Iron, Myelin, and the Brain: Neuroimaging Meets Neurobiology

Role of iron in brain development, aging, and neurodegenerative diseases

It is now understood that iron crosses the blood-brain barrier via a complex metabolic regulatory network and participates in diverse critical biological processes within the central nervous system, including oxygen transport, energy metabolism, and the synthesis and catabolism of myelin and neurotransmitters. During brain development, iron is distributed throughout the brain, playing a pivotal role in key processes such as neuronal development, myelination, and neurotransmitter synthesis. In physiological aging, iron can selectively accumulate in specific brain regions, impacting cognitive function and leading to intracellular redox imbalance, mitochondrial dysfunction, and lipid peroxidation, thereby accelerating aging and associated pathologies. Furthermore, brain iron accumulation may be a primary contributor to neurodegenerative diseases such as Alzheimer's and Parkinson's diseases. Comprehending the role of iron in brain development, aging, and neurodegenerative diseases, utilizing iron-sensitive Magnetic Resonance Imaging (MRI) technology for timely detection or prediction of abnormal neurological states, and implementing appropriate interventions may be instrumental in preserving normal central nervous system function.

A Subtracted-Added-Divided Inversion Recovery (dSIR) Approach to Visualise the Effects of Microstructure on T1 Contrast in Human White Matter

Recent evidence has demonstrated that several white matter (WM) microstructural features, such as axon diameter, fibre configurations and fibre orientation in respect to the magnetic field influence T1 relaxation. The effects from microstructural features on T1 are small in size, thus, visualising the effects of WM microstructure remains challenging in standard T1 weighted MRI in vivo. Here, we have studied an algebraic approach involving subtraction, addition and division of closely spaced inversion time images in WM imaging, the so-called dSIR approach. Images collected with short TI (300 ms at 3T and 600 ms at 7T) and long TI (600 ms at 3T and 1000 ms at 7T) with MP2RAGE MRI were combined using the dSIR processing. dSIR signal intensities were compared with absolute T1 images. We found that dSIR was linearly related with T1 relaxation time over approximately 200 ms both at 3T and 7T. The slope of the dSIR versus T1 plot was 1.6 times greater at 7T than at 3T indicative of higher dSIR contrast at 7T. dSIR contrast revealed WM tracts that are oriented with high angle (fibre-to-field angle > 75°), in addition, dSIR signal showed angular patterns that closely resembled those of T1 at both fields. The dSIR contrast due to intratissue T1 difference of order of ~50 ms generated by microstructural features, including axon fibre orientation as well as by the presence of large and giant axons in somato-motor subsection of corpus callosum were visualised. It is concluded that dSIR signal mimics T1 and that the dSIR contrast is higher at 7T than at 3T; thus, the approach will help to visualise the effects of microstructure on T1 to evaluate WM integrity.

Alterations in magnetic susceptibility correlate with higher cerebral blood flow in the right amygdala of patients with major depressive disorder

BACKGROUND

The amygdala plays a crucial role in emotion processing and is a key target for understanding the mechanisms underlying major depressive disorder (MDD). This study aimed to investigate the magnetic susceptibility of the amygdala in MDD and examine its association with structural and cerebral blood flow (CBF) changes.

METHODS

A total of 158 individuals were included in the study, comprising 86 patients with MDD and 72 healthy controls. Depression severity was assessed using Hamilton Depression Rating Scale. Quantitative susceptibility mapping (QSM), T1-weighted, and arterial spin labeling scans were conducted to measure amygdala magnetic susceptibility, volume, and CBF, respectively. Group differences were compared, and associations between susceptibility, volume, and CBF were examined.

RESULTS

The median susceptibility of the amygdala was significantly higher in MDD patients than in controls (all p < 0.01). In the MDD group, increased QSM value in the right amygdala was associated with higher CBF (r = 0.28, p = 0.01), whereas no significant correlation was found between QSM value and volume (p = 0.76). Increased QSM value in the right amygdala was associated with worse depressed mood (r = 0.30, p < 0.01).

LIMITATION

Retrospective cross-sectional study conducted at a single center.

CONCLUSION

The magnetic susceptibility of the amygdala was higher in MDD patients with than in controls. QSM changes in the right amygdala correlated with increased CBF and worse depressed mood, indicating both microstructural and functional alterations. Our results encourage further use of the QSM technique in the elucidation of MDD pathophysiology.

In Vivo Characterization of Magnetic Inclusions in the Subcortex From Nonexponential Transverse Relaxation Decay

According to theoretical studies, MRI signal decay due to transverse relaxation in brain tissue with magnetic inclusions (e.g., blood vessels and iron-rich cells) is expected to follow a transition from Gaussian behaviour at short echo times to exponential behaviour at longer times. The decay parameters carry information about the inclusions (e.g., size and volume fraction) and provide unique insights into brain microstructure. However, gradient-echo decays typically only capture the long-time exponential behaviour. We provide experimental evidence of nonexponential transverse relaxation decay in human subcortical grey matter from in vivo MRI data acquired at 3 T, allowing the subsequent characterization of the magnetic inclusions. Gradient-echo data were collected with short interecho spacings, minimal echo time (1.25 ms) and novel acquisition strategies to mitigate motion and cardiac-induced effects. The data were fitted using exponential and nonexponential models that describe the impact of magnetic inclusions on the MRI signal. Nonexponential models provided superior fits. The strongest deviations from exponential were detected in the substantia nigra and globus pallidus. Numerical simulations of the signal decay from histological maps of iron concentration in the substantia nigra replicated the experimental data, highlighting that non-haem iron can be at the source of the nonexponential decay. To investigate the potential of nonexponential decays to characterize brain microstructure, we estimated the properties of the underlying inclusions using two analytical models. Under the static dephasing regime, the magnetic susceptibility and volume fractions of the inclusions ranged between 1.8-4 and 0.02-0.04 ppm, respectively. Alternatively, under the diffusion narrowing regime, the typical inclusion size was ~2.4 μm. Both simulations and experimental data suggest an intermediate regime with a non-negligible effect of water diffusion. Nonexponential transverse relaxation decay allows to characterize the spatial distribution of magnetic material within subcortical tissue with increased specificity, with potential applications for Parkinson's disease and other pathologies.

Iron Homeostasis and Metabolism During Pregnancy: Exploring Innovative Drug Delivery Approaches for Treating Iron Deficiency Anemia in Pregnant Women

Pregnant women and small children are more prone to anemia. Even among the most affluent and educated portions of society, an estimated 50% of pregnant women, adolescent girls, and youngsters are anemic. This review recapitulates previous findings exploring advancements in anemia management in pregnant women. The published articles were searched using Google Scholar, Web of Science, Scopus, and Clinical Trials. Primary causes of anemia are an inadequate supply of dietary iron, deficiency of folate due to the lack of vegetable consumption, and thus a lack of vitamin B12, and a lack of dietary iron bioavailability from phytate and fiber-rich diets. When hemoglobin falls below 5 g/dL, the maternal mortality rate multiplies 8-10 times. Early detection and treatment of anemia during pregnancy may minimize maternal mortality, substantially decrease childhood and adolescent nutritional deficiency, and improve adult height. Maternal anemia decreases intrauterine growth, which increases the risk of premature delivery and low birth weight in babies. Intrauterine growth retardation coupled with a low birth weight leads to an inadequate growth trajectory throughout childhood, adolescence, and adulthood. Nano-delivery systems stand out as a promising avenue, utilizing nanotechnology to enhance the absorption of iron. These systems offer targeted delivery of iron supplements, overcoming challenges associated with conventional formulations. The exploration of nanotechnology in iron deficiency anemia treatment marks a significant stride toward developing advanced and tailored solutions for improving iron supplementation.

Brain iron load and neuroaxonal vulnerability in adult attention-deficit hyperactivity disorder

AIM

Adult attention deficit hyperactivity disorder (ADHD) may be associated with an increased risk of dementia in old age. Here, we investigated the liability for neurodegenerative brain disease in adult ADHD, possibly reflected by increased brain iron content and associated neuroaxonal vulnerability.

METHODS

Thirty-two adults with ADHD (35 ± 10 years) and 29 age- and sex-matched controls (32 ± 12 years) underwent magnetic resonance imaging (MRI), standardized psychometric testing and assessment of lifestyle factors. Quantitative susceptibility mapping (QSM) was used to assess magnetic abnormalities indicating local alterations of iron deposition in the brain. By calculating QSM-maps, local iron deposition was tested for statistically significant differences between ADHD and healthy controls. Plasma neurofilament light chain (NfL) levels were measured as an indicator of neuroaxonal integrity by using a fourth-generation ELLA immunoassay.

RESULTS

Brain iron content differed in persons with ADHD, with strongest effects observable in the right precentral cortex (healthy controls: 0.0033 ± 0.0017ppm; ADHD: 0.0048 ± 0.0016ppm; t(59) = 3.56, P < 0.001). Moreover, right precentral cortex iron in persons with ADHD was associated with increased blood NfL levels (F(1.57) = 13.2, P = 0.001, r2 = 0.19).

CONCLUSION

Our results indicate altered regional iron content in the brains of adults with ADHD. The observed association between increased precentral magnetic susceptibility and increased NfL suggests a connection between local excess of brain iron and neuroaxonal damage in ADHD. Given the limited sample size of the current study and the naturalistic medication plan, further longitudinal studies are needed to establish whether altered brain iron distribution in adults with ADHD may be associated with an increased risk of dementia at old age.

