Cortical glucose metabolism in Parkinson's disease without dementia

Association between gene expression and functional-metabolic architecture in Parkinson's disease

Gene expression plays a critical role in the pathogenesis of Parkinson's disease (PD). How gene expression profiles are correlated with functional-metabolic architecture remains obscure. We enrolled 34 PD patients and 25 age-and-sex-matched healthy controls for simultaneous 18 F-FDG-PET/functional MRI scanning during resting state. We investigated the functional gradients and the ratio of standard uptake value. Principal component analysis was used to further combine the functional gradients and glucose metabolism into functional-metabolic architecture. Using partial least squares (PLS) regression, we introduced the transcriptomic data from the Allen Institute of Brain Sciences to identify gene expression patterns underlying the affected functional-metabolic architecture in PD. Between-group comparisons revealed significantly higher gradient variation in the visual, somatomotor, dorsal attention, frontoparietal, default mode, and subcortical network (pFDR  < .048) in PD. Increased FDG-uptake was found in the somatomotor and ventral attention network while decreased FDG-uptake was found in the visual network (pFDR  < .008). Spatial correlation analysis showed consistently affected patterns of functional gradients and metabolism (p = 2.47 × 10-8 ). PLS analysis and gene ontological analyses further revealed that genes were mainly enriched for metabolic, catabolic, cellular response to ions, and regulation of DNA transcription and RNA biosynthesis. In conclusion, our study provided genetic pathological mechanism to explain imaging-defined brain functional-metabolic architecture of PD.

Visual Dysfunction in Parkinson's Disease

Non-motor symptoms in Parkinson's disease (PD) include ocular, visuoperceptive, and visuospatial impairments, which can occur as a result of the underlying neurodegenerative process. Ocular impairments can affect various aspects of vision and eye movement. Thus, patients can show dry eyes, blepharospasm, reduced blink rate, saccadic eye movement abnormalities, smooth pursuit deficits, and impaired voluntary and reflexive eye movements. Furthermore, visuoperceptive impairments affect the ability to perceive and recognize visual stimuli accurately, including impaired contrast sensitivity and reduced visual acuity, color discrimination, and object recognition. Visuospatial impairments are also remarkable, including difficulties perceiving and interpreting spatial relationships between objects and difficulties judging distances or navigating through the environment. Moreover, PD patients can present visuospatial attention problems, with difficulties attending to visual stimuli in a spatially organized manner. Moreover, PD patients also show perceptual disturbances affecting their ability to interpret and determine meaning from visual stimuli. And, for instance, visual hallucinations are common in PD patients. Nevertheless, the neurobiological bases of visual-related disorders in PD are complex and not fully understood. This review intends to provide a comprehensive description of visual disturbances in PD, from sensory to perceptual alterations, addressing their neuroanatomical, functional, and neurochemical correlates. Structural changes, particularly in posterior cortical regions, are described, as well as functional alterations, both in cortical and subcortical regions, which are shown in relation to specific neuropsychological results. Similarly, although the involvement of different neurotransmitter systems is controversial, data about neurochemical alterations related to visual impairments are presented, especially dopaminergic, cholinergic, and serotoninergic systems.

Quantitative kinetic modelling and mapping of cerebral glucose transport and metabolism using glucoCESL MRI

Chemical-exchange spin-lock (CESL) MRI can map regional uptake and utilisation of glucose in the brain at high spatial resolution (i.e sub 0.2 mm³ voxels). We propose two quantitative kinetic models to describe glucose-induced changes in tissue R_1ρ and apply them to glucoCESL MRI data acquired in tumour-bearing and healthy rats. When assuming glucose transport is saturable, the maximal transport capacity (T_max) measured in normal tissue was 3.2 ± 0.6 µmol/min/mL, the half saturation constant (K_t) was 8.8 ± 2.2 mM, the metabolic rate of glucose consumption (MR_glc) was 0.21 ± 0.13 µmol/min/mL, and the cerebral blood volume (v_b) was 0.006 ± 0.005 mL/mL. Values in tumour were: T_max = 7.1 ± 2.7 µmol/min/mL, K_t = 14 ± 1.7 mM, MR_glc = 0.22 ± 0.09 µmol/min/mL, v_b = 0.030 ± 0.035 mL/mL. T_max and K_t were significantly higher in tumour tissue than normal tissue (p = 0.006 and p = 0.011, respectively). When assuming glucose uptake also occurs via free diffusion, the free diffusion rate (k_d) was 0.061 ± 0.017 mL/min/mL in normal tissue and 0.12 ± 0.042 mL/min/mL in tumour. These parameter estimates agree well with literature values obtained using other approaches (e.g. NMR spectroscopy).

The role of NURR1 in metabolic abnormalities of Parkinson's disease

A constant metabolism and energy supply are crucial to all organs, particularly the brain. Age-dependent neurodegenerative diseases, such as Parkinson’s disease (PD), are associated with alterations in cellular metabolism. These changes have been recognized as a novel hot topic that may provide new insights to help identify risk in the pre-symptomatic phase of the disease, understand disease pathogenesis, track disease progression, and determine critical endpoints. Nuclear receptor-related factor 1 (NURR1), an orphan member of the nuclear receptor superfamily of transcription factors, is a major risk factor in the pathogenesis of PD, and changes in NURR1 expression can have a detrimental effect on cellular metabolism. In this review, we discuss recent evidence that suggests a vital role of NURR1 in dopaminergic (DAergic) neuron development and the pathogenesis of PD. The association between NURR1 and cellular metabolic abnormalities and its implications for PD therapy have been further highlighted.

Defects of Nutrient Signaling and Autophagy in Neurodegeneration

Neurons are post-mitotic cells that allocate huge amounts of energy to the synthesis of new organelles and molecules, neurotransmission and to the maintenance of redox homeostasis. In neurons, autophagy is not only crucial to ensure organelle renewal but it is also essential to balance nutritional needs through the mobilization of internal energy stores. A delicate crosstalk between the pathways that sense nutritional status of the cell and the autophagic processes to recycle organelles and macronutrients is fundamental to guarantee the proper functioning of the neuron in times of energy scarcity. This review provides a detailed overview of the pathways and processes involved in the balance of cellular energy mediated by autophagy, which when defective, precipitate the neurodegenerative cascade of Parkinson’s disease, frontotemporal dementia, amyotrophic lateral sclerosis or Alzheimer’s disease.

Stereopsis and Eye Movement Abnormalities in Parkinson’s Disease and Their Clinical Implications

Background

Parkinson’s disease (PD) is not exclusively a motor disorder. Among non-motor features, patients with PD possess sensory visual dysfunctions. Depth perception and oculomotor deficits can significantly impact patients’ motor performance. Stereopsis and eye behavioral study using 3D stimuli may help determine their implications in disease status.

Objective

The objective of this study is to investigate stereopsis and eye movement abnormalities in PD with reliable tools and their correlation with indicators of PD severity. We hypothesize that patients with PD exhibit different eye behaviors and that these differences may correlate to the severity of motor symptoms and cognitive status.

Methods

Control and PD participants were first evaluated for visual acuity, visual field, contrast acuity, and stereo perception with 2D and Titmus stereotests, followed by the assessment with a 3D active shutter system. Eye movement behaviors were assessed by a Tobii X2-60 eye tracker.

Results

Screening visual tests did not reveal any differences between the PD and control groups. With the 3D active shutter system, the PD group demonstrated significantly worse stereopsis. The preserved cognitive function was correlated to a more intact stereo function. Patients with PD had longer visual response times, with a higher number of fixations and bigger saccade amplitude, suggesting fixation stabilization difficulties. Such changes showed a positive correlation with the severity of motor symptoms and a negative correlation with normal cognitive status.

