Mapping of iron deposition in conjunction with assessment of nerve fiber tract integrity in amyotrophic lateral sclerosis

Basal ganglia alterations in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) has traditionally been associated with brain damage involving the primary motor cortices and corticospinal tracts. In the recent decades, most of the research studies in ALS have focused on extra-motor and subcortical brain regions. The aim of these studies was to detect additional biomarkers able to support the diagnosis and to predict disease progression. The involvement of the frontal cortices, mainly in ALS cases who develop cognitive and/or behavioral impairment, is amply recognized in the field. A potential involvement of fronto-temporal and fronto-striatal connectivity changes in the disease evolution has also been reported. On this latter regard, there is still a shortage of studies which investigated basal ganglia (BG) alterations and their role in ALS clinical manifestation and progression. The present review aims to provide an overview on the magnetic resonance imaging studies reporting structural and/or functional BG alterations in patients with ALS, to clarify the role of BG damage in the disease clinical evolution and to propose potential future developments in this field.

White Matter Tract Injury by MRI in CADASIL Patients is Associated With Iron Accumulation

BACKGROUND

Widespread white matter (WM) injury is a hallmark feature of cerebral autosomal dominant arteriopathy with subcortical infarcts and leukoencephalopathy (CADASIL). However, controversies about the mechanism of WM tract injury exist persistently. Excessive iron accumulation, frequently reported in CADASIL patients, might cause WM tract injury.

PURPOSE

To test the association between iron accumulation and WM tract injury in CADASIL patients.

STUDY TYPE

Retrospective.

POPULATION

A total of 35 CADASIL patients (age = 50.4 ± 6.4, 62.9% female) and 48 healthy controls (age = 55.7 ± 8.0, 68.8% female).

FIELD STRENGTH/SEQUENCE

Diffusion-weighted spin-echo echo-planar sequence; enhanced susceptibility-weighted angiography (ESWAN) gradient echo sequence on a 3 T scanner.

ASSESSMENT

The phase images acquired by ESWAN were used to calculate quantitative susceptibility mapping (QSM). Iron accumulation was evaluated in deep gray matters using QSM. WM tract injury was quantified by diffusion metrics based on WM major tracts skeleton. We compared iron deposition between groups and analyzed the correlation between WM tract injury and iron deposition in regions showing significant differences from healthy controls. Exploratory analysis was carried out to investigate whether WM tract injury mediated the relationship between iron deposition and cognitive impairment evaluated by Mini-Mental State Examination (MMSE).

STATISTICAL TESTS

General linear model (GLM), partial correlation, stepwise linear regression and mediation analysis were used. The threshold of statistical significance was set as p < 0.05.

RESULTS

Compared with healthy controls, CADASIL patients had significantly increased iron deposition in the caudate and putamen. Aberrant iron deposition in these two regions was significantly associated with decreased WM fractional anisotropy (FA) (caudate, r = -0.373； putamen, r = - 0.421), and increased radial diffusivity (RD) (caudate, r = 0.372; putamen, r = 0.386). Furthermore, WM tract injury mediated the relationship between iron deposition and cognitive impairment.

DATA CONCLUSION

Patients with CADASIL show increased iron deposition in the caudate and putamen that is correlated to WM tract injury, which may in turn mediate the association with cognitive impairment.

EVIDENCE LEVEL

2 TECHNICAL EFFICACY: Stage 2.

Beyond the Motor Cortex: Thalamic Iron Deposition Accounts for Disease Severity in Amyotrophic Lateral Sclerosis

Objective

Previous studies have reliably identified iron deposition in the motor cortex as potential pathogenesis of amyotrophic lateral sclerosis (ALS). Here, we intended to investigate iron deposition, gray matter (GM) atrophy, and their associations with disease severity in the motor cortex and the thalamus in patients with ALS.

Methods

A total of 34 patients with ALS (age 51.31 ± 8.24 years, 23 males) and 34 nonneurological controls (age 50.96 ± 9.35 years, 19 males) were enrolled between 2018 and 2020. The Revised ALS Functional Rating Scale (ALSFRS-R) and the Penn upper motor neuron (UMN) score were measured. MRI data included quantitative susceptibility mapping (QSM) for iron deposition and three-dimensional (3D) T1 for gray matter volume. After a between-group comparison, Pearson's correlation coefficient was used for identifying correlations of iron deposition, GM volume, and clinical measurements.

Results

The two-sample t-tests revealed increased iron deposition in the left precentral gyrus (peak voxel T = 4.78, P_SVC = 0.03) and the thalamus (peak voxel: right: T = 6.38, P_SVC < 0.001; left: T = 4.64, P_SVC = 0.02) in patients with ALS. GM volume of the precentral gyrus (T = −2.42, P = 0.02) and the bilateral thalamus (T = −4.10, P < 0.001) were reduced. Negative correlations were found between the increased QSM values and the decreased GM volume (P < 0.04, one-tailed) in patients with ALS. Iron deposition in the left precentral gyrus was positively correlated with the UMN score (R = 0.40, P = 0.02) and the GM volume was negatively correlated with the UMN score (R = −0.48, P = 0.004). Negative correlation between thalamic iron deposition and the ALSFRS-R (R = −0.36, P = 0.04) score was observed.

