Molecular Imaging of the Dopaminergic System in Idiopathic Parkinson's Disease

The Atypical Dopamine Transporter Inhibitor CE-158 Enhances Dopamine Neurotransmission in the Prefrontal Cortex of Male Rats: A Behavioral, Electrophysiological, and Microdialysis Study

BACKGROUND

Dopamine plays a key role in several physiological functions such as motor control, learning and memory, and motivation and reward. The atypical dopamine transporter inhibitor S,S stereoisomer of 5-(((S)-((S)-(3-bromophenyl)(phenyl)methyl)sulfinyl)methyl)thiazole (CE-158) has been recently reported to promote behavioral flexibility and restore learning and memory in aged rats.

METHODS

Adult male rats were i.p. administered for 1 or 10 days with CE-158 at the dose of 1 or 10 mg/kg and tested for extracellular dopamine in the medial prefrontal cortex by means of intracerebral microdialysis and single unit cell recording in the same brain area. Moreover, the effects of acute and chronic CE-158 on exploratory behavior, locomotor activity, prepulse inhibition, working memory, and behavioral flexibility were also investigated.

RESULTS

CE-158 dose-dependently potentiated dopamine neurotransmission in the medial prefrontal cortex as assessed by intracerebral microdialysis. Moreover, repeated exposure to CE-158 at 1 mg/kg was sufficient to increase the number of active pyramidal neurons and their firing frequency in the same brain area. In addition, CE-158 at the dose of 10 mg/kg stimulates exploratory behavior to the same extent after acute or chronic treatment. Noteworthy, the chronic treatment at both doses did not induce any behavioral alterations suggestive of abuse potential (e.g., motor behavioral sensitization) or pro-psychotic-like effects such as disruption of sensorimotor gating or impairments in working memory and behavioral flexibility as measured by prepulse inhibition and Y maze.

CONCLUSIONS

Altogether, these findings confirm CE-158 as a promising pro-cognitive agent and contribute to assessing its preclinical safety profile in a chronic administration regimen for further translational testing.

Diagnostic value of striatal 18F-FP-DTBZ PET in Parkinson’s disease

Background

18F-FP-DTBZ has been proven as a biomarker for quantifying the concentration of presynaptic vesicular monoamine transporter 2 (VMAT2). However, its clinical application is still limited.

Objectives

To evaluate the difference in dopaminergic integrity between patients with Parkinson’s disease (PD) and healthy controls (HC) using 18F-FP-DTBZ PET in vivo and to determine the diagnostic value of standardized uptake value ratios (SUVRs) using the Receiver Operating Characteristic (ROC) curve.

Methods

A total of 34 PD and 31 HC participants were enrolled in the PET/MR derivation cohort, while 89 PD and 18 HC participants were recruited in the PET/CT validation cohort. The Hoehn–Yahr Scale and the third part of the MDS-Unified Parkinson’s Disease Rating Scale (MDSUPDRS-III) were used to evaluate the disease staging and severity. All assessments and PET scanning were performed in drug-off states. The striatum was segmented into five subregions as follows: caudate, anterior dorsal putamen (ADP), anterior ventral putamen (AVP), posterior dorsal putamen (PDP), and posterior ventral putamen (PVP) using automatic pipeline built with the PMOD software (version 4.105). The SUVRs of the targeted subregions were calculated using the bilateral occipital cortex as the reference region.

Results

Regarding the diagnostic value, ROC curve and blind validation showed that the contralateral PDP (SUVR = 3.43) had the best diagnostic accuracy (AUC = 0.973; P < 0.05), with a sensitivity of 97.1% (95% CI: 82.9–99.8%), specificity of 100% (95% CI: 86.3–100%), positive predictive value (PPV) of 100% (95% CI: 87.0–100%), negative predictive value (NPV) of 96.9% (95% CI: 82.0–99.8%), and an accuracy of 98.5% for the diagnosis of PD in the derivation cohort. Blind validation of 18F-FP-DTBZ PET imaging diagnosis was done using the PET/CT cohort, where participants with a SUVR of the PDP <3.43 were defined as PD. Kappa test showed a consistency of 0.933 (P < 0.05) between clinical diagnosis and imaging diagnosis, with a sensitivity of 98.9% (95% CI: 93.0–99.9%), specificity of 94.4% (95% CI: 70.6–99.7%), PPV of 98.9% (95% CI: 93.0–99.9%), NPV of 94.4% (95% CI: 70.6–99.7%), and a diagnostic accuracy of 98.1%.

