycline to treat levodopa-induced dyskinesias in Parkinson's disease: a preliminary study.

BACKGROUND: Levodopa-induced dyskinesia (LID) is a common motor complication of levodopa therapy in patients with Parkinson's disease (PD). Doxycycline is a widely used and inexpensive tetracycline with anti-inflammatory properties. OBJECTIVE: To evaluate the efficacy and safety of doxycycline in patients with PD and LID. METHODS: This was an open-label, uncontrolled, single-arm, single-center, phase 2 proof-of-concept study in patients with PD with functional impact of dyskinesia, which used levodopa three times daily, in a movement disorders clinic in Brazil. Participants were treated with doxycycline 200 mg/day for 12 weeks, with evaluations at baseline, week 4, and week 12 of treatment. The primary outcome measure was the change from baseline in the Unified Dyskinesia Rating Scale (UDysRS) total score at week 12, evaluated by two blinded raters. Key secondary outcomes measures were OFF time and ON time with troublesome dyskinesia in the PD home diary. RESULTS: Eight patients with PD were treated and evaluated. Doxycycline 200 mg/day reduced the UDysRS total score at week 12, compared with baseline (Friedman χ2 = 9.6; p = 0.008). Further, doxycycline reduced the ON time with troublesome dyskinesia (Friedman χ2 = 10.8; p = 0.004) without worsening parkinsonism. There were no severe adverse events, and dyspepsia was the commonest event. CONCLUSION: In this preliminary, open-label and uncontrolled trial, doxycycline was effective in reducing LID and safe after a 12-week treatment. Further well-designed placebo-controlled clinical trials with a longer duration and a larger number of participants are needed. CLINICAL TRIAL REGISTRATION: https://ensaiosclinicos.gov.br, identifier: RBR-1047fwbf.

ANTECEDENTES: A discinesia induzida por levodopa (DIL) é uma complicação motora comum da terapia com levodopa em pacientes com doença de Parkinson (DP). A doxiciclina é uma tetraciclina amplamente usada e barata, com propriedade anti-inflamatória. OBJETIVO: Avaliar a eficácia e segurança da doxiciclina em pacientes com DP e DIL. MéTODOS: Este foi um estudo aberto, não-controlado, de braço único, monocêntrico, fase 2 e de prova de conceito, em pacientes com DP e impacto funcional das discinesias, que usavam levodopa três vezes ao dia, em um ambulatório de distúrbios de movimento no Brasil. Os participantes foram tratados com doxiciclina 200 mg/dia por 12 semanas, com avaliações na base, na semana 4 e na semana 12 do tratamento. A medida de desfecho primário foi a mudança no escore total da Unified Dyskinesia Rating Scale (UDysRS) da base à semana 12, avaliada por dois avaliadores cegos. As medidas-chave de desfecho secundário fora o tempo em OFF e tempo em ON com discinesia problemática. RESULTADOS: Oito pacientes com DP foram tratados e avaliados. A doxiciclina 200 mg/dia reduziu o escore total da UDysRS na semana 12, comparado com a avaliação inicial (χ2 de Friedman = 9.6; p = 0.008). Além disso, a doxiciclina reduziu o tempo em ON com discinesia problemática (χ2 de Friedman = 10.8; p = 0.004) sem piorar o parkinsonismo. Não houve eventos adversos graves, e dispepsia foi o evento mais comum. CONCLUSãO: No presente estudo preliminar, aberto e não-controlado, a doxiciclina foi eficaz em reduzir as DIL e segura após tratamento por 12 semanas. Estudos clínicos bem-desenhados e placebo-controlados adicionais, com duração mais longa e maior número de participantes, são necessários.

Cerebellar stimulation prevents Levodopa-induced dyskinesia in mice and normalizes activity in a motor network.

Chronic Levodopa therapy, the gold-standard treatment for Parkinson's Disease (PD), leads to the emergence of involuntary movements, called levodopa-induced dyskinesia (LID). Cerebellar stimulation has been shown to decrease LID severity in PD patients. Here, in order to determine how cerebellar stimulation induces LID alleviation, we performed daily short trains of optogenetic stimulations of Purkinje cells (PC) in freely moving LID mice. We demonstrated that these stimulations are sufficient to suppress LID or even prevent their development. This symptomatic relief is accompanied by the normalization of aberrant neuronal discharge in the cerebellar nuclei, the motor cortex and the parafascicular thalamus. Inhibition of the cerebello-parafascicular pathway counteracted the beneficial effects of cerebellar stimulation. Moreover, cerebellar stimulation reversed plasticity in D1 striatal neurons and normalized the overexpression of FosB, a transcription factor causally linked to LID. These findings demonstrate LID alleviation and prevention by daily PC stimulations, which restore the function of a wide motor network, and may be valuable for LID treatment.