Abnormalities of iron homeostasis and the dopaminergic system in Tourette syndrome revealed by 7T MRI and PET

While the implication of a dysfunctional dopaminergic system in Tourette syndrome (TS) is well established, the underlying pathophysiological mechanisms remain unclear. Apart from neurotransmitters, disturbed iron homeostasis and iron regulatory mechanisms are also suspected. Iron is a trace element of fundamental biological importance and is involved in the synthesis and metabolism of dopamine and its receptors and transporters. The goal of the current pre-registered, multi-modal, cross-sectional study was to investigate the relationship between potential iron homeostasis imbalances and dopaminergic system disturbances in patients with TS. Susceptibility-sensitive MRI at 7 Tesla was used to obtain surrogate measures for local brain iron in 25 patients with TS (age 30 ± 9 years, 6 female) and 40 matched control subjects. Additionally, dopamine D1 receptor availability was investigated with [11C]SCH23390 PET in a subgroup of 20 patients and 20 controls. Significantly reduced sub-cortical magnetic susceptibility, indicating reduced iron levels, was observed in TS patients in the caudate, pallidum, sub-thalamic nucleus, thalamus, red nucleus and substantia nigra. These reductions were accompanied by significant reductions of the [11C]SCH23390 binding potential indicating reduced availability of D1 receptors in the dorsal striatum. The D1 receptor abnormality correlated with tic severity. These results point to alterations of intra-synaptic dopamine release and reduced striatal D1 receptor binding, supporting the notion of disruption in multiple functional elements of the dopaminergic system. Such dopaminergic abnormalities appear to be associated with disturbances in iron homeostasis.

Emerging Ferroptosis Involvement in Amyotrophic Lateral Sclerosis Pathogenesis: Neuroprotective Activity of Polyphenols

Neurodegenerative diseases are a group of diseases that share common features, such as the generation of misfolded protein deposits and increased oxidative stress. Among them, amyotrophic lateral sclerosis (ALS), whose pathogenesis is still not entirely clear, is a complex neurodegenerative disease linked both to gene mutations affecting different proteins, such as superoxide dismutase 1, Tar DNA binding protein 43, Chromosome 9 open frame 72, and Fused in Sarcoma, and to altered iron homeostasis, mitochondrial dysfunction, oxidative stress, and impaired glutamate metabolism. The purpose of this review is to highlight the molecular targets common to ALS and ferroptosis. Indeed, many pathways implicated in the disease are hallmarks of ferroptosis, a recently discovered type of iron-dependent programmed cell death characterized by increased reactive oxygen species (ROS) and lipid peroxidation. Iron accumulation results in mitochondrial dysfunction and increased levels of ROS, lipid peroxidation, and ferroptosis triggers; in addition, the inhibition of the Xc- system results in reduced cystine levels and glutamate accumulation, leading to excitotoxicity and the inhibition of GPx4 synthesis. These results highlight the potential involvement of ferroptosis in ALS, providing new molecular and biochemical targets that could be exploited in the treatment of the disease using polyphenols.

Predicting Mesoscopic Larmor Frequency Shifts in White Matter With Diffusion MRI-A Monte Carlo Study in Axonal Phantoms

Magnetic susceptibility MRI offers potential insights into the chemical composition and microstructural organization of tissue. However, estimating magnetic susceptibility in white matter is challenging due to anisotropic subvoxel Larmor frequency shifts caused by axonal microstructure relative to the B0 field orientation. Recent biophysical models have analytically described how axonal microstructure influences the Larmor frequency shifts, relating these shifts to a mesoscopically averaged magnetic field that depends on the axons' fiber orientation distribution function (fODF), typically estimated using diffusion MRI. This study is aimed at validating the use of MRI to estimate mesoscopic magnetic fields and determining whether diffusion MRI can faithfully estimate the orientation dependence of the Larmor frequency shift in realistic axonal microstructure. To achieve this, we developed a framework for performing Monte Carlo simulations of MRI signals in mesoscopically sized white matter axon substrates segmented with electron microscopy. Our simulations demonstrated that with careful experimental design, it is feasible to estimate mesoscopic magnetic fields. Additionally, the fODF estimated by the standard model of diffusion in white matter could predict the orientation dependence of the mesoscopic Larmor frequency shift. We also found that incorporating the intra-axonal axial kurtosis into the standard model could explain a significant amount of signal variance, thereby improving the estimation of the Larmor frequency shift. This factor should not be neglected when fitting the standard model.

Crosstalk between ferroptosis and innate immune in diabetic kidney disease: mechanisms and therapeutic implications

Diabetic kidney disease (DKD) is a prevalent complication of diabetes mellitus (DM), and its incidence is increasing alongside the number of diabetes cases. Effective treatment and long-term management of DKD present significant challenges; thus, a deeper understanding of its pathogenesis is essential to address this issue. Chronic inflammation and abnormal cell death in the kidney closely associate with DKD development. Recently, there has been considerable attention focused on immune cell infiltration into renal tissues and its inflammatory response's role in disease progression. Concurrently, ferroptosis-a novel form of cell death-has emerged as a critical factor in DKD pathogenesis, leading to increased glomerular filtration permeability, proteinuria, tubular injury, interstitial fibrosis, and other pathological processes. The cardiorenal benefits of SGLT2 inhibitors (SGLT2-i) in DKD patients have been demonstrated through numerous large clinical trials. Moreover, further exploratory experiments indicate these drugs may ameliorate serum and urinary markers of inflammation, such as TNF-α, and inhibit ferroptosis in DKD models. Consequently, investigating the interplay between ferroptosis and innate immune and inflammatory responses in DKD is essential for guiding future drug development. This review presents an overview of ferroptosis within the context of DKD, beginning with its core mechanisms and delving into its potential roles in DKD progression. We will also analyze how aberrant innate immune cells, molecules, and signaling pathways contribute to disease progression. Finally, we discuss the interactions between ferroptosis and immune responses, as well as targeted therapeutic agents, based on current evidence. By analyzing the interplay between ferroptosis and innate immunity alongside its inflammatory responses in DKD, we aim to provide insights for clinical management and drug development in this area.

An unconstrained four pool model analysis of proton relaxation and magnetization transfer in ex vivo white matter

Understanding proton relaxation in the brain's white matter remains an active field of magnetic resonance imaging research. Models of varying complexity have been proposed to link measurements to tissue composition/microstructure, in particular myelination. Although the presence of multiple aqueous and nonaqueous proton pools is well established experimentally, so-called "quantitative MRI" is usually based on simpler models due to the large number of model parameters. In this work, a comprehensive set of parameters characterizing a four-pool model is obtained. A piece of fixed porcine spinal-cord WM was investigated at 3 T and temperatures between 21 and 35 °C. Measurements included a wide range of preparations of the spin system in combination with long echo trains to achieve sensitivity to all model parameters. The results allow the extraction of all intrinsic relaxation and exchange rates as well as assigning them to specific dynamic processes involving tissue water. A critical assessment indicates that simpler models often lack specificity to myelin.

Brain Iron Alteration in Pediatric Tourette Syndrome: A Quantitative Susceptibility Mapping Study

BACKGROUND

The cortico-striato-thalamo-cortical circuits play a crucial role in the pathogenesis of Tourette syndrome (TS). While iron deficiency has been reported in adult TS, the iron content in pediatric TS remains poorly understood. This study aims to quantitatively assess whole-brain iron deposition in pediatric TS compared to typically developing (TD) children using quantitative susceptibility mapping (QSM).

METHODS

In this prospective study, we recruited 50 children with a clinical diagnosis of TS and 50 age- and gender-matched TD controls. Whole-brain images were acquired using 3D T1 and multi-echo gradient-recalled echo sequences. QSM maps were generated using the STISuite toolbox. After normalizing the QSM maps to Montreal Neurological Institute space, voxel-based analysis was applied to compare between-group differences in iron content. Additionally, we evaluated the relationship between iron content and tic severity in TS children using the Pearson's correlation test.

RESULTS

Compared to TD children, those with TS exhibited iron deficiency in the right anterior cingulum (pFDR < 0.001). Conversely, increased QSM values were observed in the bilateral putamen of TS children (pFDR < 0.001). Notably, QSM values in the left putamen showed a significant negative correlation with tic severity (p = 0.044).

CONCLUSIONS

Our findings suggest that disturbed brain iron homeostasis in specific regions is associated with pediatric TS. These results reinforce the importance of the cortico-striato-thalamo-cortical circuits in TS pathogenesis and highlight the potential role of iron dysregulation. Furthermore, our study demonstrates that QSM could serve as a valuable auxiliary biomarker for diagnosing and potentially monitoring pediatric TS.

Oligodendrocyte Slc48a1 (Hrg1) encodes a functional heme transporter required for myelin integrity

Oligodendrocytes (OLs) of the central nervous system require iron for proteolipid biosynthesis during the myelination process. Although most heme is found complexed to hemoglobin in red blood cells, surprisingly, we found that Slc48a1, encoding the heme transporter Hrg1, is expressed at higher levels in OLs than any other cell type in rodent and humans. We confirmed in situ that Hrg1 is expressed in OLs but not their precursors (OPCs) and found that Hrg1 proteins in CNS white matter co-localized within myelin sheaths. In older Hrg1 null mutant mice we observed reduced expression of myelin associated glycoprotein (Mag) and ultrastructural myelin defects reminiscent of Mag-null animals, suggesting myelin adhesion deficiency. Further, we confirmed reduced myelin iron levels in Hrg1 null animals in vivo, and show that OLs in vitro can directly import both the fluorescent heme analogue ZnMP and heme itself, which rescued iron deficiency induced inhibition of OL differentiation in a heme-oxidase-dependent manner. Together these findings indicate OL Hrg1 encodes a functional heme transporter required for myelin integrity.