Conclusions

Our results showed that an SUVR threshold of 3.43 in the PDP could effectively distinguish patients with PD from HC.

A Multi-Atlas-Based [18F]9-Fluoropropyl-(+)-Dihydrotetrabenazine Positron Emission Tomography Image Segmentation Method for Parkinson's Disease Quantification

Objectives

[18F]9-fluoropropyl-(+)-dihydrotetrabenazine ([18F]-FP-DTBZ) positron emission tomography (PET) provides reliable information for the diagnosis of Parkinson's disease (PD). In this study, we proposed a multi-atlas-based [18F]-FP-DTBZ PET image segmentation method for PD quantification assessment.

Methods

A total of 99 subjects from Xuanwu Hospital of Capital Medical University were included in this study, and both brain PET and magnetic resonance (MR) scans were conducted. Data from 20 subjects were used to generate atlases, based on which a multi-atlas-based [18F]-FP-DTBZ PET segmentation method was developed especially for striatum and its subregions. The proposed method was compared with the template-based method through striatal subregion parcellation performance and the standard uptake value ratio (SUVR) quantification accuracy. Discriminant analysis between healthy controls (HCs) and PD patients was further performed.

Results

Segmentation results of the multi-atlas-based method showed better consistency than the template-based method with the ground truth, yielding a dice coefficient of 0.81 over 0.73 on the full striatum. The SUVRs calculated by the multi-atlas-based method had an average interclass correlation coefficient (ICC) of 0.953 with the standardized result, whereas the template-based method only reached 0.815. The SUVRs of HCs were generally higher than that of patients with PD and showed significant differences in all of the striatal subregions (all p < 0.001). The median and posterior putamen performed best in discriminating patients with PD from HCs.

Conclusion

The proposed multi-atlas-based [18F]-FP-DTBZ PET image segmentation method achieved better performance than the template-based method, indicating great potential in improving accuracy and efficiency for PD diagnosis in clinical routine.

Discovery of styrylaniline derivatives as novel alpha-synuclein aggregates ligands

Parkinson's disease (PD) is the second most common neurodegenerative disorder. Early diagnosis is the key to treatment but is still a great challenge in the clinic now. The discovery of alpha-synuclein (α-syn) aggregates ligands has become an attractive strategy to meet the early diagnosis of PD. Herein, we designed and synthesized a series of styrylaniline derivatives as novel α-syn aggregates ligands. Several compounds displayed good potency to α-syn aggregates with K_d values less than 0.1 μM. The docking study revealed that the hydrogen bonds and cation-pi interaction between ligands and α-syn aggregates would be crucial for the activity. The representative compound 7-16 not only detected α-syn aggregates in both SH-SY5Y cells and brain tissues prepared from two kinds of α-syn preformed-fibrils-injected mice models but also showed good blood-brain barrier penetration characteristics in vivo with a brain/plasma ratio over 1.0, which demonstrates its potential as a lead compound for further development of in vivo imaging agents.

VMAT2 availability in Parkinson's disease with probable REM sleep behaviour disorder

