Targeting Metals in Alzheimer’s Disease: An Update

Abstract

One pathological feature of Alzheimer’s disease (AD) is the dysregulated metal ions, e.g., zinc, copper, and iron in the affected brain regions. The dysregulation of metal homeostasis may cause neurotoxicity and directly addressing these dysregulated metals through metal chelation or mitigating the downstream neurotoxicity stands as a pivotal strategy for AD therapy. This review aims to provide an up-to-date comprehensive overview of the application of metal chelators and drugs targeting metal-related neurotoxicity, such as antioxidants (ferroptotic inhibitors), in the context of AD treatment. It encompasses an exploration of their pharmacological effects, clinical research progress, and potential underlying mechanisms.

Keywords

Alzheimer’s disease copper ferroptosis iron metal chelators zinc

INTRODUCTION

Alzheimer’s disease (AD) is a progressive neurodegenerative disease characterized by cognitive and memory impairments, accompanied by the accumulation of amyloid-β (Aβ) plaques and tau-containing neurofibrillary tangles [1, 2]. There have been five U.S. Food and Drug Administration (FDA)-approved drugs for AD before 2021, four of which (tacrine, donepezil, rivastigmine, and galantamine) are acetylcholinesterase inhibitors, while one (memantine) is an N-methyl-D-aspartate (NMDA) receptor antagonist. These approved drugs offer only symptomatic relief for mild AD forms. Substantial advancements have been made recently in drug development targeting Aβ, primarily Lecanemab [3], Aducanemab [4], Donanemab [5], and Solanezumab [6]. Several therapies were approved by the FDA with criticisms on possible side effects and uncertain efficacy. Furthermore, promising progress has been made in biomarker discovery of AD, such as plasma Aβ and p-tau231 [7 –11], coupled with emerging insights into the physiological functions of the tau protein [12 –15]. However, tangible clinical benefits for AD treatment in real-world scenarios remain limited [16 –18]. The multifaceted nature of AD highlights the necessity for a broader research perspective that goes beyond simplistic hypotheses that there is only one essential target for the disease.

The leading hypothesis in the field is the Aβ cascade hypothesis [19], where drugs following the hypothesis (such as Lecanemab) have been approved for clinical use. While Aβ is considered centric to cause degeneration, its aggregation and toxicity involve other factors such as the metal ions [20, 21]. In recent years, the essence of the metal dysregulation hypothesis has been involved. In the early 1990 s, accumulated zinc was discovered in the amyloid plaques and it can promote Aβ aggregation in vitro [22, 23]. It was hypothesized at the time that abnormal metal deposition, as observed in the AD brains, facilitated the aggregation of amyloid and thus can be targeted. Later both copper and iron were found to promote the aggregation of Aβ and tau [21], and induce oxidative stress and inflammation, leading to neuronal damage and contributing to the progression of the disease [21]. More recently, several key proteins of AD have been identified to participate in brain metal regulation, including amyloid-β protein precursor (AβPP), tau, presenilin, and ApoE [21]. The current consensus is that disease-related changes in key proteins dysregulated metal homeostasis in the brain; In turn, the abnormally accumulated metals interact with the amyloid or tau proteins, leading to neuronal toxicity. Therefore, targeting metals likely offers a feasible approach for AD-modifying therapies.

Disruptions in metal levels, deficient or excessive, have severe consequences in vivo. This includes being highly neurotoxic to healthy neuronal cells and tissues, significantly disrupting the physiological activities of neurons, and potentially leading to cell death [21]. Ferroptosis is a non-apoptotic mechanism of cell death that involves iron and lipid peroxidation, and it has been reported in various neurological disease processes [24 –28]. Recent studies have also implicated that ferroptosis may be responsible for toxicities associated with metal dysregulation in AD [29]. In general, ferroptosis occurs as a result of lipid oxidation imbalance, and several defense mechanisms through proteins such as glutathione peroxidase 4 (GPX4) and Ferroptosis suppressor protein 1 (FSP1) can regulate cell sensitivity to ferroptosis. Elevated levels of lipid peroxidation and reduced expression of glutathione (GSH) and glutathione peroxidase were observed in the AD brains [30 –32], and several genes such as presenilin and ApoE involved in AD also regulate ferroptosis, which were shown to be associated with AD [33, 34]. Therefore, targeting ferroptosis may also be able to prevent neuronal death during AD progression.

Here, we provide a comprehensive up-to-date review of clinically relevant metal chelators and antioxidants (ferroptosis inhibitors) targeting AD, summarizing the evidence supporting their use, their effects on animal models of AD, and the clinical advancements. By reviewing these data together with the refreshed view of the metal dysregulation hypothesis, we may find alternative ways to treat AD by preventing neuronal death.

METALS IN ALZHEIMER’S DISEASE

Zinc

Zinc plays a pivotal role in brain function, participating in the stabilization of protein structures and catalytic reactions within biological systems [35]. It predominantly accumulates in the glutamatergic vesicles, resulting in a high concentration of Zn²⁺ in the synaptic cleft during neurotransmission [36], an environment promoting Aβ aggregation, which was found to be associated with declining cognitive function and amyloid pathology in AD [21]. Zinc promotes the aggregation and deposition of Aβ [23]. When zinc binds to Aβ, it triggers a rapid aggregation, enhancing the stability of Aβ aggregates by promoting its resistance to proteolysis [37]. Accumulation of zinc within AD plaques has been observed in both human cases and animal models [38 –41]. Such accumulation may also affect tau phosphorylation, as it was reported that zinc regulates the activities of several kinases and phosphatases that are involved in tau post-translational modifications [42]. Evidence also suggests that zinc metabolism, regulated by ZnT3, affects cognitive function directly, which is consistent with the findings in AD brains [43].

Copper

Copper is a redox-active metal crucial for various metabolic processes in the brain. Mutations of the copper exporter, the ATPase copper transporters Alpha/Beta (ATP7A/B), lead to the loss of its function and increase the risk of AD [44, 45]. Copper also dose-dependently impacts LTP in the brain, with low copper concentrations inhibiting hippocampal LTP and high copper concentrations promoting it [46, 47], which may contribute to the synaptic dysfunction observed in AD. Reports indicate that copper concentrations in brain tissue from AD patients are lower than in healthy control tissue [48, 49], but significantly higher around the plaques [21]. Chronic copper exposure accelerates amyloid pathology in AD mouse models [50]. Conversely, reducing cellular copper levels has been shown to increase the production of Aβ [51, 52]. These findings suggest that intracellular copper deficiency may contribute to Aβ production, while extracellular Cu²⁺ accumulation facilitates Aβ precipitation. Therapeutically, a single agent that could both extract metals from extracellular amyloid and promote beneficial cellular re-uptake of the metals may be useful [53 –55]. Moreover, copper can also bind to tau protein in vitro, promoting its aggregation and regulating the phosphorylation [50, 56].

Iron

Iron is the most abundant transitional metal in the brain, playing a crucial role in various cerebral functions such as neurotransmitter synthesis, myelin formation, and mitochondrial metabolism [57]. The levels of iron in the brain are therefore tightly regulated, and both iron deficiency and overload lead to cerebral dysfunction [21]. Age-dependent iron accumulation in the brain may contribute to various neurodegenerative diseases, including AD [58]. Postmortem examinations of brains affected by AD have revealed significant iron accumulation in the frontal cortex and hippocampal regions, which are particularly affected by AD pathology [59 –61]. In vitro, Fe³⁺ binds to Aβ and promotes its neurotoxicity [62]. In the presence of Fe³⁺, Aβ fibrillation is slowed, leading to the formation of curved aggregates, particularly at higher Fe³⁺ concentrations. This indicates that Fe³⁺ may affect Aβ toxicity by altering the structure of Aβ aggregates [63]. In the human brain, a reduction in soluble tau protein, mutations in AβPP, or cleavage of AβPP by BACE1 influences neuronal iron efflux, leading to iron accumulation within the cells [14, 64]. The accumulation of iron was also shown to inhibit the activity of α-secretase and enhance the activity of β-secretase and γ-secretase, thereby affecting the AβPP cleavage process and promoting the generation of Aβ [65 –67].

TARGETING METALS FOR ALZHEIMER’S DISEASE TREATMENT

Several strategies have been developed to target the dysregulated metals in AD and hundreds of them have been tested in animal models of AD [66]. By far, the most advanced strategies are metal chelation therapy directly targeting the dysregulated metals, and anti-ferroptosis (antioxidant) therapy which targets the neuronal toxicities caused by metal dysregulation. Both of the strategies have been tested clinically, which will be introduced and discussed here.

