Pro-apoptotic signaling in neuronal cells following iron and amyloid beta peptide neurotoxicity

The role of protein phosphorylation modifications mediated by iron metabolism regulatory networks in the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a severe neurodegenerative disease characterized mainly by the formation of amyloid beta (Aβ) plaques and abnormal phosphorylation of tau. In recent years, an imbalance in iron homeostasis has been recognized to play a key role in the pathological process of AD. Abnormal iron accumulation can activate various kinases such as glycogen synthase kinase-3β, cyclin-dependent kinase 5, and mitogen-activated protein kinase, leading to abnormal phosphorylation of tau and amyloid precursor protein, and accelerating the formation of Aβ plaques and neurofibrillary tangles. In addition, iron-mediated oxidative stress not only triggers neuronal damage, but also exacerbates neuronal dysfunction by altering the phosphorylation of N-methyl-D-aspartate receptors and γ-aminobutyric acid type A receptors. Iron accumulation also affects the phosphorylation status of tyrosine hydroxylase, the rate-limiting enzyme for dopamine synthesis, interfering with the dopamine signaling pathway. On the other hand, iron affects iron transport and metabolism in the brain by regulating the phosphorylation of transferrin, further disrupting iron homeostasis. Therapeutic strategies targeting iron metabolism show promise by reducing iron accumulation, inhibiting oxidative stress, and reducing abnormal phosphorylation of key proteins. This article reviews the molecular mechanisms of phosphorylation modifications mediated by iron homeostasis imbalance in AD, and discusses the potential of interventions that regulate iron metabolism and related signaling pathways, providing a new theoretical basis for the treatment of AD.

Early chronic suppression of microglial p38α in a model of Alzheimer's disease does not significantly alter amyloid-associated neuropathology

The p38 alpha mitogen-activated protein kinase (p38α) is linked to both innate and adaptive immune responses and is under investigation as a target for drug development in the context of Alzheimer's disease (AD) and other conditions with neuroinflammatory dysfunction. While preclinical data has shown that p38α inhibition can protect against AD-associated neuropathology, the underlying mechanisms are not fully elucidated. Inhibitors of p38α may provide benefit via modulation of microglial-associated neuroinflammatory responses that contribute to AD pathology. The present study tests this hypothesis by knocking out microglial p38α and assessing early-stage pathological changes. Conditional knockout of microglial p38α was accomplished in 5-month-old C57BL/6J wild-type and amyloidogenic AD model (APPswe/PS1dE9) mice using a tamoxifen-inducible Cre/loxP system under control of the Cx3cr1 promoter. Beginning at 7.5 months of age, animals underwent behavioral assessment on the open field, followed by a later radial arm water maze test and collection of cortical and hippocampal tissues at 11 months. Additional endpoint measures included quantification of proinflammatory cytokines, assessment of amyloid burden and plaque deposition, and characterization of microglia-plaque dynamics. Loss of microglial p38α did not alter behavioral outcomes, proinflammatory cytokine levels, or overall amyloid plaque burden. However, this manipulation did significantly increase hippocampal levels of soluble Aβ42 and reduce colocalization of Iba1 and 6E10 in a subset of microglia in close proximity to plaques. The data presented here suggest that rather than reducing inflammation per se, the net effect of microglial p38α inhibition in the context of early AD-type amyloid pathology is a subtle alteration of microglia-plaque interactions. Encouragingly from a therapeutic standpoint, these data suggest no detrimental effect of even substantial decreases in microglial p38α in this context. Additionally, these results support future investigations of microglial p38α signaling at different stages of disease, as well as its relationship to phagocytic processes in this particular cell-type.

Challenges and Opportunities of Metal Chelation Therapy in Trace Metals Overload-Induced Alzheimer's Disease

Essential trace metals like zinc (Zn), iron (Fe), and copper (Cu) play an important physiological role in the metabolomics and healthy functioning of body organs, including the brain. However, abnormal accumulation of trace metals in the brain and dyshomeostasis in the different regions of the brain have emerged as contributing factors in neuronal degeneration, Aβ aggregation, and Tau formation. The link between these essential trace metal ions and the risk of AD has been widely studied, although the conclusions have been ambiguous. Despite the absence of evidence for any clinical benefit, therapeutic chelation is still hypothesized to be a therapeutic option for AD. Furthermore, the parameters like bioavailability, ability to cross the BBB, and chelation specificity must be taken into consideration while selecting a suitable chelation therapy. The data in this review summarizes that the primary intervention in AD is brain metal homeostasis along with brain metal scavenging. This review evaluates the impact of different trace metals (Cu, Zn, Fe) on normal brain functioning and their association with neurodegeneration in AD. Also, it investigates the therapeutic potential of metal chelators in the management of AD. An extensive literature search was carried out on the "Web of Science, PubMed, Science Direct, and Google Scholar" to investigate the effect of trace elements in neurological impairment and the role of metal chelators in AD. In addition, the current review highlights the advantages and limitations of chelation therapies and the difficulties involved in developing selective metal chelation therapy in AD patients.

Investigating binding mechanism of thymoquinone to human transferrin, targeting Alzheimer's disease therapy

Iron deposition in the central nervous system (CNS) is one of the causes of neurodegenerative diseases. Human transferrin (hTf) acts as an iron carrier present in the blood plasma, preventing it from contributing to redox reactions. Plant compounds and their derivatives are frequently being used in preventing or delaying Alzheimer's disease (AD). Thymoquinone (TQ), a natural product has gained popularity because of its broad therapeutic applications. TQ is one of the significant phytoconstituent of Nigella sativa. The binding of TQ to hTf was determined by spectroscopic methods and isothermal titration calorimetry. We have observed that TQ strongly binds to hTf with a binding constant (K) of 0.22 × 10⁶ M^-1 and forming a stable complex. In addition, isothermal titration calorimetry revealed the spontaneous binding of TQ with hTf. Molecular docking analysis showed key residues of the hTf that were involved in the binding to TQ. We further performed a 250 ns molecular dynamics simulation which deciphered the dynamics and stability of the hTf-TQ complex. Structure analysis suggested that the binding of TQ doesn't cause any significant alterations in the hTf structure during the course of simulation and a stable complex is formed. Altogether, we have elucidated the mechanism of binding of TQ with hTf, which can be further implicated in the development of a novel strategy for AD therapy.

