Frequency of levodopa-related dyskinesias and motor fluctuations as estimated from the cumulative literature

Phosphodiesterase inhibition and Gucy2C activation enhance tyrosine hydroxylase Ser40 phosphorylation and improve 6-hydroxydopamine-induced motor deficits

BACKGROUND

Parkinson's disease is characterized by a progressive loss of dopaminergic neurons in the nigrostriatal pathway, leading to dopamine deficiency and motor impairments. Current treatments, such as L-DOPA, provide symptomatic relief but result in off-target effects and diminished efficacy over time. This study explores an alternative approach by investigating the activation of tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis. Specifically, we explore the effects of phosphodiesterase (PDE) inhibition and guanylate cyclase-C (GUCY2C) activation on tyrosine hydroxylase Ser40 phosphorylation and their impact on motor behavior in a 6-hydroxydopamine (6-OHDA) Parkinson's disease model.

RESULTS

Our findings demonstrate that increasing cyclic nucleotide levels through PDE inhibition and GUCY2C activation significantly enhances tyrosine hydroxylase Ser40 phosphorylation. In a Pitx3-deficient mouse model, which mimics the loss of dopaminergic neurons seen in Parkinson's disease, Ser40 phosphorylation remained manipulable despite reduced tyrosine hydroxylase protein levels. Moreover, we observed no evidence of tyrosine hydroxylase degradation due to Ser40 phosphorylation, challenging previous reports. Furthermore, both PDE inhibition and GUCY2C activation resulted in improved motor behavior in the 6-OHDA Parkinson's disease mouse model, highlighting the potential therapeutic benefits of these approaches.

CONCLUSIONS

This study underscores the therapeutic potential of enhancing tyrosine hydroxylase Ser40 phosphorylation to improve motor function in Parkinson's disease. Both PDE inhibition and GUCY2C activation represent promising non-invasive strategies to modulate endogenous dopamine biosynthesis and address motor deficits. These findings suggest that targeting cyclic nucleotide pathways could lead to novel therapeutic approaches, either as standalone treatments or in combination with existing therapies like L-DOPA, aiming to provide more durable symptom relief and potentially mitigate neurodegeneration in Parkinson's disease.

Investigating the Mechanisms of Antibody Binding to Alpha-Synuclein for the Treatment of Parkinson's Disease

Parkinson's disease (PD) is an idiopathic neurodegenerative disorder with the second-highest prevalence rate behind Alzheimer's disease. The pathophysiological hallmarks of PD are both degeneration of dopaminergic neurons in the substantia nigra pars compacta and the inclusion of misfolded α-synuclein (α-syn) aggregates known as Lewy bodies. Despite decades of research for potential PD treatments, none have been developed, and developing new therapeutic agents is a time-consuming and expensive process. Computational methods can be used to investigate the properties of drug candidates currently undergoing clinical trials to determine their theoretical efficiency at targeting α-syn. Monoclonal antibodies (mAbs) are biological drugs with high specificity, and Prasinezumab (PRX002) is an mAb currently in Phase II, which targets the C-terminus (AA 118-126) of α-syn. We utilized BioLuminate and PyMol for the structure prediction and preparation of the fragment antigen-binding (Fab) region of PRX002 and 34 different conformations of α-syn. Protein-protein docking simulations were performed using PIPER, and 3 of the docking poses were selected based on the best fit. Molecular dynamics simulations were conducted on the docked protein structures in triplicate for 1000 ns, and hydrogen bonds and electrostatic and hydrophobic interactions were analyzed using MDAnalysis to determine which residues were interacting and how often. Hydrogen bonds were shown to form frequently between the HCDR2 region of PRX002 and α-syn. Free energy was calculated to determine the binding affinity. The predicted binding affinity shows a strong antibody-antigen attraction between PRX002 and α-syn. RMSD was calculated to determine the conformational change of these regions throughout the simulation. The mAb's developability was determined using computational screening methods. Our results demonstrate the efficiency and developability of this therapeutic agent.

Effect of Early Levodopa Treatment on Mortality in People with Parkinson's Disease

BACKGROUND

The ideal timing for initiating levodopa in newly diagnosed people with Parkinson's disease (PD) is uncertain due to limited data on the long-term effects of levodopa.

OBJECTIVE

The aim was to investigate whether early levodopa initiation postpones mortality (primary outcome), the requirement of device-aided therapies, and the incidence of PD-related complications, such as fall-induced injuries.

METHODS

Using nationwide claims data from Dutch hospitals (2012-2020), we grouped newly diagnosed PD individuals as "early initiators" (initiating levodopa within 2 years of diagnosis) or "nonearly initiators." We used the national death registry to assess mortality and health-care claims to assess PD-related complications and device-aided therapies. We used marginal structural models to compare mortality and device-aided therapy rates between groups, and a Poisson regression model to compare PD-related complication rates.

RESULTS

Among 29,943 newly diagnosed PD individuals (mean age at diagnosis: 71.6, 38.5% female), there were 24,847 early and 5096 nonearly levodopa initiators. Over a median 4.25 years, 8109 (27.1%) died. The causal risk ratio for mortality was 1.04 (95% confidence interval [CI] 0.92-1.19) for early versus nonearly initiators. The risk ratio of receiving any device-aided therapy was 3.19 (95% CI 2.56-5.80). No association was observed with incidence of PD-related complications (incidence rate ratio: 1.00, 95% CI 0.96-1.05).

CONCLUSIONS

Early levodopa initiation in PD does neither postpone nor accelerate mortality or PD-related complications, nor does it precipitate earlier occurrence of PD-related complications or mortality. However, we cannot exclude that the results were influenced by residual confounding due to unmeasured risk factors of mortality.

Underutilization of Injectable Parkinson's Disease Medication: An Analysis of Neurologist and Patient Perspectives

BACKGROUND

We hypothesized that many neurologists underestimate patients' willingness to self-administer injectable Parkinson's disease (PD) medication.

OBJECTIVE

To evaluate patient and physician perceptions contributing to underutilization of PD medications for acute OFF episodes.

ANALYTIC METHOD

Data were collected using an online survey including n = 4063 PD patients experiencing OFF episodes and n = 200 neurologists.

RESULTS

89% of patients were willing to self-inject rescue therapies to treat acute OFF episodes. After reviewing patient survey data, 54% of general neurologists and 37% of movement disorder specialist (MDS) demonstrated a change in perceptions about patients' willingness to use self-injected therapies (P < 0.05). 37% of general neurologists and 21% of MDS indicated a greater likelihood of prescribing these treatments (P < 0.05).

CONCLUSIONS

Most patients suffering from OFF episodes would be willing to self-inject to abort their symptoms. Neurologists underestimate this patient acceptance. Understanding patient attitudes and further education about rescue therapies is likely to increase use of these therapies.

The Development of a Quantitative Disability Assessment Tool in Patients with Idiopathic Parkinson's Disease

Background/Objectives: The objective of this study was to develop a novel quantitative disability assessment tool for patients with idiopathic Parkinson's disease (IPD). Methods: A total of 47 patients with IPD were recruited from two hospitals. A specialist in Rehabilitation Medicine utilized the modified Schwab and England Activities of Daily Living Scale (mSEADL) as a reference, conducting a comprehensive medical chart review and an in-depth interview. The novel-developed disability measurement was calculated as ((mSEADL during the on-state) × (time of on-state)) + ((mSEADL during the off-state) × (time of off-state))/(waking time). Additionally, the degree of disability was assessed using the Korean version of the Modified Barthel Index during the on-state. Results: Twenty-four participants (51.1%) exhibited the off-state during waking hours. In patients exhibiting an off-state, the mSEADL score was significantly lower during the off-state than during the on-state (p < 0.05). The novel-developed disability measurement demonstrated a higher correlation coefficient with the reference mSEADL (0.960) than with the K-MBI (0.808), with statistical significance (p < 0.05). Conclusions: The results demonstrated that larger IPD patients exhibited an on-off phenomenon with greater dependency during the off-state. Therefore, the on-off phenomenon should be considered when evaluating disability in patients with IPD, with methods such as the novel-developed disability measurement tool in this study.

Efficacy and safety of Tianqi Pingchan Granule, a compound Chinese herbal medicine, for levodopa-induced dyskinesia in Parkinson's disease: A randomized double-blind placebo-controlled trial

BACKGROUND

Patients with Parkinson's disease (PD) undergoing long-term levodopa therapy are prone to develop levodopa-induced dyskinesia (LID). Amantadine is the main drug recommended for the treatment of LID by current guidelines, but it is far from meeting clinical needs. Tianqi Pingchan Granule (TPG), a compound Chinese herbal medicine, has been developed to relieve symptom of LID.

OBJECTIVE

This randomized controlled trial evaluated the efficacy and safety of the combination of TPG and amantadine for LID.

DESIGN, SETTING, PARTICIPANTS AND INTERVENTIONS

This is a randomized double-blind placebo-controlled trial, conducted from January 2020 to August 2021 at 6 sites in Jiangsu, Zhejiang and Shanghai, China. One hundred PD patients with ≥ 0.5 h of LID were randomly assigned to either the TPG plus amantadine group (TPG group) or the placebo plus amantadine group (placebo group), and treated for a period of 12 weeks. To ensure unbiased results, all study participants, investigators and sponsors were unaware of group allocations. Additionally, the data analysts remained blinded until the analysis was finalized.

MAIN OUTCOME MEASURES

The primary outcome was assessed using the Unified Dyskinesia Rating Scale (UDysRS) (Range 0-104). The key secondary end point was improvement of motor and non-motor symptoms. Safety analyses included all enrolled patients.