Conclusion

We assessed stereopsis with a 3D active shutter system and oculomotor behaviors with the Tobii eye tracker. Patients with PD exhibit poorer stereopsis and impaired oculomotor behaviors during response time. These deficits were correlated with PD motor and cognitive status. The visual parameters may potentially serve as the clinical biomarkers for PD.

Metabolic Features of Brain Function with Relevance to Clinical Features of Alzheimer and Parkinson Diseases

Brain metabolism is comprised in Alzheimer’s disease (AD) and Parkinson’s disease (PD). Since the brain primarily relies on metabolism of glucose, ketone bodies, and amino acids, aspects of these metabolic processes in these disorders—and particularly how these altered metabolic processes are related to oxidative and/or nitrosative stress and the resulting damaged targets—are reviewed in this paper. Greater understanding of the decreased functions in brain metabolism in AD and PD is posited to lead to potentially important therapeutic strategies to address both of these disorders, which cause relatively long-lasting decreased quality of life in patients.

Metabolic imaging and plasticity

Positron emission tomography greatly advanced our understanding on the underlying neural mechanisms of movement disorders. PET with flurodeoxyglucose (FDG) is especially useful as it depicts regional metabolic activity level that can predict patients' symptoms. Multivariate pattern analysis has been used to determine and quantify the co-varying brain networks associated with specific clinical traits of neurodegenerative disease. The result is a biomarker, useful for diagnosis, treatments, and follow up studies. Parkinsonian traits and parkinsonisms are associated with specific spatial pattern of metabolic abnormality useful for differential diagnosis. This approach has also been used for monitoring disease progression and novel treatment responses mostly in Parkinson's disease. In this book chapter, we, illustrate and discuss the significance of the brain networks associated with disease and their modification with neuroplastic changes.

Impaired mitochondrial functions and energy metabolism in MPTP-induced Parkinson's disease: comparison of mice strains and dose regimens

Heterogenous diseases such as Parkinson's disease (PD) needs an efficient animal model to enhance understanding of the underlying mechanisms and to develop therapeutics. MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a neurotoxin, has been widely used to replicate the pathophysiology of PD in rodents, however, the knowledge about its effects on energy metabolism is limited. Moreover, susceptibility to different dose regimens of MPTP also varies among mice strains. Thus, the present study compares the effect of acute and sub-acute MPTP administration on mitochondrial functions in C57BL/6 and BALB/c mice. In addition, activity of enzymes involved in energy metabolism was also studied along with behavioural alterations. The findings show that acute dose of MPTP in C57BL/6 mice had more profound effect on the activity of electron transport chain complexes. Further, the activity of MAO-B was increased following acute and sub-acute MPTP administration in C57BL/6 mice. However, no significant change was observed in BALB/c mice. Acute MPTP treatment resulted in decreased mitochondrial membrane potential along with increased swelling of mitochondria in C57BL/6 mice. In addition, perturbations were observed in hexokinase, the rate limiting enzyme of glycolysis and pyruvate dehydrogenase, the enzymes that connects glycolysis and TCA cycle. The activity of TCA cycle enzymes; citrate synthase, aconitase, isocitrate dehydrogenase and fumarase were also altered following MPTP intoxication. Furthermore, acute MPTP administration led to drastic reduction in dopamine levels in striatum of C57BL/6 as compared to BALB/c mice. Behavioral tests such as open field, narrow beam walk and footprint analysis revealed severe impairment in locomotor activity in C57BL/6 mice. These results clearly demonstrate that C57BL/6 strain is more vulnerable to MPTP-induced mitochondrial dysfunctions, perturbations in energy metabolism and motor defects as compared to BALB/c strain. Thus, the findings suggest that the dose and strain of mice need to be considered for pre-clinical studies using MPTP-induced model of Parkinson's disease.

Impaired age-dependent increases in phosphoglycerate kinase activity in red blood cells of Parkinson's disease patients

BACKGROUND

Impaired bioenergetics are partially involved in the pathogenesis of Parkinson's disease (PD). Phosphoglycerate kinase (PGK), an essential enzyme for glycolysis, has recently attracted attention due to its pathogenic role in PD and as a target for disease-modifying therapies. This study is aimed to evaluate the profiles of PGK activity in red blood cells (RBCs) of PD patients and controls.

METHODS

Sixty-eight PD patients and thirty-four age-matched unrelated controls were enrolled. PGK activities of RBCs were measured by the established colorimetric assay and standardized by the same RBC samples.

RESULTS

PGK activity of the PD group was significantly higher than that of the control group in participants aged sixty-five years or younger, whereas it was not significantly different between the two groups at any age. PGK activity was positively correlated with aging in the control group, but this was not noted in the PD group. On multivariable analysis by partial correlation in the PD group, PGK activity was negatively correlated with the specific binding ratio of dopamine transporter scintigraphy in the striatum. The levodopa-equivalent daily dose was not significantly correlated with the enzyme activity.

CONCLUSION

The results support the following: 1) elevation of PGK activities in RBCs can be detected in relatively young PD patients and with normal aging; 2) the degree of striatonigral degeneration is associated with elevated PGK activities. These are important considerations when the PGK assay is applied as a diagnostic biomarker of PD and to therapeutically monitor PGK-enhancing treatments.

Regional Cerebral Cortical Atrophy is Related to Urinary Tract Symptoms in Parkinson's Disease

BACKGROUND AND PURPOSE

Lower urinary tract symptoms (LUTS) are the most common nonmotor symptoms usually occurring mid-stage of Parkinson's disease (PD); however, its underlying mechanisms are unknown. We aimed to assess whether corticometry or volumetry can identify a pattern of cerebral cortical changes in PD patients with LUTS.

METHODS

We recruited 85 idiopathic PD patients and performed corticometry and volumetry on various cortical regions using each patient's magnetic resonance imaging. To identify a correlation between the cortical thickness/volume and nonmotor symptoms scale domain 7 scores, which represent the severity of LUTS, we performed general linear model and region of interest analyses.

RESULTS

Significant regional thinning of the left precuneus, left temporal pole, left precentral, right precuneus, and right pars opercularis was correlated with nonmotor symptoms scale domain 7 scores. We also found that cortical volumes of left precuneus and left frontal pole were inversely correlated with the severity of urinary symptoms.

CONCLUSIONS

This study showed that the thicknesses and volumes of several cortical regions were significantly correlated with the severity of LUTS in PD patients. The findings of regional atrophy and thinning of specific cortical regions in this study provide additional evidence that multiple cortical regions, especially the precuneus cortex, not only may be involved in urinary dysfunctions of PD patients but also may help to elucidate the exact underlying mechanisms for LUTS in PD patients.

Shared functional neural substrates in Parkinson's disease and drug-induced parkinsonism: association with dopaminergic depletion

While drug-induced parkinsonism (DIP) is mainly caused by blockage of the dopaminergic pathway, multiple neurotransmitter systems besides the dopaminergic system are involved in Parkinson’s disease (PD). Therefore, alterations found in both DIP and PD might be manifestations of dopaminergic dysfunction. To prove this hypothesis, we aimed to define the areas commonly involved in DIP and PD and determine whether the overlapping areas were associated with the dopaminergic system. 68 PD patients, 69 DIP patients and 70 age-and sex-matched controls underwent resting-state functional MRI (rsfMRI). Regional homogeneity (ReHo), amplitude of low-frequency fluctuation (ALFF) and fractional ALFF were calculated and compared. Afterwards, we compared mean rsfMRI values extracted from the overlapping areas with uptake quantitatively measured on dopamine transporter (DAT) images and neuropsychological test results. Compared to the controls, both PD and DIP patients revealed altered rsfMRI values in the right insular cortex, right temporo-occipital cortex, and cerebellum. Among them, decreased ALFF in the right insular cortex and decreased ReHo in the right occipital cortex were correlated with decreased DAT uptake in the caudate as well as executive, visuospatial, and language function. Increased ReHo in the cerebellum was also correlated with decrease DAT uptake in the posterior and ventral anterior putamen, but not with cognitive function. In conclusion, the insular cortex, occipital cortex, and cerebellum were commonly affected in both PD and DIP patients and might be associated with altered dopaminergic modulation.

