Increased basal ganglia iron in striatonigral degeneration: in vivo estimation with magnetic resonance

MR image texture in Parkinson's disease: a longitudinal study

BACKGROUND

Few of the structural changes caused by Parkinson's disease (PD) are visible in magnetic resonance imaging (MRI) with visual inspection but there is a need for a method capable of observing the changes beyond the human eye. Texture analysis offers a technique that enables the quantification of the image gray-level patterns.

PURPOSE

To investigate the value of quantitative image texture analysis method in diagnosis and follow-up of PD patients.

MATERIAL AND METHODS

Twenty-six PD patients underwent MRI at baseline and after 2 years of follow-up. Four co-occurrence matrix-based texture parameters, describing the image homogeneity and complexity, were calculated within clinically interesting areas of the brain. In addition, correlations with clinical characteristics (Unified Parkinson's Disease Ranking Scales I-III and Mini-Mental State Examination score) along with a comparison to healthy controls were evaluated.

RESULTS

Patients at baseline and healthy volunteers differed in their brain MR image textures mostly in the areas of substantia nigra pars compacta, dentate nucleus, and basilar pons. During the 2-year follow-up of the patients, textural differences appeared mainly in thalamus and corona radiata. Texture parameters in all the above mentioned areas were also found to be significantly related to clinical scores describing the severity of PD.

CONCLUSION

Texture analysis offers a quantitative method for detecting structural changes in brain MR images. However, the protocol and repeatability of the method must be enhanced before possible clinical use.

Susceptibility-weighted imaging improves the diagnostic accuracy of 3T brain MRI in the work-up of parkinsonism

BACKGROUND AND PURPOSE

The differentiation between Parkinson disease and atypical parkinsonian syndromes can be challenging in clinical practice, especially in early disease stages. Brain MR imaging can help to increase certainty about the diagnosis. Our goal was to evaluate the added value of SWI in relation to conventional 3T brain MR imaging for the diagnostic work-up of early-stage parkinsonism.

MATERIALS AND METHODS

This was a prospective observational cohort study of 65 patients presenting with parkinsonism but with an uncertain initial clinical diagnosis. At baseline, 3T brain MR imaging with conventional and SWI sequences was performed. After clinical follow-up, probable diagnoses could be made in 56 patients, 38 patients diagnosed with Parkinson disease and 18 patients diagnosed with atypical parkinsonian syndromes, including 12 patients diagnosed with multiple system atrophy-parkinsonian form. In addition, 13 healthy controls were evaluated with SWI. Abnormal findings on conventional brain MR imaging were grouped into disease-specific scores. SWI was analyzed by a region-of-interest method of different brain structures. One-way ANOVA was performed to analyze group differences. Receiver operating characteristic analyses were performed to evaluate the diagnostic accuracy of conventional brain MR imaging separately and combined with SWI.

RESULTS

Disease-specific scores of conventional brain MR imaging had a high specificity for atypical parkinsonian syndromes (80%-90%), but sensitivity was limited (50%-80%). The mean SWI signal intensity of the putamen was significantly lower for multiple system atrophy-parkinsonian form than for Parkinson disease and controls (P < .001). The presence of severe dorsal putaminal hypointensity improved the accuracy of brain MR imaging: The area under the curve was increased from 0.75 to 0.83 for identifying multiple system atrophy-parkinsonian form, and it was increased from 0.76 to 0.82 for identifying atypical parkinsonian syndromes as a group.

CONCLUSIONS

SWI improves the diagnostic accuracy of 3T brain MR imaging in the work-up of parkinsonism by identifying severe putaminal hypointensity as a sign indicative of multiple system atrophy-parkinsonian form.

Iron regulation in C57BL/6 and DBA/2 mice subjected to iron overload

Many genes are likely involved in the control of iron metabolism in brain and in peripheral tissues, and genetically-defined murine strains present the opportunity to investigate genetic variations in iron metabolism. Weanling C57BL/6 (B6) and DBA/2 (D2) mice were divided into two treatment groups receiving distilled water with or without 5000 ppm ferric chloride ad libitum as their sole fluid source for 100 days. Iron overload increased liver, spleen and plasma iron levels in male and female B6 and female D2 mice. In D2 males, liver iron was increased relative to control, but spleen and plasma iron remained unaffected. Brain iron content was not different between control and iron-treated mice in ventral midbrain, caudate, pons or hippocampus, but D2 iron overloaded mice displayed lower iron levels in nucleus accumbens and prefrontal cortex. We conclude that genetic background influences the accumulation of excess iron in the periphery and iron regulation in the central nervous system.