Mechanism and regulation of iron absorption throughout the life cycle

BACKGROUND

Iron plays a crucial role through various life stages of human. Iron homeostasis is primarily regulated by iron absorption which is mediated via divalent metal-ion transporter 1 (DMT1), and iron export protein ferroportin (FPN), as there is no active pathway for iron excretion from the body. Recent studies have shown that the magnitude of iron absorption changes through various life stages to meet changing iron requirements.

AIM OF REVIEW

This review aims to provide an overview of recent researches on the regulation of iron absorption throughout mammalian life cycle, with the potential to reveal novel molecules and pathways at special stage of life. Such insights may pave the way for new treatments for disorders associated with aberrant iron homeostasis in the future.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review first summarize the mechanism and regulation of iron absorption throughout various life stages, highlighting that regulatory mechanisms have developed to precisely align iron absorption to iron requirements. In adults, iron absorption is enhanced when body is deficient of iron, conversely, iron absorption is reduced when iron demand decreases via systemic regulator Hepcidin and cellular regulation. In the elderly, age-related inflammation, hormonal changes, and chronic diseases may affect the production of Hepcidin, affecting iron absorption. In infants, intestinal iron absorption and its regulatory mechanism are different from that in adults and there might be an alternative pathway independent of DMT1 and FPN due to high iron absorption. Unique to the fetus, iron is absorbed from maternal stores for its own use through the placenta and is regulated by maternal iron status. This review also proposes directions for further studies, offering promising avenues for developing new treatments for disorders associated with aberrant iron homeostasis.

Different Grey Matter Microstructural Patterns in Cognitively Healthy Versus Typical Ageing Healthy Versus Typical Brain Ageing

Ageing is a complex phenomenon affecting a wide range of coexisting biological processes. The homogeneity of the studied population is an essential parameter for valid interpretations of outcomes. The presented study capitalises on the MRI data available in the Human Connectome Project-Aging (HCP-A) and, within individuals over 55 years of age who passed the HCP-A section criteria, compares a subgroup of 37 apparently neurocognitively healthy individuals selected based on stringent criteria with 37 age and sex-matched individuals still representative of typical ageing but who did not pass the stringent definition of neurocognitively healthy. Specifically, structural scans, diffusion weighted imaging and T1w/T2w ratio were utilised. Furthermore, data of 26 HCP-A participants older than 90 years as notional 'super-agers' were analysed. The relationship of age and several microstructural MRI metrics (T1w/T2w ratio, mean diffusivity, intracellular volume fraction and free water volume fraction) differed significantly between typical and healthy ageing cohort in areas highly relevant for ageing such as hippocampus, prefrontal and temporal cortex and cerebellum. However, the trajectories of the healthy ageing population did not show substantially better overlap with the findings in people older than 90 than those of the typical population. Therefore, caution must be exercised in the choice of adequate study group characteristics relevant for respective ageing-related hypotheses. Contrary to typical ageing group, the healthy ageing cohort may show generally stable levels of several MRI metrics of interest.

T1 relaxation and axon fibre configuration in human white matter

Understanding the effects of white matter (WM) axon fibre microstructure on T1 relaxation is important for neuroimaging. Here, we have studied the interrelationship between T1 and axon fibre configurations at 3T and 7T. T1 and S0 (=signal intensity at zero TI) were computed from MP2RAGE images acquired with six inversion recovery times. Multishell diffusion MRI images were analysed for fractional anisotropy (FA); MD; V1; the volume fractions for the first (f1), second (f2) and third (f3) fibre configuration; and fibre density cross-section images for the first (fdc1), second (fdc2) and third (fdc3) fibres. T1 values were plotted as a function of FA, f1, f2, f3, fdc1, fdc2 and fdc3 to examine interrelationships between the longitudinal relaxation and the diffusion MRI microstructural measures. T1 values decreased with increasing FA, f1 and f2 in a nonlinear fashion. At low FA values (from 0.2 to 0.4), a steep shortening of T1 was followed by a shallow shortening by 6%-10% at both fields. The steep shortening was associated with decreasing S0 and MD. T1 also decreased with increasing fdc1 values in a nonlinear fashion. Instead, only a small T1 change as a function of either f3 or fdc3 was observed. In WM areas selected by fdc1 only masks, T1 was shorter than in those with fdc2/fdc3. In WM areas with high single fibre populations, as delineated by f1/fdc1 masks, T1 was shorter than in tissue with high complex fibre configurations, as segmented by f2/fdc2 or f3/fdc3 masks. T1 differences between these WM areas are attributable to combined effects by T1 anisotropy and lowered FA. The current data show strong interrelationships between T1, axon fibre configuration and orientation in healthy WM. It is concluded that diffusion MRI microstructural measures are essential in the effort to interpret quantitative T1 images in terms of tissue state in health and disease.

Associations between quantitative susceptibility mapping with male obstructive sleep apnea clinical and imaging markers

PURPOSE

To quantitatively measure and compare whole-brain iron deposition between OSA patients and a healthy control group, we initially utilized QSM and evaluated its correlation with PSG results and cognitive function.

MATERIALS AND METHODS

A total of 28 OSA patients and 22 healthy control subjects matched in age, education level, and BMI were enrolled in our study. Each participant underwent scanning with 3D T1 and multi-echo GRE sequences. Additionally, PSG results were collected from OSA patients, and they underwent simple cognitive assessments. Finally, we analyzed the relationship between iron content in different brain regions, PSG results, and cognitive ability.

RESULTS

In OSA patients, iron content increased in the left temporal-pole-sup and right putamen, while it decreased in the left fusiform gyrus, left middle temporal gyrus, right inferior occipital gyrus, and right superior temporal gyrus. The correlation analysis between brain iron content and PSG results/cognitive scales is as follows: left fusiform gyrus and MMSE (r = -0.416, p = 0.028); right superior temporal gyrus and MMSE (r = 0.422, p = 0.025); left middle temporal gyrus and average oxygen saturation (r = -0.418, p = 0.027); left temporal-pole-sup and REM stage (rs = 0.466, p = 0.012); the right putamen and N1 stage (rs = 0.393. p = 0.039). Moreover, both MoCA (r = 0.598, p = 0.001) and MMSE (r = 0.456, p = 0.015) show a positive correlation with average oxygen saturation.

CONCLUSION

This study is the first to use QSM technology to show abnormal brain iron levels in OSA. Correlations between brain iron content, PSG, and cognition in OSA may reveal neuropathological mechanisms, aiding OSA diagnosis.

A human brain atlas of χ-separation for normative iron and myelin distributions

Iron and myelin are primary susceptibility sources in the human brain. These substances are essential for a healthy brain, and their abnormalities are often related to various neurological disorders. Recently, an advanced susceptibility mapping technique, which is referred to as χ-separation (pronounced as "chi"-separation), has been proposed, successfully disentangling paramagnetic iron from diamagnetic myelin. This method provided a new opportunity for generating high-resolution iron and myelin maps of the brain. Utilizing this technique, this study constructs a normative χ-separation atlas from 106 healthy human brains. The resulting atlas provides detailed anatomical structures associated with the distributions of iron and myelin, clearly delineating subcortical nuclei, thalamic nuclei, and white matter fiber bundles. Additionally, susceptibility values in a number of regions of interest are reported along with age-dependent changes. This atlas may have direct applications such as localization of subcortical structures for deep brain stimulation or high-intensity focused ultrasound and also serve as a valuable resource for future research.

The ageing central nervous system in multiple sclerosis: the imaging perspective

The interaction between ageing and multiple sclerosis is complex and carries significant implications for patient care. Managing multiple sclerosis effectively requires an understanding of how ageing and multiple sclerosis impact brain structure and function. Ageing inherently induces brain changes, including reduced plasticity, diminished grey matter volume, and ischaemic lesion accumulation. When combined with multiple sclerosis pathology, these age-related alterations may worsen clinical disability. Ageing may also influence the response of multiple sclerosis patients to therapies and/or their side effects, highlighting the importance of adjusted treatment considerations. MRI is highly sensitive to age- and multiple sclerosis-related processes. Accordingly, MRI can provide insights into the relationship between ageing and multiple sclerosis, enabling a better understanding of their pathophysiological interplay and informing treatment selection. This review summarizes current knowledge on the immunopathological and MRI aspects of ageing in the CNS in the context of multiple sclerosis. Starting from immunosenescence, ageing-related pathological mechanisms and specific features like enlarged Virchow-Robin spaces, this review then explores clinical aspects, including late-onset multiple sclerosis, the influence of age on diagnostic criteria, and comorbidity effects on imaging features. The role of MRI in understanding neurodegeneration, iron dynamics and myelin changes influenced by ageing and how MRI can contribute to defining treatment effects in ageing multiple sclerosis patients, are also discussed.