Effect of the glycine transporter 1 inhibitor ALX-5407 on dyskinesia, psychosis-like behaviours and parkinsonism in the MPTP-lesioned marmoset.

Dyskinesia and psychosis are complications encountered in advanced Parkinson's disease (PD) following long-term therapy with L-3,4-dihydroxyphenylalanine (L-DOPA). Disturbances in the glutamatergic system have been associated with both dyskinesia and psychosis, making glutamatergic modulation a potential therapeutic approach for these. Treatments thus far have sought to dampen glutamatergic transmission, for example through blockade of N-methyl-D-aspartate (NMDA) receptors or modulation of metabotropic glutamate receptors 5. In contrast, activation of the glycine-binding site on NMDA receptors is required for their physiological response. Here, we investigated whether indirectly enhancing glutamatergic transmission through inhibition of glycine re-uptake would be efficacious in diminishing both dyskinesia and psychosis-like behaviours (PLBs) in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-lesioned common marmoset. Six marmosets were rendered parkinsonian by MPTP injection. Following repeated administration of L-DOPA to induce dyskinesia and PLBs, they underwent acute challenges of the glycine transporter 1 (GlyT1) inhibitor ALX-5407 (0.01, 0.1 and 1 mg/kg) or vehicle, in combination with L-DOPA, after which the severity of dyskinesia, PLBs and parkinsonian disability was evaluated. In combination with L-DOPA, ALX-5407 0.1 and 1 mg/kg significantly reduced the severity of dyskinesia, by 51% and 41% (both P < 0.001), when compared to vehicle. ALX-5407 0.01, 0.1 and 1 mg/kg also decreased the severity of global PLBs, by 25%, 51% and 38% (all P < 0.001), when compared to vehicle. The benefits on dyskinesia and PLBs were achieved without compromising the therapeutic effect of L-DOPA on parkinsonism. Our results suggest that GlyT1 inhibition may be a novel strategy to attenuate dyskinesia and PLBs in PD, without interfering with L-DOPA anti-parkinsonian action.

Motor complications in Parkinson's disease: 13-year follow-up of the CamPaIGN cohort.

BACKGROUND: Long-term population-representative data on motor fluctuations and levodopa-induced dyskinesias in Parkinson's disease is lacking. METHODS: The Cambridgeshire Parkinson's Incidence from GP to Neurologist (CamPaIGN) cohort comprises incident PD cases followed for up to 13 years (n = 141). Cumulative incidence of motor fluctuations and levodopa-induced dyskinesias and risk factors were assessed using Kaplan-Meyer and Cox regression analyses. RESULTS: Cumulative incidence of motor fluctuations and levodopa-induced dyskinesias was 54.3% and 14.5%, respectively, at 5 years and 100% and 55.7%, respectively, at 10 years. Higher baseline UPDRS-total and SNCA rs356219(A) predicted motor fluctuations, whereas higher baseline Mini-mental State Examination and GBA mutations predicted levodopa-induced dyskinesias. Early levodopa use did not predict motor complications. Both early motor fluctuations and levodopa-induced dyskinesias predicted reduced mortality in older patients (age at diagnosis >70 years). CONCLUSIONS: Our data support the hypothesis that motor complications are related to the severity of nigrostriatal pathology rather than early levodopa use and indicate that early motor complications do not necessarily confer a negative prognosis. © 2019 International Parkinson and Movement Disorder Society.

Ondansetron, a highly selective 5-HT3 receptor antagonist, reduces L-DOPA-induced dyskinesia in the 6-OHDA-lesioned rat model of Parkinson's disease.

