Challenges associated with metal chelation therapy in Alzheimer's disease

Targeting Biometals in Alzheimer's Disease with Metal Chelating Agents Including Coumarin Derivatives

Numerous physiological processes happening in the human body, including cerebral development and function, require the participation of biometal ions such as iron, copper, and zinc. Their dyshomeostasis may, however, contribute to the onset of Alzheimer's disease (AD) and potentially other neurodegenerative diseases. Chelation of biometal ions is therefore a therapeutic strategy against AD. This review provides a survey of natural and synthetic chelating agents that are or could potentially be used to target the metal hypothesis of AD. Since metal dyshomeostasis is not the only pathological aspect of AD, and the nature of this disorder is very complex and multifactiorial, the most efficient therapeutics should target as many neurotoxic factors as possible. Various coumarin derivatives match this description and apart from being able to chelate metal ions, they exhibit the capacity to inhibit cholinesterases (ChEs) and monoamine oxidase B (MAO-B) while also possessing antioxidant, anti-inflammatory, and numerous other beneficial effects. Compounds based on the coumarin scaffold therefore represent a desirable class of anti-AD therapeutics.

Recent Advances in Targeting Transition Metals (Copper, Iron, and Zinc) in Alzheimer's Disease

Changes in the transition metal homeostasis in the brain are closely linked with Alzheimer's disease (AD), including intraneuronal iron accumulation and extracellular copper and zinc pooling in the amyloid plague. The brain copper, zinc, and iron surplus are commonly acknowledged characteristics of AD, despite disagreements among some. This has led to the theory that oxidative stress resulting from abnormal homeostasis of these transition metals may be a causative explanation behind AD. In the nervous system, the interaction of metals with proteins appears to be an essential variable in the development or suppression of neurodegeneration. Chelation treatment may be an option for treating neurodegeneration induced by transition metal ion dyshomeostasis. Some clinicians even recommend using chelating agents as an adjunct therapy for AD. The current review also looks at the therapeutic strategies that have been attempted, primarily with metal-chelating drugs. Metal buildup in the nervous system, as reported in the AD, could be the result of compensatory mechanisms designed to improve metal availability for physiological functions.

Iron Overload in Brain: Transport Mismatches, Microbleeding Events, and How Nanochelating Therapies May Counteract Their Effects

Iron overload in many brain regions is a common feature of aging and most neurodegenerative diseases. In this review, the causes, mechanisms, mathematical models, and possible therapies are summarized. Indeed, physiological and pathological conditions can be investigated using compartmental models mimicking iron trafficking across the blood-brain barrier and the Cerebrospinal Fluid-Brain exchange membranes located in the choroid plexus. In silico models can investigate the alteration of iron homeostasis and simulate iron concentration in the brain environment, as well as the effects of intracerebral iron chelation, determining potential doses and timing to recover the physiological state. Novel formulations of non-toxic nanovectors with chelating capacity are already tested in organotypic brain models and could be available to move from in silico to in vivo experiments.

Fluorescent Turn-On Anthracene-Based Aluminum(III) Sensor for a Therapeutic Study in Alzheimer's Disease Model of Drosophila

A new anthracene-based probe (E)-N'-(1-(anthracen-9-yl)ethylidene)-2-hydroxybenzohydrazide (AHB) has been efficiently synthesized and characterized by various spectroscopic methods. It exhibits extremely selective and sensitive fluorometric sensing of Al3+ ions with a large enhancement in the fluorescent intensity due to the restricted photoinduced electron transfer (PET) mechanism with a chelation-enhanced fluorescence (CHEF) effect. The AHB-Al3+ complex shows a remarkably low limit of detection at 0.498 nM. The binding mechanism has been proposed based on Job's plot, 1H NMR titration, Fourier transform infrared (FT-IR), high-resolution mass spectrometry (HRMS), and density functional theory (DFT) studies. The chemosensor is reusable and reversible in the presence of ctDNA. The practical usability of the fluorosensor has been established by a test strip kit. Further, the therapeutic potential of AHB against Al3+ ion-induced tau protein toxicity has been tested in the eye of Alzheimer's disease (AD) model of Drosophila via metal chelation therapy. AHB shows great therapeutic potential with 53.3% rescue in the eye phenotype. The in vivo interaction study of AHB with Al3+ in the gut tissue of Drosophila confirms its sensing efficiency in the biological environment. A detailed comparison table included evaluates the effectiveness of AHB.

The Role of Heme and Copper in Alzheimer's Disease and Type 2 Diabetes Mellitus

Beyond the well-explored proposition of protein aggregation or amyloidosis as the central event in amyloidogenic diseases like Alzheimer's Disease (AD), and Type 2 Diabetes Mellitus (T2Dm); there are alternative hypotheses, now becoming increasingly evident, which suggest that the small biomolecules like redox noninnocent metals (Fe, Cu, Zn, etc.) and cofactors (Heme) have a definite influence in the onset and extent of such degenerative maladies. Dyshomeostasis of these components remains as one of the common features in both AD and T2Dm etiology. Recent advances in this course reveal that the metal/cofactor-peptide interactions and covalent binding can alarmingly enhance and modify the toxic reactivities, oxidize vital biomolecules, significantly contribute to the oxidative stress leading to cell apoptosis, and may precede the amyloid fibrils formation by altering their native folds. This perspective highlights this aspect of amyloidogenic pathology which revolves around the impact of the metals and cofactors in the pathogenic courses of AD and T2Dm including the active site environments, altered reactivities, and the probable mechanisms involving some highly reactive intermediates as well. It also discusses some in vitro metal chelation or heme sequestration strategies which might serve as a possible remedy. These findings might open up a new paradigm in our conventional understanding of amyloidogenic diseases. Moreover, the interaction of the active sites with small molecules elucidates potential biochemical reactivities that can inspire designing of drug candidates for such pathologies.