REM sleep behaviour disorder (RBD) can be an early non-motor symptom of Parkinson’s disease (PD) with pathology involving mainly the pontine nuclei. Beyond the brainstem, it is unclear if RBD patients comorbid with PD have more affected striatal dopamine denervation compared to PD patients unaffected by RBD (PD-RBD−). To elucidate this, we evaluated the availability of vesicular monoamine transporter 2 (VMAT2), an index of nigrostriatal dopamine innervation, in 15 PD patients with probable RBD (PD-RBD+), 15 PD-RBD−, and 15 age-matched healthy controls (HC) using [¹¹C]DTBZ PET imaging. This technique measured VMAT2 availability within striatal regions of interest (ROI). A mixed effect model was used to compare the radioligand binding of VMAT2 between the three groups for each striatal ROI, while co-varying for sex, cognitive function and depression scores. Multiple regressions were also computed to predict clinical measures from group condition and VMAT2 binding within all ROIs explored. We observed a significant main effect of group condition on VMAT2 availability within the caudate, putamen, ventral striatum, globus pallidus, substantia nigra, and subthalamus. Specifically, our results revealed that PD-RBD+ had lower VMAT2 availability compared to HC in all these regions except for the subthalamus and substantia nigra, while PD-RBD− was significantly lower than HC in all these regions. PD-RBD− showed a negative relationship between motor severity and VMAT2 availability within the left caudate. Our findings reflect that both PD patient subgroups had similar denervation within the nigrostriatal pathway. There were no significant interactions detected between radioligand binding and clinical scores in PD-RBD+. Taken together, VMAT2 and striatal dopamine denervation in general may not be a significant contributor to the pathophysiology of RBD in PD patients. Future studies are encouraged to explore other underlying neural chemistry mechanisms contributing to RBD in PD patients.

Dopamine in Parkinson's disease

Parkinson's disease is a neurodegenerative disease caused by the death of neurons, ie, cells critical to the production of dopamine, an important neurotransmitter in the brain. Here, we present a brief review of the dopamine synthetic pathway, binding to the dopamine receptors, and subsequent action. The production of dopamine (a monoamine neurotransmitter) occurs in the ventral tegmental area (VTA) of the substantia nigra, specifically in the hypothalamic nucleus and midbrain. Compared to other monoamines, dopamine is widely distributed in the olfactory bulb, midbrain substantia nigra, hypothalamus, VTA, retina, and the periaqueductal gray area. Dopamine receptors are large G-protein coupled receptor family members, of which there are five subtypes including D1, D2, D3, D4, and D5. These subtypes are further divided into two subclasses: D1-like family receptors (types 1 and 5) and D2-like family receptors (types 2, 3, and 4). Four different pathways and functions of the dopaminergic system are presented in this review. In the oxidation of dopamine, 5,6-indolequinone, dopamine-o-quinone, and aminochrome are formed. It is difficult to separate the roles of 5,6-indolequinone and dopamine-o-quinone in the degenerative process of Parkinson's diseases due to their instability. The role of aminochrome in Parkinson's disease is to form and stabilize the neurotoxic protofibrils of alpha-synuclein, mitochondrial dysfunction, oxidative stress, and the degradation of protein by lysosomal systems and proteasomes. The neurotoxic effects of aminochrome can be inhibited by preventing the polymerization of 5,6-indolequinone, dopamine-o-quinone, and aminochrome into neuromelanin, by reducing aminochrome catalysis by DT-diaphorase, and by preventing dopamine oxidative deamination catalyzed by monoamine oxidase. In addition to these, the conversion of dopamine in the neuromelanin (NM) shows both protective and toxic roles. Therefore, the aims of this review were to discuss and explain the role of dopamine and explore its physiology and specificity in Parkinson's disease, as well as its role in other physiological functions.

Positron emission computed tomography/single photon emission computed tomography in Parkinson disease

Parkinson disease (PD) is the second-most common neurodegenerative disorder. Its main pathological mechanism is the selective degeneration and deletion of dopaminergic neurons in the dense part of the substantia nigra and the damage of dopaminergic neurons caused by the abnormal deposition of a Lewy body, leading to a decreased dopamine level. Positron emission computed tomography (PET)/single photon emission computed tomography (SPECT) is a molecular imaging technology that can directly or indirectly reflect changes in molecular levels by using a specific tracer. With the research and development on the tracers of related enzymes for labeling dopamine transporter and dopamine receptor and for being involved in dopamine formation, this imaging technology has been applied to all aspects of PD research. It not only contributes to clinical work but also provides an important theoretical basis for exploring the pathological mechanism of PD at a molecular level. Therefore, this review discusses the application value of PET/SPECT in PD in terms of early diagnosis, disease severity evaluation, clinical manifestations, differential diagnosis, and pathological mechanism.