RESULTS

One hundred patients were enrolled and randomized into the two treatment groups. The changes in UDysRS at week 12 were -11.02 for the TPG group and -4.19 for the placebo group (treatment difference -6.83 [-10.53 to -3.12]; P = 0.0004). Adverse events were reported for 2 of 50 patients (4.0%) in each of the groups.

CONCLUSION

This study indicated that a 12-week treatment of amantadine plus TPG effectively reduced UDysRS scores and was well tolerated, demonstrating the efficacy and safety of TPG for the treatment of LID in PD.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT04173832.

PLEASE CITE THIS ARTICLE AS

Zhang Y, Zhu XB, Zhao Y, Cui GY, Li WT, Yuan CX, Huang JP, Wan Y, Wu N, Song L, Zhao JH, Liang Y, Xu CY, Liu MJ, Gao C, Chen XX, Liu ZG. Efficacy and safety of Tianqi Pingchan Granule, a compound Chinese herbal medicine, for levodopa-induced dyskinesia in Parkinson's disease: A randomized double-blind placebo-controlled trial. J Integr Med. 2024; 22(5): 545-551.

Effects of home-based EEG neurofeedback training as a non-pharmacological intervention for Parkinson's disease

OBJECTIVES

Aberrant movement-related cortical activity has been linked to impaired motor function in Parkinson's disease (PD). Dopaminergic drug treatment can restore these, but dosages and long-term treatment are limited by adverse side-effects. Effective non-pharmacological treatments could help reduce reliance on drugs. This experiment reports the first study of home-based electroencephalographic (EEG) neurofeedback training as a non-pharmacological candidate treatment for PD. Our primary aim was to test the feasibility of our EEG neurofeedback intervention in a home setting.

METHODS

Sixteen people with PD received six home visits comprising symptomology self-reports, a standardised motor assessment, and a precision handgrip force production task while EEG was recorded (visits 1, 2 and 6); and 3 × 1-hr EEG neurofeedback training sessions to supress the EEG mu rhythm before initiating handgrip movements (visits 3 to 5).

RESULTS

Participants successfully learned to self-regulate mu activity, and this appeared to expedite the initiation of precision movements (i.e., time to reach target handgrip force off-medication pre-intervention = 628 ms, off-medication post-intervention = 564 ms). There was no evidence of wider symptomology reduction (e.g., Movement Disorder Society Unified Parkinson's Disease Rating Scale Part III Motor Examination, off-medication pre-intervention = 29.00, off-medication post intervention = 30.07). Interviews indicated that the intervention was well-received.

CONCLUSION

Based on the significant effect of neurofeedback on movement-related cortical activity, positive qualitative reports from participants, and a suggestive benefit to movement initiation, we conclude that home-based neurofeedback for people with PD is a feasible and promising non-pharmacological treatment that warrants further research.

Exploring causal effects of sarcopenia on risk and progression of Parkinson disease by Mendelian randomization

Previous observational studies suggested that sarcopenia is associated with Parkinson disease (PD), but it is unclear whether this association is causal. The objective of this study was to examine causal associations between sarcopenia-related traits and the risk or progression of PD using a Mendelian randomization (MR) approach. Two-sample bidirectional MR analyses were conducted to evaluate causal relationships. Genome-wide association study (GWAS) summary statistics for sarcopenia-related traits, including right handgrip strength (n = 461,089), left handgrip strength (n = 461,026), and appendicular lean mass (n = 450,243), were retrieved from the IEU OpenGWAS database. GWAS data for the risk of PD were derived from the FinnGen database (4235 cases; 373,042 controls). Summary-level data for progression of PD, including progression to Hoehn and Yahr stage 3, progression to dementia, and development of levodopa-induced dyskinesia, were obtained from a recent GWAS publication on progression of PD in 4093 patients from 12 longitudinal cohorts. Significant causal associations identified in MR analysis were verified through a polygenic score (PGS)-based approach and pathway enrichment analysis using genotype data from the Parkinson's Progression Markers Initiative. MR results supported a significant causal influence of right handgrip strength (odds ratio [OR] = 0.152, 95% confidence interval [CI] = 0.055-0.423, adjusted P = 0.0036) and appendicular lean mass (OR = 0.597, 95% CI = 0.440-0.810, adjusted P = 0.0111) on development of levodopa-induced dyskinesia. In Cox proportional hazard analysis, higher PGSs for right handgrip strength (hazard ratio [HR] = 0.225, 95% CI = 0.095-0.530, adjusted P = 0.0019) and left handgrip strength (HR = 0.303, 95% CI = 0.121-0.59, adjusted P = 0.0323) were significantly associated with a lower risk of developing levodopa-induced dyskinesia, after adjusting for covariates. Pathway enrichment analysis revealed that genome-wide significant single-nucleotide polymorphisms for right handgrip strength were substantially enriched in biological pathways involved in the control of synaptic plasticity. This study provides genetic evidence of the protective role of handgrip strength or appendicular lean mass on the development of levodopa-induced dyskinesia in PD. Sarcopenia-related traits can be promising prognostic markers for levodopa-induced dyskinesia and potential therapeutic targets for preventing levodopa-induced dyskinesia in patients with PD.

New Perspectives for Spinal Cord Stimulation in Parkinson's Disease-Associated Gait Impairment: A Systematic Review

Parkinson's Disease is a neurodegenerative disorder manifesting itself as a hypokinetic movement impairment with postural instability and gait disturbance. In case of failure and/or limited response, deep brain stimulation has been established as an alternative and effective treatment modality. However, a subset of PD patients with gait impairment represents a therapeutic challenge. A systematic review (2000-2023) was performed using PubMed, Embase, Web of Science, Scopus, and Cochrane Library databases to determine the efficacy, stimulation waveform/parameters, spine level, and outcome measures of spinal cord stimulation using different waveforms in PD patients with and without chronic pain. Spinal cord stimulation responsiveness was assessed within the pre-defined follow-up period in three groups (short-term follow-up = 0-3 months; intermediate follow-up = 3-12 months; and long-term follow-up = more than 12 months). In addition, we briefly outline alternative neurostimulation therapies and the most recent developments in closed-loop spinal cord stimulation relevant to PD. In summary, 18 publications and 70 patients from uncontrolled observational trials were included, with low-quality evidence and conflicting findings. First and foremost, the currently available data do not support the use of spinal cord stimulation to treat PD-related gait disorders but have confirmed its usefulness for PD-associated chronic pain.

Control of Dopamine Signal in High-Order Receptor Complex on Striatal Astrocytes

The receptor-receptor interaction (RRI) of G protein-coupled receptors (GPCRs) leads to new functional entities that are conceptually distinct from the simple addition of signals mediated by the activation of the receptors that form the heteromers. Focusing on astrocytes, there is evidence for the existence of inhibitory and facilitatory RRIs, including the heteromers formed by the adenosine A2A and the dopamine D2 receptors, by A2A and the oxytocin receptor (OTR), and the D2-OTR heteromers. The possible involvement of these receptors in mosaicism has never been investigated in striatal astrocytes. By biophysical and functional approaches, we focused our attention on the existence of an A2A-D2-OTR high-order receptor complex and its role in modulating cytosolic calcium levels and endogenous glutamate release, when striatal astrocyte processes were stimulated with 4-aminopyridine. Functional data indicate a permissive role of OTR on dopamine signaling in the regulation of the glutamatergic transmission, and an inhibitory control mediated by A2A on both the D2-mediated signaling and on the OTR-facilitating effect on D2. Imaging biochemical and bioinformatic evidence confirmed the existence of the A2A-D2-OTR complex and its ternary structure in the membrane. In conclusion, the D2 receptor appears to be a hotspot in the control of the glutamate release from the astrocytic processes and may contribute to the regulation and integration of different neurotransmitter-mediated signaling in the striatum by the A2A-D2-OTR heterotrimers. Considering the possible selectivity of allosteric interventions on GPCRs organized as receptor mosaics, A2A-D2-OTR heterotrimers may offer selective pharmacological targets in neuropsychiatric disorders and neurodegenerative diseases.

5-HT4R agonism reduces L-DOPA-induced dyskinesia via striatopallidal neurons in unilaterally 6-OHDA lesioned mice

Parkinson's disease is caused by a selective vulnerability and cell loss of dopaminergic neurons of the Substantia Nigra pars compacta and, consequently, striatal dopamine depletion. In Parkinson's disease therapy, dopamine loss is counteracted by the administration of L-DOPA, which is initially effective in ameliorating motor symptoms, but over time leads to a burdening side effect of uncontrollable jerky movements, termed L-DOPA-induced dyskinesia. To date, no efficient treatment for dyskinesia exists. The dopaminergic and serotonergic systems are intrinsically linked, and in recent years, a role has been established for pre-synaptic 5-HT1a/b receptors in L-DOPA-induced dyskinesia. We hypothesized that post-synaptic serotonin receptors may have a role and investigated the effect of modulation of 5-HT4 receptor on motor symptoms and L-DOPA-induced dyskinesia in the unilateral 6-OHDA mouse model of Parkinson's disease. Administration of RS 67333, a 5-HT4 receptor partial agonist, reduces L-DOPA-induced dyskinesia without altering L-DOPA's pro-kinetic effect. In the dorsolateral striatum, we find 5-HT4 receptor to be predominantly expressed in D2R-containing medium spiny neurons, and its expression is altered by dopamine depletion and L-DOPA treatment. We further show that 5-HT4 receptor agonism not only reduces L-DOPA-induced dyskinesia, but also enhances the activation of the cAMP-PKA pathway in striatopallidal medium spiny neurons. Taken together, our findings suggest that agonism of the post-synaptic serotonin receptor 5-HT4 may be a novel therapeutic approach to reduce L-DOPA-induced dyskinesia.

