PET and SPECT functional imaging in Parkinson's disease

CLR01 protects dopaminergic neurons in vitro and in mouse models of Parkinson's disease

Parkinson’s disease (PD) affects millions of patients worldwide and is characterized by alpha-synuclein aggregation in dopamine neurons. Molecular tweezers have shown high potential as anti-aggregation agents targeting positively charged residues of proteins undergoing amyloidogenic processes. Here we report that the molecular tweezer CLR01 decreased aggregation and toxicity in induced pluripotent stem cell-derived dopaminergic cultures treated with PD brain protein extracts. In microfluidic devices CLR01 reduced alpha-synuclein aggregation in cell somas when axonal terminals were exposed to alpha-synuclein oligomers. We then tested CLR01 in vivo in a humanized alpha-synuclein overexpressing mouse model; mice treated at 12 months of age when motor defects are mild exhibited an improvement in motor defects and a decreased oligomeric alpha-synuclein burden. Finally, CLR01 reduced alpha-synuclein-associated pathology in mice injected with alpha-synuclein aggregates into the striatum or substantia nigra. Taken together, these results highlight CLR01 as a disease-modifying therapy for PD and support further clinical investigation.

CLR01 is a molecular tweezer that inhibits protein aggregation. Here the authors show that CLR01 protects dopaminergic neurons in vitro and in vivo in human neurons and in mouse models showing potential as a disease-modifying therapy for Parkinson’s disease.

Reduced Gray Matter Volume and Risk of Falls in Parkinson's Disease with Dementia Patients: A Voxel-Based Morphometry Study

Purpose: Risk of falls is a common sequela affecting patients with Parkinson’s disease (PD). Although motor impairment and dementia are correlated with falls, associations of brain structure and cognition deficits with falls remain unclear. Material and Methods: Thirty-five PD patients with dementia (PDD), and 37 age- and sex-matched healthy subjects were recruited for this study. All participants received structural magnetic resonance imaging (MRI) scans, and disease severity and cognitive evaluations. Additionally, patient fall history was recorded. Regional structural differences between PDD with and without fall groups were performed using voxel-based morphometry processing. Stepwise logistic regression analysis was used to predict the fall risk in PDD patients. Results: The results revealed that 48% of PDD patients experienced falls. Significantly lower gray matter volume (GMV) in the left calcarine and right inferior frontal gyrus in PDD patients with fall compared to PDD patients without fall were noted. The PDD patients with fall exhibited worse UPDRS-II scores compared to PDD patients without fall and were negatively correlated with lower GMV in the left calcarine (p/r = 0.004/−0.492). Furthermore, lower GMV in the left calcarine and right inferior frontal gyrus correlated with poor attention and executive functional test scores. Multiple logistic regression analysis showed that the left calcarine was the only variable (p = 0.004, 95% CI = 0.00–0.00) negatively associated with the fall event. Conclusions: PDD patients exhibiting impaired motor function, lower GMV in the left calcarine and right inferior frontal gyrus, and notable cognitive deficits may have increased risk of falls.

The Place of PET to Assess New Therapeutic Effectiveness in Neurodegenerative Diseases

In vivo exploration of neurodegenerative diseases by positron emission tomography (PET) imaging has matured over the last 20 years, using dedicated radiopharmaceuticals targeting cellular metabolism, neurotransmission, neuroinflammation, or abnormal protein aggregates (beta-amyloid and intracellular microtubule inclusions containing hyperphosphorylated tau). The ability of PET to characterize biological processes at the cellular and molecular levels enables early detection and identification of molecular mechanisms associated with disease progression, by providing accurate, reliable, and longitudinally reproducible quantitative biomarkers. Thus, PET imaging has become a relevant imaging method for monitoring response to therapy, approved as an outcome measure in bioclinical trials. The aim of this paper is to review and discuss the current inputs of PET in the assessment of therapeutic effectiveness in neurodegenerative diseases connected by common pathophysiological mechanisms, including Parkinson's disease, Huntington's disease, dementia, amyotrophic lateral sclerosis, multiple sclerosis, and also in psychiatric disorders. We also discuss opportunities for PET imaging to drive more personalized neuroprotective and therapeutic strategies, taking into account individual variability, within the growing framework of precision medicine.

