Iron Chelators as Potential Therapeutic Agents for Parkinson's Disease

Type 2 Diabetes Mellitus Exacerbates Pathological Processes of Parkinson's Disease: Insights from Signaling Pathways Mediated by Insulin Receptors

Parkinson's disease (PD), a chronic and common neurodegenerative disease, is characterized by the progressive loss of dopaminergic neurons in the dense part of the substantia nigra and abnormal aggregation of alpha-synuclein. Type 2 diabetes mellitus (T2DM) is a metabolic disease characterized by chronic insulin resistance and deficiency in insulin secretion. Extensive evidence has confirmed shared pathogenic mechanisms underlying PD and T2DM, such as oxidative stress caused by insulin resistance, mitochondrial dysfunction, inflammation, and disorders of energy metabolism. Conventional drugs for treating T2DM, such as metformin and glucagon-like peptide-1 receptor agonists, affect nerve repair. Even drugs for treating PD, such as levodopa, can affect insulin secretion. This review summarizes the relationship between PD and T2DM and related therapeutic drugs from the perspective of insulin signaling pathways in the brain.

Metal dyshomeostasis in the substantia nigra of patients with Parkinson's disease or multiple sclerosis

Abnormal metal distribution in vulnerable brain regions is involved in the pathogenesis of most neurodegenerative diseases, suggesting common molecular mechanisms of metal dyshomeostasis. This study aimed to compare the intra- and extra-neuronal metal content and the expression of proteins related to metal homeostasis in the substantia nigra (SN) from patients with Parkinson's disease (PD), multiple sclerosis (MS), and control subjects. Metal quantification was performed via ion-beam micro-analysis in neuromelanin-positive neurons and the surrounding tissue. For proteomic analysis, SN tissue lysates were analyzed on a nanoflow chromatography system hyphenated to a hybrid triple-quadrupole time-of-flight mass spectrometer. We found increased amounts of iron in neuromelanin-positive neurons and surrounding tissue in patients with PD and MS compared to controls (4- to 5-fold higher) that, however, also showed large inter-individual variations. Copper content was systematically lower (-2.4-fold) in neuromelanin-positive neurons of PD patients compared with controls, whereas it remained unchanged in MS. Protein-protein interaction (PPI) network analyses revealed clusters related to Fe and Cu homeostasis among PD-deregulated proteins. An enrichment for the term "metal homeostasis" was observed for MS-deregulated proteins. Important deregulated hub proteins included hemopexin and transferrin in PD, and calreticulin and ferredoxin reductase in MS. Our findings show that PD and MS share commonalities in terms of iron accumulation in the SN. Concomitant proteomics experiments revealed PPI networks related to metal homeostasis, substantiating the results of metal quantification.

Efficacy of the iron-chelating agent, deferiprone, in patients with Parkinson's disease: A systematic review and meta-analysis

INTRODUCTION

Several studies have reported iron accumulation in the basal ganglia to be associated with the development of Parkinson's Disease (PD). Recently, a few trials have examined the efficacy of using the iron-chelating agent Deferiprone (DFP) for patients with PD. We conducted this meta-analysis to summarize and synthesize evidence from published randomized controlled trials about the efficacy of DFP for PD patients.

METHODS

A comprehensive literature search of four electronic databases was performed, spanning until February 2023. Relevant RCTs were selected, and their data were extracted and analyzed using the RevMan software. The primary outcome was the change in the Unified Parkinson's Disease Rating Scale (UPDRS-III).

RESULTS

Three RCTs with 431 patients were included in this analysis. DFP did not significantly improve UPDRS-III score compared to placebo (Standardized mean difference -0.06, 95% CI [-0.69, 0.58], low certainty evidence). However, it significantly reduced iron accumulation in the substantia nigra, putamen, and caudate as measured by T2*-weighted MRI (with high certainty evidence).

CONCLUSION

Current evidence does not support the use of DFP in PD patients. Future disease-modification trials with better population selection, adjustment for concomitant medications, and long-term follow up are recommended.

The current state of amyloidosis therapeutics and the potential role of fluorine in their treatment

Amyloidosis, commonly known as amyloid-associated diseases, is characterized by improperly folded proteins accumulating in tissues and eventually causing organ damage, which is linked to several disorders ranging from neurodegenerative to peripheral diseases. It has an enormous societal and financial impact on the global health sector. Due to the complexity of protein misfolding and intertwined aggregation, there are no effective disease-modifying medications at present, and the condition is likely mis/non-diagnosed half of the time. Nonetheless, over the last two decades, substantial research into aggregation processes has revealed the possibilities of new intervention approaches. On the other hand, fluorine has been a rising star in therapeutic development for numerous neurodegenerative illnesses and other peripheral diseases. In this study, we revised and emphasized the possible significance of fluorine-modified therapeutic molecules and fluorine-modified nanoparticles (NPs) in the modulation of amyloidogenic proteins, including insulin, amyloid beta peptide (Aβ), prion protein (PrP), transthyretin (TTR) and Huntingtin (htt).