Understanding Alzheimer's Disease and its Metal Chelation Therapeutics: A Narrative Review

The neurodegenerative disorders are age-related illnesses that cause the morphology or activity of neurons to deteriorate over time. Alzheimer's disease is the most frequent neurodegenerative illness in the long run. The rate of advancement might vary, even though it is a progressive neurological illness. Various explanations have been proposed, however the true etiology of Alzheimer's disease remains unclear. Most pharmacological interventions are based on the cholinergic theory, that is earliest idea. In accordance with the amyloid hypothesis, the buildup of beta-amyloid in brain regions is the primitive cause of illness. There is no proof that any one strategy is useful in avoiding Alzheimer's disease, though some epidemiological studies have suggested links within various modifiable variables, such as cardiovascular risk, diet and so on. Different metals like zinc, iron, and copper are naturally present in our bodies. In metal chelation therapy drugs are used to jam the metal ions from combining with other molecules in the body. Clioquinol is one of the metal chelation drugs used by researchers. Research on metal chelation is still ongoing. In the present review, we go over the latest developments in prevalence, incidence, etiology, or pathophysiology of our understanding of Alzheimer's disease. Additionally, a brief discussion on the development of therapeutic chelating agents and their viability as Alzheimer's disease medication candidates is presented. We also assess the effect of clioquinol as a potential metal chelator.

Alternative Pharmacological Strategies for the Treatment of Alzheimer's Disease: Focus on Neuromodulator Function

Alzheimer's disease (AD) is a neurodegenerative disorder, comprising 70% of dementia diagnoses worldwide and affecting 1 in 9 people over the age of 65. However, the majority of its treatments, which predominantly target the cholinergic system, remain insufficient at reversing pathology and act simply to slow the inevitable progression of the disease. The most recent neurotransmitter-targeting drug for AD was approved in 2003, strongly suggesting that targeting neurotransmitter systems alone is unlikely to be sufficient, and that research into alternate treatment avenues is urgently required. Neuromodulators are substances released by neurons which influence neurotransmitter release and signal transmission across synapses. Neuromodulators including neuropeptides, hormones, neurotrophins, ATP and metal ions display altered function in AD, which underlies aberrant neuronal activity and pathology. However, research into how the manipulation of neuromodulators may be useful in the treatment of AD is relatively understudied. Combining neuromodulator targeting with more novel methods of drug delivery, such as the use of multi-targeted directed ligands, combinatorial drugs and encapsulated nanoparticle delivery systems, may help to overcome limitations of conventional treatments. These include difficulty crossing the blood-brain-barrier and the exertion of effects on a single target only. This review aims to highlight the ways in which neuromodulator functions are altered in AD and investigate how future therapies targeting such substances, which act upstream to classical neurotransmitter systems, may be of potential therapeutic benefit in the sustained search for more effective treatments.

Iron in Alzheimer's Disease: From Physiology to Disease Disabilities

Reactive oxygen species (ROS) play a key role in the neurodegeneration processes. Increased oxidative stress damages lipids, proteins, and nucleic acids in brain tissue, and it is tied to the loss of biometal homeostasis. For this reason, attention has been focused on transition metals involved in several biochemical reactions producing ROS. Even though a bulk of evidence has uncovered the role of metals in the generation of the toxic pathways at the base of Alzheimer's disease (AD), this matter has been sidelined by the advent of the Amyloid Cascade Hypothesis. However, the link between metals and AD has been investigated in the last two decades, focusing on their local accumulation in brain areas known to be critical for AD. Recent evidence revealed a relation between iron and AD, particularly in relation to its capacity to increase the risk of the disease through ferroptosis. In this review, we briefly summarize the major points characterizing the function of iron in our body and highlight why, even though it is essential for our life, we have to monitor its dysfunction, particularly if we want to control our risk of AD.

Therapeutic roles of plants for 15 hypothesised causal bases of Alzheimer's disease

Alzheimer's disease (AD) is progressive and ultimately fatal, with current drugs failing to reverse and cure it. This study aimed to find plant species which may provide therapeutic bioactivities targeted to causal agents proposed to be driving AD. A novel toolkit methodology was employed, whereby clinical symptoms were translated into categories recognized in ethnomedicine. These categories were applied to find plant species with therapeutic effects, mined from ethnomedical surveys. Survey locations were mapped to assess how this data is at risk. Bioactivities were found of therapeutic relevance to 15 hypothesised causal bases for AD. 107 species with an ethnological report of memory improvement demonstrated therapeutic activity for all these 15 causal bases. The majority of the surveys were found to reside within biodiversity hotspots (centres of high biodiversity under threat), with loss of traditional knowledge the most common threat. Our findings suggest that the documented plants provide a large resource of AD therapeutic potential. In demonstrating bioactivities targeted to these causal bases, such plants may have the capacity to reduce or reverse AD, with promise as drug leads to target multiple AD hallmarks. However, there is a need to preserve ethnomedical knowledge, and the habitats on which this knowledge depends.

