Relationship between cortical iron and tau aggregation in Alzheimer's disease

B Vitamins Prevent Iron-Associated Brain Atrophy and Domain-Specific Effects of Iron, Copper, Aluminum, and Silicon on Cognition in Mild Cognitive Impairment

Background:

Metals, silicon, and homocysteine are linked to Alzheimer’s disease. B vitamin therapy lowers homocysteine and slows brain atrophy and cognitive decline in mild cognitive impairment (MCI).

Objective:

Examine metals and silicon as predictors of cognition/brain atrophy in MCI, their interaction with homocysteine and cysteine, and how B vitamins affect these relationships.

Methods:

MCI participants (n = 266, 77.6-year-old, 60.7% female) in VITACOG trial were randomized to receive daily folic acid (0.8 mg)/vitamin B₁₂ (0.5 mg)/vitamin B₆ (20 mg) (n = 133) or placebo for two years. At baseline and end-of-study, cranial MRIs were obtained from 168 participants, cognition was analyzed by neuropsychological tests, and serum iron, copper, arsenic, aluminum, and silicon quantified by inductively-coupled plasma mass spectrometry in 196 participants. Data were analyzed by bivariate and multiple regression.

Results:

Baseline iron, cysteine, and homocysteine were significantly associated with brain atrophy rate. Homocysteine effects on brain atrophy rate were modified by iron and cysteine. At baseline, iron, copper, aluminum, and silicon were significantly associated with one or more domains of cognition: semantic memory, verbal episodic memory, attention/processing speed, and executive function. At end-of-study, baseline iron, copper, aluminum, and silicon predicted cognition in at least one domain: semantic memory, verbal episodic memory, visuospatial episodic memory, attention/processing speed, and global cognition in the placebo but not the B vitamin group.

Conclusion:

Disparate effects of serum iron, copper, aluminum, silicon, and homocysteine on cognition and brain atrophy in MCI suggest that cognitive impairment is independent of brain atrophy. These factors showed domain-specific associations with cognition, which were abrogated by B vitamin therapy.

Genetic differences in ethanol consumption: effects on iron, copper, and zinc regulation in mouse hippocampus

One common characteristic of neurodegenerative diseases is dysregulation of iron, usually with observed increases in its concentration in various regions. Heavy alcohol consumption is believed to contribute to such iron dysregulation in the brain with accompanying dementia. To examine this effect and related genetic-based individual differences in an animal model, we subjected female mice from 12 BXD recombinant inbred strains to 16 weeks of alcohol consumption using the drinking in the dark (DID) method. Daily consumption was recorded and at the end of 16 weeks hippocampus tissues harvested. Concentrations of iron, copper and zinc were measured using X-ray fluorescence technology. The results showed that, DID increased iron overall across all strains, ranging from 3 to 68%. Copper and Zinc both decreased, ranging from 0.4-42 and 5-35% respectively. Analysis of variance revealed significant strain by treatment interactions for all three metals. Additionally, in the DID group, we observed strain differences in reduction of hippocampus mass. These findings are particularly interesting to us because high alcohol consumption in humans has been associated with neurodegeneration and dementia related to disruption of iron regulation. The findings of alcohol consumption associated decreases in copper and zinc are novel. The role of copper regulation and neurological function related to alcohol consumption is as yet largely unexplored. The role of zinc is better known as a neuromodulator in the hippocampus and appears to be protective against neurological damage. It would seem then, that the alcohol-related decrease in zinc in the hippocampus would be of concern and warrants further study.