An updated review on the versatile role of chrysin in neurological diseases: Chemistry, pharmacology, and drug delivery approaches

Neurological diseases are responsible for a large number of morbidities and mortalities in the world. Flavonoids are phytochemicals that possess various health-promoting impacts. Chrysin, a natural flavonoid isolated from diverse fruits, vegetables, and even mushrooms, has several pharmacological activities comprising antioxidant, anti-inflammatory, antiapoptotic, anticancer, and neuroprotective effects. The current study was designed to review the relationship between chrysin administration and neurological complications by discussing the feasible mechanism and signaling pathways. Herein, we mentioned the sources, pharmacological properties, chemistry, and drug delivery systems associated with chrysin pharmacotherapy. The role of chrysin was discussed in depression, anxiety, neuroinflammation, Alzheimer's disease, Parkinson's disease, Huntington's disease, epilepsy, cerebral ischemia, spinal cord injury, neuropathy, Multiple Sclerosis, and Guillain-Barré Syndrome. The findings indicate that chrysin has protective effects against neurological conditions by modulating oxidative stress, inflammation, and apoptosis in animal models. However, more studies should be done to clear the neuroprotective effects of chrysin.

Parkinson's disease: Alterations in iron and redox biology as a key to unlock therapeutic strategies

A plethora of studies indicate that iron metabolism is dysregulated in Parkinson's disease (PD). The literature reveals well-documented alterations consistent with established dogma, but also intriguing paradoxical observations requiring mechanistic dissection. An important fact is the iron loading in dopaminergic neurons of the substantia nigra pars compacta (SNpc), which are the cells primarily affected in PD. Assessment of these changes reveal increased expression of proteins critical for iron uptake, namely transferrin receptor 1 and the divalent metal transporter 1 (DMT1), and decreased expression of the iron exporter, ferroportin-1 (FPN1). Consistent with this is the activation of iron regulator protein (IRP) RNA-binding activity, which is an important regulator of iron homeostasis, with its activation indicating cytosolic iron deficiency. In fact, IRPs bind to iron-responsive elements (IREs) in the 3ꞌ untranslated region (UTR) of certain mRNAs to stabilize their half-life, while binding to the 5ꞌ UTR prevents translation. Iron loading of dopaminergic neurons in PD may occur through these mechanisms, leading to increased neuronal iron and iron-mediated reactive oxygen species (ROS) generation. The "gold standard" histological marker of PD, Lewy bodies, are mainly composed of α-synuclein, the expression of which is markedly increased in PD. Of note, an atypical IRE exists in the α-synuclein 5ꞌ UTR that may explain its up-regulation by increased iron. This dysregulation could be impacted by the unique autonomous pacemaking of dopaminergic neurons of the SNpc that engages L-type Ca+2 channels, which imparts a bioenergetic energy deficit and mitochondrial redox stress. This dysfunction could then drive alterations in iron trafficking that attempt to rescue energy deficits such as the increased iron uptake to provide iron for key electron transport proteins. Considering the increased iron-loading in PD brains, therapies utilizing limited iron chelation have shown success. Greater therapeutic advancements should be possible once the exact molecular pathways of iron processing are dissected.

Beneficial Effects of Epigallocatechin-3-O-Gallate, Chlorogenic Acid, Resveratrol, and Curcumin on Neurodegenerative Diseases

Many observational and clinical studies have shown that consumption of diets rich in plant polyphenols have beneficial effects on various diseases such as cancer, obesity, diabetes, cardiovascular diseases, and neurodegenerative diseases (NDDs). Animal and cellular studies have indicated that these polyphenolic compounds contribute to such effects. The representative polyphenols are epigallocatechin-3-O-gallate in tea, chlorogenic acids in coffee, resveratrol in wine, and curcumin in curry. The results of human studies have suggested the beneficial effects of consumption of these foods on NDDs including Alzheimer's and Parkinson's diseases, and cellular animal experiments have provided molecular basis to indicate contribution of these representative polyphenols to these effects. This article provides updated information on the effects of these foods and their polyphenols on NDDs with discussions on mechanistic aspects of their actions mainly based on the findings derived from basic experiments.

Management of Iron Overload in Resource Poor Nations: A Systematic Review of Phlebotomy and Natural Chelators

Iron is an essential element and the most abundant trace metal in the body involved in oxygen transport and oxygen sensing, electron transfer, energy metabolism, and DNA synthesis. Excess labile and unchelated iron can catalyze the formation of tissue-damaging radicals and induce oxidative stress. English abstracts were identified in PubMed and Google Scholar using multiple and various search terms based on defined inclusion and exclusion criteria. Full-length articles were selected for systematic review, and secondary and tertiary references were developed. Although bloodletting or phlebotomy remains the gold standard in the management of iron overload, this systematic review is an updated account of the pitfalls of phlebotomy and classical synthetic chelators with scientific justification for the use of natural iron chelators of dietary origin in resource-poor nations.