The pentose phosphate pathway regulates chronic neuroinflammation and dopaminergic neurodegeneration

BACKGROUND

Metabolic dysfunction and neuroinflammation are increasingly implicated in Parkinson's disease (PD). The pentose phosphate pathway (PPP, a metabolic pathway parallel to glycolysis) converts glucose-6-phosphate into pentoses and generates ribose-5-phosphate and NADPH thereby governing anabolic biosynthesis and redox homeostasis. Brains and immune cells display high activity of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the PPP. A postmortem study reveals dysregulation of G6PD enzyme in brains of PD patients. However, spatial and temporal changes in activity/expression of G6PD in PD remain undetermined. More importantly, it is unclear how dysfunction of G6PD and the PPP affects neuroinflammation and neurodegeneration in PD.

METHODS

We examined expression/activity of G6PD and its association with microglial activation and dopaminergic neurodegeneration in multiple chronic PD models generated by an intranigral/intraperitoneal injection of LPS, daily subcutaneous injection of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) for 6 days, or transgenic expression of A53T α-synuclein. Primary microglia were transfected with G6PD siRNAs and treated with lipopolysaccharide (LPS) to examine effects of G6PD knockdown on microglial activation and death of co-cultured neurons. LPS alone or with G6PD inhibitor(s) was administrated to mouse substantia nigra or midbrain neuron-glia cultures. While histological and biochemical analyses were conducted to examine microglial activation and dopaminergic neurodegeneration in vitro and in vivo, rotarod behavior test was performed to evaluate locomotor impairment in mice.

RESULTS

Expression and activity of G6PD were elevated in LPS-treated midbrain neuron-glia cultures (an in vitro PD model) and the substantia nigra of four in vivo PD models. Such elevation was positively associated with microglial activation and dopaminergic neurodegeneration. Furthermore, inhibition of G6PD by 6-aminonicotinamide and dehydroepiandrosterone and knockdown of microglial G6PD attenuated LPS-elicited chronic dopaminergic neurodegeneration. Mechanistically, microglia with elevated G6PD activity/expression produced excessive NADPH and provided abundant substrate to over-activated NADPH oxidase (NOX2) leading to production of excessive reactive oxygen species (ROS). Knockdown and inhibition of G6PD ameliorated LPS-triggered production of ROS and activation of NF-кB thereby dampening microglial activation.

CONCLUSIONS

Our findings indicated that G6PD-mediated PPP dysfunction and neuroinflammation exacerbated each other mediating chronic dopaminergic neurodegeneration and locomotor impairment. Insight into metabolic-inflammatory interface suggests that G6PD and NOX2 are potential therapeutic targets for PD.

Impact of dopamine and cognitive impairment on neural reactivity to facial emotion in Parkinson's disease

Emotional and cognitive impairments in Parkinson's disease (PD) are prevalent, hamper interpersonal relations and reduce quality of life. It is however unclear to what extent these domains interplay in PD-related deficits and how they are influenced by dopaminergic availability. This study examined the effect of cognitive impairment and dopaminergic medication on neural and behavioral mechanisms of facial emotion recognition in PD patients. PD patients on and off dopaminergic medication and matched healthy controls underwent an emotional face matching task during functional MRI. In addition, a comprehensive neuropsychological evaluation of cognitive function was conducted. Increased BOLD response to emotional faces was found in the visual cortex of PD patients relative to controls irrespective of cognitive function and medication status. Administration of dopaminergic medication in PD patients resulted in restored behavioral accuracy for emotional faces relative to controls and decreased retrosplenial cortex BOLD response to emotion relative to off-medication state. Furthermore, cognitive impairment in PD patients was associated with reduced behavioral accuracy for non-emotional stimuli and predicted BOLD response to emotion in the anterior and posterior cingulate cortices, depending on medication status. Findings of aberrant visual and retrosplenial BOLD response to emotion are suggested to stem from altered attentional and/or emotion-driven modulation from subcortical and higher cortical regions. Our results indicate neural disruptions and behavioral deficits in emotion processing in PD patients that are dependent on dopaminergic availability and independent of cognitive function. Our findings highlight the importance of dopaminergic treatment not only for the motor symptoms but also the emotional disturbances in PD.

FDG PET Parkinson's disease-related pattern as a biomarker for clinical trials in early stage disease

Background

The development of therapeutic interventions for Parkinson disease (PD) is challenged by disease complexity and subjectivity of symptom evaluation. A Parkinson's Disease Related Pattern (PDRP) of glucose metabolism via fluorodeoxyglucose positron emission tomography (FDG-PET) has been reported to correlate with motor symptom scores and may aid the detection of disease-modifying therapeutic effects.

Objectives

We sought to independently evaluate the potential utility of the PDRP as a biomarker for clinical trials of early-stage PD.

Methods

Two machine learning approaches (Scaled Subprofile Model (SSM) and NPAIRS with Canonical Variates Analysis) were performed on FDG-PET scans from 17 healthy controls (HC) and 23 PD patients. The approaches were compared regarding discrimination of HC from PD and relationship to motor symptoms.

Results

Both classifiers discriminated HC from PD (p < 0.01, p < 0.03), and classifier scores for age- and gender- matched HC and PD correlated with Hoehn & Yahr stage (R² = 0.24, p < 0.015) and UPDRS (R² = 0.23, p < 0.018). Metabolic patterns were highly similar, with hypometabolism in parieto-occipital and prefrontal regions and hypermetabolism in cerebellum, pons, thalamus, paracentral gyrus, and lentiform nucleus relative to whole brain, consistent with the PDRP. An additional classifier was developed using only PD subjects, resulting in scores that correlated with UPDRS (R² = 0.25, p < 0.02) and Hoehn & Yahr stage (R² = 0.16, p < 0.06).

Conclusions

Two independent analyses performed in a cohort of mild PD patients replicated key features of the PDRP, confirming that FDG-PET and multivariate classification can provide an objective, sensitive biomarker of disease stage with the potential to detect treatment effects on PD progression.

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The Parkinson's disease-related pattern (PDRP) of glucose metabolic effects is demonstrated in an independent cohort of early stage PD patients.

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The PDRP pattern of metabolic changes is robust to variations in image processing and choice of classification model.

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Age-related metabolic changes show partial overlap with the PDRP, suggesting that age-adjustment is an important consideration.

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The PDRP correlates with motor function as defined by Hoehn & Yahr stage and UPDRS score.

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An additional data driven metabolic classifier highlights pattern aspects associated with early stage motor decline.

