Advances in Multi-Functional Ligands and the Need for Metal-Related Pharmacology for the Management of Alzheimer Disease

Recent Advancements in Biosensors for the Detection and Characterization of Amyloids: A Review

Modern medicine has increased the human lifespan. However, with an increase in average lifespan risk of amyloidosis increases. Amyloidosis is a condition characterized by protein misfolding and aggregation. Early detection of amyloidosis is crucial, yet conventional diagnostic methods are costly and lack precision, necessitating innovative tools. This review explores recent advancements in diverse amyloid detection methodologies, highlighting the need for interdisciplinary research to develop a miniaturized electrochemical biosensor leveraging nanotechnology. However, the diagnostics industry faces obstacles such as skilled labor shortages, standardized selection processes, and concurrent multi-analyte identification challenges. Research efforts are focused on integrating electrochemical techniques into clinical applications and diagnostics, with the successful transition of miniaturized technologies from development to testing posing a significant hurdle. Label-free transduction techniques like voltammetry and electrochemical impedance spectroscopy (EIS) have gained traction due to their rapid, cost-effective, and user-friendly nature.

Structural, dynamic behaviour, in-vitro and computational investigations of Schiff's bases of 1,3-diphenyl urea derivatives against SARS-CoV-2 spike protein

The COVID-19 has had a significant influence on people's lives across the world. The viral genome has undergone numerous unanticipated changes that have given rise to new varieties, raising alarm on a global scale. Bioactive phytochemicals derived from nature and synthetic sources possess lot of potential as pathogenic virus inhibitors. The goal of the recent study is to report new inhibitors of Schiff bases of 1,3-dipheny urea derivatives against SARS COV-2 spike protein through in-vitro and in-silico approach. Total 14 compounds were evaluated, surprisingly, all the compounds showed strong inhibition with inhibitory values between 79.60% and 96.00% inhibition. Here, compounds 3a (96.00%), 3d (89.60%), 3e (84.30%), 3f (86.20%), 3g (88.30%), 3h (86.80%), 3k (82.10%), 3l (90.10%), 3m (93.49%), 3n (85.64%), and 3o (81.79%) exhibited high inhibitory potential against SARS COV-2 spike protein. While 3c also showed significant inhibitory potential with 79.60% inhibition. The molecular docking of these compounds revealed excellent fitting of molecules in the spike protein receptor binding domain (RBD) with good interactions with the key residues of RBD and docking scores ranging from - 4.73 to - 5.60 kcal/mol. Furthermore, molecular dynamics simulation for 150 ns indicated a strong stability of a complex 3a:6MOJ. These findings obtained from the in-vitro and in-silico study reflect higher potency of the Schiff bases of 1,3-diphenyl urea derivatives. Furthermore, also highlight their medicinal importance for the treatment of SARS COV-2 infection. Therefore, these small molecules could be a possible drug candidate.

Heavy metals toxicity on epigenetic modifications in the pathogenesis of Alzheimer's disease (AD)

Alzheimer's disease (AD) is a progressive decline in cognitive ability and behavior which eventually disrupts daily activities. AD has no cure and the progression rate varies unlikely. Among various causative factors, heavy metals are reported to be a significant hazard in AD pathogenesis. Metal-induced neurodegeneration has been focused globally with thorough research to unravel the mechanistic insights in AD. Recently, heavy metals suggested to play an important role in epigenetic alterations which might provide evidential results on AD pathology. Epigenetic modifications are known to play towards novel therapeutic approaches in treating AD. Though many studies focus on epigenetics and heavy metal implications in AD, there is a lack of research on heavy metal influence on epigenetic toxicity in neurological disorders. The current review aims to elucidate the plausible role of cadmium (Cd), iron (Fe), arsenic (As), copper (Cu), and lithium (Li) metals on epigenetic factors and the increase in amyloid beta and tau phosphorylation in AD. Also, the review discusses the common methods of heavy metal detection to implicate in AD pathogenesis. Hence, from this review, we can extend the need for future research on identifying the mechanistic behavior of heavy metals on epigenetic toxicity and to develop diagnostic and therapeutic markers in AD.