Protection of Iron-Induced Oxidative Damage in Neuroblastoma (SH-SY5Y) Cells by Combination of 1-(N-Acetyl-6-aminohexyl)-3-hydroxy-2-methylpyridin-4-one and Green Tea Extract

Iron is a crucial trace element and essential for many cellular processes; however, excessive iron accumulation can induce oxidative stress and cell damage. Neurodegenerative disorders, such as Alzheimer's disease and Parkinson's disease, have been associated with altered iron homoeostasis causing altered iron distribution and accumulation in brain tissue. This study aims to investigate the protective effect of 1-(N-acetyl-6-aminohexyl)-3-hydroxy-2-methylpyridin-4-one (CM1) in combination with green tea extract (GTE) on iron-induced oxidative stress in neuroblastoma (SH-SY5Y) cells. Cells were cultured in medium with or without ferric chloride loading. Their viability and mitochondrial activity were assessed using MTT and JC-1 staining methods. Levels of the cellular labile iron pool (LIP), reactive oxygen species (ROS), and lipid-peroxidation products were determined using calcein acetoxymethyl ester, 2',7'-dichlorohydrofluorescein diacetate, and TBARS-based assays, respectively. The viability of iron-loaded cells was found to be significantly increased after treatment with CM1 (10 µM) for 24 h. CM1 co-treatment with GTE resulted in a greater protective effect than their monotherapy. Combination of CM1 and GTE also reduced mitochondrial disruption and LIP content and ROS and TBARS production. In conclusion, the combination of CM1 and GTE exhibits protection against iron-induced oxidative stress in neuroblastoma cells.

Iron and Ferroptosis as Therapeutic Targets in Alzheimer's Disease

Alzheimer's disease (AD), one of the most common neurodegenerative diseases worldwide, has a devastating personal, familial, and societal impact. In spite of profound investment and effort, numerous clinical trials targeting amyloid-β, which is thought to have a causative role in the disease, have not yielded any clinically meaningful success to date. Iron is an essential cofactor in many physiological processes in the brain. An extensive body of work links iron dyshomeostasis with multiple aspects of the pathophysiology of AD. In particular, regional iron load appears to be a risk factor for more rapid cognitive decline. Existing iron-chelating agents have been in use for decades for other indications, and there are preliminary data that some of these could be effective in AD. Many novel iron-chelating compounds are under development, some with in vivo data showing potential Alzheimer's disease-modifying properties. This heretofore underexplored therapeutic class has considerable promise and could yield much-needed agents that slow neurodegeneration in AD.

The essential elements of Alzheimer's disease

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

The impact of brain iron accumulation on cognition: A systematic review

Iron is involved in many processes in the brain including, myelin generation, mitochondrial function, synthesis of ATP and DNA and the cycling of neurotransmitters. Disruption of normal iron homeostasis can result in iron accumulation in the brain, which in turn can partake in interactions which amplify oxidative damage. The development of MRI techniques for quantifying brain iron has allowed for the characterisation of the impact that brain iron has on cognition and neurodegeneration. This review uses a systematic approach to collate and evaluate the current literature which explores the relationship between brain iron and cognition. The following databases were searched in keeping with a predetermined inclusion criterion: Embase Ovid, PubMed and PsychInfo (from inception to 31st March 2020). The included studies were assessed for study characteristics and quality and their results were extracted and summarised. This review identified 41 human studies of varying design, which statistically assessed the relationship between brain iron and cognition. The most consistently reported interactions were in the Caudate nuclei, where increasing iron correlated poorer memory and general cognitive performance in adulthood. There were also consistent reports of a correlation between increased Hippocampal and Thalamic iron and poorer memory performance, as well as, between iron in the Putamen and Globus Pallidus and general cognition. We conclude that there is consistent evidence that brain iron is detrimental to cognitive health, however, more longitudinal studies will be required to fully understand this relationship and to determine whether iron occurs as a primary cause or secondary effect of cognitive decline.

Transferrin is responsible for mediating the effects of iron ions on the regulation of anterior pharynx-defective-1α/β and Presenilin 1 expression via PGE2 and PGD2 at the early stage of Alzheimer's Disease

Transferrin (Tf) is an important iron-binding protein postulated to play a key role in iron ion (Fe) absorption via the Tf receptor (TfR), which potentially contributes to the pathogenesis of Alzheimer’s disease (AD). However, the role of Tf in AD remains unknown. Using mouse-derived neurons and APP/PS1 transgenic (Tg) mice as model systems, we firstly revealed the mechanisms of APH-1α/1β and presenilin 1 (PS1) upregulation by Fe in prostaglandin (PG) E₂- and PGD₂-dependent mechanisms. Specifically, Fe stimulated the expression of mPGES-1 and the production of PGE₂ and PGD₂ via the Tf and TfR system. Highly accumulated PGE₂ markedly induced the expression of anterior pharynx-defective-1α and -1β (APH-1α/1β) and PS1 via an EP receptor-dependent mechanism. In contrast, PGD₂ suppressed the expression of APH-1α/1β and PS1 via a prostaglandin D₂ (DP) receptor-dependent mechanism. As the natural dehydrated product of PGD₂, 15d-PGJ₂ exerts inhibitory effects on the expression of APH-1α/1β and PS1 in a peroxisome proliferator-activated receptor (PPAR) γ-dependent manner. The expression of APH-1α/1β and PS1 ultimately determined the production and deposition of β-amyloid protein (Aβ), an effect that potentially contributes to the pathogenesis of AD.