Dietary nutrition for neurological disease therapy: Current status and future directions

Adequate food intake and relative abundance of dietary nutrients have undisputed effects on the brain function. There is now substantial evidence that dietary nutrition aids in the prevention and remediation of neurologic symptoms in diverse pathological conditions. The newly described influences of dietary factors on the alterations of mitochondrial dysfunction, epigenetic modification and neuroinflammation are important mechanisms that are responsible for the action of nutrients on the brain health. In this review, we discuss the state of evidence supporting that distinct dietary interventions including dietary supplement and dietary restriction have the ability to tackle neurological disorders using Alzheimer's disease, Parkinson's disease, stroke, epilepsy, traumatic brain injury, amyotrophic lateral sclerosis, Huntington's disease and multiple sclerosis as examples. Additionally, it is also highlighting that diverse potential mechanisms such as metabolic control, epigenetic modification, neuroinflammation and gut-brain axis are of utmost importance for nutrient supply to the risk of neurologic condition and therapeutic response. Finally, we also highlight the novel concept that dietary nutrient intervention reshapes metabolism-epigenetics-immunity cycle to remediate brain dysfunction. Targeting metabolism-epigenetics-immunity network will delineate a new blueprint for combating neurological weaknesses.

Ferroptosis as a mechanism of neurodegeneration in Alzheimer's disease

Alzheimer's disease (AD) is the most prevalent form of dementia, with complex pathophysiology that is not fully understood. While β-amyloid plaque and neurofibrillary tangles define the pathology of the disease, the mechanism of neurodegeneration is uncertain. Ferroptosis is an iron-mediated programmed cell death mechanism characterised by phospholipid peroxidation that has been observed in clinical AD samples. This review will outline the growing molecular and clinical evidence implicating ferroptosis in the pathogenesis of AD, with implications for disease-modifying therapies.

Upregulation of Local Hepcidin Contributes to Iron Accumulation in Alzheimer's Disease Brains

BACKGROUND

Accumulation of iron is a consistent feature of Alzheimer's disease (AD) brains. The underlying cause, however, remains debatable.

OBJECTIVE

To explore whether local hepcidin synthesized by brain cells contributes to iron accumulation in AD brains.

METHODS

Brain tissue from the cingulate cortex of 33 cases of AD pre-assigned to Braak stage I-VI, 6 cases of non-dementia, and 15 cases of non-AD dementia were analyzed for transcriptional upregulation of hepcidin by RT-qPCR and RT-PCR. Change in the expression of ferritin, ferroportin (Fpn), microglial activation marker Iba1, IL-6, and TGFβ2 was determined by western blotting. Total tissue iron was determined by colorimetry.

RESULTS

Significant transcriptional upregulation of hepcidin was observed in Braak stage III-VI relative to Braak stage I and II, non-AD dementia, and non-dementia samples. Ferritin was increased in Braak stage V, and a significant increase in tissue iron was evident in Braak stage III-VI. The expression of Iba1 and IL-6 was also increased in Braak stage III-VI relative to Braak stage I and II and non-AD dementia samples. Amyloid-β plaques were absent in most Braak stage I and II samples, and present in Braak stage III-VI samples with few exceptions.

CONCLUSION

These observations suggest that upregulation of brain hepcidin is mediated by IL-6, a known transcriptional activator of hepcidin. The consequent downregulation of Fpn on neuronal and other cells results in accumulation of iron in AD brains. The increase in hepcidin is disease-specific, and increases with disease progression, implicating AD-specific pathology in the accumulation of iron.

Regional brain iron and gene expression provide insights into neurodegeneration in Parkinson's disease

The mechanisms responsible for the selective vulnerability of specific neuronal populations in Parkinson's disease are poorly understood. Oxidative stress secondary to brain iron accumulation is one postulated mechanism. We measured iron deposition in 180 cortical regions of 96 patients with Parkinson's disease and 35 control subjects using quantitative susceptibility mapping. We estimated the expression of 15 745 genes in the same regions using transcriptomic data from the Allen Human Brain Atlas. Using partial least squares regression, we then identified the profile of gene transcription in the healthy brain that underlies increased cortical iron in patients with Parkinson's disease relative to controls. Applying gene ontological tools, we investigated the biological processes and cell types associated with this transcriptomic profile and identified the sets of genes with spatial expression profiles in control brains that correlated significantly with the spatial pattern of cortical iron deposition in Parkinson's disease. Gene ontological analyses revealed that these genes were enriched for biological processes relating to heavy metal detoxification, synaptic function and nervous system development and were predominantly expressed in astrocytes and glutamatergic neurons. Furthermore, we demonstrated that the genes differentially expressed in Parkinson's disease are associated with the pattern of cortical expression identified in this study. Our findings provide mechanistic insights into regional selective vulnerabilities in Parkinson's disease, particularly the processes involving iron accumulation.

