Nigral iron deposition occurs across motor phenotypes of Parkinson's disease

Structural and Molecular Imaging for Clinically Uncertain Parkinsonism

Neuroimaging is an important adjunct to the clinical assessment of Parkinson disease (PD). Parkinsonism can be challenging to differentiate, especially in early disease stages, when it mimics other movement disorders or when there is a poor response to dopaminergic therapies. There is also a discrepancy between the phenotypic presentation of degenerative parkinsonism and the pathological outcome. The emergence of more sophisticated and accessible neuroimaging can identify molecular mechanisms of PD, the variation between clinical phenotypes, and the compensatory mechanisms that occur with disease progression. Ultra-high-field imaging techniques have improved spatial resolution and contrast that can detect microstructural changes, disruptions in neural pathways, and metabolic and blood flow alterations. We highlight the imaging modalities that can be accessed in clinical practice and recommend an approach to the diagnosis of clinically uncertain parkinsonism.

The challenging quest of neuroimaging: From clinical to molecular-based subtyping of Parkinson disease and atypical parkinsonisms

The current framework of Parkinson disease (PD) focuses on phenotypic classification despite its considerable heterogeneity. We argue that this method of classification has restricted therapeutic advances and therefore limited our ability to develop disease-modifying interventions in PD. Advances in neuroimaging have identified several molecular mechanisms relevant to PD, variation within and between clinical phenotypes, and potential compensatory mechanisms with disease progression. Magnetic resonance imaging (MRI) techniques can detect microstructural changes, disruptions in neural pathways, and metabolic and blood flow alterations. Positron emission tomography (PET) and single-photon emission computed tomography (SPECT) imaging have informed the neurotransmitter, metabolic, and inflammatory dysfunctions that could potentially distinguish disease phenotypes and predict response to therapy and clinical outcomes. However, rapid advancements in imaging techniques make it challenging to assess the significance of newer studies in the context of new theoretical frameworks. As such, there needs to not only be a standardization of practice criteria in molecular imaging but also a rethinking of target approaches. In order to harness precision medicine, a coordinated shift is needed toward divergent rather than convergent diagnostic approaches that account for interindividual differences rather than similarities within an affected population, and focus on predictive patterns rather than already lost neural activity.

Empirical evidence for biometal dysregulation in Parkinson's disease from a systematic review and Bradford Hill analysis

The Bradford Hill model evaluates the causal inference of one variable on another by assessing whether evidence of the suspected causal variable aligns with a set of nine criteria proposed by Bradford Hill, each representing fundamental tenets of a causal relationship. The aim of this study was to use the Bradford Hill model of causation to assess the level of empirical evidence supporting our hypotheses that alterations to iron and copper levels, and iron- and copper-associated proteins and genes, contribute to Parkinson’s disease etiology. We conducted a systematic review of all available articles published to September 2019 in four online databases. 8437 articles matching search criteria were screened for pre-defined inclusion and exclusion criteria. 181 studies met study criteria and were subsequently evaluated for study quality using established quality assessment tools. Studies meeting criteria for moderate to high quality of study design (n = 155) were analyzed according to the Bradford Hill model of causation. Evidence from studies considered of high quality (n = 73) supported a causal role for iron dysregulation in Parkinson’s disease. A causal role for copper dysregulation in Parkinson’s disease was also supported by high quality studies, although substantially fewer studies investigated copper in this disorder (n = 25) compared with iron. The available evidence supports an etiological role for iron and copper dysregulation in Parkinson’s disease, substantiating current clinical trials of therapeutic interventions targeting alterations in brain levels of these metals in Parkinson’s disease.

An Updated Overview of the Magnetic Resonance Imaging of Brain Iron in Movement Disorders

Brain iron load is one of the most important neuropathological hallmarks in movement disorders. Specifically, the iron provides most of the paramagnetic metal signals in the brain and its accumulation seems to play a key role, although not completely explained, in the degeneration of the basal ganglia, as well as other brain structures. Moreover, iron distribution patterns have been implicated in depicting different movement disorders. This work reviewed current literature on Magnetic Resonance Imaging for Brain Iron Detection and Quantification (MRI-BIDQ) in neurodegenerative processes underlying movement disorders.

An Unrecognized Fundamental Relationship between Neurotransmitters: Glutamate Protects against Catecholamine Oxidation

Neurotransmitter catecholamines (dopamine, epinephrine, and norepinephrine) are liable to undergo oxidation, which copper is deeply involved in. Catecholamine oxidation-derived neurotoxicity is recognized as a pivotal pathological mechanism in neurodegenerative diseases. Glutamate, as an excitatory neurotransmitter, is enriched in the brain at extremely high concentrations. However, the chemical biology relationship of these two classes of neurotransmitters remains largely unknown. In the present study, we assessed the influences of glutamate on the autoxidation of catecholamines, the copper- and copper-containing ceruloplasmin-mediated oxidation of catecholamines, the catecholamine-induced formation of quinoprotein, catecholamine/copper-induced hydroxyl radicals, and DNA damage in vitro. The results demonstrate that glutamate, at a physiologically achievable molar ratio of glutamate/catecholamines, has a pronounced inhibitory effect on catecholamine oxidation, catecholamine oxidation-evoked hydroxyl radicals, quinoprotein, and DNA damage. The protective mechanism of glutamate against catecholamine oxidation could be attributed to its restriction of the redox activity of copper via chelation. This previously unrecognized link between glutamate, catecholamines, and copper suggests that neurodegenerative disorders may occur and develop once the built-in equilibrium is disrupted and brings new insight into developing more effective prevention and treatment strategies for neurodegenerative diseases.

Serum Ceruloplasmin Depletion is Associated With Magnetic Resonance Evidence of Widespread Accumulation of Brain Iron in Parkinson's Disease

BACKGROUND

Excessive iron accumulation is one of the main pathogeneses of Parkinson's disease (PD). Ceruloplasmin plays an important role in keeping the iron homoeostasis.

PURPOSE

To explore the association between serum ceruloplasmin depletion and subcortical iron distribution in PD.

STUDY TYPE

Prospective.

POPULATION

One hundred and twenty-one normal controls, 34 PD patients with low serum ceruloplasmin (PD-LC), and 28 patients with normal serum ceruloplasmin (PD-NC).

SEQUENCE

Enhanced susceptibility-weighted angiography (ESWAN) on a 3 T scanner.

ASSESSMENT

Quantitative susceptibility mapping was employed to quantify the regional iron content by using a semi-automatic method. Serum ceruloplasmin concentration was measured from peripheral blood sample. Clinical assessments were conducted by a neurologist.

STATISTICAL TESTS

General linear model was used to compare the intergroup difference of region iron distribution among groups, and the statistics was adjusted by Bonferroni method (P < 0.01). Partial correlation analysis was used to detect the association between regional iron distribution and serum ceruloplasmin concentration (P < 0.05).