MR Susceptibility Separation for Quantifying Lesion Paramagnetic and Diamagnetic Evolution in Relapsing-Remitting Multiple Sclerosis

BACKGROUND

Multiple sclerosis (MS) lesion evolution may involve changes in diamagnetic myelin and paramagnetic iron. Conventional quantitative susceptibility mapping (QSM) can provide net susceptibility distribution, but not the discrete paramagnetic and diamagnetic components.

PURPOSE

To apply susceptibility separation (χ separation) to follow lesion evolution in MS with comparison to R2*/R2 '/QSM.

STUDY TYPE

Longitudinal, prospective.

SUBJECTS

Twenty relapsing-remitting MS subjects (mean age: 42.5 ± 9.4 years, 13 females; mean years of symptoms: 4.3 ± 1.4 years).

FIELD STRENGTH/SEQUENCE

Three-dimensional multiple echo gradient echo (QSM and R2* mapping), two-dimensional dual echo fast spin echo (R2 mapping), T2-weighted fluid attenuated inversion recovery, and T1-weighted magnetization prepared gradient echo sequences at 3 T.

ASSESSMENT

Data were analyzed from two scans separated by a mean interval of 14.4 ± 2.0 months. White matter lesions on fluid-attenuated inversion recovery were defined by an automatic pipeline, then manually refined (by ZZ/AHW, 3/25 years' experience in MRI), and verified by a radiologist (MN, 25 years' experience in MS). Susceptibility separation yielded the paramagnetic and diamagnetic susceptibility content of each voxel. Lesions were classified into four groups based on the variation of QSM/R2* or separated into positive/negative components from χ separation.

STATISTICAL TESTS

Two-sample paired t tests for assessment of longitudinal differences. Spearman correlation coefficients to assess associations between χ separation and R2*/R2 '/QSM. Significant level: P < 0.005.

RESULTS

A total of 183 lesions were quantified. Categorizing lesions into groups based on χ separation demonstrated significant annual changes in QSM//R2*/R2 '. When lesions were grouped based on changes in QSM and R2*, both changing in unison yielded a significant dominant paramagnetic variation and both opposing yielded a dominant diamagnetic variation. Significant Spearman correlation coefficients were found between susceptibility-sensitive MRI indices and χ separation.

DATA CONCLUSION

Susceptibility separation changes in MS lesions may distinguish and quantify paramagnetic and diamagnetic evolution, potentially providing additional insight compared to R2* and QSM alone.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY: Stage 2.

Bridging the gap: Prenatal nutrition, myelination, and schizophrenia etiopathogenesis

Schizophrenia (SZ) is a complex mental illness characterized by disturbances in thinking, emotionality, and behavior, significantly impacting the quality of life for individuals affected and those around them. The etiology of SZ involves intricate interactions between genetic and environmental factors, although the precise mechanisms remain incompletely understood. Genetic predisposition, neurotransmitter dysregulation (particularly involving dopamine and serotonin), and structural brain abnormalities, including impaired prefrontal cortex function, have been implicated in SZ development. However, increasing evidence reveals the role of environmental factors, such as nutrition, during critical periods like pregnancy and lactation. Epidemiological studies suggest that early malnutrition significantly increases the risk of SZ symptoms manifesting in late adolescence, a crucial period coinciding with peak myelination and brain maturation. Prenatal undernutrition may disrupt myelin formation, rendering individuals more susceptible to SZ pathology. This review explores the potential relationship between prenatal undernutrition, myelin alterations, and susceptibility to SZ. By delineating the etiopathogenesis, examining genetic and environmental factors associated with SZ, and reviewing the relationship between SZ and myelination disorders, alongside the impact of malnutrition on myelination, we aim to examine how malnutrition might be linked to SZ by altering myelination processes, which contribute to increasing the understanding of SZ etiology and help identify targets for intervention and management.

Quantifying Remyelination Using χ-Separation in White Matter and Cortical Multiple Sclerosis Lesions

BACKGROUND AND OBJECTIVES

Myelin and iron play essential roles in remyelination processes of multiple sclerosis (MS) lesions. χ-separation, a novel biophysical model applied to multiecho T2*-data and T2-data, estimates the contribution of myelin and iron to the obtained susceptibility signal. We used this method to investigate myelin and iron levels in lesion and nonlesion brain areas in patients with MS and healthy individuals.

METHODS

This prospective MS cohort study included patients with MS fulfilling the McDonald Criteria 2017 and healthy individuals, aged 18 years or older, with no other neurologic comorbidities. Participants underwent MRI at baseline and after 2 years, including multiecho GRE-(T2*) and FAST-(T2) sequences. Using χ-separation, we generated myelin-sensitive and iron-sensitive susceptibility maps. White matter lesions (WMLs), cortical lesions (CLs), surrounding normal-appearing white matter (NAWM), and normal-appearing gray matter were segmented on fluid-attenuated inversion recovery and magnetization-prepared 2 rapid gradient echo images, respectively. Cross-sectional group comparisons used Wilcoxon rank-sum tests, longitudinal analyses applied Wilcoxon signed-rank tests. Associations with clinical outcomes (disease phenotype, age, sex, disease duration, disability measured by Expanded Disability Status Scale [EDSS], neurofilament light chain levels, and T2-lesion number and volume) were assessed using linear regression models.

RESULTS

Of 168 patients with MS (median [interquartile range (IQR)] age 47.0 [21.7] years; 101 women; 6,898 WMLs, 775 CLs) and 103 healthy individuals (age 33.0 [10.5] years, 57 women), 108 and 62 were followed for a median of 2 years, respectively (IQR 0.1; 5,030 WMLs, 485 CLs). At baseline, WMLs had lower myelin (median 0.025 [IQR 0.015] parts per million [ppm]) and iron (0.017 [0.015] ppm) than the corresponding NAWM (myelin 0.030 [0.012]; iron 0.019 [0.011] ppm; both p < 0.001). After 2 years, both myelin (0.027 [0.014] ppm) and iron had increased (0.018 [0.015] ppm; both p < 0.001). Younger age (p < 0.001, b = -5.111 × 10-5), lower disability (p = 0.04, b = -2.352 × 10-5), and relapsing-remitting phenotype (RRMS, 0.003 [0.01] vs primary progressive 0.002 [IQR 0.01], p < 0.001; vs secondary progressive 0.0004 [IQR 0.01], p < 0.001) at baseline were associated with remyelination. Increment of myelin correlated with clinical improvement measured by EDSS (p = 0.015, b = -6.686 × 10-4).

DISCUSSION

χ-separation, a novel mathematical model applied to multiecho T2*-images and T2-images shows that young RRMS patients with low disability exhibit higher remyelination capacity, which correlated with clinical disability over a 2-year follow-up.

Pathological Involvement of Protein Phase Separation and Aggregation in Neurodegenerative Diseases

Neurodegenerative diseases are the leading cause of human disability and immensely reduce patients' life span and quality. The diseases are characterized by the functional loss of neuronal cells and share several common pathogenic mechanisms involving the malfunction, structural distortion, or aggregation of multiple key regulatory proteins. Cellular phase separation is the formation of biomolecular condensates that regulate numerous biological processes, including neuronal development and synaptic signaling transduction. Aberrant phase separation may cause protein aggregation that is a general phenomenon in the neuronal cells of patients suffering neurodegenerative diseases. In this review, we summarize the pathological causes of common neurodegenerative diseases, including Alzheimer's disease, Parkinson's disease, and Huntington's disease, among others. We discuss the regulation of key amyloidogenic proteins with an emphasis of their aberrant phase separation and aggregation. We also introduce the approaches as potential therapeutic strategies to ameliorate neurodegenerative diseases through intervening protein aggregation. Overall, this review consolidates the research findings of phase separation and aggregation caused by misfolded proteins in a context of neurodegenerative diseases.

Glial ferritin maintains neural stem cells via transporting iron required for self-renewal in Drosophila

Stem cell niche is critical for regulating the behavior of stem cells. Drosophila neural stem cells (Neuroblasts, NBs) are encased by glial niche cells closely, but it still remains unclear whether glial niche cells can regulate the self-renewal and differentiation of NBs. Here, we show that ferritin produced by glia, cooperates with Zip13 to transport iron into NBs for the energy production, which is essential to the self-renewal and proliferation of NBs. The knockdown of glial ferritin encoding genes causes energy shortage in NBs via downregulating aconitase activity and NAD+ level, which leads to the low proliferation and premature differentiation of NBs mediated by Prospero entering nuclei. More importantly, ferritin is a potential target for tumor suppression. In addition, the level of glial ferritin production is affected by the status of NBs, establishing a bicellular iron homeostasis. In this study, we demonstrate that glial cells are indispensable to maintain the self-renewal of NBs, unveiling a novel role of the NB glial niche during brain development.

