The systemic iron-regulatory proteins hepcidin and ferroportin are reduced in the brain in Alzheimer's disease

Ferroptosis: A new strategy for targeting Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a complex pathogenesis, which involves the formation of amyloid plaques and neurofibrillary tangles. Many recent studies have revealed a close association between ferroptosis and the pathogenesis of AD. Factors such as ferroptosis-associated iron overload, lipid peroxidation, disturbances in redox homeostasis, and accumulation of reactive oxygen species have been found to contribute to the pathological progression of AD. In this review, we explore the mechanisms underlying ferroptosis, describe the link between ferroptosis and AD, and examine the reported efficacy of ferroptosis inhibitors in treating AD. Finally, we discuss the potential challenges to ferroptosis inhibitors use in the clinic, enabling their faster use in clinical treatment.

Excitotoxicity, Oxytosis/Ferroptosis, and Neurodegeneration: Emerging Insights into Mitochondrial Mechanisms

Mitochondrial dysfunction plays a pivotal role in the development of age-related diseases, particularly neurodegenerative disorders. The etiology of mitochondrial dysfunction involves a multitude of factors that remain elusive. This review centers on elucidating the role(s) of excitotoxicity, oxytosis/ferroptosis and neurodegeneration within the context of mitochondrial bioenergetics, biogenesis, mitophagy and oxidative stress and explores their intricate interplay in the pathogenesis of neurodegenerative diseases. The effective coordination of mitochondrial turnover processes, notably mitophagy and biogenesis, is assumed to be critically important for cellular resilience and longevity. However, the age-associated decrease in mitophagy impedes the elimination of dysfunctional mitochondria, consequently impairing mitochondrial biogenesis. This deleterious cascade results in the accumulation of damaged mitochondria and deterioration of cellular functions. Both excitotoxicity and oxytosis/ferroptosis have been demonstrated to contribute significantly to the pathophysiology of neurodegenerative diseases, including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's Disease (HD), Amyotrophic Lateral Sclerosis (ALS) and Multiple Sclerosis (MS). Excitotoxicity, characterized by excessive glutamate signaling, initiates a cascade of events involving calcium dysregulation, energy depletion, and oxidative stress and is intricately linked to mitochondrial dysfunction. Furthermore, emerging concepts surrounding oxytosis/ferroptosis underscore the importance of iron-dependent lipid peroxidation and mitochondrial engagement in the pathogenesis of neurodegeneration. This review not only discusses the individual contributions of excitotoxicity and ferroptosis but also emphasizes their convergence with mitochondrial dysfunction, a key driver of neurodegenerative diseases. Understanding the intricate crosstalk between excitotoxicity, oxytosis/ferroptosis, and mitochondrial dysfunction holds potential to pave the way for mitochondrion-targeted therapeutic strategies. Such strategies, with a focus on bioenergetics, biogenesis, mitophagy, and oxidative stress, emerge as promising avenues for therapeutic intervention.

A critical appraisal of ferroptosis in Alzheimer's and Parkinson's disease: new insights into emerging mechanisms and therapeutic targets

Neurodegenerative diseases represent a pressing global health challenge, and the identification of novel mechanisms underlying their pathogenesis is of utmost importance. Ferroptosis, a non-apoptotic form of regulated cell death characterized by iron-dependent lipid peroxidation, has emerged as a pivotal player in the pathogenesis of neurodegenerative diseases. This review delves into the discovery of ferroptosis, the critical players involved, and their intricate role in the underlying mechanisms of neurodegeneration, with an emphasis on Alzheimer's and Parkinson's diseases. We critically appraise unsolved mechanistic links involved in the initiation and propagation of ferroptosis, such as a signaling cascade resulting in the de-repression of lipoxygenase translation and the role played by mitochondrial voltage-dependent anionic channels in iron homeostasis. Particular attention is given to the dual role of heme oxygenase in ferroptosis, which may be linked to the non-specific activity of P450 reductase in the endoplasmic reticulum. Despite the limited knowledge of ferroptosis initiation and progression in neurodegeneration, Nrf2/Bach1 target genes have emerged as crucial defenders in anti-ferroptotic pathways. The activation of Nrf2 and the inhibition of Bach1 can counteract ferroptosis and present a promising avenue for future therapeutic interventions targeting ferroptosis in neurodegenerative diseases.

Exploring Potential Mechanisms Accounting for Iron Accumulation in the Central Nervous System of Patients with Alzheimer's Disease

Elevated levels of iron occur in both cortical and subcortical regions of the CNS in patients with Alzheimer's disease. This accumulation is present early in the disease process as well as in more advanced stages. The factors potentially accounting for this increase are numerous, including: (1) Cells increase their uptake of iron and reduce their export of iron, as iron becomes sequestered (trapped within the lysosome, bound to amyloid β or tau, etc.); (2) metabolic disturbances, such as insulin resistance and mitochondrial dysfunction, disrupt cellular iron homeostasis; (3) inflammation, glutamate excitotoxicity, or other pathological disturbances (loss of neuronal interconnections, soluble amyloid β, etc.) trigger cells to acquire iron; and (4) following neurodegeneration, iron becomes trapped within microglia. Some of these mechanisms are also present in other neurological disorders and can also begin early in the disease course, indicating that iron accumulation is a relatively common event in neurological conditions. In response to pathogenic processes, the directed cellular efforts that contribute to iron buildup reflect the importance of correcting a functional iron deficiency to support essential biochemical processes. In other words, cells prioritize correcting an insufficiency of available iron while tolerating deposited iron. An analysis of the mechanisms accounting for iron accumulation in Alzheimer's disease, and in other relevant neurological conditions, is put forward.

Transporters, Ion Channels, and Junctional Proteins in Choroid Plexus Epithelial Cells

The choroid plexus (CP) plays significant roles in secreting cerebrospinal fluid (CSF) and forming circadian rhythms. A monolayer of epithelial cells with tight and adherens junctions of CP forms the blood-CSF barrier to control the movement of substances between the blood and ventricles, as microvessels in the stroma of CP have fenestrations in endothelial cells. CP epithelial cells are equipped with several kinds of transporters and ion channels to transport nutrient substances and secrete CSF. In addition, junctional components also contribute to CSF production as well as blood-CSF barrier formation. However, it remains unclear how junctional components as well as transporters and ion channels contribute to the pathogenesis of neurodegenerative disorders. In this manuscript, recent findings regarding the distribution and significance of transporters, ion channels, and junctional proteins in CP epithelial cells are introduced, and how changes in expression of their epithelial proteins contribute to the pathophysiology of brain disorders are reviewed.

Iron homeostasis and post-hemorrhagic hydrocephalus: a review

Iron physiology is regulated by a complex interplay of extracellular transport systems, coordinated transcriptional responses, and iron efflux mechanisms. Dysregulation of iron metabolism can result in defects in myelination, neurotransmitter synthesis, and neuronal maturation. In neonates, germinal matrix-intraventricular hemorrhage (GMH-IVH) causes iron overload as a result of blood breakdown in the ventricles and brain parenchyma which can lead to post-hemorrhagic hydrocephalus (PHH). However, the precise mechanisms by which GMH-IVH results in PHH remain elusive. Understanding the molecular determinants of iron homeostasis in the developing brain may lead to improved therapies. This manuscript reviews the various roles iron has in brain development, characterizes our understanding of iron transport in the developing brain, and describes potential mechanisms by which iron overload may cause PHH and brain injury. We also review novel preclinical treatments for IVH that specifically target iron. Understanding iron handling within the brain and central nervous system may provide a basis for preventative, targeted treatments for iron-mediated pathogenesis of GMH-IVH and PHH.

Hepcidin deficiency impairs hippocampal neurogenesis and mediates brain atrophy and memory decline in mice

BACKGROUND

Hepcidin is the master regulator of iron homeostasis. Hepcidin downregulation has been demonstrated in the brains of Alzheimer's disease (AD) patients. However, the mechanism underlying the role of hepcidin downregulation in cognitive impairment has not been elucidated.

METHODS

In the present study, we generated GFAP-Cre-mediated hepcidin conditional knockout mice (HampGFAP cKO) to explore the effect of hepcidin deficiency on hippocampal structure and neurocognition.