Chelation therapy for Alzheimer’s disease

Clioquinol

Clioquinol (CQ), also known as chloroquine, is an 8-hydroxyquinoline derivative with the ability to chelate copper and zinc. Oral treatment of AD transgenic mice (including Tg2576 transgenic mice, APP/ PS1 transgenic mice, and the TgCRND8 mice) with CQ led to a significant reduction in brain Aβ deposition, rescued memory impairment, and resulted in a slight increase in soluble Aβ levels while maintaining stable health and body weight [68]. It significantly reduced both the quantity and size of zinc-containing plaques as designed and lowered the expression levels of key proteins involved in amyloidogenic AβPP processing, including AβPP, BACE1, and PS1. Moreover, CQ effectively modulated the copper efflux activities associated with AβPP [69], inhibited the formation of Aβ oligomers [70, 71], and mitigated Aβ-induced cellular loss [72]. It was later found that CQ can also chelate iron at a moderate capacity, and can be effective in models of neurodegeneration [73].

In a double-blind, randomized phase II clinical trial, the oral administration of CQ (125 mg twice daily from weeks 0 to 12, 250 mg twice daily from weeks 13 to 24, and 375 mg twice daily from weeks 25 to 36) demonstrated good tolerability. The CQ-treated group exhibited reduced plasma Aβ_1 - 42 levels compared to the placebo group. Notably, The placebo group experienced a significant decline in scores on the Alzheimer’s Disease Assessment Scale (ADAS-cog), whereas the CQ group showed less deterioration [74]. However, five subjects experienced serious adverse events, and subsequent Phase II/III investigations were terminated due to the contamination of di-iodo 8-hydroxyquinoline in CQ during large-scale chemical synthesis. Further research involving Tg2576 mice and human subjects revealed that the penetration of CQ into the brain is constrained, despite subsequent binding to amyloid plaques upon cerebral entry [75]. Recently, CQ has also been investigated in cancer due to its ability to modulate membrane copper transport [76].

PBT2

PBT2, a second-generation CQ analog, is also designed to target metal-induced aggregation of Aβ. Acting as a more effective Zn/Cu ionophore, it demonstrates superior blood-brain barrier (BBB) permeability compared to CQ [77]. The ionophore activity, crucial for extracting metals from extracellular plaques, plays a significant role in the metal-related mechanisms. By forming complexes with ions in the lipid bilayer, PBT2 enhances their solubility, thereby augmenting membrane permeability [77]. PBT2 was specifically designed to regulate abnormal levels of metal ions in the brain, including copper and zinc, aiming to inhibit the aggregation of Aβ and consequently reduce the pathological features associated with AD and other neurodegenerative disorders. In transgenic mouse models of AD, oral administration of PBT2 demonstrated a significant reduction in soluble brain Aβ within hours and improvement in cognitive abilities within days [77].

In a 12-week, double-blind, randomized placebo-controlled Phase II trial of PBT2, participants were randomly assigned to receive 50 mg PBT2, 250 mg PBT2, or a placebo. PBT2 has been tested for safety and efficacy, and plasma and CSF biomarkers and cognition in patients with AD were analyzed. The clinical trial showed that patients treated with PBT2 had a reduction in Aβ accumulation in the brain and a trend towards improvement in some aspects of cognitive function and quality of life [77]. More importantly, during the clinical trial for Huntington’s disease [78], PBT2 showed a specific positive impact on performance in the Trail Making Test Part B score, while no discernible improvement was observed in other cognitive tests. The efficacy of PBT2 requires additional evaluation. This also implies that metal chelation might offer more promising prospects for AD treatment.

The mechanisms of action of both CQ and PBT2 were investigated (Fig. 1). Both CQ and PBT2 can interact with the complex formed by Zn²⁺ or Cu²⁺ with Aβ, promoting the dissociation and degradation of aggregates. Additionally, they aid in the release of Zn²⁺ and Cu²⁺ from Aβ aggregates, neutralizing their surface charge, and thereby enabling their passive passage across cell membranes [77 , 80]. This promotes the recycling of Zn²⁺ and Cu²⁺ in the synaptic cleft, restoring functional fluxes. Furthermore, this process of metal redistribution occurs intracellularly, resulting in the upregulation of MMP-2 and MMP-3 activities, thereby enhancing the degradation of extracellular or membrane-associated Aβ by these metalloproteinases. [53, 54].

Fig. 1

Potential mechanisms of CQ/PBT2 in Alzheime’s disease. Zinc or copper binds to Aβ, forming protease-resistant Aβ oligomers and aggregates. CQ/PBT2 can interact with accessible Zn²⁺ and Cu²⁺, thereby promoting the dissolution, uptake, and degradation of these aggregates. Additionally, CQ/PBT2 facilitates the dissociation of Zn²⁺ and Cu²⁺ from being trapped by Aβ, allowing their passive movement across cell membranes. Furthermore, both CQ and PBT2 have the ability to redistribute metals intracellularly, leading to the upregulation of MMP-2 and MMP-3. Consequently, this enhances the degradation of extracellular or membrane-associated Aβ by these metalloproteinases. This figure was generated using BioRender.com.

Deferoxamine

Deferoxamine (DFO) was originally developed by the Swiss pharmaceutical company Novartis in the 1960 s and was found to effectively bind to free iron in the body, forming stable chelates [81]. It was approved by the FDA for the treatment of acute iron intoxication and chronic iron overload due to blood transfusions. Since it chelates iron, the potential therapeutic benefits of DFO in AD were explored in preclinical studies [21, 82]. DFO exhibits the ability to mitigate Aβ aggregation [83, 84], hyperphosphorylation of tau [85, 86], and ameliorate neuroinflammation [87, 88]. DFO treatment has been reported to lead to a reduction in cognitive deterioration and ameliorates pathological features in rodent models of AD, including APP/PS1 transgenic mice, P301 L tau transgenic mice, and intracerebroventricular streptozotocin (ICV-STZ) rat model. The ICV-STZ rat model exhibits insulin metabolic dysregulation, oxidative stress, and inflammation, and intranasal administration of DFO significantly ameliorates spatial memory and balance function in mice, reduces oxidative damage, and enhances insulin receptor expression [83 , 90]. Glycogen synthase kinase-3β (GSK-3β) is also hypothesized as a major link between the accumulation of Aβ and consequent hyperphosphorylation of tau in AD [91]. DFO was reported as an inhibitor of GSK-3β and can suppressed this process [87, 90].

In a 24-month, single-blind clinical study conducted in 1991, it was found that the administration of DFO (125 mg intramuscular injection, twice daily, five days a week, for 24 months) reduced the rate of decline in daily living skills among AD patients treated with DFO by half, compared to a group treated with an oral placebo and a no-treatment group. This suggests that intramuscular injection of DFO slows the progression of AD [92]. Side effects observed in DFO-treated patients include weight loss and loss of appetite, along with an increased formation of MF01, a monoamine oxidase-catalyzed metabolite [92]. The mechanism involves DFO chelating intracellular Fe²⁺ and undergoing various chemical reactions, thereby inhibiting the processing of AβPP and Aβ aggregation, ultimately improving memory [83 , 93]. Further, the decline in neurovascular function is considered a part of AD pathogenesis [94]. In two clinical trials, systemic administration of DFO strongly improved cerebral vasoreactivity and autoregulation [95, 96].

Deferiprone

One limitation of DFO is its restricted ability to penetrate the BBB. Deferiprone (DFP), an orally bioavailable siderophore with moderate iron-binding affinity, has been in clinical use since the 1980 s [97]. DFP efficiently crosses the BBB, chelates intracellular iron, and demonstrates gentler iron removal compared to DFO, penetrating cellular membranes to form a chelator/iron complex that exits cells and redistributes iron to transferrin for recycling. In neuronal culture models of Aβ toxicity, DFP exhibits neuroprotective effects, protecting against hydrogen peroxide and Aβ_1 - 40-induced neuronal death [98]. It also attenuates amyloid burden and tau phosphorylation in a rabbit model of AD [99]. Moreover, DFP treatment of P301 L tau transgenic mice improves cognitive function and attenuates tau pathology [100].

An actively recruiting double-blind, multicenter, randomized placebo-controlled Phase II clinical trial (NCT03234686) is underway to investigate the safety and efficacy of delayed-release DFP oral tablets (600 mg) in slowing dementia progression in patients with prodromal AD and mild AD. The primary outcome is assessed through a neuropsychological test battery, with secondary outcomes including brain iron levels measured by MRI.

Targeting the consequences of metal dysregulation for treating Alzheimer’s disease

The outcome of cell death resulting from metal imbalance is predominantly identified as ferroptosis, with iron playing a significant role. While iron is a pivotal factor, it is noteworthy that copper [101] and zinc [102] have also been implicated in ferroptosis. In the classical ferroptotic pathway, distinctive features include the accumulation of iron-dependent lipid reactive oxygen species. Additionally, the decrease in GSH levels and the inactivation of GPX4 contribute to increased susceptibility to ferroptosis [103]. GPX4 is a unique antioxidant enzyme that inhibits lipid peroxidation by reducing membrane lipid hydroperoxides to lipid alcohols. GPX4 converts toxic phospholipid hydroperoxides (lipid-OOH) to harmless phospholipid alcohols (lipid-OH) using electrons from GSH, resulting in the production of oxidized GSSG [104]. Additionally, Fe²⁺ can bind to GSH, stabilizing its ferrous state and preventing it from contributing to reactive oxygen species generation. Cytoplasmic GSH levels play a pivotal role in initiating ferroptosis.