Chelation in Antibacterial Drugs: From Nitroxoline to Cefiderocol and Beyond

In the era of escalating antimicrobial resistance, the need for antibacterial drugs with novel or improved modes of action (MOAs) is a health concern of utmost importance. Adding or improving the chelating abilities of existing drugs or finding new, nature-inspired chelating agents seems to be one of the major ways to ensure progress. This review article provides insight into the modes of action of antibacterial agents, class by class, through the perspective of chelation. We covered a wide scope of antibacterials, from a century-old quintessential chelating agent nitroxoline, currently unearthed due to its newly discovered anticancer and antibiofilm activities, over the commonly used antibacterial classes, to new cephalosporin cefiderocol and a potential future class of tetramates. We show the impressive spectrum of roles that chelation plays in antibacterial MOAs. This, by itself, demonstrates the importance of understanding the fundamental chemistry behind such complex processes.

Longitudinal Consumption of Ergothioneine Reduces Oxidative Stress and Amyloid Plaques and Restores Glucose Metabolism in the 5XFAD Mouse Model of Alzheimer's Disease

Background: Ergothioneine (ERGO) is a unique antioxidant and a rare amino acid available in fungi and various bacteria but not in higher plants or animals. Substantial research data indicate that ERGO is a physiological antioxidant cytoprotectant. Different from other antioxidants that need to breach the blood-brain barrier to enter the brain parenchyma, a specialized transporter called OCTN1 has been identified for transporting ERGO to the brain. Purpose: To assess whether consumption of ERGO can prevent the progress of Alzheimer's disease (AD) on young (4-month-old) 5XFAD mice. Methods and materials: Three cohorts of mice were tested in this study, including ERGO-treated 5XFAD, non-treated 5XFAD, and WT mice. After the therapy, the animals went through various behavioral experiments to assess cognition. Then, mice were scanned with PET imaging to evaluate the biomarkers associated with AD using [¹¹C]PIB, [¹¹C]ERGO, and [¹⁸F]FDG radioligands. At the end of imaging, the animals went through cardiac perfusion, and the brains were isolated for immunohistology. Results: Young (4-month-old) 5XFAD mice did not show a cognitive deficit, and thus, we observed modest improvement in the treated counterparts. In contrast, the response to therapy was clearly detected at the molecular level. Treating 5XFAD mice with ERGO resulted in reduced amyloid plaques, oxidative stress, and rescued glucose metabolism. Conclusions: Consumption of high amounts of ERGO benefits the brain. ERGO has the potential to prevent AD. This work also demonstrates the power of imaging technology to assess response during therapy.

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.

The Bright and Dark Sides of Reactive Oxygen Species Generated by Copper–Peptide Complexes

Copper ions bind to biomolecules (e.g., peptides and proteins) playing an essential role in many biological and physiological pathways in the human body. The resulting complexes may contribute to the initiation of neurodegenerative diseases, cancer, and bacterial and viral diseases, or act as therapeutics. Some compounds can chemically damage biological macromolecules and initiate the development of pathogenic states. Conversely, a number of these compounds may have antibacterial, antiviral, and even anticancer properties. One of the most significant current discussions in Cu biochemistry relates to the mechanisms of the positive and negative actions of Cu ions based on the generation of reactive oxygen species, including radicals that can interact with DNA molecules. This review aims to analyze various peptide–copper complexes and the mechanism of their action.

Epigenetic Modifications and Neurodegenerative Disorders: A Biochemical Perspective

Methylations in living cells are methyl groups attached to amino acids, DNA, RNA, and so on. However, their biochemical roles have not been fully defined. A theory has been postulated that methylation leads to hyperconjugation, and the electron-donating feature weakens a nearby chemical bond, which increases the bond length of C⁴-N⁴ of 5-methylcytosine, therefore weakening the C⁴-N⁴ bond and resulting in stronger protonation or hydrogen bonding of the N⁴ nitrogen atom. Protonation can give rise to the generation of mutagenic and carcinogenic strong acids such as HCl, which are also capable of solubilizing stressful, insoluble, and stiff salts. Insoluble and rigid salts such as calcium oxalate and/or calcium phosphate were recently proposed as a primary cause of some neurodegenerative disorders. Protonation of nitrogen atoms in 5-methylcytosine enhances the interaction with negatively charged phosphate groups and contributes to the formation of compact heterochromatin. The electronegativity of the oxygen atoms in the modifications of 5-hydroxymethylcytosine or 5-formylcytosine can shorten the lengths of adjacent bonds with no increase of cation affinity in N⁴. The carboxyl group in 5-carboxylcytosine is a weak acid capable of antagonizing mutagenic HCl and modestly helping solubilize insoluble salts. Electron delocalization of the methyl group in N4-methylcytosine results in a lower affinity of N⁴ to cations. The positive charge at N³ in the resonance structure of 3-methylcytosine is lessened by the electron-donating attribute of the methyl group attached to the N³ atom, consequently reducing acid formation. The electron delocalization of three methyl groups decreases the positive charge in the amino nitrogen in the side group of lysine 4 in histone H3, weakening interactions with phosphate groups and consequently activating gene expression. The carbonyl oxygen in 8-oxo-7,8-dihydroguanine draws protons and accumulates HCl, accounting for its moderate mutation propensity and potential capacity to solubilize stiff salts. The biochemical insight will further our understanding on the crosstalk of genetics and epigenetics in the etiology of neurodegenerative diseases.

