Copper promotes the trafficking of the amyloid precursor protein

Copper: From enigma to therapeutic target for neurological disorder

Neurological disorders (NDs) have a negative impact on the lives of individuals. There could be two explanations for this: unclear aetiology and lack of effective therapy. However, research in the past few years has revealed the role of bio-metals dyshomeostasis in NDs. The imbalance in copper (Cu) concentration may be one of the main causative factors in NDs. In this review, we have discussed the role of Cu in NDs, especially Alzheimer's disease (AD), including the molecular mechanisms involved in Cu-associated NDs like oxidative stress, neuroinflammation, and protein misfolding. We have also summarized the recent Cu-targeting approaches and highlighted the in vitro and in vivo studies recently being reported on the subject. Based on the earlier published reports, it could be speculated that the Cu targeting strategy might be an interesting and potential therapeutic approach for NDs. Various difficulties must be overcome to develop safe and efficient Cu-targeting medications for NDs.

The Role of Reactive Oxygen Species in Alzheimer's Disease: From Mechanism to Biomaterials Therapy

Alzheimer's disease (AD) is a chronic, insidious, and progressive neurodegenerative disease that remains a clinical challenge for society. The fully approved drug lecanemab exhibits the prospect of therapy against the pathological processes, while debatable adverse events conflict with the drug concentration required for the anticipated therapeutic effects. Reactive oxygen species (ROS) are involved in the pathological progression of AD, as has been demonstrated in much research regarding oxidative stress (OS). The contradiction between anticipated dosage and adverse event may be resolved through targeted transport by biomaterials and get therapeutic effects through pathological progression via regulation of ROS. Besides, biomaterials fix delivery issues by promoting the penetration of drugs across the blood-brain barrier (BBB), protecting the drug from peripheral degradation, and elevating bioavailability. The goal is to comprehensively understand the mechanisms of ROS in the progression of AD disease and the potential of ROS-related biomaterials in the treatment of AD. This review focuses on OS and its connection with AD and novel biomaterials in recent years against AD via OS to inspire novel biomaterial development. Revisiting these biomaterials and mechanisms associated with OS in AD via thorough investigations presents a considerable potential and bright future for improving effective interventions for AD.

Missing heritability of Wilson disease: a search for the uncharacterized mutations

Wilson disease (WD), a copper metabolism disorder caused by mutations in ATP7B, manifests heterogeneous clinical features. Interestingly, in a fraction of clinically diagnosed WD patients, mutations in ATP7B appears to be missing. In this review we discuss the plausible explanations of this missing heritability and propose a workflow that can identify the hidden mutations. Mutation analyses of WD generally includes targeted sequencing of ATP7B exons, exon-intron boundaries, and rarely, the proximal promoter region. We propose that variants in the distal cis-regulatory elements and/or deep intronic variants that impact splicing might well represent the hidden mutations. Heterozygous del/ins that remain refractory to conventional PCR-sequencing method may also represent such mutations. In this review, we also hypothesize that mutations in the key copper metabolism genes, like, ATOX1, COMMD1, and SLC31A1, could possibly lead to a WD-like phenotype. In fact, WD does present overlapping symptoms with other rare genetic disorders; hence, the possibility of a misdiagnosis and thus adding to missing heritability cannot be excluded. In this regard, it seems that whole-genome analysis will provide a comprehensive and rapid molecular diagnosis of WD. However, considering the associated cost for such a strategy, we propose an alternative customized screening schema of WD which include targeted sequencing of ATP7B locus as well as other key copper metabolism genes. Success of such a schema has been tested in a pilot study.

Relationship between copper and immunity: The potential role of copper in tumor immunity

Copper is an essential trace element in an organism, and changes in copper levels in vivo often indicate a diseased state. Copper and immunity have been discussed since the last century, with copper deficiency significantly affecting the development and function of the immune system, such as increased host susceptibility to various pathogens, decreased number and impaired function of neutrophils, reduced antibacterial activity of macrophages, decreased proliferation of splenocytes, impaired B cell ability to produce antibodies and impaired function of cytotoxic T lymphocyte and helper T cells. In the past 20 years, some studies have shown that copper ions are related to the development of many tumors, including lung cancer, acute lymphoid leukaemia, multiple myeloma and other tumors, wherein copper ion levels were significantly elevated, and current studies reveal that copper ions are involved in the development, growth and metastasis of tumors through various pathways. Moreover, recent studies have shown that copper ions can regulate the expression of PD-L1, thus, attention should be paid to the important role of copper in tumor immunity. By exploring and studying copper ions and tumor immunity, new insights into tumor immunity could be generated and novel therapeutic approaches to improve the clinical prognosis of patients can be provided.

