Iron is a potential key mediator of glutamate excitotoxicity in spinal cord motor neurons

Untargeted Pixel-by-Pixel Imaging of Metabolite Ratio Pairs as a Novel Tool for Biomedical Discovery in Mass Spectrometry Imaging

Mass spectrometry imaging (MSI) is a powerful technology used to define the spatial distribution and relative abundance of structurally identified and yet-undefined metabolites across tissue cryosections. While numerous software packages enable pixel-by-pixel imaging of individual metabolites, the research community lacks a discovery tool that images all metabolite abundance ratio pairs. Importantly, recognition of correlated metabolite pairs informs discovery of unanticipated molecules contributing to shared metabolic pathways, uncovers hidden metabolic heterogeneity across cells and tissue subregions, and indicates single-timepoint flux through pathways of interest. Here, we describe the development and implementation of an untargeted R package workflow for pixel-by-pixel ratio imaging of all metabolites detected in an MSI experiment. Considering untargeted MSI studies of murine brain and embryogenesis, we demonstrate that ratio imaging minimizes systematic data variation introduced by sample handling and instrument drift, markedly enhances spatial image resolution, and reveals previously unrecognized metabotype-distinct tissue regions. Furthermore, ratio imaging facilitates identification of novel regional biomarkers and provides anatomical information regarding spatial distribution of metabolite-linked biochemical pathways. The algorithm described herein is applicable to any MSI dataset containing spatial information for metabolites, peptides or proteins, offering a potent tool to enhance knowledge obtained from current spatial metabolite profiling technologies.

Application of Deferoxamine in Tissue Regeneration Attributed to Promoted Angiogenesis

Deferoxamine, an iron chelator used to treat diseases caused by excess iron, has had a Food and Drug Administration-approved status for many years. A large number of studies have confirmed that deferoxamine can reduce inflammatory response and promote angiogenesis. Blood vessels play a crucial role in sustaining vital life by facilitating the delivery of immune cells, oxygen, and nutrients, as well as eliminating waste products generated during cellular metabolism. Dysfunction in blood vessels may contribute significantly to the development of life-threatening diseases. Anti-angiogenesis therapy and pro-angiogenesis/angiogenesis strategies have been frequently recommended for various diseases. Herein, we describe the mechanism by which deferoxamine promotes angiogenesis and summarize its application in chronic wounds, bone repair, and diseases of the respiratory system. Furthermore, we discuss the drug delivery system of deferoxamine for treating various diseases, providing constructive ideas and inspiration for the development of new treatment strategies.

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.

Functional effects of haemoglobin can be rescued by haptoglobin in an in vitro model of subarachnoid haemorrhage

During subarachnoid haemorrhage, a blood clot forms in the subarachnoid space releasing extracellular haemoglobin (Hb), which causes oxidative damage and cell death in surrounding tissues. High rates of disability and cognitive decline in SAH survivors are attributed to loss of neurons and functional connections during secondary brain injury. Haptoglobin sequesters Hb for clearance, but this scavenging system is overwhelmed after a haemorrhage. Whilst exogenous haptoglobin application can attenuate cytotoxicity of Hb in vitro and in vivo, the functional effects of sub-lethal Hb concentrations on surviving neurons and whether cellular function can be protected with haptoglobin treatment remain unclear. Here we use cultured neurons to investigate neuronal health and function across a range of Hb concentrations to establish the thresholds for cellular damage and investigate synaptic function. Hb impairs ATP concentrations and cytoskeletal structure. At clinically relevant but sub-lethal Hb concentrations, we find that synaptic AMPAR-driven currents are reduced, accompanied by a reduction in GluA1 subunit expression. Haptoglobin co-application can prevent these deficits by scavenging free Hb to reduce it to sub-threshold concentrations and does not need to be present at stoichiometric amounts to achieve efficacy. Haptoglobin itself does not impair measures of neuronal health and function at any concentration tested. Our data highlight a role for Hb in modifying synaptic function in surviving neurons, which may link to impaired cognition or plasticity after SAH and support the development of haptoglobin as a therapy for subarachnoid haemorrhage.