Cu and Zn interactions with Aβ peptides: consequence of coordination on aggregation and formation of neurotoxic soluble Aβ oligomers

The coordination chemistry of transition metal ions (Fe, Cu, Zn) with the amyloid-β (Aβ) peptides has attracted a lot of attention in recent years due to its repercussions in Alzheimer's disease (AD).

A Multifunctional Biocompatible Drug Candidate is Highly Effective in Delaying Pathological Signs of Alzheimer's Disease in 5XFAD Mice

BACKGROUND

Metal-ion-chelation was suggested to prevent zinc and copper ions-induced amyloid-β (Aβ) aggregation and oxidative stress, both implicated in the pathophysiology of Alzheimer's disease (AD). In a quest for biocompatible metal-ion chelators potentially useful for AD therapy, we previously tested a series of nucleoside 5'-phosphorothioate derivatives as agents for decomposition of Cu(I)/Cu(II)/Zn(II)-Aβ-aggregates, and as inhibitors of OH radicals formation in Cu(I) or Fe(II) /H2O2 solution. Specifically, in our recent study we have identified 2-SMe-ADP(α-S), designated as SAS, as a most promising neuroprotectant.

OBJECTIVE

To further explore SAS ability to protect the brain from Aβ toxicity both in vitro and in vivo.

METHODS

We evaluated SAS ability to decompose or inhibit the formation of Aβ42-M(II) aggregates, and rescue primary neurons and astrocytes from Aβ42 toxicity. Furthermore, we aimed at exploring the therapeutic effect of SAS on behavioral and cognitive deficits in the 5XFAD mouse model of AD.

RESULTS

We found that SAS can rescue primary culture of neurons and astrocytes from Aβ42 toxicity and to inhibit the formation and dissolve Aβ42-Zn(II)/Cu(II) aggregates. Furthermore, we show that SAS treatment can prevent behavioral disinhibition and ameliorate spatial working memory deficits in 5XFAD mice. Notably, the mice were treated at the age of 2 months, before the onset of AD symptoms, for a duration of 2 months, while the effect was demonstrated at the age of 6 months.

CONCLUSION

Our results indicate that SAS has the potential to delay progression of core pathological characteristics of AD in the 5XFAD mouse model.

Potentiation of glutathione loss and nerve cell death by the transition metals iron and copper: Implications for age-related neurodegenerative diseases

There is growing evidence for alterations in iron and copper homeostasis during aging that are exacerbated in neurodegenerative diseases such as Alzheimer's disease (AD). However, how iron and copper accumulation leads to nerve cell damage in AD is not clear. In order to better understand how iron and copper can contribute to nerve cell death, a simple, well-defined in vitro model of cell death, the oyxtosis assay, was used. This assay uses glutamate to induce glutathione (GSH) depletion which initiates a form of oxidative stress-induced programmed cell death. A reduction in GSH is seen in the aging brain, is associated with cognitive dysfunction and is accelerated in many CNS diseases including AD. It is shown that both iron and copper potentiate both GSH loss and cell death in this model. Iron and copper also potentiate cell death induced by other GSH depleters but not by compounds that induce oxidative stress via other pathways. At least part of the effects of copper on GSH are related to its ability to reduce the activity of glutamate cysteine ligase, the rate limiting enzyme in GSH synthesis. Both metals also alter several signaling pathways involved in modulating nerve cell death. Together, these results suggest that in vivo iron and copper may specifically enhance nerve cell death under conditions where GSH levels are reduced.

Unraveling the Burden of Iron in Neurodegeneration: Intersections with Amyloid Beta Peptide Pathology

Iron overload is a hallmark of many neurodegenerative processes such as Alzheimer's, Parkinson's, and Huntington's diseases. Unbound iron accumulated as a consequence of brain aging is highly reactive with water and oxygen and produces reactive oxygen species (ROS) or free radicals. ROS are toxic compounds able to damage cell membranes, DNA, and mitochondria. Which are the mechanisms involved in neuronal iron homeostasis and in neuronal response to iron-induced oxidative stress constitutes a cutting-edge topic in metalloneurobiology. Increasing our knowledge about the underlying mechanisms that operate in iron accumulation and their consequences would shed light on the comprehension of the molecular events that participate in the pathophysiology of the abovementioned neurodegenerative diseases. In this review, current evidences about iron accumulation in the brain, the signaling mechanisms triggered by metal overload, as well as the interaction between amyloid β (Aβ) and iron, will be summarized.

Metal ions influx is a double edged sword for the pathogenesis of Alzheimer's disease

Alzheimer's disease (AD) is a common form of dementia in aged people, which is defined by two pathological characteristics: β-amyloid protein (Aβ) deposition and tau hyperphosphorylation. Although the mechanisms of AD development are still being debated, a series of evidence supports the idea that metals, such as copper, iron, zinc, magnesium and aluminium, are involved in the pathogenesis of the disease. In particular, the processes of Aβ deposition in senile plaques (SP) and the inclusion of phosphorylated tau in neurofibrillary tangles (NFTs) are markedly influenced by alterations in the homeostasis of the aforementioned metal ions. Moreover, the mechanisms of oxidative stress, synaptic plasticity, neurotoxicity, autophagy and apoptosis mediate the effects of metal ions-induced the aggregation state of Aβ and phosphorylated tau on AD development. More importantly, imbalance of these mechanisms finally caused cognitive decline in different experiment models. Collectively, reconstructing the signaling network that regulates AD progression by metal ions may provide novel insights for developing chelators specific for metal ions to combat AD.