Multiple studies suggest that lipid peroxidation and depletion of glutathione levels are features of AD [31, 32]. The levels of glutathione in the hippocampus and frontal cortex also could serve as predictive biomarkers for AD and mild cognitive impairment (MCI) [105], implying that ferroptosis may play a role in AD. Several compounds targeting this pathway have entered clinical trials, including N-acetylcysteine (NAC), Vitamin E, and selenium compounds (Fig. 2).

Fig. 2

Targeting ferroptosis by iron chelators and antioxidants in Alzheimer’s disease. Fe²⁺ binding to Aβ promotes its aggregation by enhancing resistance to proteolysis. DFO may interact with accessible Fe³⁺, facilitating the dissolution, uptake, and degradation of Aβ aggregates. Selenocysteine stimulates GPX4 synthesis, forming its active site. Iron accumulation intensifies the reaction between cytoplasmic Fe²⁺ and H₂O₂, leading to hydroxyl radical generation. This radical reacts with membrane phospholipids containing PUFA, generating lipid peroxides and initiating lipid radical propagation. Subsequently, this process disrupts the plasma membrane, leading to ferroptosis. NAC, Vitamin E, and Selenium target distinct components of this pathway to prevent ferroptosis, potentially contributing to their assumed clinical benefits in AD. This figure was generated using BioRender.com.

N-acetylcysteine

NAC is a compound used for treating acetaminophen poisoning, and it can also enhance lipid antioxidant defense by elevating cysteine, a rate-limiting substrate of GSH, which is a necessary cofactor for GPX4 [106]. Studies have revealed that NAC elevated intracellular GSH levels, thereby mitigating oxidative stress and lipid peroxidation damages [107]. Furthermore, NAC has been shown to protect neurons from oxidative damage by reducing the toxic impact of oxidative stress [108, 109].

In an AD model, NAC protects neuronal function and ameliorates learning and memory deficits by elevating GSH levels, inhibiting lipid oxidation, and reducing MDA content, which may also be associated with its anti-amyloidogenic effects [107]. Additionally, NAC, acting as an antioxidant, exerts its effects by attenuating γ-secretase activity, reducing Aβ production, and restoring calcium/calmodulin kinase activity, thereby stabilizing synaptic pathways and mitigating memory impairment and hippocampal long-term potentiation decline in APP/PS1 mice [110].

A small double-blind, randomized placebo-controlled Phase II clinical trial of NAC (n = 23 NAC, n = 20 placebo, 50 mg/kg/day in 3 divided doses) over 6 months for the treatment of probable AD was conducted [111]. Active treatment with NAC did not significantly alter primary outcome measures (including the change in Mini-Mental State Examination scores and scores derived from a scale assessing basic and instrumental activities of daily living over 6 months) in this well-matched sample of clinically diagnosed AD patients. However, the study results provide optimism for NAC’s use and the broader strategy of reducing oxidative stress in AD, as evidenced by favorable effects on certain secondary outcome measures (e.g., performance on a cognitive battery designed specifically for the trial) and well-tolerated administration [111], but have not been followed up on a larger scale. Further in-depth studies are required to explore the potential efficacy of NAC in AD treatment.

Vitamin E

Vitamin E is typically defined as a family of molecules that includes four tocopherols and four tocotrienols. While Vitamin E is a potent antioxidant, its beneficial effects in AD remain unclear [112]. Numerous studies have investigated the role of Vitamin E in mitigating oxidative stress and reducing neuronal damage, both of which are key factors in the progression of AD [113]. Vitamin E’s ability to scavenge free radicals and protect cell membranes from lipid peroxidation has garnered significant interest in its potential therapeutic application for AD. Meta-analysis reveals that a substantial intake of Vitamin E significantly reduces the risk of dementia, and there exists a significant negative correlation between the intake level of Vitamin E and the risk of AD [114].

α-Tocopherol (α-TP) serves as the primary active constituent in Vitamin E. In a double-blind, randomized placebo-controlled Phase III clinical trial (2000 IU/day of α-TP, n = 152; placebo, n = 152.) conducted over a period ranging from 6 months to 4 years for the treatment of mild to moderate AD [115], individuals with mild to moderate AD receiving 2000 IU/day of α-TP demonstrated a slower functional decline compared to those in the group [115]. These findings imply the potential benefit of α-TP in reducing caregiver burden in individuals with mild to moderate AD. In another double-blind, randomized placebo-controlled clinical trial (2000 IU/day of Vitamin E, 10 mg/day of donepezil, or placebo for three years) focusing on subjects with amnestic MCI, neither the Vitamin E group nor the donepezil group exhibited a significant difference in the likelihood of AD progression compared to the placebo group throughout the three-year treatment period [116]. The conflicting results observed in clinical trials assessing Vitamin E supplementation in AD patients may stem from variations in study design, dosages, and patient cohorts.

Studies have revealed that Vitamin E analog could inhibit the formation of Aβ fibers and oligomers, leading to reduced Aβ deposition in APP/PS1 transgenic mice and improved cognitive function in the mice [117]. Vitamin D3 and E administration improved memory and learning deficits, and decreased neuronal loss and oxidative stress in an AD model [118]. Continued studies are required to elucidate its precise mechanisms of action, optimal dosages, and potential synergies with other treatment strategies for AD.

Selenium compounds

Selenium is an essential element playing a crucial role in numerous biological processes, particularly in the context of neurodegenerative diseases, since it is involved in ferroptosis [119]. Selenium is involved in the expression and synthesis of 25 selenoproteins, including GPX4, either in the form of Selenium-containing inorganic salts used as nutritional supplements [120]. On the other hand, Selenium influences both non-enzymatic and enzymatic antioxidant defense mechanisms, contributing to the establishment of robust antioxidant defenses [121].

Selenium has long been implicated in AD pathogenesis and has shown positive effects in models of AD by reducing Aβ production [122] and tau hyperphosphorylation [123, 124]. A Selenium-deficient diet is associated with an increase in the formation of Aβ plaques in the brains of Tg2576 transgenic mice [125]. Sodium selenite has been effective in reducing tau phosphorylation through PP2A activation, improving cognitive deficits in tau transgenic mice models [123, 124]. Treatment with selenomethionine in triple transgenic AD mice expressing human APPswe, PS1M146 V, and tauP301 L mutant forms results in decreased overall tau phosphorylation, reduced inflammatory biomarkers, reverses synaptic deficit, and improved cognition [126]. These findings may underscore the novel role of Selenium in AD pathophysiology and its potential as a target for intervention.

Consistently, clinical studies have indicated a negative correlation between declining cognitive abilities and Selenium levels [127]. Elderly individuals with AD display diminished Selenium content in erythrocytes compared to controls [127, 128]. While plasma Selenium levels remain similar between healthy and MCI subjects, AD patients exhibit lower serum Selenium levels compared to healthy individuals [129]. Notably, mild AD patients exhibit lower plasma Selenium levels than age-matched healthy controls [130]. A meta-analysis indicated a decrease in brain tissue Selenium levels in the temporal, hippocampal, and cortex regions in AD [131]. These data suggest that a lack of Selenium might increase the risk of AD.

Accordingly, dietary supplementation of Brazil nuts, which are the best food source of Selenium, has resulted in improvements in cognitive performance in a clinical trial targeting Selenium-deficient patients with MCI [132]. Specifically, improvements were observed in semantic verbal fluency and constructional praxis. However, a double-blind, randomized controlled trial of Selenium supplementation with selenomethionine (200μg/day) did not reduce the incidence of dementia in a cohort of healthy men over 60 who were not Selenium-deficient [133]. In another 24-week, double-blind, randomized placebo-controlled Phase IIa clinical trial of sodium selenate (VEL015 10 mg thrice daily, n = 20, control VEL015 320μg g thrice daily, n = 10 or placebo n = 10) for mild-moderate AD [134], although selenate was found to reduce deterioration in brain structures as measured by diffusion tensor MRI, it did not have an overall impact on cognition within the 24-week period. However, in patients treated with a daily dose of 30 mg selenate, variability in elevated Selenium levels in cerebrospinal fluid was observed, and a relationship between increased cerebrospinal fluid Selenium and improved cognitive performance was found [134, 135]. The diverse outcomes of clinical trials may be explained by differences in the dosages, forms, and study populations. In particular, the type of Selenium supplementation should be considered, as it has been reported that inorganic and organic selenocompounds demonstrate different potencies against ferroptosis [119].

LESSONS FROM CLINICAL STUDIES AND FUTURE DIRECTION

In this review, we delve into metal chelators, including CQ, PBT2, DFO, and DFP, as well as antioxidants such as NAC, Vitamin E, and Selenium, to discuss potential therapeutic strategies for AD from a metal dysregulation perspective (Table 1). Clinical trials have indicated the potential benefits of copper-zinc ionophores for AD, and there is increasing interest in targeting ferroptosis to treat AD in addition to general antioxidants.