Discussion

Iron deposition in the thalamus, in addition to the motor cortex, is accompanied by GM atrophy and is associated with disease severity in patients with ALS, indicating that the thalamus is also a pathological region in patients with ALS.

Colocalization of Aluminum and Iron in Nuclei of Nerve Cells in Brains of Patients with Alzheimer's Disease

Increasing evidence indicates that metal-induced oxidative stress plays a pivotal role in the pathogenesis of Alzheimer's disease (AD). Recently, the presence of 8-hydroxydeoxyguanosine, a biomarker of oxidative DNA damage, was demonstrated in nuclear DNA (nDNA) in the AD brain. Iron (Fe) is a pro-oxidant metal capable of generating hydroxyl radicals that can oxidize DNA, and aluminum (Al) has been reported to facilitate Fe-mediated oxidation. In the present study, we examined the elements contained in the nuclei of nerve cells in AD brains using scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy (SEM-EDS). Our results demonstrated that Al and Fe were colocalized in the nuclei of nerve cells in the AD brain. Within the nuclei, the highest levels of both Al and Fe were measured in the nucleolus. The SEM-EDS analysis also revealed the colocalization of Al and Fe in the heterochromatin and euchromatin in neuronal nuclei in the AD brain. Notably, the levels of Al and Fe in the nucleus of nerve cells in the AD brain were markedly higher than those in age-matched control brains. We hypothesize that the colocalization of Al and Fe in the nucleus of nerve cells might induce oxidative damage to nDNA and concurrently inhibit the repair of oxidatively damaged nDNA. An imbalance caused by the increase in DNA damage and the decrease in DNA repair activities might lead to the accumulation of unrepaired damaged DNA, eventually causing neurodegeneration and the development of AD.

Imaging Biomarkers for the Diagnosis and Prognosis of Neurodegenerative Diseases. The Example of Amyotrophic Lateral Sclerosis

The term amyotrophic lateral sclerosis (ALS) comprises a heterogeneous group of fatal neurodegenerative disorders of largely unknown etiology characterized by the upper motor neurons (UMN) and/or lower motor neurons (LMN) degeneration. The development of brain imaging biomarkers is essential to advance in the diagnosis, stratification and monitoring of ALS, both in the clinical practice and clinical trials. In this review, the characteristics of an optimal imaging biomarker and common pitfalls in biomarkers evaluation will be discussed. Moreover, the development and application of the most promising brain magnetic resonance (MR) imaging biomarkers will be reviewed. Finally, the integration of both qualitative and quantitative multimodal brain MR biomarkers in a structured report will be proposed as a support tool for ALS diagnosis and stratification.

Serum ferritin is a candidate biomarker of disease aggravation in amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative disease. The mechanism that defines the loss of neurons in ALS is still not clearly understood, and there is no effective therapy to block its progression. Previous studies indicate that a disorder of iron homeostasis exists in ALS and based on this, the change of serum iron and ferritin and the association between iron metabolism and clinical features in Chinese Han patients with ALS was further investigated in the present study, in order to define its pathogenesis. Two cohorts were established: An ALS group consisting of 24 patients and a control group consisting of 38 healthy volunteers. Venous blood samples were collected for serum iron and ferritin analysis. The results indicated that the levels of serum iron were significantly decreased in patients with ALS (P<0.05), while there was no significant difference in serum ferritin between the ALS and control groups. However, the levels of serum ferritin were increased significantly in ALS patients with bulbar-onset (vs. limb-onset in females), dysphagia (vs. without dysphagia), longer disease duration (>12 months vs. ≤12 months in males) and lower ALS Functional Rating Scale-Revised score (<33 vs. ≥33; P<0.05). These results suggested that there was dysregulation of iron metabolism in Chinese Han patients with ALS and that serum ferritin may be a candidate biomarker of aggravation in these patients.

Detecting spinal pyramidal tract of amyotrophic lateral sclerosis patients with diffusion tensor tractography

The objective of this study was to determine alteration of corticospinal tract in patients with amyotrophic lateral sclerosis (ALS) using diffusion tensor tractograhy (DTT) focusing on the cervical spinal cord (C5) and transcranial magnetic stimulation (TMS). We recruited 38 ALS, 6 spinal and bulbar muscular atrophy (SBMA), 7 spastic paraplegia (SP) patients, and 8 age-matched normal controls, and then ALS were divided into two subgroups according to their clinical type: 28 ALS-limb and 10 ALS-bulbar. DTT was performed using the diffusion tensor image (DTI) track module to reconstruct two fiber tracts via C5. The fractional anisotropy (FA) values of ALS-total and ALS-limb patients were significantly reduced compared with normal controls, and SBMA patients. On the other hand, the mean diffusivity (MD) values were not significantly different among normal controls and the three disease groups. The rate of disease progression (ΔFRS-R) of ALS patients was significantly correlated with FA values and central motor conduction time (CMCT). In conclusion, the present study demonstrated a significant reduction of FA values in ALS patients, and the ΔFRS-R of ALS patients showed distinct regressions with FA values and CMCT, suggesting that this DTT analysis could be useful for detecting disease progression of ALS patients.