Stimulating myelin restoration with BDNF: a promising therapeutic approach for Alzheimer's disease

Alzheimer's Disease (AD) is a chronic neurodegenerative disorder constituting the most common form of dementia (60%-70% of cases). Although AD presents majorly a neurodegenerative pathology, recent clinical evidence highlights myelin impairment as a key factor in disease pathogenesis. The lack of preventive or restorative treatment is emphasizing the need to develop novel therapeutic approaches targeting to the causes of the disease. Recent studies in animals and patients have highlighted the loss of myelination of the neuronal axons as an extremely aggravating factor in AD, in addition to the formation of amyloid plaques and neurofibrillary tangles that are to date the main pathological hallmarks of the disease. Myelin breakdown represents an early stage event in AD. However, it is still unclear whether myelin loss is attributed only to exogenous factors like inflammatory processes of the tissue or to impaired oligodendrogenesis as well. Neurotrophic factors are well established protective molecules under many pathological conditions of the neural tissue, contributing also to proper myelination. Due to their inability to be used as drugs, many research efforts are focused on substituting neurotrophic activity with small molecules. Our research team has recently developed novel micromolecular synthetic neurotrophin mimetics (MNTs), selectively acting on neurotrophin receptors, and thus offering a unique opportunity for innovative therapies against neurodegenerative diseases. These small sized, lipophilic molecules address the underlying biological effect of these diseases (neuroprotective action), but also they exert significant neurogenic actions inducing neuronal replacement of the disease areas. One of the significant neurotrophin molecules in the Central Nervous System is Brain-Derived-Neurotrophin-Factor (BDNF). BDNF is a neurotrophin that not only supports neuroprotection and adult neurogenesis, but also mediates pro-myelinating effects in the CNS. BDNF binds with high-affinity on the TrkB neurotrophin receptor and enhances myelination by increasing the density of oligodendrocyte progenitor cells (OPCs) and playing an important role in CNS myelination. Conclusively, in the present review, we discuss the myelin pathophysiology in Alzheimer's Diseases, as well as the role of neurotrophins, and specifically BDNF, in myelin maintenance and restoration, revealing its valuable therapeutic potential against AD.

Harnessing myelin water fraction as an imaging biomarker of human cerebral aging, neurodegenerative diseases, and risk factors influencing myelination: A review

Myelin water fraction (MWF) imaging has emerged as a promising magnetic resonance imaging (MRI) biomarker for investigating brain function and composition. This comprehensive review synthesizes the current state of knowledge on MWF as a biomarker of human cerebral aging, neurodegenerative diseases, and risk factors influencing myelination. The databases used include Web of Science, Scopus, Science Direct, and PubMed. We begin with a brief discussion of the theoretical foundations of MWF imaging, including its basis in MR physics and the mathematical modeling underlying its calculation, with an overview of the most adopted MRI methods of MWF imaging. Next, we delve into the clinical and research applications that have been explored to date, highlighting its advantages and limitations. Finally, we explore the potential of MWF to serve as a predictive biomarker for neurological disorders and identify future research directions for optimizing MWF imaging protocols and interpreting MWF in various contexts. By harnessing the power of MWF imaging, we may gain new insights into brain health and disease across the human lifespan, ultimately informing novel diagnostic and therapeutic strategies.

Assessing Brain Iron and Its Relationship to Cognition and Comorbidity in Children With Attention-Deficit/Hyperactivity Disorder With Quantitative Susceptibility Mapping

BACKGROUND

Quantitative susceptibility mapping is a neuroimaging technique that detects local changes in magnetic susceptibility induced by brain iron. Brain iron and the dopaminergic system are linked because iron is an important cofactor for dopamine synthesis. Attention-deficit/hyperactivity disorder (ADHD) is associated with dysregulation of dopaminergic transmission. Therefore, we applied quantitative susceptibility mapping on subcortical structures to study potential alterations in brain iron and its impact on cognition and mental health in children with ADHD.

METHODS

Quantitative susceptibility mapping data (3T) of 111 participants (nADHD = 58, mean [SD] age = 13.2 [0.63] years; nControl = 53, mean [SD] age = 13.2 [0.51] years) were analyzed. Subcortical regional brain iron values were extracted. Analysis of variance was used to examine group differences for each region of interest. For dimensional approaches, Pearson correlation analysis was performed across the cohort to examine the association of brain iron with symptoms, mental health, and cognition.

RESULTS

No significant differences were found in iron susceptibility between children with ADHD and control children, between children with persistent ADHD and those with remitted ADHD, or between medicated and medication-naïve children. An unexpected finding was that children with an internalizing disorder had significantly higher iron susceptibility, but the result did not survive multiple comparison correction. Higher brain iron was associated with sustained attention, but not inhibition, IQ, or working memory.

CONCLUSIONS

This is the first study to address brain iron susceptibility and its association with comorbidities and cognition in ADHD. Alterations in brain iron may not fully account for a diagnosis of ADHD but may be an indicator of internalizing problems in children. Alterations in brain iron content in children were linked to detrimental sustained attention and may represent developmental variation in cognition.

Iron Deficiency and Sleep/Wake Behaviors: A Scoping Review of Clinical Practice Guidelines-How to Overcome the Current Conundrum?

Current evidence suggests that iron deficiency (ID) plays a key role in the pathogenesis of conditions presenting with restlessness such as attention deficit hyperactivity disorder (ADHD) and restless legs syndrome (RLS). In clinical practice, ID and iron supplementation are not routinely considered in the diagnostic work-up and/or as a treatment option in such conditions. Therefore, we conducted a scoping literature review of ID guidelines. Of the 58 guidelines included, only 9 included RLS, and 3 included ADHD. Ferritin was the most frequently cited biomarker, though cutoff values varied between guidelines and depending on additional factors such as age, sex, and comorbidities. Recommendations surrounding measurable iron biomarkers and cutoff values varied between guidelines; moreover, despite capturing the role of inflammation as a concept, most guidelines often did not include recommendations for how to assess this. This lack of harmonization on the interpretation of iron and inflammation biomarkers raises questions about the applicability of current guidelines in clinical practice. Further, the majority of ID guidelines in this review did not include the ID-associated disorders, ADHD and RLS. As ID can be associated with altered movement patterns, a novel consensus is needed for investigating and interpreting iron status in the context of different clinical phenotypes.

Quantitative susceptibility mapping of multiple system atrophy and Parkinson's disease correlates with neurotransmitter reference maps

BACKGROUND

Multiple system atrophy (MSA) and Parkinson's disease (PD) are neurodegenerative disorders characterized by α-synuclein pathology, disrupted iron homeostasis and impaired neurochemical transmission. Considering the critical role of iron in neurotransmitter synthesis and transport, our study aims to identify distinct patterns of whole-brain iron accumulation in MSA and PD, and to elucidate the corresponding neurochemical substrates.

METHODS

A total of 122 PD patients, 58 MSA patients and 78 age-, sex-matched health controls underwent multi-echo gradient echo sequences and neurological evaluations. We conducted voxel-wise and regional analyses using quantitative susceptibility mapping to explore MSA or PD-specific alterations in cortical and subcortical iron concentrations. Spatial correlation approaches were employed to examine the topographical alignment of cortical iron accumulation patterns with normative atlases of neurotransmitter receptor and transporter densities. Furthermore, we assessed the associations between the colocalization strength of neurochemical systems and disease severity.

RESULTS

MSA patients exhibited increased susceptibility in the striatal, midbrain, cerebellar nuclei, as well as the frontal, temporal, occipital lobes, and anterior cingulate gyrus. In contrast, PD patients displayed elevated iron levels in the left inferior occipital gyrus, precentral gyrus, and substantia nigra. The excessive iron accumulation in MSA or PD correlated with the spatial distribution of cholinergic, noradrenaline, glutamate, serotonin, cannabinoids, and opioid neurotransmitters, and the degree of this alignment was related to motor deficits.

CONCLUSIONS

Our findings provide evidence of the interaction between iron accumulation and non-dopamine neurotransmitters in the pathogenesis of MSA and PD, which inspires research on potential targets for pharmacotherapy.

The myelin water imaging transcriptome: myelin water fraction regionally varies with oligodendrocyte-specific gene expression

Identifying sensitive and specific measures that can quantify myelin are instrumental in characterizing microstructural changes in neurological conditions. Neuroimaging transcriptomics is emerging as a valuable technique in this regard, offering insights into the molecular basis of promising candidates for myelin quantification, such as myelin water fraction (MWF). We aimed to demonstrate the utility of neuroimaging transcriptomics by validating MWF as a myelin measure. We utilized data from a normative MWF brain atlas, comprised of 50 healthy subjects (mean age = 25 years, range = 17-42 years) scanned at 3 Tesla. Magnetic resonance imaging data included myelin water imaging to extract MWF and T1 anatomical scans for image registration and segmentation. We investigated the inter-regional distributions of gene expression data from the Allen Human Brain Atlas in conjunction with inter-regional MWF distribution patterns. Pearson correlations were used to identify genes with expression profiles mirroring MWF. The Single Cell Type Atlas from the Human Protein Atlas was leveraged to classify genes into gene sets with high cell type specificity, and a control gene set with low cell type specificity. Then, we compared the Pearson correlation coefficients for each gene set to determine if cell type-specific gene expression signatures correlate with MWF. Pearson correlation coefficients between MWF and gene expression for oligodendrocytes and adipocytes were significantly higher than for the control gene set, whereas correlations between MWF and inhibitory/excitatory neurons were significantly lower. Our approach in integrating transcriptomics with neuroimaging measures supports an emerging technique for understanding and validating MRI-derived markers such as MWF.