Model-based comparison of subcutaneous versus sublingual apomorphine administration in the treatment of motor fluctuations in Parkinson's disease

The objective of this study was to compare the effectiveness of subcutaneous (SC) and sublingual (SL) formulations of apomorphine for the treatment of motor fluctuations in Parkinson's disease using a pharmacokinetics (PK)/pharmacodynamics (PD) modeling approach. The PK of SC and SL apomorphine are best described by a one-compartment model with first-order absorption and a two-compartment model with delayed absorption, respectively. The PK/PD model relating apomorphine plasma concentrations to the Unified Parkinson's Disease Rating Scale (UPDRS) motor scores was described by a sigmoidal Emax model assuming effective concentration = drug concentration in an effect compartment. Apomorphine concentrations and UPDRS motor scores were simulated from the PK/PD models using 500 hypothetical subjects. UPDRS motor score change from baseline was evaluated using time to clinically relevant response, response duration, area under the curve, maximal response, and time to maximal response. Higher doses of each apomorphine formulation were associated with shorter time to response, longer response duration, and greater maximal response. Although the mean maximal responses to SC and SL apomorphine were comparable, the time to response was four times shorter (7 vs. 31 min) and time to maximal response was two times shorter (27 vs. 61 min) for 4 mg SC vs. 50 mg SL. Thus, faster onset of action was observed for the SC formulation compared to SL. These data may be useful for physicians when selecting "on demand" therapy for patients with Parkinson's disease experiencing motor fluctuations.

DRD4 gene polymorphism and impulse control disorder induced by dopamine agonists in Parkinson's disease

Impulse control disorders and their consequences display variability among individuals, indicating potential involvement of environmental and genetic factors. In this retrospective study, we analyzed a cohort of Parkinson's disease patients treated with dopamine agonists and investigated the influence of the dopamine D4 receptor gene polymorphism, DRD4 7R+, which is linked to psychiatric disorders, impulsive traits, and addictive behaviors. We found that DRD4 7R+ is a significant genetic risk factor associated with the severity of ICD.

Autoradiographic labelling of metabotropic glutamate type 2/3 receptors in the hemi-parkinsonian rat brain

L-3,4-dihydroxyphenylalanine (L-DOPA) is the treatment of choice for Parkinson's disease (PD) motor symptoms, but its chronic use is hindered by complications such as dyskinesia. Pre-clinical studies discovered that activation of metabotropic glutamate type 2 and 3 (mGlu2/3) receptors alleviates L-DOPA-induced dyskinesia. To gain mechanistic insight into the anti-dyskinetic activity of mGlu2/3 activation, we performed autoradiographic binding with [3H]-LY-341,495 in brain sections from L-DOPA-treated 6-hydroxydopamine (6-OHDA)-lesioned rats that developed mild or severe dyskinesia, as well as L-DOPA-untreated 6-OHDA-lesioned and sham-lesioned animals. In the ipsilateral hemisphere, mildly dyskinetic 6-OHDA-lesioned rats showed a decrease in [3H]-LY-341,495 binding in the entopeduncular nucleus (EPN, 30 % vs sham-lesioned rats, P<0.05), globus pallidus (GP, 28 % vs sham-lesioned rats, P<0.05; 23 % vs L-DOPA-untreated 6-OHDA-lesioned rats, P<0.001), and primary motor cortex (49 % vs sham-lesioned rats, P<0.05; 45 % vs L-DOPA-untreated 6-OHDA-lesioned rats, P<0.001). Severely dyskinetic 6-OHDA-lesioned rats exhibited an increase in binding in the primary motor cortex (43 % vs mildly dyskinetic 6-OHDA-lesioned rats, P<0.05). In the contralateral hemisphere, mildly dyskinetic 6-OHDA-lesioned rats harboured a decrease in binding in the EPN (30 % vs sham-lesioned rats; 24 % vs L-DOPA-untreated 6-OHDA-lesioned rats, both P<0.05), GP (34 % vs sham-lesioned rats, P<0.05; 23 % vs L-DOPA-untreated 6-OHDA-lesioned rats, P<0.001), and primary motor cortex (50 % vs sham-lesioned rats; 44 % vs L-DOPA-untreated 6-OHDA-lesioned rats, both P<0.05). Severely dyskinetic 6-OHDA-lesioned rats presented a decrease in binding in the GP (30 % vs sham-lesioned rats; 19 % vs L-DOPA-untreated 6-OHDA-lesioned rats, both P<0.05). Abnormal involuntary movements scores of 6-OHDA-lesioned animals were positively correlated with [3H]-LY-341,495 binding in the ipsilateral striatum, ipsilateral EPN, ipsilateral primary motor cortex and contralateral primary motor cortex (all P<0.05). These results suggest that alterations in mGlu2/3 receptor levels may be part of an endogenous compensatory mechanism to alleviate dyskinesia.

Differential Activation States of Direct Pathway Striatal Output Neurons during l-DOPA-Induced Dyskinesia Development

l-DOPA-induced dyskinesia (LID) is a debilitating motor side effect arising from chronic dopamine (DA) replacement therapy with l-DOPA for the treatment of Parkinson's disease. LID is associated with supersensitivity of striatal dopaminergic signaling and fluctuations in synaptic DA following each l-DOPA dose, shrinking the therapeutic window. The heterogeneous composition of the striatum, including subpopulations of medium spiny output neurons (MSNs), interneurons, and supporting cells, complicates the identification of cell(s) underlying LID. We used single-nucleus RNA sequencing (snRNA-seq) to establish a comprehensive striatal transcriptional profile during LID development. Male hemiparkinsonian mice were treated with vehicle or l-DOPA for 1, 5, or 10 d, and striatal nuclei were processed for snRNA-seq. Analyses indicated a limited population of DA D1 receptor-expressing MSNs (D1-MSNs) formed three subclusters in response to l-DOPA treatment and expressed cellular markers of activation. These activated D1-MSNs display similar transcriptional changes previously associated with LID; however, their prevalence and transcriptional behavior were differentially influenced by l-DOPA experience. Differentially expressed genes indicated acute upregulation of plasticity-related transcription factors and mitogen-activated protein kinase signaling, while repeated l-DOPA-induced synaptic remodeling, learning and memory, and transforming growth factor-β (TGF-β) signaling genes. Notably, repeated l-DOPA sensitized Inhba, an activin subunit of the TGF-β superfamily, in activated D1-MSNs, and its pharmacological inhibition impaired LID development, suggesting that activin signaling may play an essential role in LID. These data suggest distinct subsets of D1-MSNs become differentially l-DOPA-responsive due to aberrant induction of molecular mechanisms necessary for neuronal entrainment, similar to processes underlying hippocampal learning and memory.

Angiotensin-converting enzyme inhibition prevents l-dopa-induced dyskinesia in a 6-ohda-induced mouse model of Parkinson's disease

Parkinson's disease (PD) is characterised by severe movement defects and the degeneration of dopaminergic neurones in the midbrain. The symptoms of PD can be managed with dopamine replacement therapy using L-3, 4-dihydroxyphenylalanine (L-dopa), which is the gold standard therapy for PD. However, long-term treatment with L-dopa can lead to motor complications. The central renin-angiotensin system (RAS) is associated with the development of neurodegenerative diseases in the brain. However, the role of the RAS in dopamine replacement therapy for PD remains unclear. Here, we tested the co-treatment of the angiotensin-converting enzyme inhibitor (ACEI) with L-dopa altered L-dopa-induced dyskinesia (LID) in a 6-hydroxydopamine (6-OHDA)-lesioned mouse model of PD. Perindopril, captopril, and enalapril were used as ACEIs. The co-treatment of ACEI with L-dopa significantly decreased LID development in 6-OHDA-lesioned mice. In addition, the astrocyte and microglial transcripts involving Ccl2, C3, Cd44, and Iigp1 were reduced by co-treatment with ACEI and L-dopa in the 6-OHDA-lesioned striatum. In conclusion, co-treatment with ACEIs and L-dopa, such as perindopril, captopril, and enalapril, may mitigate the severity of L-DOPA-induced dyskinesia in a mouse model of PD.

Pathological cell assembly dynamics in a striatal MSN network model

Under normal conditions the principal cells of the striatum, medium spiny neurons (MSNs), show structured cell assembly activity patterns which alternate sequentially over exceedingly long timescales of many minutes. It is important to understand this activity since it is characteristically disrupted in multiple pathologies, such as Parkinson's disease and dyskinesia, and thought to be caused by alterations in the MSN to MSN lateral inhibitory connections and in the strength and distribution of cortical excitation to MSNs. To understand how these long timescales arise we extended a previous network model of MSN cells to include synapses with short-term plasticity, with parameters taken from a recent detailed striatal connectome study. We first confirmed the presence of sequentially switching cell clusters using the non-linear dimensionality reduction technique, Uniform Manifold Approximation and Projection (UMAP). We found that the network could generate non-stationary activity patterns varying extremely slowly on the order of minutes under biologically realistic conditions. Next we used Simulation Based Inference (SBI) to train a deep net to map features of the MSN network generated cell assembly activity to MSN network parameters. We used the trained SBI model to estimate MSN network parameters from ex-vivo brain slice calcium imaging data. We found that best fit network parameters were very close to their physiologically observed values. On the other hand network parameters estimated from Parkinsonian, decorticated and dyskinetic ex-vivo slice preparations were different. Our work may provide a pipeline for diagnosis of basal ganglia pathology from spiking data as well as for the design pharmacological treatments.