Multi-Target Directed Donepezil-Like Ligands for Alzheimer's Disease

HIGHLIGHTS ASS234 is a MTDL compound containing a moiety from Donepezil and the propargyl group from the PF 9601N, a potent and selective MAO B inhibitor. This compound is the most advanced anti-Alzheimer agent for preclinical studies identified in our laboratory.Derived from ASS234 both multipotent donepezil-indolyl (MTDL-1) and donepezil-pyridyl hybrids (MTDL-2) were designed and evaluated as inhibitors of AChE/BuChE and both MAO isoforms. MTDL-2 showed more high affinity toward the four enzymes than MTDL-1.MTDL-3 and MTDL-4, were designed containing the N-benzylpiperidinium moiety from Donepezil, a metal- chelating 8-hydroxyquinoline group and linked to a N-propargyl core and they were pharmacologically evaluated.The presence of the cyano group in MTDL-3, enhanced binding to AChE, BuChE and MAO A. It showed antioxidant behavior and it was able to strongly complex Cu(II), Zn(II) and Fe(III).MTDL-4 showed higher affinity toward AChE, BuChE.MTDL-3 exhibited good brain penetration capacity (ADMET) and less toxicity than Donepezil. Memory deficits in scopolamine-lesioned animals were restored by MTDL-3.MTDL-3 particularly emerged as a ligand showing remarkable potential benefits for its use in AD therapy. Alzheimer's disease (AD), the most common form of adult onset dementia, is an age-related neurodegenerative disorder characterized by progressive memory loss, decline in language skills, and other cognitive impairments. Although its etiology is not completely known, several factors including deficits of acetylcholine, β-amyloid deposits, τ-protein phosphorylation, oxidative stress, and neuroinflammation are considered to play significant roles in the pathophysiology of this disease. For a long time, AD patients have been treated with acetylcholinesterase inhibitors such as donepezil (Aricept®) but with limited therapeutic success. This might be due to the complex multifactorial nature of AD, a fact that has prompted the design of new Multi-Target-Directed Ligands (MTDL) based on the "one molecule, multiple targets" paradigm. Thus, in this context, different series of novel multifunctional molecules with antioxidant, anti-amyloid, anti-inflammatory, and metal-chelating properties able to interact with multiple enzymes of therapeutic interest in AD pathology including acetylcholinesterase, butyrylcholinesterase, and monoamine oxidases A and B have been designed and assessed biologically. This review describes the multiple targets, the design rationale and an in-house MTDL library, bearing the N-benzylpiperidine motif present in donepezil, linked to different heterocyclic ring systems (indole, pyridine, or 8-hydroxyquinoline) with special emphasis on compound ASS234, an N-propargylindole derivative. The description of the in vitro biological properties of the compounds and discussion of the corresponding structure-activity-relationships allows us to highlight new issues for the identification of more efficient MTDL for use in AD therapy.

Carvacrol protects neuroblastoma SH-SY5Y cells against Fe(2+)-induced apoptosis by suppressing activation of MAPK/JNK-NF-κB signaling pathway

AIM

Carvacrol (2-methyl-5-isopropylphenol), a phenolic monoterpene in the essential oils of the genera Origanum and Thymus, has been shown to exert a variety of therapeutic effects. Here we examined whether carvacrol protected neuroblastoma SH-SY5Y cells against Fe(2+)-induced apoptosis and explored the underlying mechanisms.

METHODS

Neuroblastoma SH-SY5Y cells were incubated with Fe(2+) for 24 h, and the cell viability was assessed with CCK-8 assay. TUNEL assay and flow cytometric analysis were performed to evaluate cell apoptosis. The mRNA levels of pro-inflammatory cytokines and NF-κB p65 were determined using qPCR. The expression of relevant proteins was determined using Western blot analysis or immunofluorescence staining.

RESULTS

Treatment of SH-SY5Y cells with Fe(2+) (50-200 μmol/L) dose-dependently decreased the cell viability, which was significantly attenuated by pretreatment with carvacrol (164 and 333 μmol/L). Treatment with Fe(2+) increased the Bax level and caspase-3 activity, and decreased the Bcl-2 level, resulting in cell apoptosis. Furthermore, treatment with Fe(2+) significantly increased the gene expression of IL-1β, IL-6 and TNF-α, and induced the nuclear translocation of NF-κB. Treatment with Fe(2+) also significantly increased the phosphorylation of p38, ERK, JNK and IKK in the cells. Pretreatment with carvacrol significantly inhibited Fe(2+)-induced activation of NF-κB, expression of the pro-inflammatory cytokines, and cell apoptosis. Moreover, pretreatment with carvacrol inhibited Fe(2+)-induced phosphorylation of JNK and IKK, but not p38 and ERK in the cells.

CONCLUSION

Carvacrol protects neuroblastoma SH-SY5Y cells against Fe(2+)-induced apoptosis, which may result from suppressing the MAPK/JNK-NF-κB signaling pathways.

ATP-γ-S-(α,β-CH2) protects against oxidative stress and amyloid beta toxicity in neuronal culture

Amyloid beta (Aβ) oligomers and oxidative stress, typical of Alzheimer's disease, are highly neurotoxic. Previously we identified ATP-γ-S as a most promising antioxidant and neuroprotectant. To further improve both potency and metabolic stability of ATP-γ-S, we designed a related analogue, ATP-γ-S-(α,β-CH2). We found that ATP-γ-S-(α,β-CH2) effectively inhibited ROS formation in PC12 cells subjected to Fe(II)-oxidation, slightly better than ATP-γ-S (IC50 0.18 and 0.20 μM, respectively). Moreover, ATP-γ-S-(α,β-CH2) rescued primary neurons from Aβ42 toxicity, 4-fold more potently than ATP-γ-S, (IC50 0.2 and 0.8 μM, respectively). In addition, the metabolic stability of ATP-γ-S-(α,β-CH2) in PC12 cells during 4 h of incubation, was up to 20% greater than that of ATP-γ-S and ATP. Previously, we found that ATP-γ-S-(α,β-CH2) resisted hydrolysis by ecto-nucleotidases such as, NPPs and TNAP, and was found to be ∼7-fold more potent agonist than ATP at P2Y11 receptor. Therefore, we propose ATP-γ-S-(α,β-CH2) as a promising agent for rescue of neurons from insults typical of Alzheimer's disease.