Is R2* a new MRI biomarker for the progression of Parkinson's disease? A longitudinal follow-up

Purpose

To study changes of iron content in basal ganglia in Parkinson’s disease (PD) through a three-year longitudinal follow-up of the effective transverse relaxation rate R₂*, a validated MRI marker of brain iron content which can be rapidly measured under clinical conditions.

Methods

Twenty-seven PD patients and 26 controls were investigated by a first MRI (t₀). Longitudinal analysis was conducted among the 18 controls and 14 PD patients who underwent a second MRI (t₁) 3 years after. The imaging protocol consisted in 6 gradient echo images obtained at different echo-times for mapping R₂*. Quantitative exploration of basal ganglia was performed by measuring the variation of R₂* [R₂*(t₁) – R₂*(t₀)] in several regions of interest.

Results

During the three-year evolution of PD, R₂* increased in Substantia nigra (SN) (by 10.2% in pars compacta, p = 0.001, and 8.1% in pars reticulata, p = 0.013) and in the caudal putamen (11.4%, p = 0.011), without significant change in controls. Furthermore, we showed a positive correlation between the variation of R₂* and the worsening of motor symptoms of PD (p = 0.028).

Conclusion

Significant variation of R₂* was longitudinally observed in the SN and caudal putamen of patients with PD evolving over a three-year period, emphasizing its interest as a biomarker of disease progression. Our results suggest that R₂* MRI follow-up could be an interesting tool for individual assessment of neurodegeneration due to PD, and also be useful for testing the efficiency of disease-modifying treatments.

Different iron-deposition patterns of multiple system atrophy with predominant parkinsonism and idiopathetic Parkinson diseases demonstrated by phase-corrected susceptibility-weighted imaging

BACKGROUND AND PURPOSE

MSA-P and IPD have similar clinical presentations that may complicate accurate clinical diagnosis. Different iron-deposition patterns of those 2 diseases have been demonstrated in histopathology. The aim was to demonstrate the different iron-deposition patterns of MSA-P and IPD by using SWI phase images.

MATERIALS AND METHODS

Sixteen patients with IPD, 8 with MSA-P, and 44 age-matched healthy controls underwent SWI of brain. The different phase shifts as well as the high iron percentage of the area in several gray nuclei were statistically evaluated. The putamen was divided into 4 subregions for further analysis.

RESULTS

Patients with MSA-P had significantly higher iron deposition in the putamen and PT compared with those with IPD (P < .05). Moreover, ROC curves indicated slightly more sensitivity in differentiating MSA-P from IPD, by means of the high-iron-deposition-percentage area than the average phase shift (putamen: AUC = 0.88 versus 0.78; PT: AUC = 0.79 versus 0.62). Moreover, the lower inner region of the putamen was the most valuable subregion in differentiating MSA-P from IPD among the 4 subregions (AUC = 0.92 and 0.91 for high-iron-percentage area and average phase shift, respectively).

CONCLUSIONS

Higher iron deposition in the putamen and PT may differentiate MSA-P from IPD, but the lower inner region of the putamen may be better compared with the PT and other subregions of the putamen. Moreover, the high iron percentage makes it possible to detect smaller increases in iron content more confidently in comparison with average phase shift.

Parkinson's disease: interhemispheric textural differences in MR images

RATIONALE AND OBJECTIVES

Early-stage diagnosis of Parkinson's disease (PD) is essential in making decisions related to treatment and prognosis. However, there is no specific diagnostic test for the diagnosis of PD. The aim of this study was to evaluate the role of texture analysis (TA) of magnetic resonance images in detecting subtle changes between the hemispheres in various brain structures in patients with early symptoms of parkinsonism. In addition, functional TA parameters for detecting textural changes are presented.