Current understanding of the molecular mechanisms in Parkinson's disease: Targets for potential treatments

Gradual degeneration and loss of dopaminergic neurons in the substantia nigra, pars compacta and subsequent reduction of dopamine levels in striatum are associated with motor deficits that characterize Parkinson’s disease (PD). In addition, half of the PD patients also exhibit frontostriatal-mediated executive dysfunction, including deficits in attention, short-term working memory, speed of mental processing, and impulsivity. The most commonly used treatments for PD are only partially or transiently effective and are available or applicable to a minority of patients. Because, these therapies neither restore the lost or degenerated dopaminergic neurons, nor prevent or delay the disease progression, the need for more effective therapeutics is critical. In this review, we provide a comprehensive overview of the current understanding of the molecular signaling pathways involved in PD, particularly within the context of how genetic and environmental factors contribute to the initiation and progression of this disease. The involvement of molecular chaperones, autophagy-lysosomal pathways, and proteasome systems in PD are also highlighted. In addition, emerging therapies, including pharmacological manipulations, surgical procedures, stem cell transplantation, gene therapy, as well as complementary, supportive and rehabilitation therapies to prevent or delay the progression of this complex disease are reviewed.

Investigation of spatial resolution improvement by use of a mouth-insert detector in the helmet PET scanner

The dominant factor limiting the intrinsic spatial resolution of a positron emission tomography (PET) system is the size of the crystal elements in the detector. To increase sensitivity and achieve high spatial resolution, it is essential to use advanced depth-of-interaction (DOI) detectors and arrange them close to the subject. The DOI detectors help maintain high spatial resolution by mitigating the parallax error caused by the thickness of the scintillator near the peripheral regions of the field-of-view. As an optimal geometry for a brain PET scanner, with high sensitivity and spatial resolution, we proposed and developed the helmet-chin PET scanner using 54 four-layered DOI detectors consisting of a 16 × 16 × 4 array of GSOZ scintillator crystals with dimensions of 2.8 × 2.8 × 7.5 mm³. All the detectors used in the helmet-chin PET scanner had the same spatial resolution. In this study, we conducted a feasibility study of a new add-on detector arrangement for the helmet PET scanner by replacing the chin detector with a segmented crystal cube, having high spatial resolution in all directions, which can be placed inside the mouth. The crystal cube (which we have named the mouth-insert detector) has an array of 20 × 20 × 20 LYSO crystal segments with dimensions of 1 × 1 × 1 mm³. Thus, the scanner is formed by the combination of the helmet and mouth-insert detectors, and is referred to as the helmet-mouth-insert PET scanner. The results show that the helmet-mouth-insert PET scanner has comparable sensitivity and improved spatial resolution near the center of the hemisphere, compared to the helmet-chin PET scanner.

A new program for highly reproducible automatic evaluation of the substantia nigra from transcranial sonographic images

AIMS

Recent studies report increased echogenicity of the substantia nigra (SN) in patients with Parkinson's disease (PD) using transcranial sonography (TCS). However, the main limitation to TCS is its dependence on the sonographer's experience. Experimental software for quantitative evaluation of the echogenic SN area was thus developed by us. The aim of this study was to test the reliability of the data using developed B-Mode Assist software in patients with parkinsonism and in healthy volunteers.

METHODS

The SN was imaged from the right temporal bone window in mesencephalic plane using TCS. DICOM images of SN were saved, converted into JPEG format, encoded and processed. Two observers performed 3 automatic evaluations of the SN area (measurements of SN area in each gray scale intensity inside the region of interest) by counting the standard deviation of all 6 measurements using developed software. The average value of all 3 measurements of each observer was used for computing Cohen's kappa coefficient to determine inter-observer correlations. Cohen's kappa coefficients as an intra-observer correlation for observer 1 and observer 2 were counted from the first 2 measurements of both observers.

RESULTS

In total, 92 images were evaluated using this software. The mean of the standard deviations was 3.87; Cohen's kappa for intra-observer agreement of two observers were 0.947, and 0.943, resp.; Cohen's kappa for inter-observers agreement was 0.880. The agreement between visual and automatic detection of SN pathology was in 97.8% images. The sensitivity, specificity, positive and negative predictive values of automatic measurement were 100, 96.2, 95.1, 100%, resp.