Brain copper may protect from cognitive decline and Alzheimer's disease pathology: a community-based study

Copper is an essential micronutrient for brain health and dyshomeostasis of copper could have a pathophysiological role in Alzheimer's disease (AD), however, there are limited data from community-based samples. In this study, we investigate the association of brain copper (assessed using ICP-MS in four regions -inferior temporal, mid-frontal, anterior cingulate, and cerebellum) and dietary copper with cognitive decline and AD pathology burden (a quantitative summary of neurofibrillary tangles, diffuse and neuritic plaques in multiple brain regions) at autopsy examination among deceased participants (N = 657; age of death: 90.2(±6.2)years, 70% women, 25% APOE-ɛ4 carriers) in the Rush Memory and Aging Project. During annual visits, these participants completed cognitive assessments using a 19-test battery and dietary assessments (using a food frequency questionnaire). Regression, linear mixed-effects, and logistic models adjusted for age at death, sex, education, and APOE-ε4 status were used. Higher composite brain copper levels were associated with slower cognitive decline (β(SE) = 0.028(0.01), p = 0.001) and less global AD pathology (β(SE) = -0.069(0.02), p = 0.0004). Participants in the middle and highest tertile of dietary copper had slower cognitive decline (T2vs.T1: β = 0.038, p = 0.0008; T3vs.T1: β = 0.028, p = 0.01) than those in the lowest tertile. Dietary copper intake was not associated with brain copper levels or AD pathology. Associations of higher brain copper levels with slower cognitive decline and with less AD pathology support a role for copper dyshomeostasis in AD pathogenesis and suggest that lower brain copper may exacerbate or indicate disease severity. Dietary and brain copper are unrelated but dietary copper is associated with slower cognitive decline via an unknown mechanism.

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

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

Effect of Sublethal Copper Overload on Cholesterol De Novo Synthesis in Undifferentiated Neuronal Cells

Although copper (Cu) is an essential trace metal for cells, it can induce harmful effects as it participates in the Fenton reaction. Involuntary exposure to Cu overload is much more common than expected and has been linked with neurodegeneration, particularly with Alzheimer's disease (AD) evidenced by a positive correlation between free Cu in plasma and the severity of the disease. It has been suggested that Cu imbalance alters cholesterol (Chol) homeostasis and that high membrane Chol promotes the amyloidogenic processing of the amyloid precursor protein (APP) secreting the β-amyloid (Aβ) peptide. Despite the wide knowledge on the effects of Cu in mature brain metabolism, the consequence of its overload on immature neurons remains unknown. Therefore, we used an undifferentiated human neuroblastoma cell line (SH-SY5Y) to analyze the effect of sublethal concentrations of Cu on 1- de novo Chol synthesis and membrane distribution; 2-APP levels in cells and its distribution in membrane rafts; 3-the levels of Aβ in the culture medium. Our results demonstrated that Cu increases reactive oxygen species (ROS) and favors Chol de novo synthesis in both ROS-dependent and independent manners. Also, at least part of these effects was due to the activation of 3-hydroxy-3-methyl glutaryl CoA reductase (HMGCR). In addition, Cu increases the Chol/PL ratio in the cellular membranes, specifically Chol content in membrane rafts. We found no changes in total APP cell levels; however, its presence in membrane rafts increases with the consequent increase of Aβ in the culture medium. We conclude that Cu overload favors Chol de novo synthesis in both ROS-dependent and independent manners, being at least in part, responsible for the high Chol levels found in the cell membrane and membrane rafts. These may promote the redistribution of APP into the rafts, favoring the amyloidogenic processing of this protein and increasing the levels of Aβ.

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

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

Copper-Mediated β-Amyloid Toxicity and its Chelation Therapy in Alzheimer's Disease

The link between bio-metals, Alzheimer's disease (AD), and its associated protein, amyloid-β (Aβ) is very complex and one of the most studied aspects currently. Alzheimer's disease, a progressive neurodegenerative disease, is proposed to occurs due to the misfolding and aggregation of Aβ. Dyshomeostasis of metal ions and their interaction with Aβ has largely been implicated in AD. Copper plays a crucial role in amyloid-β toxicity and AD development potentially occurs through direct interaction with the copper-binding motif of APP and different amino acid residues of Aβ. Previous reports suggest that high levels of copper accumulation in the AD brain result in modulation of toxic Aβ peptide levels, implicating the role of copper in the pathophysiology of AD. In this review, we explore the possible mode of copper ion interaction with Aβ which accelerates the kinetics of fibril formation and promote amyloid-β mediated cell toxicity in Alzheimer's disease and the potential use of various copper chelators in the prevention of copper-mediated Aβ toxicity.

Do glutathione and copper interact to modify Alzheimer's disease pathogenesis?

Alzheimer's disease (AD) is a progressive neurodegenerative disorder first described in 1906 that is currently estimated to impact ∼40 million people worldwide. Extensive research activities have led to a wealth of information on the pathogenesis, hallmarks, and risk factors of AD; however, therapeutic options remain extremely limited. The large number of pathogenic factors that have been reported to potentially contribute to AD include copper dyshomeostasis as well as increased oxidative stress, which is related to alterations to molecular antioxidants like glutathione (GSH). While the individual roles of GSH and copper in AD have been studied by many research groups, their interactions have received relatively little attention, although they appear to interact and affect each other's regulation. Existing knowledge on how GSH-copper interactions may affect AD is sparse and lacks focus. This review first highlights the most relevant individual roles that GSH and copper play in physiology and AD, and then collects and assesses research concerning their interactions, in an effort to provide a more accessible and understandable picture of the role of GSH, copper, and their interactions in AD.

α-Lipoic Acid Has the Potential to Normalize Copper Metabolism, Which Is Dysregulated in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is an age-dependent progressive neurodegenerative disorder and the most common cause of dementia. The treatment and prevention of AD present immense yet unmet needs. One of the hallmarks of AD is the formation of extracellular amyloid plaques in the brain, composed of amyloid-β (Aβ) peptides. Besides major amyloid-targeting approach there is the necessity to focus also on alternative therapeutic strategies. One factor contributing to the development of AD is dysregulated copper metabolism, reflected in the intracellular copper deficit and excess of extracellular copper.