RESULTS

Compared with normal controls, significant iron accumulation in substantia nigra, putamen, and red nucleus was observed in PD-LC, while the only region showing significant iron accumulation was SN in PD-NC. Between PD-NC and PD-LC, the iron accumulation in putamen remained significantly different, which had a negative correlation with serum ceruloplasmin in whole PD patients (r = -0.338, P = 0.008).

DATA CONCLUSION

Nigral iron accumulation characterizes PD patients without significant association with serum ceruloplasmin. Differentially, when PD patients appear with reduced serum ceruloplasmin, more widespread iron accumulation would be expected with additionally involving putamen and red nucleus. All these findings provide insightful evidence for the abnormal iron metabolism behind the ceruloplasmin depletion in PD. EVIDENCE LEVEL: 2 TECHNICAL EFFICACY: 2.

Neuroimaging Detectable Differences between Parkinson's Disease Motor Subtypes: A Systematic Review

BACKGROUND

The neuroanatomical substrates of Parkinson's disease (PD) with tremor-dominance (TD) and those with non-tremor dominance (nTD), postural instability and gait difficulty (PIGD), and akinetic-rigid (AR) are not fully differentiated. A better understanding of symptom specific pathoanatomical markers of PD subtypes may result in earlier diagnosis and more tailored treatment. Here, we aim to give an overview of the neuroimaging literature that compared PD motor subtypes.

METHODS

A systematic literature review on neuroimaging studies of PD subtypes was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Search terms submitted to the PubMed database included: "Parkinson's disease", "MRI" and "motor subtypes" (TD, nTD, PIGD, AR). The results are first discussed from macro to micro level of organization (i.e., (1) structural; (2) functional; and (3) molecular) and then by applied imaging methodology.

FINDINGS

Several neuroimaging methods including diffusion imaging and positron emission tomography (PET) distinguish specific PD motor subtypes well, although findings are mixed. Furthermore, our review demonstrates that nTD-PD patients have more severe neuroalterations compared to TD-PD patients. More specifically, nTD-PD patients have deficits within striato-thalamo-cortical (STC) circuitry and other thalamocortical projections related to cognitive and sensorimotor function, while TD-PD patients tend to have greater cerebello-thalamo-cortical (CTC) circuitry dysfunction.

CONCLUSIONS

Based on the literature, STC and CTC circuitry deficits seem to be the key features of PD and the subtypes. Future research should make greater use of multimodal neuroimaging and techniques that have higher sensitivity in delineating subcortical structures involved in motor diseases.

Different iron deposition patterns in Parkinson's disease subtypes: a quantitative susceptibility mapping study

Background

Parkinson's disease (PD) is a heterogeneous neurodegenerative disorder with various subtypes and uncertain pathogenesis. Iron deposition is considered to be involved in the pathological mechanisms of PD. The present study aimed to investigate the iron deposition in deep gray matter in patients with different PD subtypes using quantitative susceptibility mapping (QSM).

Methods

Forty-six PD patients and 22 healthy controls (HCs) were recruited for the study. PD patients were allocated to the tremor-dominant (TD) group (n=22), postural instability and gait disorder-dominant (PIGD) group (n=19), and intermediate group (n=5). Susceptibility values in deep gray matter nuclei measured by QSM among the PD-TD and PD-PIGD groups and the HCs, as well as the relationship between iron accumulation and clinical motor features, were investigated.

Results

Susceptibility values in the dentate nucleus (DN) were greater in the PD-TD (118.73±70.45) group than in the PD-PIGD (72.14±39.85, P=0.02) group and HCs (78.26±41.38, P=0.042). Further, a significant positive correlation was observed between the DN susceptibility values and tremor scores (r=0.324, P=0.028). Compared with the HCs (182.60±85.35), both the PD-TD (282.00±102.49, P=0.006) and PD-PIGD groups (284.91±118.54, P=0.007) exhibited greater susceptibility values in the substantia nigra (SN) pars reticulata. The susceptibility values in the SN pars compacta were also greater in the PD-PIGD group (164.51±89.44) than in the HCs (107.78±63.11, P=0.048).

Conclusions

The present study demonstrated various iron deposition patterns in different PD phenotypes. These findings give insight into the pathophysiology underlying different PD phenotypes, and potentially illustrate the involvement of iron deposition in the PD-TD and PD-PIGD subtypes.

Motoric impairment versus iron deposition gradient in the subthalamic nucleus in Parkinson's disease

OBJECTIVE

The objective of this study was to investigate the correlation between the quantitative susceptibility mapping (QSM) signal gradient of the subthalamic nucleus (STN) and motor impairment in patients with Parkinson's disease (PD).

METHODS

All PD patients who had undergone QSM MRI for presurgical deep brain stimulation (DBS) planning were eligible for inclusion in this study. The entire STN and its three functional subdivisions, as well as the adjacent white matter (WM), were segmented and measured. The QSM value difference between the entire STN and adjacent WM (STN-WM), between the limbic and associative regions of the STN (L-A), and between the associative and motor regions of the STN (A-M) were obtained as measures of gradient and were input into an unsupervised k-means clustering algorithm to automatically categorize the overall boundary distinctness between the STN and adjacent WM and between STN subdivisions (gradient blur [GB] and gradient sharp [GS] groups). Statistical tests were performed to compare clinical and image measurements for discrimination between GB and GS groups.

RESULTS

Of the 39 study patients, 19 were categorized into the GB group and 20 into the GS group, based on quantitative cluster analysis. The GB group had a significantly higher presurgical off-medication Unified Parkinson's Disease Rating Scale Part III score (51.289 ± 20.741) than the GS group (38.5 ± 16.028; p = 0.037). The GB group had significantly higher QSM values for the STN and its three subdivisions and adjacent WM than those for the GS group (p < 0.01). The GB group also demonstrated a significantly higher STN-WM gradient in the right STN (p = 0.01). The GB group demonstrated a significantly lower L-A gradient in both the left and the right STN (p < 0.02).

CONCLUSIONS

Advancing PD with more severe motor impairment leads to more iron deposition in the STN and adjacent WM, as shown in the QSM signal. Loss of the STN inner QSM signal gradient should be considered as an image marker for more severe motor impairment in PD patients.