Lutein Decreases Inflammation and Oxidative Stress and Prevents Iron Accumulation and Lipid Peroxidation at Glutamate-Induced Neurotoxicity

The xanthophyll carotenoid lutein has been widely used as supplementation due to its protective effects in light-induced oxidative stress. Its antioxidant and anti-inflammatory features suggest that it has a neuroprotective role as well. Glutamate is a major excitatory neurotransmitter in the central nervous system (CNS), which plays a key role in regulating brain function. Excess accumulation of intracellular glutamate accelerates an increase in the concentration of reactive oxygen species (ROS) in neurons leading to glutamate neurotoxicity. In this study, we focused on the effects of glutamate on SH-SY5Y neuroblastoma cells to identify the possible alterations in oxidative stress, inflammation, and iron metabolism that affect the neurological function itself and in the presence of antioxidant lutein. First, ROS measurements were performed, and then catalase (CAT) and Superoxide Dismutase (SOD) enzyme activity were determined by enzyme activity assay kits. The ELISA technique was used to detect proinflammatory TNFα, IL-6, and IL-8 cytokine secretions. Alterations in iron uptake, storage, and release were followed by gene expression measurements and Western blotting. Total iron level detections were performed by a ferrozine-based iron detection method, and a heme assay kit was used for heme measurements. The gene expression toward lipid-peroxidation was determined by RT-PCR. Our results show glutamate changes ROS, inflammation, and antioxidant enzyme activity, modulate iron accumulation, and may initiate lipid peroxidation in SH-SY5Y cells. Meanwhile, lutein attenuates the glutamate-induced effects on ROS, inflammation, iron metabolism, and lipid peroxidation. According to our findings, lutein could be a beneficial, supportive treatment in neurodegenerative disorders.

Attenuated succinate accumulation relieves neuronal injury induced by hypoxia in neonatal mice

Hypoxia causes neonatal neuronal damage. However, the underlying mechanism remains unclear. This study aimed to explore the changes in succinate levels and identify the mechanisms underlying their contribution to hypoxia-induced damage in newborn mice. The neonatal C57BL/6J mouse hypoxia model was used in our study. We evaluated the levels of succinate, iron, reactive oxygen species (ROS), and mitochondrial ROS, and assessed mitophagy, neuronal damage, and learning and memory function, after hypoxia treatment. The neonatal mice showed increased succinate levels in the early hypoxia stage, followed by increased levels of oxidative stress, iron stress, neuronal damage, and cognitive deficits. Succinate levels were significantly reduced following treatment with inhibitors of succinate dehydrogenase (SDH), purine nucleotide cycle (PNC), and malate/aspartate shuttle (MAS), with the corresponding attenuation of oxidative stress, iron stress, neuronal damage, and cognitive impairment. Reversal catalysis of SDH through fumarate from the PNC and MAS pathways might be involved in hypoxia-induced succinate accumulation. Succinate accumulation in the early period after hypoxia may crucially contribute to oxidative and iron stress. Relieving succinate accumulation at the early hypoxia stage could prevent neuronal damage and cognitive impairment in neonatal hypoxia.

Formaldehyde induces ferroptosis in hippocampal neuronal cells by upregulation of the Warburg effect

The mechanisms underlying formaldehyde (FA)-induced neurotoxicity have not yet been fully clarified. Ferroptosis is a novel regulatory cell death and the Warburg effect is involved in regulating neural function. In this study, we investigated whether FA-induced neurotoxicity is implicated in neuronal ferroptosis and determined whether the Warburg effect mediates FA-induced neuronal ferroptosis. We found that FA (0.1, 0.5 and 1.0 mM, 6 h) induced cell death in HT22 cells (a cell line of mouse hippocampal neuron), as evidenced by a decrease in cell viability and an increase in cell mortality; enhanced oxidative stress, as evidenced by a decrease in glutathione (GSH) and increases in malondialdehyde (MDA), 4-Hydroxynonenal (4-HNE), as well as reactive oxygen species (ROS); increased the iron content; and upregulated the ferroptosis-associated genes, including Ptgs2 (prostaglandin-endoperoxide synthase 2), GLS2 (glutaminase 2), solute carrier family 1 member 5 (SLC1A5), and solute carrier family 38 member 1 (SLC38A1) in HT22 cells, indicating the inductive role of FA in the ferroptosis of HT22 cells. Meanwhile, we found that FA (0.1, 1, 10 μmol) decreased the cross-sectional of mitochondria, increased the level of lipid ROS and iron content in primary hippocampal cells. We showed that FA (0.1, 0.5 and 1.0 mM, 6 h) upregulated the Warburg effect in HT22 cells, as evidenced by up-regulations of pyruvate kinase M2 (PKM2), pyruvate dehydrogenase kinase 1(PDK-1), and lactate dehydrogenase (LDHA) proteins; down-regulation of pyruvate dehydrogenase (PDH); and an increase in lactate production. Also, we found that FA (0.1, 1, 10 μmol, 7 d) upregulated the Warburg effect in hippocampal tissue, as evidenced by up-regulations of PKM2, PDK-1, and LDHA proteins; down-regulation of PDH. Furthermore, the inhibition of the Warburg effect by dichloroacetate (DCA) protected HT22 cells against FA-induced ferroptosis and cell death. Collectively, these data indicated that FA induces ferroptosis in hippocampal neuronal cells by upregulation of the Warburg effect.