OBJECTIVE

In the current study, we follow the widely accepted hypothesis that the normalization of copper metabolism leads to the prevention or slowing of the disease and search for new copper-regulating ligands.

METHODS

We used cell culture, ICP MS, and Drosophila melanogaster models of AD.

RESULTS

We demonstrate that the natural intracellular copper chelator, α-lipoic acid (LA) translocates copper from extracellular to intracellular space in an SH-SY5Y-based neuronal cell model and is thus suitable to alleviate the intracellular copper deficit characteristic of AD neurons. Furthermore, we show that supplementation with LA protects the Drosophila melanogaster models of AD from developing AD phenotype by improving locomotor activity of fruit fly with overexpression of human Aβ with Iowa mutation in the fly brain. In addition, LA slightly weakens copper-induced smooth eye phenotype when amyloid-β protein precursor (AβPP) and beta-site AβPP cleaving enzyme 1 (BACE1) are overexpressed in eye photoreceptor cells.

CONCLUSION

Collectively, these results provide evidence that LA has the potential to normalize copper metabolism in AD.

Microglia and Astrocytes in Alzheimer's Disease in the Context of the Aberrant Copper Homeostasis Hypothesis

Evidence of copper's (Cu) involvement in Alzheimer's disease (AD) is available, but information on Cu involvement in microglia and astrocytes during the course of AD has yet to be structurally discussed. This review deals with this matter in an attempt to provide an updated discussion on the role of reactive glia challenged by excess labile Cu in a wide picture that embraces all the major processes identified as playing a role in toxicity induced by an imbalance of Cu in AD.

The Beneficial Role of Exercise on Treating Alzheimer's Disease by Inhibiting β-Amyloid Peptide

Alzheimer's disease (AD) is associated with a very large burden on global healthcare systems. Thus, it is imperative to find effective treatments of the disease. One feature of AD is the accumulation of neurotoxic β-amyloid peptide (Aβ). Aβ induces multiple pathological processes that are deleterious to nerve cells. Despite the development of medications that target the reduction of Aβ to treat AD, none has proven to be effective to date. Non-pharmacological interventions, such as physical exercise, are also being studied. The benefits of exercise on AD are widely recognized. Experimental and clinical studies have been performed to verify the role that exercise plays in reducing Aβ deposition to alleviate AD. This paper reviewed the various mechanisms involved in the exercise-induced reduction of Aβ, including the regulation of amyloid precursor protein cleaved proteases, the glymphatic system, brain-blood transport proteins, degrading enzymes and autophagy, which is beneficial to promote exercise therapy as a means of prevention and treatment of AD and indicates that exercise may provide new therapeutic targets for the treatment of AD.

Up-regulation of APP endocytosis by neuronal aging drives amyloid dependent-synapse loss

Neuronal aging increases the risk of late-onset Alzheimer's disease. During normal aging, synapses decline, and β-amyloid (Aβ) accumulates intraneuronally. However, little is known about the underlying cell biological mechanisms. We studied normal neuronal aging using normal aged brain and aged mouse primary neurons that accumulate lysosomal lipofuscin and show synapse loss. We identify the up-regulation of amyloid precursor protein (APP) endocytosis as a neuronal aging mechanism that potentiates APP processing and Aβ production in vitro and in vivo. The increased APP endocytosis may contribute to the observed early endosomes enlargement in the aged brain. Mechanistically, we show that clathrin-dependent APP endocytosis requires F-actin and that clathrin and endocytic F-actin increase with neuronal aging. Finally, Aβ production inhibition reverts synaptic decline in aged neurons while Aβ accumulation, promoted by endocytosis up-regulation in younger neurons, recapitulates aging-related synapse decline. Overall, we identify APP endocytosis up-regulation as a potential mechanism of neuronal aging and, thus, a novel target to prevent late-onset Alzheimer's disease.

The M1311V variant of ATP7A is associated with impaired trafficking and copper homeostasis in models of motor neuron disease

Disruption in copper homeostasis causes a number of cognitive and motor deficits. Wilson's disease and Menkes disease are neurodevelopmental disorders resulting from mutations in the copper transporters ATP7A and ATP7B, with ATP7A mutations also causing occipital horn syndrome, and distal motor neuropathy. A 65 year old male presenting with brachial amyotrophic diplegia and diagnosed with amyotrophic lateral sclerosis (ALS) was found to harbor a p.Met1311Val (M1311V) substitution variant in ATP7A. ALS is a fatal neurodegenerative disease associated with progressive muscle weakness, synaptic deficits and degeneration of upper and lower motor neurons. To investigate the potential contribution of the ATP7A^M1311V variant to neurodegeneration, we obtained and characterized both patient-derived fibroblasts and patient-derived induced pluripotent stem cells differentiated into motor neurons (iPSC-MNs), and compared them to control cell lines. We found reduced localization of ATP7A^M1311V to the trans-Golgi network (TGN) at basal copper levels in patient-derived fibroblasts and iPSC-MNs. In addition, redistribution of ATP7A^M1311V out of the TGN in response to increased extracellular copper was defective in patient fibroblasts. This manifested in enhanced intracellular copper accumulation and reduced survival of ATP7A^M1311V fibroblasts. iPSC-MNs harboring the ATP7A^M1311V variant showed decreased dendritic complexity, aberrant spontaneous firing, and decreased survival. Finally, expression of the ATP7A^M1311V variant in Drosophila motor neurons resulted in motor deficits. Apilimod, a drug that targets vesicular transport and recently shown to enhance survival of C9orf72-ALS/FTD iPSC-MNs, also increased survival of ATP7A^M1311V iPSC-MNs and reduced motor deficits in Drosophila expressing ATP7A^M1311V. Taken together, these observations suggest that ATP7A^M1311V negatively impacts its role as a copper transporter and impairs several aspects of motor neuron function and morphology.