Regional brain iron associated with deterioration in Alzheimer's disease: A large cohort study and theoretical significance

OBJECTIVE

This paper is a proposal for an update of the iron hypothesis of Alzheimer's disease (AD), based on large-scale emerging evidence.

BACKGROUND

Iron featured historically early in AD research efforts for its involvement in the amyloid and tau proteinopathies, APP processing, genetics, and one clinical trial, yet iron neurochemistry remains peripheral in mainstream AD research. Much of the effort investigating iron in AD has focused on the potential for iron to provoke the onset of disease, by promoting proteinopathy though increased protein expression, phosphorylation, and aggregation.

NEW/UPDATED HYPOTHESIS

We provide new evidence from a large post mortem cohort that brain iron levels within the normal range were associated with accelerated ante mortem disease progression in cases with underlying proteinopathic neuropathology. These results corroborate recent findings that argue for an additional downstream role for iron as an effector of neurodegeneration, acting independently of tau or amyloid pathologies. We hypothesize that the level of tissue iron is a trait that dictates the probability of neurodegeneration in AD by ferroptosis, a regulated cell death pathway that is initiated by signals such as glutathione depletion and lipid peroxidation.

MAJOR CHALLENGES FOR THE HYPOTHESIS

While clinical biomarkers of ferroptosis are still in discovery, the demonstration of additional ferroptotic correlates (genetic or biomarker derived) of disease progression is required to test this hypothesis. The genes implicated in familial AD are not known to influence ferroptosis, although recent reports on APP mutations and apolipoprotein E allele (APOE) have shown impact on cellular iron retention. Familial AD mutations will need to be tested for their impact on ferroptotic vulnerability. Ultimately, this hypothesis will be substantiated, or otherwise, by a clinical trial of an anti-ferroptotic/iron compound in AD patients.

LINKAGE TO OTHER MAJOR THEORIES

Iron has historically been linked to the amyloid and tau proteinopathies of AD. Tau, APP, and apoE have been implicated in physiological iron homeostasis in the brain. Iron is biochemically the origin of most chemical radicals generated in biochemistry and thus closely associated with the oxidative stress theory of AD. Iron accumulation is also a well-established consequence of aging and inflammation, which are major theories of disease pathogenesis.

Immunohistochemical Study of Mitochondrial Ferritin in the Midbrain of Patients with Progressive Supranuclear Palsy

Mitochondrial ferritin (FtMt) is a novel ferritin that is localized in the mitochondria. FtMt expression is low in the liver and spleen, and high in the heart, testis, and brain. We previously detected FtMt in dopaminergic neurons in the substantia nigra pars compacta (SNc) in human and monkey midbrains. We investigated the localization and expression of FtMt in the midbrain of patients with progressive supranuclear palsy (PSP) and controls using a monoclonal antibody (C65-2) against human FtMt. FtMt immunoreactivity was weakly detected in neuromelanin-containing neurons in the SNc and ventral tegmental area (VTA) of control cases compared with PSP, which exhibited a remarkable increase in FtMt immunoreactivity. Preincubation of C65-2 with the immunizing FtMt peptide significantly reduced the staining, indicating the specificity of C65-2. Several puncta were observed outside the neurons of PSP, in contrast with the control cases. Double immunofluorescence histochemistry for FtMt and tyrosine hydroxylase (TH), glial fibrillary acidic protein, and Iba1 showed localization of FtMt in dopaminergic neurons, microglia, and astrocytes in PSP. Furthermore, FtMt immunoreactivity was detected in a few TH-negative neurons. In the SNc and VTA, FtMt immunoreactivity colocalized with phosphorylated tau immunoreactivity. Our results indicate that FtMt is involved in the pathology of PSP. Clarifying the involvement of FtMt in PSP is of great interest.