Allopregnanolone and its antagonist modulate neuroinflammation and neurological impairment

Neuroinflammation accompanies several brain disorders, either as a secondary consequence or as a primary cause and may contribute importantly to disease pathogenesis. Neurosteroids which act as Positive Steroid Allosteric GABA-A receptor Modulators (Steroid-PAM) appear to modulate neuroinflammation and their levels in the brain may vary because of increased or decreased local production or import from the systemic circulation. The increased synthesis of steroid-PAMs is possibly due to increased expression of the mitochondrial cholesterol transporting protein (TSPO) in neuroinflammatory tissue, and reduced production may be due to changes in the enzymatic activity. Microglia and astrocytes play an important role in neuroinflammation, and their production of inflammatory mediators can be both activated and inhibited by steroid-PAMs and GABA. What is surprising is the finding that both allopregnanolone, a steroid-PAM, and golexanolone, a novel GABA-A receptor modulating steroid antagonist (GAMSA), can inhibit microglia and astrocyte activation and normalize their function. This review focuses on the role of steroid-PAMs in neuroinflammation and their importance in new therapeutic approaches to CNS and liver disease.

IRL790 modulated striatal D1 neurons synaptic plasticity ameliorating levodopa-induced dyskinesia in mouse

Objective

Levodopa (L-dopa) therapy is the principal pharmacological treatment for Parkinson's disease (PD). Nevertheless, prolonged use of this drug may result in different involuntary movement symptoms caused by the medication, referred to as levodopa-induced dyskinesia (LID). LID is associated with changes in synaptic plasticity of the D1 medium spiny neurons (MSNs) located in the dorsal striatum (dStr). Within the striatum, the amount of Dopamine D3 receptor (D3R) is notably increased in LID, demonstrating colocalization with D1R expression in neurons, and the level of D3R expression is directly related to the intensity of LID. IRL 790, as a D3R antagonist, can ameliorate LID. This study aims to explore if IRL 790 improves LID by regulating the synaptic plasticity of D1+ MSNs in dStr.

Methods

The electrophysiology and synaptic spine density of D1+ MSNs in dStr were recorded for sham mice, LID mice, and LID mice treated with IRL 790. The regulation of synaptic plasticity in LID D1+ MSNs by IRL 790 was analyzed. Behavioral tests were conducted to confirm the treatment effect of IRL 790 on LID.

Results

In LID D1+ MSNs, there was persistent abnormal LTP, absence of LTD, and an increase in spontaneous excitatory postsynaptic currents (sEPSCs). IRL 790 treatment restored normal LTP, LTD, and sEPSCs. Treatment with IRL 790 also restored the reduced dendritic spine density in D1+ MSNs of LID mice. IRL790 improved dyskinetic manifestations in LID mice.

Conclusion

IRL790 ameliorates LID by regulating the synaptic structure and functional plasticity of striatal D1+ MSNs.

Neuroinflammation and Dyskinesia: A Possible Causative Relationship?

Levodopa (L-DOPA) treatment represents the gold standard therapy for Parkinson's disease (PD) patients. L-DOPA therapy shows many side effects, among them, L-DOPA-induced dyskinesias (LIDs) remain the most problematic. Several are the mechanisms underlying these processes: abnormal corticostriatal neurotransmission, pre- and post-synaptic neuronal events, changes in gene expression, and altered plasticity. In recent years, researchers have also suggested non-neuronal mechanisms as a possible cause for LIDs. We reviewed recent clinical and pre-clinical studies on neuroinflammation contribution to LIDs. Microglia and astrocytes seem to play a strategic role in LIDs phenomenon. In particular, their inflammatory response affects neuron-glia communication, synaptic activity and neuroplasticity, contributing to LIDs development. Finally, we describe possible new therapeutic interventions for dyskinesia prevention targeting glia cells.

Sublingual apomorphine in treatment of Parkinson's disease: a review

PURPOSE

A majority of advanced Parkinson's disease (PD) patients on oral levodopa experience motor fluctuations, including sudden OFF and delayed ON periods. Fast-acting rescue medications are a vital part of the clinician's armamentarium in the treatment of motor fluctuations. Sublingual apomorphine is the first sublingual rescue medication on the market for the treatment of OFF times in PD.Materials and Methods: Here, we review the development and pharmacology of apomorphine in the treatment of PD as well as the safety and efficacy of sublingual apomorphine established in clinical trials. Finally, we compare sublingual apomorphine to the other rescue medications available and provide our opinion on the use of sublingual apomorphine in clinical practice.Results: Clinical trials have demonstrated that sublingual apomorphine is a safe and effective option in the treatment of motor fluctuations in PD. In a Phase II trial, 100% of patients who achieved a full ON response did so within 30 min and 40% did so within 15 min. The mean duration of effect was 50 min. In a Phase III trial, 77.3% of patients achieved a full ON response. Side effects such as nausea, dizziness and somnolence were common but were generally mild. No patients experienced worsening dyskinesia.Conclusions: Sublingual apomorphine will provide patients with motor fluctuations due to advanced PD another safe and effective option for the treatment of OFF times.

Long-term benefits of hematopoietic stem cell-based macrophage/microglia delivery of GDNF to the CNS in a mouse model of Parkinson's disease

Glial cell line-derived neurotrophic factor (GDNF) protects dopaminergic neurons in various models of Parkinson's disease (PD). Cell-based GDNF gene delivery mitigates neurodegeneration and improves both motor and non-motor functions in PD mice. As PD is a chronic condition, this study aims to investigate the long-lasting benefits of hematopoietic stem cell (HSC)-based macrophage/microglia-mediated CNS GDNF (MMC-GDNF) delivery in an MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine) mouse model. The results indicate that GDNF treatment effectively ameliorated MPTP-induced motor deficits for up to 12 months, which coincided with the protection of nigral dopaminergic neurons and their striatal terminals. Also, the HSC-derived macrophages/microglia were recruited selectively to the neurodegenerative areas of the substantia nigra. The therapeutic benefits appear to involve two mechanisms: (1) macrophage/microglia release of GDNF-containing exosomes, which are transferred to target neurons, and (2) direct release of GDNF by macrophage/microglia, which diffuses to target neurons. Furthermore, the study found that plasma GDNF levels were significantly increased from baseline and remained stable over time, potentially serving as a convenient biomarker for future clinical trials. Notably, no weight loss, altered food intake, cerebellar pathology, or other adverse effects were observed. Overall, this study provides compelling evidence for the long-term therapeutic efficacy and safety of HSC-based MMC-GDNF delivery in the treatment of PD.

Dyskinesia and Pain in Advanced Parkinson's Disease: Post Hoc Analysis from the Phase 3b, Open-Label, Randomized DYSCOVER Study

INTRODUCTION

The DYSCOVER study was a phase 3b, open-label, randomized trial (NCT02799381) that evaluated levodopa-carbidopa intestinal gel (LCIG) versus optimized medical treatment (OMT) in patients with Parkinson's disease (PD) and a high burden of dyskinesia at baseline (defined as Unified Dyskinesia Rating Scale [UDysRS] total score ≥ 30). At week 12, patients receiving LCIG versus OMT experienced significant improvements in dyskinesia, pain, and health-related outcomes. The objective of this analysis was to examine correlations between dyskinesia, pain, and health-related outcomes in PD.

METHODS

This post hoc analysis assessed correlations between UDysRS, King's Parkinson's Disease Pain Scale (KPPS), 8-item Parkinson's Disease Questionnaire (PDQ-8), Unified Parkinson's Disease Rating Scale part II, Clinical Global Impression of Severity (CGI-S) or Change (CGI-C), and "On" time without troublesome dyskinesia at baseline and after 12 weeks of LCIG or OMT. Correlations were assessed by Pearson correlation coefficients (categorization: weak, r = 0.20-0.39; moderate, r = 0.40-0.59; strong, r ≥ 0.60).

RESULTS

Among 61 patients, moderate-to-strong positive and significant correlations were observed between UDysRS and KPPS scores (baseline, r = 0.47; week 12 change from baseline [CFB], r = 0.63; all p < 0.001). UDysRS and KPPS scores had moderate-to-strong positive and highly significant correlations with PDQ-8 scores (baseline, r = 0.45 and 0.46, respectively; CFB, r = 0.54 and 0.64, respectively; all p < 0.001). Moderate positive and significant correlations were observed between UDysRS and CGI-S/CGI-C scores (baseline, r = 0.41; CFB, r = 0.47; all p < 0.001).

CONCLUSIONS

In patients with high dyskinesia burden, positive correlations were observed between dyskinesia, pain, and health-related quality of life (HRQoL) at baseline. Improvements in dyskinesia and pain were associated with improvements in HRQoL, demonstrating the clinical burden of troublesome dyskinesia.

TRIAL REGISTRATION NUMBER

Clinicaltrials.gov identifier NCT02799381.

Parkinson's disease progression is multifaceted: Evidence for the underlying benchmarks

Long-term Parkinson's disease (PD) progression is not a homogeneous process and manifests in diverse ways over the lifetime. Recognition of progression benchmarks and their substrates is important for treatment and addressing the expectations of patients, as well as for PD research planning.