The biological pathways of Alzheimer disease: a review

Alzheimer disease is a progressive neurodegenerative disorder, mainly affecting older people, which severely impairs patients' quality of life. In the recent years, the number of affected individuals has seen a rapid increase. It is estimated that up to 107 million subjects will be affected by 2050 worldwide. Research in this area has revealed a lot about the biological and environmental underpinnings of Alzheimer, especially its correlation with β-Amyloid and Tau related mechanics; however, the precise molecular events and biological pathways behind the disease are yet to be discovered. In this review, we focus our attention on the biological mechanics that may lie behind Alzheimer development. In particular, we briefly describe the genetic elements and discuss about specific biological processes potentially associated with the disease.

Copper Dyshomeostasis in Neurodegenerative Diseases-Therapeutic Implications

Copper is one of the most abundant basic transition metals in the human body. It takes part in oxygen metabolism, collagen synthesis, and skin pigmentation, maintaining the integrity of blood vessels, as well as in iron homeostasis, antioxidant defense, and neurotransmitter synthesis. It may also be involved in cell signaling and may participate in modulation of membrane receptor-ligand interactions, control of kinase and related phosphatase functions, as well as many cellular pathways. Its role is also important in controlling gene expression in the nucleus. In the nervous system in particular, copper is involved in myelination, and by modulating synaptic activity as well as excitotoxic cell death and signaling cascades induced by neurotrophic factors, copper is important for various neuronal functions. Current data suggest that both excess copper levels and copper deficiency can be harmful, and careful homeostatic control is important. This knowledge opens up an important new area for potential therapeutic interventions based on copper supplementation or removal in neurodegenerative diseases including Wilson's disease (WD), Menkes disease (MD), Alzheimer's disease (AD), Parkinson's disease (PD), and others. However, much remains to be discovered, in particular, how to regulate copper homeostasis to prevent neurodegeneration, when to chelate copper, and when to supplement it.

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.

Attenuation of Oxidative Stress by Cannabinoids and Cannabis Extracts in Differentiated Neuronal Cells

In this proof-of-concept study, the antioxidant activity of phytocannabinoids, namely cannabidiol (CBD) and Δ9- tetrahydrocannabinol (THC), were investigated using an in vitro system of differentiated human neuronal SY-SH5Y cells. The oxidative stress was induced by hydrogen peroxide, as reactive oxygen species (ROS). Alzheimer's disease (AD)-like pathological conditions were mimicked in vitro by treating the differentiated neuronal cells with amyloid-β_1-42 (Aβ_1-42) in the presence of Cu(II). We showed that THC had a high potency to combat oxidative stress in both in vitro models, while CBD did not show a remarkable antioxidant activity. The cannabis extracts also exhibited a significant antioxidant activity, which depended on the ratio of the THC and CBD. However, our results did not suggest any antagonist effect of the CBD on the antioxidant activity of THC. The effect of cannabis extracts on the cell viability of differentiated human neuronal SY-SH5Y cells was also investigated, which emphasized the differences between the bioactivity of cannabis extracts due to their composition. Our preliminary results demonstrated that cannabis extracts and phytocannabinoids have a promising potential as antioxidants, which can be further investigated to develop novel pharmaceuticals targeting oxidative stress therapy.

Copper Toxicity Links to Pathogenesis of Alzheimer's Disease and Therapeutics Approaches

Alzheimer's disease (AD) is an irreversible, age-related progressive neurological disorder, and the most common type of dementia in aged people. Neuropathological lesions of AD are neurofibrillary tangles (NFTs), and senile plaques comprise the accumulated amyloid-beta (Aβ), loaded with metal ions including Cu, Fe, or Zn. Some reports have identified metal dyshomeostasis as a neurotoxic factor of AD, among which Cu ions seem to be a central cationic metal in the formation of plaque and soluble oligomers, and have an essential role in the AD pathology. Cu-Aβ complex catalyzes the generation of reactive oxygen species (ROS) and results in oxidative damage. Several studies have indicated that oxidative stress plays a crucial role in the pathogenesis of AD. The connection of copper levels in AD is still ambiguous, as some researches indicate a Cu deficiency, while others show its higher content in AD, and therefore there is a need to increase and decrease its levels in animal models, respectively, to study which one is the cause. For more than twenty years, many in vitro studies have been devoted to identifying metals' roles in Aβ accumulation, oxidative damage, and neurotoxicity. Towards the end, a short review of the modern therapeutic approach in chelation therapy, with the main focus on Cu ions, is discussed. Despite the lack of strong proofs of clinical advantage so far, the conjecture that using a therapeutic metal chelator is an effective strategy for AD remains popular. However, some recent reports of genetic-regulating copper transporters in AD models have shed light on treating this refractory disease. This review aims to succinctly present a better understanding of Cu ions' current status in several AD features, and some conflicting reports are present herein.