RESULTS

We found that the HampGFAP cKO mice developed AD-like brain atrophy and memory deficits. In particular, the weight of the hippocampus and the number of granule neurons in the dentate gyrus were significantly reduced. Further investigation demonstrated that the morphological change in the hippocampus of HampGFAP cKO mice was attributed to impaired neurogenesis caused by decreased proliferation of neural stem cells. Regarding the molecular mechanism, increased iron content after depletion of hepcidin followed by an elevated level of the inflammatory factor tumor necrosis factor-α accounted for the impairment of hippocampal neurogenesis in HampGFAP cKO mice. These observations were further verified in GFAP promoter-driven hepcidin knockdown mice and in Nestin-Cre-mediated hepcidin conditional knockout mice.

CONCLUSIONS

The present findings demonstrated a critical role for hepcidin in hippocampal neurogenesis and validated the importance of iron and associated inflammatory cytokines as key modulators of neurodevelopment, providing insights into the potential pathogenesis of cognitive dysfunction and related treatments.

Aging-Related Protein Alterations in the Brain

Aging is an intrinsic aspect of an organism's life cycle and is characterized by progressive physiological decline and increased susceptibility to mortality. Many age-associated disorders, including neurological disorders, are most commonly linked with the aging process, such as Alzheimer's disease (AD). This review aims to provide a comprehensive overview of the effects of aging and AD on the molecular pathways and levels of different proteins in the brain, including metalloproteins, neurotrophic factors, amyloid proteins, and tau proteins. AD is caused by the aggregation of amyloid proteins in the brain. Factors such as metal ions, protein ligands, and the oligomerization state of amyloid precursor protein significantly influence the proteolytic processing of amyloid-β protein precursor (AβPP). Tau, a disordered cytosolic protein, serves as the principal microtubule-associated protein in mature neurons. AD patients exhibit decreased levels of nerve growth factor within their nervous systems and cerebrospinal fluid. Furthermore, a significant increase in brain-derived neurotrophic factor resulting from the neuroprotective effect of glial cell line-derived neurotrophic factor suggests that the synergistic action of these proteins plays a role in inhibiting neuronal degeneration and atrophy. The mechanism through which Aβ and AβPP govern Cu2+ transport and their influence on Cu2+ and other metal ion pools requires elucidation in future studies. A comprehensive understanding of the influence of aging and AD on molecular pathways and varying protein levels may hold the potential for the development of novel diagnostic and therapeutic methods for the treatment of AD.

Molecular mechanism and potential therapeutic targets of necroptosis and ferroptosis in Alzheimer's disease

Alzheimer's disease (AD), a neurodegenerative condition, is defined by neurofibrillary tangles, amyloid plaques, and gradual cognitive decline. Regardless of the advances in understanding AD's pathogenesis and progression, its causes are still contested, and there are currently no efficient therapies for the illness. The post-mortem analyses revealed widespread neuronal loss in multiple brain regions in AD, evidenced by a decrease in neuronal density and correlated with the disease's progression and cognitive deterioration. AD's neurodegeneration is complicated, and different types of neuronal cell death, alone or in combination, play crucial roles in this process. Recently, the involvement of non-apoptotic programmed cell death in the neurodegenerative mechanisms of AD has received a lot of attention. Aberrant activation of necroptosis and ferroptosis, two newly discovered forms of regulated non-apoptotic cell death, is thought to contribute to neuronal cell death in AD. In this review, we first address the main features of necroptosis and ferroptosis, cellular signaling cascades, and the mechanisms involved in AD pathology. Then, we discuss the latest therapies targeting necroptosis and ferroptosis in AD animal/cell models and human research to provide vital information for AD treatment.

Iron and Targeted Iron Therapy in Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease worldwide. β-amyloid plaque (Aβ) deposition and hyperphosphorylated tau, as well as dysregulated energy metabolism in the brain, are key factors in the progression of AD. Many studies have observed abnormal iron accumulation in different regions of the AD brain, which is closely correlated with the clinical symptoms of AD; therefore, understanding the role of brain iron accumulation in the major pathological aspects of AD is critical for its treatment. This review discusses the main mechanisms and recent advances in the involvement of iron in the above pathological processes, including in iron-induced oxidative stress-dependent and non-dependent directions, summarizes the hypothesis that the iron-induced dysregulation of energy metabolism may be an initiating factor for AD, based on the available evidence, and further discusses the therapeutic perspectives of targeting iron.

HMGB1 induces hepcidin upregulation in astrocytes and causes an acute iron surge and subsequent ferroptosis in the postischemic brain

Dysregulation of brain iron levels causes functional disturbances and damages neurons. Hepcidin (a peptide hormone) plays a principal role in regulating intracellular iron levels by modulating ferroportin (FPN, the only known iron exporter) through triggering its internalization and lysosomal degradation. We observed a significant and rapid iron surge in the cortices of ischemic hemispheres at 3 h after cerebral ischemia (middle cerebral artery occlusion, MCAO) that was maintained until 4 d post-MCAO. We showed upregulation of hepcidin expression in the brain as early as 3 h post-MCAO, mainly in astrocytes, and significant hepcidin accumulation in serum from 6 h post-MCAO, and these inductions were maintained for 1 day and 7 days, respectively. High mobility group box 1 (HMGB1), a prototypic danger-associated molecular pattern, accumulates markedly after transient MCAO and plays critical roles in damage aggravation via its proinflammatory effects. Here, we demonstrated that treatment with recombinant HMGB1 stimulated astrocytes to induce hepcidin expression in a TLR4- and CXCR4-dependent manner. Furthermore, hepcidin-mediated intracellular iron accumulation in neurons was confirmed by an experiment using N-methyl-D-aspartate (NMDA)-conditioned medium-treated primary astrocytes and fresh primary cortical neurons treated with hepcidin-containing astrocyte-conditioned medium. Moreover, HMGB1-mediated local hepcidin upregulation and subsequent local iron surge were found to cause ferroptosis in the postischemic brain, which was suppressed by the functional blocking of HMGB1 using intranasally administered HMGB1 A box or anti-HMGB1 antibody. These findings show that HMGB1 serves as a ferroptosis inducer by upregulating hepcidin in astrocytes and thus aggravates acute damage in the postischemic brain.

The Azalea Hypothesis of Alzheimer Disease: A Functional Iron Deficiency Promotes Neurodegeneration

Chlorosis in azaleas is characterized by an interveinal yellowing of leaves that is typically caused by a deficiency of iron. This condition is usually due to the inability of cells to properly acquire iron as a consequence of unfavorable conditions, such as an elevated pH, rather than insufficient iron levels. The causes and effects of chlorosis were found to have similarities with those pertaining to a recently presented hypothesis that describes a pathogenic process in Alzheimer disease. This hypothesis states that iron becomes sequestered (e.g., by amyloid β and tau), causing a functional deficiency of iron that disrupts biochemical processes leading to neurodegeneration. Additional mechanisms that contribute to iron becoming unavailable include iron-containing structures not undergoing proper recycling (e.g., disrupted mitophagy and altered ferritinophagy) and failure to successfully translocate iron from one compartment to another (e.g., due to impaired lysosomal acidification). Other contributors to a functional deficiency of iron in patients with Alzheimer disease include altered metabolism of heme or altered production of iron-containing proteins and their partners (e.g., subunits, upstream proteins). A review of the evidence supporting this hypothesis is presented. Also, parallels between the mechanisms underlying a functional iron-deficient state in Alzheimer disease and those occurring for chlorosis in plants are discussed. Finally, a model describing the generation of a functional iron deficiency in Alzheimer disease is put forward.