Neuroimaging Studies Illustrate the Commonalities Between Ageing and Brain Diseases

The lack of specificity in neuroimaging studies of neurological and psychiatric diseases suggests that these different diseases have more in common than is generally considered. Potentially, features that are secondary effects of different pathological processes may share common neurobiological underpinnings. Intriguingly, many of these mechanisms are also observed in studies of normal (i.e., non-pathological) brain ageing. Different brain diseases may be causing premature or accelerated ageing to the brain, an idea that is supported by a line of "brain ageing" research that combines neuroimaging data with machine learning analysis. In reviewing this field, I conclude that such observations could have important implications, suggesting that we should shift experimental paradigm: away from characterizing the average case-control brain differences resulting from a disease toward methods that place individuals in their age-appropriate context. This will also lead naturally to clinical applications, whereby neuroimaging can contribute to a personalized-medicine approach to improve brain health.

Clinical utility of FDG PET in Parkinson's disease and atypical parkinsonism associated with dementia

Purpose

There are no comprehensive guidelines for the use of FDG PET in the following three clinical scenarios: (1) diagnostic work-up of patients with idiopathic Parkinson’s disease (PD) at risk of future cognitive decline, (2) discriminating idiopathic PD from progressive supranuclear palsy, and (3) identifying the underlying neuropathology in corticobasal syndrome.

Methods

We therefore performed three literature searches and evaluated the selected studies for quality of design, risk of bias, inconsistency, imprecision, indirectness and effect size. Critical outcomes were the sensitivity, specificity, accuracy, positive/negative predictive value, area under the receiving operating characteristic curve, and positive/negative likelihood ratio of FDG PET in detecting the target condition. Using the Delphi method, a panel of seven experts voted for or against the use of FDG PET based on published evidence and expert opinion.

Results

Of 91 studies selected from the three literature searches, only four included an adequate quantitative assessment of the performance of FDG PET. The majority of studies lacked robust methodology due to lack of critical outcomes, inadequate gold standard and no head-to-head comparison with an appropriate reference standard. The panel recommended the use of FDG PET for all three clinical scenarios based on nonquantitative evidence of clinical utility.

Conclusion

Despite widespread use of FDG PET in clinical practice and extensive research, there is still very limited good quality evidence for the use of FDG PET. However, in the opinion of the majority of the panellists, FDG PET is a clinically useful imaging biomarker for idiopathic PD and atypical parkinsonism associated with dementia.

Brain Atrophy and Reorganization of Structural Network in Parkinson's Disease With Hemiparkinsonism

Hemiparkinsonism duration in patients with Parkinson's disease (PD) is a key time window to study early pathology of PD. We aimed to comprehensively explore the alterations of deformation and structural network in PD patients with hemiparkinsonism, which could potentially disclose the early biomarker for PD. Thirty-one PD patients with hemiparkinsonism and 37 age- and gender- matched normal controls were included in the present study. First of all, we normalized the left hemisphere of structural images as the contralateral side to the affected limbs. Deformation-based morphometry (DBM) was conducted to evaluate the brain atrophy and/or enlargement. structural networks were constructed by thresholding gray matter volume correlation matrices of 116 regions and analyzed using graph theoretical approaches (e.g., small-worldness, global, and nodal measures). Significantly decreased deformation values were observed in the temporoparietal regions like bilateral middle temporal gyri, ipsilateral precuneus and contralateral Rolandic operculum extending to supramarginal and postcentral gyri. Lower deformation values in contralateral middle temporal gyrus were negatively correlated with higher motor impairment which was dominated by akinesia/rigidity. Moreover, nodal reorganization of structural network mainly located in frontal, temporal, subcortex and cerebellum was bilaterally explored in PD patients with hemiparkinsonism. Increased nodal properties could be commonly observed in frontal lobes. Disruption of subcortex including basal ganglia and amygdala was detected by nodal local efficiency and nodal clustering coefficient. Twelve hubs, mainly from paralimbic-limbic and heteromodal networks, were disrupted and, alternatively, 14 hubs, most of which were located in frontal lobes, were additionally detected in PD patients with hemiparkinsonism. In conclusion, during hemiparkinsonism period, mild brain atrophy in the temporoparietal regions and widespread reorganization of structural network, e.g., enhanced frontal function and disruption of basal ganglia nodes, occurred in both hemispheres. With our data, we can also argue that MTG contralateral to the affected limbs (expressing clinically verified brain atrophy) might be a potential living biomarker to monitor disease progression. Therefore, the combination of DBM and structural network analyses can provide a comprehensive and sensitive evaluation for potential pathogenesis of early PD patients with hemiparkinsonism.

Metabolic Dysfunction in Parkinson's Disease: Bioenergetics, Redox Homeostasis and Central Carbon Metabolism

The loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) and the accumulation of protein inclusions (Lewy bodies) are the pathological hallmarks of Parkinson's disease (PD). PD is triggered by genetic alterations, environmental/occupational exposures and aging. However, the exact molecular mechanisms linking these PD risk factors to neuronal dysfunction are still unclear. Alterations in redox homeostasis and bioenergetics (energy failure) are thought to be central components of neurodegeneration that contribute to the impairment of important homeostatic processes in dopaminergic cells such as protein quality control mechanisms, neurotransmitter release/metabolism, axonal transport of vesicles and cell survival. Importantly, both bioenergetics and redox homeostasis are coupled to neuro-glial central carbon metabolism. We and others have recently established a link between the alterations in central carbon metabolism induced by PD risk factors, redox homeostasis and bioenergetics and their contribution to the survival/death of dopaminergic cells. In this review, we focus on the link between metabolic dysfunction, energy failure and redox imbalance in PD, making an emphasis in the contribution of central carbon (glucose) metabolism. The evidence summarized here strongly supports the consideration of PD as a disorder of cell metabolism.

Visual Dysfunction in Parkinson's Disease

This chapter describes the visual problems likely to be encountered in Parkinson's disease (PD) and whether such signs are useful in differentiating the parkinsonian syndromes. Visual dysfunction in PD may involve visual acuity, contrast sensitivity, color discrimination, pupil reactivity, saccadic and pursuit eye movements, motion perception, visual fields, and visual processing speeds. In addition, disturbance of visuospatial orientation, facial recognition problems, rapid eye movement (REM) sleep behavior disorder, and chronic visual hallucinations may be present. Problems affecting pupil reactivity, stereopsis, pursuit eye movement, and visuomotor adaptation, when accompanied by REM sleep behavior disorder, could be early features of PD. Dementia associated with PD is associated with enhanced eye movement problems, visuospatial deficits, and visual hallucinations. Visual dysfunction may be a useful diagnostic feature in differentiating PD from other parkinsonian symptoms, visual hallucinations, visuospatial dysfunction, and variation in saccadic eye movement problems being particularly useful discriminating features.

Visual dysfunction in Parkinson's disease

Patients with Parkinson's disease have a number of specific visual disturbances. These include changes in colour vision and contrast sensitivity and difficulties with complex visual tasks such as mental rotation and emotion recognition. We review changes in visual function at each stage of visual processing from retinal deficits, including contrast sensitivity and colour vision deficits to higher cortical processing impairments such as object and motion processing and neglect. We consider changes in visual function in patients with common Parkinson's disease-associated genetic mutations including GBA and LRRK2 . We discuss the association between visual deficits and clinical features of Parkinson's disease such as rapid eye movement sleep behavioural disorder and the postural instability and gait disorder phenotype. We review the link between abnormal visual function and visual hallucinations, considering current models for mechanisms of visual hallucinations. Finally, we discuss the role of visuo-perceptual testing as a biomarker of disease and predictor of dementia in Parkinson's disease.