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.

HFE gene variants, iron, and lipids: a novel connection in Alzheimer's disease

Iron accumulation and associated oxidative stress in the brain have been consistently found in several neurodegenerative diseases. Multiple genetic studies have been undertaken to try to identify a cause of neurodegenerative diseases but direct connections have been rare. In the iron field, variants in the HFE gene that give rise to a protein involved in cellular iron regulation, are associated with iron accumulation in multiple organs including the brain. There is also substantial epidemiological, genetic, and molecular evidence of disruption of cholesterol homeostasis in several neurodegenerative diseases, in particular Alzheimer's disease (AD). Despite the efforts that have been made to identify factors that can trigger the pathological events associated with neurodegenerative diseases they remain mostly unknown. Because molecular phenotypes such as oxidative stress, synaptic failure, neuronal loss, and cognitive decline, characteristics associated with AD, have been shown to result from disruption of a number of pathways, one can easily argue that the phenotype seen may not arise from a linear sequence of events. Therefore, a multi-targeted approach is needed to understand a complex disorder like AD. This can be achieved only when knowledge about interactions between the different pathways and the potential influence of environmental factors on them becomes available. Toward this end, this review discusses what is known about the roles and interactions of iron and cholesterol in neurodegenerative diseases. It highlights the effects of gene variants of HFE (H63D- and C282Y-HFE) on iron and cholesterol metabolism and how they may contribute to understanding the etiology of complex neurodegenerative diseases.

Nucleoside 5'-phosphorothioate derivatives are highly effective neuroprotectants

The brain is especially sensitive to oxidative stress due to its high rate of oxidative metabolism, relatively low levels of antioxidant enzymes, and high concentrations of Fe/Cu ions. During the neurodegeneration process, the aggregation of proteins Aβ, accompanies oxidative stress. We explored the potential of thiophosphate derivatives to rescue neurons from oxidative stress and Aβ toxicity. We evaluated the neuroprotective effect of ATP-γ-S, ADP-β-S, and GDP-β-S on primary cortical neuronal cells exposed to several insults, including treatment with FeSO4, co-application of H2O2 and FeSO4, and addition of Aβ42. Upon treatment with FeSO4, phosphorothioate analogues exhibited up to 3000-fold better neuroprotectant activity than the corresponding parent nucleotides. Likewise, phosphorothioate analogues proved to be up to 30-fold better neuroprotectants than the corresponding parent nucleotides upon treatment with both H2O2 and FeSO4. When we exposed primary neuron and astrocyte cultures to 50 μM Aβ42-induced cell death, we found that ATP-γ-S significantly improved cell morphology and maintained culture viability with an IC50 value of 0.8 μM. Finally, we evaluated the viability of neuroblastoma cells under hypoxic conditions in the presence of ATP-γ-S and found that the latter was involved in the regulation of HIF-1a and stabilized mRNA levels of vascular endothelial growth factor (VEGF) and glucose transporter 1 (GLUT-1), which promote cell survival and proliferation. Based on its high potency as a neuroprotectant, we propose ATP-γ-S as a highly promising, biocompatible, and water-soluble drug candidate for the treatment of neurodegenerative disorders.

The effect of Cu(2+) and Zn(2+) on the Aβ42 peptide aggregation and cellular toxicity

The coordination chemistry of Cu and Zn metal ions with the amyloid β (Aβ) peptides has attracted a lot of attention in recent years due to its implications in Alzheimer's disease. A number of reports indicate that Cu and Zn have profound effects on Aβ aggregation. However, the impact of these metal ions on Aβ oligomerization and fibrillization is still not well understood, especially for the more rapidly aggregating and more neurotoxic Aβ42 peptide. Here we report the effect of Cu(2+) and Zn(2+) on Aβ42 oligomerization and aggregation using a series of methods such as Thioflavin T (ThT) fluorescence, native gel and Western blotting, transmission electron microscopy (TEM), and cellular toxicity studies. Our studies suggest that both Cu(2+) and Zn(2+) ions inhibit Aβ42 fibrillization. While presence of Cu(2+) stabilizes Aβ42 oligomers, Zn(2+) leads to formation of amorphous, non-fibrillar aggregates. The effects of temperature, buffer, and metal ion concentration and stoichiometry were also studied. Interestingly, while Cu(2+) increases the Aβ42-induced cell toxicity, Zn(2+) causes a significant decrease in Aβ42 neurotoxicity. While previous reports have indicated that Cu(2+) can disrupt β-sheets and lead to non-fibrillar Aβ aggregates, the neurotoxic consequences were not investigated in detail. The data presented herein including cellular toxicity studies strongly suggest that Cu(2+) increases the neurotoxicity of Aβ42 due to stabilization of soluble Aβ42 oligomers.

Metallostasis in Alzheimer's disease

2012 has been another year in which multiple large-scale clinical trials for Alzheimer's disease (AD) have failed to meet their clinical endpoints. With the social and financial burden of this disease increasing every year, the onus is now on the field of AD researchers to investigate alternative ideas to deliver outcomes for patients. Although several major clinical trials targeting Aβ have failed, three smaller clinical trials targeting metal interactions with Aβ have all shown benefit for patients. Here we review the genetic, pathological, biochemical, and pharmacological evidence that underlies the metal hypothesis of AD. The AD-affected brain suffers from metallostasis, or fatigue of metal trafficking, resulting in redistribution of metals into inappropriate compartments. The metal hypothesis is built upon a triad of transition elements: iron, copper, and zinc. The hypothesis has matured from early investigations showing amyloidogenic and oxidative stress consequences of these metals; recently, disease-related proteins, APP, tau, and presenilin, have been shown to have major roles in metal regulation, which provides insight into the pathway of neurodegeneration in AD and illuminates potential new therapeutic avenues.