Pharmacological Inhibition of Ferroptosis as a Therapeutic Target for Neurodegenerative Diseases and Strokes

Emerging evidence suggests that ferroptosis, a unique regulated cell death modality that is morphologically and mechanistically different from other forms of cell death, plays a vital role in the pathophysiological process of neurodegenerative diseases, and strokes. Accumulating evidence supports ferroptosis as a critical factor of neurodegenerative diseases and strokes, and pharmacological inhibition of ferroptosis as a therapeutic target for these diseases. In this review article, the core mechanisms of ferroptosis are overviewed and the roles of ferroptosis in neurodegenerative diseases and strokes are described. Finally, the emerging findings in treating neurodegenerative diseases and strokes through pharmacological inhibition of ferroptosis are described. This review demonstrates that pharmacological inhibition of ferroptosis by bioactive small-molecule compounds (ferroptosis inhibitors) could be effective for treatments of these diseases, and highlights a potential promising therapeutic avenue that could be used to prevent neurodegenerative diseases and strokes. This review article will shed light on developing novel therapeutic regimens by pharmacological inhibition of ferroptosis to slow down the progression of these diseases in the future.

Ferroportin1 in the brain

Despite years of research, it remains unclear why certain brain regions of patients with neurodegenerative diseases (NDs) have abnormally high levels of iron, although it has long been suggested that disrupted expression of iron-metabolizing proteins due to genetic or non-genetic factors is responsible for the enhancement in brain iron contents. In addition to the increased expression of cell-iron importers lactoferrin (lactotransferrin) receptor (LfR) in Parkinson's disease (PD) and melanotransferrin (p97) in Alzheimer's disease (AD), some investigations have suggested that cell-iron exporter ferroportin 1 (Fpn1) may be also associated with the elevated iron observed in the brain. The decreased expression of Fpn1 and the resulting decrease in the amount of iron excreted from brain cells has been thought to be able to enhance iron levels in the brain in AD, PD and other NDs. Cumulative results also suggest that the reduction of Fpn1 can be induced by hepcidin-dependent and -independent pathways. In this article, we discuss the current understanding of Fpn1 expression in the brain and cell lines of rats, mice and humans, with emphasis on the potential involvement of reduced Fpn1 in brain iron enhancement in patients with AD, PD and other NDs.

The Role of Iron Metabolism, Lipid Metabolism, and Redox Homeostasis in Alzheimer's Disease: from the Perspective of Ferroptosis

In the development of Alzheimer's disease (AD), cell death is common. Novel cell death form-ferroptosis is discovered in recent years. Ferroptosis is an iron-regulated programmed cell death mechanism and has been identified in AD clinical samples. Typical characteristics of ferroptosis involve the specific changes in cell morphology, iron-dependent aggregation of reactive oxygen species (ROS) and lipid peroxides, loss of glutathione (GSH), inactivation of glutathione peroxidase 4 (GPX4), and a unique group of regulatory genes. Increasing evidence demonstrates that ferroptosis may be associated with neurological dysfunction in AD. However, the underlying mechanisms have not been fully elucidated. This article reviews the potential role of ferroptosis in AD, the involvement of ferroptosis in the pathological progression of AD through the mechanisms of iron metabolism, lipid metabolism, and redox homeostasis, as well as a range of potential therapies targeting ferroptosis for AD. Intervention strategies based on ferroptosis are promising for Alzheimer's disease treatment at present, but further researches are still needed.

Revisiting the intersection of microglial activation and neuroinflammation in Alzheimer's disease from the perspective of ferroptosis

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by chronic neuroinflammation with amyloid beta-protein deposition and hyperphosphorylated tau protein. The typical clinical manifestation of AD is progressive memory impairment, and AD is considered a multifactorial disease with various etiologies (genetic factors, aging, lifestyle, etc.) and complicated pathophysiological processes. Previous research identified that neuroinflammation and typical microglial activation are significant mechanisms underlying AD, resulting in dysfunction of the nervous system and progression of the disease. Ferroptosis is a novel modality involved in this process. As an iron-dependent form of cell death, ferroptosis, characterized by iron accumulation, lipid peroxidation, and irreversible plasma membrane disruption, promotes AD by accelerating neuronal dysfunction and abnormal microglial activation. In this case, disturbances in brain iron homeostasis and neuronal ferroptosis aggravate neuroinflammation and lead to the abnormal activation of microglia. Abnormally activated microglia release various pro-inflammatory factors that aggravate the dysregulation of iron homeostasis and neuroinflammation, forming a vicious cycle. In this review, we first introduce ferroptosis, microglia, AD, and their relationship. Second, we discuss the nonnegligible role of ferroptosis in the abnormal microglial activation involved in the chronic neuroinflammation of AD to provide new ideas for the identification of potential therapeutic targets for AD.

Recent Development in the Understanding of Molecular and Cellular Mechanisms Underlying the Etiopathogenesis of Alzheimer's Disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder that leads to dementia and patient death. AD is characterized by intracellular neurofibrillary tangles, extracellular amyloid beta (Aβ) plaque deposition, and neurodegeneration. Diverse alterations have been associated with AD progression, including genetic mutations, neuroinflammation, blood-brain barrier (BBB) impairment, mitochondrial dysfunction, oxidative stress, and metal ion imbalance.Additionally, recent studies have shown an association between altered heme metabolism and AD. Unfortunately, decades of research and drug development have not produced any effective treatments for AD. Therefore, understanding the cellular and molecular mechanisms underlying AD pathology and identifying potential therapeutic targets are crucial for AD drug development. This review discusses the most common alterations associated with AD and promising therapeutic targets for AD drug discovery. Furthermore, it highlights the role of heme in AD development and summarizes mathematical models of AD, including a stochastic mathematical model of AD and mathematical models of the effect of Aβ on AD. We also summarize the potential treatment strategies that these models can offer in clinical trials.

Distribution of Copper, Iron, and Zinc in the Retina, Hippocampus, and Cortex of the Transgenic APP/PS1 Mouse Model of Alzheimer's Disease

A mis-metabolism of transition metals (i.e., copper, iron, and zinc) in the brain has been recognised as a precursor event for aggregation of Amyloid-β plaques, a pathological hallmark of Alzheimer's disease (AD). However, imaging cerebral transition metals in vivo can be extremely challenging. As the retina is a known accessible extension of the central nervous system, we examined whether changes in the hippocampus and cortex metal load are also mirrored in the retina. Laser ablation inductively coupled plasma-mass spectrometry (LA-ICP-MS) was used to visualise and quantify the anatomical distribution and load of Cu, Fe, and Zn in the hippocampus, cortex, and retina of 9-month-old Amyloid Precursor Protein/Presenilin 1 (APP/PS1, n = 10) and Wild Type (WT, n = 10) mice. Our results show a similar metal load trend between the retina and the brain, with the WT mice displaying significantly higher concentrations of Cu, Fe, and Zn in the hippocampus (p < 0.05, p < 0.0001, p < 0.01), cortex (p < 0.05, p = 0.18, p < 0.0001) and the retina (p < 0.001, p = 0.01, p < 0.01) compared with the APP/PS1 mice. Our findings demonstrate that dysfunction of the cerebral transition metals in AD is also extended to the retina. This could lay the groundwork for future studies on the assessment of transition metal load in the retina in the context of early AD.

Exploring Whether Iron Sequestration within the CNS of Patients with Alzheimer’s Disease Causes a Functional Iron Deficiency That Advances Neurodegeneration

The involvement of iron in the pathogenesis of Alzheimer’s disease (AD) may be multifaceted. Besides potentially inducing oxidative damage, the bioavailability of iron may be limited within the central nervous system, creating a functionally iron-deficient state. By comparing staining results from baseline and modified iron histochemical protocols, iron was found to be more tightly bound within cortical sections from patients with high levels of AD pathology compared to subjects with a diagnosis of something other than AD. To begin examining whether the bound iron could cause a functional iron deficiency, a protein-coding gene expression dataset of initial, middle, and advanced stages of AD from olfactory bulb tissue was analyzed for iron-related processes with an emphasis on anemia-related changes in initial AD to capture early pathogenic events. Indeed, anemia-related processes had statistically significant alterations, and the significance of these changes exceeded those for AD-related processes. Other changes in patients with initial AD included the expressions of transcripts with iron-responsive elements and for genes encoding proteins for iron transport and mitochondrial-related processes. In the latter category, there was a decreased expression for the gene encoding pitrilysin metallopeptidase 1 (PITRM1). Other studies have shown that PITRM1 has an altered activity in patients with AD and is associated with pathological changes in this disease. Analysis of a gene expression dataset from PITRM1-deficient or sufficient organoids also revealed statistically significant changes in anemia-like processes. These findings, together with supporting evidence from the literature, raise the possibility that a pathogenic mechanism of AD could be a functional deficiency of iron contributing to neurodegeneration.