L-3,4-dihydroxyphenylalanine (L-DOPA) has been the standard treatment for Parkinson's disease (PD), despite that its chronic use leads to motor fluctuations and dyskinesia in as many as 95% of patients. Previous studies have shown that serotonin type 3 (5-HT3) receptor blockade reduces dopamine levels within the striatum, suggesting that it could potentially lead to a reduction of dyskinesia. Here, we assessed the effects of ondansetron on L-DOPA-induced abnormal involuntary movements (AIMs) in the 6-hydroxydopamine (6-OHDA)-lesioned rat. We performed two series of experiments. First, rats exhibiting stable AIMs were administered ondansetron (0.0001, 0.001, 0.01, 0.1 and 1 mg/kg) or vehicle in combination with L-DOPA, following which the effect of ondansetron on AIMs was assessed. In the second series of experiments, following 6-OHDA lesion, rats received daily administration of ondansetron (0.0001, 0.001 mg/kg) or vehicle, started concurrently with the first L-DOPA dose, and treatments were continued for 22 days. After a washout period, an acute L-DOPA challenge was administered and AIMs severity was assessed. The effect of ondansetron on L-DOPA anti-parkinsonian action was also determined. We found that the addition of ondansetron 0.0001 mg/kg to L-DOPA resulted in a significant reduction of AIMs severity (by 31%, P < 0.001), when compared to vehicle. Ondansetron 0.0001 mg/kg, when started concurrently with L-DOPA, also attenuated the development of AIMs, with AIMs being 64% less severe (P < 0.05), when compared to L-DOPA/vehicle. Ondansetron did not impair L-DOPA anti-parkinsonian action. Our results suggest that selective 5-HT3 blockade is a promising strategy to reduce the severity of L-DOPA-induced dyskinesia and may also attenuate its development.

Pharmacogenetics of tardive dyskinesia in schizophrenia: The role of CHRM1 and CHRM2 muscarinic receptors.

Objectives: Acetylcholine M (muscarinic) receptors are possibly involved in tardive dyskinesia (TD). The authors tried to verify this hypothesis by testing for possible associations between two muscarinic receptor genes (CHRM1 and CHRM2) polymorphisms and TD in patients with schizophrenia.Methods: A total of 472 patients with schizophrenia were recruited. TD was assessed cross-sectionally using the Abnormal Involuntary Movement Scale. Fourteen allelic variants of CHRM1 and CHRM2 were genotyped using Applied Biosystems amplifiers (USA) and the MassARRAY System by Agena Bioscience.Results: The prevalence of the rs1824024*GG genotype of the CHRM2 gene was lower in TD patients compared to the group without it (χ2 = 6.035, p = 0.049). This suggested that this genotype has a protective effect for the development of TD (OR = 0.4, 95% CI: 0.19-0.88). When age, gender, duration of schizophrenia and dosage of antipsychotic treatment were added as covariates in regression analysis, the results did not reach statistical significance.Conclusions: This study did identify associations between CHRM2 variations and TD; the results of logistic regression analysis with covariates suggest that the association is, however, likely to be secondary to other concomitant factors.

Neurosurgical Approaches to Levodopa-Induced Dyskinesia.

Levodopa has long been the standard of care for Parkinson disease (PD); however, the eventual onset of motor fluctuations and levodopa-induced dyskinesia (LID) complicates its utility in advanced PD. Current neurosurgical interventions remain some of the best options for LID. Deep brain stimulation (DBS) is currently the procedure of choice for patients with advanced PD, patients refractory to medical management, and patients with motor complications from levodopa therapy. Significant progress has been achieved in recent years, however, as newer techniques are making their way through preclinical and clinical studies. Use of interventional magnetic resonance imaging (iMRI) and a skull-mounted aiming device to guide electrode placement has improved accuracy in recent DBS studies. Adaptive "closed-loop" DBS represents another exciting advancement in the field, in which real-time feedback allows dynamic modulation of the stimulation delivered to the basal ganglia. Magnetic resonance-guided focused ultrasound (MRgFUS) is a novel approach to creating precise lesioning in the brain that has shown promising results in preliminary studies for various movement disorders, including dyskinesias, and may transform the neuroablation field. Transcranial magnetic stimulation, which can induce local and distant effects in cortical and subcortical areas, has shown efficacy in managing certain PD and LID symptoms in early studies. Finally, direct stimulation of the motor cortex and the cerebellum has shown therapeutic effects in PD and LID patients in certain studies. Taken together, many of these new techniques have shown great promise in early studies and may eventually be preferred treatment options for LID patients.

Viewpoint: Developing drugs for levodopa-induced dyskinesia in PD: Lessons learnt, what does the future hold?