Glucose Metabolism and AMPK Signaling Regulate Dopaminergic Cell Death Induced by Gene (α-Synuclein)-Environment (Paraquat) Interactions

While environmental exposures are not the single cause of Parkinson's disease (PD), their interaction with genetic alterations is thought to contribute to neuronal dopaminergic degeneration. However, the mechanisms involved in dopaminergic cell death induced by gene-environment interactions remain unclear. In this work, we have revealed for the first time the role of central carbon metabolism and metabolic dysfunction in dopaminergic cell death induced by the paraquat (PQ)-α-synuclein interaction. The toxicity of PQ in dopaminergic N27 cells was significantly reduced by glucose deprivation, inhibition of hexokinase with 2-deoxy-D-glucose (2-DG), or equimolar substitution of glucose with galactose, which evidenced the contribution of glucose metabolism to PQ-induced cell death. PQ also stimulated an increase in glucose uptake, and in the levels of glucose transporter type 4 (GLUT4) and Na⁺-glucose transporters isoform 1 (SGLT1) proteins, but only inhibition of GLUT-like transport with STF-31 or ascorbic acid reduced PQ-induced cell death. Importantly, while autophagy protein 5 (ATG5)/unc-51 like autophagy activating kinase 1 (ULK1)-dependent autophagy protected against PQ toxicity, the inhibitory effect of glucose deprivation on cell death progression was largely independent of autophagy or mammalian target of rapamycin (mTOR) signaling. PQ selectively induced metabolomic alterations and adenosine monophosphate-activated protein kinase (AMPK) activation in the midbrain and striatum of mice chronically treated with PQ. Inhibition of AMPK signaling led to metabolic dysfunction and an enhanced sensitivity of dopaminergic cells to PQ. In addition, activation of AMPK by PQ was prevented by inhibition of the inducible nitric oxide syntase (iNOS) with 1400W, but PQ had no effect on iNOS levels. Overexpression of wild type or A53T mutant α-synuclein stimulated glucose accumulation and PQ toxicity, and this toxic synergism was reduced by inhibition of glucose metabolism/transport and the pentose phosphate pathway (6-aminonicotinamide). These results demonstrate that glucose metabolism and AMPK regulate dopaminergic cell death induced by gene (α-synuclein)-environment (PQ) interactions.

The trajectory of disturbed resting-state cerebral function in Parkinson's disease at different Hoehn and Yahr stages

OBJECTIVE

We aim to investigate the disturbance of neural network associated with the different clinical stages of Parkinson's disease (PD).

METHOD

We recruited 80 patients at different H&Y stages of PD (28 at H&Y stage I, 28 at H&Y stage II, 24 at H&Y stage III) and 30 normal controls. All participants underwent resting-state fMRI scans on a 3-T MR system. The amplitude of low-frequency fluctuation (ALFF) of blood oxygen level-dependent signals was used to characterize regional cerebral function. Functional integration across the brain regions was evaluated by a seed voxel correlation approach.

RESULTS

PD patients had decreased regional activities in left occipital and lingual regions; these regions show decreased functional connection pattern with temporal regions, which is deteriorating as H&Y stage ascending. In addition, PD patients, especially those at stage II, exhibit increased regional activity in the posterior regions of default mode network (DMN), increased anticorrelation between posterior cingulate cortex (PCC) and cortical regions outside DMN, and higher temporal coherence within DMN. Those indicate more highly functioned DMN in PD patients at stage II.

CONCLUSIONS

Our study demonstrated the trajectories of resting-state cerebral function disturbance in PD patients at different H&Y stages. Impairment in functional integration of occipital-temporal cortex might be a promising measurement to evaluate and potentially track functional substrates of disease evolution of PD.

Oculo-Visual Dysfunction in Parkinson's Disease

This review describes the oculo-visual problems likely to be encountered in Parkinson's disease (PD) with special reference to three questions: (1) are there visual symptoms characteristic of the prodromal phase of PD, (2) is PD dementia associated with specific visual changes, and (3) can visual symptoms help in the differential diagnosis of the parkinsonian syndromes, viz. PD, progressive supranuclear palsy (PSP), dementia with Lewy bodies (DLB), multiple system atrophy (MSA), and corticobasal degeneration (CBD)? Oculo-visual dysfunction in PD can involve visual acuity, dynamic contrast sensitivity, colour discrimination, pupil reactivity, eye movement, motion perception, and visual processing speeds. In addition, disturbance of visuo-spatial orientation, facial recognition problems, and chronic visual hallucinations may be present. Prodromal features of PD may include autonomic system dysfunction potentially affecting pupil reactivity, abnormal colour vision, abnormal stereopsis associated with postural instability, defects in smooth pursuit eye movements, and deficits in visuo-motor adaptation, especially when accompanied by idiopathic rapid eye movement (REM) sleep behaviour disorder. PD dementia is associated with the exacerbation of many oculo-visual problems but those involving eye movements, visuo-spatial function, and visual hallucinations are most characteristic. Useful diagnostic features in differentiating the parkinsonian symptoms are the presence of visual hallucinations, visuo-spatial problems, and variation in saccadic eye movement dysfunction.

Deep-brain stimulation associates with improved microvascular integrity in the subthalamic nucleus in Parkinson's disease

Deep brain stimulation (DBS) of the subthalamic nucleus (STN) has become an accepted treatment for motor symptoms in a subset of Parkinson's disease (PD) patients. The mechanisms why DBS is effective are incompletely understood, but previous studies show that DBS targeted in brain structures other than the STN may modify the microvasculature. However, this has not been studied in PD subjects who have received STN-DBS. Here we investigated the extent and nature of microvascular changes in post-mortem STN samples from STN-DBS PD patients, compared to aged controls and PD patients who had not been treated with STN-DBS. We used immunohistochemical and immunofluorescent methods to assess serial STN-containing brain sections from PD and STN-DBS PD cases, compared to similar age controls using specific antibodies to detect capillaries, an adherens junction and tight junction-associated proteins as well as activated microglia. Cellular features in stained sections were quantified by confocal fluorescence microscopy and stereological methods in conjunction with in vitro imaging tools. We found significant upregulation of microvessel endothelial cell thickness, length and density but lowered activated microglia density and striking upregulation of all analysed adherens junction and tight junction-associated proteins in STN-DBS PD patients compared to non-DBS PD patients and controls. Moreover, in STN-DBS PD samples, expression of an angiogenic factor, vascular endothelial growth factor (VEGF), was significantly upregulated compared to the other groups. Our findings suggest that overexpressed VEGF and downregulation of inflammatory processes may be critical mechanisms underlying the DBS-induced microvascular changes.

Abnormal functional connectivity density in Parkinson's disease

The pathology of Parkinson's disease (PD) is not confined to the nigrostriatal pathway, but also involves widespread cerebral cortical areas. Using seed-based resting state functional connectivity, many previous studies have demonstrated that PD patients have abnormal functional integration. However, this technique strongly relies on a priori selection of the seed regions and may miss important unpredictable findings. Using an ultrafast voxel-wise functional connectivity density approach, this study performed a whole brain functional connectivity analysis to investigate the abnormal resting-state functional activities in PD patients. Compared with healthy controls, PD patients exhibited decreased short-range functional connectivity densities in regions that were mainly located in the ventral visual pathway and decreased long-range functional connectivity densities in the right middle and superior frontal gyrus, which have been speculated to be associated with visual hallucinations and cognitive dysfunction, respectively. PD patients also exhibited increased short- and long-range functional connectivity densities in the bilateral precuneus and posterior cingulate cortex, which may represent a compensatory process for maintaining normal brain function. The observed functional connectivity density alterations might be related to the disturbed structural connectivity of PD patients, leading to abnormal functional integration. Our results suggest that functional connectivity density mapping may provide a useful means to assess PD-related neurodegeneration and to study the pathophysiology of PD.