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.

PI3K-ERK1/2 activation contributes to extracellular H2O2 generation in amyloid β toxicity

Amyloid β peptide (Aβ) induces hydrogen peroxide (H2O2) and superoxide generation, leading to neuronal death. Many studies have shown the involvement of NADPH oxidase, but the isotype-specific role was not assessed. Moreover, the activation status of phosphoinositide 3-kinase (PI3K) and extracellular signal-regulated kinase (ERK) 1/2 is unclear in extracellular H2O2 generation. In this paper, we showed that Aβ1-42 induced extracellular H2O2 generation and the resulting cytotoxicity in a concentration-dependent manner. Nox2- and Nox4-specific siRNAs suppressed H2O2 and superoxide generation. LY294002 and U0126, inhibitors of PI3K and ERK1/2, respectively, reduced H2O2 generation in concentration-dependent manners. Furthermore, PI3K activation is responsible for ERK1/2 phosphorylation. An additional increase in H2O2 generation and corresponding cytotoxicity was observed after treatment with Aβ1-42 and glutamate. These results suggest that Aβ1-42 enhances the neuronal vulnerability to oxidative injury in Alzheimer's disease (AD) by increasing H2O2 generation.

Affinity of Cu+ for the copper-binding domain of the amyloid-β peptide of Alzheimer's disease

The role of metal ions in Alzheimer's disease etiology is unresolved. For the redox-active metal ions iron and copper, the formation of reactive oxygen species by metal amyloid complexes has been proposed to contribute to Alzheimer's disease neurodegeneration. For copper, reactive oxygen species are generated by copper redox cycling between its 1+ and 2+ oxidation states. Thus, the AβCu(I) complex is potentially a critical reactant associated with Alzheimer's disease etiology. Through competitive chelation, we have measured the affinity of the soluble copper-binding domain of the amyloid-β peptide for Cu(I). The dissociation constants are in the femtomolar range for both wild-type and histidine-to-alanine mutants. These results indicate that Cu(I) binds more tightly to monomeric amyloid-β than Cu(II) does, which leads us to propose that Cu(I) is a relevant in vivo oxidation state.

Iron-induced cardiac damage: role of apoptosis and deferasirox intervention

Excess cardiac iron levels are associated with cardiac damage and can result in increased morbidity and mortality. Here, we hypothesize that elevations in tissue iron can activate caspase-dependent signaling, which leads to increased cardiac apoptosis and fibrosis, and that these alterations can be attenuated by iron chelation. Using an iron-overloaded gerbil model, we show that increased cardiac iron is associated with reduced activation of Akt (Ser473 and Thr308), diminished phosphorylation of the proapoptotic regulator Bad (Ser136), and an increased Bax/Bcl-2 ratio. These iron-overload-induced alterations in Akt/Bad phosphorylation and Bax/Bcl-2 ratio were coupled with increased activation of the downstream caspase-9 (40/38- and 17-kDa fragments) and apoptosis executioner caspase-3 (19- and 17-kDa fragments), which were accompanied by evidence of elevated cytoskeletal α-fodrin cleavage (150- and 120-kDa fragments), discontinuity of myocardial membrane dystrophin immunoreactivity, increases in the number of terminal deoxynucleotidyl transferase dUTP nick-end labeling (TUNEL)-positive cells (nucleic DNA fragmentation), and cardiac fibrosis. We demonstrate that the administration of deferasirox, a tridentate iron chelator, is associated with diminished tissue iron deposition, attenuated activation of caspases, reduced α-fodrin cleavage, improved membrane integrity, decreased TUNEL reactivity, and attenuated cardiac fibrosis. These results suggest that the activation of caspase-dependent signaling may play a role in the development of iron-induced cardiac apoptosis and fibrosis, and deferasirox, via a reduction in cardiac tissue iron levels, may be useful for decreasing the extent of iron-induced cardiac damage.

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.

Iron overload triggers redox-sensitive signals in human IMR-32 neuroblastoma cells

Excessive neuronal iron has been proposed to contribute to the pathology of several neurodegenerative diseases including Alzheimer's and Parkinson's diseases. This work characterized human neuroblastoma IMR-32 cells exposure to ferric ammonium citrate (FAC) as a model of neuronal iron overload and neurodegeneration. The consequences of FAC treatment on neuronal oxidative stress and on the modulation of the oxidant-sensitive transcription factors AP-1 and NF-κB were investigated. Incubation with FAC (150μM) resulted in a time (3-72h)-dependent increase in cellular iron content, and was associated with cell oxidant increase. FAC caused a time-dependent (3-48h) increase in nuclear AP-1- and NF-κB-DNA binding. This was associated with the upstream activation of the mitogen activated kinases ERK1/2, p38 and JNK and of IκBα phosphorylation and degradation. After 72h incubation with FAC, cell viability was 40% lower than in controls. Iron overload caused apoptotic cell death. After 48-72h of incubation with FAC, caspase 3 activity was increased, and chromatin condensation and nuclear fragmentation were observed. In summary, the exposure of IMR-32 cells to FAC is associated with increased oxidant cell levels, activation of redox-sensitive signals, and apoptosis.