Iron potentiates microglial interleukin-1β secretion induced by amyloid-β

Alzheimer's disease (AD) is characterized by accumulation of amyloid-beta (Aβ) senile plaques in patients' brain tissues. Elevated levels of interleukin-1beta (IL-1β) have been identified in cerebrospinal fluid of living AD patients and in animal models of AD. Increased expression of IL-1β and iron accumulation have been identified in microglial cells that cluster around amyloid plaques in AD mouse models and post-mortem brain tissues of AD patients. The goals of this study were to determine the effects of Aβ on the secretion of IL-1β by microglial cells and whether iron status influences this pro-inflammatory signaling cue. Immortalized microglial (IMG) cells were incubated with Aβ with or without iron. qRT-PCR and western blot analyses showed that Aβ induces biosynthesis of IL-1β by IMG cells. IMG cells secrete the mature form of IL-1β in a caspase 1-dependent manner. Incubation with iron provoked a greater pro-inflammatory response. Inhibition of the iron transporter divalent metal transporter 1 protected IMG cells against Aβ-induced inflammation. Potentiation of Aβ-elicited IL-1β induction by iron was also antagonized by ROS inhibitors, supporting the model that divalent metal transporter 1-mediated iron loading and subsequent increase in ROS contribute to the inflammatory effects of Aβ in microglia. Immunoblotting and immunofluorescence microscopy indicate that iron enhances Aβ activation of NF-κB signaling to promote IL-1β synthesis. These results support the hypothesis that Aβ stimulates IL-1β expression by activating NF-κB signaling in microglia cells. Most importantly, iron appears to exacerbate the pro-inflammatory effects of Aβ to increase IL-1β levels.

The relationship between measurement of in vivo brain glutamate and markers of iron metabolism: A proton magnetic resonance spectroscopy study in healthy adults

Fundamental human studies which address associations between glutamate and iron metabolism are needed. Basic research reports associations between glutamate and iron metabolism. Human studies report sex differences in iron metabolism and glutamate concentrations, which suggest that these relationships may differ by sex. We hypothesised associations would be apparent between in vivo glutamate and peripheral markers of iron metabolism, and these associations would differ by sex. To test this, we recruited 40 healthy adults (20 men, 20 women) and measured (a) standard clinical biomarker concentrations for iron metabolism and (b) an in vivo proxy for glutamate concentration, glutamate with glutamine in relation to total creatine containing metabolites using proton magnetic resonance spectroscopy studies with a two-dimensional chemical shift imaging slice, with voxels located in bilateral dorsolateral prefrontal cortices, anterior cingulate cortices and frontal white matter. Only the female group reported significant associations between peripheral markers of iron metabolism and Glx:tCr concentration: (a) right dorsolateral prefrontal cortex Glx:tCr associated positively with serum transferrin (r = .60, p = .006) and negatively with transferrin saturation (r = -.62, p = .004) and (b) right frontal white matter Glx:tCr associated negatively with iron concentration (r = -.59, p = .008) and transferrin saturation (r = -.65, p = .002). Our results support associations between iron metabolism and our proxy for in vivo glutamate concentration (Glx:tCr). These associations were limited to women, suggesting a stronger regulatory control between iron and glutamate metabolism. These associations support additional fundamental research into the molecular mechanisms of this regulatory control.

Deciphering the Iron Side of Stroke: Neurodegeneration at the Crossroads Between Iron Dyshomeostasis, Excitotoxicity, and Ferroptosis

In general, iron represents a double-edged sword in metabolism in most tissues, especially in the brain. Although the high metabolic demands of brain cells require iron as a redox-active metal for ATP-producing enzymes, the brain is highly vulnerable to the devastating consequences of excessive iron-induced oxidative stress and, as recently found, to ferroptosis as well. The blood-brain barrier (BBB) protects the brain from fluctuations in systemic iron. Under pathological conditions, especially in acute brain pathologies such as stroke, the BBB is disrupted, and iron pools from the blood gain sudden access to the brain parenchyma, which is crucial in mediating stroke-induced neurodegeneration. Each brain cell type reacts with changes in their expression of proteins involved in iron uptake, efflux, storage, and mobilization to preserve its internal iron homeostasis, with specific organelles such as mitochondria showing specialized responses. However, during ischemia, neurons are challenged with excess extracellular glutamate in the presence of high levels of extracellular iron; this causes glutamate receptor overactivation that boosts neuronal iron uptake and a subsequent overproduction of membrane peroxides. This glutamate-driven neuronal death can be attenuated by iron-chelating compounds or free radical scavenger molecules. Moreover, vascular wall rupture in hemorrhagic stroke results in the accumulation and lysis of iron-rich red blood cells at the brain parenchyma and the subsequent presence of hemoglobin and heme iron at the extracellular milieu, thereby contributing to iron-induced lipid peroxidation and cell death. This review summarizes recent progresses made in understanding the ferroptosis component underlying both ischemic and hemorrhagic stroke subtypes.