The effects of age, genotype and diet on hippocampal subfield iron dysregulation and Alzheimer's disease biomarkers in an ApoE mouse model

Current theories regarding accumulation of Alzheimer's disease-related deposits of abnormal intra- and extracellular proteins include reactions to inflammation and mitochondrial dysfunction. In this study, we explored whether age, genotype and inflammation via diet have a greater effect on dysregulatory protein accumulation in any particular subfield of the hippocampus. We stained for ferritin, ferroportin, hyperphosphorylated tau and β-amyloid proteins in the hippocampal region of Apolipoprotein E2 (ApoE2), ApoE3 or ApoE4 mice fed a control diet or a hypothesized inflammation-inducing methionine diet and euthanized at 3, 6, 9 or 12 months. We analysed stains based on hippocampal subfield and compared the protein accumulation levels within each group. We found significantly decreased ferritin expression in ApoE4 mice in the CA1 and Hi regions and decreased ferroportin expression in ApoE4 mice in the Hi region. There was also a significant effect on hyperphosphorylated tau protein levels based upon a given mouse genotype and diet interaction. Additionally, there were nonsignificant trends in each hippocampal subfield of increasing ferroportin and hyperphosphorylated tau after 6 months of age and decreasing β-amyloid and ferritin with age. This study identified that there are changes in iron regulatory molecules based on genotype in the Hi and CA1 regions. Our findings also suggest a diet-genotype interaction, which affects levels of specific Alzheimer's disease biomarkers in the hippocampus. Additionally, we identified a trend toward increased ability to clear β-amyloid and decreased ability to clear hyperphosphorylated tau with age in all subfields, in addition to evidence of increasing iron load with time.

Overview of the blood biomarkers in Alzheimer's disease: Promises and challenges

The increasing number of people with advanced Alzheimer's disease (AD) represents a significant psychological and financial cost to the world population. Accurate detection of the earliest phase of preclinical AD is of major importance for the success of preventive and therapeutic strategies (Cullen et al., 2021). Advances in analytical techniques have been essential for the development of sensitive, specific and reliable diagnostic tests for AD biomarkers in biological fluids (cerebrospinal fluid and blood). Blood biomarkers hold promising potential for early and minimally invasive detection of AD, but also for differential diagnosis of dementia and for monitoring the course of the disease. The aim of this review is to provide an overview of current blood biomarkers of AD, from tau proteins and amyloid peptides to biomarkers of neuronal degeneration and inflammation, reactive and metabolic factors. We thus discuss the informative value of currently candidate blood biomarkers and their potential to be integrated into clinical practice for the management of AD in the near future.

Amelioration of White Matter Injury Through Mitigating Ferroptosis Following Hepcidin Treatment After Spinal Cord Injury

Spinal cord injury (SCI) usually introduces permanent or long-lasting neurological impairments. Maintaining the integrity of the limited number of white matter bundles (5-10%) preserves wholly or partially locomotor following SCI. Considering that the basic structure of white matter bundles is axon wrapped by oligodendrocytes, promoting oligodendrocytes survival might be a feasible strategy for reducing white matter injury (WMI) after SCI. Oligodendrocytes are rich in unsaturated fatty acid and susceptible to ferroptosis-induced damage. Hence, exploring method to reduce ferroptosis is supposed to expedite oligodendrocytes survival, thereafter mitigating WMI to facilitate functional recovery post-SCI. Here, the results indicated the administration of hepcidin reduced iron accumulation to promote oligodendrocytes survival and to decrease spinal cord atrophy, therefore facilitating functional recovery. Then, the WMI was evidently decreased owing to attenuating ferroptosis. Subsequently, the results revealed that the expression of divalent metal transporter 1 (DMT1) and transferrin receptor (TfR) was expressed in CC1⁺ cells. The expression level of DMT1 and TfR was significantly increased, while this phenomenon was obviously neutralized with the administration of hepcidin in the epicenter of spinal cord after SCI. Afterward, the application of hepcidin downregulated reactive oxygen species (ROS) overload, which was evidently increased with the treatment of 20 μM FeCl₃, therefore increasing cell viability and reducing lactate dehydrogenase (LDH) activity through downregulating the expression of DMT1 and TfR to inhibit ferroptosis in oligodendrocyte progenitor cells (OPCs). The present study provides evidence that the application of hepcidin facilitates oligodendrocytes survival to alleviate WMI via reducing the expression of DMT1 and TfR.

Aducanumab-Hope or Disappointment for Alzheimer's Disease

In June 2021, the world was informed about a new drug for Alzheimer's disease approved by the FDA. Aducanumab (BIIB037, ADU), being a monoclonal antibody IgG1, is the newest AD treatment. The activity of the drug is targeted towards amyloid β, which is considered one of the main causes of Alzheimer's disease. Clinical trials have revealed time- and dose-dependent activity towards Aβ reduction, as well as cognition improvement. Biogen, the company responsible for conducting research and introducing the drug to the market, presents the drug as a solution to cognitive impairment, but its limitations, costs, and side effects are controversial. The framework of the paper focuses on the mechanism of aducanumab's action along with the positive and negative sides of the therapy. The review presents the basis of the amyloid hypothesis that is the cornerstone of therapy, as well as the latest information about aducanumab, its mechanism of action, and the possibility of the use of the drug.

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.

Multi-Target Neuroprotection of Thiazolidinediones on Alzheimer's Disease via Neuroinflammation and Ferroptosis

Alzheimer's disease (AD) is the main cause of dementia in older age. The prevalence of AD is growing worldwide, causing a tremendous burden to societies and families. Due to the complexity of its pathogenesis, the current treatment of AD is not satisfactory, and drugs acting on a single target may not prevent AD progression. This review summarizes the multi-target pharmacological effects of thiazolidinediones (TZDs) on AD. TZDs act as peroxisome proliferator-activated receptor gamma (PPARγ) agonists and long-chain acyl-CoA synthetase family member 4 (ACSL4) inhibitors. TZDs ameliorated neuroinflammation and ferroptosis in preclinical models of AD. Here, we discussed recent findings from clinical trials of pioglitazone in the treatment of AD, ischemic stroke, and atherosclerosis. We also dissected the major limitations in the clinical application of pioglitazone and explained the potential benefit of pioglitazone in AD. We recommend the use of pioglitazone to prevent cognitive decline and lower AD risk in a specific group of patients.

Hyperbaric oxygen protects HT22 cells and PC12 cells from damage caused by oxygen-glucose deprivation/reperfusion via the inhibition of Nrf2/System Xc-/GPX4 axis-mediated ferroptosis

This study was to investigate the protective effect of hyperbaric oxygen (HBO) on HT22 and PC12 cell damage caused by oxygen-glucose deprivation/reperfusion-induced ferroptosis. A 2-h oxygen-glucose deprivation and 24-h reperfusion model on HT22 and PC12 cells was used to simulate cerebral ischemia-reperfusion injury. Cell viabilities were detected by Cell Counting Kit-8 (CCK-8) method. The levels of reactive oxygen species (ROS) and lipid reactive oxygen species (Lipid ROS) were detected by fluorescent probes Dihydroethidium (DHE) and C11 BODIPY 581/591. Iron Colorimetric Assay Kit, malondialdehyde (MDA) and glutathione (GSH) activity assay kits were used to detect intracellular iron ion, MDA and GSHcontent. Cell ferroptosis-related ultrastructures were visualized using transmission electron microscopy (TEM). Furthermore, PCR and Western blot analyses were used to detect the expressions of ferroptosis-related genes and proteins. After receiving oxygen-glucose deprivation/reperfusion, the viabilities of HT22 and PC12 cells were significantly decreased; ROS, Lipid ROS, iron ions and MDA accumulation occurred in the cells; GSH contents decreased; TEM showed that cells were ruptured and blebbed, mitochondria atrophied and became smaller, mitochondrial ridges were reduced or even disappeared, and apoptotic bodies appeared. And the expressions of Nrf2, SLC7A11 and GPX4 genes were reduced; the expressions of p-Nrf2/Nrf2, xCT and GPX4 proteins were reduced. Notably, these parameters were significantly reversed by HBO, indicating that HBO can protect HT22 cells and PC12 cells from damage caused by oxygen-glucosedeprivation/reperfusion via the inhibition of Nrf2/System Xc-/GPX4 axis-mediated ferroptosis.