Metallobiology and therapeutic chelation of biometals (copper, zinc and iron) in Alzheimer's disease: Limitations, and current and future perspectives

BACKGROUND

Alzheimer's disease (AD) is the most prevalent cause of cognitive impairment and dementia worldwide. The pathobiology of the disease has been studied in the form of several hypotheses, ranging from oxidative stress, amyloid-beta (Aβ) aggregation, accumulation of tau forming neurofibrillary tangles (NFT) through metal dysregulation and homeostasis, dysfunction of the cholinergic system, and to inflammatory and autophagic mechanism. However, none of these hypotheses has led to confirmed diagnostics or approved cure for the disease.

OBJECTIVE

This review is aimed as a basic and an encyclopedic short course into metals in AD and discusses the advances in chelation strategies and developments adopted in the treatment of the disease. Since there is accumulating evidence of the role of both biometal dyshomeostasis (iron (Fe), copper (Cu), and zinc (Zn)) and metal-amyloid interactions that lead to the pathogenesis of AD, this review focuses on unraveling therapeutic chelation strategies that have been considered in the treatment of the disease, aiming to sequester free and protein-bound metal ions and reducing cerebral metal burden. Promising compounds possessing chemically modified moieties evolving as multi-target ligands used as anti-AD drug candidates are also covered.

RESULTS AND CONCLUSION

Several multidirectional and multifaceted studies on metal chelation therapeutics show the need for improved synthesis, screening, and analysis of compounds to be able to effectively present chelating anti-AD drugs. Most drug candidates studied have limitations in their physicochemical properties; some enhance redistribution of metal ions, while others indirectly activate signaling pathways in AD. The metal chelation process in vivo still needs to be established and the design of potential anti-AD compounds that bi-functionally sequester metal ions as well as inhibit the Aβ aggregation by competing with the metal ions and reducing metal-induced oxidative damage and neurotoxicity may signal a bright end in chelation-based therapeutics of AD.

A review of plant metabolites with metal interaction capacity: a green approach for industrial applications

Rapid industrial development is responsible for severe problems related to environmental pollution. Many human and industrial activities require different metals and, as a result, great amounts of metals/heavy metals are discharged into the water and soil making them dangerous for both human and ecosystems and this is being aggravated by intensive demand and utilization. In addition, compounds with metal binding capacities are needed to be used for several purposes including in activities related to the removal and/or recovery of metals from effluents and soils, as metals' corrosion inhibitors, in the synthesis of metallic nanoparticles and as metal related pharmaceuticals, preferably a with minimum risks associated to the environment. Plants are able to synthesize an uncountable number of compounds with numerous functions, including compounds with metal binding capabilities. In fact, some of the plants' secondary metabolites can bind to various metals through different mechanisms, as such they are excellent sources of such compounds due to their high availability and vast diversity. In addition, the use of plant-based compounds is desirable from an environmental and economical point of view, thus being potential candidates for utilization in different industrial activities, replacing conventional physiochemical methods. This review focuses on the ability of some classes of compounds that can be found in relatively high concentrations in plants, having good metal binding capacities and thus with potential utilization in metal based industrial activities and that can be involved in the progressive development of new environmentally friendly strategies.

Potential molecular and graphene oxide chelators to dissolve amyloid-β plaques in Alzheimer's disease: a density functional theory study

The onset of Alzheimer's disease (AD) is caused by amyloid-β (Aβ) aggregation. Elevated levels of metals, specifically copper, zinc, iron, and aluminum, accumulate in senile Aβ; plaque deposits, disrupting normal brain homeostasis and cognitive functions. In this investigation, we studied the potential of several molecular and graphene oxide chelators to be used for future AD research and chelation therapy. To understand the interactions between selected metals (Cu, Zn, Fe, and Al), the Aβ peptide, and various potential metal chelating compounds, we implemented the density functional theory (DFT) method to calculate the binding energies of each metal-molecule complex. The binding energy of each metal-chelator complex was compared with that of the metal-Aβ compound to determine the chelation potential of the selected chelator. The potential chelating agents studied were 8-hydroxyquinoline-2-carboxaldehyde isonicotinoyl hydrazone (INNHQ), 8-hydroxyquinoline-2-carboxaldehyde 2-furoyl hydrazone (HQFUH), quercetin, and graphene oxide (GO). Our calculated binding energies revealed that the HQFUH molecule holds direct ability to chelate copper, zinc, iron, and aluminum. In addition, the GO complex with a 12.5% oxygen concentration demonstrates aluminum chelation ability. Our results demonstrate that HQFUH and GO can be used in future AD drug development research and therapy to target toxic metal-Aβ interactions and reduce Aβ aggregation.

Benzofuran–stilbene hybrid compounds: an antioxidant assessment – a DFT study

The kinetic reaction of the benzofuran–stilbene hybrid compound 5-(2-(2-(4-hydroxyphenyl)benzofuran-5-yl)vinyl)benzene-1,3-diol captures the HOO˙ free radical.