Deferoxamine promotes recovery of traumatic spinal cord injury by inhibiting ferroptosis

Ferroptosis is an iron-dependent novel cell death pathway. Deferoxamine, a ferroptosis inhibitor, has been reported to promote spinal cord injury repair. It has yet to be clarified whether ferroptosis inhibition represents the mechanism of action of Deferoxamine on spinal cord injury recovery. A rat model of Deferoxamine at thoracic 10 segment was established using a modified Allen's method. Ninety 8-week-old female Wistar rats were used. Rats in the Deferoxamine group were intraperitoneally injected with 100 mg/kg Deferoxamine 30 minutes before injury. Simultaneously, the Sham and Deferoxamine groups served as controls. Drug administration was conducted for 7 consecutive days. The results were as follows: (1) Electron microscopy revealed shrunken mitochondria in the spinal cord injury group. (2) The Basso, Beattie and Bresnahan locomotor rating score showed that recovery of the hindlimb was remarkably better in the Deferoxamine group than in the spinal cord injury group. (3) The iron concentration was lower in the Deferoxamine group than in the spinal cord injury group after injury. (4) Western blot assay revealed that, compared with the spinal cord injury group, GPX4, xCT, and glutathione expression was markedly increased in the Deferoxamine group. (5) Real-time polymerase chain reaction revealed that, compared with the Deferoxamine group, mRNA levels of ferroptosis-related genes Acyl-CoA synthetase family member 2 (ACSF2) and iron-responsive element-binding protein 2 (IREB2) were up-regulated in the Deferoxamine group. (6) Deferoxamine increased survival of neurons and inhibited gliosis. These findings confirm that Deferoxamine can repair spinal cord injury by inhibiting ferroptosis. Targeting ferroptosis is therefore a promising therapeutic approach for spinal cord injury.

Brain Iron Homeostasis: A Focus on Microglial Iron

Iron is an essential trace element required for important brain functions including oxidative metabolism, synaptic plasticity, myelination, and the synthesis of neurotransmitters. Disruptions in brain iron homeostasis underlie many neurodegenerative diseases. Increasing evidence suggests that accumulation of brain iron and chronic neuroinflammation, characterized by microglia activation and secretion of proinflammatory cytokines, are hallmarks of neurodegenerative disorders including Alzheimer’ s disease. While substantial efforts have led to an increased understanding of iron metabolism and the role of microglial cells in neuroinflammation, important questions still remain unanswered. Whether or not increased brain iron augments the inflammatory responses of microglial cells, including the molecular cues that guide such responses, is still unclear. How these brain macrophages accumulate, store, and utilize intracellular iron to carry out their various functions under normal and disease conditions is incompletely understood. Here, we describe the known and emerging mechanisms involved in microglial cell iron transport and metabolism as well as inflammatory responses in the brain, with a focus on AD.

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

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

Hemoglobin metabolism by-products are associated with an inflammatory response in patients with hemorrhagic stroke

Objective

To evaluate the relationships of brain iron and heme with the inflammatory response of the systemic and central nervous systems and to investigate the role of defensive systems against the toxicity of iron and heme in the central nervous system.

Methods

We assessed a prospective cohort of patients presenting with intracerebral and subarachnoid hemorrhage. We assayed plasma and cerebrospinal fluid samples for the presence of iron, heme, hemopexin, haptoglobin, enolase, S100-β and cytokines for the first three days following hemorrhagic stroke. We also analyzed the dynamic changes in these components within both fluids and their relationship with early mortality rates.

Results

Hemopexin and haptoglobin concentrations were nearly negligible in the brain after intracerebral and subarachnoid hemorrhage. Cerebrospinal fluid iron and heme concentrations correlated with a pro-inflammatory response in the central nervous system, and plasmatic and cerebrospinal fluid inflammatory profiles on the third day after hemorrhagic stroke were related to early mortality rates. Interleukin 4 levels within the cerebrospinal fluid during the first 24 hours after hemorrhagic stroke were found to be higher in survivors than in non-survivors.