Conservative iron chelation for neurodegenerative diseases such as Parkinson's disease and amyotrophic lateral sclerosis

Focal iron accumulation associated with brain iron dyshomeostasis is a pathological hallmark of various neurodegenerative diseases (NDD). The application of iron-sensitive sequences in magnetic resonance imaging has provided a useful tool to identify the underlying NDD pathology. In the three major NDD, degeneration occurs in central nervous system (CNS) regions associated with memory (Alzheimer's disease, AD), automaticity (Parkinson's disease, PD) and motor function (amyotrophic lateral sclerosis, ALS), all of which require a high oxygen demand for harnessing neuronal energy. In PD, a progressive degeneration of the substantia nigra pars compacta (SNc) is associated with the appearance of siderotic foci, largely caused by increased labile iron levels resulting from an imbalance between cell iron import, storage and export. At a molecular level, α-synuclein regulates dopamine and iron transport with PD-associated mutations in this protein causing functional disruption to these processes. Equally, in ALS, an early iron accumulation is present in neurons of the cortico-spinal motor pathway before neuropathology and secondary iron accumulation in microglia. High serum ferritin is an indicator of poor prognosis in ALS and the application of iron-sensitive sequences in magnetic resonance imaging has become a useful tool in identifying pathology. The molecular pathways that cascade down from such dyshomeostasis still remain to be fully elucidated but strong inroads have been made in recent years. Far from being a simple cause or consequence, it has recently been discovered that these alterations can trigger susceptibility to an iron-dependent cell-death pathway with unique lipoperoxidation signatures called ferroptosis. In turn, this has now provided insight into some key modulators of this cell-death pathway that could be therapeutic targets for the NDD. Interestingly, iron accumulation and ferroptosis are highly sensitive to iron chelation. However, whilst chelators that strongly scavenge intracellular iron protect against oxidative neuronal damage in mammalian models and are proven to be effective in treating systemic siderosis, these compounds are not clinically suitable due to the high risk of developing iatrogenic iron depletion and ensuing anaemia. Instead, a moderate iron chelation modality that conserves systemic iron offers a novel therapeutic strategy for neuroprotection. As demonstrated with the prototype chelator deferiprone, iron can be scavenged from labile iron complexes in the brain and transferred (conservatively) either to higher affinity acceptors in cells or extracellular transferrin. Promising preclinical and clinical proof of concept trials has led to several current large randomized clinical trials that aim to demonstrate the efficacy and safety of conservative iron chelation for NDD, notably in a long-term treatment regimen.

The Fluorescent Quenching Mechanism of N and S Co-Doped Graphene Quantum Dots with Fe3+ and Hg2+ Ions and Their Application as a Novel Fluorescent Sensor

The fluorescence intensity of N, S co-doped graphene quantum dots (N, S-GQDs) can be quenched by Fe3+ and Hg2+. Density functional theory (DFT) simulation and experimental studies indicate that the fluorescence quenching mechanisms for Fe3+ and Hg2+ detection are mainly attributed to the inner filter effect (IFE) and dynamic quenching process, respectively. The electronegativity difference between C and doped atoms (N, S) in favor to introduce negative charge sites on the surface of N, S-GQDs leads to charge redistribution. Those negative charge sites facilitate the adsorption of cations on the N, S-GQDs' surface. Atomic population analysis results show that some charge transfer from Fe3+ and Hg2+ to N, S-GQDs, which relate to the fluorescent quenching of N, S-GQDs. In addition, negative adsorption energy indicates the adsorption of Hg2+ and Fe2+ is energetically favorable, which also contributes to the adsorption of quencher ions. Blue fluorescent N, S-GQDs were synthesized by a facile one-pot hydrothermal treatment. Fluorescent lifetime and UV-vis measurements further validate the fluorescent quenching mechanism is related to the electron transfer dynamic quenching and IFE quenching. The as-synthesized N, S-GQDs were applied as a fluorescent probe for Fe3+ and Hg2+ detection. Results indicate that N, S-GQDs have good sensitivity and selectivity on Fe3+ and Hg2+ with a detection limit as low as 2.88 and 0.27 nM, respectively.

The Role of Iron in Friedreich's Ataxia: Insights From Studies in Human Tissues and Cellular and Animal Models

Friedreich's ataxia (FRDA) is a rare early-onset degenerative disease that affects both the central and peripheral nervous systems, and other extraneural tissues, mainly the heart and endocrine pancreas. This disorder progresses as a mixed sensory and cerebellar ataxia, primarily disturbing the proprioceptive pathways in the spinal cord, peripheral nerves and nuclei of the cerebellum. FRDA is an inherited disease with an autosomal recessive pattern caused by an insufficient amount of the nuclear-encoded mitochondrial protein frataxin, which is an essential and highly evolutionary conserved protein whose deficit results in iron metabolism dysregulation and mitochondrial dysfunction. The first experimental evidence connecting frataxin with iron homeostasis came from Saccharomyces cerevisiae; iron accumulates in the mitochondria of yeast with deletion of the frataxin ortholog gene. This finding was soon linked to previous observations of iron deposits in the hearts of FRDA patients and was later reported in animal models of the disease. Despite advances made in the understanding of FRDA pathophysiology, the role of iron in this disease has not yet been completely clarified. Some of the questions still unresolved include the molecular mechanisms responsible for the iron accumulation and iron-mediated toxicity. Here, we review the contribution of the cellular and animal models of FRDA and relevance of the studies using FRDA patient samples to gain knowledge about these issues. Mechanisms of mitochondrial iron overload are discussed considering the potential roles of frataxin in the major mitochondrial metabolic pathways that use iron. We also analyzed the effect of iron toxicity on neuronal degeneration in FRDA by reactive oxygen species (ROS)-dependent and ROS-independent mechanisms. Finally, therapeutic strategies based on the control of iron toxicity are considered.