Agricultural Use of Copper and Its Link to Alzheimer's Disease

Copper is an essential nutrient for plants, animals, and humans because it is an indispensable component of several essential proteins and either lack or excess are harmful to human health. Recent studies revealed that the breakdown of the regulation of copper homeostasis could be associated with Alzheimer's disease (AD), the most common form of dementia. Copper accumulation occurs in human aging and is thought to increase the risk of AD for individuals with a susceptibility to copper exposure. This review reports that one of the leading causes of copper accumulation in the environment and the human food chain is its use in agriculture as a plant protection product against numerous diseases, especially in organic production. In the past two decades, some countries and the EU have invested in research to reduce the reliance on copper. However, no single alternative able to replace copper has been identified. We suggest that agroecological approaches are urgently needed to design crop protection strategies based on the complementary actions of the wide variety of crop protection tools for disease control.

Redox active metals in neurodegenerative diseases

Copper (Cu) and iron (Fe) are redox active metals essential for the regulation of cellular pathways that are fundamental for brain function, including neurotransmitter synthesis and release, neurotransmission, and protein turnover. Cu and Fe are tightly regulated by sophisticated homeostatic systems that tune the levels and localization of these redox active metals. The regulation of Cu and Fe necessitates their coordination to small organic molecules and metal chaperone proteins that restrict their reactions to specific protein centres, where Cu and Fe cycle between reduced (Fe²⁺, Cu⁺) and oxidised states (Fe³⁺, Cu²⁺). Perturbation of this regulation is evident in the brain affected by neurodegeneration. Here we review the evidence that links Cu and Fe dyshomeostasis to neurodegeneration as well as the promising preclinical and clinical studies reporting pharmacological intervention to remedy Cu and Fe abnormalities in the treatment of Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS).

Dialing in on pharmacological features for a therapeutic antioxidant small molecule

The pyridinophane molecule L2 (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-trien-13-ol) has shown promise as a therapuetic for neurodegenerative diseases involving oxidative stress and metal ion misregulation. Protonation and metal binding stability constants with Mg2+, Ca2+, Cu2+, and Zn2+ ions were determined to further explore the therapeutic and pharmacological potential of this water soluble small molecule. These studies show that incorporation of an -OH group in position 4 of the pyridine ring decreases the pI values compared to cyclen and L1 (3,6,9,15-tetraazabicyclo[9.3.1]penta-deca-1(15),11,13-triene). Furthermore, this approach tunes the basicity of the tetra-aza macrocyclic ligand through the enhanced resonance stabilization of the -OH in position 4 and rigidity of the pyridine ring such that L2 has increased basicity compared to previously reported tetra-aza macrocycles. A metal binding preference for Cu2+, a redox cycling agent known to produce oxidative stress, indicates that this would be the in vivo metal target of L2. However, the binding constant of L2 with Cu2+ is moderated compared to cyclen due to the rigidity of the ligand and shows how ligand design can be used to tune metal selectivity. An IC50 = 298.0 μM in HT-22 neuronal cells was observed. Low metabolic liability was determined in both Phase I and II in vitro models. Throughout these studies other metal binding systems were used for comparison and as appropriate controls. The reactivity reported to date and pharmacological features described herein warrant further studies in vivo and the pursuit of L2 congeners using the knowledge that pyridine substitution in a pyridinophane can be used to tune the structure of the ligand and retain the positive therapeutic outcomes.

Copper homeostasis as target of both consolidated and innovative strategies of anti-tumor therapy

BACKGROUND

Copper was reported to be involved in the onset and progression of cancer. Proteins in charge of copper uptake and distribution, as well as cuproenzymes, are altered in cancer. More recently, proteins involved in signaling cascades, regulating cell proliferation, and anti-apoptotic protein factors were found to interact with copper. Therefore, therapeutic strategies using copper complexing molecules have been proposed for cancer therapy and used in clinical trials.

OBJECTIVES

This review will focus on novel findings about the involvement of copper and cupro-proteins in cancer dissemination process, epithelium to mesenchymal transition and vascularization. Particularly, implication of well-established (e.g. lysil oxidase) or newly identified copper-binding proteins (e.g. MEMO1), as well as their interplay, will be discussed. Moreover, we will describe recently synthesized copper complexes, including plant-derived ones, and their efficacy in contrasting cancer development.

CONCLUSIONS

The research on the involvement of copper in cancer is still an open field. Further investigation is required to unveil the mechanisms involved in copper delivery to the novel copper-binding proteins, which may identify other possible gene and protein targets for cancer therapy.

"Dual Disease" TgAD/GSS mice exhibit enhanced Alzheimer's disease pathology and reveal PrPC-dependent secretion of Aβ

To address the question of cross-talk between prion protein (PrP) and Alzheimer's disease (AD), we generated TgAD/GSS mice that develop amyloid-β (Aβ) plaques of AD and PrP (specifically mutated PrP^A116V) plaques of Gerstmann-Sträussler-Scheinker disease (GSS) and compared plaque-related features in these mice to AD mice that express normal (TgAD), high (TgAD/HuPrP), or no (TgAD/PrP^-/-) PrP^C. In contrast to PrP^C, PrP^A116V weakly co-localized to Aβ plaques, did not co-immunoprecipitate with Aβ, and poorly bound to Aβ in an ELISA-based binding assay. Despite the reduced association of PrP^A116V with Aβ, TgAD/GSS and TgAD/HuPrP mice that express comparable levels of PrP^A116V and PrP^C respectively, displayed similar increases in Aβ plaque burden and steady state levels of Aβ and its precursor APP compared with TgAD mice. Our Tg mouse lines also revealed a predominance of intracellular Aβ plaques in mice lacking PrP^C (TgAD/PrP^-/-, TgAD/GSS) compared with an extracellular predominance in PrP^C-expressing mice (TgAD, TgAD/HuPrP). Parallel studies in N2aAPPswe cells revealed a direct dependence on PrP^C but not PrP^A116V for exosome-related secretion of Aβ. Overall, our findings are two-fold; they suggest that PrP expression augments Aβ plaque production, at least in part by an indirect mechanism, perhaps by increasing steady state levels of APP, while they also provide support for a fundamental role of PrP^C to bind to and deliver intraneuronal Aβ to exosomes for secretion.