Conclusion

Iron and heme are associated with a pro-inflammatory response in the central nervous system following hemorrhagic stroke, and protections against hemoglobin and heme are lacking within the human brain. Patient inflammatory profiles were associated with a poorer prognosis, and local anti-inflammatory responses appeared to have a protective role.

Neuroprotective effect of deferoxamine on N-methyl-d-aspartate-induced excitotoxicity in RGC-5 cells

Many N-methyl-d-aspartate (NMDA) receptor antagonists have been used to treat neurodegenerative diseases induced by glutamate excitotoxicity in clinics. However, the universality of the glutamic acid neurotransmitter system makes the glutamic acid receptor blockers inefficient and unsafe. Thus, regulating the downstream signaling pathway in the excitotoxicity of glutamic acid may be a more effective and safer way to antagonize the glutamic acid receptor. In this study, we investigated the effect of deferoxamine (DFO), an iron chelator, on the NMDA-induced excitotoxicity. RGC-5 cells were cultured and identified in vitro, and the NMDA-induced injury was assessed. Then the MTT assay was used to estimate the cell survival and JC-1 staining was performed to detect changes in mitochondrial membrane potential. Immunofluorescent staining and western blot analysis were used to analyze the expressions of respiratory chain proteins. It was found that DFO increased the survival rate of RGC-5 cells and that this effect was positively correlated with the concentration of DFO and the treatment time. The mitochondrial membrane potential and the expression levels of succinate dehydrogenase subunit A and cytochrome c oxidase subunit IV were also increased after DFO treatment, while NMDA reduced their expression levels. These data demonstrate that DFO has significant neuroprotective activity against NMDA-induced excitotoxicity in RGC-5 cells.

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

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

New Insights into the Crosstalk between NMDARs and Iron: Implications for Understanding Pathology of Neurological Diseases

Both iron dyshomeostasis and N-methyl-D-aspartate receptors (NMDARs)-mediated neurotoxicity have been shown to have an important role in neurological diseases such as Parkinson’s disease (PD) and Alzheimer’s disease (AD). Evidence proved that activation of NMDARs could promote iron overload and iron-induced neurotoxicity by enhancing iron importer divalent metal transporter 1 (DMT1)-mediated iron uptake and iron releasing from lysosome. Also, iron overload could regulate NMDARs-mediated synaptic transmission. This indicates that there might be a possible relationship between iron and activation of NMDARs in neurological diseases. Understanding this interaction between iron and activation of NMDARs may provide new therapeutic avenues for a more targeted neurotherapeutic strategy for these diseases. Therefore, in this review article, we will describe the dysfunction of iron metabolism and NMDARs in neurological diseases including PD and AD, and summarize the new insight into the mechanisms underlying the interaction between iron and activation of NMDARs.

Proteomic profile of embryonic stem cells with low survival motor neuron protein is consistent with developmental dysfunction

Spinal muscular atrophy is an autosomal recessive motor neuron disease caused by a genetic defect carried by as many as one in 75 people. Unlike most neurological disorders, we know exactly what the genetic basis is of the disorder, but in spite of this, have little understanding of why the low levels of one protein, survival motor neuron protein, results in the specific progressive die back of only one cell type in the body, the motor neuron. Given the fact that all cells in the body of a patient with spinal muscular atrophy share the same low abundance of the protein throughout development, an appropriate approach is to ask how lower levels of survival motor neuron protein affects the proteome of embryonic stem cells prior to development. Convergent biostatistical analyses of a discovery proteomic analysis of these cells provide results that are consistent with the pathomechanistic fate of the developed motor neuron.

Molecular, Cellular and Clinical Aspects of Intracerebral Hemorrhage: Are the Enemies Within?

Hemorrhagic stroke is a disease with high incidence and mortality rates. In addition to the mass lesions that result from hemorrhagic stroke, substances such as the blood-derived products (BDP) (hemoglobin (Hb), heme and iron) induce a potent inflammatory response and exert direct toxic effects on neurons, astrocytes, and microglia. In the present review, we discuss the mechanisms of brain injury secondary to hemorrhagic stroke, focusing on the involvement of BDP as major players of cellular redox imbalance, inflammation, and glutamate excitotoxicity. Potential natural mechanisms of protection against free Hb and heme such as haptoglobin and hemopexin, respectively, are highlighted. We finally discuss the experimental and clinical trials targeting free iron and heme scavenging as well as inflammation, as potential new therapies to minimize the devastating effects of hemorrhagic stroke on brain structure and function.