Iron Imaging as a Diagnostic Tool for Parkinson's Disease: A Systematic Review and Meta-Analysis

Background: Parkinson's disease (PD) is a progressive neurodegenerative disease whose main neuropathological feature is the loss of dopaminergic neurons of the substantia nigra (SN). There is also an increase in iron content in the SN in postmortem and imaging studies using iron-sensitive MRI techniques. However, MRI results are variable across studies. Objectives: We performed a systematic meta-analysis of SN iron imaging studies in PD to better understand the role of iron-sensitive MRI quantification to distinguish patients from healthy controls. We also studied the factors that may influence iron quantification and analyzed the correlations between demographic and clinical data and iron load. Methods: We searched PubMed and ScienceDirect databases (from January 1994 to December 2019) for studies that analyzed iron load in the SN of PD patients using T2^*, R2^*, susceptibility weighting imaging (SWI), or quantitative susceptibility mapping (QSM) and compared the values with healthy controls. Details for each study regarding participants, imaging methods, and results were extracted. The effect size and confidence interval (CI) of 95% were calculated for each study as well as the pooled weighted effect size for each marker over studies. Hence, the correlations between technical and clinical metrics with iron load were analyzed. Results: Forty-six articles fulfilled the inclusion criteria including 27 for T2^*/R2^* measures, 10 for SWI, and 17 for QSM (3,135 patients and 1,675 controls). Eight of the articles analyzed both R2^* and QSM. A notable effect size was found in the SN in PD for R2^* increase (effect size: 0.84, 95% CI: 0.60 to 1.08), for SWI measurements (1.14, 95% CI: 0.54 to 1.73), and for QSM increase (1.13, 95% CI: 0.86 to 1.39). Correlations between imaging measures and Unified Parkinson's Disease Rating Scale (UPDRS) scores were mostly observed for QSM. Conclusions: The consistent increase in MRI measures of iron content in PD across the literature using R2^*, SWI, or QSM techniques confirmed that these measurements provided reliable markers of iron content in PD. Several of these measurements correlated with the severity of motor symptoms. Lastly, QSM appeared more robust and reproducible than R2^* and more suited to multicenter studies.

Impairment of Motor Function Correlates with Neurometabolite and Brain Iron Alterations in Parkinson's Disease

We took advantage of magnetic resonance imaging (MRI) and spectroscopy (MRS) as non-invasive methods to quantify brain iron and neurometabolites, which were analyzed along with other predictors of motor dysfunction in Parkinson’s disease (PD). Tapping hits, tremor amplitude, and the scores derived from part III of the Movement Disorder Society-Sponsored Revision of the Unified Parkinson Disease Rating Scale (MDS-UPDRS3 scores) were determined in 35 male PD patients and 35 controls. The iron-sensitive MRI relaxation rate R2* was measured in the globus pallidus and substantia nigra. γ-aminobutyric acid (GABA)-edited and short echo-time MRS was used for the quantification of neurometabolites in the striatum and thalamus. Associations of R2*, neurometabolites, and other factors with motor function were estimated with Spearman correlations and mixed regression models to account for repeated measurements (hands, hemispheres). In PD patients, R2* and striatal GABA correlated with MDS-UPDRS3 scores if not adjusted for age. Patients with akinetic-rigid PD subtype (N = 19) presented with lower creatine and striatal glutamate and glutamine (Glx) but elevated thalamic GABA compared to controls or mixed PD subtype. In PD patients, Glx correlated with an impaired dexterity when adjusted for covariates. Elevated myo-inositol was associated with more tapping hits and lower MDS-UPDRS3 scores. Our neuroimaging study provides evidence that motor dysfunction in PD correlates with alterations in brain iron and neurometabolites.

Beyond Dopamine: GABA, Glutamate, and the Axial Symptoms of Parkinson Disease

Introduction: The axial symptoms of Parkinson disease (PD) include difficulties with balance, posture, speech, swallowing, and locomotion with freezing of gait, as well as axial rigidity. These axial symptoms impact negatively on quality of life for many patients, yet remain poorly understood. Dopaminergic treatments typically have little effect on the axial symptoms of PD, suggesting that disruptions in other neurotransmitter systems beyond the dopamine system may underlie these symptoms. The purpose of the present study was to examine the relationship between the axial symptoms of PD and GABA and glutamate levels quantified with magnetic resonance spectroscopy.

Methods: The participant group included 20 patients with PD and 17 healthy control participants. Water-scaled GABA and Glx (glutamate + glutamine) concentrations were derived from GABA-edited MEGA-PRESS spectra acquired from the left basal ganglia and prefrontal cortex, and additional water-scaled Glx concentrations were acquired from standard PRESS spectra acquired from the pons. Spectra were analyzed with LCModel. The axial symptoms of PD were evaluated from subscales of the Unified Parkinson's Disease rating scale (MDS-UPDRS).

Results: PD patients demonstrated significantly higher GABA levels in the basal ganglia, which correlated with the degree of gait disturbance. Basal ganglia Glx levels and prefrontal GABA and Glx levels did not differ significantly between patient and control groups, but within the PD group prefrontal Glx levels correlated negatively with difficulties turning in bed. Results from an exploratory subgroup analysis indicate that the associations between GABA, Glx, and axial symptoms scores are typically more prominent in akinetic-rigid patients than in tremor-dominant patients.

Conclusion: Alterations in GABAergic and glutamatergic neurotransmission may contribute to some of the axial symptoms of PD.

Elevated microRNA-520d-5p in the serum of patients with Parkinson's disease, possibly through regulation of cereloplasmin expression

Iron metabolism dysfunction and redox-active iron-induced oxidative stress in the brain may contribute to the pathogenesis of Parkinson's disease. We have previously demonstrated that reduced serum ceruloplasmin level exacerbates nigral iron deposition in Parkinson's disease, although the underlying cause of the low serum ceruloplasmin level in Parkinson's disease remains unknown. Fluorescent quantitative real-time polymerase chain reaction analysis revealed that patients with Parkinson's disease had higher serum levels of microRNA (miR)-520d-5p than controls (p = 0.0011). Patients with Alzheimer's disease or multiple system atrophy did not have significantly elevated miR-520d-5p levels. Expression of miR-520d-5p did not correlate with disease severity or the motor phenotype of Parkinson's disease. Luciferase assays confirmed that miR-520d-5p was associated with ceruloplasmin gene expression, as predicted by the TargetScan tool and miRBase. In vitro experiments showed that miR-520d-5p reduced ceruloplasmin gene expression in the U251 astrocyte cell line. Our data suggest that miR-520d-5p may be a potential regulator of ceruloplasmin gene expression in vitro.

Quantitative susceptibility mapping as an indicator of subcortical and limbic iron abnormality in Parkinson's disease with dementia

Late stage Parkinson's disease (PD) patients were commonly observed with other non-motor comorbidities such as dementia and psychosis. While abnormal iron level in the substantia nigra was clinically accepted as a biomarker of PD, it was also suggested that the increased iron deposition could impair other brain regions and induce non-motor symptoms. A new Magnetic Resonance Imaging (MRI) called Quantitative Susceptibility Mapping (QSM) has been found to measure iron concentration in the grey matter reliably. In this study, we investigated iron level of different subcortical and limbic structures of Parkinson's disease (PD) patients with and without dementia by QSM. QSM and volumetric analysis by MRI were performed in 10 PD dementia (PDD) patients (73 ± 6 years), 31 PD patients (63 ± 8 years) and 27 healthy controls (62 ± 7 years). No significant differences were observed in the L-Dopa equivalent dosage for the two PD groups (p = 0.125). Putative iron content was evaluated in different subcortical and limbic structures of the three groups, as well as its relationship with cognitive performance. One-way ANCOVA with FDR adjustment at level of 0.05, adjusted for age and gender, showed significant group differences for left and right hippocampus (p = 0.015 & 0.032, respectively, BH-corrected for multiple ROIs) and right thalamus (p = 0.032, BH-corrected). Post-hoc test with Bonferroni's correction suggested higher magnetic susceptibility in PDD patients than healthy controls in the left and right hippocampus (p = 0.001 & 0.047, respectively, Bonferroni's corrected), while PD patients had higher magnetic susceptibility than the healthy controls in right hippocampus and right thalamus (p = 0.006 & 0.005, respectively, Bonferroni's corrected). PDD patients also had higher susceptibility than the non-demented PD patients in left hippocampus (p = 0.046, Bonferroni's corrected). The magnetic susceptibilities of the left and right hippocampus were negatively correlated with the Mini-Mental State Examination score (r = -0.329 & -0.386, respectively; p < 0.05). This study provides support for iron accumulation in limbic structures of PDD and PD patients and its correlation with cognitive performance, however, its putative involvement in development of non-motor cognitive dysfunction in PD pathogenesis remains to be elucidated.