CONCLUSIONS

The results show very reliable measurement of SN features using designed application with "almost perfect" inter-observer and intra-observer agreements.

Positron emission tomography for benign and malignant disease

Functional imaging using radiolabeled probes that specifically bind and accumulate in target tissues has improved the sensitivity and specificity of conventional imaging. Fluorodeoxyglucose (FDG)-positron emission tomography (PET) has shown improved diagnostic accuracy in differentiating benign from malignant lesions in the setting of solitary pulmonary nodules. FDG-PET has become useful in preoperative staging of patients with lung cancer, and is being tested with many other malignancies for its ability to change patient management. This article provides an overview of the current status of FDG-PET and presents the challenges of moving toward routine use.

Single-photon emission computed tomography and positron emission tomography evaluations of patients with central motor disorders

Neuroimaging biomarkers in movement disorders during the past decade have served as diagnostic agents (Europe), tools for evaluation of novel therapeutics, and a powerful means for describing pathophysiology by revealing in vivo changes at different stages of disease and within the course of an individual patient's illness. As imaging with agents tracking dopaminergic function become more available, the next decade promises to enhance our clinical sophistication in the optimal use of dopaminergic imaging biomarkers for differential diagnosis, characterization of at-risk populations, guiding selection and management of appropriate treatments. The clinical role of these agents as clinical tools goes hand in hand with the development and availability of disease-modifying drugs, which carry the additional requirement for early and accurate diagnosis and improved clinical monitoring once treatment is initiated. Challenges remain in the ideal application of neuroimaging in the clinical algorithms for patient assessment and management. Further, the application of imaging to other targets, both monamineric and nonmonoaminergic, could serve a function beyond the important delineation of pathologic change occurring in patients with Parkinson's disease to suggest some role in improved phenotyping and classification of patients with Parkinson's disease presenting with different symptom clusters. New areas of focus based on the elucidation of mechanisms at the cellular and molecular level, including intense interest in alpha-synuclein and other protein inclusions in neurons and glia, have piqued interest in their in vivo assessment using scinitigraphic methods. Perhaps ultimately, treatment that is targeted to a better delineated pathophysiology-based characterization of movement disorder patients will emerge. The application of neuroimaging biomarkers to multiple ends in movement disorders provides an important model for the multiple roles diagnostic imaging agents can serve in neurodegenerative disorders; for diagnosis, for elaborating pathophysiology in patient populations, for developing new drugs, ultimately for improving clinical management.

SPECT neuroimaging in translational research of CNS disorders

High resolution SPECT imaging is an emerging field and there are only limited studies as yet available in this direction. Still there is continuous effort to achieve better spatial and temporal resolution in order to obtain detailed structural and functional information of different brain regions in small experimental animals. Recently, SPECT imaging system has been used to perform in vivo imaging using specific radioligands to further elucidate the role of dopaminergic, serotonergic, and cholinergic neurotransmission in relation to regional cerebral blood flow in various human CNS disorders and in gene-manipulated mouse models of neurodegeneration. Although in vivo and non-invasive translational research can be performed by high-resolution microPET imaging system, its limited spatial resolution restricts detailed anatomical and functional information of different brain regions involved in disease process. Recently developed NanoSPECT/CT imaging system has a better spatial resolution hence can be used to correlate and confirm microPET imaging data and determine the precise structural and functional anatomy of CNS disorders and their remission. Moreover SPECT imaging system reduces the cost and number of animals and provides detailed information of CNS disorders at the cellular, molecular and genetic level. Furthermore, SPECT system is economical, provides less radiation burden, and can be used to study bio-distribution of newly synthesized radioligands with increased target to non-target ratios, quality control, and clinical applications. It is envisaged that high-resolution SPECT imaging system will further improve in vivo non-invasive translational research on CNS disorders of unknown etiopathogenesis and their treatment in future.