Deferoxamine, Cerebrovascular Hemodynamics, and Vascular Aging: Potential Role for Hypoxia-Inducible Transcription Factor-1-Regulated Pathways

BACKGROUND AND PURPOSE

Iron chelation therapy is emerging as a novel neuroprotective strategy. The mechanisms of neuroprotection are diverse and include both neuronal and vascular pathways. We sought to examine the effect of iron chelation on cerebrovascular function in healthy aging and to explore whether hypoxia-inducible transcription factor-1 activation may be temporally correlated with vascular changes.

METHODS

We assessed cerebrovascular function (autoregulation, vasoreactivity, and neurovascular coupling) and serum concentrations of vascular endothelial growth factor and erythropoietin, as representative measures of hypoxia-inducible transcription factor-1 activation, during 6 hours of deferoxamine infusion in 24 young and 24 older healthy volunteers in a randomized, blinded, placebo-controlled cross-over study design. Cerebrovascular function was assessed using the transcranial Doppler ultrasound. Vascular endothelial growth factor and erythropoietin serum protein assays were conducted using the Meso Scale Discovery platform.

RESULTS

Deferoxamine elicited a strong age- and time-dependent increase in the plasma concentrations of erythropoietin and vascular endothelial growth factor, which persisted ≤3 hours post infusion (age effect P=0.04; treatment×time P<0.01). Deferoxamine infusion also resulted in a significant time- and age-dependent improvement in cerebral vasoreactivity (treatment×time P<0.01; age P<0.01) and cerebral autoregulation (gain: age×time×treatment P=0.04).

CONCLUSIONS

Deferoxamine infusion improved cerebrovascular function, particularly in older individuals. The temporal association between improved cerebrovascular function and increased serum vascular endothelial growth factor and erythropoietin concentrations is supportive of shared hypoxia-inducible transcription factor-1-regulated pathways. Therefore, pharmacological activation of hypoxia-inducible transcription factor-1 to enhance cerebrovascular function may be a promising neuroprotective strategy in acute and chronic ischemic syndromes, especially in elderly patients.

CLINICAL TRIAL REGISTRATION

URL: http://www.clinicaltrials.gov. Unique identifier: NCT013655104.

Biometals and their therapeutic implications in Alzheimer's disease

No disease modifying therapy exists for Alzheimer's disease (AD). The growing burden of this disease to our society necessitates continued investment in drug development. Over the last decade, multiple phase 3 clinical trials testing drugs that were designed to target established disease mechanisms of AD have all failed to benefit patients. There is, therefore, a need for new treatment strategies. Changes to the transition metals, zinc, copper, and iron, in AD impact on the molecular mechanisms of disease, and targeting these metals might be an alternative approach to treat the disease. Here we review how metals feature in molecular mechanisms of AD, and we describe preclinical and clinical data that demonstrate the potential for metal-based drug therapy.

Iron in multiple sclerosis: roles in neurodegeneration and repair

MRI and histological studies have shown global alterations in iron levels in the brains of patients with multiple sclerosis (MS), including increases in the iron stored by macrophages and microglia. Excessive free iron can be toxic, and accumulation of iron in MS has generally been thought to be detrimental. However, iron maintains the integrity of oligodendrocytes and myelin, and facilitates their regeneration following injury. The extracellular matrix, a key regulator of remyelination, might also modulate iron levels. This Review highlights key histological and MRI studies that have investigated changes in iron distribution associated with MS. Potential sources of iron, as well as iron regulatory proteins and the detrimental roles of excessive iron within the CNS, are also discussed, with emphasis on the importance of iron within cells for oxidative metabolism, proliferation and differentiation of oligodendrocytes, and myelination. In light of the beneficial and detrimental properties of iron within the CNS, we present considerations for treatments that target iron in MS. Such treatments must balance trophic and toxic properties of iron, by providing sufficient iron levels for remyelination and repair while avoiding excesses that might overwhelm homeostatic mechanisms and contribute to damage.