Levodopa-Entacapone-Carbidopa Intestinal Gel in the Treatment of Advanced Parkinson's Disease: A Single Center Real-World Experience

Levodopa-entacapone-carbidopa intestinal gel infusion is a relatively new treatment option for advanced Parkinson's disease. We aimed to describe and analyze the characteristics of de novo levodopa-entacapone-carbidopa intestinal gel therapy in 20 consecutive patients with advanced Parkinson's disease. We assessed the profile of motor complications by evaluating the following: motor fluctuations, dyskinesias, and the freezing phenomenon at baseline (before the testing period) and before discharge. The treatment significantly reduced the duration of daily hours spent in off time compared with baseline pre-treatment values from a mean of 4.8 ± 0.9 h/day to a mean of 1.4 ± 0.5 h per day (p < 0.001). The duration and severity of peak-dose dyskinesia were also significantly reduced compared with baseline values. Out of the 10 patients who reported freezing, 8 did not present this complication at the pre-discharge assessment. Significant improvements were observed in Hoehn and Yahr scale scores in both the on and off states. The levodopa-entacapone-carbidopa intestinal gel therapy was well tolerated during the follow-up period immediately after initiation. Despite a relatively severe stage of the disease, all patients experienced a significant improvement in motor fluctuations, dyskinesias, and the freezing phenomenon.

Unraveling the interplay between dyskinesia and overactive bladder symptoms in Parkinson's disease: a comprehensive cohort study based on the long-term follow-up database of Parkinson's disease

OBJECTIVES

Overactive bladder (OAB) and dyskinesia are frequent complications in patients with Parkinson's disease (PD). However, the correlation between OAB and dyskinesia has been insufficiently explored. The purpose of this study was to examine the relationship between dyskinesia, OAB, and clinical characteristics among individuals with PD.

METHODS

1338 PD patients were included in the present study. Demographic features were compared between patients with or without dyskinesia and OAB symptoms. Logistic regression was conducted on dyskinesia to screen clinically relevant factors. Overactive Bladder Symptom Score (OABSS) was further used to stratify the association between the severity of OAB and the occurrence of dyskinesia.

RESULTS

This study indicates that both dyskinesia and OAB are significantly related to disease severity and cognitive status. PD patients with dyskinesia and OAB having higher UPDRS scores (p < 0.001), H-Y scores (p < 0.001), NMSQ (p < 0.001) and MoCA scores (p < 0.001), and lower MMSE scores (p < 0.001) are identified. The multivariate logistic regression confirms that disease duration (p = 0.041), LEDD (p < 0.001), UPDRSII (p < 0.001), MoCA (p = 0.024), urgency (p < 0.001), frequency (p < 0.001), and nocturia (p = 0.002) are independent risk factors for dyskinesia. Trend analysis indicates that the risk of dyskinesia significantly increases when patients exhibit moderate to severe OAB symptoms (OABSS > 5) (p < 0.001). No significant interactions were found between OABSS and age, gender, disease duration, LEDD, and NMSQ scores in different subgroups, indicating that dyskinesia is more pronounced in patients with OABSS > 5.

DISCUSSION

This study provides compelling evidence supporting the strong correlation between OAB and dyskinesia in PD patients, emphasizing the presence of shared pathogenic mechanisms between these two conditions. Our findings underscore the importance of considering both OAB and dyskinesia in the clinical management of PD, investigating the intricate connections between OAB and dyskinesia could unveil valuable insights into the complex pathophysiology of PD and potentially identify novel therapeutic targets for more effective PD treatment strategies.

Association of dopamine receptor D3 polymorphism with Levodopa-induced Dyskinesia: A study on Parkinson's disease patients from India

INTRODUCTION

Levodopa-induced dyskinesia (LID) is a debilitating motor feature in a subset of patients with Parkinson's disease (PD) after prolonged therapeutic administration of levodopa. Preliminary animal and human studies are suggestive of a key role of dopamine type 3 (D3) receptor polymorphism (Ser9Gly; rs6280) in LID. Its contribution to development of LID among Indian PD patients has remained relatively unexplored and merits further investigation.

METHODS AND MATERIALS

200 well-characterised PD patients (100 without LID and 100 with LID) and 100 age-matched healthy controls were recruited from the outpatient department of Institute of Neurosciences Kolkata. MDS-UPDRS (Unified Parkinson's Disease Rating Scale from International Movement Disorder Society) Part III and AIMS (abnormal involuntary movement scale) were performed for estimation of severity of motor features and LID respectively in the ON state of the disease. Participants were analysed for the presence of Ser9Gly single nucleotide variant (SNV) (rs6280) by polymerase chain reaction followed by restriction fragment length polymorphism techniques.

RESULTS

The frequency of AA genotype (serine type) was more frequently present in PD patients with LID compared to PD patients without LID (50 % vs 28 %; P = 0.002; OR = 2.57, 95 % CI: 1.43 - 4.62). The abnormal involuntary movement scale score was significantly higher in PD patients with AA genotype compared to carriers of glycine allele (AG + GG) (4.08 ± 3.35; P = 0.002).

CONCLUSION

We observed a significant association of serine type SNV (rs6280) in D3 receptor gene in a cohort of PD patients with LID from India. More severe motor severity was found in patients with glycine substitution of the same SNV. The current study emphasised the role of D3 receptor in the pathogenesis of LID.

The Expression and Functionality of CB1R-NMDAR Complexes Are Decreased in A Parkinson's Disease Model

One of the hallmarks of Parkinson's disease (PD) is the alteration in the expression and function of NMDA receptor (NMDAR) and cannabinoid receptor 1 (CB1R). The presence of CB1R-NMDAR complexes has been described in neuronal primary cultures. The activation of CB1R in CB1R-NMDAR complexes was suggested to counteract the detrimental NMDAR overactivation in an AD mice model. Thus, we aimed to explore the role of this receptor complex in PD. By using Bioluminescence Resonance Energy Transfer (BRET) assay, it was demonstrated that α-synuclein induces a reorganization of the CB1R-NMDAR complex in transfected HEK-293T cells. Moreover, α-synuclein treatment induced a decrease in the cAMP and MAP kinase (MAPK) signaling of both CB1R and NMDAR not only in transfected cells but also in neuronal primary cultures. Finally, the interaction between CB1R and NMDAR was studied by Proximity Ligation Assay (PLA) in neuronal primary cultures, where it was observed that the expression of CB1R-NMDAR complexes was decreased upon α-synuclein treatment. These results point to a role of CB1R-NMDAR complexes as a new therapeutic target in Parkinson's disease.

Starting with 24-h levodopa carbidopa intestinal gel at initiation in a large cohort of advanced Parkinson's disease patients

Continuous intra-jejunal infusion of levodopa-carbidopa intestinal gel (LCIG) is a long-term proven and effective treatment in advanced Parkinson's Disease (APD). Efficacy and safety of 16-h administration of LCIG has already been established. Additional benefits of 24-h LCIG administration have been reported in several case series and small clinical studies. The aim of this retrospective study was to compare the characteristics of patients who needed 24-h LCIG from the beginning of the DAT (device-aided treatment) with those who remained with the standard 16-h LCIG treatment and to identify particular motives if any. We initiated LCIG in 150 patients out of which in case of 62 patients (41,3%) due to unsatisfactory initial clinical benefits continuous 24-h LCIG was deemed necessary. Despite the subjective complaints and more severe clinical condition, at baseline evaluation we found statistically significant differences between 16-h LCIG cohort and 24-h LCIG cohort only in case of incidence of freezing (47% vs 65%, p = 0.03) and sudden off (32% vs 48%, p = 0.04). Wake hours/daytime LCIG does not always sufficiently improve the patient's quality of life in some patients due to persistent nighttime troublesome symptoms. Instead of labeling the patient as a non-responder, it is worth trying the 24-h LCIG dosage in a carefully selected group of patients, as there is currently no consensus on reliable criteria that serve the decision in these patients.

Microstructural and functional alterations of the ventral pallidum are associated with levodopa-induced dyskinesia in Parkinson's disease

BACKGROUND AND PURPOSE

The ventral pallidum (VP) regulates involuntary movements, but it is unclear whether the VP regulates the abnormal involuntary movements in Parkinson's disease (PD) patients who have levodopa-induced dyskinesia (LID). To further understand the role of the VP in PD patients with LID (PD-LID), we explored the structural and functional characteristics of the VP in such patients using multimodal magnetic resonance imaging (MRI).

METHODS

Thirty-one PD-LID patients, 39 PD patients without LID (PD-nLID), and 28 healthy controls (HCs) underwent T1-weighted MRI, quantitative susceptibility mapping, multi-shell diffusion MRI, and resting-state functional MRI (rs-fMRI). Different measures characterizing the VP were obtained using a region-of-interest-based approach.

RESULTS

The left VP in the PD-LID group showed significantly higher intracellular volume fraction (ICVF) and isotropic volume fraction (IsoVF) compared with the PD-nLID and HC groups. Rs-MRI revealed that, compared with the PD-nLID group, the PD-LID group in the medication 'off' state had higher functional connectivity (FC) between the left VP and the left anterior caudate, left middle frontal gyrus and left precentral gyrus, as well as between the right VP and the right posterior ventral putamen and right mediodorsal thalamus. In addition, the ICVF values of the left VP, the FC between the left VP and the left anterior caudate and left middle frontal gyrus were positively correlated with Unified Dyskinesia Rating Scale scores.