Neuromelanin-sensitive MRI of the substantia nigra: An imaging biomarker to differentiate essential tremor from tremor-dominant Parkinson's disease

INTRODUCTION

We aimed to evaluate whether neuromelanin-sensitive MRI (NM-MRI) features in the substantia nigra pars compacta (SNc) were of diagnostic value to differentiate untreated essential tremor (ET) from de novo tremor-dominant Parkinson's disease (PD_T).

METHODS

Eighteen untreated ET patients, 21 de novo PD_T patients and 21 healthy control subjects were recruited. All the subjects underwent clinical examination, motor and cognitive evaluations, as well as NM-MRI. High signal intensity of the lateral, central and medial SNc subregions on NM-MRI were evaluated using the width, signal intensity (contrast-to-noise ratio, CNR) and visual analysis. Diagnostic test performance of SNc values was investigated by using receiver operating characteristic analysis and net reclassification improvement (NRI).

RESULTS

The width and CNR values of the lateral and central SNc subregions in PD_T were significantly decreased compared with those in ET and control group. Using visual analysis, the total visual score of all SNc subregions was significantly reduced in PD_T when compared with ET and control group. The width of the lateral SNc subregion allowed the best differentiation between ET and PD_T, and visual analysis also showed good diagnostic value. NRI result indicated that visual analysis and the width of the lateral SNc subregion had the same diagnostic power.

CONCLUSIONS

The neuromelanin changes of SNc in ET and PD_T follow the different patterns. Both the measurements and visual analysis of SNc on NM-MRI provide high diagnostic accuracy for differentiating ET from PD_T subtype. NM-MRI is a potential tool in diagnostic work-up of tremor disorders.

Ceruloplasmin in Parkinson's disease and the nonmotor symptoms

OBJECTIVES

To investigate the relationship between ceruloplasmin (CP) and Parkinson's disease (PD), and the correlation between CP level and the time difference between nonmotor symptoms and motor symptoms and the diagnosis were also mentioned.

MATERIALS AND METHODS

Sixty-six patients diagnosed with PD for the first time were included in the study. They were divided into CP reduction group (31 cases) and CP normal group (35 cases) according to their CP level. The estimated time difference between nonmotor symptoms and motor symptoms and the diagnosis were recorded respectively. The magnetic sensitive nigra phase value was measured by susceptibility weighted imaging (SWI).

RESULTS

Ceruloplasmin level was middling correlated with age (r = .561, p < .001). There was strong negative correlation between CP level and UPDRS scores (r = -.727, p < .001). The CP level was significantly correlated with the magnetic sensitive nigra phase value (r = .891, p < .001). CP level showed moderate correlation with the time difference from nonmotor symptoms to motor symptoms (r = .559, p < .001), besides, the time difference between nonmotor symptoms and the diagnosis (r = .525, p < .001) and CP level was also moderately related.

CONCLUSIONS

Ceruloplasmin interference in iron metabolism was closely related with PD development. And there were slight corrections between CP level and the time difference from nonmotor symptoms to motor symptoms or the diagnosis.

Quantifying iron deposition within the substantia nigra of Parkinson's disease by quantitative susceptibility mapping

BACKGROUND

Iron deposition within the substantia nigra (SN) has been postulated to play a vital role in Parkinson's disease (PD). The aim of this study was to explore the inherent link of PD patients between their substantia nigra iron accumulation and clinical status using quantitative susceptibility mapping (QSM) which is now considered to be the only quantitative imaging technique of brain iron deposition.

METHODS

44 PD patients and 31 age- and gender-matched healthy controls underwent quantitative susceptibility mapping (QSM) were recruited in this study. We firstly divided the patients into mild symptom severity (MSP) and advanced symptom severity (ASP) groups concerning their disease stage, aiming to illuminate the relationship between iron deposition in SN of PD and disease progression. Then, we classified the patients with Parkinson's disease into three subgroups: tremor-dominant PD (TD), akinetic/rigidity-dominant PD (AR), mixed-PD (M) according to their dominant motor symptoms in order to investigate whether there are any effects of SN iron accumulation to different subtypes of PD patients.

RESULTS

Compared to healthy controls, patients with PD have increased QSM magnetic values in the substantia nigra (138.039±37.320 vs 179.553±65.715; P=0.001). More prominent statistically significance of the difference of SN iron deposition between healthy controls (HC) and advanced symptom severity (ASP) subgroup was displayed (138.039±37.320 vs 232.827±92.040; P<0.001). Besides, among the three clinical phenotypes both TD and AR subgroup showed significant difference compared with healthy controls concerning the QSM values (138.039±37.320 vs 185.864±99.851; P=0.013; 188.148±52.958 vs 138.039±37.320; P=0.001). Furthermore, the iron content in the SN of PD patients was significantly correlated with the Hoehn-Yahr stage, the Unified Parkinson's Disease Rating Scale (UPDRS), Montgomery Asberg Depression Rating Scale (MADRS) and Hamilton Anxiety Scale (HAMA) scores (r=0.417, P=0.005; r=0.300, P=0.048; r=0.540, P<0.001; r=0.553, P<0.001). In MSP the significantly correlation was displayed only in MADRS, HAMA scores (r=0.429, P=0.013; r=0.492, P=0.004), when disease progressed into advanced severity stage all these clinical measures (Hoehn-Yahr stage, UPDRS-3, UPDRS, HAMA, and MADRS scores) we had recruited into this study shown prominent correlation to SN iron content (r=0.650, P=0.030; r=0.709, P=0.015; r=0.708, P=0.015; r=0.758, P=0.007; r=0.683, P=0.020). In the three phenotypes the correlation between iron content and MADRS, HAMA scores (r=0.686, P=0.002; r=0.633, P=0.006) was found in AR subgroups exclusively.

CONCLUSIONS

Patients with PD exhibited significantly higher magnetic susceptibility values, especially in those who are in advanced disease severity stage, which confirmed that iron accumulation in the SN is in line with Parkinson's disease progression. Furthermore, we testified that there are actually some inherent effects of substantia nigra iron deposition to the clinical symptoms of Parkinson's disease. Moreover, it seems that akinetic/rigidity-dominant PD subgroup was affected most by SN iron accumulation.