Effects of epigallocatechin‑3‑gallate on iron metabolism in spinal cord motor neurons

Accumulating evidence suggests that iron homeostasis is disordered in amyotrophic lateral sclerosis (ALS). In view of the promising performance of epigallocatechin‑3‑gallate (EGCG) in neuroprotection studies, the present study aimed to verify whether EGCG protects motor neurons in an ALS model, and whether it has any effects on iron metabolism using an ELISA and western blotting. The results demonstrated that EGCG decreased oxidative stress and protected motor neurons in the organotypic culture of the rat spinal cord. Furthermore, total iron levels increased significantly in the spinal cord following 3 weeks of treatment with threo‑hydroxyaspartate. In addition, the expression of influx proteins (transferrin receptor and divalent metal‑ion transporter 1) increased significantly. However, EGCG demonstrated no effect on total iron levels and the expression of influx proteins. In conclusion, EGCG leads to a decrease in oxidative stress levels, leading to motor neuron protection in the organotypic culture of a rat spinal cord; however, EGCG does not alter iron metabolism protein expression regulation.

Multimodal assessment of white matter tracts in amyotrophic lateral sclerosis

Several quantitative magnetic resonance imaging (MRI) techniques have been proposed to investigate microstructural tissue changes in amyotrophic lateral sclerosis (ALS) including diffusion tensor imaging (DTI), magnetization transfer imaging, and R2* mapping. Here, in this study, we compared these techniques with regard to their capability for detecting ALS related white matter (WM) changes in the brain and their association with clinical findings. We examined 27 ALS patients and 35 age-matched healthy controls. MRI was performed at 3T, after which we analyzed the diffusion properties, the magnetization transfer ratio (MTR), and the effective transversal relaxation rate R2* in 18 WM tracts that were obtained by a fully automated segmentation technique. ALS patients, especially with a bulbar onset, showed a bilateral increase in radial and mean diffusivity, as well as a reduction in fractional anisotropy of the corticospinal tract (CST), and diffusion changes in the parietal and temporal superior longitudinal fasciculus. A reduction of the MTR was found in both CSTs and an R2* reduction was seen only in the left CST. Tract-specific diffusion properties were not related to clinical status in a cross-sectional manner but demonstrated some association with disease progression over three subsequent months. DTI reveals more widespread WM tissue changes than MTR and R2*. These changes are not restricted to the CST, but affect also other WM tracts (especially in patients with bulbar onset), and are associated with the short term course of the disease.

Iron quantification with susceptibility

Iron is an essential trace element involved in a variety of biological mechanisms in the human body. Disturbances of iron homeostasis have been observed in several inflammatory and degenerative diseases, which have raised strong interest in non-invasive iron mapping techniques. Numerous MRI techniques have been proposed so far, mostly based on the field changes induced by the magnetic properties of iron. Each of these approaches has a specific sensitivity for iron and its microstructural environment. Quantitative susceptibility mapping is the latest development and provides a direct measure of bulk susceptibility. However, field changes induced by iron are not always directly related to the concentration of iron, but rather reflect the structure of iron compounds and its cellular distribution. This review provides an overview of the most relevant iron compounds in the human body, their magnetic properties and their cellular distribution. In addition, MRI methods based on direct or indirect susceptibility changes are presented and discussed with respect to technical aspects and clinical applicability. Copyright © 2016 John Wiley & Sons, Ltd.

Lithium suppression of tau induces brain iron accumulation and neurodegeneration

Lithium is a first-line therapy for bipolar affective disorder. However, various adverse effects, including a Parkinson-like hand tremor, often limit its use. The understanding of the neurobiological basis of these side effects is still very limited. Nigral iron elevation is also a feature of Parkinsonian degeneration that may be related to soluble tau reduction. We found that magnetic resonance imaging T₂ relaxation time changes in subjects commenced on lithium therapy were consistent with iron elevation. In mice, lithium treatment lowers brain tau levels and increases nigral and cortical iron elevation that is closely associated with neurodegeneration, cognitive loss and parkinsonian features. In neuronal cultures lithium attenuates iron efflux by lowering tau protein that traffics amyloid precursor protein to facilitate iron efflux. Thus, tau- and amyloid protein precursor-knockout mice were protected against lithium-induced iron elevation and neurotoxicity. These findings challenge the appropriateness of lithium as a potential treatment for disorders where brain iron is elevated (for example, Alzheimer's disease), and may explain lithium-associated motor symptoms in susceptible patients.