Iron overload accelerates neuronal amyloid-β production and cognitive impairment in transgenic mice model of Alzheimer's disease

Iron dyshomeostasis is proving increasingly likely to be involved in the pathology of Alzheimer's disease (AD); yet, its mechanism is not well understood. Here, we investigated the AD-related mechanism(s) of iron-sulfate exposure in vitro and in vivo, using cultured primary cortical neurons and APP/PS1 AD-model mice, respectively. In both systems, we observed iron-induced disruptions of amyloid precursor protein (APP) processing, neuronal signaling, and cognitive behavior. Iron overload increased production of amyloidogenic KPI-APP and amyloid beta. Further, this APP misprocessing was blocked by MK-801 in vitro, suggesting the effect was N-methyl-D-aspartate receptor (NMDAR) dependent. Calcium imaging confirmed that 24 hours iron exposure led to disrupted synaptic signaling by augmenting GluN2B-containing NMDAR expression-GluN2B messenger RNA and protein levels were increased and promoting excessing extrasynaptic NMDAR signaling. The disrupted GluN2B expression was concurrent with diminished expression of the splicing factors, sc35 and hnRNPA1. In APP/PS1 mice, chronic iron treatment led to hastened progression of cognitive impairment with the novel object recognition discrimination index, revealing a deficit at the age of 4 months, concomitant with augmented GluN2B expression. Together, these data suggest iron-induced APP misprocessing and hastened cognitive decline occur through inordinate extrasynaptic NMDAR activation.

Iron chelation and multiple sclerosis

Histochemical and MRI studies have demonstrated that MS (multiple sclerosis) patients have abnormal deposition of iron in both gray and white matter structures. Data is emerging indicating that this iron could partake in pathogenesis by various mechanisms, e.g., promoting the production of reactive oxygen species and enhancing the production of proinflammatory cytokines. Iron chelation therapy could be a viable strategy to block iron-related pathological events or it can confer cellular protection by stabilizing hypoxia inducible factor 1α, a transcription factor that normally responds to hypoxic conditions. Iron chelation has been shown to protect against disease progression and/or limit iron accumulation in some neurological disorders or their experimental models. Data from studies that administered a chelator to animals with experimental autoimmune encephalomyelitis, a model of MS, support the rationale for examining this treatment approach in MS. Preliminary clinical studies have been performed in MS patients using deferoxamine. Although some side effects were observed, the large majority of patients were able to tolerate the arduous administration regimen, i.e., 6-8 h of subcutaneous infusion, and all side effects resolved upon discontinuation of treatment. Importantly, these preliminary studies did not identify a disqualifying event for this experimental approach. More recently developed chelators, deferasirox and deferiprone, are more desirable for possible use in MS given their oral administration, and importantly, deferiprone can cross the blood-brain barrier. However, experiences from other conditions indicate that the potential for adverse events during chelation therapy necessitates close patient monitoring and a carefully considered administration regimen.

Comparison of deferoxamine and methylprednisolone: protective effect of pharmacological agents on lipid peroxidation in spinal cord injury in rats

STUDY DESIGN

Experimental study.

OBJECTIVE

To investigate the protective effect of deferoxamine (DFO) administration in comparison with methylprednisolone (MP) on lipid peroxidation and antioxidants after spinal cord injury (SCI) in rats.

SUMMARY OF BACKGROUND DATA

DFO is used for treating an iron-chelating agent, which is also used in the treatment of iron poisoning and thalassaemia. The neuroprotective effect of DFO was evaulated as a therapeutic agent for SCI.

METHODS

Forty Wistar rats were randomly divided into 5 groups as sham laminectomy (n = 8), laminectomy with SCI (n = 8), laminectomy with SCI and 0.9% saline intraperitoneal (i.p.) (n = 8), laminectomy with SCI and 30 mg/kg MP i.p. (n = 8), and laminectomy with SCI and 30 mg/kg DFO i.p. (n = 8). Neurological deficits were examined 24 hours after trauma, and all rats were killed. Spinal cord segments were harvested for both biochemical and histopathological evaluation.

RESULTS

At 24 hours post-SCI, whereas malondialdehyde levels were increased, superoxide dismutase, catalase, and glutathione peroxidase levels were decreased in groups I, II, and III. MP and DFO treatment decreased MDA levels and increased superoxide dismutase CAT, and glutathione peroxidase levels in control and study groups. There was no statistically significant difference between treatment with MP and DFO (P> 0.05). All rats were paraplegic after SCI, except in the sham group. Histopathological improvement was observed in control and study groups.

CONCLUSION

This study indicates that beneficial effects may be provided and further studies need to investigate the dose-dependent beneficial and side effects of DFO in SCI.

LEVEL OF EVIDENCE

N/A.

Iron depletion induced by bloodletting and followed by rhEPO administration as a therapeutic strategy in progressive multiple sclerosis: a pilot, open-label study with neurophysiological measurements

OBJECTIVES

To evaluate the concept that iron depletion (ID) induced by bloodletting and followed by recombinant human erythropoietin (rhEPO) administration could be a therapeutic strategy in progressive multiple sclerosis (PMS) and that it could be assessed by neurophysiological measurements.