Liquid-liquid phase separation in Alzheimer's disease

The pathological aggregation and misfolding of tau and amyloid-β play a key role in Alzheimer's disease (AD). However, the underlying pathological mechanisms remain unclear. Emerging evidences indicate that liquid-liquid phase separation (LLPS) has great impacts on regulating human health and diseases, especially neurodegenerative diseases. A series of studies have revealed the significance of LLPS in AD. In this review, we summarize the latest progress of LLPS in AD, focusing on the impact of metal ions, small-molecule inhibitors, and proteinaceous partners on tau LLPS and aggregation, as well as toxic oligomerization, the role of LLPS on amyloid-β (Aβ) aggregation, and the cross-interactions between amyloidogenic proteins in AD. Eventually, the fundamental methods and techniques used in LLPS study are introduced. We expect to present readers a deeper understanding of the relationship between LLPS and AD.

Treatment with 1, 10 Phenanthroline-5-Amine Reduced Amyloid Burden in a Mouse Model of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is the most prevalent age-related dementia, and, despite numerous attempts to halt or reverse its devastating progression, no effective therapeutics have yet been confirmed clinically. However, one class of agents that has shown promise is certain metal chelators.

OBJECTIVE

For the novel assessment of the effect of oral administration of 1,10-phenanthroline-5-amine (PAA) on the severity of amyloid plaque load, we used a transgenic (Tg) mouse model with inserted human autosomally dominant (familial) AD genes: amyloid-β protein precursor (AβPP) and tau.

METHODS

AβPP/Tau transgenic mice that model AD were allotted into one of two groups. The control group received no treatment while the experimental group received PAA in their drinking water starting at 4 months of age. All animals were sacrificed at 1 year of age and their brains were stained with two different markers of amyloid plaques, Amylo-Glo+ and HQ-O.

RESULTS

The control animals exhibited numerous dense core plaques throughout the neo- and allo- cortical brain regions. The experimental group treated with PAA, however, showed 62% of the amyloid plaque burden seen in the control group.

CONCLUSIONS

Oral daily dosing with PAA will significantly reduce the amyloid plaque burden in transgenic mice that model AD. The underlying mechanism for this protection is not fully known; however, one proposed mechanism involves inhibiting the "metal-seeding" of Aβ.

Drug Discovery Based on Oxygen and Nitrogen (Non-)Heterocyclic Compounds Developed @LAQV-REQUIMTE/Aveiro

Artur Silva's research group has a long history in the field of medicinal chemistry. The development of new synthetic methods for oxygen (mostly polyphenols, e.g., 2- and 3-styrylchromones, xanthones, flavones) and nitrogen (e.g., pyrazoles, triazoles, acridones, 4-quinolones) heterocyclic compounds in order to be assessed as antioxidant, anti-inflammatory, antidiabetic, and anticancer agents has been the main core work of our research interests. Additionally, the synthesis of steroid-type compounds as anti-Alzheimer drugs as well as of several chromophores as important dyes for cellular imaging broadened our research scope. In this review article, we intend to provide an enlightened appraisal of all the bioactive compounds and their biological properties that were synthesized and studied by our research group in the last two decades.

A Potential Link Between Visceral Obesity and Risk of Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia characterized by the deposition of amyloid beta (Aβ) plaques and tau-neurofibrillary tangles in the brain. Visceral obesity (VO) is usually associated with low-grade inflammation due to higher expression of pro-inflammatory cytokines by adipose tissue. The objective of the present review was to evaluate the potential link between VO and the development of AD. Tissue hypoxia in obesity promotes tissue injury, production of adipocytokines, and release of pro-inflammatory cytokines leading to an oxidative-inflammatory loop with induction of insulin resistance. Importantly, brain insulin signaling is involved in the pathogenesis of AD and lower cognitive function. Obesity and enlargement of visceral adipose tissue are associated with the deposition of Aβ. All of this is consonant with VO increasing the risk of AD through the dysregulation of adipocytokines which affect the development of AD. The activated nuclear factor kappa B (NF-κB) pathway in VO might be a potential link in the development of AD. Likewise, the higher concentration of advanced glycation end-products in VO could be implicated in the pathogenesis of AD. Taken together, different inflammatory signaling pathways are activated in VO that all have a negative impact on the cognitive function and progression of AD except hypoxia-inducible factor 1 which has beneficial and neuroprotective effects in mitigating the progression of AD. In addition, VO-mediated hypoadiponectinemia and leptin resistance may promote the progression of Aβ formation and tau phosphorylation with the development of AD. In conclusion, VO-induced AD is mainly mediated through the induction of oxidative stress, inflammatory changes, leptin resistance, and hypoadiponectinemia that collectively trigger Aβ formation and neuroinflammation. Thus, early recognition of VO by visceral adiposity index with appropriate management could be a preventive measure against the development of AD in patients with VO.

