Inflaming the Brain with Iron

Inflammation in Metal-Induced Neurological Disorders and Neurodegenerative Diseases

Essential metals play critical roles in maintaining human health as they participate in various physiological activities. Nonetheless, both excessive accumulation and deficiency of these metals may result in neurotoxicity secondary to neuroinflammation and the activation of microglia and astrocytes. Activation of these cells can promote the release of pro-inflammatory cytokines. It is well known that neuroinflammation plays a critical role in metal-induced neurotoxicity as well as the development of neurological disorders, such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Initially seen as a defense mechanism, persistent inflammatory responses are now considered harmful. Astrocytes and microglia are key regulators of neuroinflammation in the central nervous system, and their excessive activation may induce sustained neuroinflammation. Therefore, in this review, we aim to emphasize the important role and molecular mechanisms underlying metal-induced neurotoxicity. Our objective is to raise the awareness on metal-induced neuroinflammation in neurological disorders. However, it is not only just neuroinflammation that different metals could induce; they can also cause harm to the nervous system through oxidative stress, apoptosis, and autophagy, to name a few. The primary pathophysiological mechanism by which these metals induce neurological disorders remains to be determined. In addition, given the various pathways through which individuals are exposed to metals, it is necessary to also consider the effects of co-exposure to multiple metals on neurological disorders.

Visceral adiposity is associated with iron deposition and myelin loss in the brains of aged mice

Iron deposition and myelin loss are observed in the brain with aging, and iron accumulation is suggested to be involved in myelin damage. However, the exact mechanism of iron deposition with aging remains unclear. This study was aimed to determine whether expanded visceral adipose tissue contributes to iron deposition and myelin loss by inducing hepcidin in the brains of aged male mice. Compared with young adult mice, levels of hepcidin in the brain, epididymal adipose tissue, and circulation were increased in aged mice, which had expanded visceral adipose tissue with inflammation. An increase in expressions of ferritin, an indicator of intracellular iron status, was accompanied by decreased levels of proteins related to myelin sheath in the brains of aged mice. These age-related changes in the brain were improved by visceral fat removal. In addition, IL-6 level, activation of microglia/macrophages, and nuclear translocation of phosphorylated Smad1/5 (pSmad1/5) inducing hepcidin expression were reduced in the brains of aged mice after visceral fat removal, accompanied by decreases of pSmad1/5- and ferritin-positive microglia/macrophages and mature oligodendrocytes. These findings indicate that visceral adiposity contributes to hepcidin-mediated iron deposition and myelin loss with inflammation in the aged brain. Our results support the importance of preventing visceral adiposity for maintaining brain health in older individuals.

The Role of Iron Metabolism in Sepsis-associated Encephalopathy: a Potential Target

Sepsis-associated encephalopathy (SAE) is an acute cerebral dysfunction secondary to infection, and the severity can range from mild delirium to deep coma. Disorders of iron metabolism have been proven to play an important role in a variety of neurodegenerative diseases by inducing cell damage through iron accumulation in glial cells and neurons. Recent studies have found that iron accumulation is also a potential mechanism of SAE. Systemic inflammation can induce changes in the expression of transporters and receptors on cells, especially high expression of divalent metal transporter1 (DMT1) and low expression of ferroportin (Fpn) 1, which leads to iron accumulation in cells. Excessive free Fe2+ can participate in the Fenton reaction to produce reactive oxygen species (ROS) to directly damage cells or induce ferroptosis. As a result, it may be of great help to improve SAE by treatment of targeting disorders of iron metabolism. Therefore, it is important to review the current research progress on the mechanism of SAE based on iron metabolism disorders. In addition, we also briefly describe the current status of SAE and iron metabolism disorders and emphasize the therapeutic prospect of targeting iron accumulation as a treatment for SAE, especially iron chelator. Moreover, drug delivery and side effects can be improved with the development of nanotechnology. This work suggests that treating SAE based on disorders of iron metabolism will be a thriving field.

A commentary on studies of brain iron accumulation during ageing

Brain iron content is widely reported to increase during "ageing", across multiple species from nematodes, rodents (mice and rats) and humans. Given the redox-active properties of iron, there has been a large research focus on iron-mediated oxidative stress as a contributor to tissue damage during natural ageing, and also as a risk factor for neurodegenerative disease. Surprisingly, however, the majority of published studies have not investigated brain iron homeostasis during the biological time period of senescence, and thus knowledge of how brain homeostasis changes during this critical stage of life largely remains unknown. This commentary examines the literature published on the topic of brain iron homeostasis during ageing, providing a critique on limitations of currently used experimental designs. The commentary also aims to highlight that although much research attention has been given to iron accumulation or iron overload as a pathological feature of ageing, there is evidence to support functional iron deficiency may exist, and this should not be overlooked in studies of ageing or neurodegenerative disease.

Could Alcohol-Related Cognitive Decline Be the Result of Iron-Induced Neuroinflammation?

Excessive and prolonged alcohol use can have long-term severe neurological consequences. The mechanisms involved may be complicated; however, new evidence seems to indicate the involvement of iron accumulation and neuroinflammation. Prolonged alcohol consumption has been linked to the accumulation of iron in specific regions of the brain. Evidence suggests that excess iron in the brain can trigger microglia activation in response. This activation leads to the release of pro-inflammatory cytokines and reactive oxygen species, which can cause damage to neurons and surrounding brain tissue. Additionally, iron-induced oxidative stress and inflammation can disrupt the blood-brain barrier, allowing immune cells from the periphery to infiltrate the brain. This infiltration can lead to further neuroinflammatory responses. Inflammation in the brain subsequently disrupts neuronal networks, impairs synaptic plasticity, and accelerates neuronal cell death. Consequently, cognitive functions such as memory, attention, and decision-making are compromised. Additionally, chronic neuroinflammation can hasten the development and progression of neurodegenerative diseases, further exacerbating cognitive impairment. Therefore, alcohol could act as a trigger for iron-induced neuroinflammation and cognitive decline. Overall, the mechanisms at play here seem to strongly link alcohol with cognitive decline, with neuroinflammation resulting from alcohol-induced iron accumulation playing a pivotal role.

Melatonin: a ferroptosis inhibitor with potential therapeutic efficacy for the post-COVID-19 trajectory of accelerated brain aging and neurodegeneration

The unprecedented pandemic of COVID-19 swept millions of lives in a short period, yet its menace continues among its survivors in the form of post-COVID syndrome. An exponentially growing number of COVID-19 survivors suffer from cognitive impairment, with compelling evidence of a trajectory of accelerated aging and neurodegeneration. The novel and enigmatic nature of this yet-to-unfold pathology demands extensive research seeking answers for both the molecular underpinnings and potential therapeutic targets. Ferroptosis, an iron-dependent cell death, is a strongly proposed underlying mechanism in post-COVID-19 aging and neurodegeneration discourse. COVID-19 incites neuroinflammation, iron dysregulation, reactive oxygen species (ROS) accumulation, antioxidant system repression, renin-angiotensin system (RAS) disruption, and clock gene alteration. These events pave the way for ferroptosis, which shows its signature in COVID-19, premature aging, and neurodegenerative disorders. In the search for a treatment, melatonin shines as a promising ferroptosis inhibitor with its repeatedly reported safety and tolerability. According to various studies, melatonin has proven efficacy in attenuating the severity of certain COVID-19 manifestations, validating its reputation as an anti-viral compound. Melatonin has well-documented anti-aging properties and combating neurodegenerative-related pathologies. Melatonin can block the leading events of ferroptosis since it is an efficient anti-inflammatory, iron chelator, antioxidant, angiotensin II antagonist, and clock gene regulator. Therefore, we propose ferroptosis as the culprit behind the post-COVID-19 trajectory of aging and neurodegeneration and melatonin, a well-fitting ferroptosis inhibitor, as a potential treatment.