Iron metabolism: pathways and proteins in homeostasis

Iron is essential to human survival. The biological role and trafficking of this trace essential inorganic element which is also a potential toxin is constantly being researched and unfolded. Vital for oxygen transport, DNA synthesis, electron transport, neurotransmitter biosynthesis and present in numerous other heme and non-heme enzymes the physiological roles are immense. Understanding the molecules and pathways that regulate this essential element at systemic and cellular levels are of importance in improving therapeutic strategies for iron related disorders. This review highlights the progress in understanding the metabolism and trafficking of iron along with the pathophysiology of iron related disorders.

Iron Deposition in Brain: Does Aging Matter?

The alteration of iron homeostasis related to the aging process is responsible for increased iron levels, potentially leading to oxidative cellular damage. Iron is modulated in the Central Nervous System in a very sensitive manner and an abnormal accumulation of iron in the brain has been proposed as a biomarker of neurodegeneration. However, contrasting results have been presented regarding brain iron accumulation and the potential link with other factors during aging and neurodegeneration. Such uncertainties partly depend on the fact that different techniques can be used to estimate the distribution of iron in the brain, e.g., indirect (e.g., MRI) or direct (post-mortem estimation) approaches. Furthermore, recent evidence suggests that the propensity of brain cells to accumulate excessive iron as a function of aging largely depends on their anatomical location. This review aims to collect the available data on the association between iron concentration in the brain and aging, shedding light on potential mechanisms that may be helpful in the detection of physiological neurodegeneration processes and neurodegenerative diseases such as Alzheimer's disease.

Exposure of metal toxicity in Alzheimer’s disease: An extensive review

Metals serve important roles in the human body, including the maintenance of cell structure and the regulation of gene expression, the antioxidant response, and neurotransmission. High metal uptake in the nervous system is harmful because it can cause oxidative stress, disrupt mitochondrial function, and impair the activity of various enzymes. Metal accumulation can cause lifelong deterioration, including severe neurological problems. There is a strong association between accidental metal exposure and various neurodegenerative disorders, including Alzheimer’s disease (AD), the most common form of dementia that causes degeneration in the aged. Chronic exposure to various metals is a well-known environmental risk factor that has become more widespread due to the rapid pace at which human activities are releasing large amounts of metals into the environment. Consequently, humans are exposed to both biometals and heavy metals, affecting metal homeostasis at molecular and biological levels. This review highlights how these metals affect brain physiology and immunity and their roles in creating harmful proteins such as β-amyloid and tau in AD. In addition, we address findings that confirm the disruption of immune-related pathways as a significant toxicity mechanism through which metals may contribute to AD.

Astrocyte-derived hepcidin controls iron traffic at the blood-brain-barrier via regulating ferroportin 1 of microvascular endothelial cells

Brain iron dysregulation associated with aging is closely related to motor and cognitive impairments in neurodegenerative diseases. The regulation of iron traffic at the blood-brain barrier (BBB) is crucial to maintain brain iron homeostasis. However, the specific mechanism has not been clarified in detail. Using various conditional gene knockout and overexpression mice, as well as cell co-culture of astrocyte and bEND.3 in the transwell, we found that astrocyte hepcidin knockdown increased the expression of ferroportin 1 (FPN1) of brain microvascular endothelial cells (BMVECs), and that it also induced brain iron overload and cognitive decline in mice. Moreover, BMVECs FPN1 knockout decreased iron contents in the cortex and hippocampus. Furthermore, hepcidin regulates the level of FPN1 of BMVECs with conditional gene overexpression in vivo and in vitro. Our results revealed that astrocytes responded to the intracellular high iron level and increased the secretion of hepcidin, which in turn diminished iron uptake at BBB from circulation through directly regulating FPN1 of BMVECs. Our results demonstrate that FPN1 of BMVECs is a gateway for iron transport into the brain from circulation, and the controller of this gateway is hepcidin secreted by astrocyte at its endfeet through physical contact with BMVECs. This regulation is indeed the major checkpoint for iron transport from the blood circulation to the brain. This study delineates the pathway and regulation of iron entry into the brain, providing potential therapeutic targets for iron dysregulation-related neurological diseases.

Expression of antimicrobial host defence peptides in the central nervous system during health and disease

Antimicrobial host defence peptides (HDP) are critical for the first line of defence against bacterial, viral, and fungal pathogens. Over the past decade we have become more aware that, in addition to their antimicrobial roles, they also possess the potent immunomodulatory capacity. This includes chemoattracting immune cells, activating dendritic cells and macrophages, and altering T-cell differentiation. Most examinations of their immunomodulatory roles have focused on tissues in which they are very abundant, such as the intestine and the inflamed skin. However, HDP have now been detected in the brain and the spinal cord during a number of conditions. We propose that their presence in the central nervous system (CNS) during homeostasis, infection, and neurodegenerative disease has the potential to contribute to immunosurveillance, alter host responses and skew developing immunity. Here, we review the evidence for HDP expression and function in the CNS in health and disease. We describe how a wide range of HDP are expressed in the CNS of humans, rodents, birds, and fish, suggesting a conserved role in protecting the brain from pathogens, with evidence of production by resident CNS cells. We highlight differences in methodology used and how this may have resulted in the immunomodulatory roles of HDP being overlooked. Finally, we discuss what HDP expression may mean for CNS immune responses.

Current understanding of the interactions between metal ions and Apolipoprotein E in Alzheimer's disease

Alzheimer's disease (AD), the most common type of dementia in the elderly, is a chronic and progressive neurodegenerative disorder with no effective disease-modifying treatments to date. Studies have shown that an imbalance in brain metal ions, such as zinc, copper, and iron, is closely related to the onset and progression of AD. Many efforts have been made to understand metal-related mechanisms and therapeutic strategies for AD. Emerging evidence suggests that interactions of brain metal ions and apolipoprotein E (ApoE), which is the strongest genetic risk factor for late-onset AD, may be one of the mechanisms for neurodegeneration. Here, we summarize the key points regarding how metal ions and ApoE contribute to the pathogenesis of AD. We further describe the interactions between metal ions and ApoE in the brain and propose that their interactions play an important role in neuropathological alterations and cognitive decline in AD.

Emerging Mechanisms and Targeted Therapy of Ferroptosis in Neurological Diseases and Neuro-oncology

Ferroptosis is a novel type of cell death characterized by iron-dependent lipid peroxidation that involves a variety of biological processes, such as iron metabolism, lipid metabolism, and oxidative stress. A growing body of research suggests that ferroptosis is associated with cancer and neurodegenerative diseases, such as glioblastoma, Alzheimer's disease, Parkinson's disease, and stroke. Building on these findings, we can selectively induce ferroptosis for the treatment of certain cancers, or we can treat neurodegenerative diseases by inhibiting ferroptosis. This review summarizes the relevant advances in ferroptosis, the regulatory mechanisms of ferroptosis, the participation of ferroptosis in brain tumors and neurodegenerative diseases, and the corresponding drug therapies to provide new potential targets for its treatment.