Alterations in energy/redox metabolism induced by mitochondrial and environmental toxins: a specific role for glucose-6-phosphate-dehydrogenase and the pentose phosphate pathway in paraquat toxicity

Parkinson’s disease (PD) is a multifactorial disorder with a complex etiology including genetic risk factors, environmental exposures, and aging. While energy failure and oxidative stress have largely been associated with the loss of dopaminergic cells in PD and the toxicity induced by mitochondrial/environmental toxins, very little is known regarding the alterations in energy metabolism associated with mitochondrial dysfunction and their causative role in cell death progression. In this study, we investigated the alterations in the energy/redox-metabolome in dopaminergic cells exposed to environmental/mitochondrial toxins (paraquat, rotenone, 1-methyl-4-phenylpyridinium [MPP⁺], and 6-hydroxydopamine [6-OHDA]) in order to identify common and/or different mechanisms of toxicity. A combined metabolomics approach using nuclear magnetic resonance (NMR) and direct-infusion electrospray ionization mass spectrometry (DI-ESI-MS) was used to identify unique metabolic profile changes in response to these neurotoxins. Paraquat exposure induced the most profound alterations in the pentose phosphate pathway (PPP) metabolome. ¹³C-glucose flux analysis corroborated that PPP metabolites such as glucose-6-phosphate, fructose-6-phosphate, glucono-1,5-lactone, and erythrose-4-phosphate were increased by paraquat treatment, which was paralleled by inhibition of glycolysis and the TCA cycle. Proteomic analysis also found an increase in the expression of glucose-6-phosphate dehydrogenase (G6PD), which supplies reducing equivalents by regenerating nicotinamide adenine dinucleotide phosphate (NADPH) levels. Overexpression of G6PD selectively increased paraquat toxicity, while its inhibition with 6-aminonicotinamide inhibited paraquat-induced oxidative stress and cell death. These results suggest that paraquat “hijacks” the PPP to increase NADPH reducing equivalents and stimulate paraquat redox cycling, oxidative stress, and cell death. Our study clearly demonstrates that alterations in energy metabolism, which are specific for distinct mitochondiral/environmental toxins, are not bystanders to energy failure but also contribute significant to cell death progression.

Upregulation of a small vault RNA (svtRNA2-1a) is an early event in Parkinson disease and induces neuronal dysfunction

MicroRNAs (miRNAs) and other small non-coding RNAs (sncRNAs) are post-transcriptional regulators of gene expression, playing key roles in neuronal development, plasticity, and disease. Transcriptome deregulation caused by miRNA dysfunction has been associated to neurodegenerative diseases. Parkinson disease (PD) is the second most common neurodegenerative disease showing deregulation of the coding and small non-coding transcriptome. On profiling sncRNA in PD brain areas differently affected, we found that upregulation of a small vault RNA (svtRNA2-1a) is widespread in PD brains, occurring early in the course of the disease (at pre-motor stages). SvtRNA2-1a biogenesis was dependent on Dicer activity on its precursor (vtRNA2-1) but independent of Drosha endonuclease, unlike the canonical miRNAs. Although endogenous svtRNA2-1a was enriched in Ago-2 immunoprecipitates in differentiated SH-SY5Y neuronal cells, overexpression of svtRNA2-1a induced subtle transcriptomic changes, suggesting that gene expression regulation may involve other mechanisms than mRNA decay only. Function enrichment analysis of the genes deregulated by svtRNA2-1a overexpression or svtRNA2-1a predicted targets identified pathways related to nervous system development and cell type specification. The expression pattern of svtRNA2-1a during development and aging of the human brain and the detrimental consequences of a svtRNA2-1a mimic overexpression in neuronal cells further indicate that low svtRNA2-1a levels may be important for the maintenance of neurons. Our results suggest that early svtRNA2-1a upregulation in PD may contribute to perturbations of gene expression networks, underlying metabolic impairment and cell dysfunction. A better understanding of the pathways regulated by svtRNA2-a, and also the mechanisms regulating its expression should facilitate the identification of new targets for therapeutic approaches in PD.

Microglia, amyloid, and glucose metabolism in Parkinson's disease with and without dementia

[(11)C](R)PK11195-PET measures upregulation of translocator protein, which is associated with microglial activation, [(11)C]PIB-PET is a marker of amyloid, while [(18)F]FDG-PET measures cerebral glucose metabolism (rCMRGlc). We hypothesize that microglial activation is an early event in the Parkinson's disease (PD) spectrum and is independent of the amyloid pathology. The aim of this study is to evaluate in vivo the relationship between microglial activation, amyloid deposition, and glucose metabolism in Parkinson's disease dementia (PDD) and PD subjects without dementia. Here, we evaluated 11 PDD subjects, 8 PD subjects without dementia, and 24 control subjects. Subjects underwent T1 and T2 MRI, [(11)C](R)PK11195, [(18)F]FDG, and [(11)C]PIB PET scans. Parametric maps of [(11)C](R)PK11195 binding potential, rCMRGlc, and [(11)C]PIB uptake were interrogated using region of interest and SPM (statistical parametric mapping) analysis. The PDD patients showed a significant increase of microglial activation in anterior and posterior cingulate, striatum, frontal, temporal, parietal, and occipital cortical regions compared with the controls. The PD subjects also showed a statistically significant increase in microglial activation in temporal, parietal, and occipital regions. [(11)C]PIB uptake was marginally increased in PDD and PD. There was a significant reduction in glucose metabolism in PDD and PD. We have also demonstrated pixel-by-pixel correlation between mini-mental state examination (MMSE) score and microglial activation, and MMSE score and rCMRGlc. In conclusion, we have demonstrated that cortical microglial activation and reduced glucose metabolism can be detected early on in this disease spectrum. Significant microglial activation may be a factor in driving the disease process in PDD. Given this, agents that affect microglial activation could have an influence on disease progression.

Regional cerebral metabolism in mouse under chronic manganese exposure: implications for manganism

Chronic manganese (Mn) exposure in rodents, non-human primates and humans has been linked to Parkinson's disease like condition known as Manganism. Mn being a cofactor for many enzymes in brain has been known to be accumulated in various regions differentially and thus exert toxic effect upon chronic overexposure. In present study, neuropathology of Manganism was investigated by evaluating regional neuronal and astroglial metabolism in mice under chronic Mn exposure. Male C57BL6 mice were treated with MnCl(2) (25 mg/kg, i.p.) for 21 days. Cerebral metabolism was studied by co-infusing [U-(13)C(6)]glucose and [2-(13)C]acetate, and monitoring (13)C labeling of amino acids in brain tissue extract using (1)H-[(13)C] and (13)C-[(1)H]-NMR spectroscopy. Glutamate, choline, N-acetyl aspartate and myo-inositol were found to be reduced in thalamus and hypothalamus indicating a loss in neuronal and astroglial cells due to Mn neurotoxicity. Reduced labeling of Glu(C4) from [U-(13)C(6)]glucose and [2-(13)C]acetate indicates an impairment of glucose oxidation by glutamatergic neurons and glutamate-glutamine neurotransmitter cycle in cortex, striatum, thalamus-hypothalamus and olfactory bulb with chronic Mn exposure. Additionally, reduced labeling of Gln(C4) from [2-(13)C]acetate indicates a decrease in acetate oxidation by astroglia in the same regions. However, GABAergic function was alleviated only in thalamus-hypothalamus. Our findings indicate that chronic Mn impairs excitatory (glutamatergic) function in the majority of regions of brain while inhibitory (GABAergic) activity is perturbed only in basal ganglia.