Table 1

Agents in clinical trials of Alzheimer’s disease metal chelators and antioxidants

Agent	CQ [74]	PBT2 [78]	DFO [92]	NAC [111]	Vitamin E [115]	Selenium compounds [134]
Dose	125 mg twice daily from weeks 0 to 12, 250 mg twice daily from weeks 13 to 24, and 375 mg twice daily from weeks 25 to 36	50 mg or 250 mg/day	125 mg intramuscular injection, twice daily, five days a week	50 mg/kg/day in 3 divided doses	2000 IU/day of α-TP	VEL015 10 mg thrice daily, and control VEL015 320μgg thrice daily
Role	Copper and Zinc chelating agent	Copper and Zinc chelating agent	Iron chelating agent	Antioxidants or ferroptosis inhibitors	Antioxidants or ferroptosis inhibitors	Antioxidants or ferroptosis inhibitors
Duration	36 weeks	12 weeks	24 months	6 months	36 months	24 weeks
Cohort	Probable AD (n = 36)	Early AD (n = 78)	Probable AD (n = 48)	Probable AD (n = 43)	Possible or probable AD (n = 212)	Mild-moderate AD (n = 40)
Outcome	The CQ group showed the least deterioration in ADAS-cog score compared to the placebo group.	A reduction in the accumulation of Aβ protein in the brain and a trend towards improvement in some aspects of cognitive function and quality of life	Deterioration of placebo group was double that of the DFO group	No significant impact on primary outcome measures, had a favorable effect on secondary measures	A slower functional decline in mild to moderate AD patients	A negative correlation between selenium levels and cognitive decline, but no significant impact on cognitive progression

Iron is tightly regulated in the brain, where both iron deficiency and iron overload may lead to brain dysfunction. Currently, there are three FDA-approved iron chelators, namely DFO (1968), Deferasirox (2005), and DFP (2011) for various diseases. They are more commonly applied in cases of transfusion-dependent iron overload, where potential disparities between the central nervous system and peripheral regions should be considered when applying them to AD patients [136]. Among the three drugs, DFO and DFP have been investigated in AD, while Deferasirox is primarily investigated within the context of anemia queues [136]. Due to the short plasma half-life of DFO, prolonged intravenous infusion or intramuscular injection is necessary. However, the presence of the BBB poses a challenge in achieving therapeutically meaningful drug concentrations in the brain. Furthermore, even if such concentrations can be achieved, the administration of high doses can result in significant side effects of DFO, such as gastrointestinal reactions, hepatorenal toxicity, and granulocytopenia [137].

Therefore, the potential side effects of iron chelation may not be overlooked. Recently, in a 36-week, double-blind, randomized placebo-controlled Phase II trial [138], DFP successfully reduced the brain iron levels but did not prevent the progression of Parkinson’s disease in participants who had not previously used levodopa. Conversely, during the 36-week duration, iron chelation therapy was linked to a worsening of both motor and non-motor symptoms, which contrasts with prior research findings [139, 140]. It was speculated that iron may play a crucial role as a necessary co-factor in the synthesis of dopamine by tyrosine hydroxylase, and the absence of concurrent levodopa treatment may influence the progression of the condition. Similar outcomes may be expected for the ongoing AD study. A more specific chelator with a mild ability of iron binding may be necessary for future studies.

The pathological mechanisms of AD are highly intricate, involving disruptions in metal ion homeostasis, oxidative stress, aggregation of Aβ and tau proteins, and various other factors. The inconsistencies in clinical trial outcomes also underscore the complexities of AD treatment research. Given this, there is a strategy for drug development that focuses on multitarget-directed ligands, which can simultaneously target several key pathways associated with AD. For example, the development of rivastigmine-indole hybrids and multitarget-directed ligands with chelating functions, which have demonstrated the ability to inhibit Aβ aggregation and scavenge free radicals, presents a promising approach for the treatment of AD [138]. On the other hand, ferroptosis, induced by iron-dependent lipid peroxidation, becomes a worthwhile target for AD. As a proof-of-concept, antioxidants that inhibit ferroptosis have demonstrated efficacy in clinical AD treatment, such as NAC, Vitamin E, and Selenium. To differentiate from the antioxidant hypothesis of AD, more specific BBB-permeable ferroptosis inhibitors may be worth testing in the future.

In conclusion, the metal dysregulation hypothesis for AD, in its almost thirtieth year of research, is still a tractable target worth investigating, although the essence of the work may be shifted to target the mechanisms of cell death induced by metal dysregulation. Future progress will be dependent on the discovery of new chemicals and new key molecules within the pathway and multitarget-directed ligands may be worth exploring.

AUTHOR CONTRIBUTIONS

Bin Du (Investigation; Writing – original draft; Writing – review & editing); Kang Chen (Investigation; Writing – original draft); Weiwei Wang (Investigation); Peng Lei (Funding acquisition; Investigation; Project administration; Writing – original draft; Writing – review & editing).

Footnotes

ACKNOWLEDGMENTS

The authors have no acknowledgments to report.

FUNDING

This work was supported by Sichuan Science and Technology Program (2024YFHZ0010), the West China Hospital 1.3.5 project for disciplines of excellence (ZYYC23016), and the Major Science & Technology Program of Sichuan Province (2022ZDZX0021).

CONFLICT OF INTEREST

P.L. is an Editorial Board Member of this journal but was not involved in the peer-review process of this article nor had access to any information regarding its peer-review. All other authors declare no conflict of interest.

DATA AVAILABILITY

Data sharing is not applicable to this article as no datasets were generated or analyzed during this study.

References

Karran

, Mercken

, De Strooper

(2011) The amyloid cascade hypothesis for Alzheimer’s disease: An appraisal for the development of therapeutics. Nat Rev Drug Discov10, 698–712.

Mandelkow

, Mandelkow

(1993) Tau as a marker for Alzheimer’s disease. Trends Biochem Sci18, 480–483.

van Dyck

, Swanson

, Aisen

, Bateman

, Chen

, Gee

, Kanekiyo

, Li

, Reyderman

, Cohen

, Froelich

, Katayama

, Sabbagh

, Vellas

, Watson

, Dhadda

, Irizarry

, Kramer

, Iwatsubo

(2023) Lecanemab in early Alzheimer’s disease. N Engl J Med388, 9–21.

Sevigny

, Chiao

, Bussière

, Weinreb

, Williams

, Maier

, Dunstan

, Salloway

, Chen

, Ling

, O’Gorman

, Qian

, Arastu

, Li

, Chollate

, Brennan

, Quintero-Monzon

, Scannevin

, Arnold

, Engber

, Rhodes

, Ferrero

, Hang

, Mikulskis

, Grimm

, Hock

, Nitsch

, Sandrock

(2016) The antibody aducanumab reduces Aβ plaques in Alzheimer’s disease. Nature537, 50–56.

Sims

, Zimmer

, Evans

, Lu

, Ardayfio

, Sparks

, Wessels

, Shcherbinin

, Wang

, Monkul Nery

, Collins

, Solomon

, Salloway

, Apostolova

, Hansson

, Ritchie

, Brooks

, Mintun

, Skovronsky

(2023) Donanemab in early symptomatic Alzheimer disease: The TRAILBLAZER-ALZ 2 randomized clinical trial. JAMA330, 512–527.

Sperling

, Donohue

, Raman

, Rafii

, Johnson

, Masters

, van Dyck

, Iwatsubo

, Marshall

, Yaari

, Mancini

, Holdridge

, Case

, Sims

, Aisen

(2023) Trial of solanezumab in preclinical Alzheimer’s disease. N Engl J Med389, 1096–1107.

Ding

, Zhang

, Jiang

, Wang

, Li

, Lei

(2021) Ultrasensitive assays for detection of plasma tau and phosphorylated tau 181 in Alzheimer’s disease: A systematic review and meta-analysis. Transl Neurodegener10, 10.

Ding

, Tuo

, Lei

(2021) An introduction to ultrasensitive assays for plasma tau detection. J Alzheimers Dis80, 1353–1362.

Jiang

, Ding

, Wang

, Yang

, Li

, Lei

(2022) Head-to-head comparison of different blood collecting tubes for quantification of Alzheimer’s disease biomarkers in plasma. Biomolecules12, 1194.

10.

Meng

, Lei

(2020) Plasma pTau181 as a biomarker for Alzheimer’s disease. MedComm (2020)1, 74–76.

11.

Kwapong

, Tang

, Liu

, Zhang

, Cao

, Feng

, Yang

, Shu

, Xu

, Lu

, Zhao

, Chong

, Wu

, Liu

, Lei

, Zhang

(2024) Choriocapillaris reduction accurately discriminates against early-onset Alzheimer’s disease. Alzheimers Dement20, 4185–4198.

12.

Mangiafico

, Tuo

, Li

, Liu

, Haralambous

, Ding

, Ayton

, Wang

, Laybutt

, Chan

, Zhang

, Kos

, Thomas

, Loudovaris

, Yang

, Joannides

, Lamont

, Dai

, He

, Dong

, Andrikopoulos

, Bush

, Lei

(2023) Tau suppresses microtubule-regulated pancreatic insulin secretion. Mol Psychiatry28, 3982–3993.