Mechanisms of Ferroptosis and Emerging Links to the Pathology of Neurodegenerative Diseases

Neurodegenerative diseases are a diverse class of diseases attributed to chronic progressive neuronal degeneration and synaptic loss in the brain and/or spinal cord, including Alzheimer’s disease, Parkinson’s disease, Huntington’s disease, amyotrophic lateral sclerosis and multiple sclerosis. The pathogenesis of neurodegenerative diseases is complex and diverse, often involving mitochondrial dysfunction, neuroinflammation, and epigenetic changes. However, the pathogenesis of neurodegenerative diseases has not been fully elucidated. Recently, accumulating evidence revealed that ferroptosis, a newly discovered iron-dependent and lipid peroxidation-driven type of programmed cell death, provides another explanation for the occurrence and progression of neurodegenerative diseases. Here, we provide an overview of the process and regulation mechanisms of ferroptosis, and summarize current research progresses that support the contribution of ferroptosis to the pathogenesis of neurodegenerative diseases. A comprehensive understanding of the emerging roles of ferroptosis in neurodegenerative diseases will shed light on the development of novel therapeutic technologies and strategies for slowing down the progression of these diseases.

Iron Dyshomeostasis and Ferroptosis: A New Alzheimer’s Disease Hypothesis?

Iron plays a crucial role in many physiological processes of the human body, but iron is continuously deposited in the brain as we age. Early studies found iron overload is directly proportional to cognitive decline in Alzheimer’s disease (AD). Amyloid precursor protein (APP) and tau protein, both of which are related to the AD pathogenesis, are associated with brain iron metabolism. A variety of iron metabolism-related proteins have been found to be abnormally expressed in the brains of AD patients and mouse models, resulting in iron deposition and promoting AD progression. Amyloid β (Aβ) and hyperphosphorylated tau, two pathological hallmarks of AD, can also promote iron deposition in the brain, forming a vicious cycle of AD development-iron deposition. Iron deposition and the subsequent ferroptosis has been found to be a potential mechanism underlying neuronal loss in many neurodegenerative diseases. Iron chelators, antioxidants and hepcidin were found useful for treating AD, which represents an important direction for AD treatment research and drug development in the future. The review explored the deep connection between iron dysregulation and AD pathogenesis, discussed the potential of new hypothesis related to iron dyshomeostasis and ferroptosis, and summarized the therapeutics capable of targeting iron, with the expectation to draw more attention of iron dysregulation and corresponding drug development.

Interplay of Ferritin Accumulation and Ferroportin Loss in Ageing Brain: Implication for Protein Aggregation in Down Syndrome Dementia, Alzheimer’s, and Parkinson’s Diseases

Iron accumulates in the ageing brain and in brains with neurodegenerative diseases such as Alzheimer’s disease (AD), Parkinson’s disease (PD), Huntington’s disease (HD), and Down syndrome (DS) dementia. However, the mechanisms of iron deposition and regional selectivity in the brain are ill-understood. The identification of several proteins that are involved in iron homeostasis, transport, and regulation suggests avenues to explore their function in neurodegenerative diseases. To uncover the molecular mechanisms underlying this association, we investigated the distribution and expression of these key iron proteins in brain tissues of patients with AD, DS, PD, and compared them with age-matched controls. Ferritin is an iron storage protein that is deposited in senile plaques in the AD and DS brain, as well as in neuromelanin-containing neurons in the Lewy bodies in PD brain. The transporter of ferrous iron, Divalent metal protein 1 (DMT1), was observed solely in the capillary endothelium and in astrocytes close to the ventricles with unchanged expression in PD. The principal iron transporter, ferroportin, is strikingly reduced in the AD brain compared to age-matched controls. Extensive blood vessel damage in the basal ganglia and deposition of punctate ferritin heavy chain (FTH) and hepcidin were found in the caudate and putamen within striosomes/matrix in both PD and DS brains. We suggest that downregulation of ferroportin could be a key reason for iron mismanagement through disruption of cellular entry and exit pathways of the endothelium. Membrane damage and subsequent impairment of ferroportin and hepcidin causes oxidative stress that contributes to neurodegeneration seen in DS, AD, and in PD subjects. We further propose that a lack of ferritin contributes to neurodegeneration as a consequence of failure to export toxic metals from the cortex in AD/DS and from the substantia nigra and caudate/putamen in PD brain.

Endoplasmic reticulum stress and mitochondrial dysfunctions in metal-induced neurological pathology

Although essential metal ions are required in the body, neurotoxicity occurs when exposed to a concentration of metal that the body cannot accommodate. In the case of non-essential metals which are important in industry, these elements have the property of causing neurotoxicity even at small concentrations. When such neurotoxicity progresses chronically, it can contribute to various neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease. Therefore, research on the relationships between neurotoxicity and metal metabolism are being actively conducted, and some recent research has suggested that the mechanisms of metal-induced neurotoxicity critically involve endoplasmic reticulum (ER) stress and mitochondrial dysfunction. Hence, this mini-review is to summarize some examples of such evidence and raise new questions in attempting to address metal-induced neurotoxicity with ER stress and mitochondria dysfunctions, two important topics for the effects of metals in neurodegenerative diseases. Taken together, to study the molecular programs of integrating ER stress with mitochondrial dysfunction should be an important area of future research for appreciating the mechanisms of as well as developing strategies and targets for metal-induced neurological diseases.

Relation of Serum Hepcidin Levels and Restless Legs Syndrome in Patients Undergoing Peritoneal Dialysis

Introduction: Restless legs syndrome is a common and severe complication in patients undergoing peritoneal dialysis (PD), which seriously affects the life quality and prognosis of patients undergoing PD. Unfortunately, there are still no effective prevention and treatment measures. Serum hepcidin was demonstrated to be related to primary restless legs syndrome (RLS), whereas there are no studies on the relationship between serum hepcidin and RLS in patients undergoing PD. We aimed to evaluate the role and function of serum hepcidin in patients undergoing PD with RLS.

Methods: A total of 51 patients undergoing PD with RLS and 102 age-and gender-matched patients undergoing PD without RLS were included. We collected the clinical data including serum hepcidin of those patients undergoing PD. We scored the severity of RLS according to the International restless leg Syndrome Research Group rating scale (IRLS). We compared the clinical characteristics of the two groups and evaluated the determinant factors of RLS by Logistic regression analysis. In addition, we evaluated the diagnostic value of serum hepcidin in patients undergoing PD with RLS by receiver operating characteristic (ROC) curve. We also analyzed the influencing factors of IRLS by multivariate linear regression analysis.

Results: The duration of PD, serum hepcidin, and calcium were found to be significantly higher in patients undergoing PD with RLS than those patients undergoing PD without RLS (P < 0.001, P < 0.001, and P = 0.002, respectively). The level of hemoglobin, albumin, and RKF were significantly lower in patients undergoing PD with RLS (P = 0.002, P = 0.042, and P < 0.001, respectively). The duration of PD [odds ratio (OR) 1.038, 95% CI: 1.017, 1.060, P < 0.001], hemoglobulin level (OR 0.969, 95% CI: 0.944, 0.995, P = 0.019), calcium level (OR 9.224, 95% CI: 1.261, 67.450, P = 0.029), albumin level (OR 0.835, 95% CI: 0.757, 0.921, P < 0.001), hepcidin level (OR 1.023, 95% CI: 1.009, 1.038, P = 0.001), and RKF (OR 0.65, 95% CI: 0.495, 0.856, P = 0.002) are independent determinant factors of RLS in patients undergoing PD. Multivariate linear regression analysis revealed that, in addition to albumin, they were also independently associated with the severity of RLS.

Conclusion: A significant relation was detected between serum hepcidin level and RLS in patients undergoing PD.

Activation of vitamin D receptor inhibits Tau phosphorylation is associated with reduction of iron accumulation in APP/PS1 transgenic mice

Vitamin D deficiency and iron accumulation are prevalent in the brains of Alzheimer's disease (AD) patients, however, whether Vitamin D has a role in the regulations of iron metabolism in the condition of AD remains unknown. Our previous studies revealed that vitamin D deficiency promotes β-amyloid (Aβ) deposition in the APP/PS1 mouse brains, while supplemented with a specific agonist of vitamin D receptor (VDR), paricalcitol (PAL), significantly reduced Aβ production via promoting the lysosomal degradation of β-site APP cleavage enzyme 1 (BACE1). In this study, our data suggested that activation of VDR by PAL significantly reduced the iron accumulation in the cortex and hippocampus of APP/PS1 mice through downregulation of Transferrin receptor (TFR) by reducing iron-regulatory protein 2 (IRP2) expression. Furthermore, activation of VDR effectively reduced the phosphorylations of Tau at Ser396 and Thr181 sites via inhibiting the GSK3β phosphorylation (Tyr216). Taken together, our data suggest that activation of VDR could inhibit the phosphorylations of Tau possibly by repressing the iron accumulation-induced upregulation of GSK3β activity in the brains of APP/PS1 mice. Thus, activation of VDR may be an effective strategy for treating AD.