Polyphenols as Potential Metal Chelation Compounds Against Alzheimer's Disease

Alzheimer's disease (AD) is the most common neurodegenerative disease affecting more than 50 million people worldwide. The pathology of this multifactorial disease is primarily characterized by the formation of amyloid-β (Aβ) aggregates; however, other etiological factors including metal dyshomeostasis, specifically copper (Cu), zinc (Zn), and iron (Fe), play critical role in disease progression. Because these transition metal ions are important for cellular function, their imbalance can cause oxidative stress that leads to cellular death and eventual cognitive decay. Importantly, these transition metal ions can interact with the amyloid-β protein precursor (AβPP) and Aβ42 peptide, affecting Aβ aggregation and increasing its neurotoxicity. Considering how metal dyshomeostasis may substantially contribute to AD, this review discusses polyphenols and the underlying chemical principles that may enable them to act as natural chelators. Furthermore, polyphenols have various therapeutic effects, including antioxidant activity, metal chelation, mitochondrial function, and anti-amyloidogenic activity. These combined therapeutic effects of polyphenols make them strong candidates for a moderate chelation-based therapy for AD.

Iron and Ferroptosis as Therapeutic Targets in Alzheimer's Disease

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

Secondary Chemical Bonding between Insoluble Calcium Oxalate and Carbonyl Oxygen Atoms of GLY and VAL Residues Triggers the Formation of Aβ Aggregates and Their Deposition in the Brain

Despite intense efforts, the cause of Alzheimer's disease is still not fully understood. A chemical and biochemical perspective could shed light on this disorder. Secondary chemical bonding between calcium and carbonyl oxygen atoms of glycine and valine might give rise to aggregates in the brain, which may later result in cell senescence. The decrease of solubility caused by amino acid substitutions in specific risk factors compounds insolubility issue and likely triggers early-onset Alzheimer's disease. Occasionally the enhancement of hydrogen bonding by amino acid replacements can reinforce the aggregates. Therefore, secondary chemical bonding to cations can generate cellular stresses in patients with Alzheimer's disease in addition to other chemical and biochemical interactions such as salt bridge. The distinction between early-onset and late-onset Alzheimer's disease risk factors may lie in the total capacity of a protein or local potency of a protein fragment to bind calcium or/and oxalate as calcium oxalate is highly insoluble and stressful.

Zinc Complexes with Nitrogen Donor Ligands as Anticancer Agents

The search for anticancer metal-based drugs alternative to platinum derivatives could not exclude zinc derivatives due to the importance of this metal for the correct functioning of the human body. Zinc, the second most abundant trace element in the human body, is one of the most important micro-elements essential for human physiology. Its ubiquity in thousands of proteins and enzymes is related to its chemical features, in particular its lack of redox activity and its ability to support different coordination geometries and to promote fast ligands exchange. Analogously to other trace elements, the impairment of its homeostasis can lead to various diseases and in some cases can be also related to cancer development. However, in addition to its physiological role, zinc can have beneficial therapeutic and preventive effects on infectious diseases and, compared to other metal-based drugs, Zn(II) complexes generally exert lower toxicity and offer few side effects. Zinc derivatives have been proposed as antitumor agents and, among the great number of zinc coordination complexes which have been described so far, this review focuses on the design, synthesis and biological studies of zinc complexes comprising N-donor ligands and that have been reported within the last five years.

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 Function of Transthyretin Complexes with Metallothionein in Alzheimer's Disease

Alzheimer’s disease (AD) is one of the most frequently diagnosed types of dementia in the elderly. An important pathological feature in AD is the aggregation and deposition of the β-amyloid (Aβ) in extracellular plaques. Transthyretin (TTR) can cleave Aβ, resulting in the formation of short peptides with less activity of amyloid plaques formation, as well as being able to degrade Aβ peptides that have already been aggregated. In the presence of TTR, Aβ aggregation decreases and toxicity of Aβ is abolished. This may prevent amyloidosis but the malfunction of this process leads to the development of AD. In the context of Aβplaque formation in AD, we discuss metallothionein (MT) interaction with TTR, the effects of which depend on the type of MT isoform. In the brains of patients with AD, the loss of MT-3 occurs. On the contrary, MT-1/2 level has been consistently reported to be increased. Through interaction with TTR, MT-2 reduces the ability of TTR to bind to Aβ, while MT-3 causes the opposite effect. It increases TTR-Aβ binding, providing inhibition of Aβ aggregation. The protective effect, assigned to MT-3 against the deposition of Aβ, relies also on this mechanism. Additionally, both Zn₇MT-2 and Zn₇MT-3, decrease Aβ neurotoxicity in cultured cortical neurons probably because of a metal swap between Zn₇MT and Cu(II)Aβ. Understanding the molecular mechanism of metals transfer between MT and other proteins as well as cognition of the significance of TTR interaction with different MT isoforms can help in AD treatment and prevention.