Transferrin and HFE genes interact in Alzheimer's disease risk: the Epistasis Project

Iron overload may contribute to the risk of Alzheimer's disease (AD). In the Epistasis Project, with 1757 cases of AD and 6295 controls, we studied 4 variants in 2 genes of iron metabolism: hemochromatosis (HFE) C282Y and H63D, and transferrin (TF) C2 and -2G/A. We replicated the reported interaction between HFE 282Y and TF C2 in the risk of AD: synergy factor, 1.75 (95% confidence interval, 1.1-2.8, p = 0.02) in Northern Europeans. The synergy factor was 3.1 (1.4-6.9; 0.007) in subjects with the APOEε4 allele. We found another interaction, between HFE 63HH and TF -2AA, markedly modified by age. Both interactions were found mainly or only in Northern Europeans. The interaction between HFE 282Y and TF C2 has now been replicated twice, in altogether 2313 cases of AD and 7065 controls, and has also been associated with increased iron load. We therefore suggest that iron overload may be a causative factor in the development of AD. Treatment for iron overload might thus be protective in some cases.

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.

Calpastatin overexpression attenuates amyloid-beta-peptide toxicity in differentiated PC12 cells

Amyloid beta peptide (Abeta) plays a major role in the pathogenesis of Alzheimer's disease (AD). Abeta is toxic to neurons, possibly through causing initial synaptic dysfunction and neuronal membrane dystrophy, promoted by increased cellular Ca(2+). Calpain (Ca(2+)-dependent protease) and caspase have been implicated in AD. Previously, we used calpain and caspase pharmacological inhibitors to study effects of Abeta25-35 (sAbeta) on neuronal-like differentiated PC12 cells. We reported that sAbeta-treated cells exhibited calpain activation and protein degradation (due to both calpain and caspase-8). We have now found that overexpression of the calpain specific inhibitor calpastatin in differentiated PC12 cells significantly inhibited the sAbeta-induced calpain activation and decreased the protease activity. Calpastatin overexpression inhibited the sAbeta-promoted degradation of fodrin, protein kinase Cepsilon, beta-catenin (membrane structural proteins and proteins involved in signal transduction pathways), and prevented the sAbeta-induced alteration of neurite structure (manifested by varicosities). Overexpression of calpastatin also inhibited Ca(2+)-promoted calpain activation and protein degradation; this is consistent with the notion that the Abeta-induced increase in calpain activity results from a rise in cellular Ca(2+), provided the calpastatin level is not so high as to strongly inhibit calpain. Carrying out transfection without selection allowed the comparison in the same culture of calpastatin-overexpressing with non-overexpressing cells. In cultures transfected with green fluorescent protein (GFP)-calpastatin plasmid, calpastatin overexpression (indicated by GFP-labeling) led to inhibition in sAbeta-induced membrane propidium iodide (PI) permeability, whereas non-transfected, GFP-unlabeled cells exhibited PI permeability. Overall, the results demonstrate that the effects of Abeta-toxicity studied here were attenuated to a large extent by calpastatin overexpression, indicating that the protease calpain is involved in Abeta-toxicity (obviating a primary, direct role for caspases). Increased expression of calpastatin and/or decrease in calpain may serve as one of the means for ameliorating some of the early symptoms of AD.

Iron contributes to dopamine-induced toxicity in oligodendrocyte progenitors

Iron is potentially toxic to oligodendrocyte progenitors due to its high intracellular levels and its ability to catalyse oxidant-producing reactions. Oxidative stress resulting from a hypoxic-ischaemic insult has been implicated in death of oligodendrocyte progenitors that occurs in the hypomyelinating disorder periventricular leucomalacia. Ischaemic insults induce the release of various neurotransmitters, including dopamine (DA), and we previously showed that DA is toxic to cultured oligodendrocytes, by inducing oxidative stress and apoptosis. Therefore, we investigated the role of iron in DA-induced cell death in oligodendrocyte progenitors. Intracellular iron levels were altered using an iron chelator, deferoxamine (DFO), and supplementation with ferrous sulphate (FeSO(4)). Addition of FeSO(4) to cultures increased DA-induced toxicity as assessed by mitochondrial dehydrogenase activity and cellular release of lactate dehydrogenase. Furthermore, FeSO(4) increased expression of the stress protein heme oxygenase-1 (HO-1), nuclear condensation and caspase-3 activation. In contrast, preincubation with DFO reduced these events as well as cleavage of alpha-spectrin, a caspase-3 substrate. In addition, FeSO(4) reversed the protective effect of DFO on DA-induced cytotoxicity, HO-1 expression and caspase-3 activation. These results indicate that elevated levels of free iron contribute to DA-induced toxicity in oligodendrocyte progenitors.

Metal ion and antioxidant alterations in leaves between different sexes of Ginkgo biloba L

A comparative study was carried out to determine some valuable phytochemical components, macro- and microelement and redox parameters in leaves of male and female Ginkgo biloba trees and in extracts made from them. G. biloba extracts have become more popular as a therapeutic agent in the modern pharmacology in neurodegenerative diseases, in which increased brain metal levels can be observed and free radical reactions are involved. Macro- and microelement components, total phenol content, H-donating activity and reducing power as well as total scavenger capacity were determined in the samples. Well detectable differences were obtained for micro- and macroelement contents between male and female samples, but no toxic elements could be detected in the extracts. Male extracts contained more hazardous metals (e.g. Fe) compared to the female ones, while extracts from female leaves had higher levels of ions, which are known to have beneficial effects in neurodegenerative diseases. The ethanolic extracts of male leaves showed the highest H-donating activity, reducing power and total phenol content, as well as the best total scavenger activity. Ginkgo extracts due to the antioxidant properties may have favourable effects as dietary supplements in several neurodegenerative diseases, but this study draws the attention that critical evaluation is required in view of the potential hazard induced by their metal ion constitution. Our results lead us to the conclusion that although the aqueous extracts of female leaves are characterized by relatively lower antioxidant properties, they may be more eligible for these purposes due to their favourable metal ion constitution.