N-Propargylamine-hydroxypyridinone hybrids as multitarget agents for the treatment of Alzheimer's disease

AD is a progressive brain disorder. Because of the lack of remarkable single-target drugs against neurodegenerative disorders, the multitarget-directed ligand strategy has received attention as a promising therapeutic approach. Herein, we rationally designed twenty-nine hybrids of N-propargylamine-hydroxypyridinone. The designed hybrids possessed excellent iron-chelating activity (pFe³⁺ = 17.09-22.02) and potent monoamine oxidase B inhibitory effects. Various biological evaluations of the optimal compound 6b were performed step by step, including inhibition screening of monoamine oxidase (hMAO-B IC₅₀ = 0.083 ± 0.001 µM, hMAO-A IC₅₀ = 6.11 ± 0.08 µM; SI = 73.5), prediction of blood-brain barrier permeability and mouse behavioral research. All of these favorable results proved that the N-propargylamine-hydroxypyridinone scaffold is a promising structure for the discovery of multitargeted ligands for AD therapy.

Nasal Delivery of D-Penicillamine Hydrogel Upregulates a Disintegrin and Metalloprotease 10 Expression via Melatonin Receptor 1 in Alzheimer's Disease Models

Alzheimer's disease (AD) is a type of neurodegenerative disease that is associated with the accumulation of amyloid plaques. Increasing non-amyloidogenic processing and/or manipulating amyloid precursor protein signaling could reduce AD amyloid pathology and cognitive impairment. D-penicillamine (D-Pen) is a water-soluble metal chelator and can reduce the aggregation of amyloid-β (Aβ) with metals in vitro. However, the potential mechanism of D-Pen for treating neurodegenerative disorders remains unexplored. In here, a novel type of chitosan-based hydrogel to carry D-Pen was designed and the D-Pen-CS/β-glycerophosphate hydrogel were characterized by scanning electron microscopy and HPLC. Behavior tests investigated the learning and memory levels of APP/PS1 mice treated through the D-Pen hydrogel nasal delivery. In vivo and in vitro findings showed that nasal delivery of D-Pen-CS/β-GP hydrogel had properly chelated metal ions that reduced Aβ deposition. Furthermore, D-Pen mainly regulated A disintegrin and metalloprotease 10 (ADAM10) expression via melatonin receptor 1 (MTNR1α) and the downstream PKA/ERK/CREB pathway. The present data demonstrated D-Pen significantly improved the cognitive ability of APP/PS1 mice and reduced Aβ generation through activating ADAM10 and accelerating non-amyloidogenic processing. Hence, these findings indicate the potential of D-Pen as a promising agent for treating AD.

Deferoxamine reduces amyloid-beta peptides genesis and alleviates neural apoptosis after traumatic brain injury

Traumatic brain injury (TBI) is recognized as the most influential risk factor for neurodegenerative diseases later in life, including Alzheimer's disease. The aberrant genesis of amyloid-β peptides, which is triggered by TBI, is associated with the development of Alzheimer's disease. Evidence suggests that iron plays a role in both the production of amyloid-β and its neurotoxicity, and iron overload has been noted in the brain after TBI. We therefore investigated the effects of an iron-chelating treatment on amyloid-β genesis in a weight-drop model of TBI in mice. Human brain samples were obtained from patients undergoing surgery for severe brain trauma. The Institute of Cancer Research mice were treated with deferoxamine by intraperitoneal injection after TBI induction. Changes in amyloid-β(1-42) were assessed using western blot and immunohistochemical staining. Ferritin was also detected using western blot to investigate iron deposition in the mice brain. Immunofluorescent terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling was also performed to evaluate neural apoptosis. The amyloid-β(1-42) was markedly elevated after TBI in both humans and mice. Deferoxamine treatment in mice significantly decreased the levels of both amyloid-β(1-42) and ferritin in the brain, and reduced TBI-induced neural cell apoptosis. The iron chelator deferoxamine can alleviate the increase of amyloid-β(1-42) in the brain after TBI, and may therefore be a potential therapeutic strategy to prevent TBI patients from undergoing neurodegenerative processes.