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.

Iron imbalance in neurodegeneration

Iron is an essential element for the development and functionality of the brain, and anomalies in its distribution and concentration in brain tissue have been found to be associated with the most frequent neurodegenerative diseases. When magnetic resonance techniques allowed iron quantification in vivo, it was confirmed that the alteration of brain iron homeostasis is a common feature of many neurodegenerative diseases. However, whether iron is the main actor in the neurodegenerative process, or its alteration is a consequence of the degenerative process is still an open question. Because the different iron-related pathogenic mechanisms are specific for distinctive diseases, identifying the molecular mechanisms common to the various pathologies could represent a way to clarify this complex topic. Indeed, both iron overload and iron deficiency have profound consequences on cellular functioning, and both contribute to neuronal death processes in different manners, such as promoting oxidative damage, a loss of membrane integrity, a loss of proteostasis, and mitochondrial dysfunction. In this review, with the attempt to elucidate the consequences of iron dyshomeostasis for brain health, we summarize the main pathological molecular mechanisms that couple iron and neuronal death.

Microglial SLC25A28 Deficiency Ameliorates the Brain Injury After Intracerebral Hemorrhage in Mice by Restricting Aerobic Glycolysis

The microglia overactivation-induced neuroinflammation is a significant cause of the brain injury after intracerebral hemorrhage (ICH). Iron homeostasis is crucial for microglia activation, but the mechanism and causality still need further study. This study aimed to explore the roles and mechanism of the mitochondrial iron transporter SLC25A28 in microglia activation after ICH. Intrastriatal injection of autologous blood was used to establish ICH model, and the neuroinflammation, iron metabolism and brain injuries were assessed in wildtype or microglia-specific SLC25A28 knockout mice after ICH. Mitochondria iron levels and microglial function were determined in SLC25A28 overexpressed or deleted microglia. The extracellular acidification rate (ECAR), lactate production, and glycolytic enzyme levels were used to determine aerobic glycolysis. The results showed that ICH stimulated mitochondrial iron overload, and synchronously upregulated the SLC25A28 expression. In vitro, SLC25A28 overexpression increased mitochondrial iron levels in microglia. Interestingly, microglial SLC25A28 deficiency ameliorated neuroinflammation, brain edema, blood-brain barrier injury and ethological alterations in mice after ICH. Mechanically, SLC25A28 deficiency inhibited microglial activation by restricting the aerobic glycolysis. Moreover, zinc protoporphyrin could reduce SLC25A28 expression and mitigated brain injury. SLC25A28 plays crucial roles in mitochondrial iron homeostasis and microglia activation after ICH, and it might be a potential therapeutic target for ICH.

The Interplay between Ferroptosis and Neuroinflammation in Central Neurological Disorders

Central neurological disorders are significant contributors to morbidity, mortality, and long-term disability globally in modern society. These encompass neurodegenerative diseases, ischemic brain diseases, traumatic brain injury, epilepsy, depression, and more. The involved pathogenesis is notably intricate and diverse. Ferroptosis and neuroinflammation play pivotal roles in elucidating the causes of cognitive impairment stemming from these diseases. Given the concurrent occurrence of ferroptosis and neuroinflammation due to metabolic shifts such as iron and ROS, as well as their critical roles in central nervous disorders, the investigation into the co-regulatory mechanism of ferroptosis and neuroinflammation has emerged as a prominent area of research. This paper delves into the mechanisms of ferroptosis and neuroinflammation in central nervous disorders, along with their interrelationship. It specifically emphasizes the core molecules within the shared pathways governing ferroptosis and neuroinflammation, including SIRT1, Nrf2, NF-κB, Cox-2, iNOS/NO·, and how different immune cells and structures contribute to cognitive dysfunction through these mechanisms. Researchers' findings suggest that ferroptosis and neuroinflammation mutually promote each other and may represent key factors in the progression of central neurological disorders. A deeper comprehension of the common pathway between cellular ferroptosis and neuroinflammation holds promise for improving symptoms and prognosis related to central neurological disorders.

Research progress on ferroptosis in the pathogenesis and treatment of neurodegenerative diseases

Globally, millions of individuals are impacted by neurodegenerative disorders including Huntington's disease (HD), amyotrophic lateral sclerosis (ALS), Parkinson's disease (PD), and Alzheimer's disease (AD). Although a great deal of energy and financial resources have been invested in disease-related research, breakthroughs in therapeutic approaches remain elusive. The breakdown of cells usually happens together with the onset of neurodegenerative diseases. However, the mechanism that triggers neuronal loss is unknown. Lipid peroxidation, which is iron-dependent, causes a specific type of cell death called ferroptosis, and there is evidence its involvement in the pathogenic cascade of neurodegenerative diseases. However, the specific mechanisms are still not well known. The present article highlights the basic processes that underlie ferroptosis and the corresponding signaling networks. Furthermore, it provides an overview and discussion of current research on the role of ferroptosis across a variety of neurodegenerative conditions.

Microglial-specific knockdown of iron import gene, Slc11a2, blunts LPS-induced neuroinflammatory responses in a sex-specific manner

Neuroinflammation and microglial iron load are significant hallmarks found in several neurodegenerative diseases. In in vitro systems, microglia preferentially upregulate the iron importer, divalent metal transporter 1 (DMT1, gene name Slc11a2) in response to inflammatory stimuli, and it has been shown that iron can augment cellular inflammation, suggesting a feed-forward loop between mechanisms involved in iron import and inflammatory signaling. However, it is not understood how microglial iron import mechanisms contribute to inflammation in vivo, or whether altering a microglial iron-related gene affects the inflammatory response. These studies aimed to determine the effect of knocking down microglial iron import gene Slc11a2 on the inflammatory response in vivo. We generated a novel model of tamoxifen-inducible, microglial-specific Slc11a2 knockdown using Cx3cr1Cre-ERT2 mice. Transgenic male and female mice were administered intraperitoneal saline or lipopolysaccharide (LPS) and assessed for sickness behavior post-injection. Plasma cytokines and microglial bulk RNA sequencing (RNASeq) analyses were performed at 4 h post-LPS, and microglia were collected for gene expression analysis after 24 h. A subset of mice was assessed in a behavioral test battery following LPS-induced sickness recovery. Control male, but not female, mice significantly upregulated microglial Slc11a2 at 4 and 24 h following LPS. In Slc11a2 knockdown mice, we observed an improvement in the acute behavioral sickness response post-LPS in male, but not female, animals. Microglia from male, but not female, knockdown animals exhibited a significant decrease in LPS-provoked pro-inflammatory cytokine expression after 24 h. RNASeq data from male knockdown microglia 4 h post-LPS revealed a robust downregulation in inflammatory genes including Il6, Tnfα, and Il1β, and an increase in anti-inflammatory and homeostatic markers (e.g., Tgfbr1, Cx3cr1, and Trem2). This corresponded with a profound decrease in plasma pro-inflammatory cytokines 4 h post-LPS. At 4 h, male knockdown microglia also upregulated expression of markers of iron export, iron recycling, and iron homeostasis and decreased iron storage and import genes, along with pro-oxidant markers such as Cybb, Nos2, and Hif1α. Overall, this work elucidates how manipulating a specific gene involved in iron import in microglia alters acute inflammatory signaling and overall cell activation state in male mice. These data highlight a sex-specific link between a microglial iron import gene and the pro-inflammatory response to LPS in vivo, providing further insight into the mechanisms driving neuroinflammatory disease.