A link between synaptic plasticity and reorganization of brain activity in Parkinson's disease

The link between synaptic plasticity and reorganization of brain activity in health and disease remains a scientific challenge. We examined this question in Parkinson's disease (PD) where functional up-regulation of postsynaptic D₂ receptors has been documented while its significance at the neural activity level has never been identified. We investigated cortico-subcortical plasticity in PD using the oculomotor system as a model to study reorganization of dopaminergic networks. This model is ideal because this system reorganizes due to frontal-to-parietal shifts in blood oxygen level-dependent (BOLD) activity. We tested the prediction that functional activation plasticity is associated with postsynaptic dopaminergic modifications by combining positron emission tomography/functional magnetic resonance imaging to investigate striatal postsynaptic reorganization of dopamine D₂ receptors (using ¹¹C-raclopride) and neural activation in PD. We used covariance (connectivity) statistics at molecular and functional levels to probe striato-cortical reorganization in PD in on/off medication states to show that functional and molecular forms of reorganization are related. D₂ binding across regions defined by prosaccades showed increased molecular connectivity between both caudate/putamen and hyperactive parietal eye fields in PD in contrast with frontal eye fields in controls, in line with the shift model. Concerning antisaccades, parietal-striatal connectivity dominated in again in PD, unlike frontal regions. Concerning molecular-BOLD covariance, a striking sign reversal was observed: PD patients showed negative frontal-putamen functional-molecular associations, consistent with the reorganization shift, in contrast with the positive correlations observed in controls. Follow-up analysis in off-medication PD patients confirmed the negative BOLD-molecular correlation. These results provide a link among BOLD responses, striato-cortical synaptic reorganization, and neural plasticity in PD.

Contributions of PET and MRI imaging in the evaluation of CNS drugs in human neurodegenerative diseases

This manuscript reviews the contributions of the neuroimaging methods including PET, conventional and advanced MRI methods to monitor the effect of new disease modifying drugs in neurodegenerative diseases. It now seems obvious that in many pathologies these two techniques are more and more complementary.

Novel PET Biomarkers to Disentangle Molecular Pathways across Age-Related Neurodegenerative Diseases

There is a need to disentangle the etiological puzzle of age-related neurodegenerative diseases, whose clinical phenotypes arise from known, and as yet unknown, pathways that can act distinctly or in concert. Enhanced sub-phenotyping and the identification of in vivo biomarker-driven signature profiles could improve the stratification of patients into clinical trials and, potentially, help to drive the treatment landscape towards the precision medicine paradigm. The rapidly growing field of neuroimaging offers valuable tools to investigate disease pathophysiology and molecular pathways in humans, with the potential to capture the whole disease course starting from preclinical stages. Positron emission tomography (PET) combines the advantages of a versatile imaging technique with the ability to quantify, to nanomolar sensitivity, molecular targets in vivo. This review will discuss current research and available imaging biomarkers evaluating dysregulation of the main molecular pathways across age-related neurodegenerative diseases. The molecular pathways focused on in this review involve mitochondrial dysfunction and energy dysregulation; neuroinflammation; protein misfolding; aggregation and the concepts of pathobiology, synaptic dysfunction, neurotransmitter dysregulation and dysfunction of the glymphatic system. The use of PET imaging to dissect these molecular pathways and the potential to aid sub-phenotyping will be discussed, with a focus on novel PET biomarkers.

The Gene Polymorphism of VMAT2 Is Associated with Risk of Schizophrenia in Male Han Chinese

OBJECTIVE

To investigate the association between gene polymorphism of vesicular monoamine transporter type 2(VMAT2) and schizophrenia in Han Chinese population.

METHODS

430 patients with schizophrenia and 470 age-sex matched controls were recruited from four mental health centers. All patients were diagnosed by two psychiatrists based on the Structured Clinical Interview for DSM Disorders (SCID). The ligase detection reactions (LDR) method was used to assess the polymorphism of the two SNPs (rs363371 and rs363324) of VMAT2.