Associations between Serum Iron Indices and Self-Assessed Multiple Intelligence Scores among Adolescents in Riyadh, Saudi Arabia

Micronutrient deficiencies, including iron deficiency, are linked to different cognitive impairments and sensory functions. However, whether circulating iron levels affect self-assessed multiple intelligence (MI) scores in adolescents remains uninvestigated. This study aimed to investigate associations between serum iron levels and self-assessed MI scores in adolescents in Riyadh, Saudi Arabia. Recruiting 434 Saudi adolescents (174 boys and 260 girls, aged 12-17), we administered the McKenzie questionnaire to assess MI across nine categories. Anthropometrics and fasting blood samples were collected to measure circulating iron and transferrin levels. Total iron-binding capacity (TIBC) and transferrin saturation (TSAT) levels were calculated. Notably, girls exhibited significantly higher MI scores in the interactive domain than boys (age and BMI-adjusted OR = 1.36, 95% confidence interval = 1.07-1.73, p = 0.01). No significant correlations were observed between serum iron and MI. However, normal TSAT levels (TSAT > 20%) corresponded with higher age and BMI-adjusted odds of MI scores in the musical (OR = 1.59, 95%CI = 1.1-2.2, p = 0.006), linguistic (1.57, 1.1-2.3, p = 0.016), kinesthetic (1.48, 1.1-2.1, p = 0.024), spatial (1.45, 1.1-2.1, p = 0.03), and existential (1.56, 1.1-2.1, p = 0.01) categories compared to ones with lower TSAT levels (TSAT ≤ 20%), only in boys. In conclusion, serum iron levels may not directly influence MI domains in adolescents in Riyadh, Saudi Arabia; however, lower TSAT levels, indicative of iron-deficiency anemia, may influence MI, only in boys, indicating a possible relationship between iron metabolism and cognitive functions.

Cerebrospinal Fluid-In Gradient of Cortical and Deep Gray Matter Damage in Multiple Sclerosis

BACKGROUND AND OBJECTIVES

A CSF-in gradient in cortical and thalamic gray matter (GM) damage has been found in multiple sclerosis (MS). We concomitantly explored the patterns of cortical, thalamic, and caudate microstructural abnormalities at progressive distances from CSF using a multiparametric MRI approach.

METHODS

For this cross-sectional study, from 3T 3D T1-weighted scans, we sampled cortical layers at 25%-50%-75% depths from pial surface and thalamic and caudate bands at 2-3-4 voxels from the ventricular-GM interface. Using linear mixed models, we tested between-group comparisons of magnetization transfer ratio (MTR) and R2* layer-specific z-scores, CSF-in across-layer z-score changes, and their correlations with clinical (disease duration and disability) and structural (focal lesions, brain, and choroid plexus volume) MRI measures.

RESULTS

We enrolled 52 patients with MS (33 relapsing-remitting [RRMS], 19 progressive [PMS], mean age: 46.4 years, median disease duration: 15.1 years, median: EDSS 2.0) and 70 controls (mean age 41.5 ± 12.8). Compared with controls, RRMS showed lower MTR values in the outer and middle cortical layers (false-discovery rate [FDR]-p ≤ 0.025) and lower R2* values in all 3 cortical layers (FDR-p ≤ 0.016). PMS had lower MTR values in the outer and middle cortical (FDR-p ≤ 0.016) and thalamic (FDR-p ≤ 0.048) layers, and in the outer caudate layer (FDR-p = 0.024). They showed lower R2* values in the outer cortical layer (FDR-p = 0.003) and in the outer thalamic layer (FDR-p = 0.046) and higher R2* values in all 3 caudate layers (FDR-p ≤ 0.031). Both RRMS and PMS had a gradient of damage, with lower values closer to the CSF, for cortical (FDR-p ≤ 0.002) and thalamic (FDR-p ≤ 0.042) MTR. PMS showed a gradient of damage for cortical R2* (FDR-p = 0.005), thalamic R2* (FDR-p = 0.004), and caudate MTR (FDR-p ≤ 0.013). Lower MTR and R2* of outer cortical, thalamic, and caudate layers and steeper gradient of damage toward the CSF were significantly associated with older age, higher T2-hyperintense white matter lesion volume, higher thalamic lesion volume, and lower brain volume (β ≥ 0.08, all FDR-p ≤ 0.040). Lower MTR of outer caudate layer was associated with more severe disability (β = -0.26, FDR-p = 0.040). No correlations with choroid plexus volume were found.

DISCUSSION

CSF-in damage gradients are heterogeneous among different GM regions and through MS course, possibly reflecting different dynamics of demyelination and iron loss/accumulation.

Chaos and COSMOS-Considerations on QSM methods with multiple and single orientations and effects from local anisotropy

PURPOSE

Field-to-susceptibility inversion in quantitative susceptibility mapping (QSM) is ill-posed and needs numerical stabilization through either regularization or oversampling by acquiring data at three or more object orientations. Calculation Of Susceptibility through Multiple Orientations Sampling (COSMOS) is an established oversampling approach and regarded as QSM gold standard. It achieves a well-conditioned inverse problem, requiring rotations by 0°, 60° and 120° in the yz-plane. However, this is impractical in vivo, where head rotations are typically restricted to a range of ±25°. Non-ideal sampling degrades the conditioning with residual streaking artifacts whose mitigation needs further regularization. Moreover, susceptibility anisotropy in white matter is not considered in the COSMOS model, which may introduce additional bias. The current work presents a thorough investigation of these effects in primate brain.

METHODS

Gradient-recalled echo (GRE) data of an entire fixed chimpanzee brain were acquired at 7 T (350 μm resolution, 10 orientations) including ideal COSMOS sampling and realistic rotations in vivo. Comparisons of the results included ideal COSMOS, in-vivo feasible acquisitions with 3-8 orientations and single-orientation iLSQR QSM.

RESULTS

In-vivo feasible and optimal COSMOS yielded high-quality susceptibility maps with increased SNR resulting from averaging multiple acquisitions. COSMOS reconstructions from non-ideal rotations about a single axis required additional L2-regularization to mitigate residual streaking artifacts.

CONCLUSION

In view of unconsidered anisotropy effects, added complexity of the reconstruction, and the general challenge of multi-orientation acquisitions, advantages of sub-optimal COSMOS schemes over regularized single-orientation QSM appear limited in in-vivo settings.

Quantitative MRI at 7-Tesla reveals novel frontocortical myeloarchitecture anomalies in major depressive disorder

Whereas meta-analytical data highlight abnormal frontocortical macrostructure (thickness/surface area/volume) in Major Depressive Disorder (MDD), the underlying microstructural processes remain uncharted, due to the use of conventional MRI scanners and acquisition techniques. We uniquely combined Ultra-High Field MRI at 7.0 Tesla with Quantitative Imaging to map intracortical myelin (proxied by longitudinal relaxation time T1) and iron concentration (proxied by transverse relaxation time T2*), microstructural processes deemed particularly germane to cortical macrostructure. Informed by meta-analytical evidence, we focused specifically on orbitofrontal and rostral anterior cingulate cortices among adult MDD patients (N = 48) and matched healthy controls (HC; N = 10). Analyses probed the association of MDD diagnosis and clinical profile (severity, medication use, comorbid anxiety disorders, childhood trauma) with aforementioned microstructural properties. MDD diagnosis (p's < 0.05, Cohen's D = 0.55-0.66) and symptom severity (p's < 0.01, r = 0.271-0.267) both related to decreased intracortical myelination (higher T1 values) within the lateral orbitofrontal cortex, a region tightly coupled to processing negative affect and feelings of sadness in MDD. No relations were found with local iron concentrations. These findings allow uniquely fine-grained insights on frontocortical microstructure in MDD, and cautiously point to intracortical demyelination as a possible driver of macroscale cortical disintegrity in MDD.

Quantitative susceptibility mapping in the brain reflects spatial expression of genes involved in iron homeostasis and myelination

Quantitative susceptibility mapping (QSM) is an MRI modality used to non-invasively measure iron content in the brain. Iron exhibits a specific anatomically varying pattern of accumulation in the brain across individuals. The highest regions of accumulation are the deep grey nuclei, where iron is stored in paramagnetic molecule ferritin. This form of iron is considered to be what largely contributes to the signal measured by QSM in the deep grey nuclei. It is also known that QSM is affected by diamagnetic myelin contents. Here, we investigate spatial gene expression of iron and myelin related genes, as measured by the Allen Human Brain Atlas, in relation to QSM images of age-matched subjects. We performed multiple linear regressions between gene expression and the average QSM signal within 34 distinct deep grey nuclei regions. Our results show a positive correlation (p < .05, corrected) between expression of ferritin and the QSM signal in deep grey nuclei regions. We repeated the analysis for other genes that encode proteins thought to be involved in the transport and storage of iron in the brain, as well as myelination. In addition to ferritin, our findings demonstrate a positive correlation (p < .05, corrected) between the expression of ferroportin, transferrin, divalent metal transporter 1, several gene markers of myelinating oligodendrocytes, and the QSM signal in deep grey nuclei regions. Our results suggest that the QSM signal reflects both the storage and active transport of iron in the deep grey nuclei regions of the brain.