Machine Learning Profiling of Alzheimer's Disease Patients Based on Current Cerebrospinal Fluid Markers and Iron Content in Biofluids

Alzheimer's disease (AD) is the most common form of dementia, characterized by a complex etiology that makes therapeutic strategies still not effective. A true understanding of key pathological mechanisms and new biomarkers are needed, to identify alternative disease-modifying therapies counteracting the disease progression. Iron is an essential element for brain metabolism and its imbalance is implicated in neurodegeneration, due to its potential neurotoxic effect. However, the role of iron in different stages of dementia is not clearly established. This study aimed to investigate the potential impact of iron both in cerebrospinal fluid (CSF) and in serum to improve early diagnosis and the related therapeutic possibility. In addition to standard clinical method to detect iron in serum, a precise quantification of total iron in CSF was performed using graphite-furnace atomic absorption spectrometry in patients affected by AD, mild cognitive impairment, frontotemporal dementia, and non-demented neurological controls. The application of machine learning techniques, such as clustering analysis and multiclassification algorithms, showed a new potential stratification of patients exploiting iron-related data. The results support the involvement of iron dysregulation and its potential interaction with biomarkers (Tau protein and Amyloid-beta) in the pathophysiology and progression of dementia.

Iron loading is a prominent feature of activated microglia in Alzheimer's disease patients

Brain iron accumulation has been found to accelerate disease progression in amyloid-β(Aβ) positive Alzheimer patients, though the mechanism is still unknown. Microglia have been identified as key players in the disease pathogenesis, and are highly reactive cells responding to aberrations such as increased iron levels. Therefore, using histological methods, multispectral immunofluorescence and an automated in-house developed microglia segmentation and analysis pipeline, we studied the occurrence of iron-accumulating microglia and the effect on its activation state in human Alzheimer brains. We identified a subset of microglia with increased expression of the iron storage protein ferritin light chain (FTL), together with increased Iba1 expression, decreased TMEM119 and P2RY12 expression. This activated microglia subset represented iron-accumulating microglia and appeared morphologically dystrophic. Multispectral immunofluorescence allowed for spatial analysis of FTL+Iba1+-microglia, which were found to be the predominant Aβ-plaque infiltrating microglia. Finally, an increase of FTL+Iba1+-microglia was seen in patients with high Aβ load and Tau load. These findings suggest iron to be taken up by microglia and to influence the functional phenotype of these cells, especially in conjunction with Aβ.

Quantitative Susceptibility Mapping of the Hippocampal Fimbria in Alzheimer's Disease

BACKGROUND

The fimbria is a small white matter bundle that connects the hippocampus to the rest of the brain. Damage to the hippocampal gray matter is established in Alzheimer's disease (AD), but the hippocampal fimbrial status in the pathogenesis of AD is unclear. AD-related demyelination and iron deposition alter the diamagnetic and paramagnetic composition of tissues, which can be measured by quantitative susceptibility mapping (QSM).

HYPOTHESIS

AD is associated with microstructural changes in the fimbria that might be detected by QSM.

STUDY TYPE

Retrospective cross-sectional study.

SUBJECTS

In all, 53 adults comprised of controls (n = 30), subjects with early stage AD (n = 13), and late stage AD (n = 10) who were classified according to their amyloid and tau status and presence of hippocampal atrophy.

FIELD STRENGTH / SEQUENCE

3T; 3D fast-field echo sequence for QSM analysis and 3D T₁ -weighted MP-RAGE sequence for anatomical analysis.

ASSESSMENT

Segmentation of the left hippocampal fimbria subfield was performed on T₁ -weighted images and was applied to the coregistered QSM map for extraction of the mean, median, minimum, and maximum values of QSM.

STATISTICAL TESTS

Group comparison of QSM values using analysis of variance (ANOVA) with post-hoc Tukey's test, accuracy of binary differentiation using receiver operating characteristic (ROC), and individual classification using discriminant analysis.