Serum hepcidin / ferroportin levels in bipolar disorder and schizophrenia

BACKGROUND

Despite several alternatives for cellular iron influx, the only mechanism for cellular iron efflux is ferroportin mediated active transport. In cases of ferroportin dysfunction, iron accumulates in the cell and causes ferroptosis. Hepcidin suppresses ferroportin levels and inflammatory activation increases hepcidin production. Mild inflammation in schizophrenia and bipolar disorder may alter hepcidin and ferroportin.

METHODS

The study included a total of 137 patients aged 18-65 years, 57 diagnosed with schizophrenia and 80 with bipolar disorder, according to the DSM-IV diagnostic criteria, and a control group (HC) of 42 healthy individuals. Biochemical analyses, thyroid function tests, hemogram, serum iron level, iron-binding capacity, and ferritin levels were examined. Serum levels of hepcidin and ferroportin were measured with enzyme-linked immunosorbent assay (ELISA) method.

RESULTS

A statistically significant difference was determined between the groups in terms of the serum ferroportin levels (F = 15.69, p < 0.001). Post-hoc analyses showed that the schizophrenia group had higher ferroportin levels than in the bipolar group (p < 0.001) and HCs (p < 0.001). Hepcidin levels did not differ between the groups. Chlorpromazine equivalent doses of antipsychotics correlated with ferroportin levels (p = 0.024).

CONCLUSION

Ferroportin levels were increased in the schizophrenia group, although iron and hepcidin levels were within normal ranges. Antipsychotics may alter the mechanisms which control ferroportin levels. Further studies are needed to examine the relationships between antipsychotics and iron metabolism for determination of causal relationship.

Upregulation of brain hepcidin in prion diseases

Accumulation of redox-active iron in human sporadic Creutzfeldt-Jakob disease (sCJD) brain tissue and scrapie-infected mouse brains has been demonstrated previously. Here, we explored whether upregulation of local hepcidin secreted within the brain is the underlying cause of iron accumulation and associated toxicity. Using scrapie-infected mouse brains, we demonstrate transcriptional upregulation of hepcidin relative to controls. As a result, ferroportin (Fpn), the downstream effector of hepcidin and the only known iron export protein was downregulated, and ferritin, an iron storage protein was upregulated, suggesting increased intracellular iron. A similar transcriptional and translational upregulation of hepcidin, and decreased expression of Fpn and an increase in ferritin expression was observed in sCJD brain tissue. Further evaluation in human neuroblastoma cells (M17) exposed to synthetic mini-hepcidin showed downregulation of Fpn, upregulation of ferritin, and an increase in reactive oxygen species (ROS), resulting in cytotoxicity in a dose-dependent manner. Similar effects were noted in primary neurons isolated from mouse brain. As in M17 cells, primary neurons accumulated ferritin and ROS, and showed toxicity at five times lower concentration of mini-hepcidin. These observations suggest that upregulation of brain hepcidin plays a significant role in iron accumulation and associated neurotoxicity in human and animal prion disorders.

A-Lipoic Acid Alleviates Folic Acid-Induced Renal Damage Through Inhibition of Ferroptosis

Folic acid (FA)-induced acute kidney injury (AKI) is characterized by the disturbance of redox homeostasis, resulting in massive tubular necrosis and inflammation. Α-lipoic acid (LA), as an antioxidant, has been reported to play an important role in renal protection, but the underlying mechanism remains poorly explored. The aim of this study is to investigate the protective effect of LA on FA-induced renal damage. Our findings showed that LA could ameliorate renal dysfunction and histopathologic damage induced by FA overdose injection. Moreover, FA injection induced severe inflammation, indicated by increased release of pro-inflammatory cytokines tumor necrosis factor (TNF)-α and IL-1β, as well as infiltration of macrophage, which can be alleviated by LA supplementation. In addition, LA not only reduced the cellular iron overload by upregulating the expressions of Ferritin and ferroportin (FPN), but also mitigated reactive oxygen species (ROS) accumulation and lipid peroxidation by increasing the levels of antioxidant glutathione (GSH) and glutathione peroxidase-4 (GPX4). More importantly, we found that LA supplementation could reduce the number of Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL)-positive tubular cells caused by FA, indicating that the tubular cell death mediated by ferroptosis may be inhibited. Further study demonstrated that LA supplementation could reverse the decreased expression of cystine/glutamate antiporter xCT (SLC7A11), which mediated GSH synthesis. What is more, mechanistic study indicated that p53 activation was involved in the inhibitory effect of SLC7A11 induced by FA administration, which could be suppressed by LA supplementation. Taken together, our findings indicated that LA played the protective effect on FA-induced renal damage mainly by inhibiting ferroptosis.

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.

Ferroptosis, a Potential Therapeutic Target in Alzheimer's Disease

Cell death is a common phenomenon in the progression of Alzheimer’s disease (AD). However, the mechanism of triggering the death of neuronal cells remains unclear. Ferroptosis is an iron-dependent lipid peroxidation-driven cell death and emerging evidences have demonstrated the involvement of ferroptosis in the pathological process of AD. Moreover, several hallmarks of AD pathogenesis were consistent with the characteristics of ferroptosis, such as excess iron accumulation, elevated lipid peroxides, and reactive oxygen species (ROS), reduced glutathione (GSH), and glutathione peroxidase 4 (GPX4) levels. Besides, some ferroptosis inhibitors can relieve AD-related pathological symptoms in AD mice and exhibit potential clinical benefits in AD patients. Therefore, ferroptosis is gradually being considered as a distinct cell death mechanism in the pathogenesis of AD. However, direct evidence is still lacking. In this review, we summarize the features of ferroptosis in AD, its underlying mechanisms in AD pathology, and review the application of ferroptosis inhibitors in both AD clinical trials and mice/cell models, to provide valuable information for future treatment and prevention of this devastating disease.

Regular Physical Exercise Modulates Iron Homeostasis in the 5xFAD Mouse Model of Alzheimer's Disease

Dysregulation of brain iron metabolism is one of the pathological features of aging and Alzheimer's disease (AD), a neurodegenerative disease characterized by progressive memory loss and cognitive impairment. While physical inactivity is one of the risk factors for AD and regular exercise improves cognitive function and reduces pathology associated with AD, the underlying mechanisms remain unclear. The purpose of the study is to explore the effect of regular physical exercise on modulation of iron homeostasis in the brain and periphery of the 5xFAD mouse model of AD. By using inductively coupled plasma mass spectrometry and a variety of biochemical techniques, we measured total iron content and level of proteins essential in iron homeostasis in the brain and skeletal muscles of sedentary and exercised mice. Long-term voluntary running induced redistribution of iron resulted in altered iron metabolism and trafficking in the brain and increased iron content in skeletal muscle. Exercise reduced levels of cortical hepcidin, a key regulator of iron homeostasis, coupled with interleukin-6 (IL-6) decrease in cortex and plasma. We propose that regular exercise induces a reduction of hepcidin in the brain, possibly via the IL-6/STAT3/JAK1 pathway. These findings indicate that regular exercise modulates iron homeostasis in both wild-type and AD mice.

Systematic review of human post-mortem immunohistochemical studies and bioinformatics analyses unveil the complexity of astrocyte reaction in Alzheimer's disease

AIMS

Reactive astrocytes in Alzheimer's disease (AD) have traditionally been demonstrated by increased glial fibrillary acidic protein (GFAP) immunoreactivity; however, astrocyte reaction is a complex and heterogeneous phenomenon involving multiple astrocyte functions beyond cytoskeletal remodelling. To better understand astrocyte reaction in AD, we conducted a systematic review of astrocyte immunohistochemical studies in post-mortem AD brains followed by bioinformatics analyses on the extracted reactive astrocyte markers.