Use of Curcumin, a Natural Polyphenol for Targeting Molecular Pathways in Treating Age-Related Neurodegenerative Diseases

Progressive accumulation of misfolded amyloid proteins in intracellular and extracellular spaces is one of the principal reasons for synaptic damage and impairment of neuronal communication in several neurodegenerative diseases. Effective treatments for these diseases are still lacking but remain the focus of much active investigation. Despite testing several synthesized compounds, small molecules, and drugs over the past few decades, very few of them can inhibit aggregation of amyloid proteins and lessen their neurotoxic effects. Recently, the natural polyphenol curcumin (Cur) has been shown to be a promising anti-amyloid, anti-inflammatory and neuroprotective agent for several neurodegenerative diseases. Because of its pleotropic actions on the central nervous system, including preferential binding to amyloid proteins, Cur is being touted as a promising treatment for age-related brain diseases. Here, we focus on molecular targeting of Cur to reduce amyloid burden, rescue neuronal damage, and restore normal cognitive and sensory motor functions in different animal models of neurodegenerative diseases. We specifically highlight Cur as a potential treatment for Alzheimer's, Parkinson's, Huntington's, and prion diseases. In addition, we discuss the major issues and limitations of using Cur for treating these diseases, along with ways of circumventing those shortcomings. Finally, we provide specific recommendations for optimal dosing with Cur for treating neurological diseases.

Lipopolysaccharide-binding protein (LBP) can reverse the amyloid state of fibrin seen or induced in Parkinson's disease

The thrombin-induced polymerisation of fibrinogen to form fibrin is well established as a late stage of blood clotting. It is known that Parkinson's Disease (PD) is accompanied by dysregulation in blood clotting, but it is less widely known as a coagulopathy. In recent work, we showed that the presence of tiny amounts of bacterial lipopolysaccharide (LPS) in healthy individuals could cause clots to adopt an amyloid form, and this could be observed via scanning electron microscopy (SEM) or via the fluorescence of thioflavin-T. This could be prevented by the prior addition of lipopolysaccharide-binding protein (LBP). We had also observed by SEM this unusual clotting in the blood of patients with Parkinson's Disease. We hypothesised, and here show, that this too can be prevented by LBP in the context of PD. This adds further evidence implicating inflammatory microbial cell wall products as an accompaniment to the disease, and may be part of its aetiology. This may lead to novel treatment strategies in PD designed to target microbes and their products.

Deferiprone Rescues Behavioral Deficits Induced by Mild Iron Exposure in a Mouse Model of Alpha-Synuclein Aggregation

Parkinson's disease (PD) is the most common neurodegenerative movement disorder, and its causes remain unknown. A major hallmark of the disease is the increasing presence of aggregated alpha-synuclein (aSyn). Furthermore, there is a solid consensus on iron (Fe) accumulation in several regions of PD brains during disease progression. In our study, we focused on the interaction of Fe and aggregating aSyn in vivo in a transgenic mouse model overexpressing human aSyn bearing the A53T mutation (prnp.aSyn.A53T). We utilized a neonatal iron-feeding model to exacerbate the motor phenotype of the transgenic mouse model. Beginning from day 100, mice were treated with deferiprone (DFP), a ferric chelator that is able to cross the blood-brain barrier and is currently used in clinics as treatment for hemosiderosis. Our paradigm resulted in an impairment of the learning abilities in the rotarod task and the novel object recognition test. DFP treatment significantly improved the performance in both tasks. Although this was not accompanied by alterations in aSyn aggregation, our results support DFP as possible therapeutic option in PD.

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.

Zinc-binding sites on selected flavonoids

Flavonoids have attracted increased attention due to their broad bioactivities related to health and diseases. Modulating metal homeostasis may play an important role in their bioactivities. Recent studies have suggested that dietary flavonoids may affect zinc homeostasis, uptake, and transport. In this work, the zinc-binding sites on a few selected flavonoids have been investigated by (1)H NMR spectroscopy under physiological relevant pH and the species formed were verified by mass spectrometry. Zinc binding induces distinct changes in the proton resonances on the flavonoid rings, providing useful information to locate the Zn-binding sites. No Zn-binding was observed with flavone which lacks a chelation site. Zinc was found to bind to the 3-hydroxyl-4-keto, catechol, and 5-hydroxyl-4-keto chelation sites of flavonol, 3',4'-dihydroxylflavone and chrysin, respectively. Kaempferol and myricetin chelate zinc at the 3-hydroxyl-4-keto site while rutin binds zinc preferentially at the 5-hydroxyl-4-keto site. However, morin appears to bind zinc at the 1-ether-2-hydroxyl site.

Cell penetrating peptide (CPP)-conjugated desferrioxamine for enhanced neuroprotection: synthesis and in vitro evaluation

Iron overload causes progressive and sometimes irreversible damage due to accelerated production of reactive oxygen species. Desferrioxamine (DFO), a siderophore, has been used clinically to remove excess iron. However, the applications of DFO are limited because of its inability to access intracellular labile iron. Cell penetrating peptides (CPPs) have become an efficient delivery vector for the enhanced internalization of drugs into the cytosol. We describe, herein, an efficient method for covalently conjugating DFO to the CPPs TAT(47-57) and Penetratin. Both conjugates suppressed the redox activity of labile plasma iron in buffered solutions and in iron-overloaded sera. Enhanced access to intracellular labile iron compared to the parent siderophore was achieved in HeLa and RBE4 (a model of blood-brain-barrier) cell lines. Iron complexes of both conjugates also had better permeability in both cell models. DFO antioxidant and iron binding properties were preserved and its bioavailability was increased upon CPP conjugation, which opens new therapeutic possibilities for neurodegenerative processes associated with brain iron overload.