Statins Use in Alzheimer Disease: Bane or Boon from Frantic Search and Narrative Review

Alzheimer’s disease (AD) was used to describe pre-senile dementia to differentiate it from senile dementia, which develops in the adult age group of more than 65 years. AD is characterized by the deposition of amyloid beta (Aβ) plaque and tau-neurofibrillary tangles (TNTs) in the brain. The neuropathological changes in AD are related to the deposition of amyloid plaques, neurofibrillary tangles, and progression of neuroinflammation, neuronal mitochondrial dysfunction, autophagy dysfunction, and cholinergic synaptic dysfunction. Statins are one of the main cornerstone drugs for the management of cardiovascular disorders regardless of dyslipidemia status. Increasing the use of statins, mainly in the elderly groups for primary and secondary prevention of cardiovascular diseases, may affect their cognitive functions. Extensive and prolonged use of statins may affect cognitive functions in healthy subjects and dementia patients. Statins-induced cognitive impairments in both patients and health providers had been reported according to the post-marketing survey. This survey depends mainly on sporadic cases, and no cognitive measures were used. Evidence from prospective and observational studies gives no robust conclusion regarding the beneficial or detrimental effects of statins on cognitive functions in AD patients. Therefore, this study is a narrative review aimed with evidences to the beneficial, detrimental, and neutral effects of statins on AD.

Design, Synthesis, and In Vitro, In Silico and In Cellulo Evaluation of New Pyrimidine and Pyridine Amide and Carbamate Derivatives as Multi-Functional Cholinesterase Inhibitors

Alzheimer disease is an age-linked neurodegenerative disorder representing one of the greatest medical care challenges of our century. Several drugs are useful in ameliorating the symptoms, even if none could stop or reverse disease progression. The standard approach is represented by the cholinesterase inhibitors (ChEIs) that restore the levels of acetylcholine (ACh) by inhibiting the acetylcholinesterase (AChE). Still, their limited efficacy has prompted researchers to develop new ChEIs that could also reduce the oxidative stress by exhibiting antioxidant properties and by chelating the main metals involved in the disease. Recently, we developed some derivatives constituted by a 2-amino-pyrimidine or a 2-amino-pyridine moiety connected to various aromatic groups by a flexible amino-alkyl linker as new dual inhibitors of AChE and butyrylcholinesterase (BChE). Following our previous studies, in this work we explored the role of the flexible linker by replacing the amino group with an amide or a carbamic group. The most potent compounds showed higher selectivity against BChE in respect to AChE, proving also to possess a weak anti-aggregating activity toward Aβ₄₂ and tau and to be able to chelate Cu²⁺ and Fe³⁺ ions. Molecular docking and molecular dynamic studies proposed possible binding modes with the enzymes. It is noteworthy that these compounds were predicted as BBB-permeable and showed low cytotoxicity on the human brain cell line.