CONCLUSION

Our multimodal imaging findings show that the microstructural changes of the VP (i.e., the higher ICVF and IsoVF) and the functional change in the ventral striatum-VP-mediodorsal thalamus-cortex network may be associated with pathophysiological mechanisms of PD-LID.

The multifaceted functions of β-arrestins and their therapeutic potential in neurodegenerative diseases

Arrestins are multifunctional proteins that regulate G-protein-coupled receptor (GPCR) desensitization, signaling, and internalization. The arrestin family consists of four subtypes: visual arrestin1, β-arrestin1, β-arrestin2, and visual arrestin-4. Recent studies have revealed the multifunctional roles of β-arrestins beyond GPCR signaling, including scaffolding and adapter functions, and physically interacting with non-GPCR receptors. Increasing evidence suggests that β-arrestins are involved in the pathogenesis of a variety of neurodegenerative diseases, including Alzheimer's disease (AD), frontotemporal dementia (FTD), and Parkinson's disease (PD). β-arrestins physically interact with γ-secretase, leading to increased production and accumulation of amyloid-beta in AD. Furthermore, β-arrestin oligomers inhibit the autophagy cargo receptor p62/SQSTM1, resulting in tau accumulation and aggregation in FTD. In PD, β-arrestins are upregulated in postmortem brain tissue and an MPTP model, and the β2AR regulates SNCA gene expression. In this review, we aim to provide an overview of β-arrestin1 and β-arrestin2, and describe their physiological functions and roles in neurodegenerative diseases. The multifaceted roles of β-arrestins and their involvement in neurodegenerative diseases suggest that they may serve as promising therapeutic targets.

Identification of SV2C and DENR as Key Biomarkers for Parkinson's Disease Based on Bioinformatics, Machine Learning, and Experimental Verification

The objective of this study is to investigate the potential biomarkers and therapeutic target genes for Parkinson's disease (PD). We analyzed four datasets (GSE8397, GSE20292, GSE20163, GSE20164) from the Gene Expression Omnibus database. We employed weighted gene co-expression network analysis and differential expression analysis to select genes and perform functional analysis. We applied three algorithms, namely, random forest, support vector machine recursive feature elimination, and least absolute shrinkage and selection operator, to identify hub genes, perform functional analysis, and assess their clinical diagnostic potential using receiver operating characteristic (ROC) curve analysis. We employed the xCell website to evaluate differences in the composition patterns of immune cells in the GEO datasets. We also collected serum samples from PD patients and established PD cell model to validate the expression of hub genes using enzyme-linked immunosorbent assay and quantitative real-time polymerase chain reaction. Our findings identified SV2C and DENR as two hub genes for PD and decreased in PD brain tissue compared with controls. ROC analysis showed effectively value of SV2C and DENR to diagnose PD, and they were downregulated in the serum of PD patients and cell model. Functional analysis revealed that dopamine vesicle transport and synaptic vesicle recycling are crucial pathways in PD. Besides, the differences in the composition of immune cells, especially basophils and T cells, were discovered between PD and controls. In summary, our study identifies SV2C and DENR as potential biomarkers for diagnosing PD and provides a new perspective for exploring the molecular mechanisms of PD.

Effect of Levodopa on Heat Hypersensitivity and Complex Motor Parkinsonism

OBJECTIVES

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

MATERIALS AND METHODS

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

RESULTS

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

CONCLUSIONS

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

Early-onset and late-onset Parkinson's disease exhibit a different profile of gait and posture features based on the Kinect

INTRODUCTION

Gait and posture abnormalities are the common disabling motor symptoms in Parkinson's disease (PD). This study aims to investigate the differential characteristics of gait and posture in early-onset PD (EOPD) and late-onset PD (LOPD) using the Kinect depth camera.

METHODS

Eighty-eight participants, including two subgroups of 22 PD patients and two subgroups of 22 healthy controls (HC) matched for age, sex, and height, were enrolled. Gait and posture features were quantitatively assessed using a Kinect-based system. A two-way analysis of variance was used to compare the difference between different subgroups.

RESULTS

EOPD had a significantly higher Gait score than LOPD (p = 0.031). Specifically, decreased swing phase (p = 0.034) was observed in the EOPD group. Although the Posture score was similar between the two groups, LOPD was characterized by an increased forward flexion angle of the trunk at the thorax (p = 0.042) and a decreased forward flexion angle of the head relative to the trunk (p = 0.009). Additionally, age-independent features were observed in both PD subgroups, and post hoc tests revealed that EOPD generally performed worse gait features. In comparison, LOPD was characterized by worse performance in posture features.

CONCLUSIONS

EOPD and LOPD exhibit different profiles of gait and posture features. The phenotype-specific characteristics likely reflect the distinct neurodegenerative processes between them.

Metabotropic Glutamate Receptor 4 (mGlu4) Positive Allosteric Modulators Lack Efficacy in Rat and Marmoset Models of L-DOPA-Induced Dyskinesia

Background

Increased activity across corticostriatal glutamatergic synapses may contribute to L-DOPA-induced dyskinesia in Parkinson's disease. Given the weak efficacy and side-effect profile of amantadine, alternative strategies to reduce glutamate transmission are being investigated. Metabotropic glutamate receptor 4 (mGlu4) is a promising target since its activation would reduce glutamate release.

Objective

We hypothesized that two mGlu4 positive allosteric modulators, Lu AF21934 ((1 S,2 R)-N1-(3,4-dichlorophenyl)cyclohexane-1,2-dicarboxamide) and ADX88178 (5-Methyl-N-(4-methylpyrimidin-2-yl)-4-(1H-pyrazol-4-yl)thiazol-2-amine), would provide relief in rat and primate models of L-DOPA-induced dyskinesia.

Methods

The ability of Lu AF21934 or ADX88178 to reverse pre-established dyskinesia was examined in L-DOPA-primed 6-hydroxydopamine-lesioned rats expressing abnormal involuntary movements (AIMs) or in 1-methyl-4-phenyl,1,2,3,6-tetrahydropyridine (MPTP)-treated common marmosets expressing L-DOPA-induced dyskinesia. Additionally, the ability of Lu AF21934 to prevent the development of de novo L-DOPA-induced AIMs was explored in the 6-hydroxydopamine-lesioned rats.

Results

Neither Lu AF21934 (10 or 30 mg/kg p.o.) nor ADX88178 (10 or 30 mg/kg p.o.) reduced pre-established AIMs in 6-hydroxydopamine-lesioned rats. Similarly, in L-DOPA-primed common marmosets, no reduction in established dyskinesia was observed with Lu AF21934 (3 or 10 mg/kg p.o.). Conversely, amantadine significantly reduced (>40%) the expression of dyskinesia in both models. Lu AF21934 also failed to suppress the development of AIMs in 6-hydroxydopamine-lesioned rats.

Conclusions

This study found no benefit of mGlu4 positive allosteric modulators in tackling L-DOPA-induced dyskinesia. These findings are concordant with the recent failure of foliglurax in phase II clinical trials supporting the predictive validity of these pre-clinical dyskinesia models, while raising further doubt on the anti-dyskinetic potential of mGlu4 positive allosteric modulators.

Real-world evidence on levodopa dose escalation in patients with Parkinson's disease treated with istradefylline

OBJECTIVE

Istradefylline, a selective adenosine A2A receptor antagonist, is indicated in the US and Japan as adjunctive treatment to levodopa/decarboxylase inhibitors in adults with Parkinson's disease (PD) experiencing OFF time. This study aimed to observe patterns of dose escalation of levodopa over time in patients initiated on istradefylline.

METHODS

Using Japanese electronic health record data, interrupted time series analyses were used to compare levodopa daily dose (LDD, mg/day) gradients in patients before and after initiation of istradefylline. Data were analyzed by period relative to istradefylline initiation (Month 1): pre-istradefylline (Months -72 to 0), early istradefylline (Months 1 to 24), and late istradefylline (Months 25 to 72). Subgroup analyses included LDD before istradefylline initiation (<400, ≥400 to <600, ≥600 mg/day) and treatment with or without monoamine oxidase-B (MAO-B) inhibitors, catechol-O-methyltransferase (COMT) inhibitors, or dopamine agonists before istradefylline initiation.

RESULTS

The analysis included 4026 patients; mean (SD) baseline LDD was 419.27 mg (174.19). Patients receiving ≥600 mg/day levodopa or not receiving MAO-B inhibitors or COMT inhibitors demonstrated a significant reduction in LDD increase gradient for pre-istradefylline vs late-phase istradefylline (≥600 mg/day levodopa, -6.259 mg/day each month, p<0.001; no MAO-B inhibitors, -1.819 mg/day each month, p = 0.004; no COMT inhibitors, -1.412 mg/day each month, p = 0.027).

CONCLUSIONS

This real-world analysis of Japanese prescription data indicated that slowing of LDD escalation was observed in patients initiated on istradefylline, particularly in those receiving ≥600 mg/day levodopa, suggesting istradefylline may slow progressive LDD increases. These findings suggest that initiating istradefylline before other levodopa-adjunctive therapies may mitigate LDD increases, potentially reducing occurrence or severity of levodopa-induced complications in long-term istradefylline treatment.

Recent Advances in Drug Discovery Toxicology

Major advances in scientific discovery and insights that stem from the development and use of new techniques and models can bring remarkable progress to conventional toxicology. Although animal testing is still considered as the "gold standard" in traditional toxicity testing, there is a necessity for shift from animal testing to alternative methods regarding the drug safety testing owing to the emerging state-of-art techniques and the proposal of 3Rs (replace, reduce, and refine) towards animal welfare. This review describes some recent research methods in drug discovery toxicology, including in vitro cell and organ-on-a-chip, imaging systems, model organisms (C. elegans, Danio rerio, and Drosophila melanogaster), and toxicogenomics in modern toxicology testing.