The value of magnetic resonance imaging as a biomarker for amyotrophic lateral sclerosis: a systematic review

BACKGROUND

Amyotrophic lateral sclerosis (ALS) is a fatal, rapidly progressive neurodegenerative disease that mainly affects the motor system. A number of potentially neuroprotective and neurorestorative disease-modifying drugs are currently in clinical development. At present, the evaluation of a drug's clinical efficacy in ALS is based on the ALS Functional Rating Scale Revised, motor tests and survival. However, these endpoints are general, variable and late-stage measures of the ALS disease process and thus require the long-term assessment of large cohorts. Hence, there is a need for more sensitive radiological biomarkers. Various sequences for magnetic resonance imaging (MRI) of the brain and spinal cord have may have value as surrogate biomarkers for use in future clinical trials. Here, we review the MRI findings in ALS, their clinical correlations, and their limitations and potential role as biomarkers.

METHODS

The PubMed database was screened to identify studies using MRI in ALS. We included general MRI studies with a control group and an ALS group and longitudinal studies even if a control group was lacking.

RESULTS

A total of 116 studies were analysed with MRI data and clinical correlations. The most disease-sensitive MRI patterns are in motor regions but the brain is more broadly affected.

CONCLUSION

Despite the existing MRI biomarkers, there is a need for large cohorts with long term MRI and clinical follow-up. MRI assessment could be improved by standardized MRI protocols with multicentre studies.

Iron-sulfur cluster damage by the superoxide radical in neural tissues of the SOD1(G93A) ALS rat model

Extensive clinical investigations, in hand with biochemical and biophysical research, have associated brain iron accumulation with the pathogenesis of the amyotrophic lateral sclerosis (ALS) disease. The origin of iron is still not identified, but it is proposed that it forms redox active complexes that can participate in the Fenton reaction generating the toxic hydroxyl radical. In this paper, the state of iron in the neural tissues isolated from SOD1(G93A) transgenic rats was investigated using low temperature EPR spectroscopy and is compared with that of nontransgenic (NTg) littermates. The results showed that iron in neural tissues is present as high- and low-spin, heme and non-heme iron. It appears that the SOD1(G93A) rat neural tissues were most likely exposed in vivo to higher amounts of reactive oxygen species when compared to the corresponding NTg tissues, as they showed increased oxidized [3Fe-4S](1+) cluster content relative to [4Fe-4S](1+). Also, the activity of cytochrome c oxidase (CcO) was found to be reduced in these tissues, which may be associated with the observed uncoupling of heme a3 Fe and CuB in the O2-reduction site of the enzyme. Furthermore, the SOD1(G93A) rat spinal cords and brainstems contained more manganese, presumably from MnSOD, than those of NTg rats. The addition of potassium superoxide to all neural tissues ex vivo, led to the [4Fe-4S]→[3Fe-4S] cluster conversion and concurrent release of Fe. These results suggest that the superoxide anion may be the cause of the observed oxidative damage to SOD1(G93A) rat neural tissues and that the iron-sulfur clusters may be the source of poorly liganded redox active iron implicated in ALS pathogenesis. Low temperature EPR spectroscopy appears to be a valuable tool in assessing the role of metals in neurodegenerative diseases.

A Potential Biomarker in Amyotrophic Lateral Sclerosis: Can Assessment of Brain Iron Deposition with SWI and Corticospinal Tract Degeneration with DTI Help?

BACKGROUND AND PURPOSE

Iron-mediated oxidative stress plays a pivotal role in the pathogenesis of amyotrophic lateral sclerosis. This study aimed to assess iron deposition qualitatively and quantitatively by using SWI and microstructural changes in the corticospinal tract by using DTI in patients with amyotrophic lateral sclerosis.

MATERIALS AND METHODS

Seventeen patients with amyotrophic lateral sclerosis and 15 age- and sex-matched controls underwent brain MR imaging with SWI and DTI. SWI was analyzed for both signal-intensity scoring and quantitative estimation of iron deposition in the anterior and posterior banks of the motor and sensory cortices and deep gray nuclei. The diffusion measurements along the corticospinal tract at the level of pons and medulla were obtained by ROI analysis.

RESULTS

Patients with amyotrophic lateral sclerosis showed reduced signal-intensity grades in the posterior bank of the motor cortex bilaterally. Quantitative analysis confirmed significantly higher iron content in the posterior bank of the motor cortex in patients with amyotrophic lateral sclerosis. In contrast, no significant differences were noted for the anterior bank of the motor cortex, anterior and posterior banks of the sensory cortex, and deep nuclei. Receiver operating characteristic comparison showed a cutoff of 35μg Fe/g of tissue with an area under the curve of 0.78 (P = .008) for the posterior bank of the motor cortex in discriminating patients with amyotrophic lateral sclerosis from controls. Fractional anisotropy was lower in the pyramidal tracts of patients with amyotrophic lateral sclerosis at the pons and medulla on either side, along with higher directionally averaged mean diffusivity values. The combination of SWI and DTI revealed an area under the curve of 0.784 for differentiating patients with amyotrophic lateral sclerosis from controls.