Eryptosis as a marker of Parkinson's disease

A major trend in recent Parkinson's disease (PD) research is the investigation of biological markers that could help in identifying at-risk individuals or to track disease progression and response to therapies. Central to this is the knowledge that inflammation is a known hallmark of PD and of many other degenerative diseases. In the current work, we focus on inflammatory signalling in PD, using a systems approach that allows us to look at the disease in a more holistic way. We discuss cyclooxygenases, prostaglandins, thromboxanes and also iron in PD. These particular signalling molecules are involved in PD pathophysiology, but are also very important in an aberrant coagulation/hematology system. We present and discuss a hypothesis regarding the possible interaction of these aberrant signalling molecules implicated in PD, and suggest that these molecules may affect the erythrocytes of PD patients. This would be observable as changes in the morphology of the RBCs and of PD patients relative to healthy controls. We then show that the RBCs of PD patients are indeed rather dramatically deranged in their morphology, exhibiting eryptosis (a kind of programmed cell death). This morphological indicator may have useful diagnostic and prognostic significance.

Role of iron in UPS impairment model of Parkinson's disease

Iron homeostasis requires the regulation of iron influx, iron efflux and iron storage, which are all essential to the execution of the multiple functions of the central nervous system. Abnormal accumulation of iron in the brain has been implicated in several neurodegenerative diseases, including Parkinson's disease (PD) and neurodegeneration with brain iron accumulation (NBIA). Although the cause of the neurodegenerative process in PD remains unclear, recent evidence suggests that failure of the ubiquitin-proteasome system (UPS) may play an important role in the pathogenesis of this disease. Our studies have shown that injection of the proteasome inhibitor lactacystin in the substantia nigra (SN) of rodents causes significant loss of dopamine (DA) neurons and induces intracellular inclusion body formation, which is accompanied by excessive iron accumulation in the midbrain. In the in vitro model, lactacystin causes a marked increase in labile iron, reactive oxygen species, alteration of iron regulatory protein (IRP)/iron response element expression levels, and an increase in the aggregation of ubiquitin-conjugated proteins prior to cell injury and death. Furthermore, we have demonstrated that synthetic iron chelators and a genetic iron chelator are neuroprotective against proteasome inhibitor-induced DA neuron degeneration, suggesting that iron chelation might be a promising therapeutic target for PD.

Brain iron homeostasis: from molecular mechanisms to clinical significance and therapeutic opportunities

Iron has emerged as a significant cause of neurotoxicity in several neurodegenerative conditions, including Alzheimer's disease (AD), Parkinson's disease (PD), sporadic Creutzfeldt-Jakob disease (sCJD), and others. In some cases, the underlying cause of iron mis-metabolism is known, while in others, our understanding is, at best, incomplete. Recent evidence implicating key proteins involved in the pathogenesis of AD, PD, and sCJD in cellular iron metabolism suggests that imbalance of brain iron homeostasis associated with these disorders is a direct consequence of disease pathogenesis. A complete understanding of the molecular events leading to this phenotype is lacking partly because of the complex regulation of iron homeostasis within the brain. Since systemic organs and the brain share several iron regulatory mechanisms and iron-modulating proteins, dysfunction of a specific pathway or selective absence of iron-modulating protein(s) in systemic organs has provided important insights into the maintenance of iron homeostasis within the brain. Here, we review recent information on the regulation of iron uptake and utilization in systemic organs and within the complex environment of the brain, with particular emphasis on the underlying mechanisms leading to brain iron mis-metabolism in specific neurodegenerative conditions. Mouse models that have been instrumental in understanding systemic and brain disorders associated with iron mis-metabolism are also described, followed by current therapeutic strategies which are aimed at restoring brain iron homeostasis in different neurodegenerative conditions. We conclude by highlighting important gaps in our understanding of brain iron metabolism and mis-metabolism, particularly in the context of neurodegenerative disorders.

A glutathione derivative with chelating and in vitro neuroprotective activities: synthesis, physicochemical properties, and biological evaluation

Metal-ion dysregulation and oxidative stress have been linked to the progressive neurological decline associated with neurodegenerative disorders such as Alzheimer's and Parkinson's diseases. Herein we report the synthesis and chelating, antioxidant, and in vitro neuroprotective activities of a novel derivative of glutathione, GS(HQ)H, endowed with an 8-hydroxyquinoline group as a metal-chelating moiety. In vitro results showed that GS(HQ)H may be stable enough to be absorbed unmodified and arrive intact to the blood-brain barrier, that it may be able to remove Cu(II) and Zn(II) from the Aβ peptide without causing any copper or zinc depletion in vivo, and that it protects SHSY-5Y human neuroblastoma cells against H2 O2 - and 6-OHDA-induced damage. Together, these findings suggest that GS(HQ)H could be a potential neuroprotective agent for the treatment of neurodegenerative diseases in which a lack of metal homeostasis has been reported as a key factor.