Evidence Implicating Blood-Brain Barrier Impairment in the Pathogenesis of Acquired Epilepsy following Acute Organophosphate Intoxication

Organophosphate (OP) poisoning can trigger cholinergic crisis, a life-threatening toxidrome that includes seizures and status epilepticus. These acute toxic responses are associated with persistent neuroinflammation and spontaneous recurrent seizures (SRS), also known as acquired epilepsy. Blood-brain barrier (BBB) impairment has recently been proposed as a pathogenic mechanism linking acute OP intoxication to chronic adverse neurologic outcomes. In this review, we briefly describe the cellular and molecular components of the BBB, review evidence of altered BBB integrity following acute OP intoxication, and discuss potential mechanisms by which acute OP intoxication may promote BBB dysfunction. We highlight the complex interplay between neuroinflammation and BBB dysfunction that suggests a positive feedforward interaction. Lastly, we examine research from diverse models and disease states that suggest mechanisms by which loss of BBB integrity may contribute to epileptogenic processes. Collectively, the literature identifies BBB impairment as a convergent mechanism of neurologic disease and justifies further mechanistic research into how acute OP intoxication causes BBB impairment and its role in the pathogenesis of SRS and potentially other long-term neurologic sequelae. Such research is critical for evaluating BBB stabilization as a neuroprotective strategy for mitigating OP-induced epilepsy and possibly seizure disorders of other etiologies. SIGNIFICANCE STATEMENT: Clinical and preclinical studies support a link between blood-brain barrier (BBB) dysfunction and epileptogenesis; however, a causal relationship has been difficult to prove. Mechanistic studies to delineate relationships between BBB dysfunction and epilepsy may provide novel insights into BBB stabilization as a neuroprotective strategy for mitigating epilepsy resulting from acute organophosphate (OP) intoxication and non-OP causes and potentially other adverse neurological conditions associated with acute OP intoxication, such as cognitive impairment.

A closer look at the role of iron in glioblastoma

Glioblastoma (GBM) is among the deadliest malignancies facing modern oncology. While our understanding of certain aspects of GBM biology has significantly increased over the last decade, other aspects, such as the role of bioactive metals in GBM progression, remain understudied. Iron is the most abundant transition metal found within the earth's crust and plays an intricate role in human physiology owing to its ability to participate in oxidation-reduction reactions. The importance of iron homeostasis in human physiology is apparent when examining the clinical consequences of iron deficiency or iron overload. Despite this, the role of iron in GBM progression has not been well described. Here, we review and synthesize the existing literature examining iron's role in GBM progression and patient outcomes, as well as provide a survey of iron's effects on the major cell types found within the GBM microenvironment at the molecular and cellular level. Iron represents an accessible target given the availability of already approved iron supplements and chelators. Improving our understanding of iron's role in GBM biology may pave the way for iron-modulating approaches to improve patient outcomes.

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.

Iron in multiple sclerosis - Neuropathology, immunology, and real-world considerations

Iron is an essential element involved in a multitude of bodily processes. It is tightly regulated, as elevated deposition in tissues is associated with diseases such as multiple sclerosis (MS). Iron accumulation in the central nervous system (CNS) of MS patients is linked to neurotoxicity through mechanisms including oxidative stress, glutamate excitotoxicity, misfolding of proteins, and ferroptosis. In the past decade, the combination of MRI and histopathology has enhanced our understanding of iron deposition in MS pathophysiology, including in the pro-inflammatory and neurotoxicity of iron-laden rims of chronic active lesions. In this regard, iron accumulation may not only have an impact on different CNS-resident cells but may also promote the innate and adaptive immune dysfunctions in MS. Although there are discordant results, most studies indicate lower levels of iron but higher amounts of the iron storage molecule ferritin in the circulation of people with MS. Considering the importance of iron, there is a need for evidence-guided recommendation for dietary intake in people living with MS. Potential novel therapeutic approaches include the regulation of iron levels using next generation iron chelators, as well as therapies to interfere with toxic consequences of iron overload including antioxidants in MS.

Deep gray matters iron deposition is positively associated with white matter hyperintensity in hypertension

The association and underlying mechanisms between iron deposition and white matter hyperintensity (WMH) remain unclear. In this study, quantitative susceptibility mapping (QSM) was used to quantify deep gray matters iron deposition and to explore the association from both global and regional perspectives. A total of 84 patients with hypertension and 26 healthy controls underwent a strategically acquired gradient echo (STAGE) protocol, and the multi-echo data were used to reconstruct QSM images. The susceptibilities were used to describe iron content. Global region (RI) susceptibilities were measured in regions of interest, and age-related thresholds were used to determine high-iron content region (RII) susceptibilities. Compared with healthy controls, hypertension had higher total WMH scores and regional scores (all p = .001) and higher susceptibilities using the RI or RII analysis (all p < .05). In healthy controls, there was no significant association between susceptibilities and WMH scores. In hypertension, the susceptibilities of deep gray matters were positively correlated with WMH scores (RI analysis: right putamen; RII analysis: bilateral caudate nucleus head, putamen, red nucleus, substantia nigra, and dentate nucleus; age and education corrected p < .05). These findings suggest that iron deposition in deep gray matters was positively associated with WMH in hypertension, especially using the RII analysis.

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.

Induction Mechanism of Ferroptosis, Necroptosis, and Pyroptosis: A Novel Therapeutic Target in Nervous System Diseases

In recent years, three emerging cell deaths, ferroptosis, necroptosis and pyroptosis, have gradually attracted everyone's attention, and they also play an important role in the occurrence and development of various diseases. Ferroptosis is an idiographic iron-dependent form regulated cell death with the hallmark of accumulation of the intracellular reactive oxygen species (ROS). Necroptosis is a form of regulated necrotic cell death mediated by the receptor-interacting protein kinase 1(RIPK1) and receptor-interacting protein kinase 3RIPK3. Pyroptosis, also known as cell inflammatory necrosis, is a programmed cell necrosis mediated by Gasdermin D (GSDMD). It is manifested by the continuous swelling of the cells until the cell membrane ruptures, resulting in the release of the cell contents and the activation of a strong inflammatory response. Neurological disorders remain a clinical challenge and patients do not respond well to conventional treatments. Nerve cell death can aggravate the occurrence and development of neurological diseases. This article reviews the specific mechanisms of these three types of cell death and their relationship with neurological diseases and the evidence for the role of the three types of cell death in neurological diseases; understanding these pathways and their mechanisms is helpful for the treatment of neurological diseases.

Effect of Organic Selenium on the Homeostasis of Trace Elements, Lipid Peroxidation, and mRNA Expression of Antioxidant Proteins in Mouse Organs

(1) In this study we determined the effect of long-term selenomethionine administration on the oxidative stress level and changes in antioxidant protein/enzyme activity; mRNA expression; and the levels of iron, zinc, and copper. (2) Experiments were performed on 4-6-week-old BALB/c mice, which were given selenomethionine (0.4 mg Se/kg b.w.) solution for 8 weeks. The element concentration was determined via inductively coupled plasma mass spectrometry. mRNA expression of SelenoP, Cat, and Sod1 was quantified using real-time quantitative reverse transcription. Malondialdehyde content and catalase activity were determined spectrophotometrically. (3) After long-term SeMet administration, the amount of Se increased by 12-fold in mouse blood, 15-fold in the liver, and 42-fold in the brain, as compared to that in the control. Exposure to SeMet decreased amounts of Fe and Cu in blood, but increased Fe and Zn levels in the liver and increased the levels of all examined elements in the brain. Se increased malondialdehyde content in the blood and brain but decreased it in liver. SeMet administration increased the mRNA expression of selenoprotein P, dismutase, and catalase, but decreased catalase activity in brain and liver. (4) Eight-week-long selenomethionine consumption elevated Se levels in the blood, liver, and especially in the brain and disturbed the homeostasis of Fe, Zn, and Cu. Moreover, Se induced lipid peroxidation in the blood and brain, but not in the liver. In response to SeMet exposure, significant up-regulation of the mRNA expression of catalase, superoxide dismutase 1, and selenoprotein P in the brain, and especially in the liver, was determined.