CONCLUSIONS

Measurements of motor cortex iron deposition and diffusion tensor parameters of the corticospinal tract may be useful biomarkers for the diagnosis of clinically suspected amyotrophic lateral sclerosis.

Iron and Neurodegeneration: Is Ferritinophagy the Link?

Mounting evidence indicates that the lysosome-autophagy pathway plays a critical role in iron release from ferritin, the main iron storage cellular protein, hence in the distribution of iron to the cells. The recent identification of nuclear receptor co-activator 4 as the receptor for ferritin delivery to selective autophagy sheds further light on the understanding of the mechanisms underlying this pathway. The emerging view is that iron release from ferritin through the lysosomes is a general mechanism in normal and tumour cells of different tissue origins, but it has not yet been investigated in brain cells. Defects in the lysosome-autophagy pathway are often involved in the pathogenesis of neurodegenerative disorders, and brain iron homeostasis disruption is a hallmark of many of these diseases. However, in most cases, it has not been established whether iron dysregulation is directly involved in the pathogenesis of the diseases or if it is a secondary effect derived from other pathogenic mechanisms. The recent evidence of the crucial involvement of autophagy in cellular iron handling offers new perspectives about the role of iron in neurodegeneration, suggesting that autophagy dysregulation could cause iron dyshomeostasis. In this review, we recapitulate our current knowledge on the routes through which iron is released from ferritin, focusing on the most recent advances. We summarise the current evidence concerning lysosome-autophagy pathway dysfunctions and those of iron metabolism and discuss their potential interconnections in several neurodegenerative disorders, such as Alzheimer's, Parkinson's and Huntington's diseases; amyotrophic lateral sclerosis; and frontotemporal lobar dementia.

Quantitative assessment of brain iron by R2* relaxometry in patients with cervical dystonia

BACKGROUND

The pathophysiology of cervical dystonia is poorly understood. Increased brain iron deposition has been described in different movement disorders. Our aim was to investigate brain iron content in patients with cervical dystonia, using R2* relaxation rate, a validated MRI marker of brain iron level.

METHODS

Twelve female patients with primary focal cervical dystonia (mean age: 45.4 ± 8.0 years) and 12 age-matched healthy female subjects (mean age: 45.0 ± 8.0 years) underwent 3T MRI to obtain regional R2* relaxation rates of the thalamus, caudate nucleus, putamen, and globus pallidus (GP). Regions of interest were delineated automatically on T1-weighted MRIs.

RESULTS

R2* values in the putamen were positively correlated with age. Patients with cervical dystonia showed elevated R2* values in the GP.

CONCLUSIONS

This pilot study provides the first quantitative support for increased brain iron deposition in cervical dystonia. Further studies are needed to explore the implications of this finding.

Susceptibility-weighted imaging provides insight into white matter damage in amyotrophic lateral sclerosis

Background

Amyotrophic lateral sclerosis (ALS) is a fatal, progressive neurodegenerative disorder, characterised by widespread white matter damage. There is growing evidence that disturbances in iron metabolism contribute to white matter alterations.

Materials & Methods

We analysed the data of susceptibility-weighted imaging (SWI) of white matter in a cohort of 27 patients with ALS and 30 healthy age-matched controls.

Results

Signal alterations were found on SWI in the corpus callosum; along the corticospinal tract (subcortical motor cortex, posterior limb of the internal capsule and brainstem levels) and in the subgyral regions of frontal, parietal, temporal, occipital and limbic lobes. Alterations of white matter in the corpus callosum correlated with disease severity as assessed by the revised ALS functional rating scale.

Conclusion

SWI is capable of indicating iron and myelin disturbances in white matter of ALS patients. The SWI patterns observed in this study suggest that widespread alterations due to iron disturbances occur in patients with ALS and correlate with disease severity.

The potential for transition metal-mediated neurodegeneration in amyotrophic lateral sclerosis

Modulations of the potentially toxic transition metals iron (Fe) and copper (Cu) are implicated in the neurodegenerative process in a variety of human disease states including amyotrophic lateral sclerosis (ALS). However, the precise role played by these metals is still very much unclear, despite considerable clinical and experimental data suggestive of a role for these elements in the neurodegenerative process. The discovery of mutations in the antioxidant enzyme Cu/Zn superoxide dismutase 1 (SOD-1) in ALS patients established the first known cause of ALS. Recent data suggest that various mutations in SOD-1 affect metal-binding of Cu and Zn, in turn promoting toxic protein aggregation. Copper homeostasis is also disturbed in ALS, and may be relevant to ALS pathogenesis. Another set of interesting observations in ALS patients involves the key nutrient Fe. In ALS patients, Fe loading can be inferred by studies showing increased expression of serum ferritin, an Fe-storage protein, with high serum ferritin levels correlating to poor prognosis. Magnetic resonance imaging of ALS patients shows a characteristic T₂ shortening that is attributed to the presence of Fe in the motor cortex. In mutant SOD-1 mouse models, increased Fe is also detected in the spinal cord and treatment with Fe-chelating drugs lowers spinal cord Fe, preserves motor neurons, and extends lifespan. Inflammation may play a key causative role in Fe accumulation, but this is not yet conclusive. Excess transition metals may enhance induction of endoplasmic reticulum (ER) stress, a system that is already under strain in ALS. Taken together, the evidence suggests a role for transition metals in ALS progression and the potential use of metal-chelating drugs as a component of future ALS therapy.