Visual symptoms in Parkinson's disease

Parkinson's disease (PD) is a common disorder of middle-aged and elderly people in which degeneration of the extrapyramidal motor system causes significant movement problems. In some patients, however, there are additional disturbances in sensory systems including loss of the sense of smell and auditory and/or visual problems. This paper is a general overview of the visual problems likely to be encountered in PD. Changes in vision in PD may result from alterations in visual acuity, contrast sensitivity, colour discrimination, pupil reactivity, eye movements, motion perception, visual field sensitivity, and visual processing speeds. Slower visual processing speeds can also lead to a decline in visual perception especially for rapidly changing visual stimuli. In addition, there may be disturbances of visuospatial orientation, facial recognition problems, and chronic visual hallucinations. Some of the treatments used in PD may also have adverse ocular reactions. The pattern electroretinogram (PERG) is useful in evaluating retinal dopamine mechanisms and in monitoring dopamine therapies in PD. If visual problems are present, they can have an important effect on the quality of life of the patient, which can be improved by accurate diagnosis and where possible, correction of such defects.

Hippocampal responsiveness to 17β-estradiol and equol after long-term ovariectomy: implication for a therapeutic window of opportunity

A 'critical window of opportunity' has been proposed for the efficacy of ovarian hormone intervention in peri- and post-menopausal women. We sought to address this hypothesis using a long-term ovariectomized non-human primate (NHP) model, the cynomolgus macaque (Macaca fascicularis). In these studies, we assessed the ability of 17β-estradiol and equol to regulate markers of hippocampal bioenergetic capacity. Results indicated that 17β-estradiol treatment significantly increased expression of mitochondrial respiratory chain proteins complex-I and -III in the hippocampus when compared to non-hormone-treated animals. Expression of the TCA cycle protein succinate dehydrogenase α was decreased in animals treated with equol compared to those treated with 17β-estradiol. There were no significant effects of either 17β-estradiol or equol treatment on glycolytic protein expression in the hippocampus, nor were there significant effects of treatment on expression levels of antioxidant enzymes. Similarly, 17β-estradiol and equol treatment had no effect on mitochondrial fission and fusion protein expression. In summary, findings indicate that while 17β-estradiol induced a significant increase in several proteins, the overall profile of bioenergetic system proteins was neutral to slightly positively responsive. The profile of responses with the ERβ-preferring molecule equol was consistent with overall nonresponsiveness. Collectively, the data indicate that long-term ovariectomy is associated with a decline in response to estrogens and estrogen-like compounds. By extension, the data are consistent with a primary tenet of the critical window hypothesis, i.e., that the brains of post-menopausal women ultimately lose their ability to respond positively to estrogenic stimulation.

Lipid pathway alterations in Parkinson's disease primary visual cortex

BACKGROUND

We present a lipidomics analysis of human Parkinson's disease tissues. We have focused on the primary visual cortex, a region that is devoid of pathological changes and Lewy bodies; and two additional regions, the amygdala and anterior cingulate cortex which contain Lewy bodies at different disease stages but do not have as severe degeneration as the substantia nigra.

METHODOLOGY/PRINCIPAL FINDINGS

Using liquid chromatography mass spectrometry lipidomics techniques for an initial screen of 200 lipid species, significant changes in 79 sphingolipid, glycerophospholipid and cholesterol species were detected in the visual cortex of Parkinson's disease patients (n = 10) compared to controls (n = 10) as assessed by two-sided unpaired t-test (p-value <0.05). False discovery rate analysis confirmed that 73 of these 79 lipid species were significantly changed in the visual cortex (q-value <0.05). By contrast, changes in 17 and 12 lipid species were identified in the Parkinson's disease amygdala and anterior cingulate cortex, respectively, compared to controls; none of which remained significant after false discovery rate analysis. Using gas chromatography mass spectrometry techniques, 6 out of 7 oxysterols analysed from both non-enzymatic and enzymatic pathways were also selectively increased in the Parkinson's disease visual cortex. Many of these changes in visual cortex lipids were correlated with relevant changes in the expression of genes involved in lipid metabolism and an oxidative stress response as determined by quantitative polymerase chain reaction techniques.

CONCLUSIONS/SIGNIFICANCE

The data indicate that changes in lipid metabolism occur in the Parkinson's disease visual cortex in the absence of obvious pathology. This suggests that normalization of lipid metabolism and/or oxidative stress status in the visual cortex may represent a novel route for treatment of non-motor symptoms, such as visual hallucinations, that are experienced by a majority of Parkinson's disease patients.

Molecular imaging and the neuropathologies of Parkinson's disease

The main motor symptoms of Parkinson's disease (PD) are linked to degeneration of the nigrostriatal dopamine (DA) fibers, especially those innervating the putamen. This degeneration can be assessed in molecular imaging studies with presynaptic tracers such as [(18)F]-fluoro-L-DOPA (FDOPA) and ligands for DA transporter ligands. However, the pathologies of PD are by no means limited to nigrostriatal loss. Results of post mortem and molecular imaging studies reveal parallel degenerations of cortical noradrenaline (NA) and serotonin (5-HT) innervations, which may contribute to affective and cognitive changes of PD. Especially in advanced PD, cognitive impairment can come to resemble that seen in Alzheimer's dementia, as can the degeneration of acetylcholine innervations arising in the basal forebrain. The density of striatal DA D(2) receptors increases in early untreated PD, consistent with denervation upregulation, but there is an accelerated rate of DA receptor loss as the disease advances. Animal studies and post mortem investigations reveal changes in brain opioid peptide systems, but these are poorly documented in imaging studies of PD. Relatively minor changes in the binding sites for GABA are reported in cortex and striatum of PD patients. There remains some controversy about the expression of the 18 kDa translocator protein (TSPO) in activated microglia as an indicator of an active inflammatory component of neurodegeneration in PD. A wide variety of autonomic disturbances contribute to the clinical syndrome of PD; the degeneration of myocardial sympathetic innervation can be revealed in SPECT studies of PD patients with autonomic failure. Considerable emphasis has been placed on investigations of cerebral blood flow and energy metabolism in PD. Due to the high variance of these physiological estimates, researchers have often employed normalization procedures for the sensitive detection of perturbations in relatively small patient groups. However, a widely used normalization to the global mean must be used with caution, as it can result in spurious findings of relative hypermetabolic changes in subcortical structures. A meta-analysis of the quantitative studies to date shows that there is in fact widespread hypometabolism and cerebral blood flow in the cerebral cortex, especially in frontal cortex and parietal association areas. These changes can bias the use of global mean normalization, and probably represent the pathophysiological basis of the cognitive impairment of PD.

Cortical hypometabolism and hypoperfusion in Parkinson's disease is extensive: probably even at early disease stages

Recent cerebral blood flow (CBF) and glucose consumption (CMRglc) studies of Parkinson's disease (PD) revealed conflicting results. Using simulated data, we previously demonstrated that the often-reported subcortical hypermetabolism in PD could be explained as an artifact of biased global mean (GM) normalization, and that low-magnitude, extensive cortical hypometabolism is best detected by alternative data-driven normalization methods. Thus, we hypothesized that PD is characterized by extensive cortical hypometabolism but no concurrent widespread subcortical hypermetabolism and tested it on three independent samples of PD patients. We compared SPECT CBF images of 32 early-stage and 33 late-stage PD patients with that of 60 matched controls. We also compared PET FDG images from 23 late-stage PD patients with that of 13 controls. Three different normalization methods were compared: (1) GM normalization, (2) cerebellum normalization, (3) reference cluster normalization (Yakushev et al.). We employed standard voxel-based statistics (fMRIstat) and principal component analysis (SSM). Additionally, we performed a meta-analysis of all quantitative CBF and CMRglc studies in the literature to investigate whether the global mean (GM) values in PD are decreased. Voxel-based analysis with GM normalization and the SSM method performed similarly, i.e., both detected decreases in small cortical clusters and concomitant increases in extensive subcortical regions. Cerebellum normalization revealed more widespread cortical decreases but no subcortical increase. In all comparisons, the Yakushev method detected nearly identical patterns of very extensive cortical hypometabolism. Lastly, the meta-analyses demonstrated that global CBF and CMRglc values are decreased in PD. Based on the results, we conclude that PD most likely has widespread cortical hypometabolism, even at early disease stages. In contrast, extensive subcortical hypermetabolism is probably not a feature of PD.