MATERIALS AND METHODS

Fifty-one patients with symptoms of PD and 20 healthy controls were imaged using a 3-T magnetic resonance device. Co-occurrence matrix-based TA was applied to detect changes in textures between the hemispheres in the following clinically interesting areas: dentate nucleus, basilar pons, substantia nigra, globus pallidus, thalamus, putamen, caudate nucleus, corona radiata, and centrum semiovale. The TA results were statistically evaluated using the Mann-Whitney U test.

RESULTS

The results showed interhemispheric textural differences among the patients, especially in the area of basilar pons and midbrain. Concentrating on this clinically interesting area, the four most discriminant parameters were defined: co-occurrence matrix correlation, contrast, difference variance, and sum variance. With these parameters, differences were also detected in the dentate nucleus, globus pallidus, and corona radiata.

CONCLUSIONS

On the basis of this study, interhemispheric differences in the magnetic resonance images of patients with PD can be identified by the means of co-occurrence matrix-based TA. The detected areas correlate with the current pathophysiologic and neuroanatomic knowledge of PD.

MRI estimates of brain iron concentration in normal aging using quantitative susceptibility mapping

Quantifying tissue iron concentration in vivo is instrumental for understanding the role of iron in physiology and in neurological diseases associated with abnormal iron distribution. Herein, we use recently-developed Quantitative Susceptibility Mapping (QSM) methodology to estimate the tissue magnetic susceptibility based on MRI signal phase. To investigate the effect of different regularization choices, we implement and compare ℓ1 and ℓ2 norm regularized QSM algorithms. These regularized approaches solve for the underlying magnetic susceptibility distribution, a sensitive measure of the tissue iron concentration, that gives rise to the observed signal phase. Regularized QSM methodology also involves a pre-processing step that removes, by dipole fitting, unwanted background phase effects due to bulk susceptibility variations between air and tissue and requires data acquisition only at a single field strength. For validation, performances of the two QSM methods were measured against published estimates of regional brain iron from postmortem and in vivo data. The in vivo comparison was based on data previously acquired using Field-Dependent Relaxation Rate Increase (FDRI), an estimate of MRI relaxivity enhancement due to increased main magnetic field strength, requiring data acquired at two different field strengths. The QSM analysis was based on susceptibility-weighted images acquired at 1.5 T, whereas FDRI analysis used Multi-Shot Echo-Planar Spin Echo images collected at 1.5 T and 3.0 T. Both datasets were collected in the same healthy young and elderly adults. The in vivo estimates of regional iron concentration comported well with published postmortem measurements; both QSM approaches yielded the same rank ordering of iron concentration by brain structure, with the lowest in white matter and the highest in globus pallidus. Further validation was provided by comparison of the in vivo measurements, ℓ1-regularized QSM versus FDRI and ℓ2-regularized QSM versus FDRI, which again yielded perfect rank ordering of iron by brain structure. The final means of validation was to assess how well each in vivo method detected known age-related differences in regional iron concentrations measured in the same young and elderly healthy adults. Both QSM methods and FDRI were consistent in identifying higher iron concentrations in striatal and brain stem ROIs (i.e., caudate nucleus, putamen, globus pallidus, red nucleus, and substantia nigra) in the older than in the young group. The two QSM methods appeared more sensitive in detecting age differences in brain stem structures as they revealed differences of much higher statistical significance between the young and elderly groups than did FDRI. However, QSM values are influenced by factors such as the myelin content, whereas FDRI is a more specific indicator of iron content. Hence, FDRI demonstrated higher specificity to iron yet yielded noisier data despite longer scan times and lower spatial resolution than QSM. The robustness, practicality, and demonstrated ability of predicting the change in iron deposition in adult aging suggest that regularized QSM algorithms using single-field-strength data are possible alternatives to tissue iron estimation requiring two field strengths.