Amyloid-beta neurotoxicity is mediated by FISH adapter protein and ADAM12 metalloprotease activity

Based on a variety of genetic, biochemical, and neuropathological evidence, amyloid-beta peptide (Abeta) has been suggested to be causal in Alzheimer's disease (AD). Abeta has been shown to mediate neurodegenerative and inflammatory changes associated with amyloid plaques, as well as exert direct neurotoxicity through oligomeric forms of Abeta. The mechanism of Abeta toxicity, however, remains largely unknown. In this work, we show that an early event after exposure of postmitotic neurons to Abeta is tyrosine phosphorylation of FISH adapter protein. FISH binds to and potentially regulates certain ADAM family members. We present evidence that FISH and ADAM12 mediate the neurotoxic effect of Abeta. Expression of an ADAM12 protease-deficient mutant (ADAM12DeltaMP) blocks Abeta-induced neuronal death, and expression of an N-terminal fragment of FISH reduces Abeta toxicity. The C-terminal fragment of FISH containing the ADAMs binding region is found to be sufficient for induction of neuronal death, which is prevented by coexpression of the ADAM12DeltaMP. Abeta treatment, as well as expression of the C-terminal toxic FISH fragment, induces accumulation of ADAM12 N-terminal cleavage product in conditioned medium, demonstrating activation of the ADAM metalloprotease/sheddase activity. ADAM12 protein is reduced in AD brains, pointing to a possible increase in ADAM12 proteolytic activity. These data suggest that Abeta toxicity is mediated by FISH and ADAM12 and may provide insights into therapeutic strategies for AD treatment.

Enhancement of NMDA responses by β-amyloid peptides in the hippocampus in vivo

The effects of Alzheimer's disease-related beta-amyloid (Abeta) peptides on the N-methyl-D-aspartate (NMDA)-evoked cell firing rate were studied in hippocampal CA1 neurons of the rat. Extracellular single-unit recordings were combined with iontophoretic applications that allowed quantitative analyses of the interactions between Abeta peptides and NMDA receptor-mediated events in vivo. The NMDA responses were significantly increased both by the full length Abeta1-42 and by its model fragment Abeta25-35. Enhancements of the NMDA responses by the Abeta peptides lasted about 15 min and were irreversible. The effects of Abeta25-35 were prevented by the pentapeptide Lys-Leu-Val-Gly-Phe-amide (KLVGF) and were not evoked when its reversed sequence (Abeta35-25) was applied.

Generation of ROS in response to CCK-8 stimulation in mouse pancreatic acinar cells

In the present study we have studied the changes in the intracellular reduction-oxidation state in mouse pancreatic acinar cells following stimulation with cholecystokinin octapeptide (CCK-8) and its dependence on Ca2+ mobilization. In our investigations cytosolic Ca2+ concentration and reactive oxygen species (ROS) production were determined by loading of cells with fura-2 and CM-H2DCF-DA, respectively. Changes in these parameters were determined by following changes in fluorescence in the cuvette of a spectrofluorimeter. The results show that stimulation of cells with CCK-8 and/or the sarco-endoplasmic reticulum Ca2+ pump inhibitor, thapsigargin (Tps), both induced changes in cytosolic free Ca2+ concentration and led to an increase in fluorescence of CM-H2DCF-DA, reflecting an increase in oxidation. In the presence of Tps, addition of CCK-8 did not significantly increase fluorescence compared to that evoked by the SERCA inhibitor. Similar results were obtained in the absence of extracellular Ca2+ and in the presence of EGTA. When the cells were challenged in the presence of the intracellular Ca2+ chelator BAPTA and in the absence of extracellular Ca2+ the responses to both CCK-8 and Tps were reduced although not completely inhibited. The mitochondrial uncoupler carbonyl cyanide p-trifluoromethoxy-phenylhydrazone and the inhibitor of the electron transport chain, antimycin, evoked a marked increase in CM-H2DCF-DA fluorescence and completely inhibited CCK-8 and Tps-evoked responses, indicating that ROS are generated in the mitochondria. In summary, stimulation of mouse pancreatic acinar cells with CCK-8 leads to generation of ROS, and this effect may be derived from Ca2+ mobilization from intracellular stores and involves mitochondrial metabolism.

Apolipoprotein E and β-amyloid (1-42) regulation of glycogen synthase kinase-3β

Glycogen synthase kinase-3beta (GSK-3beta) is implicated in regulating apoptosis and tau protein hyperphosphorylation in Alzheimer's disease (AD). We investigated the effects of two key AD molecules, namely apoE (E3 and E4 isoforms) and beta-amyloid (Abeta) 1-42 on GSK-3beta and its major upstream regulators, intracellular calcium and protein kinases C and B (PKC and PKB) in human SH-SY5Y neuroblastoma cells. ApoE3 induced a mild, transient, Ca2+-independent and early activation of GSK-3beta. ApoE4 effects were biphasic, with an early strong GSK-3beta activation that was partially dependent on extracellular Ca2+, followed by a GSK-3beta inactivation. ApoE4 also activated PKC-alpha and PKB possibly giving the subsequent GSK-3beta inhibition. Abeta(1-42) effects were also biphasic with a strong activation dependent partially on extracellular Ca2+ followed by an inactivation. Abeta(1-42) induced an early and potent activation of PKC-alpha and a late decrease of PKB activity. ApoE4 and Abeta(1-42) were more toxic than apoE3 as shown by MTT reduction assays and generation of activated caspase-3. ApoE4 and Abeta(1-42)-induced early activation of GSK-3beta could lead to apoptosis and tau hyperphosphorylation. A late inhibition of GSK-3beta through activation of upstream kinases likely compensates the effects of apoE4 and Abeta(1-42) on GSK-3beta, the unbalanced regulation of which may contribute to AD pathology.