The ratio of M1 to M2 microglia in the striatum determines the severity of L-Dopa-induced dyskinesias

L-Dopa, while treating motor symptoms of Parkinson's disease, can lead to debilitating L-Dopa-induced dyskinesias, limiting its use. To investigate the causative relationship between neuro-inflammation and dyskinesias, we assessed if striatal M1 and M2 microglia numbers correlated with dyskinesia severity and whether the anti-inflammatories, minocycline and indomethacin, reverse these numbers and mitigate against dyskinesia. In 6-OHDA lesioned mice, we used stereology to assess numbers of striatal M1 and M2 microglia populations in non-lesioned (naïve) and lesioned mice that either received no L-Dopa (PD), remained non-dyskinetic even after L-Dopa (non-LID) or became dyskinetic after L-Dopa treatment (LID). We also assessed the effect of minocycline/indomethacin treatment on striatal M1 and M2 microglia and its anti-dyskinetic potential via AIMs scoring. We report that L-Dopa treatment leading to LIDs exacerbates activated microglia numbers beyond that associated with the PD state; the severity of LIDs is strongly correlated to the ratio of the striatal M1 to M2 microglial numbers; in non-dyskinetic mice, there is no M1/M2 microglia ratio increase above that seen in PD mice; and reducing M1/M2 microglia ratio using anti-inflammatories is anti-dyskinetic. Parkinson's disease is associated with increased inflammation, but this is insufficient to underpin dyskinesia. Given that L-Dopa-treated non-LID mice show the same ratio of M1/M2 microglia as PD mice that received no L-Dopa, and, given minocycline/indomethacin reduces both the ratio of M1/M2 microglia and dyskinesia severity, our data suggest the increased microglial M1/M2 ratio that occurs following L-Dopa treatment is a contributing cause of dyskinesias.

Aberrations in temporal dynamics of cognitive processing induced by Parkinson's disease and Levodopa

The motor symptoms of Parkinson's disease (PD) have been shown to significantly improve by Levodopa. However, despite the widespread adoption of Levodopa as a standard pharmaceutical drug for the treatment of PD, cognitive impairments linked to PD do not show visible improvement with Levodopa treatment. Furthermore, the neuronal and network mechanisms behind the PD-induced cognitive impairments are not clearly understood. In this work, we aim to explain these cognitive impairments, as well as the ones exacerbated by Levodopa, through examining the differential dynamic patterns of the phase-amplitude coupling (PAC) during cognitive functions. EEG data recorded in an auditory oddball task performed by a cohort consisting of controls and a group of PD patients during both on and off periods of Levodopa treatment were analyzed to derive the temporal dynamics of the PAC across the brain. We observed distinguishing patterns in the PAC dynamics, as an indicator of information binding, which can explain the slower cognitive processing associated with PD in the form of a latency in the PAC peak time. Thus, considering the high-level connections between the hippocampus, the posterior and prefrontal cortices established through the dorsal and ventral striatum acting as a modulatory system, we posit that the primary issue with cognitive impairments of PD, as well as Levodopa's cognitive deficit side effects, can be attributed to the changes in temporal dynamics of dopamine release influencing the modulatory function of the striatum.

Efficacy of exercises in early-stage Parkinson's disease (PARK-EASE trial): single-blind, randomised, controlled trial

Objectives

To assess the efficacy of exercises in early-stage Parkinson's disease (PD).

Design

Single-blind, randomised controlled trial.

Setting

Tertiary rehabilitation care centre.

Participants

Forty individuals (≥18 years, either gender) with newly diagnosed PD (Hoehn and Yahr stage ≤2) on a stable dose of PD medications were randomised (1:1) to the intervention group (IG) and control group (CG).

Interventions

The IG received strengthening (30 min/day, 2 days/week), aerobic (30 min/day, 3 days/week) and agility (30 min/day, 2 days/week) exercises in a structured format for 12 weeks. CG received stretching exercises for 12 weeks.

Main outcome measures

Unified PD Rating Scale (UPDRS) III (motor) at week 12 (primary), UPDRS I (mentation, behaviour and mood), UPDRS II and VI (Schwab and England Activities of daily living Scale) and Parkinson's Disease Quality of Life (PDQL) at week 12 (secondary).

Results

36 participants completed 12-week study period. UPDRS III (lesser scores reflect improvement) at 12 weeks showed a significant between-group difference (-5.05 points (95% CI: -9.38 to -0.71), p=0.02). At 4 and 8 weeks, UPDRS III did not show a statistically significant between-group difference (-2.15 points (95% CI: -6.77 to 2.47) and -4.1 points (95% CI: -8.54 to 0.34), respectively). From baseline to 12 weeks, UPDRS III in the IG showed a 6.5-point (95% CI (4.85 to 8.14)) reduction, and the CG showed a 0.8-point increase (95% CI (-3.06 to 1.46)), PDQL (higher scores reflect improvement) in the IG showed a 8.45-point (95% CI (-12.78 to -4.11)) increase and CG showed a 2.75-point (95% CI (0.16 to 5.33)) reduction.

Conclusions

Structured exercises improve motor symptoms and quality of life in early-stage PD. Consistent adherence for at least 12 weeks is crucial for clinical improvement. Early initiation of exercises as neurorehabilitation is recommended. Further research on specific types, dosing and intensity of exercises with a larger sample size is warranted in early-stage PD.

Trial registration number

CTRI/2018/05/014241.

Serum zinc deficiency is a potential risk factor for the occurrence of levodopa-induced dyskinesia in drug-naïve Parkinson's disease

Background

Since environmental factors, especially heavy metals, were highlighted in the pathogenesis of Parkinson's disease (PD), there are many epidemiologic studies regarding heavy metals and PD risk. However, longitudinal studies regarding the impacts of heavy metals on motor and nonmotor symptoms of PD are scarce.

Methods

In the current study, we compared the serum levels of five heavy metals, such as zinc(Zn), copper(Cu), lead(Pb), mercury(Hg), and manganese(Mn), in 111 previously drug-naïve PD patients (n = 111) retrospectively. Among these 111 patients, 65 were PD patients without levodopa-induced dyskinesia (LID), while the other 46 had LID. We assembled clinical characteristics of PD and performed correlation analysis with heavy metal levels. At baseline, all subjects were examined with 18F-N-(3-fluoropropyl)-2β-carboxymethoxy-3β-(4-iodophenyl) nortropane positron emission tomography/computed tomography (FP-CIT PET/CT). We used Cox proportional hazards regression analysis for determining factors relevant to the time to LID development in PD subjects.

Results

Zn deficiency was significantly higher in the PD with LID group than in the PD without LID group (79.58 ± 12.28 versus 88.16 ± 15.15 μg/L). Lower serum Zn levels were significantly correlated with age of onset, levodopa equivalent daily dose (LEDD) at 3 months, and Korean version of the Mini-Mental State Examination (K-MMSE) scores (r = 0.16, p < 0.05, r = - 0.20, p < 0.01, r = 0.28, p < 0.01). Additionally, Zn deficiency was associated with a reduced time to LID development in the adjusted model (HR 0.978, 95% CI 0.956-0.999).

Conclusion

This study suggests that serum Zn deficiency might be a risk factor for LID in drug-naïve PD patients.

Towards improved access to device-aided therapies in advanced PD: the importance of cooperation of different disciplines

Managing the many issues in advanced Parkinson's disease (PD) requires education, continuous support, and specialized outpatient care involving a variety of allied healthcare professionals. It would be greatly appreciated if general neurologists and professionals from various disciplines who work with people diagnosed with Parkinson's disease (PwP) could remain knowledgeable about the existing therapies and their respective roles within the treatment continuum. The movement disorders specialist and the PD nurse are key actors in the coordination of a targeted and patient-empowering multidisciplinary approach for advanced PD. Affordable and timely access to these therapies for the PwP who may need them is presently a challenge for health systems. Education, training, and support for all the involved stakeholders in the process of PD care may improve quality of life both for PwP and caregivers, and reduce inadequate, expensive, time-consuming, and unsuccessful prolongation of standard medical therapies.

Levodopa/Carbidopa to Augment the Treatment of Amblyopia: A Report by the American Academy of Ophthalmology

PURPOSE

To review the published literature on the use of levodopa/carbidopa to augment the treatment of amblyopia.

METHODS

Literature searches for English language studies were last conducted in October 2022 in the PubMed database with no date restrictions. The combined searches yielded 55 articles, of which 23 were reviewed in full text. Twelve of these were considered appropriate for inclusion in this assessment and were assigned a level of evidence rating by the panel methodologist. Nine studies were rated level I, and 3 studies were rated level II; there were no level III studies.

RESULTS

The duration of treatment was limited to 3 to 16 weeks because of concern about long-term adverse effects such as tardive dyskinesia. This complication was not reported in any of the study participants. The dose of levodopa ranged from 1.5 to 8.3 mg/kg/day, generally divided into 3 daily doses. The carbidopa dose was approximately 25% of the levodopa dose in all treatments. Evidence from these studies indicates that augmenting traditional patch occlusion therapy with the oral administration of levodopa/carbidopa can improve the vision of amblyopic children, but the effect was small (0.17-0.3 logarithm of the minimum angle of resolution [logMAR] units) and only statistically significant when compared with patching alone in 2 of the 12 studies cited. Regression of vision was reported in the majority of studies (9 of 12 reported; range, 0-0.17 logMAR unit regression) after discontinuation of therapy. Short-term side effects of the medications were not consistently reported but were most frequently mild and included headache and nausea.