Reproducibility of sonographic measurement of the substantia nigra

The aim of this study was to evaluate inter-reader, intra-investigator and inter-investigator reproducibility and correlations in the assessment of substantia nigra (SN) echogenicity and area measurement by a physician-sonographer (PS), a sonographic laboratory assistant (SLA) and a physician without sonographic experience (PN). A total of 22 patients with extrapyramidal symptoms were examined using transcranial sonography (TCS). SN images were encoded and evaluated by the three readers. A second TCS examination was performed after 7+/-2 d. A second investigator performed TCS examination 1 mo later. Spearman rank correlation and Pearson's correlation coefficient were used when assessing the agreement between readers. All three readers identified the same 15 patients with SN echogenicity III or more. Inter-reader SN echogenicity and area measurement correlations were r=0.55 to 0.82 and r=0.31 to 0.74 between PS and SLA and r=0.55 to 0.77 and 0.49 to 0.62 between PS and PN, respectively (p<0.05 in all cases). Intra-reader echogenicity and area measurement correlations (r=0.85 to 0.96 and r=0.51 to 0.69) were statistically significant only for PS (p<0.001). All intra- and inter-investigator correlations of SN area measurement (r=0.69 to 0.88 and r=0.5 to 0.61) and SN echogenicity (r=0.64 to 0.92 and r=0.51 to 0.69) were statistically significant (p<0.05). Semiquantitative evaluation of SN echogenicity and area using TCS is highly dependent on the experience of the sonographer. Only an experienced sonographer was able to produce very reproducible results with statistically significant correlations; SLA and PN intra-reader correlations were poor.

Current Pharmacotherapeutic Treatment Options in Parkinson’s Disease

Treatment options for Parkinson's disease have greatly expanded in recent years. Pharmacological treatments, such as levodopa, dopamine receptor agonists, anticholinergic medications, monoamine oxidase B inhibitors, and the catechol-O-methyl transferase inhibitors, remain the mainstay of therapeutic intervention and are reviewed. Additionally, the traditional and new roles for amantadine are explained. Despite the great efficacy of levodopa, "levodopa-sparing strategies" in early Parkinson's disease are emphasized in order to delay the development of difficult-to-manage motor fluctuations and dyskinesias.

Molecular imaging in hereditary forms of parkinsonism

The development of in vivo molecular imaging to evaluate the dopamine (DA) system with positron-emission tomography and single photon emission computed tomography has been of key importance on monitoring in vivo nigrostriatal neuronal loss in Parkinson's disease (PD), mostly through assessments of pre- and post-synaptic DA receptors. The discoveries of genes related to hereditary forms of parkinsonism (PARK1, PARK2, PARK6, PARK7 and PARK8) have increased our understanding either of distinct subtypes of clinical expression in PD or its etiology. This article revises current data on molecular neuroimaging of genetic forms of parkinsonism comparing and contrasting its main features with the classical sporadic forms. Awareness of the spectrum variance in the genotype and its respective PD phenotype are useful to distinguish different pathophysiological mechanisms of PD.

Magnetic resonance imaging-based volumetric analysis of basal ganglia nuclei and substantia nigra in patients with Parkinson's disease

OBJECTIVE

Parkinson's disease (PD) is associated with well-documented morphological changes in substantia nigra and basal ganglia nuclei. This study evaluates the ability of magnetic resonance imaging to detect these changes and investigates the relationship between severity of clinical findings and degree of morphological change. This correlation may provide valuable information in early diagnosis of PD.

METHODS

Sixteen patients with early stage PD, eight patients with advanced PD, and eight normal controls were studied by 3T magnetic resonance imaging. The whole brain volume and the volumes of the caudate, putamen, globus pallidus, and substantia nigra were calculated on three-dimensional reconstructed images.

RESULTS

Putamen volume was significantly diminished in patients with early PD and advanced PD compared with that in controls (P < 0.05), and the percentage of atrophy was 12.5 and 26.5%, respectively. The putamen volume was negatively correlated with Hoehn and Yahr staging (r = -0.720, P < 0.001). Pallidal volume was reduced only in advanced PD (P = 0.023). There were no significant differences in total brain, caudate, or substantia nigra among these three groups

CONCLUSION

Magnetic resonance imaging-based volumetric measurement is a sensitive method in the assessment of morphological changes of PD in vivo. The putamen atrophy was correlated with the severity of clinical findings. The volumetric measurement of putamen could potentially be a useful indicator of PD in the early stage.