Revealing the MRI-Contrast in Optically Cleared Brains

The current consensus holds that optically-cleared specimens are unsuitable for Magnetic Resonance Imaging (MRI); exhibiting absence of contrast. Prior studies combined MRI with tissue-clearing techniques relying on the latter's ability to eliminate lipids, thereby fostering the assumption that lipids constitute the primary source of ex vivo MRI-contrast. Nevertheless, these findings contradict an extensive body of literature that underscores the contribution of other features to contrast. Furthermore, it remains unknown whether non-delipidating clearing methods can produce MRI-compatible specimens or whether MRI-contrast can be re-established. These limitations hinder the development of multimodal MRI-light-microscopy (LM) imaging approaches. This study assesses the relation between MRI-contrast, and delipidation in optically-cleared whole brains following different tissue-clearing approaches. It is demonstrated that uDISCO and ECi-brains are MRI-compatible upon tissue rehydration, despite both methods' substantial delipidating-nature. It is also demonstrated that, whereas Scale-clearing preserves most lipids, Scale-cleared brain lack MRI-contrast. Furthermore, MRI-contrast is restored to lipid-free CLARITY-brains without introducing lipids. Our results thereby dissociate between the essentiality of lipids to MRI-contrast. A tight association is found between tissue expansion, hyperhydration and loss of MRI-contrast. These findings then enabled us to develop a multimodal MRI-LM-imaging approach, opening new avenues to bridge between the micro- and mesoscale for biomedical research and clinical applications.

Glycyl-l-histidyl-l-lysine prevents copper- and zinc-induced protein aggregation and central nervous system cell death in vitro

Common features of neurodegenerative diseases are oxidative and inflammatory imbalances as well as the misfolding of proteins. An excess of free metal ions can be pathological and contribute to cell death, but only copper and zinc strongly promote protein aggregation. Herein we demonstrate that the endogenous copper-binding tripeptide glycyl-l-histidyl-l-lysine (GHK) has the ability to bind to and reduce copper redox activity and to prevent copper- and zinc-induced cell death in vitro. In addition, GHK prevents copper- and zinc-induced bovine serum albumin aggregation and reverses aggregation through resolubilizing the protein. We further demonstrate the enhanced toxicity of copper during inflammation and the ability of GHK to attenuate this toxicity. Finally, we investigated the effects of copper on enhancing paraquat toxicity and report a protective effect of GHK. We therefore conclude that GHK has potential as a cytoprotective compound with regard to copper and zinc toxicity, with positive effects on protein solubility and aggregation that warrant further investigation in the treatment of neurodegenerative diseases.

Research trends and hotspots of ferroptosis in neurodegenerative diseases from 2013 to 2023: A bibliometrics study

Background

With the aging population, the incidence of neurodegenerative diseases increases yearly, seriously impacting human health. Various journals have published studies on the pathogenesis of ferroptosis in neurodegenerative diseases. However, bibliometric analysis in this field is still lacking. The study aims to visually analyze global research trends in this field over the past decade.

Methods

The articles and reviews regarding ferroptosis in neurodegenerative diseases were retrieved from the Web of Science on September 1, 2023. Citespace [version 6.2. R4 (64-bit)] and VOSviewer (version 1.6.18) were used to conduct the bibliometric and knowledge-map analysis.

Results

In total, 370 studies were included in the paper and ranked by their citation frequency. Many articles on ferroptosis in neurodegenerative diseases have been published in the past decade. The country, institution, author, and journal with the highest publications were China, Guangzhou Medical University, Maher, Pamela, and Free Radical Biology And Medicine, respectively. The analysis of keyword co-occurrence indicated that research frontiers were molecular mechanisms of ferroptosis in neurodegenerative diseases, especially a few key pathways that triggered ferroptosis in these diseases, including lipid peroxidation signaling, iron metabolism, and GSH/GPX4 signaling. In addition, ferroptosis inhibitors such as liproxstatins and ferrostatins had protective effects in animal models of neurodegenerative diseases. Therefore, future attention should also be focused on therapeutic drugs that target ferroptosis.

Conclusion

This study comprehensively analyzed the publications on ferroptosis in neurodegenerative diseases from a bibliometric perspective. Research on this topic is currently expanding at a rapid pace, and the China holds a leading position in this field by its scientific achievements and productivity. Moreover, the research frontiers were molecular mechanisms of ferroptosis in neurodegenerative diseases and developing targeted therapeutic drugs. In summary, our results showed an all-sided overview of the knowledge atlas and a valuable reference for the future research in this field.

Associations of quantitative susceptibility mapping with cortical atrophy and brain connectome in Alzheimer's disease: A multi-parametric study

Aberrant susceptibility due to iron level abnormality and brain network disconnections are observed in Alzheimer's disease (AD), with disrupted iron homeostasis hypothesized to be linked to AD pathology and neuronal loss. However, whether associations exist between abnormal quantitative susceptibility mapping (QSM), brain atrophy, and altered brain connectome in AD remains unclear. Based on multi-parametric brain imaging data from 30 AD patients and 26 healthy controls enrolled at the China-Japan Friendship Hospital, we investigated the abnormality of the QSM signal and volumetric measure across 246 brain regions in AD patients. The structural and functional connectomes were constructed based on diffusion MRI tractography and functional connectivity, respectively. The network topology was quantified using graph theory analyses. We identified seven brain regions with both reduced cortical thickness and abnormal QSM (p < 0.05) in AD, including the right superior frontal gyrus, left superior temporal gyrus, right fusiform gyrus, left superior parietal lobule, right superior parietal lobule, left inferior parietal lobule, and left precuneus. Correlations between cortical thickness and network topology computed across patients in the AD group resulted in statistically significant correlations in five of these regions, with higher correlations in functional compared to structural topology. We computed the correlation between network topological metrics, QSM value and cortical thickness across regions at both individual and group-averaged levels, resulting in a measure we call spatial correlations. We found a decrease in the spatial correlation of QSM and the global efficiency of the structural network in AD patients at the individual level. These findings may provide insights into the complex relationships among QSM, brain atrophy, and brain connectome in AD.

Exploring antioxidant strategies in the pathogenesis of ALS

The central nervous system is essential for maintaining homeostasis and controlling the body's physiological functions. However, its biochemical characteristics make it highly vulnerable to oxidative damage, which is a common factor in neurodegenerative diseases like amyotrophic lateral sclerosis (ALS). ALS is a leading cause of motor neuron disease, characterized by a rapidly progressing and incurable condition. ALS often results in death from respiratory failure within 3-5 years from the onset of the first symptoms, underscoring the urgent need to address this medical challenge. The aim of this study is to present available data supporting the role of oxidative stress in the mechanisms underlying ALS and to discuss potential antioxidant therapies currently in development. These therapies aim to improve the quality of life and life expectancy for patients affected by this devastating disease.

Radiation damping at clinical field strength: Characterization and compensation in quantitative measurements

PURPOSE

In any MR experiment, the bulk magnetization acts on itself, caused by the induced current in the RF receiver circuit that generates an oscillating damping field. This effect, known as "radiation damping" (RD), is usually weak and, therefore, unconsidered in MRI, but can affect quantitative studies performed with dedicated coils that provide a high SNR. The current work examined RD in a setup for investigations of small tissue specimens including a quantitative characterization of the spin-coil system.

THEORY AND METHODS

A custom-made Helmholtz coil (radius and spacing 16 mm) was interfaced to a transmit-receive (Tx/Rx) switch with integrated passive feedback for modulation or suppression of RD similar to preamplifier decoupling. Pulse sequences included pulse-width arrays to demonstrate the absence/ presence of RD and difference techniques employing gradient pulses or composite RF pulses to quantify RD effects during free precession and transmission, respectively. Experiments were performed at 3T in small samples of MnCl2 solution.

RESULTS

Significant RD effects may impact RF pulse application and evolution periods. Effective damping time constants were comparable to typical T2 * times or echo spacings in multi-echo sequences. Measurements of the phase relation showed that deviations from the commonly assumed 90° angle between the damping field and the transverse magnetization may occur.

CONCLUSION

Radiation damping may affect the accuracy of quantitative MR measurements performed with dedicated RF coils. Efficient mitigation can be achieved hardware-based or by appropriate consideration in the pulse sequence.

Iron overload promotes the progression of MLL-AF9 induced acute myeloid leukemia by upregulation of FOS

Systemic iron overload is a common clinical challenge leading to significantly serious complications in patients with acute myeloid leukemia (AML), which affects both the quality of life and the overall survival of patients. Symptoms can be relieved after iron chelation therapy in clinical practice. However, the roles and mechanisms of iron overload on the initiation and progression of leukemia remain elusive. Here we studied the correlation between iron overload and AML clinical outcome, and further explored the role and pathophysiologic mechanism of iron overload in AML by using two mouse models: an iron overload MLL-AF9-induced AML mouse model and a nude xenograft mouse model. Patients with AML had an increased ferritin level, particularly in the myelomonocytic (M4) or monocytic (M5) subtypes. High level of iron expression correlated with a worsened prognosis in AML patients and a shortened survival time in AML mice. Furthermore, iron overload increased the tumor load in the bone marrow (BM) and extramedullary tissues by promoting the proliferation of leukemia cells through the upregulation of FOS. Collectively, our findings provide new insights into the roles of iron overload in AML. Additionally, this study may provide a potential therapeutic target to improve the outcome of AML patients and a rationale for the prospective evaluation of iron chelation therapy in AML.

An update on the role of magnetic resonance imaging in predicting and monitoring multiple sclerosis progression

INTRODUCTION

While magnetic resonance imaging (MRI) is established in diagnosing and monitoring disease activity in multiple sclerosis (MS), its utility in predicting and monitoring disease progression is less clear.

AREAS COVERED

The authors consider changing concepts in the phenotypic classification of MS, including progression independent of relapses; pathological processes underpinning progression; advances in MRI measures to assess them; how well MRI features explain and predict clinical outcomes, including models that assess disease effects on neural networks, and the potential role for machine learning.