A Mechanistic Evaluation of Antioxidant Nutraceuticals on Their Potential against Age-Associated Neurodegenerative Diseases

Nutraceuticals have been extensively studied worldwide due to its neuroprotective effects in in vivo and in vitro studies, attributed by the antioxidative properties. Alzheimer (AD) and Parkinson disease (PD) are the two main neurodegenerative disorders that are discussed in this review. Both AD and PD share the similar involvement of oxidative stress in their pathophysiology. Nutraceuticals exert their antioxidative effects via direct scavenging of free radicals, prevent damage to biomolecules, indirectly stimulate the endogenous antioxidative enzymes and gene expressions, inhibit activation of pro-oxidant enzymes, and chelate metals. In addition, nutraceuticals can act as modulators of pro-survival, pro-apoptotic, and inflammatory signaling pathways. They have been shown to be effective particularly in preclinical stages, due to their multiple mechanisms of action in attenuating oxidative stress underlying AD and PD. Natural antioxidants from food sources and natural products such as resveratrol, curcumin, green tea polyphenols, and vitamin E are promising therapeutic agents in oxidative stress-mediated neurodegenerative disease as they have fewer adverse effects, more tolerable, cheaper, and sustainable for long term consumption.

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.

The Role of Copper in Tau-Related Pathology in Alzheimer's Disease

All tauopathies, including Alzheimer's disease (AD), are characterized by the intracellular accumulation of abnormal forms of tau protein in neurons and glial cells, which negatively affect microtubule stability. Under physiological conditions, tubulin-associated unit (Tau) protein is intrinsically disordered, almost without secondary structure, and is not prone to aggregation. In AD, it assembles, and forms paired helical filaments (PHFs) that further build-up neurofibrillary tangles (NFTs). Aggregates are composed of hyperphosphorylated tau protein that is more prone to aggregation. The pathology of AD is also linked to disturbed copper homeostasis, which promotes oxidative stress (OS). Copper imbalance is widely observed in AD patients. Deregulated copper ions may initiate and exacerbate tau hyperphosphorylation and formation of β-sheet-rich tau fibrils that ultimately contribute to synaptic failure, neuronal death, and cognitive decline observed in AD patients. The present review summarizes factors affecting the process of tau aggregation, conformational changes of small peptide sequences in the microtubule-binding domain required for these motifs to act as seeding sites in aggregation, and the role of copper in OS induction, tau hyperphosphorylation and tau assembly. A better understanding of the various factors that affect tau aggregation under OS conditions may reveal new targets and novel pharmacological approaches for the therapy of AD.

Toxicity of bean cooking media containing EDTA in mice

The possible renal and hepatic toxicities of ethylenediaminetetraacetic acid (EDTA) in bean cooking media were studied using 100 male albino mice. Two sublethal doses of EDTA were used to explore their toxic effects; 20 mg/kg and 200 mg/kg, which corresponded to 1/100th and 1/10th of LD₅₀, respectively. Accordingly, the toxicity study was performed using 50 mice, divided into five groups (n = 10/group) as follows: group 1 (Gp1) served as a negative control and was orally administered normal saline; group 2 (Gp2) was administered the bean cooking medium; group 3 (Gp3) was administered EDTA (200 mg/kg); group 4 (Gp4) was administered bean cooking medium containing 20 mg/kg of EDTA; and group 5 (Gp5) was administered bean cooking medium containing 200 mg/kg of EDTA. The results showed no significant changes in liver and kidney functions in Gp2 while Gp3, Gp4, and Gp5 exhibited significant increases in adverse liver and kidney function markers. Hematocrit values were significantly decreased in Gp3 and Gp5, while the total white blood cells counts were significantly decreased in Gp3 and significantly increased in Gp5. The number of platelets was decreased in Gp3, Gp4, and Gp5. The blood levels of sodium (Na⁺), iron (Fe²⁺), and calcium (Ca²⁺) were decreased in Gp3, Gp4, and Gp5 due to the chelating effects of EDTA. The hepatic and renal architectures were disorganized in Gp3, Gp4, and Gp5 with some hemorrhagic manifestations in livers and kidneys of mice. These results demonstrate that EDTA in bean cooking is harmful in mice under the conditions of this study, and the potentially harmful effects in humans supports restricting its use.

Importance of Biometals as Targets in Medicinal Chemistry: An Overview about the Role of Zinc (II) Chelating Agents

Zinc (II) is an important biometal in human physiology. Moreover, in the last two decades, it was deeply studied for its involvement in several pathological states. In particular, the regulation of its concentration in synaptic clefts can be fundamental for the treatment of neurodegenerative diseases, such as Alzheimer’s disease (AD). Zinc (II) is also a constituent of metalloenzymes (i.e., matrix metalloproteinases, MMPs, and carbonic anhydrases, CAs) with catalytic function; therefore, it can be an important target for the inhibition of these proteins, frequently involved in cancer onset. This review is focused on the significance of zinc (II) chelating agents in past and future medicinal chemistry research, and on the importance of selectivity in order to revamp the possibility of their use in therapy, often hindered by possible side effects.

Pervasive Genomic Damage in Experimental Intracerebral Hemorrhage: Therapeutic Potential of a Mechanistic-Based Carbon Nanoparticle