CONCLUSIONS

The best available evidence is currently insufficient to show that augmenting amblyopia therapy using up to 16 weeks of levodopa/carbidopa will result in meaningful improvement in visual acuity. Given the potential for significant side effects such as tardive dyskinesia with long-term therapy, levodopa/carbidopa does not appear to be a viable option for amblyopia therapy FINANCIAL DISCLOSURE(S): The author(s) have no proprietary or commercial interest in any materials discussed in this article.

Should continuous dopaminergic stimulation be a standard of care in advanced Parkinson's disease?

The standard of care is a term that refers to the level of care, skill, and treatment that a healthcare provider should offer to a patient based on the current scientific evidence and the level of medical knowledge available in the field. For Parkinson's disease (PD), the standard care is mostly considered to be oral treatment with dopaminergic drugs, particularly levodopa which remains the 'gold standard'. However, effective management with levodopa during the later stages of the disease becomes increasingly challenging due to the ongoing neurodegenerative process, the consequences of its pulsatile dopaminergic stimulation, and the gastrointestinal barriers to effective drug absorption. As a result, the concept of applying continuous dopaminergic stimulation has emerged with infusion therapies (continuous subcutaneous apomorphine, levodopa-carbidopa intestinal gel, and levodopa-entacapone-carbidopa intestinal gel infusion). These therapies seek to provide continuous stimulation of striatal dopamine receptors that is efficient not only in alleviating clinical symptoms, but also in delaying, reducing, and possibly preventing the onset of levodopa-related motor (fluctuations, dyskinesia) and non-motor complications; and they are also associated with clinically relevant side effects. Clinical studies and real-life experience support the notion that infusion therapies should be accepted as part of the standard of care for patients with advanced PD who have refractory, severe, and disabling motor complications that affect their quality of life. However, they should be considered based on the needs of individualized patients and the access to these advanced therapies needs to be made more accessible to the general PD population.

Levodopa-Carbidopa Intestinal Gel Injection for Patient with Severe Parkinson's Disease Followed by Total Hip Arthroplasty: A Case Report and Literature Review

BACKGROUND

Patients with Parkinson's disease have a high dislocation rate after total hip arthroplasty (THA). This study describes a case with severe Parkinson's disease who developed rapidly destructive coxarthrosis (RDC) and underwent THA using a dual mobility cup after a levodopa-carbidopa intestinal gel (LCIG) infusion.

CASE PRESENTATION

The patient is a 59-year-old female with a ten-year history of Parkinson's disease, which was first treated with oral levodopa. The patient developed RDC of the right hip joint. However, THA was difficult owing to Parkinson's disease and its treatment side effects, such as wearing-off, dyskinesia, and freezing of the gait, Thus, LCIG was initiated, and improvement in wearing-off and dyskinesia was observed. Two months after the LCIG therapy, the disease was controlled well. THA was subsequently performed using a dual mobility cup to prevent postoperative dislocation. Postoperatively, LCIG therapy was continuously administered to carefully manage the disease, which was controlled well with no increase in wearing-off and dyskinesia after surgery. At 1 year after surgery, the walking speed, stride length, and the Harris hip score improved compared to preoperatively. The UPDRS III motor score improved to eight without signs of wearing-off or dyskinesia. The Hoehn-Yahr scale was II in the "on" period and remained unchanged 1 year after surgery. The patient could walk without a cane and had satisfactory functional outcomes.

CONCLUSION

This case proved that LCIG treatment performed preoperatively, followed by THA using a dual mobility cup, and strict management of Parkinson's disease could result in a satisfactory clinical course without recurrence of wearing-off and dyskinesia. Similar procedures may benefit other patients with Parkinson's disease who have previously been deemed unsuitable for THA.

Application of single wrist-wearable accelerometry for objective motor diary assessment in fluctuating Parkinson's disease

Advanced Parkinson's disease (PD) is characterized by motor fluctuations including unpredictable oscillations remarkably impairing quality of life. Effective management and development of novel therapies for these response fluctuations largely depend on clinical rating instruments such as the widely-used PD home diary, which are associated with biases and errors. Recent advancements in digital health technologies provide user-friendly wearables that can be tailored for continuous monitoring of motor fluctuations. Their criterion validity under real-world conditions using clinical examination as the gold standard remains to be determined. We prospectively examined this validity of a wearable accelerometer-based digital Parkinson's Motor Diary (adPMD) using the Parkinson's Kinetigraph (PKG®) in an alternative application by converting its continuous data into one of the three motor categories of the PD home diary (Off, On and Dyskinetic state). Sixty-three out of 91 eligible participants with fluctuating PD (46% men, average age 66) had predefined sufficient adPMD datasets (>70% of half-hour periods) from 2 consecutive days. 92% of per-protocol assessments were completed. adPMD monitoring of daily times in motor states showed moderate validity for Off and Dyskinetic state (ICC = 0.43-0.51), while inter-rating methods agreements on half-hour-level can be characterized as poor (median Cohen's κ = 0.13-0.21). Individualization of adPMD thresholds for transferring accelerometer data into diary categories improved temporal agreements up to moderate level for Dyskinetic state detection (median Cohen's κ = 0.25-0.41). Here we report that adPMD real-world-monitoring captures daily times in Off and Dyskinetic state in advanced PD with moderate validities, while temporal agreement of adPMD and clinical observer diary data is limited.

Shared GABA transmission pathology in dopamine agonist- and antagonist-induced dyskinesia

Dyskinesia is involuntary movement caused by long-term medication with dopamine-related agents: the dopamine agonist 3,4-dihydroxy-L-phenylalanine (L-DOPA) to treat Parkinson's disease (L-DOPA-induced dyskinesia [LID]) or dopamine antagonists to treat schizophrenia (tardive dyskinesia [TD]). However, it remains unknown why distinct types of medications for distinct neuropsychiatric disorders induce similar involuntary movements. Here, we search for a shared structural footprint using magnetic resonance imaging-based macroscopic screening and super-resolution microscopy-based microscopic identification. We identify the enlarged axon terminals of striatal medium spiny neurons in LID and TD model mice. Striatal overexpression of the vesicular gamma-aminobutyric acid transporter (VGAT) is necessary and sufficient for modeling these structural changes; VGAT levels gate the functional and behavioral alterations in dyskinesia models. Our findings indicate that lowered type 2 dopamine receptor signaling with repetitive dopamine fluctuations is a common cause of VGAT overexpression and late-onset dyskinesia formation and that reducing dopamine fluctuation rescues dyskinesia pathology via VGAT downregulation.

Dyskinesia and impulsive compulsive behaviour in Parkinson's disease are not related: Insights from a study with a wearable sensor

INTRODUCTION

Previous studies have suggested an association between Impulsive Compulsive Behaviour (ICB) and dyskinesia in Parkinson's disease (PD). However, none of these studies have employed an objective home-based measure of dyskinesia.

OBJECTIVES

To evaluate in advanced PD the relationship between ICB and dyskinesia, objectively measured with a wearable device.

METHODS

In this cross-sectional study, ICB and other neuropsychiatric symptoms were assessed by means of structured clinical interview and specific screening instruments. Presence and severity of motor fluctuations and dyskinesia were rated with patient's and clinician's based rating instruments. Motor fluctuations and dyskinesia were also measured at home for 5-days using a validated wearable devise, the Parkinson's KinetiGraph™(PKG).

RESULTS

We included 89 subjects with PD (29 females, 62 ± 7 years, disease duration 10.3 ± 4.5), of whom 36 (40%) had ICB. Patients with and without ICB did not differ by presence and severity of dyskinesia measured by clinical scales and PKG. There was no association between the presence of ICB and dyskinesia in the whole sample.

CONCLUSION

Our data suggest that ICB and dyskinesia are common but unrelated disorders in advanced PD.

Drugs targeting adenosine signaling pathways: A current view

Adenosine is an endogenous nucleoside that regulates many physiological and pathological processes. It is derived from either the intracellular or extracellular dephosphorylation of adenosine triphosphate and interacts with cell-surface G-protein-coupled receptors. Adenosine plays a substantial role in protecting against cell damage in areas of increased tissue metabolism and preventing organ dysfunction in pathological states. Targeting adenosine metabolism and receptor signaling may be an effective therapeutic approach for human diseases, including cardiovascular and central nervous system disorders, rheumatoid arthritis, asthma, renal diseases, and cancer. Several lines of evidence have shown that many drugs exert their beneficial effects by modulating adenosine signaling pathways but this knowledge urgently needs to be summarized, and most importantly, actualized. The present review collects pharmaceuticals and pharmacological or diagnostic tools that target adenosine signaling in their primary or secondary mode of action. We overviewed FDA-approved drugs as well as those currently being studied in clinical trials. Among them are already used in clinic A2A adenosine receptor modulators like istradefylline or regadenoson, but also plenty of anti-platelet, anti-inflammatory, or immunosuppressive, and anti-cancer drugs. On the other hand, we investigated dozens of specific adenosine pathway regulators that are tested in clinical trials to treat human infectious and noninfectious diseases. In conclusion, targeting purinergic signaling represents a great therapeutic challenge. The actual knowledge of the involvement of adenosinergic signaling as part of the mechanism of action of old drugs has open a path not only for drug-repurposing but also for new therapeutic strategies.