RESULTS

QSM_mean and QSM_median values were significantly different among the three groups (P < 0.05) and showed a shifting from negative in the control group to positive in the AD group. The control and early AD subjects, who have normal hippocampal volumes, were differentiated by the QSM_mean value (area under the curve [AUC] 0.744, P < 0.05) and the QSM_median value (AUC 0.782, P < 0.05). Up to 76% of subjects (inclusive of 26 controls and six with early AD) were correctly classified using a model incorporating clinical and radiologic data.

DATA CONCLUSION

The fimbria showed higher magnetic susceptibility in AD compared with controls.

LEVEL OF EVIDENCE

2 TECHNICAL EFFICACY STAGE: 3.

New Insights Into Drug Discovery Targeting Tau Protein

Microtubule-associated protein tau is characterized by the fact that it is an intrinsically disordered protein due to its lack of a stable conformation and high flexibility. Intracellular inclusions of fibrillar forms of tau with a β-sheet structure accumulate in the brain of patients with Alzheimer's disease and other tauopathies. Accordingly, detachment of tau from microtubules and transition of tau from a disordered state to an abnormally aggregated state are essential events preceding the onset of tau-related diseases. Many reports have shown that this transition is caused by post-translational modifications, including hyperphosphorylation and acetylation. The misfolded tau is self-assembled and forms a tau oligomer before the appearance of tau inclusions. Animal and pathological studies using human samples have demonstrated that tau oligomer formation contributes to neuronal loss. During the progression of tauopathies, tau seeds are released from cells and incorporated into other cells, leading to the propagation of pathological tau aggregation. Accumulating evidence suggests several potential approaches for blocking tau-mediated toxicity: (1) direct inhibition of pathological tau aggregation and (2) inhibition of tau post-translational modifications that occur prior to pathological tau aggregation, (3) inhibition of tau propagation and (4) stabilization of microtubules. In addition to traditional low-molecular-weight compounds, newer drug discovery approaches such as the development of medium-molecular-weight drugs (peptide- or oligonucleotide-based drugs) and high-molecular-weight drugs (antibody-based drugs) provide alternative pathways to preventing the formation of abnormal tau. Of particular interest are recent studies suggesting that tau droplet formation by liquid-liquid phase separation may be the initial step in aberrant tau aggregation, as well results that implicate roles for tau in dendritic and nuclear functions. Here, we review the mechanisms through which drugs can target tau and consider recent clinical trials for the treatment of tauopathies. In addition, we discuss the utility of these newer strategies and propose future directions for research on tau-targeted therapeutics.

The essential elements of Alzheimer's disease

Treatments for Alzheimer’s disease (AD) directed against the prominent amyloid plaque neuropathology are yet to be proved effective despite many phase 3 clinical trials. There are several other neurochemical abnormalities that occur in the AD brain that warrant renewed emphasis as potential therapeutic targets for this disease. Among those are the elementomic signatures of iron, copper, zinc, and selenium. Here, we review these essential elements of AD for their broad potential to contribute to Alzheimer’s pathophysiology, and we also highlight more recent attempts to translate these findings into therapeutics. A reinspection of large bodies of discovery in the AD field, such as this, may inspire new thinking about pathogenesis and therapeutic targets.

Cerebrospinal Fluid Metals and the Association with Cerebral Small Vessel Disease

BACKGROUND

Brain metal homeostasis is essential for brain health, and deregulation can result in oxidative stress on the brain parenchyma.

OBJECTIVE

Our objective in this study was to focus on two hemorrhagic MRI manifestations of small vessel disease [cerebral microbleeds (CMBs) and cortical superficial siderosis (cSS)] and associations with cerebrospinal fluid (CSF) iron levels. In addition, we aimed to analyze CSF biomarkers for dementia and associations with CSF metal levels.

METHODS

This is a cross-sectional study of 196 patients who underwent memory clinic investigation, including brain MRI. CSF was collected and analyzed for metals, amyloid-β (Aβ) 42, total tau (T-tau), and phosphorylated tau (P-tau), and CSF/serum albumin ratios. Statistical analyses were performed using generalized linear models.