Differential effects of age and history of hypertension on regional brain volumes and iron

Aging affects various structural and metabolic properties of the brain. However, associations among various aspects of brain aging are unclear. Moreover, those properties and associations among them may be modified by age-associated increase in vascular risk. In this study, we measured volume of brain regions that vary in their vulnerability to aging and estimated local iron content via T2* relaxometry. In 113 healthy adults (19-83 years old), we examined prefrontal cortex (PFC), primary visual cortex (VC), hippocampus (HC), entorhinal cortex (EC), caudate nucleus (Cd), and putamen (Pt). In some regions (PFC, VC, Cd, and Pt) age-related differences in iron and volume followed similar patterns. However, in the medial-temporal structures, volume and iron content exhibited different age trajectories. Whereas age-related volume reduction was mild in HC and absent in EC, iron content evidenced significant age-related declines. In hypertensive participants significantly greater iron content was noted in all examined regions. Thus, iron content as measured by T2* may be a sensitive index of regional brain aging and may reveal declines that are more prominent than gross anatomical shrinkage.

Quantitative estimation of regional brain iron with magnetic resonance imaging

Biochemical studies have reported increased iron content in the substantia nigra pars compacta (SNc) in Parkinson disease (PD), with changes most marked in severe disease, suggesting that measurement of regional iron content in the nigra may provide an indication of the pathologic severity of the disease. Although basal ganglia structures, including the substantia nigra, are readily visualized with MRI, in part because of their high iron content, conventional imaging techniques have failed to show definitive abnormalities in individuals with PD. We have developed MRI-based methodology to estimate regional iron content utilizing a 1.5 tesla system and have shown a correlation between age and striatal iron, as well as a significant increase in putaminal and pallidal iron in PD that correlated with the severity of clinical symptomatology. Several investigators have utilized novel MR techniques implemented on 3 tesla magnets and have suggested the presence of increased nigral iron content in treated patients with PD, in addition to a correlation between nigral iron and simple reaction time. We have applied a modification of our original method to determine whether SNc changes evident at 3 tesla corresponded anatomically to the distribution of neuropathologic changes reported previously. Our results indicate the presence of lateral SNc abnormalities in untreated patients with early PD, consistent with increased iron content and corresponding to the known distribution of neuronal loss occurring in this disorder. We suggest that this may ultimately provide an imaging marker for disease progression in PD, although longitudinal studies are required.

Diffusion tensor imaging of deep gray matter brain structures: effects of age and iron concentration

Diffusion tensor imaging (DTI) of the brain has become a mainstay in the study of normal aging of white matter, and only recently has attention turned to the use of DTI to examine aging effects in gray matter structures. Of the many changes in the brain that occur with advancing age is increased presence of iron, notable in selective deep gray matter structures. In vivo detection and measurement of iron deposition is possible with magnetic resonance imaging (MRI) because of iron's effect on signal intensity. In the process of a DTI study, a series of diffusion-weighted images (DWI) is collected, and while not normally considered as a major dependent variable in research studies, they are used clinically and they reveal striking conspicuity of the globus pallidus and putamen caused by signal loss in these structures, presumably due to iron accumulation with age. These iron deposits may in turn influence DTI metrics, especially of deep gray matter structures. The combined imaging modality approach has not been previously used in the study of normal aging. The present study used legacy DTI data collected in 10 younger (22-37 years) and 10 older (65-79 years) men and women at 3.0T and fast spin-echo (FSE) data collected at 1.5T and 3.0T to derive an estimate of the field-dependent relaxation rate increase (the "FDRI estimate") in the putamen, caudate nucleus, globus pallidus, thalamus, and a frontal white matter sample comparison region. The effect of age on the diffusion measures in the deep gray matter structures was distinctly different from that reported in white matter. In contrast to lower anisotropy and higher diffusivity typical in white matter of older relative to younger adults observed with DTI, both anisotropy and diffusivity were higher in the older than younger group in the caudate nucleus and putamen; the thalamus showed little effect of age on anisotropy or diffusivity. Signal intensity measured with DWI was lower in the putamen of elderly than young adults, whereas the opposite was observed for the white matter region and thalamus. As a retrospective study based on legacy data, the FDRI estimates were based on FSE sequences, which underestimated the classical FDRI index of brain iron. Nonetheless, the differential effects of age on DTI metrics in subcortical gray matter structures compared with white matter tracts appears to be related, at least in part, to local iron content, which in the elderly of the present study was prominent in the FDRI estimate of the putamen and visibly striking in the diffusion-weighted image of the basal ganglia structures.

