Blood Flow and Glucose Metabolism Dissociation in the Putamen Is Predictive of Levodopa Induced Dyskinesia in Parkinson's Disease Patients

Consistent abnormal activity in the putamen by dopamine modulation in Parkinson's disease: A resting-state neuroimaging meta-analysis

OBJECTIVE

This study aimed to elucidate brain areas mediated by oral anti-parkinsonian medicine that consistently show abnormal resting-state activation in PD and to reveal their functional connectivity profiles using meta-analytic approaches.

METHODS

Searches of the PubMed, Web of Science databases identified 78 neuroimaging studies including PD OFF state (PD-OFF) versus (vs.) PD ON state (PD-ON) or PD-ON versus healthy controls (HCs) or PD-OFF versus HCs data. Coordinate-based meta-analysis and functional meta-analytic connectivity modeling (MACM) were performed using the activation likelihood estimation algorithm.

RESULTS

Brain activation in PD-OFF vs. PD-ON was significantly changed in the right putamen and left inferior parietal lobule (IPL). Contrast analysis indicated that PD-OFF vs. HCs had more consistent activation in the right paracentral lobule, right middle frontal gyrus, right thalamus, left superior parietal lobule and right putamen, whereas PD-ON vs. HCs elicited more consistent activation in the bilateral middle temporal gyrus, left occipital gyrus, right inferior frontal gyrus and right caudate. MACM revealed coactivation of the right putamen in the direct contrast of PD-OFF vs. PD-ON. Subtraction analysis of significant coactivation clusters for PD-OFF vs. PD-ON with the medium of HCs showed effects in the sensorimotor, top-down control, and visual networks. By overlapping the MACM maps of the two analytical strategies, we demonstrated that the coactivated brain region focused on the right putamen.

CONCLUSIONS

The convergence of local brain regions and co-activation neural networks are involved the putamen, suggesting its potential as a specific imaging biomarker to monitor treatment efficacy.

SYSTEMATIC REVIEW REGISTRATION

[https://www.crd.york.ac.uk/PROSPERO/], identifier [CRD CRD42022304150].

Synaptic loss and its association with symptom severity in Parkinson's disease

Parkinson's disease (PD) is the fastest growing neurodegenerative disease, but at present there is no cure, nor any disease-modifying treatments. Synaptic biomarkers from in vivo imaging have shown promise in imaging loss of synapses in PD and other neurodegenerative disorders. Here, we provide new clinical insights from a cross-sectional, high-resolution positron emission tomography (PET) study of 30 PD individuals and 30 age- and sex-matched healthy controls (HC) with the radiotracer [11C]UCB-J, which binds to synaptic vesicle glycoprotein 2A (SV2A), and is therefore, a biomarker of synaptic density in the living brain. We also examined a measure of relative brain perfusion from the early part of the same PET scan. Our results provide evidence for synaptic density loss in the substantia nigra that had been previously reported, but also extend this to other early-Braak stage regions known to be affected in PD (brainstem, caudate, olfactory cortex). Importantly, we also found a direct association between synaptic density loss in the nigra and severity of symptoms in patients. A greater extent and wider distribution of synaptic density loss in PD patients with longer illness duration suggests that [11C]UCB-J PET can be used to measure synapse loss with disease progression. We also demonstrate lower brain perfusion in PD vs. HC groups, with a greater extent of abnormalities in those with longer duration of illness, suggesting that [11C]UCB-J PET can simultaneously provide information on changes in brain perfusion. These results implicate synaptic imaging as a useful PD biomarker for future disease-modifying interventions.

Predictability of inter-regional cerebral perfusion similarity on dopamine responsiveness and the moderation role of cognition in PD patients

BACKGROUND

Large heterogeneity can be found in dopamine responsiveness of patients with Parkinson's disease (PD). Instantly and objectively understanding dopamine responsiveness of patients may help clinical practice.

PURPOSE

This PD study explored the predictability of off-state inter-regional cerebral blood flow (CBF) perfusion similarity on patient's dopamine responsiveness and tested whether the predictive power could be moderated by patient's cognitive status.

MATERIALS AND METHOD

The PD cohort with 192 patients (containing off state and on state (PD-off and PD-on)) and the normal control (NC) cohort with 92 subjects were included. The intra-individual CBF relative variation networks were constructed and compared between PD-off and PD-on, PD-off and NC to identify the alterations caused by dopamine depletion. Based on that, regression analysis of off-state inter-regional CBF perfusion similarity on patient's dopamine responsiveness was performed. Finally, moderation analysis was conducted to test the moderation role of cognition on the regression model.

RESULTS

In the PD-off cohort, a total of 82 edges in the network were identified that affected by dopamine depletion. Off-state inter-regional CBF perfusion similarity was found that had a significant influence on patient's dopamine responsiveness. Cognitive status was validated that positively moderated the relationship between off-state inter-regional CBF perfusion similarity and dopamine responsiveness.