The drive to develop drugs to treat PD starts and ends with the patient. Herein, we discuss how the experience with drug development for LID has led the field in translational studies in PD with advancing ground-breaking science via rigorous clinical trial design, to deliver clinical proof-of-concepts across multiple therapeutic targets. However, issues remain in advancing drugs efficacious preclinically to the clinic, and future studies need to learn from past successes and failures. Such lessons include implementing better early indicators of tolerability, for instance evaluating non-motor symptoms in preclinical models; improving patient-related outcome measures in clinical trials, as well as considering the unique nature of dyskinesia in an individual patient. The field of translational studies needs to become more patient focused to improve successful outcomes.

Acupuncture Alleviates Levodopa-Induced Dyskinesia via Melanin-Concentrating Hormone in Pitx3-Deficient aphakia and 6-Hydroxydopamine-Lesioned Mice.

Although L-3,4-dihydroxyphenylalanine (L-DOPA) is currently the most effective medication for treating Parkinson's disease (PD) motor symptoms, its prolonged administration causes several adverse effects, including dyskinesia. To identify the mechanisms underlying the effects of acupuncture on L-DOPA-induced dyskinesia (LID), antidyskinetic effects of acupuncture were investigated in two mouse models of PD. Acupuncture stimulation at GB34 alleviated abnormal involuntary movements (AIMs) in Pitx3-deficient aphakia mice (ak/ak) following L-DOPA administration and these effects were reproduced in 6-hydroxydopamine (6-OHDA)-lesioned mice with LID. A transcriptome analysis of the hypothalamus revealed pro-melanin-concentrating hormone (Pmch) gene was highly expressed in acupuncture-treated mouse from ak/ak model of LID as well as 6-OHDA model of LID. Acupuncture combined with the administration of MCH receptor antagonist did not have any beneficial effects on dyskinesia in L-DOPA-injected ak/ak mice, but the intranasal administration of MCH attenuated LID to the same degree as acupuncture in both ak/ak and 6-OHDA mice with LID. A gene expression profile with a hierarchical clustering analysis of the dyskinesia-induced ak/ak mouse brain revealed an association between the mechanisms underlying acupuncture and MCH. Additionally, altered striatal responses to L-DOPA injection were observed after prolonged acupuncture and MCH treatments, which suggests that these treatment modalities influenced the compensatory mechanisms of LID. In summary, present study demonstrated that acupuncture decreased LID via hypothalamic MCH using L-DOPA-administered ak/ak and 6-OHDA mouse models and that MCH administration resulted in novel antidyskinetic effects in these models. Thus, acupuncture and MCH might be valuable therapeutic candidates for PD patients suffering from LID.

Genetic Knockdown of mGluR5 in Striatal D1R-Containing Neurons Attenuates L-DOPA-Induced Dyskinesia in Aphakia Mice.

L-DOPA is the main pharmacological therapy for Parkinson's disease. However, long-term exposure to L-DOPA induces involuntary movements termed dyskinesia. Clinical trials show that dyskinesia is attenuated by metabotropic glutamate receptor type 5 (mGluR5) antagonists. Further, the onset of dyskinesia is delayed by nicotine and mGluR5 expression is lower in smokers than in non-smokers. However, the mechanisms by which mGluR5 modulates dyskinesia and how mGluR5 and nicotine interact have not been established. To address these issues, we studied the role of mGluR5 in D1R-containing neurons in dyskinesia and examined whether nicotine reduces dyskinesia via mGluR5. In the aphakia mouse model of Parkinson's disease, we selectively knocked down mGluR5 in D1R-containing neurons (aphakia-mGluR5KD-D1). We found that genetic downregulation of mGluR5 decreased dyskinesia in aphakia mice. Although chronic nicotine increased the therapeutic effect of L-DOPA in both aphakia and aphakia-mGluR5KD-D1 mice, it caused a robust reduction in dyskinesia only in aphakia, and not in aphakia-mGluR5KD-D1 mice. Downregulating mGluR5 or nicotine treatment after L-DOPA decreased ERK and histone 3 activation, and FosB expression. Combining nicotine and mGluR5 knockdown did not have an added antidyskinetic effect, indicating that the effect of nicotine might be mediated by downregulation of mGluR5 expression. Treatment of aphakia-mGluR5KD-D1 mice with a negative allosteric modulator did not further modify dyskinesia, suggesting that mGluR5 in non-D1R-containing neurons does not play a role in its development. In conclusion, this work suggests that mGluR5 antagonists reduce dyskinesia by mainly affecting D1R-containing neurons and that the effect of nicotine on dyskinetic signs in aphakia mice is likely via mGluR5.