Putaminal lesion in multiple system atrophy: postmortem MR-pathological correlations

INTRODUCTION

Posterior putaminal atrophy, putaminal T2-hyper and/or hyposignal changes have been observed in patients with multiple system atrophy (MSA) with parkinsonism.

METHODS

Postmortem T2-weighted images were compared with histological findings in seven autopsy-proven cases of putaminal lesions of MSA. All cases were evaluated on 1.5T magnetic resonance imaging (MRI) scanners and three cases were evaluated on 3T scanners.

RESULTS

There were three types of putaminal changes: Type 1, mild putaminal atrophy and isointensity; Type 2, putaminal atrophy and diffuse hyperintensity with a hyperintense putaminal rim (HPR); Type 3, putaminal atrophy and iso-or-hypointensity with HPR. The signal intensities of the putamen in Types 1 and 3 were more hypointense on 3T images than on 1.5T images. In Type 1, mild putaminal atrophy showed mild neuronal loss and gliosis and diffuse ferritin deposition. In Types 2 and 3, the areas of putaminal atrophy, severe in the posterior region, showed severe neuronal loss and gliosis, many pigments that were positive for ferritin and Fe (3+) and diffuse ferritin deposition. Although, tissue rarefaction was more severe in Type 2 than in Type 3, pigment deposition was more severe in Type 3. The HPR showed a severe loss of myelin and axons with tissue rarefaction of the external capsule or putaminal rim in Types 2 and 3.

CONCLUSION

Posterior putaminal atrophy reflects neuronal loss and gliosis. While putaminal iso-or -hypointensity reflects diffuse ferritin and Fe(3+) deposition, hyperintensity reflects tissue rarefaction. The HPR reflects degeneration of the putaminal lateral margin and/or external capsule. These findings reflect characteristic histological findings of MSA with parkinsonism.

Iron metabolism in Parkinsonian syndromes

Growing evidence suggests an involvement of iron in the pathophysiology of neurodegenerative diseases. Several of the diseases are associated with parkinsonian syndromes, induced by degeneration of basal ganglia regions that contain the highest amount of iron within the brain. The group of neurodegenerative disorders associated with parkinsonian syndromes with increased brain iron content can be devided into two groups: (1) parkinsonian syndromes associated with brain iron accumulation, including Parkinson's disease, diffuse Lewy body disease, parkinsonian type of multiple system atrophy, progressive supranuclear palsy, corticobasal ganglionic degeneration, and Westphal variant of Huntington's disease; and (2) monogenetically caused disturbances of brain iron metabolism associated with parkinsonian syndromes, including aceruloplasminemia, hereditary ferritinopathies affecting the basal ganglia, and panthotenate kinase associated neurodegeneration type 2. Although it is still a matter of debate whether iron accumulation is a primary cause or secondary event in the first group, there is no doubt that iron-induced oxidative stress contributes to neurodegeneration. Parallels concerning pathophysiological as well as clinical aspects can be drawn between disorders of both groups. Results from animal models and reduction of iron overload combined with at least partial relief of symptoms by application of iron chelators in patients of the second group give hope that targeting the iron overload might be one possibility to slow down the neurodegenerative cascade also in the first group of inevitably progressive neurodegenerative disorders.

Role of iron in neurodegenerative disorders

Although the pathophysiology underlying a number of neurodegenerative diseases is complex and, in many aspects, only partly understood, increased iron levels in pathologically relevant brain areas and iron-mediated oxidative stress seem to play a central role in many of them. Much has been learned from monogenetically caused disturbances of brain iron metabolism including pantothenate kinase-associated neurodegeneration type 2, hereditary ferritinopathies affecting the basal ganglia, and aceruloplasminemia that may well be applied to the most common neurodegenerative disorders associated with brain iron accumulation including Parkinson disease and Alzheimer disease. Iron-mediated oxidative stress in neurodegenerative diseases caused by other genetic pathways like Huntington disease and Friedreich ataxia underscore the complex interaction of this trace metal and genetic variations. Therapeutical strategies derived from application of iron chelators in monogenetically caused disturbances of brain iron metabolism and new iron and oxidative stress diminishing substances in animal models of Parkinson disease are promising and warrant further investigational effort.