Iron and Ferroptosis More than a Suspect: Beyond the Most Common Mechanisms of Neurodegeneration for New Therapeutic Approaches to Cognitive Decline and Dementia

Neurodegeneration is a multifactorial process that involves multiple mechanisms. Examples of neurodegenerative diseases are Parkinson's disease, multiple sclerosis, Alzheimer's disease, prion diseases such as Creutzfeldt-Jakob's disease, and amyotrophic lateral sclerosis. These are progressive and irreversible pathologies, characterized by neuron vulnerability, loss of structure or function of neurons, and even neuron demise in the brain, leading to clinical, functional, and cognitive dysfunction and movement disorders. However, iron overload can cause neurodegeneration. Dysregulation of iron metabolism associated with cellular damage and oxidative stress is reported as a common event in several neurodegenerative diseases. Uncontrolled oxidation of membrane fatty acids triggers a programmed cell death involving iron, ROS, and ferroptosis, promoting cell death. In Alzheimer's disease, the iron content in the brain is significantly increased in vulnerable regions, resulting in a lack of antioxidant defenses and mitochondrial alterations. Iron interacts with glucose metabolism reciprocally. Overall, iron metabolism and accumulation and ferroptosis play a significant role, particularly in the context of diabetes-induced cognitive decline. Iron chelators improve cognitive performance, meaning that brain iron metabolism control reduces neuronal ferroptosis, promising a novel therapeutic approach to cognitive impairment.

Effects of liraglutide on astrocyte polarization and neuroinflammation in db/db mice: focus on iron overload and oxidative stress

Neuroinflammation plays a crucial role in the occurrence and development of cognitive impairment in type 2 diabetes mellitus (T2DM), but the specific injury mechanism is not fully understood. Astrocyte polarization has attracted new attention and has been shown to be directly and indirectly involved in neuroinflammation. Liraglutide has been shown to have beneficial effects on neurons and astrocytes. However, the specific protection mechanism still needs to be clarified. In this study, we assessed the levels of neuroinflammation and A1/A2-responsive astrocytes in the hippocampus of db/db mice and examined their relationships with iron overload and oxidative stress. First, in db/db mice, liraglutide alleviated the disturbance of glucose and lipid metabolism, increased the postsynaptic density, regulated the expression of NeuN and BDNF, and partially restored impaired cognitive function. Second, liraglutide upregulated the expression of S100A10 and downregulated the expression of GFAP and C3, and decreased the secretion of IL-1β, IL-18, and TNF-α, which may confirm that it regulates the proliferation of reactive astrocytes and A1/A2 phenotypes polarize and attenuate neuroinflammation. In addition, liraglutide reduced iron deposition in the hippocampus by reducing the expression of TfR1 and DMT1 and increasing the expression of FPN1; at the same time, liraglutide by up-regulating the levels of SOD, GSH, and SOD2 expression, as well as downregulation of MDA levels and NOX2 and NOX4 expression to reduce oxidative stress and lipid peroxidation. The above may attenuate A1 astrocyte activation. This study preliminarily explored the effect of liraglutide on the activation of different astrocyte phenotypes and neuroinflammation in the hippocampus of a T2DM model and further revealed its intervention effect on cognitive impairment in diabetes. Focusing on the pathological consequences of astrocytes may have important implications for the treatment of diabetic cognitive impairment.

Maintenance of mitochondrial homeostasis for Alzheimer's disease: Strategies and challenges

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases, and its early onset is closely related to mitochondrial energy metabolism. The brain is only 2% of body weight, but consumes 20% of total energy needs. Mitochondria are responsible for providing energy in cells, and maintaining their homeostasis ensures an adequate supply of energy to the brain. Mitochondrial homeostasis is constituted by mitochondrial quantity and quality control, which is dynamically regulated by mitochondrial energy metabolism, mitochondrial dynamics and mitochondrial quality control. Impaired energy metabolism of brain cells occurs early in AD, and maintaining mitochondrial homeostasis is a promising therapeutic target in the future. We summarized the mechanism of mitochondrial homeostasis in AD, its influence on the pathogenesis of early AD, strategies for maintaining mitochondrial homeostasis, and mitochondrial targeting strategies. This review concludes with the authors' opinions on future research and development for mitochondrial homeostasis of early AD.

The synthesis and properties of mitochondrial targeted iron chelators

Iron levels in mitochondria are critically important for the normal functioning of the organelle. Abnormal levels of iron and the associated formation of toxic oxygen radicals have been linked to a wide range of diseases and consequently it is important to be able to both monitor and control levels of the mitochondrial labile iron pool. To this end a series of iron chelators which are targeted to mitochondria have been designed. This overview describes the synthesis of some of these molecules and their application in monitoring mitochondrial labile iron pools and in selectively removing excess iron from mitochondria.

A proteogenomic view of Parkinson's disease causality and heterogeneity

The pathogenesis and clinical heterogeneity of Parkinson's disease (PD) have been evaluated from molecular, pathophysiological, and clinical perspectives. High-throughput proteomic analysis of cerebrospinal fluid (CSF) opened new opportunities for scrutinizing this heterogeneity. To date, this is the most comprehensive CSF-based proteomics profiling study in PD with 569 patients (350 idiopathic patients, 65 GBA + mutation carriers and 154 LRRK2 + mutation carriers), 534 controls, and 4135 proteins analyzed. Combining CSF aptamer-based proteomics with genetics we determined protein quantitative trait loci (pQTLs). Analyses of pQTLs together with summary statistics from the largest PD genome wide association study (GWAS) identified 68 potential causal proteins by Mendelian randomization. The top causal protein, GPNMB, was previously reported to be upregulated in the substantia nigra of PD patients. We also compared the CSF proteomes of patients and controls. Proteome differences between GBA + patients and unaffected GBA + controls suggest degeneration of dopaminergic neurons, altered dopamine metabolism and increased brain inflammation. In the LRRK2 + subcohort we found dysregulated lysosomal degradation, altered alpha-synuclein processing, and neurotransmission. Proteome differences between idiopathic patients and controls suggest increased neuroinflammation, mitochondrial dysfunction/oxidative stress, altered iron metabolism and potential neuroprotection mediated by vasoactive substances. Finally, we used proteomic data to stratify idiopathic patients into "endotypes". The identified endotypes show differences in cognitive and motor disease progression based on previously reported protein-based risk scores.Our findings not only contribute to the identification of new therapeutic targets but also to shape personalized medicine in CNS neurodegeneration.

Microglial Hemoxygenase-1 Deletion Reduces Inflammation in the Retina of Old Mice with Tauopathy

Tauopathies such as Alzheimer's disease are characterized by the accumulation of neurotoxic aggregates of tau protein. With aging and, especially, in Alzheimer's patients, the inducible enzyme heme oxygenase 1 (HO-1) progressively increases in microglia, causing iron accumulation, neuroinflammation, and neurodegeneration. The retina is an organ that can be readily accessed and can reflect changes that occur in the brain. In this context, we evaluated how the lack of microglial HO-1, using mice that do not express HO-1 in microglia (HMO-KO), impacts retinal macro and microgliosis of aged subjects (18 months old mice) subjected to tauopathy by intrahippocampal delivery of AAV-hTauP301L (TAU). Our results show that although tauopathy, measured as anti-TAUY9 and anti-AT8 positive immunostaining, was not observed in the retina of WT-TAU or HMO-KO+TAU mice, a morphometric study of retinal microglia and macroglia showed significant retinal changes in the TAU group compared to the WT group, such as: (i) increased number of activated microglia, (ii) retraction of microglial processes, (iii) increased number of CD68+ microglia, and (iv) increased retinal area occupied by GFAP (AROA) and C3 (AROC3). This retinal inflammatory profile was reduced in HMO-KO+TAU mice. Conclusion: Reduction of microglial HO-1 could be beneficial to prevent tauopathy-induced neuroinflammation.