13.

Tuo

, Lei

, Jackman

, Li

, Xiong

, Li

, Liuyang

, Roisman

, Zhang

, Ayton

, Wang

, Crouch

, Ganio

, Wang

, Pei

, Adlard

, Lu

, Cappai

, Wang

, Liu

, Bush

(2017) Tau-mediated iron export prevents ferroptotic damage after ischemic stroke. Mol Psychiatry22, 1520–1530.

14.

Lei

, Ayton

, Finkelstein

, Spoerri

, Ciccotosto

, Wright

, Wong

, Adlard

, Cherny

, Lam

, Roberts

, Volitakis

, Egan

, McLean

, Cappai

, Duce

, Bush

(2012) Tau deficiency induces parkinsonism with dementia by impairing APP-mediated iron export. Nat Med18, 291–295.

15.

Lei

, Ayton

(2023) TRIMming the tangles. Sci Bull (Beijing)68, 2507–2509.

16.

Zhang

, Zhu

, Tang

, Lu

(2023) Targeting autophagy in Alzheimer’s disease: Animal models and mechanisms. Zool Res44, 1132–1145.

17.

Kim

, Syty

, Wu

, Ge

(2022) Adult hippocampal neurogenesis and its impairment in Alzheimer’s disease. Zool Res43, 481–496.

18.

Chen

, Zhang

(2022) Animal models of Alzheimer’s disease: Applications, evaluation, and perspectives. Zool Res43, 1026–1040.

19.

Beyreuther

, Masters

(1991) Amyloid precursor protein (APP) and beta A4 amyloid in the etiology of Alzheimer’s disease: Precursor-product relationships in the derangement of neuronal function. Brain Pathol1, 241–251.

20.

Selkoe

, Hardy

(2016) The amyloid hypothesis of Alzheimer’s disease at 25 years. EMBO Mol Med8, 595–608.

21.

Lei

, Ayton

, Bush

(2021) The essential elements of Alzheimer’s disease. J Biol Chem296, 100105.

22.

Bush

, Multhaup

, Moir

, Williamson

, Small

, Rumble

, Pollwein

, Beyreuther

, Masters

(1993) A novel zinc(II) binding site modulates the function of the beta A4 amyloid protein precursor of Alzheimer’s disease. J Biol Chem268, 16109–16112.

23.

Bush

, Pettingell

, Multhaup

, d Paradis

, Vonsattel

, Gusella

, Beyreuther

, Masters

, Tanzi

(1994) Rapid induction of Alzheimer A beta amyloid formation by zinc. Science265, 1464–1467.

24.

Tuo

, Liu

, Xiang

, Yan

, Zou

, Shu

, Ding

, Zou

, Xu

, Tang

, Gong

, Li

, Guo

, Zheng

, Deng

, Yang

, Li

, Zhang

, Ayton

, Bush

, Xu

, Dai

, Dong

, Lei

(2022) Thrombin induces ACSL4-dependent ferroptosis during cerebral ischemia/reperfusion. Signal Transduct Target Ther7, 59.

25.

Luoqian

, Yang

, Ding

, Tuo

, Xiang

, Zheng

, Guo

, Li

, Guan

, Ayton

, Dong

, Zhang

, Hu

, Lei

(2022) Ferroptosis promotes T-cell activation-induced neurodegeneration in multiple sclerosis. Cell Mol Immunol19, 913–924.

26.

Yan

, Tuo

, Yin

, Lei

(2020) The pathological role of ferroptosis in ischemia/reperfusion-related injury. Zool Res41, 220–230.

27.

Yan

, Tuo

, Lei

(2024) Cell density impacts the susceptibility to ferroptosis by modulating IRP1-mediated iron homeostasis.. J Neurochem168, 1359–1373.

28.

, Tuo

, Meng

, Wu

, Li

, Lei

(2024) Thrombin induces ferroptosis in triple-negative breast cancer through the cPLA2α/ACSL4 signaling pathway. Transl Oncol39, 101817.

29.

Yan

, Zou

, Tuo

, Xu

, Li

, Belaidi

, Lei

(2021) Ferroptosis: Mechanisms and links with diseases. Signal Transduct Target Ther6, 49.

30.

Ashraf

, Jeandriens

, Parkes

, So

(2020) Iron dyshomeostasis, lipid peroxidation and perturbed expression of cystine/glutamate antiporter in Alzheimer’s disease: Evidence of ferroptosis. Redox Biol32, 101494.

31.

Mandal

, Saharan

, Tripathi

, Murari

(2015) Brain glutathione levels–a novel biomarker for mild cognitive impairment and Alzheimer’s disease. Biol Psychiatry78, 702–710.

32.

Ansari

, Scheff

(2010) Oxidative stress in the progression of Alzheimer disease in the frontal cortex. J Neuropathol Exp Neurol69, 155–167.

33.

Greenough

, Lane

DJR

, Balez

, Anastacio

HTD

, Zeng

, Ganio

, McDevitt

, Acevedo

, Belaidi

, Koistinaho

, Ooi

, Ayton

, Bush

(2022) Selective ferroptosis vulnerability due to familial Alzheimer’s disease presenilin mutations. Cell Death Differ29, 2123–2136.

34.

Belaidi

, Masaldan

, Southon

, Kalinowski

, Acevedo

, Appukuttan

, Portbury

, Lei

, Agarwal

, Leurgans

, Schneider

, Conrad

, Bush

, Ayton

(2022) Apolipoprotein E potently inhibits ferroptosis by blocking ferritinophagy. Mol Psychiatry29, 211–220.

35.

Stiles

, Ferrao

, Mehta

(2024) Role of zinc in health and disease. Clin Exp Med24, 38.

36.

Vogt

, Mellor

, Tong

, Nicoll

(2000) The actions of synaptically released zinc at hippocampal mossy fiber synapses. Neuron26, 187–196.

37.

Huang

, Atwood

, Moir

, Hartshorn

, Vonsattel

, Tanzi

, Bush

(1997) Zinc-induced Alzheimer’s Abeta1-40 aggregation is mediated by conformational factors. J Biol Chem272, 26464–26470.

38.

Lovell

, Robertson

, Teesdale

, Campbell

, Markesbery

(1998) Copper, iron and zinc in Alzheimer’s disease senile plaques. J Neurol Sci158, 47–52.

39.

Religa

, Strozyk

, Cherny

, Volitakis

, Haroutunian

, Winblad

, Naslund

, Bush

(2006) Elevated cortical zinc in Alzheimer disease. Neurology67, 69–75.

40.

Stoltenberg

, Bush

, Bach

, Smidt

, Larsen

, Rungby

, Lund

, Doering

, Danscher

(2007) Amyloid plaques arise from zinc-enriched cortical layers in APP/PS1 transgenic mice and are paradoxically enlarged with dietary zinc deficiency. Neuroscience150, 357–369.

41.

Ichinohe

, Hayashi

, Wakabayashi

, Rockland

(2009) Distribution and progression of amyloid-beta deposits in the amygdala of the aged macaque monkey, and parallels with zinc distribution. Neuroscience159, 1374–1383.

42.

Gao

, Zhong

, Wang

, Zhang

, Zeng

, Hu

, Dang

, Chen

, Liang

(2022) Zinc enhances liquid-liquid phase separation of Tau protein and aggravates mitochondrial damages in cells. Int J Biol Macromol209, 703–715.

43.

Enache

, Pereira

, Jelic

, Winblad

, Nilsson

, Aarsland

, Bereczki

(2020) Increased cerebrospinal fluid concentration of ZnT3 is associated with cognitive impairment in Alzheimer’s disease. J Alzheimers Dis77, 1143–1155.

44.

Squitti

, Polimanti

, Bucossi

, Ventriglia

, Mariani

, Manfellotto

, Vernieri

, Cassetta

, Ursini

, Rossini

(2013) Linkage disequilibrium and haplotype analysis of the ATP7B gene in Alzheimer’s disease. Rejuvenation Res16, 3–10.

45.

Bucossi

, Polimanti

, Mariani

, Ventriglia

, Bonvicini

, Migliore

, Manfellotto

, Salustri

, Vernieri

, Rossini

, Squitti

(2012) Association of K832R and R952K SNPs of Wilson’s disease gene with Alzheimer’s disease. J Alzheimers Dis29, 913–919.

46.

Doreulee

, Yanovsky

, Haas

(1997) Suppression of long-term potentiation in hippocampal slices by copper. Hippocampus7, 666–669.

47.

Peters

, Munoz

, Sepulveda

, Urrutia

, Quiroz

, Luza

, De Ferrari

, Aguayo

, Opazo

(2011) Biphasic effects of copper on neurotransmission in rat hippocampal neurons. J Neurochem119, 78–88.

48.

Rembach

, Hare

, Lind

, Fowler

, Cherny

, McLean

, Bush

, Masters

, Roberts

(2013) Decreased copper in Alzheimer’s disease brain is predominantly in the soluble extractable fraction. Int J Alzheimers Dis2013, 623241.