RESULTS

No significant difference was found between CSF metal levels across diagnostic groups. Higher iron and copper levels were associated with higher CSF levels of Aβ42, T-tau, P-tau, and CSF/serum albumin ratios (p < 0.05). Zinc was associated with higher CSF/serum albumin ratios. There was no significant association between CMBs or cSS and CSF iron levels. An increase in CSF iron with the number of CMBs was seen in APOEɛ4 carriers.

CONCLUSION

CSF iron levels are elevated with cerebral microbleeds in APOEɛ4 carriers, with no other association seen with hemorrhagic markers of small vessel disease. The association of elevated CSF iron and copper with tau could represent findings of increased neurodegeneration in these patients.

What's That (Blue) Spot on my MRI? Multimodal Neuroimaging of the Locus Coeruleus in Neurodegenerative Disease

The locus coeruleus (LC) has long been underappreciated for its role in the pathophysiology of Alzheimer’s disease (AD), Parkinson’s disease (PD), and other neurodegenerative disorders. While AD and PD are distinct in clinical presentation, both are characterized by prodromal protein aggregation in the LC, late-stage degeneration of the LC, and comorbid conditions indicative of LC dysfunction. Many of these early studies were limited to post-mortem histological techniques due to the LC’s small size and location deep in the brainstem. Thus, there is a growing interest in utilizing in vivo imaging of the LC as a predictor of preclinical neurodegenerative processes and biomarker of disease progression. Simultaneously, neuroimaging in animal models of neurodegenerative disease holds promise for identifying early alterations to LC circuits, but has thus far been underutilized. While still in its infancy, a handful of studies have reported effects of single gene mutations and pathology on LC function in disease using various neuroimaging techniques. Furthermore, combining imaging and optogenetics or chemogenetics allows for interrogation of network connectivity in response to changes in LC activity. The purpose of this article is twofold: (1) to review what magnetic resonance imaging (MRI) and positron emission tomography (PET) have revealed about LC dysfunction in neurodegenerative disease and its potential as a biomarker in humans, and (2) to explore how animal models can be used to test hypotheses derived from clinical data and establish a mechanistic framework to inform LC-focused therapeutic interventions to alleviate symptoms and impede disease progression.

Associations of quantitative susceptibility mapping with Alzheimer's disease clinical and imaging markers

Altered iron metabolism has been hypothesized to be associated with Alzheimer’s disease pathology, and prior work has shown associations between iron load and beta amyloid plaques. Quantitative susceptibility mapping (QSM) is a recently popularized MR technique to infer local tissue susceptibility secondary to the presence of iron as well as other minerals. Greater QSM values imply greater iron concentration in tissue. QSM has been used to study relationships between cerebral iron load and established markers of Alzheimer’s disease, however relationships remain unclear. In this work we study QSM signal characteristics and associations between susceptibility measured on QSM and established clinical and imaging markers of Alzheimer’s disease. The study included 421 participants (234 male, median age 70 years, range 34–97 years) from the Mayo Clinic Study of Aging and Alzheimer’s Disease Research Center; 296 (70%) had a diagnosis of cognitively unimpaired, 69 (16%) mild cognitive impairment, and 56 (13%) amnestic dementia. All participants had multi-echo gradient recalled echo imaging, PiB amyloid PET, and Tauvid tau PET. Variance components analysis showed that variation in cortical susceptibility across participants was low. Linear regression models were fit to assess associations with regional susceptibility. Expected increases in susceptibility were found with older age and cognitive impairment in the deep and inferior gray nuclei (pallidum, putamen, substantia nigra, subthalamic nucleus) (betas: 0.0017 to 0.0053 ppm for a 10 year increase in age, p = 0.03 to < 0.001; betas: 0.0021 to 0.0058 ppm for a 5 point decrease in Short Test of Mental Status, p = 0.003 to p < 0.001). Effect sizes in cortical regions were smaller, and the age associations were generally negative. Higher susceptibility was significantly associated with higher amyloid PET SUVR in the pallidum and putamen (betas: 0.0029 and 0.0012 ppm for a 20% increase in amyloid PET, p = 0.05 and 0.02, respectively), higher tau PET in the basal ganglia with the largest effect size in the pallidum (0.0082 ppm for a 20% increase in tau PET, p < 0.001), and with lower cortical gray matter volume in the medial temporal lobe (0.0006 ppm for a 20% decrease in volume, p = 0.03). Overall, these findings suggest that susceptibility in the deep and inferior gray nuclei, particularly the pallidum and putamen, may be a marker of cognitive decline, amyloid deposition, and off-target binding of the tau ligand. Although iron has been demonstrated in amyloid plaques and in association with neurodegeneration, it is of insufficient quantity to be reliably detected in the cortex using this implementation of QSM.