Brain iron accumulation in aging and neurodegenerative disorders

Over the decades, various studies have established an association between accumulation of iron and both aging and neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease. Excess levels of iron can lead to increased oxidative stress through Fenton chemistry, and depletion of iron can similarly have deleterious effects. In addition, metal ions are known to be involved in both Alzheimer's disease and Parkinson's disease protein aggregation. Metal ion chelators have been extensively investigated in preclinical models, and may prove to be appropriate for modulating brain iron levels in age-related neurodegenerative disorders. Investigating age-related iron deposition is vital, and can possibly aid in determining at-risk groups and diagnosing neurodegenerative diseases at an early stage. Novel imaging methods have enabled researchers to examine iron deposition in vivo, and offer a noninvasive method of monitoring the progression of accumulation, and possible therapeutic effects of chelating compounds.

Neuroprotective effect of EGb761® and low-dose whole-body γ-irradiation in a rat model of Parkinson's disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder after Alzheimer's disease. The present study was undertaken to investigate the pretreatment effects of standardized Ginkgo biloba extract (EGb761(®)) and low-dose whole-body γ-irradiation on the neurological dysfunction in the reserpine model of PD. Male Wistar rats were pretreated orally with EGb761 or fractionated low-dose whole-body γ-irradiation or their combination, then subjected to intraperitoneal injection of reserpine (5 mg/kg body weight) 24 h after the final dose of EGb761 or radiation. Reserpine injection resulted in the depletion of striatal dopamine (DA) level, increased catalepsy score, increased oxidative stress indicated via depletion of glutathione (GSH), increased malondialdehyde (MDA) and iron levels, decreased DA metabolites metabolizing enzymes; indicated by inhibition by glutathione-S-transferase, and nicotinamide adenine dinucleotide phosphate (NADPH)-quinone oxidoreductase (NQO) activities, mitochondrial dysfunction; indicated by declined complex I activity, and adenosine triphosphate (ATP) level and increased apoptosis; indicated by decreased mitochondrial B cell lymphoma-2 (Bcl-2) protein level and by transmission electron microscope. EGb761 and low-dose γ-radiation ameliorated the reserpine-induced state of oxidative stress, mitochondrial dysfunction, and apoptosis in brain. It can be concluded that EGb761, a widely used herbal medicine and low dose of γ-irradiation have protective effects for combating Parkinsonism possibly via replenishment of GSH levels.

A new carbazole-based Schiff-base as fluorescent chemosensor for selective detection of Fe3+ and Cu2+

A new carbazole-based Schiff-base (1) as a multi-functional fluorescent chemosensor was designed, synthesized and characterized, which can selectively recognized Fe(3+) and Cu(2+) ions over a number of other metal ions. Compound 1 could detect Fe(3+) and Cu(2+) by UV-Vis method and fluorescence method. The stoichiometry ratio of 1-Fe(3+) and 1-Cu(2+) are 2:1 and 1:1, respectively, by the method of Job's plot. Moreover, the detection limits were calculated to be 4.23×10(-6) mol/L for Fe(3+) ion and 5.67×10(-6) mol/L for Cu(2+) ion. In the presence of Fe(3+)/Cu(2+) ions, the fluorescence enhancement was attributed to the inhibited C=N isomerization and the obstructed excited state intramolecular proton transfer (ESIPT) of compound 1. At the same time, the interactions of compounds 1 with other ions were also investigated and unobvious UV-Vis absorption and fluorescence spectral changes were observed. Thus a new kind of chemosensor for Fe(3+)/Cu(2+)with high sensitivity and selectivity was introduced.

Brain iron MRI: a biomarker for amyotrophic lateral sclerosis

PURPOSE

To evaluate the usefulness of MRI detection of hypointensity areas (iron deposits) in the brain using a dedicated MRI technique in patients with ALS in establishing this sign as a potential surrogate biomarker that correlates with the severity of disease.

MATERIALS AND METHODS

Forty-six ALS patients and 26 age-matched controls were examined by MRI. The ALS Functional Rating Scale (ALSFRS) score was determined before the first MRI examination. The sub-set of 25 ALS patients was re-examined around 6 months after the first MRI examination. The MRI examination consisted of routine T1W, T2W, and FLAIR sequences with the addition of a thin slice heavily T2* weighted sequence to accentuate magnetic susceptibility artifacts.

RESULTS

T2*W sequence is superior to any other MRI sequence in detecting hypointensities in the brain of ALS patients. Hypointensities were found only in the precentral gyruses gray matter (PGGM) and were detected in 42 patients. The extent of hypointensities was measured and scored (0-3) and correlated with ALSFRS (r = -0.545). Twenty-five patients were re-examined 6 months later, and the majority of them showed the shift toward higher MRI scores. No control subjects had hypointensities in PGGM.

CONCLUSION

The detection of hypointensities in PGGM appears to be a very promising surrogate MRI biomarker for ALS due to its simplicity, high sensitivity and specificity, suitability for longitudinal studies, and relationship with the pathogenesis of the disease.