Levodopa-induced dyskinesia in Parkinson disease: Sleep matters.

OBJECTIVE: The spectrum of clinical symptom changes during the course of Parkinson disease (PD). Levodopa therapy, while offering remarkable control of classical motor symptoms, causes abnormal involuntary movements as the disease progresses. This levodopa-induced dyskinesia (LID) has been associated with abnormal cortical plasticity. Because slow wave activity (SWA) of nonrapid eye movement (NREM) sleep underlies adjustment of cortical excitability, we sought to elucidate the relationship between this physiological process and LID. METHODS: Thirty-six patients at different stages of PD underwent whole-night video polysomnography-high-density electroencephalography (vPSG-hdEEG), preceded by 1 week of actigraphy. To represent the broad spectrum of the disease, patients were divided into 3 groups by disease stage-(1) de novo (n = 9), (2) advanced (n = 13), and (3) dyskinetic (DYS; n = 14)-were compared to an age-matched control group (n = 12). The SWA-NREM content of the vPSG-hdEEG was then temporally divided into 10 equal parts, from T1 to T10, and power and source analyses were performed. T2-T3-T4 were considered early sleep and were compared to T7-T8-T9, representing late sleep. RESULTS: We found that all groups, except the DYS group, manifested a clear-cut SWA decrease between early and late sleep. INTERPRETATION: Our data demonstrate a strong pathophysiological association between sleep and PD. Given that SWA may be a surrogate for synaptic strength, our data suggest that DYS patients do not have adequate synaptic downscaling. Further analysis is needed to determine the effect of drugs that can enhance cortical SWA in LID. Ann Neurol 2018;84:905-917.

▼ Safinamide for Parkinson's disease.

▼ Safinamide (Xadago - Zambon S.p.A) is a monoamine-oxidase B (MAO-B) inhibitor licensed as add-on therapy for people with idiopathic Parkinson's disease who are experiencing motor fluctuations with levodopa.1 Currently there is no cure for Parkinson's disease and drugs are used to reduce motor symptoms and improve daily activities.2,3 Here, we review the evidence for this MAO-B inhibitor.

Cardinal Motor Features of Parkinson's Disease Coexist with Peak-Dose Choreic-Type Drug-Induced Dyskinesia.

BACKGROUND: Clinical and anecdotal observations propose that patients with Parkinson's disease (PD) may show drug-induced dyskinesia (DID) concomitantly with cardinal motor features. However, the extent of the concomitant presence of DID and cardinal features remains to be determined. OBJECTIVES: This cross-sectional study measured peak-dose choreic-type DID in a quantitative manner in patients diagnosed with PD, and determined whether symptoms such as tremor, bradykinesia, rigidity, postural instability or freezing of gait (FoG) were still detectable in these patients. METHODS: 89 patients diagnosed with PD were recruited and assessed using a combination of quantitative measures using inertial measurement units to capture DID, tremor, bradykinesia, and FoG. Clinical evaluations were also used to assess rigidity and postural instability. Motor symptoms of PD were assessed 3 times during the testing period, and a series of activities of daily living were repeated twice, in between clinical tests, during which the level of DID was quantified. Peak-dose was identified as the period during which patients had the highest levels of DID. Levels of tremor, rigidity, bradykinesia, postural instability, and FoG were used to determine the percentage of patients showing these motor symptoms simultaneously with DID. RESULTS: 72.4% of patients tested presented with measurable DID during the experiment. Rest, postural and kinetic tremor (12.7% , 38.1% , and 15.9% respectively), bradykinesia (28.6% ), rigidity (55.6% ), postural instability (71.4% ) and FoG (9.5% ) were detected simultaneously with DID. CONCLUSIONS: PD symptomatology remains present in patients showing peak-dose choreic-type DID, illustrating the challenge facing physicians when trying to avoid dyskinesia while attempting to alleviate motor symptoms.

Poor nighttime sleep is positively associated with dyskinesia in Parkinson's disease patients.