METHODS

NCBI PubMed, APA PsycInfo and WoS-SCIE databases were interrogated for original English research articles with the search terms 'Alzheimer's disease' AND 'astrocytes.' Bioinformatics analyses included protein-protein interaction network analysis, pathway enrichment, and transcription factor enrichment, as well as comparison with public human -omics datasets.

RESULTS

A total of 306 articles meeting eligibility criteria rendered 196 proteins, most of which were reported to be upregulated in AD vs control brains. Besides cytoskeletal remodelling (e.g., GFAP), bioinformatics analyses revealed a wide range of functional alterations including neuroinflammation (e.g., IL6, MAPK1/3/8 and TNF), oxidative stress and antioxidant defence (e.g., MT1A/2A, NFE2L2, NOS1/2/3, PRDX6 and SOD1/2), lipid metabolism (e.g., APOE, CLU and LRP1), proteostasis (e.g., cathepsins, CRYAB and HSPB1/2/6/8), extracellular matrix organisation (e.g., CD44, MMP1/3 and SERPINA3), and neurotransmission (e.g., CHRNA7, GABA, GLUL, GRM5, MAOB and SLC1A2), among others. CTCF and ESR1 emerged as potential transcription factors driving these changes. Comparison with published -omics datasets validated our results, demonstrating a significant overlap with reported transcriptomic and proteomic changes in AD brains and/or CSF.

CONCLUSIONS

Our systematic review of the neuropathological literature reveals the complexity of AD reactive astrogliosis. We have shared these findings as an online resource available at www.astrocyteatlas.org.

Impaired Iron Homeostasis and Haematopoiesis Impacts Inflammation in the Ageing Process in Down Syndrome Dementia

Down syndrome (DS) subjects are more likely to develop the clinical features of Alzheimer's disease (AD) very early in the disease process due to the additional impact of neuroinflammation and because of activation of innate immunity. Many factors involved in the neuropathology of AD in DS, including epigenetic factors, innate immunity and impaired haematopoiesis, contribute significantly towards the pathophysiology and the enhanced ageing processes seen in DS and as a consequence of the triplication of genes RUNX1, S100β and OLIG2, together with the influence of proteins that collectively protect from cellular defects and inflammation, which include hepcidin, ferritin, IL-6 and TREM2. This study is aimed at determining whether genetic variants and inflammatory proteins are involved in haematopoiesis and cellular processes in DS compared with age-matched control participants, particularly with respect to neuroinflammation and accelerated ageing. Serum protein levels from DS, AD and control participants were measured by enzyme-linked immunosorbent assay (ELISA). Blood smears and post-mortem brain samples from AD and DS subjects were analysed by immunohistochemistry. RUNX1 mRNA expression was analysed by RT-PCR and in situ hybridisation in mouse tissues. Our results suggest that hepcidin, S100β and TREM2 play a critical role in survival and proliferation of glial cells through a common shared pathway. Blood smear analysis showed the presence of RUNX1 in megakaryocytes and platelets, implying participation in myeloid cell development. In contrast, hepcidin was expressed in erythrocytes and in platelets, suggesting a means of possible entry into the brain parenchyma via the choroid plexus (CP). The gene product of RUNX1 and hepcidin both play a critical role in haematopoiesis in DS. We propose that soluble TREM2, S100β and hepcidin can migrate from the periphery via the CP, modulate the blood-brain immune axis in DS and could form an important and hitherto neglected avenue for possible therapeutic interventions to reduce plaque formation.

Loss of ferroportin induces memory impairment by promoting ferroptosis in Alzheimer's disease

Iron homeostasis disturbance has been implicated in Alzheimer's disease (AD), and excess iron exacerbates oxidative damage and cognitive defects. Ferroptosis is a nonapoptotic form of cell death dependent upon intracellular iron. However, the involvement of ferroptosis in the pathogenesis of AD remains elusive. Here, we report that ferroportin1 (Fpn), the only identified mammalian nonheme iron exporter, was downregulated in the brains of APPswe/PS1dE9 mice as an Alzheimer's mouse model and Alzheimer's patients. Genetic deletion of Fpn in principal neurons of the neocortex and hippocampus by breeding Fpnfl/fl mice with NEX-Cre mice led to AD-like hippocampal atrophy and memory deficits. Interestingly, the canonical morphological and molecular characteristics of ferroptosis were observed in both Fpnfl/fl/NEXcre and AD mice. Gene set enrichment analysis (GSEA) of ferroptosis-related RNA-seq data showed that the differentially expressed genes were highly enriched in gene sets associated with AD. Furthermore, administration of specific inhibitors of ferroptosis effectively reduced the neuronal death and memory impairments induced by Aβ aggregation in vitro and in vivo. In addition, restoring Fpn ameliorated ferroptosis and memory impairment in APPswe/PS1dE9 mice. Our study demonstrates the critical role of Fpn and ferroptosis in the progression of AD, thus provides promising therapeutic approaches for this disease.

Hepcidin Increases Cytokines in Alzheimer's Disease and Down's Syndrome Dementia: Implication of Impaired Iron Homeostasis in Neuroinflammation

The liver-derived hormone hepcidin, a member of the defensin family of antimicrobial peptides, plays an important role in host defense and innate immunity due to its broad antibacterial and antiviral properties. Ferritin, an iron storage protein is often associated with iron deficiency, hypoferritinemia, hypoxia, and immune complications, which are all significant concerns for systemic infection in Alzheimer’s disease (AD) and Down’s syndrome (DS) dementia. Serum and post-mortem brain samples were collected from AD, DS and age-matched control subjects. Serum samples were analyzed with ELISA for ferritin, hepcidin and IL-6. Additionally, post-mortem brain sections were assessed by immunohistochemistry for iron-related and inflammatory proteins. A significant increase in serum hepcidin levels was found in DS, compared to controls and AD subjects (p < 0.0001). Hepcidin protein was visible in the epithelial cells of choroid plexus, meningeal macrophages and in the astrocytes close to the endothelium of blood vessels. Hepcidin co-localized with IL-6, indicating its anti-inflammatory properties. We found significant correlation between hypoferritinemia and elevated levels of serum hepcidin in AD and DS. Hepcidin can be transported via macrophages and the majority of the vesicular hepcidin enters the brain via a compromised blood brain barrier (BBB). Our findings provide further insight into the molecular implications of the altered iron metabolism in acute inflammation, and can aid towards the development of preventive strategies and novel treatments in the fight against neuroinflammation.

Effect of sevoflurane on iron homeostasis and toxicity in the brain of mice

Sevoflurane (Sev), a commonly used volatile anesthetic, could induce nerve damage and cognitive deficiency. Oxidative stress induced by iron overload promotes nerve damage and cell apoptosis in the brain. This study revealed a new toxic mechanism of Sev to the brain occurred through the dysfunction of iron metabolism. Twelve-month-old C57BL/6 mice were randomly assigned to the following three groups: control group; 2% Sev (6 h) group; and Sev plus iron deficiency group. Iron levels and iron metabolism-related proteins and apoptosis-related factors in hippocampus and cortex tissues were detected by using synchrotron radiation micro-X-ray fluorescence (μ-XRF) and western blotting. Our results showed that a decline in cognitive function was observed in mice treated with Sev. Sev significantly induced iron accumulation through upregulating ferritin and downregulating transferrin receptor 1 which involved in ferroportin1 (Fpn1)/hepcidin pathway and increasing reactive oxygen species (ROS) and malondialdehyde (MDA) content of hippocampus and cortex. Sev aggravated BACE1 expression and Aβ accumulation. Changes in the ratio of Bcl2/Bax and Tau/p-Tau intensified the cell apoptosis in hippocampus and cortex tissues. Interestingly, the cognitive deficiency and neurotoxicity induced by Sev could be ameliorated significantly by feeding a low-iron diet to mice prior to anesthesia. The data uncovered a new lesion mechanism of Sev from the role of iron metabolism. This study also suggested that the reduction in iron levels could protect the brain against neurological damage induced by Sev.