49.

, Church

, Patassini

, Begley

, Waldvogel

, Curtis

, Faull

RLM

, Unwin

, Cooper

GJS

(2017) Evidence for widespread, severe brain copper deficiency in Alzheimer’s dementia. Metallomics9, 1106–1119.

50.

Kitazawa

, Cheng

, Laferla

(2009) Chronic copper exposure exacerbates both amyloid and tau pathology and selectively dysregulates cdk5 in a mouse model of AD. J Neurochem108, 1550–1560.

51.

Cater

, McInnes

, Li

, Volitakis

, La Fontaine

, Mercer

, Bush

(2008) Intracellular copper deficiency increases amyloid-beta secretion by diverse mechanisms. Biochem J412, 141–152.

52.

Borchardt

, Camakaris

, Cappai

, Masters

, Beyreuther

, Multhaup

(1999) Copper inhibits beta-amyloid production and stimulates the non-amyloidogenic pathway of amyloid-precursor-protein secretion. Biochem J344(Pt 2), 461–467.

53.

White

, Du

, Laughton

, Volitakis

, Sharples

, Xilinas

, Hoke

, Holsinger

, Evin

, Cherny

, Hill

, Barnham

, Li

, Bush

, Masters

(2006) Degradation of the Alzheimer disease amyloid beta-peptide by metal-dependent up-regulation of metalloprotease activity. J Biol Chem281, 17670–17680.

54.

Crouch

, Tew

, Du

, Nguyen

, Caragounis

, Filiz

, Blake

, Trounce

, Soon

, Laughton

, Perez

, Li

, Cherny

, Masters

, Barnham

, White

(2009) Restored degradation of the Alzheimer’s amyloid-beta peptide by targeting amyloid formation. J Neurochem108, 1198–1207.

55.

Crouch

, Hung

, Adlard

, Cortes

, Lal

, Filiz

, Perez

, Nurjono

, Caragounis

, Du

, Laughton

, Volitakis

, Bush

, Li

, Masters

, Cappai

, Cherny

, Donnelly

, White

, Barnham

(2009) Increasing Cu bioavailability inhibits Abeta oligomers and tau phosphorylation. Proc Natl Acad Sci U S A106, 381–386.

56.

Voss

, Harris

, Ralle

, Duffy

, Murchison

, Quinn

(2014) Modulation of tau phosphorylation by environmental copper. Transl Neurodegener3, 24.

57.

Hare

, Ayton

, Bush

, Lei

(2013) A delicate balance: Iron metabolism and diseases of the brain. Front Aging Neurosci5, 34.

58.

Xiong

, Tuo

, Guo

, Lei

(2019) Diagnostics and treatments of iron-related CNS diseases. Adv Exp Med Biol1173, 179–194.

59.

Hare

, Raven

, Roberts

, Bogeski

, Portbury

, McLean

, Masters

, Connor

, Bush

, Crouch

, Doble

(2016) Laser ablation-inductively coupled plasma-mass spectrometry imaging of white and gray matter iron distribution in Alzheimer’s disease frontal cortex. Neuroimage137, 124–131.

60.

van Duijn

, Bulk

, van Duinen

, Nabuurs

RJA

, van Buchem

, van der Weerd

, Natte

(2017) Cortical iron reflects severity of Alzheimer’s disease. J Alzheimers Dis60, 1533–1545.

61.

Cruz-Alonso

, Fernandez

, Navarro

, Junceda

, Astudillo

, Pereiro

(2019) Laser ablation ICP-MS for simultaneous quantitative imaging of iron and ferroportin in hippocampus of human brain tissues with Alzheimer’s disease. Talanta197, 413–421.

62.

Liu

, Moloney

, Meehan

, Morris

, Thomas

, Serpell

, Hider

, Marciniak

, Lomas

, Crowther

(2011) Iron promotes the toxicity of amyloid beta peptide by impeding its ordered aggregation. J Biol Chem286, 4248–4256.

63.

Chen

, Liao

, Yu

, Cheng

, Chen

(2011) Distinct effects of Zn2+, Cu2+, Fe3+, and Al3+on amyloid-beta stability, oligomerization, and aggregation: Amyloid-beta destabilization promotes annular protofibril formation. J Biol Chem286, 9646–9656.

64.

Ayton

, Lei

, Bush

(2013) Metallostasis in Alzheimer’s disease. Free Radic Biol Med62, 76–89.

65.

Banerjee

, Sahoo

, Anand

, Bir

, Chakrabarti

(2016) The oral iron chelator, deferasirox, reverses the age-dependent alterations in iron and amyloid-beta homeostasis in rat brain: Imlications in the therapy of Alzheimer’s disease. J Alzheimers Dis49, 681–693.

66.

Banerjee

, Sahoo

, Anand

, Ganguly

, Righi

, Bovicelli

, Saso

, Chakrabarti

(2014) Multiple mechanisms of iron-induced amyloid beta-peptide accumulation in SHSY5Y cells: Protective action of negletein. Neuromolecular Med16, 787–798.

67.

, Liu

, Zheng

, Yao

, Cheng

, Bu

, Xu

, Zhang

(2013) Ferritin light chain interacts with PEN-2 and affects gamma-secretase activity. Neurosci Lett548, 90–94.

68.

Cherny

, Atwood

, Xilinas

, Gray

, Jones

, McLean

, Barnham

, Volitakis

, Fraser

, Kim

, Huang

, Goldstein

, Moir

, Lim

, Beyreuther

, Zheng

, Tanzi

, Masters

, Bush

(2001) Treatment with a copper-zinc chelator markedly and rapidly inhibits beta-amyloid accumulation in Alzheimer’s disease transgenic mice. Neuron30, 665–676.

69.

Treiber

, Simons

, Strauss

, Hafner

, Cappai

, Bayer

, Multhaup

(2004) Clioquinol mediates copper uptake and counteracts copper efflux activities of the amyloid precursor protein of Alzheimer’s disease. J Biol Chem279, 51958–51964.

70.

LeVine

, 3rd , Ding

, Walker

, Voss

, Augelli-Szafran

(2009) Clioquinol and other hydroxyquinoline derivatives inhibit Abeta(1-42) oligomer assembly. Neurosci Lett465, 99–103.

71.

Mancino

, Hindo

, Kochi

, Lim

(2009) Effects of clioquinol on metal-triggered amyloid-beta aggregation revisited. Inorg Chem48, 9596–9598.

72.

Stoppelkamp

, Bell

, Palacios-Filardo

, Shewan

, Riedel

, Platt

(2011) In vitro modelling of Alzheimer’s disease: Degeneration and cell death induced by viral delivery of amyloid and tau. Exp Neurol229, 226–237.

73.

Lei

, Ayton

, Appukuttan

, Volitakis

, Adlard

, Finkelstein

, Bush

(2015) Clioquinol rescues Parkinsonism and dementia phenotypes of the tau knockout mouse. Neurobiol Dis81, 168–175.

74.

Ritchie

, Bush

, Mackinnon

, Macfarlane

, Mastwyk

, MacGregor

, Kiers

, Cherny

, Li

, Tammer

, Carrington

, Mavros

, Volitakis

, Xilinas

, Ames

, Davis

, Beyreuther

, Tanzi

, Masters

(2003) Metal-protein attenuation with iodochlorhydroxyquin (clioquinol) targeting Abeta amyloid deposition and toxicity in Alzheimer disease: A pilot phase 2 clinical trial. Arch Neurol60, 1685–1691.

75.

Opazo

, Luza

, Villemagne

, Volitakis

, Rowe

, Barnham

, Strozyk

, Masters

, Cherny

, Bush

(2006) Radioiodinated clioquinol as a biomarker for beta-amyloid: Zn complexes in Alzheimer’s disease. Aging Cell5, 69–79.

76.

Perez

, Sklar

, Chigaev

(2019) Clioquinol: To harm or heal. Pharmacol Ther199, 155–163.

77.

Adlard

, Cherny

, Finkelstein

, Gautier

, Robb

, Cortes

, Volitakis

, Liu

, Smith

, Perez

, Laughton

, Li

, Charman

, Nicolazzo

, Wilkins

, Deleva

, Lynch

, Kok

, Ritchie

, Tanzi

, Cappai

, Masters

, Barnham

, Bush

(2008) Rapid restoration of cognition in Alzheimer’s transgenic mice with 8-hydroxy quinoline analogs is associated with decreased interstitial Abeta. Neuron59, 43–55.

78.

Huntington Study Group Reach2HD Investigators (2015) Safety, tolerability, and efficacy of PBT2 in Huntington’s disease: A phase 2, randomised, double-blind, placebo-controlled trial. Lancet Neurol14, 39–47.

79.

Adlard

, Bica

, White

, Nurjono

, Filiz

, Crouch

, Donnelly

, Cappai

, Finkelstein

, Bush

(2011) Metal ionophore treatment restores dendritic spine density and synaptic protein levels in a mouse model of Alzheimer’s disease. PLoS One6, e17669.

80.