Novel gene therapeutic strategies for neurodegenerative diseases

The convergent pathobiologic model of Parkinson's disease stipulates that disparate insults initiate a disease process that obligately share a common pathway leading to cell death. A combinatorial treatment which targets various steps in this pathway is likely to be the most successful therapeutic strategy. As advances are made in the field of neuroimaging and pharmacogenomics, early detection of sporadic PD will become a reality. Early intervention will likely spare more dopaminergic neurons and extend the quality of life for the patient. Continued advancements in the fields of pharmacology, neurosurgery, and gene therapy will strengthen the armamentarium available for the treatment of PD patients.

Striatal dopamine transporter binding in Parkinson's disease associated with theLRRK2 Gly2019Ser mutation

We measured striatal dopamine transporter binding using [(123)I]ioflupane and SPECT in patients with Parkinson's disease associated with the LRRK2 (PARK8) Gly2019Ser gene mutation (LRRK2-PD) and in gene-negative patients with idiopathic Parkinson's disease (IPD) of comparable disease duration and severity. The LRRK2-PD group consisted of a total of 10 patients (3 sporadic) with mean age 62 +/- 14 years, disease duration 9 +/- 3 years, and UPDRS III motor score 21.60 +/- 6.65. The control IPD group consisted of 15 patients with mean age 59 +/- 9 years, disease duration 9 +/- 5 years, and UPDRS III motor score 23.80 +/- 8.69. [(123)I]ioflupane-specific uptake ratios were calculated for caudate nucleus and putamen using the occipital cortex as reference region. We found no differences between the LRRK2-PD group and IPD in all items studied. In particular, putamen and caudate uptake values as well as side asymmetry indexes and putamen/caudate ratios all revealed comparable between-group values. We conclude that in these patients carrying the LRRK2 Gly2019Ser mutation, the neurodegenerative process results in a pattern of nigrostriatal dopaminergic dysfunction similar to that observed in IPD.

Genetic, clinical, and imaging characterization of one patient with late-onset, slowly progressive, pantothenate kinase-associated neurodegeneration

We report on a patient with late-onset, pantothenate kinase-associated neurodegeneration (PKAN) who revealed two new heterozygous mutations at gene testing and showed asymmetric moderately reduced striatal dopamine transporter binding with single photon emission computed tomography, possibly due to prolonged neuroleptic treatment. These findings expand the genetic and imaging spectrum of this rare disorder.

A slowly developing dysfunction of dopaminergic nigrostriatal neurons induced by long-term paraquat administration in rats: an animal model of preclinical stages of Parkinson's disease?

The aim of the present study was to examine the influence of the long-term paraquat administration on the dopaminergic nigrostriatal system in rats. Paraquat was injected at a dose of 10 mg/kg i.p. for 4-24 weeks. We found that this pesticide reduced the number of tyrosine hydroxylase-immunoreactive neurons of the substantia nigra; after the 4-week treatment the reduction (17%, nonsignificant) was confined to the rostrocentral region of this structure but, after 24 weeks, had spread along its whole length and was approximately 37%. Moreover, it induced a biphasic effect on dopaminergic transmission. First, levels of dopamine, its metabolites and turnover were elevated (4-8 weeks) in the caudate-putamen, then all these parameters returned to control values (12 weeks) and dropped by 25-30% after 24 weeks. The binding of [3H]GBR 12,935 to dopamine transporter in the caudate-putamen was decreased after 4-8 weeks, then returned to control values after 12 weeks but was again decreased after 24 weeks. Twenty-four-week paraquat administration also decreased the level of tyrosine hydroxylase (Western blot) in the caudate-putamen. In addition, paraquat activated serotonin and noradrenaline transmission during the first 12 weeks of treatment but no decreases in levels of these neurotransmitters were observed after 24 weeks. The above results seem to suggest that long-term paraquat administration produces a slowly progressing degeneration of nigrostriatal neurons, leading to delayed deficits in dopaminergic transmission, which may resemble early, presymptomatic, stages of Parkinson's disease.