Interrelations of Alzheimer´s disease candidate biomarkers neurogranin, fatty acid-binding protein 3 and ferritin to neurodegeneration and neuroinflammation

There is growing evidence that promising biomarkers of inflammation in Alzheimer´s disease (AD) and other neurodegenerative diseases correlate strongest to levels of tau or neurofilament, indicating an inflammatory response to neuronal damage or death. To test this hypothesis, we investigated three AD candidate markers (ferritin, fatty acid binding protein 3 (FABP-3), and neurogranin) in interrelation to established AD and inflammatory protein markers. We further aimed to determine if such interrelations would be evident in pathological subjects only or also under non-pathological circumstances. Cerebrospinal fluid levels of the three proteins were quantified in samples from the University Clinic of Bonn (UKB) Department of Neurodegenerative Diseases & Geriatric Psychiatry, Germany. Data were analyzed based on clinical or biomarker-defined stratification of subjects with adjustment for covariates age, sex, and APOE status. Levels of ferritin, FABP-3 and neurogranin were elevated in subjects with pathological levels of t-tau independent of beta-amyloid status. The three markers correlated with each other, tau isoforms, age, and those inflammatory markers previously described as related to neurodegeneration, predominantly sTREM2, macrophage migration inhibitory factor, soluble vascular endothelial growth factor receptor, soluble vascular cell adhesion molecule 1 (sVCAM-1), and C1q. These interrelations existed in subjects with pathological and sub-pathological tau levels, in particular for FABP-3 and neurogranin. Relations to ferritin were independent of absolute levels of tau, too, but showed differing trajectories between pathological and non-pathological subjects. A specific set of inflammatory markers is highly related to markers of neuronal damage such as tau, neurogranin, or FABP-3. These proteins could be used as readouts of the inflammatory response during the neurodegeneration phase of AD.

Quantitative Study of the Changes in Cerebral Blood Flow and Iron Deposition During Progression of Alzheimer's Disease

BACKGROUND

Advanced Alzheimer's disease (AD) has no effective treatment, and identifying early diagnosis markers can provide a time window for treatment.

OBJECTIVE

To quantify the changes in cerebral blood flow (CBF) and iron deposition during progression of AD.

METHODS

94 subjects underwent brain imaging on a 3.0-T MRI scanner with techniques of three-dimensional arterial spin labeling (3D-ASL) and quantitative susceptibility mapping (QSM). The subjects included 22 patients with probable AD, 22 patients with mild cognitive impairment (MCI), 25 patients with subjective cognitive decline (SCD), and 25 normal controls (NC). The CBF and QSM values were obtained using a standardized brain region method based on the Brainnetome Atlas. The differences in CBF and QSM values were analyzed between and within groups using variance analysis and correlation analysis.

RESULTS

CBF and QSM identified several abnormal brain regions of interest (ROIs) at different stages of AD (p < 0.05). Regionally, the CBF values in several ROIs of the AD and MCI subjects were lower than for NC subjects (p < 0.001). Higher QSM values were observed in the globus pallidus. The CBF and QSM values in multiple ROI were negatively correlated, while the putamen was the common ROI of the three study groups (p < 0.05). The CBF and QSM values in hippocampus were cross-correlated with scale scores during the progression of AD (p < 0.05).

CONCLUSION

Iron deposition in the basal ganglia and reduction in blood perfusion in multiple regions existed during the progression of AD. The QSM values in putamen can be used as an imaging biomarker for early diagnosis of AD.