Safe coordinated trafficking of heme and iron with copper maintain cell homeostasis: modules from the hemopexin system

Studies with patients, animal models of human disease and hemopexin null mice have shown that the heme-binding protein hemopexin is vital for the protection of a variety of cell types and tissues against heme toxicity. The presence of hemopexin in all biological fluids examined to date indicates wide roles in abrogating heme toxicity in human tissues; and, thus, is clinically relevant. Heme-hemopexin endocytosis leads to coordinated trafficking of heme, iron and copper as heme traffics from endosomes to heme oxygenases (HOs) in the smooth endoplasmic reticulum and to the nucleus. This is safe redox-metal trafficking, without oxidative stress, as iron released from heme catabolism by HOs as well as copper taken up with heme-hemopexin move through the cell. To our knowledge, this coordinated metal trafficking has been described only for the hemopexin system and differs from the cell's response to non-protein bound heme, which can be toxic. We propose that defining how cells respond to heme-hemopexin endocytosis, a natural cytoprotective system, will aid our understanding of how cells adapt as they safely respond to increases in heme, Fe(II) and copper. This is relevant for many genetic hemolytic diseases and conditions, stroke and hemorrhage as well as neurodegeneration. Such analyses will help to define a pattern of events that can be utilized to characterize how dysfunctional redox and transition metal handling is linked to the development of pathology in disease states such as Alzheimer's disease when metal homeostasis is not restored; and potentially provide novel targets and approaches to improve therapies.

Metal Toxicity Links to Alzheimer's Disease and Neuroinflammation

As the median age of the population increases, the number of individuals with Alzheimer's disease (AD) and the associated socio-economic burden are predicted to worsen. While aging and inherent genetic predisposition play major roles in the onset of AD, lifestyle, physical fitness, medical condition, and social environment have emerged as relevant disease modifiers. These environmental risk factors can play a key role in accelerating or decelerating disease onset and progression. Among known environmental risk factors, chronic exposure to various metals has become more common among the public as the aggressive pace of anthropogenic activities releases excess amount of metals into the environment. As a result, we are exposed not only to essential metals, such as iron, copper, zinc and manganese, but also to toxic metals including lead, aluminum, and cadmium, which perturb metal homeostasis at the cellular and organismal levels. Herein, we review how these metals affect brain physiology and immunity, as well as their roles in the accumulation of toxic AD proteinaceous species (i.e., β-amyloid and tau). We also discuss studies that validate the disruption of immune-related pathways as an important mechanism of toxicity by which metals can contribute to AD. Our goal is to increase the awareness of metals as players in the onset and progression of AD.

Copper-64: a real theranostic agent

Ongoing studies of physiological and pathological processes have led to a corresponding need for new radiopharmaceuticals, especially when studies are limited by the absence of a particular radiolabeled target. Thus, the development of new radioactive tracers is highly relevant and can represent a significant contribution to efforts to elucidate important phenomena in biology. Currently, theranostics represents a new frontier in the fields of medicine and nuclear medicine, with the same compound being used for both diagnosis and treatment. In the human body, copper (Cu) is the third most abundant metal and it plays a crucial role in many biological functions. Correspondingly, in various acquired and inherited pathological conditions, such as cancer and Alzheimer’s disease, alterations in Cu levels have been found. Moreover, a wide spectrum of neurodegenerative disorders are associated with higher or lower levels of Cu, as well as inappropriately bound or distributed levels of Cu in the brain. In human cells, the membrane protein, hCtr1, binds Cu in its Cu(I) oxidation state in an energy-dependent manner. Copper-64 (⁶⁴Cu) is a cyclotron-produced radionuclide that has exhibited physical properties that are complementary for diagnosis and/or therapeutic purposes. To date, very few reports have described the clinical development of ⁶⁴Cu as a radiotracer for cancer imaging. In this review, we highlight recent insights in our understanding and use of ⁶⁴CuCl₂ as a theranostic agent for various types of tumors. To the best of our knowledge, no adverse effects or clinically observable pharmacological effects have been described for ⁶⁴CuCl₂ in the literature. Thus, ⁶⁴Cu represents a revolutionary radiopharmaceutical for positron emission tomography imaging and opens a new era in the theranostic field.