Disrupted Functional Connectivity of Basal Ganglia across Tremor-Dominant and Akinetic/Rigid-Dominant Parkinson's Disease

It is well known that disruption of basal ganglia function generates the motor symptoms in PD, however, these are presented in a heterogeneous manner; patients can be divided into tremor-dominant and akinesia/rigidity-dominant subtypes. To date, it is unknown if these differences in the motor symptoms could be explained by differences on the functional connectivity of basal ganglia with specific brain regions. In this study, we aimed to explore the alterations of the network-based and global functional connectivity linking to basal ganglia between the PD-TD and PD-AR patients. One hundred and six PD patients and 52 normal controls were recruited. According to the subscales of UPDRS motor scale, PD patients were divided into the PD-TD (n = 57) and PD-AR (n = 49) subtypes. We performed independent component analysis to identify basal ganglia network (BGN) involving connected brain regions having coactivation with basal ganglia. Eigenvector centrality mapping were processed and the eigenvector centrality in the subcortical component of BGN including the bilateral caudate nuclei, putamen, thalami and pallidum were extracted to measure the global connectivity. Compared with controls, whole PD patients or PD subtypes showed decreases of functional connectivity within the subcortical component of BGN, e.g., thalamus, pallidum and putamen. Compared with controls, decreased functional connectivity of precuneus and amygdala with basal ganglia was observed in the PD-TD while that of occipital lobule and precuneus was observed in the PD-AR. Compared with the PD-TD, significantly decreased functional connectivity between occipital lobule and cerebellum posterior lobule and basal ganglia was observed in the PD-AR, and such connectivity had positive correlations with tremor and negative correlations with akinesia/rigidity. We also observed enhanced global connectivity in the caudate nucleus and thalamus in the PD subtypes compared with controls. In conclusion, PD patients independent of motor subtypes consistently express similar alterations of functional connectivity within the subcortical component of BGN including network-based connectivity and global connectivity. Functional connectivity of cerebellum posterior lobule and occipital lobule with basal ganglia play important roles in the modulation of parkinsonian motor symptoms.

Iron Deposition Leads to Neuronal α-Synuclein Pathology by Inducing Autophagy Dysfunction

Growing evidence has indicated that iron deposition in the substantia nigra plays an important role in Parkinson’s disease (PD). However, the underlying mechanism is still elusive. Using primary dopaminergic neurons and SH-SY5Y cells cultured in vitro, we observed that iron loading increased α-synuclein and reactive oxygen species (ROS) levels in these cells but did not affect the intracellular α-synuclein mRNA levels. Furthermore, iron loading significantly downregulated Beclin-1 levels and decreased the ratio of microtubule-associated protein 1 light chain 3 isoforms (LC3 II/LC3 I). However, a significant change in the levels of autophagy-related gene 5 (Atg5) was not observed in either neurons or SH-SY5Y cells after iron treatment. After treatment with rapamycin, the iron loading-induced increase in the α-synuclein level was significantly reversed and ROS generation was alleviated in both cultured neurons and SH-SY5Y cells. These results indicate that the inhibition of autophagy is critical for the pathological alterations in α-synuclein induced by iron loading. Moreover, treatment with vitamin E did not affect the increase in the α-synuclein levels but significantly eliminated the iron-induced ROS production. Together, our study shows that autophagy dysfunction contributes to iron-induced α-synuclein pathology.

Motor associations of iron accumulation in deep grey matter nuclei in Parkinson's disease: a cross-sectional study of iron-related magnetic resonance imaging susceptibility

BACKGROUND AND PURPOSE

To determine whether iron deposition in deep brain nuclei assessed using high-pass filtered phase imaging plays a role in motor disease severity in Parkinson's disease (PD).

METHODS

Seventy patients with mild to moderate PD and 20 age- and gender-matched healthy volunteers (HVs) underwent susceptibility-weighted imaging on a 3 T magnetic resonance imaging scanner. Phase shifts (radians) in deep brain nuclei were derived from high-pass filtered phase images and compared between groups. Analysis of clinical laterality and correlations with motor severity (Unified Parkinson's Disease Rating Scale, Part III, UPDRS-III) were performed. Phase shifts (in radians) were compared between HVs and three PD subgroups divided according to UPDRS-III scores using analysis of covariance, adjusting for age and regional area.

RESULTS

Parkinson's disease patients had significantly (P < 0.001) higher radians than HVs bilaterally in the putamen, globus pallidus and substantia nigra (SN). The SN contralateral to the most affected side showed higher radians (P < 0.001) compared to the less affected side. SN radians positively correlated with UPDRS-III and bradykinesia-rigidity subscores, but not with tremor subscores. ancova followed by post hoc Bonferroni-adjusted pairwise comparisons revealed that SN radians were significantly greater in the PD subgroup with higher UPDRS-III scores compared to both lowest UPDRS-III PD and HV groups (P < 0.001).

CONCLUSIONS

Increased nigral iron accumulation in PD appears to be stratified according to disease motor severity and correlates with symptoms related to dopaminergic neurodegeneration. This semi-quantitative in vivo iron assessment could prove useful for objectively monitoring PD progression, especially in clinical trials concerning iron chelation therapies.

Oxidative modification of human ceruloplasmin induced by a catechol neurotoxin, salsolinol

Salsolinol (SAL), a compound derived from dopamine metabolism, is the most probable neurotoxin involved in the pathogenesis of Parkinson's disease (PD). In this study, we investigated the modification and inactivation of human ceruloplasmin (hCP) induced by SAL. Incubation of hCP with SAL increased the protein aggregation and enzyme inactivation in a dose-dependent manner. Reactive oxygen species scavengers and copper chelators inhibited the SAL-mediated hCP modification and inactivation. The formation of dityrosine was detected in SAL-mediated hCP aggregates. Amino acid analysis post the exposure of hCP to SAL revealed that aspartate, histidine, lysine, threonine and tyrosine residues were particularly sensitive. Since hCP is a major copper transport protein, oxidative damage of hCP by SAL may induce perturbation of the copper transport system, which subsequently leads to deleterious conditions in cells. This study of the mechanism by which ceruloplasmin is modified by salsolinol may provide an explanation for the deterioration of organs under neurodegenerative disorders such as PD.

Utility of susceptibility-weighted imaging in Parkinson's disease and atypical Parkinsonian disorders

In the clinic, the diagnosis of Parkinson's disease (PD) largely depends on clinicians' experience. When the diagnosis is made, approximately 80% of dopaminergic cells in the substantia nigra (SN) have been lost. Additionally, it is rather challenging to differentiate PD from atypical parkinsonian disorders (APD). Clinially-available 3T conventional MRI contributes little to solve these problems. The pathologic alterations of parkinsonism show abnormal brain iron deposition, and therefore susceptibility-weighted imaging (SWI), which is sensitive to iron concentration, has been applied to find iron-related lesions for the diagnosis and differentiation of PD in recent decades. Until now, the majority of research has revealed that in SWI the signal intensity changes in deep brain nuclei, such as the SN, the putamen (PUT), the globus pallidus (GP), the thalamus (TH), the red nucleus (RN) and the caudate nucleus (CN), thereby raising the possibility of early diagnosis and differentiation. Furthermore, the signal changes in SN, PUT and TH sub-regions may settle the issues with higher accuracy. In this article, we review the brain iron deposition of PD, MSA-P and PSP in SWI in the hope of exhibiting a profile of SWI features in PD, MSA and PSP and its clinical values.