Multiple system atrophy: a sporadic synucleinopathy

Multiple system atrophy (MSA) is a sporadic neurodegenerative disease characterized clinically by varying degrees of Parkinsonism, cerebellar ataxia and autonomic dysfunction and pathologically by degeneration in the substantia nigra, putamen, olivary nucleus, pontine nuclei and cerebellum. In addition to selective neuronal loss, iron pigment accumulation and gliosis, myelin pathology is increasingly recognized. In affected white matter, myelin displays signs of degeneration and oligodendroglia contain argyrophilic inclusion bodies, so-called glial cytoplasmic inclusions (GCI). GCI are composed of 10-15-nm diameter coated filaments that are immunoreactive for ubiquitin and alpha-synuclein. Similar inclusions are occasionally found in neuronal cell bodies and cell processes in MSA. Given the presence of inclusion bodies composed of synuclein, it is reasonable to assume that biochemical alterations would be detected in synuclein in MSA and indeed this is the case. In MSA synuclein has biophysical properties that suggest increasing insolubility such as sedimentation in dense fractions in sucrose gradients and ready extraction into detergents and formic acid. Surprisingly, these biochemical modifications in synuclein are more widespread in the brain that the obvious pathology and suggest a fundamental molecular characteristic of the disorder. Similar neuronal, and less frequently glial, inclusions are detected in Lewy body disease, where there is also evidence for biophysical alterations in synuclein. Thus, MSA and LBD are both synucleinopathies, and they may comprise different poles of a disease spectrum that includes sporadic disorders as well as genetically determined disorders such as familial Lewy body Parkinsonism.

Clinical applications of neuroimaging with susceptibility-weighted imaging

Susceptibility-weighted imaging (SWI) consists of using both magnitude and phase images from a high-resolution, three-dimensional, fully velocity compensated gradient-echo sequence. Postprocessing is applied to the magnitude image by means of a phase mask to increase the conspicuity of the veins and other sources of susceptibility effects. This article gives a background of the SWI technique and describes its role in clinical neuroimaging. SWI is currently being tested in a number of centers worldwide as an emerging technique to improve the diagnosis of neurological trauma, brain neoplasms, and neurovascular diseases because of its ability to reveal vascular abnormalities and microbleeds.

Modifications of the iron-neuromelanin system in Parkinson's disease

Parkinson's disease is a common neurodegenerative disorder with a mainly sporadic aetiology, although a number of monogenic familiar forms are known. Most of the motor symptoms are due to selective depletion of dopaminergic, neuromelanin-containing neurones of the substantia nigra pars compacta. Neuromelanin is the dark insoluble macromolecule that confers the black (substantia nigra) or grey (locus coeruleus) colour to monoaminergic basal ganglia. In particular, nigral neurones are pigmented because of the accumulation of by-products of oxidative metabolism of the neurotransmitter dopamine. The occurrence of dopamine (and all the enzymatic machinery required for dopamine synthesis, re-uptake and disposal) and neuromelanin, and a large amount of iron ions that interact with them, makes dopaminergic nigral neurones peculiarly susceptible to oxidative stress conditions that, in turn, may become amplified by the iron-neuromelanin system itself. In this mini-review we describe biophysical evidence for iron-neuromelanin modifications that support this hypothesis. Furthermore, we discuss the formation of the covalent linkage between alpha-synuclein and neuromelanin from the early stages of the disease.

Iron in neurodegenerative disorders

Increasing evidence implicates a role of iron in the pathogenesis of numerous neurodegenerative diseases due to its capacity to enhance production of toxic reactive radicals and to induce protein aggregation. The underlying mechanism of iron accumulation in areas of the brain specific for the respective disease, however, is still unknown. Recent molecular and biochemical studies provide new insights into the consequences of impairment of brain iron metabolism. This review summarizes our understanding of the regulation of iron in the brain and defines the current knowledge on the involvement of iron metabolism in neurodegenerative diseases with genetically determined iron accumulation in the brain.