Evaluation of body image and self-concept and their correlation with depressive symptoms in Parkinson's disease

OBJECTIVE: To identify characteristics of body image and self-concept in individuals over fifty years of age with Parkinson's disease (PD). The secondary objectives are to analyze whether body image and self-concept are influenced by the severity of PD and to verify if there is correlation between depression, self-concept and body image in cases of PD. METHOD: Participating in the study were 48 individuals, being 26 with PD and 22 Controls. The instruments used were: The Mini Exam of Mental State, The My Body Image Test, The Factorial Self-concept Test, The Beck Depression Inventory, the motor section of The Unified Parkinson's Disease Rating Scale and The Modified Hoehn and Yahr Scale. RESULTS: In PD the perception of body image and self-concept demonstrated significantly reduced values p<0.001 and p=0.012 respectively, and the presence of depression symptomatology was significantly more (p=0.002). CONCLUSION: Individuals with PD present alteration of body image and self-concept and also present lower personal confidence and lower social receptivity, correlated with depressive symptoms.

Data-driven intensity normalization of PET group comparison studies is superior to global mean normalization

BACKGROUND

Global mean (GM) normalization is one of the most commonly used methods of normalization in PET and SPECT group comparison studies of neurodegenerative disorders. It requires that no between-group GM difference is present, which may be strongly violated in neurodegenerative disorders. Importantly, such GM differences often elude detection due to the large intrinsic variance in absolute values of cerebral blood flow or glucose consumption. Alternative methods of normalization are needed for this type of data.

MATERIALS AND METHODS

Two types of simulation were performed using CBF images from 49 controls. Two homogeneous groups of 20 subjects were sampled repeatedly. In one group, cortical CBF was artificially decreased moderately (simulation I) or slightly (simulation II). The other group served as controls. Ratio normalization was performed using five reference regions: (1) Global mean; (2) An unbiased VOI; (3) Data-driven region extraction (Andersson); (4-5) Reference cluster methods (Yakushev et al.). Using voxel-based statistics, it was determined how much of the original signal was detected following each type of normalization.

RESULTS

For both simulations, global mean normalization performed poorly, with only a few percent of the original signal recovered. Global mean normalization moreover created artificial increases. In contrast, the data-driven reference cluster method detected 65-95% of the original signal.

CONCLUSION

In the present simulation, the reference cluster method was superior to GM normalization. We conclude that the reference cluster method will likely yield more accurate results in the study of patients with early to moderate stage neurodegenerative disorders.

Positron emission tomography of monoaminergic vesicular binding in aging and Parkinson disease

The type-2 vesicular monoamine transporter (VMAT2) might serve as an objective biomarker of Parkinson disease (PD) severity. Thirty-one subjects with early-stage PD and 75 normal subjects underwent continuous intravenous infusion of (+)-[(11)C]dihydrotetrabenazine (DTBZ) and positron emission tomography (PET) imaging to estimate the striatal VMAT2 binding site density with equilibrium tracer modeling. Parkinson disease patients were evaluated clinically in the practically defined 'off' state with the Unified Parkinson Disease Rating Scale (UPDRS), the Hoehn and Yahr Scale (HY), and the Schwab and England Activities of Daily Living Scale (SE). In normal subjects there was age-related decline in striatal DTBZ binding, approximating 0.5% per year. In PD subjects, specific DTBZ binding was reduced in the caudate nucleus (CD; -44%), anterior putamen (-68%), and posterior putamen (PP; -77%). The PP-to-CD ratio of binding was reduced significantly in PD subjects. Dihydrotetrabenazine binding was also reduced by approximately 50% in the PD substantia nigra. Striatal binding reductions correlated significantly with PD duration and SE scores, but not with HY stage or with UPDRS motor subscale (UPDRS(III)) scores. Striatal and midbrain DTBZ binding was asymmetric in PD subjects, with greatest reductions contralateral to the most clinically affected limbs. There was significant correlation between asymmetry of DTBZ binding and clinical asymmetry measured with the UPDRS(III). In HY stage 1 and 1.5 subjects (n=16), PP DTBZ binding contralateral to the clinically unaffected body side was reduced by 73%, indicating substantial preclinical nigrostriatal pathology in PD. We conclude that (+)-[(11)C]DTBZ-PET imaging displays many properties necessary of a PD biomarker.

Altered expression of vesicular glutamate transporters VGLUT1 and VGLUT2 in Parkinson disease

Glutamatergic pathways play a key role in the functional organization of neuronal circuits involved in Parkinson disease (PD). Recently, three vesicular glutamate transporters (VGLUT1-3) were identified. VGLUT1 and VGLUT2 are responsible for the uploading of glutamate into synaptic vesicles and are the first specific markers of glutamatergic neurons available. Here, we analyzed the expression of VGLUT1 and VGLUT2 in autopsy tissues of PD patients and matched controls using Western blot and immunoautoradiography. VGLUT1 and VGLUT2 expression was increased in the Parkinsonian putamen by 24% and 29%, respectively (p<0.01). In contrast, only VGLUT1 was dramatically decreased in the prefrontal and temporal cortex of PD patients (approximately 50%, p<0.01 and p<0.001, respectively). These findings demonstrate the existence of profound alterations of glutamatergic transmission in PD, which are likely to contribute to the motor and cognitive impairments associated with the disease, and should thus be taken into account in the treatment of PD.

Parkinson's disease and brain mitochondrial dysfunction: a functional phosphorus magnetic resonance spectroscopy study

In spite of several evidences for a mitochondrial impairment in Parkinson's disease (PD), so far it has not been possible to show in vivo mitochondrial dysfunction in the human brain of PD patients. The authors used the high temporal and spatial resolution 31 phosphorus magnetic resonance spectroscopy (31P MRS) technique, which they have previously developed in normal subjects and in patients with mitochondrial diseases to study mitochondrial function by observing high-energy phosphates (HEPs) and intracellular pH (pH) in the visual cortex of 20 patients with PD and 20 normal subjects at rest, during, and after visual activation. In normal subjects, HEPs remained unchanged during activation, but rose significantly (by 16%) during recovery, and pH increased during visual activation with a slow return to rest values. In PD patients, HEPs were within the normal range at rest and did not change during activation, but fell significantly (by 36%) in the recovery period; pH did not reveal a homogeneous pattern with a wide spread of values. Energy unbalance under increased oxidative metabolism requirements, that is, the postactivation phase, discloses a mitochondrial dysfunction that is present in the brain of patients with PD even in the absence of overt clinical manifestations, as in the visual cortex. This is in agreement with our previous findings in patients with mitochondrial disease without clinical central nervous system (CNS) involvement. The heterogeneity of the physicochemical environment (i.e., pH) suggests various degrees of subclinical brain involvement in PD. The combined use of MRS and brain activation is fundamental for the study of brain energetics in patients with PD and may prove an important tool for diagnostic purposes and, possibly, to monitor therapeutic interventions.