New Target for Prevention and Treatment of Neuroinflammation: Microglia Iron Accumulation and Ferroptosis

Microglia play an important role in maintaining central nervous system homeostasis and are the major immune cells in the brain. In response to internal or external inflammatory stimuli, microglia are activated and release numerous inflammatory factors, thus leading to neuroinflammation. Inflammation and microglia iron accumulation promote each other and jointly promote the progression of neuroinflammation. Inhibiting microglia iron accumulation prevents neuroinflammation. Ferroptosis is an iron-dependent phospholipid peroxidation-driven type of cell death regulation. Cell iron accumulation causes the peroxidation of cell membrane phospholipids and damages the cell membrane. Ultimately, this process leads to cell ferroptosis. Iron accumulation or phospholipid peroxidation in microglia releases a large number of inflammatory factors. Thus, inhibiting microglia ferroptosis may be a new target for the prevention and treatment of neuroinflammation.

Multimodal magnetic resonance imaging of youth sport-related concussion reveals acute changes in the cerebellum, basal ganglia, and corpus callosum that resolve with recovery

Magnetic resonance imaging (MRI) can provide a number of measurements relevant to sport-related concussion (SRC) symptoms; however, most studies to date have used a single MRI modality and whole-brain exploratory analyses in attempts to localize concussion injury. This has resulted in highly variable findings across studies due to wide ranging symptomology, severity and nature of injury within studies. A multimodal MRI, symptom-guided region-of-interest (ROI) approach is likely to yield more consistent results. The functions of the cerebellum and basal ganglia transcend many common concussion symptoms, and thus these regions, plus the white matter tracts that connect or project from them, constitute plausible ROIs for MRI analysis. We performed diffusion tensor imaging (DTI), resting-state functional MRI, quantitative susceptibility mapping (QSM), and cerebral blood flow (CBF) imaging using arterial spin labeling (ASL), in youth aged 12-18 years following SRC, with a focus on the cerebellum, basal ganglia and white matter tracts. Compared to controls similar in age, sex and sport (N = 20), recent SRC youth (N = 29; MRI at 8 ± 3 days post injury) exhibited increased susceptibility in the cerebellum (p = 0.032), decreased functional connectivity between the caudate and each of the pallidum (p = 0.035) and thalamus (p = 0.021), and decreased diffusivity in the mid-posterior corpus callosum (p < 0.038); no changes were observed in recovered asymptomatic youth (N = 16; 41 ± 16 days post injury). For recent symptomatic-only SRC youth (N = 24), symptom severity was associated with increased susceptibility in the superior cerebellar peduncles (p = 0.011) and reduced activity in the cerebellum (p = 0.013). Fewer days between injury and MRI were associated with reduced cerebellar-parietal functional connectivity (p < 0.014), reduced activity of the pallidum (p = 0.002), increased CBF in the caudate (p = 0.005), and reduced diffusivity in the central corpus callosum (p < 0.05). Youth SRC is associated with acute cerebellar inflammation accompanied by reduced cerebellar activity and cerebellar-parietal connectivity, as well as structural changes of the middle regions of the corpus callosum accompanied by functional changes of the caudate, all of which resolve with recovery. Early MRI post-injury is important to establish objective MRI-based indicators for concussion diagnosis, recovery assessment and prediction of outcome.

The mechanism of ferroptosis regulating oxidative stress in ischemic stroke and the regulation mechanism of natural pharmacological active components

Cerebrovascular diseases, such as ischemic stroke, pose serious medical challenges worldwide due to their high morbidity and mortality and limitations in clinical treatment strategies. Studies have shown that reactive oxygen species (ROS)-mediated inflammation, excitotoxicity, and programmed cell death of each neurovascular unit during post-stroke hypoxia and reperfusion play an important role in the pathological cascade. Ferroptosis, a programmed cell death characterized by iron-regulated accumulation of lipid peroxidation, is caused by abnormal metabolism of lipids, glutathione (GSH), and iron, and can accelerate acute central nervous system injury. Recent studies have gradually uncovered the pathological process of ferroptosis in the neurovascular unit of acute stroke. Some drugs such as iron chelators, ferrostatin-1 (Fer-1) and liproxstatin-1 (Lip-1) can protect nerves after neurovascular unit injury in acute stroke by inhibiting ferroptosis. In addition, combined with our previous studies on ferroptosis mediated by natural compounds in ischemic stroke, this review summarized the progress in the regulation mechanism of natural chemical components and herbal chemical components on ferroptosis in recent years, in order to provide reference information for future research on ferroptosis and lead compounds for the development of ferroptosis inhibitors.

New Players in Neuronal Iron Homeostasis: Insights from CRISPRi Studies

Selective regional iron accumulation is a hallmark of several neurodegenerative diseases, including Alzheimer’s disease and Parkinson’s disease. The underlying mechanisms of neuronal iron dyshomeostasis have been studied, mainly in a gene-by-gene approach. However, recent high-content phenotypic screens using CRISPR/Cas9-based gene perturbations allow for the identification of new pathways that contribute to iron accumulation in neuronal cells. Herein, we perform a bioinformatic analysis of a CRISPR-based screening of lysosomal iron accumulation and the functional genomics of human neurons derived from induced pluripotent stem cells (iPSCs). Consistent with previous studies, we identified mitochondrial electron transport chain dysfunction as one of the main mechanisms triggering iron accumulation, although we substantially expanded the gene set causing this phenomenon, encompassing mitochondrial complexes I to IV, several associated assembly factors, and coenzyme Q biosynthetic enzymes. Similarly, the loss of numerous genes participating through the complete macroautophagic process elicit iron accumulation. As a novelty, we found that the impaired synthesis of glycophosphatidylinositol (GPI) and GPI-anchored protein trafficking also trigger iron accumulation in a cell-autonomous manner. Finally, the loss of critical components of the iron transporters trafficking machinery, including MON2 and PD-associated gene VPS35, also contribute to increased neuronal levels. Our analysis suggests that neuronal iron accumulation can arise from the dysfunction of an expanded, previously uncharacterized array of molecular pathways.

Neuroprotective Role of α-Lipoic Acid in Iron-Overload-Mediated Toxicity and Inflammation in In Vitro and In Vivo Models

Hemoglobin and iron overload is considered the major contributor to intracerebral hemorrhage (ICH)-induced brain injury. Accumulation of iron in the brain leads to microglia activation, inflammation and cell loss. Current available treatments for iron overload-mediated disorders are characterized by severe adverse effects, making such conditions an unmet clinical need. We assessed the potential of α-lipoic acid (ALA) as an iron chelator, antioxidant and anti-inflammatory agent in both in vitro and in vivo models of iron overload. ALA was found to revert iron-overload-induced toxicity in HMC3 microglia cell line, preventing cell apoptosis, reactive oxygen species generation and reducing glutathione depletion. Furthermore, ALA regulated gene expression of iron-related markers and inflammatory cytokines, such as IL-6, IL-1β and TNF. Iron toxicity also affects mitochondria fitness and biogenesis, impairments which were prevented by ALA pre-treatment in vitro. Immunocytochemistry assay showed that, although iron treatment caused inflammatory activation of microglia, ALA treatment resulted in increased ARG1 expression, suggesting it promoted an anti-inflammatory phenotype. We also assessed the effects of ALA in an in vivo zebrafish model of iron overload, showing that ALA treatment was able to reduce iron accumulation in the brain and reduced iron-mediated oxidative stress and inflammation. Our data support ALA as a novel approach for iron-overload-induced brain damage.