CONCLUSION

Dopamine responsiveness of PD patient could be predicted by off-state inter-regional CBF perfusion similarity. Patient's cognitive status might have a positive moderation effect on his/her dopamine responsiveness.

Transcranial Magnetic Stimulation Alleviates Levodopa-Induced Dyskinesia in Parkinson's Disease and the Related Mechanisms: A Mini-Review

After long-term use of levodopa, Parkinson's patients almost inevitably develop dyskinesia, a kind of drug side effect manifesting as uncontrollable choreic movements and dystonia, which could be crippling yet have limited therapeutic options. Transcranial magnetic stimulation is the most widely studied non-invasive neuromodulation technology to treat levodopa-induced dyskinesia. Many studies have shown that transcranial magnetic stimulation has beneficial effects on levodopa-induced dyskinesia and is patient-tolerable, barely with reported adverse effects. Changes in brain connectivity, neuroplasticity, neurotransmitter, neurorestoration, and blood flow modulation could play crucial roles in the efficacy of transcranial magnetic stimulation for levodopa-induced dyskinesia. The appearance of new modes and application for emerging targets are possible solutions for transcranial magnetic stimulation to achieve sustained efficacy. Since the sample size in all available studies is small, more randomized double-blind controlled studies are needed to elucidate the specific treatment mechanisms and optimize treatment parameters.

Histological Correlates of Neuroanatomical Changes in a Rat Model of Levodopa-Induced Dyskinesia Based on Voxel-Based Morphometry

Long-term therapy with levodopa (L-DOPA) in patients with Parkinson’s disease (PD) often triggers motor complications termed as L-DOPA-induced dyskinesia (LID). However, few studies have explored the pathogenesis of LID from the perspective of neuroanatomy. This study aimed to investigate macroscopic structural changes in a rat model of LID and the underlying histological mechanisms. First, we established the hemiparkinsonism rat model through stereotaxic injection of 6-hydroxydopamine (6-OHDA) into the right medial forebrain bundle, followed by administration of saline (PD) or L-DOPA to induce LID. Magnetic resonance imaging (MRI) and behavioral evaluations were performed at different time points. Histological analysis was conducted to assess the correlations between MRI signal changes and cellular contributors. Voxel-based morphometry (VBM) analysis revealed progressive bilateral volume reduction in the cortical and subcortical areas in PD rats compared with the sham rats. These changes were partially reversed by chronic L-DOPA administration; moreover, there was a significant volume increase mainly in the dorsolateral striatum, substantia nigra, and piriform cortex of the lesioned side compared with that of PD rats. At the striatal cellular level, glial fibrillary acidic protein-positive (GFAP+) astrocytes were significantly increased in the lesioned dorsolateral striatum of PD rats compared with the intact side and the sham group. Prolonged L-DOPA treatment further increased GFAP levels. Neither 6-OHDA damage nor L-DOPA treatment influenced the striatal expression of vascular endothelial growth factor (VEGF). Additionally, there was a considerable increase in synapse-associated proteins (SYP, PSD95, and SAP97) in the lesioned striatum of LID rats relative to the PD rats. Golgi-Cox staining analysis of the dendritic spine morphology revealed an increased density of dendritic spines after chronic L-DOPA treatment. Taken together, our findings suggest that striatal volume changes in LID rats involve astrocyte activation, enrichment of synaptic ultrastructure and signaling proteins in the ipsilateral striatum. Meanwhile, the data highlight the enormous potential of structural MRI, especially VBM analysis, in determining the morphological phenotype of rodent models of LID.

Current Knowledge on the Background, Pathophysiology and Treatment of Levodopa-Induced Dyskinesia-Literature Review

Levodopa remains the primary drug for controlling motor symptoms in Parkinson’s disease through the whole course, but over time, complications develop in the form of dyskinesias, which gradually become more frequent and severe. These abnormal, involuntary, hyperkinetic movements are mainly characteristic of the ON phase and are triggered by excess exogenous levodopa. They may also occur during the OFF phase, or in both phases. Over the past 10 years, the issue of levodopa-induced dyskinesia has been the subject of research into both the substrate of this pathology and potential remedial strategies. The purpose of the present study was to review the results of recent research on the background and treatment of dyskinesia. To this end, databases were reviewed using a search strategy that included both relevant keywords related to the topic and appropriate filters to limit results to English language literature published since 2010. Based on the selected papers, the current state of knowledge on the morphological, functional, genetic and clinical features of levodopa-induced dyskinesia, as well as pharmacological, genetic treatment and other therapies such as deep brain stimulation, are described.