Crouch

, Savva

, Hung

, Donnelly

, Mot

, Parker

, Greenough

, Volitakis

, Adlard

, Cherny

, Masters

, Bush

, Barnham

, White

(2011) The Alzheimer’s therapeutic PBT2 promotes amyloid-beta degradation and GSK3 phosphorylation via a metal chaperone activity. J Neurochem119, 220–230.

81.

Epstein

, Achong

, Barr

(1964) Desferrioxamine and Iron. Lancet1, 708–709.

82.

King

(1985) Desferrioxamine and Alzheimer’s dementia. Med J Aust142, 352.

83.

Guo

, Wang

, Zheng

, Shan

, Teng

, Wang

(2013) Intranasal deferoxamine reverses iron-induced memory deficits and inhibits amyloidogenic APP processing in a transgenic mouse model of Alzheimer’s disease. Neurobiol Aging34, 562–575.

84.

Zhang

, He

(2017) Deferoxamine enhances alternative activation of microglia and inhibits amyloid beta deposits in APP/PS1 mice. Brain Res1677, 86–92.

85.

Guo

, Wang

, Zhong

, Wang

, Huang

, Li

, Wang

(2013) Deferoxamine inhibits iron induced hippocampal tau phosphorylation in the Alzheimer transgenic mouse brain. Neurochem Int62, 165–172.

86.

Savory

, Huang

, Wills

, Herman

(1998) Reversal by desferrioxamine of tau protein aggregates following two days of treatment in aluminum-induced neurofibrillary degeneration in rabbit: Implications for clinical trials in Alzheimer’s disease. Neurotoxicology19, 209–214.

87.

Zhang

, Cao

, Zhang

, Li

, Mi

(2015) Deferoxamine attenuates lipopolysaccharide-induced neuroinflammation and memory impairment in mice. J Neuroinflammation12, 20.

88.

, Pan

, Chen

, Ning

, Li

, Yang

, Terrando

, Gu

, Tao

(2016) Deferoxamine regulates neuroinflammation and iron homeostasis in a mouse model of postoperative cognitive dysfunction. J Neuroinflammation13, 268.

89.

Fine

, Forsberg

, Stroebel

, Faltesek

, Verden

, Hamel

, Raney

, Crow

, Haase

, Knutzen

, Kaczmarczek

, Frey

, Hanson

(2017) Intranasal deferoxamine affects memory loss, oxidation, and the insulin pathway in the streptozotocin rat model of Alzheimer’s disease. J Neurol Sci380, 164–171.

90.

Fine

, Baillargeon

, Renner

, Hoerster

, Tokarev

, Colton

, Pelleg

, Andrews

, Sparley

, Krogh

, Frey

, Hanson

(2012) Intranasal deferoxamine improves performance in radial arm water maze, stabilizes HIF-1alpha, and phosphorylates GSK3beta in P301L tau transgenic mice. Exp Brain Res219, 381–390.

91.

Zhang

, Gannon

, Chen

, Yan

, Zhang

, Feng

, Tao

, Sha

, Liu

, Saito

, Saido

, Keene

, Jiao

, Roberson

, Xu

, Wang

(2020) beta-amyloid redirects norepinephrine signaling to activate the pathogenic GSK3beta/tau cascade. Sci Transl Med12, eaay6931.

92.

Crapper McLachlan

, Dalton

, Kruck

, Bell

, Smith

, Kalow

, Andrews

(1991) Intramuscular desferrioxamine in patients with Alzheimer’s disease. Lancet337, 1304–1308.

93.

Guo

, Zhang

, Wang

, Zhong

, Yang

, Hao

, Chai

, Zhang

(2015) Intranasal deferoxamine attenuates synapse loss via up-regulating the P38/HIF-1alpha pathway on the brain of APP/PS1 transgenic mice. Front Aging Neurosci7, 104.

94.

Zacchigna

, Lambrechts

, Carmeliet

(2008) Neurovascular signalling defects in neurodegeneration. Nat Rev Neurosci9, 169–181.

95.

Sorond

, Shaffer

, Kung

, Lipsitz

(2009) Desferroxamine infusion increases cerebral blood flow: A potential association with hypoxia-inducible factor-1. Clin Sci (Lond)116, 771–779.

96.

Sorond

, Tan

, LaRose

, Monk

, Fichorova

, Ryan

, Lipsitz

(2015) Deferoxamine, cerebrovascular hemodynamics, and vascular aging: Potential role for hypoxia-inducible transcription factor-1-regulated pathways. Stroke46, 2576–2583.

97.

Entezari

, Haghi

, Norouzkhani

, Sahebnazar

, Vosoughian

, Akbarzadeh

, Islampanah

, Naghsh

, Abbasalizadeh

, Deravi

(2022) Iron chelators in treatment of iron overload. J Toxicol2022, 4911205.

98.

Molina-Holgado

, Gaeta

, Francis

, Williams

, Hider

(2008) Neuroprotective actions of deferiprone in cultured cortical neurones and SHSY-5Y cells. J Neurochem105, 2466–2476.

99.

Prasanthi

, Schrag

, Dasari

, Marwarha

, Dickson

, Kirsch

, Ghribi

(2012) Deferiprone reduces amyloid-β and tau phosphorylation levels but not reactive oxygen species generation in hippocampus of rabbits fed a cholesterol-enriched diet. J Alzheimers Dis30, 167–182.

100.

Sripetchwandee

, Wongjaikam

, Krintratun

, Chattipakorn

(2016) A combination of an iron chelator with an antioxidant effectively diminishes the dendritic loss, tau-hyperphosphorylation, amyloids-β accumulation and brain mitochondrial dynamic disruption in rats with chronic iron-overload. Neuroscience332, 191–202.

101.

Xue

, Yan

, Chen

, Li

, Kang

, Klionsky

, Kroemer

, Chen

, Tang

, Liu

(2023) Copper-dependent autophagic degradation of GPX4 drives ferroptosis. Autophagy19, 1982–1996.

102.

, Tian

, Mao

, Li

, Lin

, Hu

, Huang

, Zhang

, Mei

(2021) Zinc attenuates ferroptosis and promotes functional recovery in contusion spinal cord injury by activating Nrf2/GPX4 defense pathway. CNS Neurosci Ther27, 1023–1040.

103.

Yan

, Zhang

(2019) Iron metabolism, ferroptosis, and the links with Alzheimer’s disease. Front Neurosci13, 1443.

104.

Forcina

, Dixon

(2019) GPX4 at the crossroads of lipid homeostasis and ferroptosis. Proteomics19, e1800311.

105.

Mandal

, Maroon

, Garg

, Arora

, Bansal

, Kaushik

, Samkaria

, Kumaran

, Arora

(2023) Blood biomarkers in Alzheimer’s disease. ACS Chem Neurosci14, 3975–3978.

106.

Nikseresht

, Bush

, Ayton

(2019) Treating Alzheimer’s disease by targeting iron. Br J Pharmacol176, 3622–3635.

107.

Plascencia-Villa

, Perry

(2021) Preventive and therapeutic strategies in Alzheimer’s disease: Focus on oxidative stress, redox metals, and ferroptosis. Antioxid Redox Signal34, 591–610.

108.

Alkandari

, Madhyastha

, Rao

(2023) N-acetylcysteine amide against Abeta-induced Alzheimer’s-like pathology in rats. Int J Mol Sci24, 12733.

109.

Yoo

, Lee

, Kim

, Baik

, Lee

, Woo

(2023) Multiple low-dose radiation-induced neuronal cysteine transporter expression and oxidative stress are rescued by N-acetylcysteine in neuronal SH-SY5Y cells. Neurotoxicology95, 205–217.

110.

Hsiao

, Kuo

, Chen

, Gean

(2012) Amelioration of social isolation-triggered onset of early Alzheimer’s disease-related cognitive deficit by N-acetylcysteine in a transgenic mouse model. Neurobiol Dis45, 1111–1120.

111.

Adair

, Knoefel

, Morgan

(2001) Controlled trial of N-acetylcysteine for patients with probable Alzheimer’s disease. Neurology57, 1515–1517.

112.

Halliwell

(2024) Understanding mechanisms of antioxidant action in health and disease. Nat Rev Mol Cell Biol25, 13–33.

113.

Icer

, Arslan

, Gezmen-Karadag

(2021) Effects of vitamin E on neurodegenerative diseases: An update. Acta Neurobiol Exp (Wars)81, 21–33.

114.

Zhao

, Han

, Zhang

, Liu

, Zhang

, Zhao

, Jiang

, Li

, Cai

, You

(2022) Association of vitamin E intake in diet and supplements with risk of dementia: A meta-analysis. Front Aging Neurosci14, 955878.

115.

Dysken

, Sano

, Asthana

, Vertrees

, Pallaki

, Llorente

, Love

, Schellenberg

, McCarten

, Malphurs

, Prieto

, Chen

, Loreck

, Trapp

, Bakshi

, Mintzer

, Heidebrink

, Vidal-Cardona

, Arroyo

, Cruz

, Zachariah

, Kowall

, Chopra

, Craft

, Thielke

, Turvey

, Woodman

, Monnell

, Gordon

, Tomaska

, Segal

, Peduzzi

, Guarino

(2014) Effect of vitamin E and memantine on functional decline in Alzheimer disease: The TEAM-AD VA cooperative randomized trial. JAMA311, 33–44.