HAMP as a Prognostic Biomarker for Colorectal Cancer Based on Tumor Microenvironment Analysis

Colorectal cancer (CRC) is the most common digestive tumor in the world and has a high mortality rate. The development and treatment of CRC are related to the immune microenvironment, but immune response-related prognostic biomarkers are lacking. In this study, we used The Cancer Genome Atlas (TCGA) to explore the tumor microenvironment (TME) and weighted gene coexpression network analysis (WGCNA) to identify significant prognostic genes. We also identified differentially expressed genes in the TCGA data and explored immune-related genes and transcription factors (TFs). Then, we built a TF regulatory network and performed a comprehensive prognostic analysis of an lncRNA-associated competitive endogenous RNA network (ceRNA network) to build a prognostic model. CCR8 and HAMP were identified both in the WGCNA key module and as immune-related genes. HAMP had good prognostic value for CRC and was highly expressed in CRC tissues and had a negative correlation with CD4⁺ T cells and M0 macrophages based on immunohistochemistry and immunofluorescence staining of clinical specimens.We found that HAMP had high prognostic and therapeutic target value for CRC and was associated with liver metastasis. These analysis results revealed that HAMP may be a candidate immune-related prognostic biomarker for CRC.

Roots of Astragalus propinquus Schischkin Regulate Transmembrane Iron Transport and Ferroptosis to Improve Cerebral Ischemia-Reperfusion Injury

Background

The dried roots of the Astragalus propinquus Schischkin (RAP) plant, as a traditional Chinese medicine, has been widely used to treat stroke, cerebral ischemia, qi deficiency, and hypertension. Buyang Huanwu decoction is traditionally used to treat stroke in China for more than 200 years and has a significant effect on cerebral ischemia, and RAP is monarch medicine of Buyang Huanwu decoction. Therefore, this study was designed to observe the regulatory effect of RAP on transmembrane iron transporters and ferroptosis-related factors in cerebral ischemia-reperfusion injury (CIRI) in rats.

Methods

Middle cerebral artery occlusion (MCAO) was used to block blood flow in the blood supply area of the middle cerebral artery in seventy male SD rats to induce focal CIRI to establish a rat model of CIRI. RAP was administered to explore the regulatory effect of RAP on iron transmembrane transport under the condition of CIRI. The infarct size was measured using 2,3,5-triphenyl-tetrazolium chloride (TTC) staining, the pathological structure of brain tissue was observed by HE staining, and neuronal injury was evaluated by Nissl staining after treatment. Then, changes in the iron transporters ferritin (Fn), ferritin heavy chain (FHC), ferritin light chain (FLC), transferrin (Tf), transferrin receptor (TfR), divalent metal transporter 1 (DMT1), L-type calcium channel (LTCC), transient receptor potential canonical 6 (TRPC6), and ferroportin 1 (FPN1) were observed by immunohistochemistry staining (IHC) and Western blotting. The expression of key factors of ferroptosis, including the membrane sodium-dependent cystine/glutamate antiporter System Xc⁻ (System Xc⁻) light chain subunit (XCT) and heavy chain subunit (SLC3A2), glutathione peroxidase 4 (GPX4), nuclear factor erythroid 2-related factor (NRF2), heme oxygenase-1 (HO-1), and iron-responsive element-binding protein 2 (IREB2) in the brain tissues of rats was assessed by Western blotting. RAP decreased the infarct size and neuronal injury after CIRI in rats. Similarly, RAP treatment regulated the expression of iron transporters. As such, RAP was able to reduce the expression of Fn, FHC, FLC, Tf, TfR, DMT1, and TRPC6 and increase the expression of FPN1 through a Tf/TfR-independent pathway after CIRI in rats.

Conclusion

RAP stimulation inhibited ferroptosis by regulating the expression of the key ferroptosis factors XCT, SLC3A2, GPX4, NRF2, HO-1, and IREB2. In conclusion, RAP regulates transmembrane iron transport and ferroptosis to improve CIRI.

GSK-3β-mediated regulation of Nrf2/HO-1 signaling as a new therapeutic approach in the treatment of movement disorders

Movement disorders are neurological conditions characterized by involuntary motor movements, such as dystonia, ataxia, chorea myoclonus, tremors, Huntington's disease (HD), and Parkinson's disease (PD). It is classified into two categories: hypokinetic and hyperkinetic movements. Globally, movement disorders are a major cause of death. The pathophysiological process is initiated by excessive ROS generation, mitochondrial dysfunction, neuroinflammation, and neurotransmitters imbalance that lead to motor dysfunction in PD and HD patients. Several endogenous targets including Nrf2 maintain oxidative balance in the body. Activation of Nrf2 signaling is regulated by the enzyme glycogen synthase kinase (GSK-3β). In the cytoplasm, inhibition of GSK-3β regulates cellular proliferation, homeostasis, and apoptotic process by stimulating the nuclear factor erythroid 2 (Nrf2) pathway which is involved in the elevation of the cellular antioxidant enzymes which controls the ROS generation. The activation of Nrf2 increases the expression of antioxidant response elements (ARE), such as (Hemeoxygenase-1) HO-1, which decreases excessive cellular stress, mitochondrial dysfunction, apoptosis, and neuronal degeneration, which is the major cause of motor dysfunction. The present review explores the GSK-3β-mediated neuroprotection in various movement disorders through the Nrf2/HO-1 antioxidant pathway. This review provides a link between GSK-3β and the Nrf2/HO-1 signaling pathway in the treatment of PD and HD. In addition to that it highlights various GSK-3β inhibitors and the Nrf2/HO-1 activators, which exert robust neuroprotection against motor disorders. Therefore, the present review will help in the discovery of new therapy for PD and HD patients.

The Associations of Cerebrospinal Fluid Ferritin with Neurodegeneration and Neuroinflammation Along the Alzheimer's Disease Continuum

BACKGROUND

Increasing evidence has suggested that iron accumulation plays an important role in the onset and development of Alzheimer's disease (AD). However, the potential mechanism remains unclear.

OBJECTIVE

The present study investigated the associations of cerebrospinal fluid (CSF) ferritin, an indicator for brain iron load, with neurodegenerative and inflammatory changes in AD.

METHODS

The study involved 302 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI). They were classified as normal controls (A-T-N-, n = 48), AD continuum (A+TN-, n = 46; A+TN+, n = 166), and suspected non-AD pathology (A-TN+, n = 42), according to the amyloid/tau/neurodegeneration (ATN) system. Group comparisons of CSF ferritin among groups were performed using one-way ANOVA. Linear regression models were used to test the relationships between CSF ferritin and cognitive assessments, and the associations between CSF ferritin and other biomarkers, respectively.

RESULTS

We found that CSF ferritin showed significant differences among the ATN groups, with higher concentration in more advanced categories (A+TN+). Furthermore, CSF ferritin level was independently related to cognitive performance (MMSE, ADAS-Cog13, and ADNI-mem). Linear regression analysis indicated positive relationships between CSF ferritin and phosphorylated tau and total tau, rather than Aβ42. Significant associations were revealed between CSF ferritin and inflammatory proteins, including TNF-α, TNFR1, TNFR2, ICAM1, VCAM1, TGF-β1, IL-9, and IP-10, respectively.

CONCLUSION

Our results provide new insight into iron dysfunction in AD pathology and highlight elevated brain iron as a possible mechanism of neurodegeneration and neuroinflammation along AD continuum.