The Vasomotor Response to Dopamine Is Altered in the Rat Model of l-dopa-Induced Dyskinesia

BACKGROUND

Levodopa (l-dopa) is the frontline treatment for motor symptoms of Parkinson's disease. However, prolonged use of l-dopa results in a motor complication known as levodopa-induced dyskinesia (LID) in ~50% of patients over 5 years.

OBJECTIVES

We investigated neurovascular abnormalities in a rat model of LID by examining changes in angiogenesis and dopamine-dependent vessel diameter changes.

METHODS

Differences in striatal and nigral angiogenesis in a parkinsonian rat model (6-OHDA lesion) treated with 2 doses of l-dopa (saline, 2, and 10 mg/kg/day subcutaneous l-dopa treatment for 22 days) by 5-bromo-2'-deoxyuridine (BrdU)-RECA1 co-immunofluorescence. Difference in the vasomotor response to dopamine was examined with 2-photon laser scanning microscopy and Dodt gradient imaging.

RESULTS

We found that the 10 mg/kg l-dopa dosing regimen induced LID in all animals (n = 5) and induced significant angiogenesis in the striatum and substantia nigra. In contrast, the 2 mg/kg treatment induced LID in 6 out of 12 rats and led to linearly increasing LID severity over the 22-day treatment period, making this a promising model for studying LID progression longitudinally. However, no significantly different level of angiogenesis was observed between LID versus non-LID animals. Dopamine-induced vasodilatory responses were exaggerated only in rats that show LID-like signs compared to the rest of groups. Additionally, in juvenile rats, we showed that DA-induced vasodilation is preceded by increased Ca2+ release in the adjacent astrocytes.

CONCLUSION

This finding supports that astrocytic dopamine signaling controls striatal blood flow bidirectionally, and the balance is altered in LID. © 2020 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Imaging Cerebral Glucose Metabolism during Dual-Task Walking in Patients with Parkinson's disease

BACKGROUND AND PURPOSE

Gait impairment is a hallmark of Parkinson's disease (PD). Natural walking involves more cognitive demand than treadmill walking or in-laboratory walking tests because patients have to actively work on navigation and top-down cognitive control which taxes cognitive reserve in the prefrontal cortex. To mimic the prefrontal engagement occurring with natural walking in a controlled and safe environment, dual-task (DT) treadmill walking has been developed. In this study, we tested the feasibility of imaging DT walking-related changes in brain glucose metabolism in patients with PD.

METHODS

Fifteen patients with PD were scanned with fluorodeoxyglucose (FDG) positron emission tomography. Five patients performed DT walking, and 10 patients were rested during the FDG uptake period. First, the images were contrasted between the groups. Second, the walking-related brain glucose metabolism was inspected at the individual level.

RESULTS

Consistently increased glucose metabolism was identified in DT walking versus rest in the primary visual/sensorimotor areas, thalamus, superior colliculus, and cerebellum. In individual level analysis, patients with less progressed disease (n = 3) showed prefrontal activity during DT walking while patients with more progressed disease (n = 2) did not.

CONCLUSION

This study confirms the feasibility of imaging glucose metabolism during DT walking in patients with PD. We also report that during DT walking, there is a lesser degree of prefrontal engagement in the patients with more progressed disease compared to those with less progressed disease, implying increased degrees of frontal dysfunction with PD progression.

Elevated caudate connectivity in cognitively normal Parkinson's disease patients

Mild cognitive impairment (MCI) is common in Parkinson’s disease patients. However, its underlying mechanism is not well understood, which has hindered new treatment discoveries specific to MCI. The aim of this study was to investigate functional connectivity changes of the caudate nucleus in cognitively impaired Parkinson’s patients. We recruited 18 Parkinson’s disease patients—10 PDNC [normal cognition Parkinson’s disease; Montreal Cognitive Assessment (MoCA) ≥ 26], 8 PDLC (low cognition Parkinson’s disease; MoCA < 26) —and 10 age-matched healthy controls. All subjects were scanned with resting-state functional magnetic resonance imaging (MRI) and perfusion MRI. We analyzed these data for graph theory metrics and Alzheimer’s disease-like pattern score, respectively. A strong positive correlation was found between the functional connectivity of the right caudate nucleus and MoCA scores in Parkinson’s patient groups, but not in healthy control subjects. Interestingly, PDNC’s functional connectivity of the right caudate was significantly higher than both PDLC and healthy controls, while PDLC and healthy controls were not significantly different from each other. We found that Alzheimer’s disease-like metabolic/perfusion pattern score correlated with MoCA scores in healthy controls, but not in Parkinson’s disease. Increased caudate connectivity may be related to a compensatory mechanism found in cognitively normal patients with Parkinson’s disease. Our findings support and complement the dual syndrome hypothesis.