Iron and neurodegeneration: from cellular homeostasis to disease

Accumulation of iron (Fe) is often detected in the brains of people suffering from neurodegenerative diseases. High Fe concentrations have been consistently observed in Parkinson's, Alzheimer's, and Huntington's diseases; however, it is not clear whether this Fe contributes to the progression of these diseases. Other conditions, such as Friedreich's ataxia or neuroferritinopathy are associated with genetic factors that cause Fe misregulation. Consequently, excessive intracellular Fe increases oxidative stress, which leads to neuronal dysfunction and death. The characterization of the mechanisms involved in the misregulation of Fe in the brain is crucial to understand the pathology of the neurodegenerative disorders and develop new therapeutic strategies. Saccharomyces cerevisiae, as the best understood eukaryotic organism, has already begun to play a role in the neurological disorders; thus it could perhaps become a valuable tool also to study the metalloneurobiology.

In vivo iron quantification in collagenase-induced microbleeds in rat brain

Brain microbleeds (BMB) are associated with chronic and acute cerebrovascular disease. Because BMB present in the brain is a source of potentially cytotoxic iron proportional to the volume of extravasated blood, BMB iron content is a potentially valuable biomarker both to assess tissue risk and small cerebral vessel health. We recently reported methods to quantify focal iron sources using phase images that were tested in phantoms and BMB in postmortem tissue. In this study, we applied our methods to small hemorrhagic lesions induced in the in vivo rat brain using bacterial collagenase. As expected by theory, measurements of geometric features in phase images correlated with lesion iron content measured by graphite furnace atomic absorption spectrometry. Iron content estimation following BMB in an in vivo rodent model could shed light on the role and temporal evolution of iron-mediated tissue damage and efficacy of potential treatments in cerebrovascular diseases associated with BMB.

Advances in iron chelation: an update

INTRODUCTION

Oxidative stress (caused by excess iron) can result in tissue damage, organ failure and finally death, unless treated by iron chelators. The causative factor in the etiology of a variety of disease states is the presence of iron-generated reactive oxygen species (ROS), which can result in cell damage or which can affect the signaling pathways involved in cell necrosis-apoptosis or organ fibrosis, cancer, neurodegeneration and cardiovascular, hepatic or renal dysfunctions. Iron chelators can reduce oxidative stress by the removal of iron from target tissues. Equally as important, removal of iron from the active site of enzymes that play key roles in various diseases can be of considerable benefit to the patients.

AREAS COVERED

This review focuses on iron chelators used as therapeutic agents. The importance of iron in oxidative damage is discussed, along with the three clinically approved iron chelators.

EXPERT OPINION

A number of iron chelators are used as approved therapeutic agents in the treatment of thalassemia major, asthma, fungal infections and cancer. However, as our knowledge about the biochemistry of iron and its role in etiologies of seemingly unrelated diseases increases, new applications of the approved iron chelators, as well as the development of new iron chelators, present challenging opportunities in the areas of drug discovery and development.

Iron and mechanisms of neurotoxicity

The accumulation of transition metals (e.g., copper, zinc, and iron) and the dysregulation of their metabolism are a hallmark in the pathogenesis of several neurodegenerative diseases. This paper will be focused on the mechanism of neurotoxicity mediated by iron. This metal progressively accumulates in the brain both during normal aging and neurodegenerative processes. High iron concentrations in the brain have been consistently observed in Alzheimer's (AD) and Parkinson's (PD) diseases. In this connection, metalloneurobiology has become extremely important in establishing the role of iron in the onset and progression of neurodegenerative diseases. Neurons have developed several protective mechanisms against oxidative stress, among them, the activation of cellular signaling pathways. The final response will depend on the identity, intensity, and persistence of the oxidative insult. The characterization of the mechanisms mediating the effects of iron-induced increase in neuronal dysfunction and death is central to understanding the pathology of a number of neurodegenerative disorders.

Clinically available iron chelators induce neuroprotection in the 6-OHDA model of Parkinson's disease after peripheral administration

The iron content of the substantia nigra pars compacta increases in the brains of Parkinson's disease patients. Hence, its removal by iron chelators may retard the progression of the disease. However, information on the ability of clinically available iron chelators to cross the blood brain barrier and be neuroprotective is limited. In this present study three iron chelators, which are currently approved for clinical use, namely the hexadendate, deferrioxamine, the bidentate deferiprone and the tridendate chelator deferasirox have been investigated for their efficacy to induce neuroprotection. Previous studies have shown that both deferiprone and deferrioxamine exert neuroprotection in the 6-hydroxy dopamine (6-OHDA) model but no such studies have investigated deferasirox. Focal administration of deferasirox (0.5, 2 and 10 μg) into the substantia nigra pars compacta of rats significantly attenuated the loss of dopaminergic neurons and striatal dopamine content resulting from 6-OHDA toxicity. Systemic administration of deferasirox (20 mg/kg), deferiprone (10 mg/kg) or deferrioxamine (30 mg/kg), to the 6-OHDA rat model of Parkinson's disease, significantly attenuated the loss of dopaminergic neurons and striatal dopamine content. Further studies to comprehend the action of these chelators showed that local application of either 0.4 mM deferrioxamine, or 1 mM deferasirox, via a microdialysis probe into the striatum, prior to that of 200 μM 6-OHDA, prevented the generation of hydroxyl radicals. Our results confirm that the administration of these chelators show therapeutic efficacy and should be considered as therapeutic agents for the treatment of Parkinson's disease.