Neuroinflammation in Friedreich's Ataxia

Friedreich's ataxia (FRDA) is a rare genetic disorder caused by mutations in the gene frataxin, encoding for a mitochondrial protein involved in iron handling and in the biogenesis of iron-sulphur clusters, and leading to progressive nervous system damage. Although the overt manifestations of FRDA in the nervous system are mainly observed in the neurons, alterations in non-neuronal cells may also contribute to the pathogenesis of the disease, as recently suggested for other neurodegenerative disorders. In FRDA, the involvement of glial cells can be ascribed to direct effects caused by frataxin loss, eliciting different aberrant mechanisms. Iron accumulation, mitochondria dysfunction, and reactive species overproduction, mechanisms identified as etiopathogenic in neurons in FRDA, can similarly affect glial cells, leading them to assume phenotypes that can concur to and exacerbate neuron loss. Recent findings obtained in FRDA patients and cellular and animal models of the disease have suggested that neuroinflammation can accompany and contribute to the neuropathology. In this review article, we discuss evidence about the involvement of neuroinflammatory-related mechanisms in models of FRDA and provide clues for the modulation of glial-related mechanisms as a possible strategy to improve disease features.

Cerebral Iron Deposition in Neurodegeneration

Disruption of cerebral iron regulation appears to have a role in aging and in the pathogenesis of various neurodegenerative disorders. Possible unfavorable impacts of iron accumulation include reactive oxygen species generation, induction of ferroptosis, and acceleration of inflammatory changes. Whole-brain iron-sensitive magnetic resonance imaging (MRI) techniques allow the examination of macroscopic patterns of brain iron deposits in vivo, while modern analytical methods ex vivo enable the determination of metal-specific content inside individual cell-types, sometimes also within specific cellular compartments. The present review summarizes the whole brain, cellular, and subcellular patterns of iron accumulation in neurodegenerative diseases of genetic and sporadic origin. We also provide an update on mechanisms, biomarkers, and effects of brain iron accumulation in these disorders, focusing on recent publications. In Parkinson’s disease, Friedreich’s disease, and several disorders within the neurodegeneration with brain iron accumulation group, there is a focal siderosis, typically in regions with the most pronounced neuropathological changes. The second group of disorders including multiple sclerosis, Alzheimer’s disease, and amyotrophic lateral sclerosis shows iron accumulation in the globus pallidus, caudate, and putamen, and in specific cortical regions. Yet, other disorders such as aceruloplasminemia, neuroferritinopathy, or Wilson disease manifest with diffuse iron accumulation in the deep gray matter in a pattern comparable to or even more extensive than that observed during normal aging. On the microscopic level, brain iron deposits are present mostly in dystrophic microglia variably accompanied by iron-laden macrophages and in astrocytes, implicating a role of inflammatory changes and blood–brain barrier disturbance in iron accumulation. Options and potential benefits of iron reducing strategies in neurodegeneration are discussed. Future research investigating whether genetic predispositions play a role in brain Fe accumulation is necessary. If confirmed, the prevention of further brain Fe uptake in individuals at risk may be key for preventing neurodegenerative disorders.

Interaction between macrophages and ferroptosis

Abstract

Ferroptosis, a newly discovered iron-dependent cell death pathway, is characterized by lipid peroxidation and GSH depletion mediated by iron metabolism and is morphologically, biologically and genetically different from other programmed cell deaths. Besides, ferroptosis is usually found accompanied by inflammatory reactions. So far, it has been found participating in the development of many kinds of diseases. Macrophages are a group of immune cells that widely exist in our body for host defense and play an important role in tissue homeostasis by mediating inflammation and regulating iron, lipid and amino acid metabolisms through their unique functions like phagocytosis and efferocytosis, cytokines secretion and ROS production under different polarization. According to these common points in ferroptosis characteristics and macrophages functions, it’s obvious that there must be relationship between macrophages and ferroptosis. Therefore, our review aims at revealing the interaction between macrophages and ferroptosis concerning three metabolisms and integrating the application of certain relationship in curing diseases, mostly cancer. Finally, we also provide inspirations for further studies in therapy for some diseases by targeting certain resident macrophages in distinct tissues to regulate ferroptosis.

Facts

Ferroptosis is considered as a newly discovered form characterized by its nonapoptotic and iron-dependent lipid hydroperoxide, concerning iron, lipid and amino acid metabolisms.

Ferroptosis has been widely found playing a crucial part in various diseases, including hepatic diseases, neurological diseases, cancer, etc.

Macrophages are phagocytic immune cells, widely existing and owning various functions such as phagocytosis and efferocytosis, cytokines secretion and ROS production.

Macrophages are proved to participate in mediating metabolisms and initiating immune reactions to maintain balance in our body.

Recent studies try to treat cancer by altering macrophages’ polarization which damages tumor microenvironment and induces ferroptosis of cancer cells.

Open questions

How do macrophages regulate ferroptosis of other tissue cells specifically?

Can we use the interaction between macrophages and ferroptosis in treating diseases other than cancer?

What can we do to treat diseases related to ferroptosis by targeting macrophages?

Is the use of the relationship between macrophages and ferroptosis more effective than other therapies when treating diseases?

The Emerging Role of Ferroptosis in Sepsis

Ferroptosis is a novel form of cell death characterized by the iron-dependent accumulation of lipid peroxides and is different from other types of cell death. The mechanisms of ferroptosis are discussed in the review, including System Xc-, Glutathione Peroxidase 4 pathway, Ferroptosis Suppressor Protein 1 and Dihydroorotate Dehydrogenase pathway. Ferroptosis is associated with the occurrence of various diseases, including sepsis. Research in recent years has displayed that ferroptosis is involved in sepsis occurrence and development. Iron chelators can inhibit the development of sepsis and improve the survival rate of septic mice. The ferroptotic cells can release damage-associated molecular patterns and lipid peroxidation, which further mediate inflammatory responses. Ferroptosis inhibitors can resist sepsis-induced multiple organ dysfunction and inflammation. Finally, we reviewed ferroptosis, an iron-dependent form of cell death that is different from other types of cell death in biochemistry, morphology, and major regulatory mechanisms, which is involved in multiple organ injuries caused by sepsis. Exploring the relationship between sepsis and ferroptosis may yield new treatment targets for sepsis.

Forsythoside A Mitigates Alzheimer's-like Pathology by Inhibiting Ferroptosis-mediated Neuroinflammation via Nrf2/GPX4 Axis Activation

Ferroptosis and neuroinflammation play crucial roles in Alzheimer's disease (AD) pathophysiology. Forsythoside A (FA), the main constituent of Forsythia suspensa (Thunb.) Vahl., possesses anti-inflammatory, antibacterial, antioxidant, and neuroprotective properties. The present study aimed to investigate the potential role of FA in AD neuropathology using male APP/PS1 double transgenic AD mice, Aβ_1-42-exposed N2a cells, erastin-stimulated HT22 cells, and LPS-induced BV2 cells. FA treatment significantly improved mitochondrial function and inhibited lipid peroxidation in Aβ_1-42-exposed N2a cells. In LPS-stimulated BV2 cells, FA treatment decreased the formation of the pro-inflammatory factors IL-6, IL-1β, and NO. In male APP/PS1 mice, FA treatment ameliorated memory and cognitive impairments and suppressed Aβ deposition and p-tau levels in the brain. Analyses using proteomics, immunohistochemistry, ELISA, and western blot revealed that FA treatment significantly augmented dopaminergic signaling, inhibited iron deposition and lipid peroxidation, prevented the activation of IKK/IκB/NF-κB signaling, reduced the secretion of pro-inflammatory factors, and promoted the production of anti-inflammatory factors in the brain. FA treatment exerted anti-ferroptosis and anti-neuroinflammatory effects in erastin-stimulated HT22 cells, and the Nrf2/GPX4 axis played a key role in these effects. Collectively, these results demonstrate the protective effects of FA and highlight its therapeutic potential as a drug component for AD treatment.