Magnetic investigations of human mesencephalic neuromelanin

Pigmentation of neurons in substantia nigra is due to neuromelanin, a pigment that stores large amounts of iron. Human mesencephalic neuromelanin has been investigated by means of magnetic susceptibility measurements as a function of temperature. Magnetic measurements provide a physico-chemical characterization of the iron cluster buried in the organic melanin matrix and support the view that iron is not simply chelated, but rather is organized in a three-dimensional network. The paramagnetism of isolated iron ions is observed, in agreement with electron paramagnetic resonance spectroscopy. Furthermore, antiferromagnetic grains with a large size distribution function are present. These grains contain N spins coupled antiferromagnetically; however, N(1/2) spins are decoupled from the grain bulk and parallelly aligned. The latter subgrains are superparamagnetic with a blocking temperature ranging between 5 K and room temperature. This behavior has not been observed in synthetic melanin, where the paramagnetic contribution is strongly enhanced. Preliminary results on pigment isolated from patients affected by Parkinson's disease, a neurodegenerative pathology involving primarily pigmented neurons in substantia nigra pars compacta, show a lower total magnetization compared to control neuromelanin. The temperature behavior of zero field cooling and field cooling magnetizations is similar for both. The significant depletion of iron content in Parkinson's disease neuromelanin could indicate a progressive Fe migration from its storage environment to the cytosol.

Iron and Parkinson's disease

Multiple studies implicate iron in the pathophysiology of Parkinson's disease (PD). In the brains of patients with PD, iron levels are elevated and the levels of iron-binding proteins are abnormal. Iron has been suspected to contribute to PD because Fe(II) is known to promote oxidative damage. Recent studies suggest that an additional mechanism by which iron might contribute to PD is by inducing aggregation of the alpha-synuclein, which is a protein that accumulates in Lewy bodies in PD.

Quantitative model for the interecho time dependence of the CPMG relaxation rate in iron-rich gray matter

A quantitative model is proposed for computing the dependence on the interecho time of the NMR relaxation rate in iron-rich gray matter obtained with a Carr-Purcell-Meiboom-Gill sequence. The model consists of representing oligodendrocytes as identical magnetic spheres arranged in a spatially random pattern, and in approximating water diffusion as isotropic and unrestricted. Predictions of the model are calculated numerically using a Monte Carlo technique and, for the weak field limit, using an analytic formula. The model is shown to provide a good fit to experimental measurements of in vitro samples of monkey brain at field levels of 1.0 T and 1.5 T. These field levels are not sufficient to fully determine the model parameters, but it is argued that this may be possible at 3.0 T. The model is potentially of value for multiple-spin-echo MRI studies of iron-related neurodegenerative disorders, such as Parkinson's disease. In particular, the model can be applied to correlate MRI data with the cellular distribution of iron in gray matter. Magn Reson Med 46:159-165, 2001.

The A53T alpha-synuclein mutation increases iron-dependent aggregation and toxicity

Parkinson's disease (PD) is the most common motor disorder affecting the elderly. PD is characterized by the formation of Lewy bodies and death of dopaminergic neurons. The mechanisms underlying PD are unknown, but the discoveries that mutations in alpha-synuclein can cause familial PD and that alpha-synuclein accumulates in Lewy bodies suggest that alpha-synuclein participates in the pathophysiology of PD. Using human BE-M17 neuroblastoma cells overexpressing wild-type, A53T, or A30P alpha-synuclein, we now show that iron and free radical generators, such as dopamine or hydrogen peroxide, stimulate the production of intracellular aggregates that contain alpha-synuclein and ubiquitin. The aggregates can be identified by immunocytochemistry, electron microscopy, or the histochemical stain thioflavine S. The amount of aggregation occurring in the cells is dependent on the amount of alpha-synuclein expressed and the type of alpha-synuclein expressed, with the amount of alpha-synuclein aggregation following a rank order of A53T > A30P > wild-type > untransfected. In addition to stimulating aggregate formation, alpha-synuclein also appears to induce toxicity. BE-M17 neuroblastoma cells overexpressing alpha-synuclein show up to a fourfold increase in vulnerability to toxicity induced by iron. The vulnerability follows the same rank order as for aggregation. These data raise the possibility that alpha-synuclein acts in concert with iron and dopamine to induce formation of Lewy body pathology in PD and cell death in PD.