Therapy for intracerebral hemorrhage (ICH) remains elusive, in part dependent on the severity of the hemorrhage itself as well as multiple deleterious effects of blood and its breakdown products such as hemin and free iron. While oxidative injury and genomic damage have been seen following ICH, the details of this injury and implications remain unclear. Here, we discovered that, while free iron produced mostly reactive oxygen species (ROS)-related single-strand DNA breaks, hemin unexpectedly induced rapid and persistent nuclear and mitochondrial double-strand breaks (DSBs) in neuronal and endothelial cell genomes and in mouse brains following experimental ICH comparable to that seen with γ radiation and DNA-complexing chemotherapies. Potentially as a result of persistent DSBs and the DNA damage response, hemin also resulted in senescence phenotype in cultured neurons and endothelial cells. Subsequent resistance to ferroptosis reported in other senescent cell types was also observed here in neurons. While antioxidant therapy prevented senescence, cells became sensitized to ferroptosis. To address both senescence and resistance to ferroptosis, we synthesized a modified, catalytic, and rapidly internalized carbon nanomaterial, poly(ethylene glycol)-conjugated hydrophilic carbon clusters (PEG-HCC) by covalently bonding the iron chelator, deferoxamine (DEF). This multifunctional nanoparticle, DEF-HCC-PEG, protected cells from both senescence and ferroptosis and restored nuclear and mitochondrial genome integrity in vitro and in vivo. We thus describe a potential molecular mechanism of hemin/iron-induced toxicity in ICH that involves a rapid induction of DSBs, senescence, and the consequent resistance to ferroptosis and provide a mechanistic-based combinatorial therapeutic strategy.

Mercury-induced autoimmunity: Drifting from micro to macro concerns on autoimmune disorders

Mercury (Hg) is widely recognized as a neurotoxic metal, besides it can also act as a proinflammatory agent and immunostimulant, depending on individual exposure and susceptibility. Mercury exposure may arise from internal body pathways, such as via dental amalgams, preservatives in drugs and vaccines, and seafood consumption, or even from external pathways, i.e., occupational exposure, environmental pollution, and handling of metallic items and cosmetics containing Hg. In susceptible individuals, chronic low Hg exposure may trigger local and systemic inflammation, even exacerbating the already existing autoimmune response in patients with autoimmunity. Mercury exposure can trigger dysfunction of the autoimmune responses and aggravate immunotoxic effects associated with elevated serum autoantibodies titers. The purpose of the present review is to provide a critical overview of the many issues associated with Hg exposure and autoimmunity. In addition, the paper focuses on individual susceptibility and other health effects of Hg.

Monoisoamyl DMSA reduced copper-induced neurotoxicity by lowering 8-OHdG level, amyloid beta and Tau protein expressions in Sprague-Dawley rats

Copper dyshomeostasis has long been linked with several neurodegenerative disorders.

Revisiting the intersection of amyloid, pathologically modified tau and iron in Alzheimer's disease from a ferroptosis perspective

The complexity of Alzheimer's disease (AD) complicates the search for effective treatments. While the key roles of pathologically modified proteins has occupied a central role in hypotheses of the pathophysiology, less attention has been paid to the potential role for transition metals overload, subsequent oxidative stress, and tissue injury. The association of transition metals, the major focus heretofore iron and amyloid, the same can now be said for the likely pathogenic microtubular associated tau (MAPT). This review discusses the interplay between iron, pathologically modified tau and oxidative stress, and connects many related discoveries. Basic principles of the transition to pathological MAPT are discussed. Iron, its homeostatic mechanisms, the recently described phenomenon of ferroptosis and purported, although still controversial roles in AD are reviewed as well as considerations to overcome existing hurdles of iron-targeted therapeutic avenues that have been attempted in AD. We summarize the involvement of multiple pathological pathways at different disease stages of disease progression that supports the potential for a combinatorial treatment strategy targeting multiple factors.

Non-enzymatic hydrogen sulfide production from cysteine in blood is catalyzed by iron and vitamin B6

Hydrogen sulfide (H2S) plays important roles in metabolism and health. Its enzymatic generation from sulfur-containing amino acids (SAAs) is well characterized. However, the existence of non-enzymatic H2S production from SAAs, the chemical mechanism, and its biological implications remain unclear. Here we present non-enzymatic H2S production in vitro and in blood via a reaction specific for the SAA cysteine serving as substrate and requires coordinated catalysis by Vitamin B6, pyridoxal(phosphate), and iron under physiological conditions. An initial cysteine-aldimine is formed by nucleophilic attack of the cysteine amino group to the pyridoxal(phosphate) aldehyde group. Free or heme-bound iron drives the formation of a cysteine-quinonoid, thiol group elimination, and hydrolysis of the desulfurated aldimine back to pyridoxal(phosphate). The reaction ultimately produces pyruvate, NH3, and H2S. This work highlights enzymatic production is inducible and robust in select tissues, whereas iron-catalyzed production contributes underappreciated basal H2S systemically with pathophysiological implications in hemolytic, iron overload, and hemorrhagic disorders.

Unravelling protein aggregation as an ageing related process or a neuropathological response

Protein aggregation is normally associated with amyloidosis, namely motor neurone, Alzheimer's, Parkinson's or prion diseases. However, recent results have unveiled a concept of gradual increase of protein aggregation associated with the ageing process, apparently not necessarily associated with pathological conditions. Given that protein aggregation is sufficient to activate stress-response and inflammation, impairing protein synthesis and quality control mechanisms, the former is assumed to negatively affect cellular metabolism and behaviour. In this review the state of the art in protein aggregation research is discussed, namely the relationship between pathology and proteostasis. The role of pathology and ageing in overriding protein quality-control mechanisms, and consequently, the effect of these faulty cellular processes on pathological and healthy ageing, are also addressed.