Potentiating role of copper on spatial memory deficit induced by beta amyloid and evaluation of mitochondrial function markers in the hippocampus of rats

Mounting evidence suggests that copper, a crucial element in normal brain function, plays an important role in the etiology of Alzheimer's disease, which is known as a neurodegenerative mitochondrial disorder. However, the precise mechanisms of its effects on cognitive and mitochondrial functions through the CNS have not been thoroughly recognized yet. In this study, we aimed to investigate the long-term (3-week) effects of copper sulfate (50, 100 and 200 mg kg^-1 day^-1) exposure on learning and memory as well as on mitochondrial function in the hippocampus of rats in the presence and absence of beta amyloid (1 μg μl^-1 per side) intrahippocampally (IH). After three weeks of copper exposure through drinking water, acquisition and retention of spatial memory were measured by the Morris water maze (MWM) test. Various parameters of mitochondrial function were also evaluated. Our data show that copper damaged the spatial learning and memory and also exacerbated the memory deficit induced by Aβ injection in rats in a dose-dependent manner. Mitochondria isolated from the hippocampus of rats treated with copper showed significant increases in ROS formation, mitochondrial swelling, lipid peroxidation, glutathione oxidation, outer membrane damage, and collapse of MMP, decreased cytochrome c oxidase activity, and finally increased ADP/ATP ratios. Our results indicate that copper overloading in the hippocampus of rats causes mitochondrial dysfunction and subsequent oxidative stress leading to cognitive impairment. This study also reveals that copper can potentiate Aβ deleterious effects on spatial memory and brain mitochondrial function.

Role of Copper in the Onset of Alzheimer's Disease Compared to Other Metals

Alzheimer's disease (AD) is a neurodegenerative disorder that is characterized by amyloid plaques in patients' brain tissue. The plaques are mainly made of β-amyloid peptides and trace elements including Zn2+, Cu2+, and Fe2+. Some studies have shown that AD can be considered a type of metal dyshomeostasis. Among metal ions involved in plaques, numerous studies have focused on copper ions, which seem to be one of the main cationic elements in plaque formation. The involvement of copper in AD is controversial, as some studies show a copper deficiency in AD, and consequently a need to enhance copper levels, while other data point to copper overload and therefore a need to reduce copper levels. In this paper, the role of copper ions in AD and some contradictory reports are reviewed and discussed.

Dimerization leads to changes in APP (amyloid precursor protein) trafficking mediated by LRP1 and SorLA

Proteolytic cleavage of the amyloid precursor protein (APP) by α-, β- and γ-secretases is a determining factor in Alzheimer's disease (AD). Imbalances in the activity of all three enzymes can result in alterations towards pathogenic Aβ production. Proteolysis of APP is strongly linked to its subcellular localization as the secretases involved are distributed in different cellular compartments. APP has been shown to dimerize in cis-orientation, affecting Aβ production. This might be explained by different substrate properties defined by the APP oligomerization state or alternatively by altered APP monomer/dimer localization. We investigated the latter hypothesis using two different APP dimerization systems in HeLa cells. Dimerization caused a decreased localization of APP to the Golgi and at the plasma membrane, whereas the levels in the ER and in endosomes were increased. Furthermore, we observed via live cell imaging and biochemical analyses that APP dimerization affects its interaction with LRP1 and SorLA, suggesting that APP dimerization modulates its interplay with sorting molecules and in turn its localization and processing. Thus, pharmacological approaches targeting APP oligomerization properties might open novel strategies for treatment of AD.

Copper signaling in the brain and beyond

Transition metals have been recognized and studied primarily in the context of their essential roles as structural and metabolic cofactors for biomolecules that compose living systems. More recently, an emerging paradigm of transition-metal signaling, where dynamic changes in transitional metal pools can modulate protein function, cell fate, and organism health and disease, has broadened our view of the potential contributions of these essential nutrients in biology. Using copper as a canonical example of transition-metal signaling, we highlight key experiments where direct measurement and/or visualization of dynamic copper pools, in combination with biochemical, physiological, and behavioral studies, have deciphered sources, targets, and physiological effects of copper signals.

Biometal Dyshomeostasis and Toxic Metal Accumulations in the Development of Alzheimer's Disease

Biometal dyshomeostasis and toxic metal accumulation are common features in many neurodegenerative disorders, including Alzheimer’s disease (AD), Parkinson’s disease, and Huntington’s disease. The neurotoxic effects of metal imbalance are generally associated with reduced enzymatic activities, elevated protein aggregation and oxidative stress in the central nervous system, in which a cascade of events lead to cell death and neurodegeneration. Although the links between biometal imbalance and neurodegenerative disorders remain elusive, a major class of endogenous proteins involved in metal transport has been receiving increasing attention over recent decades. The abnormal expression of these proteins has been linked to biometal imbalance and to the pathogenesis of AD. Here, we present a brief overview of the physiological roles of biometals including iron, zinc, copper, manganese, magnesium and calcium, and provide a detailed description of their transporters and their synergistic involvement in the development of AD. In addition, we also review the published data relating to neurotoxic metals in AD, including aluminum, lead, cadmium, and mercury.

Nexus between mitochondrial function, iron, copper and glutathione in Parkinson's disease

Parkinson's disease is neuropathologically characterised by loss of catecholamine neurons in vulnerable brain regions including substantia nigra pars compacta and locus coeruleus. This review discusses how the susceptibility of these regions is defined by their shared biochemical characteristics that differentiate them from other neurons. Parkinson's disease is biochemically characterised by mitochondrial dysfunction, accumulation of iron, diminished copper content and depleted glutathione levels in these regions. This review also discusses this neuropathology, and provides evidence for how these pathological features are mechanistically linked to each other. This leads to the conclusion that disruption of mitochondrial function, or iron, copper or glutathione metabolism in isolation provokes the pathological impairment of them all. This creates a vicious cycle that drives pathology leading to mitochondrial failure and neuronal cell death in vulnerable brain regions.

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.