Influence of regional iron on the motor impairments of Parkinson's disease: A quantitative susceptibility mapping study

PURPOSE

Because the roles of striatal-thalamo-cortical and cerebello-thalamo-cortical circuits in the heterogeneous motor impairments of Parkinson's disease (PD) are becoming recognized, this study was designed to investigate the relationships between regional iron in the cardinal subcortical nuclei in these circuits and the different motor impairments.

MATERIALS AND METHODS

Sixty-two PD patients and 40 normal subjects were included and accepted for Enhanced T₂ -Star Weighted Angiography Scanning (3.0T). According to the Unified Parkinson's Disease Rating Scale, patients were divided into tremor-dominant (PD-TD) and akinetic/rigid-dominant groups (PD-AR). The intergroup differences of magnetic susceptibility in those cardinal nuclei were measured. Correlation analyses between magnetic susceptibility and motor impairments were performed in all patients.

RESULTS

Nigral magnetic susceptibility significantly increased for each PD group compared with controls (P < 0.001 for PD-TD; P = 0.001 for PD-AR). Magnetic susceptibility in the dentate nucleus (DN) and red nucleus (RN) for the PD-TD patients were significantly increased compared with controls (P < 0.001 and P = 0.004, respectively). Magnetic susceptibility in these regions was also significantly correlated with tremor severity (r = 0.444, P = 0.001 for DN; r = 0.418, P = 0.001 for RN). Significant correlation between caudate magnetic susceptibility and akinetic/rigid severity were observed (r = -0.322, P = 0.015).

CONCLUSION

This study provides evidence that nigral iron accumulation is a common characteristic in PD, while iron accumulation in the DN and RN is correlated with tremor symptoms. Our data also indicate that caudate iron content may be a potential marker for akinetic/rigid progression.

LEVEL OF EVIDENCE

3 J. MAGN. RESON. IMAGING 2017;45:1335-1342.

Nonmotor features of Parkinson's disease subtypes

Parkinson's disease is highly heterogeneous in early clinical features and later outcomes. This makes classifying subgroups of PD relevant to clinical research and practice, particularly if they are prognostically relevant. Subgroups have been defined both on the basis of motor and nonmotor features, and subgroups have been determined either empirically, based on clinical observation, or using data-driven analytic techniques. Previous studies have examined both the overall number and the nature of nonmotor symptoms and signs in tremor-dominant compared with non-tremor-dominant subtypes, and longitudinal studies identify nonmotor symptoms as important markers of prognosis and important defining features of PD subtypes. Autonomic features seem to preferentially affect individuals with non-tremor-dominant PD subtype early in the disease. Later in the disease cognitive disturbance distinguishes this phenotype. Pathological and neuroimaging studies provide substantial evidence for fundamental biological differences between tremor-dominant and postural instability gait disorder/akinetic-rigid subtypes. Biomarker studies point toward non-tremor-dominant PD as representing more advanced and diffuse neurodegeneration than tremor-dominant PD, encompassing dopaminergic and nondopaminergic as well as synuclein and nonsynuclein (Abeta) pathologies. This aligns with clinical studies that find a higher burden of nonmotor symptoms in non-tremor-dominant PD. The mounting evidence for the relevance of nonmotor features in PD subtypes behooves us to begin to investigate the biological underpinnings of subtypes defined by both motor and nonmotor features. This may be challenging, as PD subtypes are unlikely to be distinct nonoverlapping entities but are more likely to represent typical phenotypes within a multidimensional spectrum resulting from variable contributions of a number of simultaneous pathological processes. © 2016 International Parkinson and Movement Disorder Society.

Region-specific disturbed iron distribution in early idiopathic Parkinson's disease measured by quantitative susceptibility mapping

In Parkinson's disease (PD), iron elevation in specific brain regions as well as selective loss of dopaminergic neurons is a major pathologic feature. A reliable quantitative measure of iron deposition is a potential biomarker for PD and may contribute to the investigation of iron-mediated PD. The primary purpose of this study is to assess iron variations in multiple deep grey matter nuclei in early PD with a novel MRI technique, quantitative susceptibility mapping (QSM). The inter-group differences of susceptibility and R2* value in deep grey matter nuclei, namely head of caudate nucleus (CN), putamen (PUT), global pallidus (GP), substantia nigra (SN), and red nucleus (RN), and the correlations between regional iron deposition and the clinical features were explored in forty-four early PD patients and 35 gender and age-matched healthy controls. Susceptibility values were found to be elevated within bilateral SN and RN contralateral to the most affected limb in early PD compared with healthy controls (HCs). The finding of increased susceptibility in bilateral SN is consistent with work on a subgroup of patients at the earliest clinical detectable state (Hoehn and Yahr [1967]: Neurology 17:427-442; Stage I). However, increased R2* values were only seen within SN contralateral to the most affected limb in the PD group when compared with controls. Furthermore, bilateral SN magnetic susceptibility positively correlated with disease duration and UPDRS-III scores in early PD. This finding supports the potential value of QSM as a non-invasive quantitative biomarker of early PD.

Magnetic resonance susceptibility weighted imaging in neurosurgery: current applications and future perspectives

Susceptibility weighted imaging (SWI) is a relatively new imaging technique. Its high sensitivity to hemorrhagic components and ability to depict microvasculature by means of susceptibility effects within the veins allow for the accurate detection, grading, and monitoring of brain tumors. This imaging modality can also detect changes in blood flow to monitor stroke recovery and reveal specific subtypes of vascular malformations. In addition, small punctate lesions can be demonstrated with SWI, suggesting diffuse axonal injury, and the location of these lesions can help predict neurological outcome in patients. This imaging technique is also beneficial for applications in functional neurosurgery given its ability to clearly depict and differentiate deep midbrain nuclei and close submillimeter veins, both of which are necessary for presurgical planning of deep brain stimulation. By exploiting the magnetic susceptibilities of substances within the body, such as deoxyhemoglobin, calcium, and iron, SWI can clearly visualize the vasculature and hemorrhagic components even without the use of contrast agents. The high sensitivity of SWI relative to other imaging techniques in showing tumor vasculature and microhemorrhages suggests that it is an effective imaging modality that provides additional information not shown using conventional MRI. Despite SWI's clinical advantages, its implementation in MRI protocols is still far from consistent in clinical usage. To develop a deeper appreciation for SWI, the authors here review the clinical applications in 4 major fields of neurosurgery: neurooncology, vascular neurosurgery, neurotraumatology, and functional neurosurgery. Finally, they address the limitations of and future perspectives on SWI in neurosurgery.