A Mathematical Model for Amyloid-𝜷 Aggregation in the Presence of Metal Ions: A Timescale Analysis for the Progress of Alzheimer Disease

The aggregation of amyloid-𝛽 (A𝛽) proteins through their self-assembly into oligomers, fibrils, or senile plaques is advocated as a key process of Alzheimer's disease. Recent studies have revealed that metal ions play an essential role in modulating the aggregation rate of amyloid-𝛽 (A𝛽) into senile plaques because of high binding affinity between A𝛽 proteins and metal ions. In this paper, we proposed a mathematical model as a set of coupled kinetic equations that models the self-assembly of amyloid-𝛽 (A𝛽) proteins in the presence of metal ions. The numerical simulations capture four timescales in the A𝛽 dynamics associated with three important events which include the formation of the amyloid-metal complex, the homogeneous aggregation of the amyloid-metal complexes, and the non-homogeneous aggregation of the amyloid-metal complexes. The method of singular perturbation is used to identify these timescales in the framework of slow-fast systems.

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.

An overview of plant-based interventions to ameliorate arsenic toxicity

The industrial and technological advancements in the world have also contributed to the rapid deterioration in the environment quality through introduction of obnoxious pollutants that threaten to destroy the subtle balance in the ecosystem. The environment contaminants cause severe adverse effects to humans, flora and fauna that are mostly irreversible. Chief among these toxicants is arsenic, a metalloid, which is considered among the most dangerous environmental toxins that leads to various diseases which affect the quality of life even when present in small quantities. Treatment of arsenic-mediated disorders still remains a challenge due to lack of effective options. Chelation therapy has been the most widely used method to detoxify arsenic. But this method is associated with deleterious effects leading various toxicities such as hepatotoxicity, neurotoxicity and other adverse effects. It has been discovered that indigenous drugs of plant origin display effective and progressive relief from arsenic-mediated toxicity without any side-effects. Further, these phytochemicals have also been found to aid the elimination of arsenic from the biological system and therefore can be more effective than conventional therapeutic agents in ameliorating arsenic-mediated toxicity. This review presents an overview of the toxic effects of arsenic and the therapeutic strategies that are available to mitigate the toxic effects with emphasis on chelation as well as protective and detoxifying activities of different phytochemicals and herbal drugs against arsenic. This information may serve as a primer in identifying novel prophylactic as well as therapeutic formulations against arsenic-induced toxicity.

Bifunctionality of Iminodiacetic Acid-Modified Lysozyme on Inhibiting Zn2+-Mediated Amyloid β-Protein Aggregation

Aggregation of amyloid β-proteins (Aβ) mediated by metal ions such as Zn²⁺ has been suggested to be implicated in the progression of Alzheimer's disease (AD). Hence, development of bifunctional agents capable of inhibiting Aβ aggregation and modulating metal-Aβ species is an effective strategy for the treatment of AD. In this work, we modified iminodiacetic acid (IDA) onto human lysozyme (hLys) surface to create an inhibitor of Zn²⁺-mediated Aβ aggregation and cytotoxicity. The IDA-modified hLys (IDA-hLys) retained the stability and biocompatibility of native hLys. Extensive biophysical and biological analyses indicated that IDA-hLys significantly attenuated Zn²⁺-mediated Aβ aggregation and cytotoxicity due to its strong binding affinity for Zn²⁺, whereas native hLys showed little effect. Stopped-flow fluorescence spectroscopy showed that IDA-hLys could protect Aβ from Zn²⁺-induced aggregation and rapidly depolymerize Zn²⁺-Aβ aggregates. The research indicates that IDA-hLys is a bifunctional agent capable of inhibiting Aβ fibrillization and modulating Zn²⁺-mediated Aβ aggregation and cytotoxicity as a strong Zn²⁺ chelator.

Membrane partition of bis-(3-hydroxy-4-pyridinonato) zinc(ii) complexes revealed by molecular dynamics simulations

The class of 3-hydroxy-4-pyridinone ligands is widely known and valuable for biomedical and pharmaceutical purposes. Their chelating properties towards biologically-relevant transition metal ions highlight their potential biomedical utility. A set of 3-hydroxy-4-pyridinone Zn(ii) complexes at different concentrations was studied for their ability to interact with lipid phases. We employed umbrella sampling simulations to attain the potential-of-mean force for a set of ligands and one Zn(ii) complex, as these permeated a 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) hydrated bilayer system. In addition, we used conventional molecular dynamics simulations to study the behavior of various Zn(ii) complexes in hydrated bilayer systems. This work discusses: (i) the partition of 3-hydroxy-4-pyridinone ligands to bilayer phases; (ii) self-aggregation in crowded environments of Zn(ii) complexes; and (iii) possible mechanisms for the membrane translocation of Zn(ii) complexes. We observed distinct interactions for the studied complexes, and distinct membrane partition coefficients (K_mem) depending on the considered ligand. The more hydrophobic ligand, 1-hexyl-3-hydroxy-2-methyl-4(1H)-pyridinone, partitioned more favorably to lipid phases (at least two orders of magnitude higher K_mem when compared to the other ligands), and the corresponding Zn(ii) complex was also prone to self-aggregation when an increased concentration of the complex was employed. We also observed that the inclusion of a coordinated water molecule in the parameterization of the Zn(ii) coordination sphere, as proposed in the available crystallographic structure of the complex, decreased the partition coefficient and membrane permeability for the tested complex.

The membrane partition of hydroxypyridinones and of zinc complexes explored by molecular dynamics.