RESULTS

No associations of two SNPs with schizophrenia was found. When we stratified males and females for the analysis, we found that that in the recessive model of rs363371, there was an obvious significant association between rs363371 and schizophrenia in males (OR=0.564, 95% CI=0.357-0.892, p=0.014) but not females. For the association between rs363324 and schizophrenia, no association was found in either males or females. No association was found when stratifying early-onset schizophrenia and late-onset schizophrenia.

CONCLUSION

Our findings indicate that both rs363371 and rs363324 were not associated with schizophrenia, while it seemed that the AA genotype of rs363371 plays a protective effect in male Chinese in developing schizophrenia.

Parkinson's Disease: Available Clinical and Promising Omics Tests for Diagnostics, Disease Risk Assessment, and Pharmacotherapy Personalization

Parkinson's disease is the second most frequent neurodegenerative disease, representing a significant medical and socio-economic problem. Modern medicine still has no answer to the question of why Parkinson's disease develops and whether it is possible to develop an effective system of prevention. Therefore, active work is currently underway to find ways to assess the risks of the disease, as well as a means to extend the life of patients and improve its quality. Modern studies aim to create a method of assessing the risk of occurrence of Parkinson's disease (PD), to search for the specific ways of correction of biochemical disorders occurring in the prodromal stage of Parkinson's disease, and to personalize approaches to antiparkinsonian pharmacotherapy. In this review, we summarized all available clinically approved tests and techniques for PD diagnostics. Then, we reviewed major improvements and recent advancements in genomics, transcriptomics, and proteomics studies and application of metabolomics in PD research, and discussed the major metabolomics findings for diagnostics and therapy of the disease.

Newly Developed Prodrugs and Prodrugs in Development; an Insight of the Recent Years

BACKGROUND

The design and development of prodrugs is the most common and effective strategy to overcome pharmacokinetic and pharmacodynamic drawbacks of active drugs. A respected number of prodrugs have been reached the drugs market throughout history and the recent years have witnessed a significant increase in the use of prodrugs as a replacement of their parent drugs for an efficient treatment of various ailment.

METHODS

A Scan conducted to find recent approved prodrugs and prodrugs in development.

RESULTS

Selected prodrugs were reported and categorized in accordance to their target systems.

CONCLUSIONS

the prodrug approach has shown many successes and still remains a viable and effective approach to deliver new active agents. This conclusion is supported by the recent approved prodrugs and the scan of clinical trials conducted between 2013-2018.

The Design and Application of an Appropriate Parkinson's Disease Animal Model in Regenerative Medicine

OBJECTIVES

Aging as an inevitable and complex physiological process occurs through a progressive decrease in the potential of tissue regeneration. Given the increasing global outbreak of aging and age-related disorders, it is important to control this phenomenon. Parkinson's disease (one of the age-related neurodegenerative and progressive disorders) resulted from predominant dopaminergic neurons deficiency. Usual Parkinson's disease treatments just can lead to symptomatically relieving. Recently, cell therapy and regenerative medicine a great promise in the treatment of several types of disorders including Parkinson's disease. Herein, before starting clinical trials, preclinical studies should be performed to answer some fundamental questions about the safety and efficacy of various treatments. Additionally, developing a well-designed and approved study is required to provide an appropriate animal model with strongly reliable validation methods. Hereupon, this review will discuss about the design and application of an appropriate Parkinson's disease animal model in regenerative medicine.

EVIDENCE ACQUISITION

In order to conduct the present review, numbers of Parkinson's disease preclinical studies, as well as literatures related to the animal modeling, were considered.

RESULTS

Appropriate animal models which approved by related authorize committees should have a high similarity to humans from anatomical, physiological, behavioral, and genetic characteristics view of point.

CONCLUSION

It is concluded that animal studies before starting clinical trials have an important role in answering the crucial questions about the various treatments safety and efficacy. Therein, it is recommended that all of animal modeling stages be assessed by animal ethics and welfare guidelines and also evaluated by different validation tests. However, it is better to find some alternatives to replacement, refinement, and, reduction of animals. Nowadays, some novel technologies such as using imaging methods have been introduced.