BACKGROUND: Dyskinesia is a troublesome complication of long-term dopaminergic medications in Parkinson's disease (PD) patients. Many factors are reported to be associated with dyskinesia in PD. OBJECTIVE: To investigate the association between sleep quality and dyskinesia in patients with PD. METHODS: Four hundred twenty-five patients with PD were enrolled in this study. Demographic information was collected. Unified Parkinson's Disease Rating Scale (UPDRS) and Hoehn and Yahr (H-Y) stage scale were also performed. Epworth Sleepiness Scale (ESS) and Pittsburgh Sleep Quality Index (PSQI) were applied to evaluate daytime sleepiness and overall nighttime sleep quality, respectively, in PD patients. RESULTS: Patients with dyskinesia tended to have a longer duration of disease, higher daily levodopa-equivalent dose (LED), H-Y stage, UPDRS II and PSQI score, and a higher percentage of levodopa treatment than those without dyskinesia. After adjusting for age, sex, age at onset of PD, disease duration, UPDRS I, UPDRS II, UPDRS III, cigarette smoking, use of different antiparkinsonian drugs, phenotype, daily LED, and restless leg syndrome (RLS), PSQI score was still associated with dyskinesia, with corresponding ORs 1.111 (95% CI, 1.004-1.229) as a continuous variable, and 2.469 (95% CI, 1.051-5.800) as a categorical variable, respectively. Further analysis of PSQI components showed that subjective sleep quality and sleep latency were associated with dyskinesia in PD patients. CONCLUSIONS: Our data showed that poor nighttime sleep is positively associated with dyskinesia in PD patients. Attention to the management of nighttime sleep quality may be beneficial to dyskinesia in patients with PD.

The Kinase Fyn As a Novel Intermediate in L-DOPA-Induced Dyskinesia in Parkinson's Disease.

Dopamine replacement therapy with L-DOPA is the treatment of choice for Parkinson's disease; however, its long-term use is frequently associated with L-DOPA-induced dyskinesia (LID). Many molecules have been implicated in the development of LID, and several of these have been proposed as potential therapeutic targets. However, to date, none of these molecules have demonstrated full clinical efficacy, either because they lie downstream of dopaminergic signaling, or due to adverse side effects. Therefore, discovering new strategies to reduce LID in Parkinson's disease remains a major challenge. Here, we have explored the tyrosine kinase Fyn, as a novel intermediate molecule in the development of LID. Fyn, a member of the Src kinase family, is located in the postsynaptic density, where it regulates phosphorylation of the NR2B subunit of the N-methyl-D-aspartate (NMDA) receptor in response to dopamine D1 receptor stimulation. We have used Fyn knockout and wild-type mice, lesioned with 6-hydroxydopamine and chronically treated with L-DOPA, to investigate the role of Fyn in the induction of LID. We found that mice lacking Fyn displayed reduced LID, ΔFosB accumulation and NR2B phosphorylation compared to wild-type control mice. Pre-administration of saracatinib (AZD0530), an inhibitor of Fyn activity, also significantly reduced LID in dyskinetic wild-type mice. These results support that Fyn has a critical role in the molecular pathways affected during the development of LID and identify Fyn as a novel potential therapeutic target for the management of dyskinesia in Parkinson's disease.

Metformin Inhibits the Development of L-DOPA-Induced Dyskinesia in a Murine Model of Parkinson's Disease.

Metformin is a medication that is widely prescribed for the management of type 2 diabetes. In addition to its anti-diabetic uses, metformin has been proposed as a therapeutically effective drug candidate in various central nervous system disorders, including Parkinson's disease (PD). PD is characterized by severe movement defects and is commonly treated with the dopamine (DA) precursor 3,4-dihydroxyphenyl-l-alanine (L-DOPA). However, prolonged use of L-DOPA can lead to the development of L-DOPA-induced dyskinesia (LID). Here, we hypothesized that metformin co-treatment would improve LID in the 6-hydroxydopamine (6-OHDA)-lesioned mouse model of PD. Metformin did not interfere the pharmacotherapeutic effects of L-DOPA in the cylinder test. Furthermore, metformin co-treatment with L-DOPA attenuated the development of LID in unilaterally 6-OHDA-lesioned mice. Metformin showed a long-lasting effect on axial, limb, and orofacial abnormal involuntary movement scores for up to 20 days after treatment initiation. Interestingly, persistent enhancement of the mammalian target of rapamycin, dopamine D1 receptor, and extracellular signaling-regulated kinase 1/2 signaling was maintained in the DA-denervated striatum during metformin treatment. Metformin globally normalized the increased glycogen synthase kinase 3ß activity induced by chronic treatment of L-DOPA in a manner associated with Akt activation in unilaterally 6-OHDA-lesioned mice. These findings suggest that metformin may have therapeutic potential for the suppression or management of L-DOPA-induced motor complications in patients with PD.