PATIENTS AND METHODS

In four patients with PMS, bloodletting was performed until ID was induced, and then rhEPO was administered (300 UI/kg/week). The changes induced by the treatment were assessed by clinical scores, biological tests, and neurophysiological study of cortical excitability using transcranial magnetic stimulation techniques.

RESULTS

The treatment was well tolerated except for muscle cramps and one popliteal vein thrombosis in a patient confined to chair. ID was obtained within 28 weeks and was associated with endogenous production of EPO. No bloodletting was further required during a six-month period after introduction of rhEPO. At the end of the follow-up (up to one year), fatigue and walking capacities tended to improve in two patients. Neurophysiological changes were characterized by an increased cortical excitability, including a decrease of motor thresholds and an enhancement of intracortical facilitation and cerebellothalamocortical inhibition.

CONCLUSIONS

The combined ID-rhEPO therapy could authorize a prolonged administration of rhEPO in PMS patients, able to modify cortical excitability of the glutamatergic and gabaergic circuits. These preliminary data are encouraging to design a larger, controlled therapeutical trial to assess the value of such a strategy to improve functional symptoms in PMS patients, and maybe to prevent axonal degeneration. Neurophysiological measurements based on cortical excitability studies could provide sensitive parameters to evaluate treatment-induced changes in this context.

A delicate balance: Iron metabolism and diseases of the brain

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

Systemic iron chelation results in limited functional and histological recovery after traumatic spinal cord injury in rats

Excess iron accumulation within the spinal cord is thought to exacerbate tissue damage and limit functional recovery after traumatic spinal cord injury (SCI). An optimal treatment to reverse or prevent damage would be to deliver an iron chelator systemically. Thus, we tested oral delivery of deferasirox (Exjade) in multiple studies using a rat model of mid-thoracic spinal contusion. Female Sprague-Dawley rats received a moderate contusion at vertebral level T8 and were given daily deferasirox for the first 7 or 14 days post-injury. The first two studies showed modest improvements in hindlimb function with limited improvement in tissue sparing. Two subsequent experiments to assess chronic functional changes and test longer-duration treatments failed to produce significant improvements. Testing a 2-fold higher deferasirox dose resulted in toxic side effects. To verify iron chelation treatment was effective, hepatic iron levels were measured which revealed that deferasirox robustly and significantly reduced systemic iron levels. Overall, this study suggests that oral iron chelation with deferasirox may lead to small but significant improvements in locomotor recovery or tissue sparing. However, given the lack of robust beneficial effects combined with potentially detrimental side effects such as exacerbated systemic anemia, oral administration of iron chelators may not be ideal for minimizing intraspinal iron-mediated pathology after SCI.

Pathogenic implications of iron accumulation in multiple sclerosis

Iron, an essential element used for a multitude of biochemical reactions, abnormally accumulates in the CNS of patients with multiple sclerosis (MS). The mechanisms of abnormal iron deposition in MS are not fully understood, nor do we know whether these deposits have adverse consequences, that is, contribute to pathogenesis. With some exceptions, excess levels of iron are represented concomitantly in multiple deep gray matter structures often with bilateral representation, whereas in white matter, pathological iron deposits are usually located at sites of inflammation that are associated with veins. These distinct spatial patterns suggest disparate mechanisms of iron accumulation between these regions. Iron has been postulated to promote disease activity in MS by various means: (i) iron can amplify the activated state of microglia resulting in the increased production of proinflammatory mediators; (ii) excess intracellular iron deposits could promote mitochondria dysfunction; and (iii) improperly managed iron could catalyze the production of damaging reactive oxygen species (ROS). The pathological consequences of abnormal iron deposits may be dependent on the affected brain region and/or accumulation process. Here, we review putative mechanisms of enhanced iron uptake in MS and address the likely roles of iron in the pathogenesis of this disease.

Epigallocatechin-3-gallate protects motor neurons and regulates glutamate level

Epigallocatechin-3-gallate (EGCG) is a major component of green tea polyphenols which displays potential properties of anticancer and neuroprotection. Here we show that protection of motor neuron by EGCG is associated with regulating glutamate level in organotypic culture of rat spinal cord. In this model, EGCG blocked glutamate excitotoxicity caused by threohydroxyaspartate, an inhibitor of glutamate transporter. This property of EGCG may be not due to its intrinsic antioxidative activity, because another antioxidant could not regulate glutamate level under the same condition. These results show that EGCG may be a potential therapeutic candidate for neurodegenerative diseases involving glutamate excitotoxicity such as ALS.