116.

Petersen

, Thomas

, Grundman

, Bennett

, Doody

, Ferris

, Galasko

, Jin

, Kaye

, Levey

, Pfeiffer

, Sano

, van Dyck

, Thal

, Alzheimer’s Disease Cooperative Study Group(2005) Vitamin E and donepezil for the treatment of mild cognitive impairment. N Engl J Med352, 2379–2388.

117.

Ibrahim

, Yanagisawa

, Durani

, Hamezah

, Damanhuri

, Wan Ngah

, Tsuji

, Kiuchi

, Ono

, Tooyama

(2017) Tocotrienol-rich fraction modulates amyloid pathology and improves cognitive function in AbetaPP/PS1 mice. J Alzheimers Dis55, 597–612.

118.

Mehrabadi

, Sadr

(2020) Administration of Vitamin D(3) and E supplements reduces neuronal loss and oxidative stress in a model of rats with Alzheimer’s disease. Neurol Res42, 862–868.

119.

Tuo

, Masaldan

, Southon

, Mawal

, Ayton

, Bush

, Lei

, Belaidi

(2021) Characterization of selenium compounds for anti-ferroptotic activity in neuronal cells and after cerebral ischemia-reperfusion injury. Neurotherapeutics18, 2682–2691.

120.

Zhou

, Zhang

, Cao

, Lian

, Li

, Nie

, Huang

, Zhao

, He

, Liu

(2023) Association of selenium levels with neurodegenerative disease: A systemic review and meta-analysis. Nutrients15, 3706.

121.

Surai

, Kochish , II (2019) Nutritional modulation of the antioxidant capacities in poultry: The case of selenium. Poult Sci98, 4231–4239.

122.

Ishrat

, Parveen

, Khan

, Khuwaja

, Khan

, Yousuf

, Ahmad

, Shrivastav

, Islam

(2009) Selenium prevents cognitive decline and oxidative damage in rat model of streptozotocin-induced experimental dementia of Alzheimer’s type. Brain Res1281, 117–127.

123.

van Eersel

, Ke

, Liu

, Delerue

, Kril

, Gotz

, Ittner

(2010) Sodium selenate mitigates tau pathology, neurodegeneration, and functional deficits in Alzheimer’s disease models. Proc Natl Acad Sci U S A107, 13888–13893.

124.

Corcoran

, Martin

, Hutter-Paier

, Windisch

, Nguyen

, Nheu

, Sundstrom

, Costello

, Hovens

(2010) Sodium selenate specifically activates PP2A phosphatase, dephosphorylates tau and reverses memory deficits in an Alzheimer’s disease model. J Clin Neurosci17, 1025–1033.

125.

Haratake

, Yoshida

, Mandai

, Fuchigami

, Nakayama

(2013) Elevated amyloid-beta plaque deposition in dietary selenium-deficient Tg2576 transgenic mice. Metallomics5, 479–483.

126.

Song

, Zhang

, Wen

, Chen

, Shi

, Zhang

, Ni

, Liu

(2014) Selenomethionine ameliorates cognitive decline, reduces tau hyperphosphorylation, and reverses synaptic deficit in the triple transgenic mouse model of Alzheimer’s disease. J Alzheimers Dis41, 85–99.

127.

Rita Cardoso

, Silva Bandeira

, Jacob-Filho

, Franciscato Cozzolino

(2014) Selenium status in elderly: Relation to cognitive decline. J Trace Elem Med Biol28, 422–426.

128.

Cardoso

, Hare

, Bush

, Li

, Fowler

, Masters

, Martins

, Ganio

, Lothian

, Mukherjee

, Kapp

, Roberts

, group

(2017) Selenium levels in serum, red blood cells, and cerebrospinal fluid of Alzheimer’s disease patients: A report from the Australian Imaging, Biomarker & Lifestyle Flagship Study of Ageing (AIBL). J Alzheimers Dis57, 183–193.

129.

Cardoso

, Ong

, Jacob-Filho

, Jaluul

, Freitas

, Cozzolino

(2010) Nutritional status of selenium in Alzheimer’s disease patients. Br J Nutr103, 803–806.

130.

Olde Rikkert

, Verhey

, Sijben

, Bouwman

, Dautzenberg

, Lansink

, Sipers

, van Asselt

, van Hees

, Stevens

, Vellas

, Scheltens

(2014) Differences in nutritional status between very mild Alzheimer’s disease patients and healthy controls. J Alzheimers Dis41, 261–271.

131.

Varikasuvu

, Prasad

, Kothapalli

, Manne

(2019) Brain Selenium in Alzheimer’s Disease (BRAIN SEAD Study): A systematic review and meta-analysis. Biol Trace Elem Res189, 361–369.

132.

Rita Cardoso

, Apolinario

, da Silva Bandeira

, Busse

, Magaldi

, Jacob-Filho

, Cozzolino

(2016) Effects of Brazil nut consumption on selenium status and cognitive performance in older adults with mild cognitive impairment: A randomized controlled pilot trial. Eur J Nutr55, 107–116.

133.

Kryscio

, Abner

, Caban-Holt

, Lovell

, Goodman

, Darke

, Yee

, Crowley

, Schmitt

(2017) Association of antioxidant supplement use and dementia in the Prevention of Alzheimer’s Disease by Vitamin E and Selenium Trial (PREADViSE). JAMA Neurol74, 567–573.

134.

Malpas

, Vivash

, Genc

, Saling

, Desmond

, Steward

, Hicks

, Callahan

, Brodtmann

, Collins

, Macfarlane

, Corcoran

, Hovens

, Velakoulis

, O’Brien

(2016) A phase IIa randomized control trial of VEL015 (sodium selenate) in mild-moderate Alzheimer’s disease. J Alzheimers Dis54, 223–232.

135.

Cardoso

, Roberts

, Malpas

, Vivash

, Genc

, Saling

, Desmond

, Steward

, Hicks

, Callahan

, Brodtmann

, Collins

, Macfarlane

, Corcoran

, Hovens

, Velakoulis

, O’Brien

, Hare

, Bush

(2019) Supranutritional sodium selenate supplementation delivers selenium to the central nervous system: Results from a randomized controlled pilot trial in Alzheimer’s disease. Neurotherapeutics16, 192–202.

136.

Holbein

, Lehmann

(2023) Dysregulated iron homeostasis as common disease etiology and promising therapeutic target. Antioxidants (Basel)12, 671.

137.

Kosyakovsky

, Fine

, Frey

, 2nd , Hanson

(2021) Mechanisms of intranasal deferoxamine in neurodegenerative and neurovascular disease. Pharmaceuticals (Basel)14, 95.

138.

Devos

, Labreuche

, Rascol

, Corvol

, Duhamel

, Guyon Delannoy

, Poewe

, Compta

, Pavese

, Růžička

, Dušek

, Post

, Bloem

, Berg

, Maetzler

, Otto

, Habert

, Lehericy

, Ferreira

, Dodel

, Tranchant

, Eusebio

, Thobois

, Marques

, Meissner

, Ory-Magne

, Walter

, de Bie

RMA

, Gago

, Vilas

, Kulisevsky

, Januario

, Coelho

MVS

, Behnke

, Worth

, Seppi

, Ouk

, Potey

, Leclercq

, Viard

, Kuchcinski

, Lopes

, Pruvo

, Pigny

, Garçon

, Simonin

, Carpentier

, Rolland

, Nyholm

, Scherfler

, Mangin

, Chupin

, Bordet

, Dexter

, Fradette

, Spino

, Tricta

, Ayton

, Bush

, Devedjian

, Duce

, Cabantchik

, Defebvre

, Deplanque

, Moreau

(2022) Trial of deferiprone in Parkinson’s disease. N Engl J Med387, 2045–2055.

139.

Martin-Bastida

, Ward

, Newbould

, Piccini

, Sharp

, Kabba

, Patel

, Spino

, Connelly

, Tricta

, Crichton

, Dexter

(2017) Brain iron chelation by deferiprone in a phase 2 randomised double-blinded placebo controlled clinical trial in Parkinson’s disease. Sci Rep7, 1398.

140.

Devos

, Moreau

, Devedjian

, Kluza

, Petrault

, Laloux

, Jonneaux

, Ryckewaert

, Garcon

, Rouaix

, Duhamel

, Jissendi

, Dujardin

, Auger

, Ravasi

, Hopes

, Grolez

, Firdaus

, Sablonniere

, Strubi-Vuillaume

, Zahr

, Destee

, Corvol

, Poltl

, Leist

, Rose

, Defebvre

, Marchetti

, Cabantchik

, Bordet

(2014) Targeting chelatable iron as a therapeutic modality in Parkinson’s disease. Antioxid Redox Signal21, 195–210.