A Distinct Hibiscus sabdariffa Extract Prevents Iron Neurotoxicity, a Driver of Multiple Sclerosis Pathology

Iron deposition in the brain begins early in multiple sclerosis (MS) and continues unabated. Ferrous iron is toxic to neurons, yet the therapies used in MS do not counter iron neurotoxicity. Extracts of Hibiscus sabdariffa (HS) are used in many cultures for medicinal purposes. We collected a distinct HS extract and found that it abolished the killing of neurons by iron in culture; medications used in MS were ineffective when similarly tested. Neuroprotection by HS was not due to iron chelation or anthocyanin content. In free radical scavenging assays, HS was equipotent to alpha lipoic acid, an anti-oxidant being tested in MS. However, alpha lipoic acid was only modestly protective against iron-mediated killing. Moreover, a subfraction of HS without radical scavenging activity negated iron toxicity, whereas a commercial hibiscus preparation with anti-oxidant activity could not. The idea that HS might have altered properties within neurons to confer neuroprotection is supported by its amelioration of toxicity caused by other toxins: beta-amyloid, rotenone and staurosporine. Finally, in a mouse model of MS, HS reduced disability scores and ameliorated the loss of axons in the spinal cord. HS holds therapeutic potential to counter iron neurotoxicity, an unmet need that drives the progression of disability in MS.

Mechanistic Insights Expatiating the Redox-Active-Metal-Mediated Neuronal Degeneration in Parkinson's Disease

Parkinson’s disease (PD) is a complicated and incapacitating neurodegenerative malady that emanates following the dopaminergic (DArgic) nerve cell deprivation in the substantia nigra pars compacta (SN-PC). The etiopathogenesis of PD is still abstruse. Howbeit, PD is hypothesized to be precipitated by an amalgamation of genetic mutations and exposure to environmental toxins. The aggregation of α-synucelin within the Lewy bodies (LBs), escalated oxidative stress (OS), autophagy-lysosome system impairment, ubiquitin-proteasome system (UPS) impairment, mitochondrial abnormality, programmed cell death, and neuroinflammation are regarded as imperative events that actively participate in PD pathogenesis. The central nervous system (CNS) relies heavily on redox-active metals, particularly iron (Fe) and copper (Cu), in order to modulate pivotal operations, for instance, myelin generation, synthesis of neurotransmitters, synaptic signaling, and conveyance of oxygen (O₂). The duo, namely, Fe and Cu, following their inordinate exposure, are viable of permeating across the blood–brain barrier (BBB) and moving inside the brain, thereby culminating in the escalated OS (through a reactive oxygen species (ROS)-reliant pathway), α-synuclein aggregation within the LBs, and lipid peroxidation, which consequently results in the destruction of DArgic nerve cells and facilitates PD emanation. This review delineates the metabolism of Fe and Cu in the CNS, their role and disrupted balance in PD. An in-depth investigation was carried out by utilizing the existing publications obtained from prestigious medical databases employing particular keywords mentioned in the current paper. Moreover, we also focus on decoding the role of metal complexes and chelators in PD treatment. Conclusively, metal chelators hold the aptitude to elicit the scavenging of mobile/fluctuating metal ions, which in turn culminates in the suppression of ROS generation, and thereby prelude the evolution of PD.

Low plasma serotonin linked to higher nigral iron in Parkinson's disease

A growing body of evidence suggests nigral iron accumulation plays an important role in the pathophysiology of Parkinson's disease (PD), contributing to dopaminergic neuron loss in the substantia nigra pars compacta (SNc). Converging evidence suggests this accumulation might be related to, or increased by, serotonergic dysfunction, a common, often early feature of the disease. We investigated whether lower plasma serotonin in PD is associated with higher nigral iron. We obtained plasma samples from 97 PD patients and 89 controls and MRI scans from a sub-cohort (62 PD, 70 controls). We measured serotonin concentrations using ultra-high performance liquid chromatography and regional iron content using MRI-based quantitative susceptibility mapping. PD patients had lower plasma serotonin (p < 0.0001) and higher nigral iron content (SNc: p < 0.001) overall. Exclusively in PD, lower plasma serotonin was correlated with higher nigral iron (SNc: r(58) =  - 0.501, p < 0.001). This correlation was significant even in patients newly diagnosed (< 1 year) and stronger in the SNc than any other region examined. This study reveals an early, linear association between low serotonin and higher nigral iron in PD patients, which is absent in controls. This is consistent with a serotonin-iron relationship in the disease process, warranting further studies to determine its cause and directionality.

Ferroptosis as a Major Factor and Therapeutic Target for Neuroinflammation in Parkinson's Disease

Mounting evidence suggests that ferroptosis is not just a consequence but also a fundamental contributor to the development and progression of Parkinson’s disease (PD). Ferroptosis is characterized as iron-dependent regulated cell death caused by excessive lipid peroxidation, leading to plasma membrane rupture, release of damage-associated molecular patterns, and neuroinflammation. Due to the crucial role of intracellular iron in mediating the production of reactive oxygen species and the formation of lipid peroxides, ferroptosis is intimately controlled by regulators involved in many aspects of iron metabolism, including iron uptake, storage and export, and by pathways constituting the antioxidant systems. Translational and transcriptional regulation of iron homeostasis and redox status provide an integrated network to determine the sensitivity of ferroptosis. We herein review recent advances related to ferroptosis, ranging from fundamental mechanistic discoveries and cutting-edge preclinical animal studies, to clinical trials in PD and the regulation of neuroinflammation via ferroptosis pathways. Elucidating the roles of ferroptosis in the survival of dopaminergic neurons and microglial activity can enhance our understanding of the pathogenesis of PD and provide opportunities for the development of novel prevention and treatment strategies.

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.

Glutamate, Glutamine, GABA and Oxidative Products in the Pons Following Cortical Injury and Their Role in Motor Functional Recovery

Brain injury leads to an excitatory phase followed by an inhibitory phase in the brain. The clinical sequelae caused by cerebral injury seem to be a response to remote functional inhibition of cerebral nuclei located far from the motor cortex but anatomically related to the injury site. It appears that such functional inhibition is mediated by an increase in lipid peroxidation (LP). To test this hypothesis, we report data from 80 rats that were allocated to the following groups: the sham group (n = 40), in which rats received an intracortical infusion of artificial cerebrospinal fluid (CSF); the injury group (n = 20), in which rats received CSF containing ferrous chloride (FeCl₂, 50 mM); and the recovery group (n = 20), in which rats were injured and allowed to recover. Beam-walking, sensorimotor and spontaneous motor activity tests were performed to evaluate motor performance after injury. Lipid fluorescent products (LFPs) were measured in the pons. The total pontine contents of glutamate (GLU), glutamine (GLN) and gamma-aminobutyric acid (GABA) were also measured. In injured rats, the motor deficits, LFPs and total GABA and GLN contents in the pons were increased, while the GLU level was decreased. In contrast, in recovering rats, none of the studied variables were significantly different from those in sham rats. Thus, motor impairment after cortical injury seems to be mediated by an inhibitory pontine response, and functional recovery may result from a pontine restoration of the GLN-GLU-GABA cycle, while LP may be a primary mechanism leading to remote pontine inhibition after cortical injury.

The Macrophage Iron Signature in Health and Disease

Throughout life, macrophages are located in every tissue of the body, where their main roles are to phagocytose cellular debris and recycle aging red blood cells. In the tissue niche, they promote homeostasis through trophic, regulatory, and repair functions by responding to internal and external stimuli. This in turn polarizes macrophages into a broad spectrum of functional activation states, also reflected in their iron-regulated gene profile. The fast adaptation to the environment in which they are located helps to maintain tissue homeostasis under physiological conditions.