EXPERT OPINION

Relapsing-remitting and progressive MS have evolved from being viewed as mutually exclusive to having considerable overlap. Progression is likely the consequence of several pathological elements, each important in building more holistic prognostic models beyond conventional phenotypes. MRI is well placed to assess pathogenic processes underpinning progression, but we need to bridge the gap between MRI measures and clinical outcomes. Mapping pathological effects on specific neural networks may help and machine learning methods may be able to optimize predictive markers while identifying new, or previously overlooked, clinically relevant features. The ever-increasing ability to measure features on MRI raises the dilemma of what to measure and when, and the challenge of translating research methods into clinically useable tools.

Distance from main arteries influences microstructural and functional brain tissue characteristics

Given the substantial dependence of neurons on continuous supply of energy, the distribution of major cerebral arteries opens a question whether the distance from the main supply arteries constitutes a modulating factor for the microstructural and functional properties of brain tissue. To tackle this question, multimodal MRI acquisitions of 102 healthy volunteers over the full adult age span were utilised. Relaxation along a fictitious field in the rotating frame of rank n = 4 (RAFF4), adiabatic T1ρ, T2ρ,  and intracellular volume fraction (fICVF) derived from diffusion-weighted imaging were implemented to quantify microstructural (cellularity, myelin density, iron concentration) tissue characteristics and degree centrality and fractional amplitude of low-frequency fluctuations to probe for functional metrics. Inverse correlation of arterial distance with robust homogeneity was detected for T1ρ, T2ρ and RAFF4 for cortical grey matter and white matter, showing substantial complex microstructural differences between brain tissue close and farther from main arterial trunks. Albeit with wider variability, functional metrics pointed to increased connectivity and neuronal activity in areas farther from main arteries. Surprisingly, multiple of these microstructural and functional distance-based gradients diminished with higher age, pointing to uniformization of brain tissue with ageing. All in all, this pilot study provides a novel insight on brain regionalisation based on artery distance, which merits further investigation to validate its biological underpinnings.

Aberrant dentato-rubro-thalamic pathway in action tremor but not rest tremor: A multi-modality magnetic resonance imaging study

AIMS

The purpose of this study was to clarify the dentato-rubro-thalamic (DRT) pathway in action tremor in comparison to normal controls (NC) and disease controls (i.e., rest tremor) by using multi-modality magnetic resonance imaging (MRI).

METHODS

This study included 40 essential tremor (ET) patients, 57 Parkinson's disease (PD) patients (29 with rest tremor, 28 without rest tremor), and 41 NC. We used multi-modality MRI to comprehensively assess major nuclei and fiber tracts of the DRT pathway, which included decussating DRT tract (d-DRTT) and non-decussating DRT tract (nd-DRTT), and compared the differences in DRT pathway components between action and rest tremor.

RESULTS

Bilateral dentate nucleus (DN) in the ET group had excessive iron deposition compared with the NC group. Compared with the NC group, significantly decreased mean diffusivity and radial diffusivity were observed in the left nd-DRTT in the ET group, which were negatively correlated with tremor severity. No significant difference in each component of the DRT pathway was observed between the PD subgroup or the PD and NC.

CONCLUSION

Aberrant changes in the DRT pathway may be specific to action tremor and were indicating that action tremor may be related to pathological overactivation of the DRT pathway.

The diamagnetic component map from quantitative susceptibility mapping (QSM) source separation reveals pathological alteration in Alzheimer's disease-driven neurodegeneration

A sensitive and accurate imaging technique capable of tracking the disease progression of Alzheimer's Disease (AD) driven amnestic dementia would be beneficial. A currently available method for pathology detection in AD with high accuracy is Positron Emission Tomography (PET) imaging, despite certain limitations such as low spatial resolution, off-targeting error, and radiation exposure. Non-invasive MRI scanning with quantitative magnetic susceptibility measurements can be used as a complementary tool. To date, quantitative susceptibility mapping (QSM) has widely been used in tracking deep gray matter iron accumulation in AD. The present work proposes that by compartmentalizing quantitative susceptibility into paramagnetic and diamagnetic components, more holistic information about AD pathogenesis can be acquired. Particularly, diamagnetic component susceptibility (DCS) can be a powerful indicator for tracking protein accumulation in the gray matter (GM), demyelination in the white matter (WM), and relevant changes in the cerebrospinal fluid (CSF). In the current work, voxel-wise group analysis of the WM and the CSF regions show significantly lower |DCS| (the absolute value of DCS) value for amnestic dementia patients compared to healthy controls. Additionally, |DCS| and τ PET standardized uptake value ratio (SUVr) were found to be associated in several GM regions typically affected by τ deposition in AD. Therefore, we propose that the separated diamagnetic susceptibility can be used to track pathological neurodegeneration in different tissue types and regions of the brain. With the initial evidence, we believe the usage of compartmentalized susceptibility demonstrates substantive potential as an MRI-based technique for tracking AD-driven neurodegeneration.

Magnetic resonance imaging detection of deep gray matter iron deposition in multiple sclerosis: A systematic review

Multiple sclerosis (MS) is a chronic inflammatory and neurodegenerative disease involving immune-mediated damage. Iron deposition in deep gray matter (DGM) structures like the thalamus and basal ganglia have been suggested to play a role in MS pathogenesis. Magnetic Resonance Imaging (MRI) imaging methods like T2 and T2* imaging, susceptibility-weighted imaging, and quantitative susceptibility mapping can track iron deposition storage in the brain primarily from ferritin and hemosiderin (paramagnetic iron storage proteins) with varying levels of tissue contrast and sensitivity. In this systematic review, we evaluated the role of DGM iron deposition as detected by MRI techniques in relation to MS-related neuroinflammation and its potential as a novel therapeutic target. We searched through PubMed, Embase, and Web of Science databases following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines, against predetermined inclusion and exclusion criteria. We included 89 articles (n = 6630 patients), and then grouped them into different categories: i) methodological techniques to measure DGM iron, ii) cross-sectional and group comparison of DGM iron content, iii) longitudinal comparisons of DGM iron, iv) associations between DGM iron and other imaging and neurobiological markers, v) associations with disability, and vi) associations with cognitive impairment. The review revealed that iron deposition in DGM is independent yet concurrent with demyelination, and that these iron deposits contribute to MS-related cognitive impairment and disability. Variability in iron distributions appears to rely on a positive feedback loop between inflammation, and release of iron by oligodendrocytes. DGM iron seems to be a promising prognostic biomarker for MS pathophysiology.

Quantitative myelin water imaging using short TR adiabatic inversion recovery prepared echo-planar imaging (STAIR-EPI) sequence

Introduction

Numerous techniques for myelin water imaging (MWI) have been devised to specifically assess alterations in myelin. The biomarker employed to measure changes in myelin content is known as the myelin water fraction (MWF). The short TR adiabatic inversion recovery (STAIR) sequence has recently been identified as a highly effective method for calculating MWF. The purpose of this study is to develop a new clinical transitional myelin water imaging (MWI) technique that combines STAIR preparation and echo-planar imaging (EPI) (STAIR-EPI) sequence for data acquisition.

Methods

Myelin water (MW) in the brain has shorter T1 and T2 relaxation times than intracellular and extracellular water. In the proposed STAIR-EPI sequence, a short TR (e.g., ≤300 ms) together with an optimized inversion time enable robust long T1 water suppression with a wide range of T1 values [i.e., (600, 2,000) ms]. The EPI allows fast data acquisition of the remaining MW signals. Seven healthy volunteers and seven patients with multiple sclerosis (MS) were recruited and scanned in this study. The apparent myelin water fraction (aMWF), defined as the signal ratio of MW to total water, was measured in the lesions and normal-appearing white matter (NAWM) in MS patients and compared with those measured in the normal white matter (NWM) in healthy volunteers.

Results

As seen in the STAIR-EPI images acquired from MS patients, the MS lesions show lower signal intensities than NAWM do. The aMWF measurements for both MS lesions (3.6 ± 1.3%) and NAWM (8.6 ± 1.2%) in MS patients are significantly lower than NWM (10 ± 1.3%) in healthy volunteers (P < 0.001).

Discussion

The proposed STAIR-EPI technique, which can be implemented in MRI scanners from all vendors, is able to detect myelin loss in both MS lesions and NAWM in MS patients.

Non-invasive assessment of normal and impaired iron homeostasis in the brain

Strict iron regulation is essential for normal brain function. The iron homeostasis, determined by the milieu of available iron compounds, is impaired in aging, neurodegenerative diseases and cancer. However, non-invasive assessment of different molecular iron environments implicating brain tissue's iron homeostasis remains a challenge. We present a magnetic resonance imaging (MRI) technology sensitive to the iron homeostasis of the living brain (the r1-r2* relaxivity). In vitro, our MRI approach reveals the distinct paramagnetic properties of ferritin, transferrin and ferrous iron ions. In the in vivo human brain, we validate our approach against ex vivo iron compounds quantification and gene expression. Our approach varies with the iron mobilization capacity across brain regions and in aging. It reveals brain tumors' iron homeostasis, and enhances the distinction between tumor tissue and non-pathological tissue without contrast agents. Therefore, our approach may allow for non-invasive research and diagnosis of iron homeostasis in living human brains.