Increased iron level in motor cortex of amyotrophic lateral sclerosis patients: an in vivo MR study

Amyotrophic lateral sclerosis (ALS) is one of the most common neurodegenerative disorders, but no definite mechanism has been defined on the loss of motor neurons in ALS and currently no therapy can block its progression. Many lines of evidence indicate that there is a disorder of iron homeostasis in ALS, and thus we sought to test the iron level in ALS patients by susceptibility weighted imaging (SWI). Sixteen ALS patients and 16 healthy persons underwent brain scans using SWI with a 3T Siemens MR scanner. The red nucleus, substantia nigra, globus pallidus, putamen, the head of caudate nucleus, and motor cortex were measured in the filtered phase images and analysed for their SWI phase values as relative marker for iron content. We found that phase shift values were significantly higher in the motor cortex of ALS patients by SWI, indicating increased iron level in this area. In contrast, we found that there were no differences of phase shift values between ALS patients and healthy controls in the other nuclei including the red nucleus, substantia nigra, globus pallidus, putamen and the head of the caudate nucleus. Furthermore, we found that there were no relationships between SWI signal and some clinical features of ALS. In conclusion, these results demonstrate that iron level increases in the motor cortex of ALS and that SWI is a reliable method to test iron in the brain.

An improved method for retrospective motion correction in quantitative T2* mapping

A new method for motion correction of T2*-weighted data and resulting quantitative T2* maps is presented. For this method, additional data sets with a reduced number of phase encoding steps covering the k-space centre are acquired. Motion correction is based on a 3-step procedure: (1) calculation of improved input data sets with reduced artefact levels from the original data, (2) creation of a target data set free of movement artefacts on the basis of the improved input data sets, and (3) fitting of original data to the target data set, yielding an optimum combination of acquired k-space data which suppresses lines affected by movement. The method was tested on healthy subjects performing pre-trained movement. Motion correction was successful unless the same k-space line was affected by movement in all data sets acquired on a specific subject. The method was applied to patients suffering from subarachnoid haemorrhage (group 1) or tumours (group 2) with accompanying edema in the brain. Motion correction improved the interpretability of T2*-weighted patient data and resulting quantitative T2* maps considerably by allowing a clear delineation between ventricle and edema and a clear localisation of haemorrhage (group 1) or a clear delineation of tumour accompanying edema (group 2) which was not possible in data affected by movement.

A delicate balance: Iron metabolism and diseases of the brain

Iron is the most abundant transition metal within the brain, and is vital for a number of cellular processes including neurotransmitter synthesis, myelination of neurons, and mitochondrial function. Redox cycling between ferrous and ferric iron is utilized in biology for various electron transfer reactions essential to life, yet this same chemistry mediates deleterious reactions with oxygen that induce oxidative stress. Consequently, there is a precise and tightly controlled mechanism to regulate iron in the brain. When iron is dysregulated, both conditions of iron overload and iron deficiencies are harmful to the brain. This review focuses on how iron metabolism is maintained in the brain, and how an alteration to iron and iron metabolism adversely affects neurological function.

Brain iron MRI: a biomarker for amyotrophic lateral sclerosis

PURPOSE

To evaluate the usefulness of MRI detection of hypointensity areas (iron deposits) in the brain using a dedicated MRI technique in patients with ALS in establishing this sign as a potential surrogate biomarker that correlates with the severity of disease.

MATERIALS AND METHODS

Forty-six ALS patients and 26 age-matched controls were examined by MRI. The ALS Functional Rating Scale (ALSFRS) score was determined before the first MRI examination. The sub-set of 25 ALS patients was re-examined around 6 months after the first MRI examination. The MRI examination consisted of routine T1W, T2W, and FLAIR sequences with the addition of a thin slice heavily T2* weighted sequence to accentuate magnetic susceptibility artifacts.

RESULTS

T2*W sequence is superior to any other MRI sequence in detecting hypointensities in the brain of ALS patients. Hypointensities were found only in the precentral gyruses gray matter (PGGM) and were detected in 42 patients. The extent of hypointensities was measured and scored (0-3) and correlated with ALSFRS (r = -0.545). Twenty-five patients were re-examined 6 months later, and the majority of them showed the shift toward higher MRI scores. No control subjects had hypointensities in PGGM.

CONCLUSION

The detection of hypointensities in PGGM appears to be a very promising surrogate MRI biomarker for ALS due to its simplicity, high sensitivity and specificity, suitability for longitudinal studies, and relationship with the pathogenesis of the disease.