Towards a unifying, systems biology understanding of large-scale cellular death and destruction caused by poorly liganded iron: Parkinson's, Huntington's, Alzheimer's, prions, bactericides, chemical toxicology and others as examples

Exposure to a variety of toxins and/or infectious agents leads to disease, degeneration and death, often characterised by circumstances in which cells or tissues do not merely die and cease to function but may be more or less entirely obliterated. It is then legitimate to ask the question as to whether, despite the many kinds of agent involved, there may be at least some unifying mechanisms of such cell death and destruction. I summarise the evidence that in a great many cases, one underlying mechanism, providing major stresses of this type, entails continuing and autocatalytic production (based on positive feedback mechanisms) of hydroxyl radicals via Fenton chemistry involving poorly liganded iron, leading to cell death via apoptosis (probably including via pathways induced by changes in the NF-κB system). While every pathway is in some sense connected to every other one, I highlight the literature evidence suggesting that the degenerative effects of many diseases and toxicological insults converge on iron dysregulation. This highlights specifically the role of iron metabolism, and the detailed speciation of iron, in chemical and other toxicology, and has significant implications for the use of iron chelating substances (probably in partnership with appropriate anti-oxidants) as nutritional or therapeutic agents in inhibiting both the progression of these mainly degenerative diseases and the sequelae of both chronic and acute toxin exposure. The complexity of biochemical networks, especially those involving autocatalytic behaviour and positive feedbacks, means that multiple interventions (e.g. of iron chelators plus antioxidants) are likely to prove most effective. A variety of systems biology approaches, that I summarise, can predict both the mechanisms involved in these cell death pathways and the optimal sites of action for nutritional or pharmacological interventions.

A novel profluorescent probe for detecting oxidative stress induced by metal and H(2)O(2) in living cells

A profluorescent probe that has no fluorescent response to H(2)O(2), iron or copper ions but can be readily activated in the presence of both H(2)O(2) and Fe (or Cu) ion has been developed; the probe is capable of detecting oxidative stress promoted by Fe (or Cu) and H(2)O(2) (i.e. the Fenton reaction conditions) in living cells.

Iron in neuronal function and dysfunction

Iron (Fe) is an essential element for many metabolic processes, serving as a cofactor for heme and nonheme proteins. Cellular iron deficiency arrests cell growth and leads to cell death; however, like most transition metals, an excess of intracellular iron is toxic. The ability of Fe to accept and donate electrons can lead to the formation of reactive nitrogen and oxygen species, and oxidative damage to tissue components; contributing to disease and, perhaps, aging itself. It has also been suggested that iron-induced oxidative stress can play a key role in the pathogenesis of several neurodegenerative diseases. Iron progressively accumulates in the brain both during normal aging and neurodegenerative processes. However, iron accumulation occurs without the concomitant increase in tissue ferritin, which could increase the risk of oxidative stress. Moreover, high iron concentrations in the brain have been consistently observed in Alzheimer's disease (AD) and Parkinson's disease (PD). In this regard, metalloneurobiology has become extremely important in understanding the role of iron in the onset and progression of neurodegenerative diseases. Neurons have developed several protective mechanisms against oxidative stress, among them the activation of cellular signaling pathways. The final response will depend on the identity, intensity, and persistence of the oxidative insult. The characterization of the mechanisms involved in high iron induced in neuronal dysfunction and death is central to understanding the pathology of a number of neurodegenerative disorders.

Iron-binding and anti-Fenton properties of baicalein and baicalin

Baicalein and baicalin, the major bioactive compounds found in the Chinese herb Scutellaria baicalensis, have been shown to be effective against cancer, bacterial infections and oxidative stress diseases. However, little is known about their mechanisms of action. To probe whether iron homeostasis modulation may play a role in their bioactivity, we have investigated their iron binding characteristics under physiologically relevant conditions. A 2:1 baicalein-ferrous complex was readily formed in 20mM phosphate buffer, pH 7.2, with a binding constant approximately 2-9 x 10(11)M(-2), whereas a 1:1 baicalein-ferric complex was formed, under the same conditions, with an apparent binding constant approximately 1-3 x 10(6)M(-1). Baicalein appears to bind the ferrous ion more strongly than ferrozine, a well known iron(II) chelator. Using (1) H NMR and Zn(2+) and Ga(3+) as probes, the iron-binding site on baicalein was elucidated to be at the O6/O7 oxygen atoms of the A-ring. No binding was observed for baicalin under the same NMR conditions. Furthermore, baicalein strongly inhibits the Fe-promoted Fenton chemistry via a combination of chelation and radical scavenging mechanism while baicalin can provide only partial protection against radical damage. These results indicate that baicalein is a strong iron chelator under physiological conditions and hence may play a vital role in modulating the body's iron homeostasis. Modulation of metal homeostasis and the inhibition of Fenton chemistry may be one of the possible mechanisms for herbal medicine.

A novel H2O2-triggered anti-Fenton fluorescent pro-chelator excitable with visible light

A chelator and a pro-chelator that can be activated by H(2)O(2) and subsequently sequesters iron and attenuates the Fenton reaction have been developed; both molecules are fluorescent excitable by visible light, and H(2)O(2)-activation, as well as iron-chelation, induces remarkable changes in fluorescence.