Single-nucleotide polymorphisms and haplotypes of non-coding area in the CP gene are correlated with Parkinson's disease

Our previous studies have demonstrated that ceruloplasmin (CP) dysmetabolism is correlated with Parkinson's disease (PD). However, the causes of decreased serum CP levels in PD patients remain to be clarified. This study aimed to explore the potential association between genetic variants of the CP gene and PD. Clinical features, serum CP levels, and the CP gene (both promoter and coding regions) were analyzed in 60 PD patients and 50 controls. A luciferase reporter system was used to investigate the function of promoter single-nucleotide polymorphisms (SNPs). High-density comparative genomic hybridization microarrays were also used to detect large-scale copy-number variations in CP and an additional 47 genes involved in PD and/or copper/iron metabolism. The frequencies of eight SNPs (one intronic SNP and seven promoter SNPs of the CP gene) and their haplotypes were significantly different between PD patients, especially those with lowered serum CP levels, and controls. However, the luciferase reporter system revealed no significant effect of the risk haplotype on promoter activity of the CP gene. Neither these SNPs nor their haplotypes were correlated with the Hoehn and Yahr staging of PD. The results of this study suggest that common genetic variants of CP are associated with PD and further investigation is needed to explore their functions in PD.

Differentiating multiple-system atrophy from Parkinson's disease

The purpose of this review is to illustrate the differentiating features of multiple-system atrophy from Parkinson's disease at MRI. The various MRI sequences helpful in the differentiation will be discussed, including newer methods, such as diffusion tensor imaging, MR spectroscopy, and nuclear imaging.

Behavioral characterization of mouse models of neuroferritinopathy

Ferritin is the main intracellular protein of iron storage with a central role in the regulation of iron metabolism and detoxification. Nucleotide insertions in the last exon of the ferritin light chain cause a neurodegenerative disease known as Neuroferritinopathy, characterized by iron deposition in the brain, particularly in the cerebellum, basal ganglia and motor cortex. The disease progresses relentlessly, leading to dystonia, chorea, motor disability and neuropsychiatry features. The characterization of a good animal model is required to compare and contrast specific features with the human disease, in order to gain new insights on the consequences of chronic iron overload on brain function and behavior. To this aim we studied an animal model expressing the pathogenic human FTL mutant 498InsTC under the phosphoglycerate kinase (PGK) promoter. Transgenic (Tg) mice showed strong accumulation of the mutated protein in the brain, which increased with age, and this was accompanied by brain accumulation of ferritin/iron bodies, the main pathologic hallmark of human neuroferritinopathy. Tg-mice were tested throughout development and aging at 2-, 8- and 18-months for motor coordination and balance (Beam Walking and Footprint tests). The Tg-mice showed a significant decrease in motor coordination at 8 and 18 months of age, with a shorter latency to fall and abnormal gait. Furthermore, one group of aged naïve subjects was challenged with two herbicides (Paraquat and Maneb) known to cause oxidative damage. The treatment led to a paradoxical increase in behavioral activation in the transgenic mice, suggestive of altered functioning of the dopaminergic system. Overall, data indicate that mice carrying the pathogenic FTL498InsTC mutation show motor deficits with a developmental profile suggestive of a progressive pathology, as in the human disease. These mice could be a powerful tool to study the neurodegenerative mechanisms leading to the disease and help developing specific therapeutic targets.

The neurotoxicity of iron, copper and manganese in Parkinson's and Wilson's diseases

Impaired cellular homeostasis of metals, particularly of Cu, Fe and Mn may trigger neurodegeneration through various mechanisms, notably induction of oxidative stress, promotion of α-synuclein aggregation and fibril formation, activation of microglial cells leading to inflammation and impaired production of metalloproteins. In this article we review available studies concerning Fe, Cu and Mn in Parkinson's disease and Wilson's disease. In Parkinson's disease local dysregulation of iron metabolism in the substantia nigra (SN) seems to be related to neurodegeneration with an increase in SN iron concentration, accompanied by decreased SN Cu and ceruloplasmin concentrations and increased free Cu concentrations and decreased ferroxidase activity in the cerebrospinal fluid. Available data in Wilson's disease suggest that substantial increases in CNS Cu concentrations persist for a long time during chelating treatment and that local accumulation of Fe in certain brain nuclei may occur during the course of the disease. Consequences for chelating treatment strategies are discussed.

Quantitative susceptibility mapping (QSM): Decoding MRI data for a tissue magnetic biomarker

In MRI, the main magnetic field polarizes the electron cloud of a molecule, generating a chemical shift for observer protons within the molecule and a magnetic susceptibility inhomogeneity field for observer protons outside the molecule. The number of water protons surrounding a molecule for detecting its magnetic susceptibility is vastly greater than the number of protons within the molecule for detecting its chemical shift. However, the study of tissue magnetic susceptibility has been hindered by poor molecular specificities of hitherto used methods based on MRI signal phase and T2* contrast, which depend convolutedly on surrounding susceptibility sources. Deconvolution of the MRI signal phase can determine tissue susceptibility but is challenged by the lack of MRI signal in the background and by the zeroes in the dipole kernel. Recently, physically meaningful regularizations, including the Bayesian approach, have been developed to enable accurate quantitative susceptibility mapping (QSM) for studying iron distribution, metabolic oxygen consumption, blood degradation, calcification, demyelination, and other pathophysiological susceptibility changes, as well as contrast agent biodistribution in MRI. This paper attempts to summarize the basic physical concepts and essential algorithmic steps in QSM, to describe clinical and technical issues under active development, and to provide references, codes, and testing data for readers interested in QSM.

Eryptosis as a marker of Parkinson's disease

A major trend in recent Parkinson's disease (PD) research is the investigation of biological markers that could help in identifying at-risk individuals or to track disease progression and response to therapies. Central to this is the knowledge that inflammation is a known hallmark of PD and of many other degenerative diseases. In the current work, we focus on inflammatory signalling in PD, using a systems approach that allows us to look at the disease in a more holistic way. We discuss cyclooxygenases, prostaglandins, thromboxanes and also iron in PD. These particular signalling molecules are involved in PD pathophysiology, but are also very important in an aberrant coagulation/hematology system. We present and discuss a hypothesis regarding the possible interaction of these aberrant signalling molecules implicated in PD, and suggest that these molecules may affect the erythrocytes of PD patients. This would be observable as changes in the morphology of the RBCs and of PD patients relative to healthy controls. We then show that the RBCs of PD patients are indeed rather dramatically deranged in their morphology, exhibiting eryptosis (a kind of programmed cell death). This morphological indicator may have useful diagnostic and prognostic significance.

Serum microRNA-133b is associated with low ceruloplasmin levels in Parkinson's disease

INTRODUCTION

The cause of low serum ceruloplasmin levels in Parkinson's disease (PD) remains to be clarified. In this study, we explored serum miR-133b expression to determine whether it correlates with serum ceruloplasmin level in PD patients.