Dysregulation of iron protein expression in the G93A model of amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disorder characterized by selective loss of motor neurons which leads to progressive paralysis and death by respiratory failure. Although the cause of sporadic ALS is still unknown, oxidative stress is suggested to play a major role in the pathogenesis of this disease and of the rare familial form, which often exhibits mutations of the superoxide dismutase 1 (SOD1) gene. Since enhanced iron levels are discussed to participate in oxidative stress and neuronal death, we analyzed the expression levels of Fe-related mRNAs in a cell culture ALS model with the G93A mutation of SOD1. We observed an increased total iron content in G93A-SOD1 SH-SY5Y neuroblastoma cells compared to wild-type (WT)-SOD1 cells. mRNA expression for transferrin receptor 1 (TfR1) and divalent metal transporter 1 was increased in G93A-SOD1 cells, which was in accordance with higher iron uptake. Experiments with the iron chelator deferoxamine revealed a normal reaction of WT and mutant cells to cytoplasmic iron depletion, i.e. TfR1 upregulation, suggesting a basically conserved function of the iron-responsive element/iron regulatory protein (IRE/IRP) pathway, designed to adapt gene expression to iron levels. Expression levels of mitoferrin 1 and 2, frataxin, and iron-sulfur cluster scaffold protein were also significantly increased in G93A-SOD1 cells, suggesting higher mitochondrial iron import and utilization in biosynthetic pathways within the mitochondria. Moreover, expression of these transcripts was further enhanced, if G93A-SOD1 cells were differentiated by retinoic acid (RA). Since RA treatment increased cytoplasmic reactive oxygen species (ROS) levels in these cells, an IRE/IRP independent, ROS-mediated mechanism may account for dysregulation of iron-related genes.

Amyotrophic lateral sclerosis: new insights into underlying molecular mechanisms and opportunities for therapeutic intervention

Recent years have witnessed a renewed interest in the pathogenic mechanisms of amyotrophic lateral sclerosis (ALS), a late-onset progressive degeneration of motor neurons. The discovery of new genes associated with the familial form of the disease, along with a deeper insight into pathways already described for this disease, has led scientists to reconsider previous postulates. While protein misfolding, mitochondrial dysfunction, oxidative damage, defective axonal transport, and excitotoxicity have not been dismissed, they need to be re-examined as contributors to the onset or progression of ALS in the light of the current knowledge that the mutations of proteins involved in RNA processing, apparently unrelated to the previous "old partners," are causative of the same phenotype. Thus, newly envisaged models and tools may offer unforeseen clues on the etiology of this disease and hopefully provide the key to treatment.

Neuroimaging in amyotrophic lateral sclerosis

The catastrophic system failure in amyotrophic lateral sclerosis is characterized by progressive neurodegeneration within the corticospinal tracts, brainstem nuclei and spinal cord anterior horns, with an extra-motor pathology that has overlap with frontotemporal dementia. The development of computed tomography and, even more so, MRI has brought insights into neurological disease, previously only available through post-mortem study. Although largely research-based, radionuclide imaging has continued to provide mechanistic insights into neurodegenerative disorders. The evolution of MRI to use advanced sequences highly sensitive to cortical and white matter structure, parenchymal metabolites and blood flow, many of which are now applicable to the spinal cord as well as the brain, make it a uniquely valuable tool for the study of a multisystem disorder such as amyotrophic lateral sclerosis. This comprehensive review considers the full range of neuroimaging techniques applied to amyotrophic lateral sclerosis over the last 25 years, the biomarkers they have revealed and future developments.

Involvement of globus pallidus and midbrain nuclei in pantothenate kinase-associated neurodegeneration: measurement of T2 and T2* time

PURPOSE

To quantify involvement of globus pallidus and two midbrain nuclei (substantia nigra and red nucleus) in Pantothenate Kinase-Associated Neurodegeneration (PKAN).

MATERIAL AND METHODS

We performed T2 and T2* weighted imaging with calculation of the corresponding relaxation times on a subset of 5 patients from a larger group of 20 patients with PKAN from the southwest part of the Dominican Republic. Examinations were carried out on a 3T scanner and included a multi-echo spin-echo as well as a multi-echo gradient echo sequence. Results were compared to a control group of 19 volunteers.

RESULTS

T2 and T2* weighted sequences showed abnormal signal reduction in the globus pallidus of all patients. On T2* weighted imaging, abnormal signal in the substantia nigra could reliably be detected in 75% of cases, but differentiation from normal was less reliable in T2 weighted scans. Correspondingly, relaxation times differed from normal with very high significance (p < 0.0001) in the globus pallidus, but with with less significance in the substantia nigra (p ≤ 0.03). The red nucleus was not affected.

CONCLUSIONS

Signal reduction in the globus pallidus, which probably is due to abnormal accumulation of iron, is severe in PKAN and can be differentiated from normal with high reliability. The substantia nigra is affected to a lesser degree, and the red nucleus is not involved. The reason for this selective susceptibility of normally iron-rich brain structures for pathological accumulation of iron remains speculative. Our quantitative results might be helpful to assess the value of an iron chelation approach to therapy.