Gene expression patterns in the progression of canine copper-associated chronic hepatitis

Copper is an essential trace element, but can become toxic when present in abundance. The severe effects of copper-metabolism imbalance are illustrated by the inherited disorders Wilson disease and Menkes disease. The Labrador retriever dog breed is a novel non-rodent model for copper-storage disorders carrying mutations in genes known to be involved in copper transport. Besides disease initiation and progression of copper accumulation, the molecular mechanisms and pathways involved in progression towards copper-associated chronic hepatitis still remain unclear. Using expression levels of targeted candidate genes as well as transcriptome micro-arrays in liver tissue of Labrador retrievers in different stages of copper-associated hepatitis, pathways involved in progression of the disease were studied. At the initial phase of increased hepatic copper levels, transcriptomic alterations in livers mainly revealed enrichment for cell adhesion, developmental, inflammatory, and cytoskeleton pathways. Upregulation of targeted MT1A and COMMD1 mRNA shows the liver's first response to rising intrahepatic copper concentrations. In livers with copper-associated hepatitis mainly an activation of inflammatory pathways is detected. Once the hepatitis is in the chronic stage, transcriptional differences are found in cell adhesion adaptations and cytoskeleton remodelling. In view of the high similarities in copper-associated hepatopathies between men and dog extrapolation of these dog data into human biomedicine seems feasible.

Structure and Synaptic Function of Metal Binding to the Amyloid Precursor Protein and its Proteolytic Fragments

Alzheimer’s disease (AD) is ultimately linked to the amyloid precursor protein (APP). However, current research reveals an important synaptic function of APP and APP-like proteins (APLP1 and 2). In this context various neurotrophic and neuroprotective functions have been reported for the APP proteolytic fragments sAPPα, sAPPβ and the monomeric amyloid-beta peptide (Aβ). APP is a metalloprotein and binds copper and zinc ions. Synaptic activity correlates with a release of these ions into the synaptic cleft and dysregulation of their homeostasis is linked to different neurodegenerative diseases. Metal binding to APP or its fragments affects its structure and its proteolytic cleavage and therefore its physiological function at the synapse. Here, we summarize the current data supporting this hypothesis and provide a model of how these different mechanisms might be intertwined with each other.

Zinc and Copper Differentially Modulate Amyloid Precursor Protein Processing by γ-Secretase and Amyloid-β Peptide Production

Recent evidence suggests involvement of biometal homeostasis in the pathological mechanisms in Alzheimer's disease (AD). For example, increased intracellular copper or zinc has been linked to a reduction in secreted levels of the AD-causing amyloid-β peptide (Aβ). However, little is known about whether these biometals modulate the generation of Aβ. In the present study we demonstrate in both cell-free and cell-based assays that zinc and copper regulate Aβ production by distinct molecular mechanisms affecting the processing by γ-secretase of its Aβ precursor protein substrate APP-C99. We found that Zn²⁺ induces APP-C99 dimerization, which prevents its cleavage by γ-secretase and Aβ production, with an IC₅₀ value of 15 μm Importantly, at this concentration, Zn²⁺ also drastically raised the production of the aggregation-prone Aβ43 found in the senile plaques of AD brains and elevated the Aβ43:Aβ40 ratio, a promising biomarker for neurotoxicity and AD. We further demonstrate that the APP-C99 histidine residues His-6, His-13, and His-14 control the Zn²⁺-dependent APP-C99 dimerization and inhibition of Aβ production, whereas the increased Aβ43:Aβ40 ratio is substrate dimerization-independent and involves the known Zn²⁺ binding lysine Lys-28 residue that orientates the APP-C99 transmembrane domain within the lipid bilayer. Unlike zinc, copper inhibited Aβ production by directly targeting the subunits presenilin and nicastrin in the γ-secretase complex. Altogether, our data demonstrate that zinc and copper differentially modulate Aβ production. They further suggest that dimerization of APP-C99 or the specific targeting of individual residues regulating the production of the long, toxic Aβ species, may offer two therapeutic strategies for preventing AD.

Copper comes of age in Melbourne

When we were asked to produce articles for this volume, it seemed appropriate to us to co-author an article on the history and impact of copper research in Melbourne. It is appropriate because over many years, decades in fact, we worked closely together and with Professor David Danks to identify the molecular defect in Menkes disease. This work was always carried out with the intention of understanding the nature of the copper homeostatic mechanisms and a "copper pathway" in the cell, that David had the prescience to predict must exist despite scepticism from granting agencies! He indeed inspired us to pursue research careers in this field. This article outlines some of this history.

Metallo-pathways to Alzheimer's disease: lessons from genetic disorders of copper trafficking

Copper is an essential metal ion that provides catalytic function to numerous enzymes and also regulates neurotransmission and intracellular signaling. Conversely, a deficiency or excess of copper can cause chronic disease in humans. Menkes and Wilson disease are two rare heritable disorders of copper transport that are characterized by copper deficiency and copper overload, respectively. Changes to copper status are also a common feature of several neurodegenerative disorders including Alzheimer's disease (AD), Parkinson's disease (PD) and Amyotrophic lateral sclerosis (ALS). In the case of AD, which is characterized by brain copper depletion, changes in the distribution of copper has been linked with various aspects of the disease process; protein aggregation, defective protein degradation, oxidative stress, inflammation and mitochondrial dysfunction. Although AD is a multifactorial disease that is likely caused by a breakdown in multiple cellular pathways, copper and other metal ions such as iron and zinc play a central role in many of these cellular processes. Pioneering work by researchers who have studied relatively rare copper transport diseases has shed light on potential metal ion related disease mechanisms in other forms of neurodegeneration such as 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.