METHODS

Forty-six patients with PD and forty-six control subjects were evaluated for miR-133b expression using qRT-PCR. The serum ceruloplasmin levels in all of the subjects were also determined.

RESULTS

Serum miR-133b expression levels were significantly decreased in PD patients compared with those in the control subjects. Furthermore, PD patients with low serum ceruloplasmin levels also exhibited significantly lower expression of miR-133b compared with that of patients with normal ceruloplasmin levels. MiR-133b expression was correlated with the ceruloplasmin level in patients with PD, whereas no correlation was found between miR-133b and disease severity or motor phenotype.

CONCLUSION

Our observations suggest that miR-133b might be involved in ceruloplasmin dysmetabolism in PD patients and a further investigation is warranted to confirm this hypothesis.

Iron accumulation confers neurotoxicity to a vulnerable population of nigral neurons: implications for Parkinson's disease

Background

The substantia nigra (SN) midbrain nucleus is constitutively iron rich. Iron levels elevate further with age, and pathologically in Parkinson’s disease (PD). Iron accumulation in PD SN involves dysfunction of ceruloplasmin (CP), which normally promotes iron export. We previously showed that ceruloplasmin knockout (CP KO) mice exhibit Parkinsonian neurodegeneration (~30% nigral loss) by 6 months, which is prevented by iron chelation. Here, we explored whether known iron-stressors of the SN (1) aging and (2) MPTP, would exaggerate the lesion severity of CP KO mice.

Findings

We show that while 5 month old CP KO mice exhibited nigral iron elevation and loss of SN neurons, surprisingly, aging CP KO mice to 14 months did not exacerbate iron elevation or SN neuronal loss. Unlike young mice, iron chelation therapy in CP KO mice between 9–14 months did not rescue neuronal loss. MPTP exaggerated iron elevation in young CP KO mice but did not increase cell death when compared to WTs.

Conclusions

We conclude that there may exist a proportion of substantia nigra neurons that depend on CP for protection against iron neurotoxicity and could be protected by iron-based therapeutics. Death of the remaining neurons in Parkinson’s disease is likely caused by parallel disease mechanisms, which may call for additional therapeutic options.

Nigral iron elevation is an invariable feature of Parkinson's disease and is a sufficient cause of neurodegeneration

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor deficits accompanying degeneration of substantia nigra pars compactor (SNc) neurons. Although familial forms of the disease exist, the cause of sporadic PD is unknown. Symptomatic treatments are available for PD, but there are no disease modifying therapies. While the neurodegenerative processes in PD may be multifactorial, this paper will review the evidence that prooxidant iron elevation in the SNc is an invariable feature of sporadic and familial PD forms, participates in the disease mechanism, and presents as a tractable target for a disease modifying therapy.

Effects of hemochromatosis and transferrin gene mutations on peripheral iron dyshomeostasis in mild cognitive impairment and Alzheimer's and Parkinson's diseases

Deregulation of iron metabolism has been observed in patients with neurodegenerative diseases. We have carried out a molecular analysis investigating the interaction between iron specific gene variants [transferrin (TF, P589S), hemochromatosis (HFE) C282Y and (H63D)], iron biochemical variables [iron, Tf, ceruloplasmin (Cp), Cp:Tf ratio and % of Tf saturation (% Tf-sat)] and apolipoprotein E (APOE) gene variants in 139 Alzheimer's disease (AD), 27 Mild Cognitive Impairment (MCI), 78 Parkinson's disease (PD) patients and 139 healthy controls to investigate mechanisms of iron regulation or toxicity. No difference in genetic variant distributions between patients and controls was found in our Italian sample, but the stratification for the APOEε4 allele revealed that among the APOEε4 carriers was higher the frequency of those carriers of at least a mutated TF P589S allele. Decreased Tf in both AD and MCI and increased Cp:Tf ratio in AD vs. controls were detected. A multinomial logistic regression model revealed that increased iron and Cp:Tf ratio and being man instead of woman increased the risk of having PD, that increased values of Cp:Tf ratio corresponded to a 4-fold increase of the relative risk of having MCI, while higher Cp levels were protective for PD and MCI. Our study has some limitations: the small size of the samples, one ethnic group considered, the rarity of some alleles which prevent the statistical power of some genetic analysis. Even though they need confirmation in larger cohorts, our data suggest the hypothesis that deregulation of iron metabolism, in addition to other factors, has some effect on the PD disease risk.

Brain iron accumulation in aging and neurodegenerative disorders

Over the decades, various studies have established an association between accumulation of iron and both aging and neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Excess levels of iron can lead to increased oxidative stress through Fenton chemistry, and depletion of iron can similarly have deleterious effects. In addition, metal ions are known to be involved in both Alzheimer's disease and Parkinson's disease protein aggregation. Metal ion chelators have been extensively investigated in preclinical models, and may prove to be appropriate for modulating brain iron levels in age-related neurodegenerative disorders. Investigating age-related iron deposition is vital, and can possibly aid in determining at-risk groups and diagnosing neurodegenerative diseases at an early stage. Novel imaging methods have enabled researchers to examine iron deposition in vivo, and offer a noninvasive method of monitoring the progression of accumulation, and possible therapeutic effects of chelating compounds.

Ceruloplasmin dysfunction and therapeutic potential for Parkinson disease

Ceruloplasmin is an iron-export ferroxidase that is abundant in plasma and also expressed in glia. We found a ∼80% loss of ceruloplasmin ferroxidase activity in the substantia nigra of idiopathic Parkinson disease (PD) cases, which could contribute to the pro-oxidant iron accumulation that characterizes the pathology. Consistent with a role for ceruloplasmin in PD etiopathogenesis, ceruloplasmin knockout mice developed parkinsonism that was rescued by iron chelation. Additionally, peripheral infusion of ceruloplasmin attenuated neurodegeneration and nigral iron elevation in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine mouse model for PD. These findings show, in principle, that intravenous ceruloplasmin may have therapeutic potential in PD.

Recent advances in structural MRI in Parkinson’s disease and atypical parkinsonian syndromes

SUMMARY In the past 2 years, technical developments in conventional and advanced MRI, such as ultra-high-field MRI or mapping of brain mineralization, has allowed novel insights into the nature of Parkinson’s disease (PD) and atypical parkinsonian syndromes, which may aid diagnostic accuracy and differential diagnosis. In addition, sophisticated post-processing analyses, such as morphometry- and surface-based classifications and automated whole-brain analyses, have become available; in PD, this has led to direct visualization of structural substantia nigra abnormalities, monitoring disease progression or screening for brain atrophy associated with dementia. Based on conventional MRI, new MRI rating scales have been established for progressive supranuclear palsy and multiple system atrophy and have been further assessed with a view to their diagnostic accuracy. Clinicopathological series of patients with tauopathies imply that correlations between clinical syndromes, imaging patterns and underlying histopathology are not always strong. Here, some of the issues related to conventional and advanced MRI for the diagnostic accuracy of PD and atypical parkinsonian syndromes are reviewed.