Missense PANK2 mutation without "eye of the tiger" sign: MR findings in a large group of patients with pantothenate kinase-associated neurodegeneration (PKAN)

PURPOSE

To present some unusual MR findings in a group of patients from the south-west of the Dominican Republic suffering from Pantothenate Kinase Associated Neurodegeneration (PKAN).

MATERIALS AND METHODS

Twenty patients and one preclinical case homozygous for the PANK2 mutation, 13 heterozygous gene carriers and 14 healthy volunteers were scanned prospectively using a 3 Tesla system.

RESULTS

All patients showed the typical signal reduction within the globus pallidus and the substantia nigra. A surprising finding was the absence of the bright spot ("tiger's eye") in the medial part of the pallidum in 6 patients, but not in the preclinical case. Both fractional anisotropy (FA) and mean diffusivity (MD) were increased with high significance in the globus pallidus, whereas a reduction of FA in the anterior parts of the internal capsule was accompanied by an elevation of MD.

CONCLUSION

Our findings support the hypothesis that the absence of the "tiger's eye" in PKAN might be secondary, probably caused by an increased accumulation of iron. This could artificially increase FA and MD values and change fiber tracking results. Except for the fronto-basal tracts, white matter was preserved well. This encouraging finding might support efforts to develop further therapeutic strategies in this devastating dystonia.

New considerations in the design of clinical trials for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis is a devastating neurodegenerative disease caused by loss of motor neurons. Its pathophysiology remains unknown, but progress has been made in understanding its genetic and biochemical basis. Clinical trialists are working to translate basic science successes into human trials with more efficiency, in the hope of finding successful treatments. In the future, new preclinical models, including patient-derived stem cells may augment transgenic animal models as preclinical tools. Biomarker discovery projects aim to identify markers of disease onset and progression for use in clinical trials. New trial designs are reducing study time, improving efficiency and helping to keep pace with the increasing rate of basic and translational discoveries. Ongoing trials with novel designs are paving the way for amyotrophic lateral sclerosis clinical research.

Quantitative T*2-mapping based on multi-slice multiple gradient echo flash imaging: retrospective correction for subject motion effects

Numerous clinical and research applications for quantitative mapping of the effective transverse relaxation time T*(2) have been described. Subject motion can severely deteriorate the quality and accuracy of results. A correction method for T*(2) maps acquired with multi-slice multiple gradient echo FLASH imaging is presented, based on acquisition repetition with reduced spatial resolution (and consequently reduced acquisition time) and weighted averaging of both data sets, choosing weighting factors individually for each k-space line to reduce the influence of motion. In detail, the procedure is based on the fact that motion artifacts reduce the correlation between acquired and exponentially fitted data. A target data set is constructed in image space, choosing the data yielding best correlation from the two acquired data sets. The k-space representation of the target is subsequently approximated as linear combination of original raw data, yielding the required weighting factors. As this method only requires a single acquisition repetition with reduced spatial resolution, it can be employed on any clinical system offering a suitable sequence with export of modulus and phase images. Experimental results show that the method works well for sparse motion, but fails for strong motion affecting the same k-space lines in both acquisitions.

Advances in the application of MRI to amyotrophic lateral sclerosis

IMPORTANCE OF THE FIELD: With the emergence of therapeutic candidates for the incurable and rapidly progressive neurodegenerative condition of amyotrophic lateral sclerosis (ALS), it will be essential to develop easily obtainable biomarkers for diagnosis, as well as monitoring, in a disease where clinical examination remains the predominant diagnostic tool. Magnetic resonance imaging (MRI) has greatly developed over the past thirty years since its initial introduction to neuroscience. With multi-modal applications, MRI is now offering exciting opportunities to develop practical biomarkers in ALS. AREAS COVERED IN THIS REVIEW: The historical application of MRI to the field of ALS, its state-of-the-art and future aspirations will be reviewed. Specifically, the significance and limitations of structural MRI to detect gross morphological tissue changes in relation to clinical presentation will be discussed. The more recent application of diffusion tensor imaging (DTI), magnetic resonance spectroscopy (MRS), functional and resting-state MRI (fMRI & R-fMRI) will be contrasted in relation to these more conventional MRI assessments. Finally, future aspirations will be sketched out in providing a more disease mechanism-based molecular MRI. WHAT THE READER WILL GAIN: This review will equip the reader with an overview of the application of MRI to ALS and illustrate its potential to develop biomarkers. This discussion is exemplified by key studies, demonstrating the strengths and limitations of each modality. The reader will gain an expert opinion on both the current and future developments of MR imaging in ALS. TAKE HOME MESSAGE: MR imaging generates potential diagnostic, prognostic and therapeutic monitoring biomarkers of ALS. The emerging fusion of structural, functional and potentially molecular imaging will improve our understanding of wider cerebral connectivity and holds the promise of biomarkers sensitive to the earliest changes.