Synthesis, physicochemical characterization and neuroprotective evaluation of novel 1-hydroxypyrazin-2(1H)-one iron chelators in an in vitro cell model of Parkinson's disease

Iron dysregulation, dopamine depletion, cellular oxidative stress and α-synuclein protein mis-folding are key neuronal pathological features seen in the progression of Parkinson's disease. Iron chelators endowed with one or more therapeutic modes of action have long been suggested as disease modifying therapies for its treatment. In this study, novel 1-hydroxypyrazin-2(1H)-one iron chelators were synthesized and their physicochemical properties, iron chelation abilities, antioxidant capacities and neuroprotective effects in a cell culture model of Parkinson's disease were evaluated. Physicochemical properties (log β, log D7.4, pL0.5) suggest that these ligands have a poorer ability to penetrate cell membranes and form weaker iron complexes than the closely related 1-hydroxypyridin-2(1H)-ones. Despite this, we show that levels of neuroprotection provided by these ligands against the catecholaminergic neurotoxin 6-hydroxydopamine in vitro were comparable to those seen previously with the 1-hydroxypyridin-2(1H)-ones and the clinically used iron chelator Deferiprone, with two of the ligands restoring cell viability to ≥89% compared to controls. Two of the ligands were endowed with additional phenol moieties in an attempt to derive multifunctional chelators with dual iron chelation/antioxidant activity. However, levels of neuroprotection with these ligands were no greater than ligands lacking this moiety, suggesting the neuroprotective properties of these ligands are due primarily to chelation and passivation of intracellular labile iron, preventing the generation of free radicals and reactive oxygen species that otherwise lead to the neuronal cell death seen in Parkinson's disease.

Umbelliferyloxymethyl phosphonate compounds-weakly binding zinc ionophores with neuroprotective properties

Umbelliferone is a member of the coumarin family of compounds which are known for diverse pharmacological activity including in targets relevant to Alzheimers disease, AD. The toxicity associated with some forms of the amyloid protein, Aβ, and the role of Zn2+ (and other biometals) dyshomeostasis in this, are of great interest in AD and make metal ionophore capability desirable in so called multi target drug ligands MTDLs. A new series of umbelliferyloxymethyl phosphonic acid diethylester compounds (umbelliferyloxymethyl phosphonates) bearing a phosphonate at the 7-position (compounds 1, 3-6), hydrolysis products 2, 2a and 2b from 1 and analogues 7 and 8 of 1 with 7-O to 7-S and 1-O to 1-NH substitutions, are reported. Single crystal X-ray structures of compounds 1, 2 and 2a were determined. In terms of neuroprotective properties, the compounds 1, 2, 3, 4, 5 and 6 at 1 μM concentration, inhibited the toxicity of Aβ1-42 (Aβ42) in both toxic Amyloid Derived Diffusible Ligand (ADDL) and fibrillar (fibril) forms towards rat hippocampal cells. Compound 7 displayed cytotoxicity and 8 failed to inhibit Aβ42 toxicity. Concerning compound-metal ionophore activity (assessed using chemical experiments), despite weak binding to Zn2+ determined from 31P NMR titration of 1 and 2 by ZnCl2, compounds 1, 3, 4, 5 and 6 demonstrated ionophore assisted partition of Zn2+ from water to octanol at micromolar concentrations with efficacy on a par with or better than the chelator MTDL clioquinol (5-chloro-7-iodo-8-hydroxyquinoline). Partition was assessed using furnace Atomic Absorption Spectroscopy (AAS). In further experiments interaction of compound 1 with Zn2+ or it's pathways was inferred by (i) delayed fluorescence response with added Zn2+ in cells treated with FluoZin-3 and (ii) by suppression of Zn2+ promoted aggregation of Aβ42.

Design, synthesis and biological evaluation of naringenin carbamate derivatives as potential multifunctional agents for the treatment of Alzheimer's disease

A series of naringenin derivatives were designed and synthesized as multifunctional anti-Alzheimer's disease (AD) agents. The results showed that these derivatives displayed moderate-to-good acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities at the micromolar range (IC₅₀, 12.91 ~ 62.52 μM for AChE and 0.094 ~ 13.72 μM for BuChE). Specifically, compound 1 showed the highest inhibitory activity against BuChE with the IC₅₀ value of (0.094 ± 0.0054) μM. A Lineweaver-Burk plot and molecular docking studies demonstrated that 1 targeted both the catalytically active site (CAS) and the peripheral anion site (PAS) of BuChE. Besides, all derivatives showed excellent hydroxyl free radicals (·OH) scavenging ability than vitamin C and cyclic voltammetry results displayed that 1 could effectively scavenge superoxide anion radical (·O₂^-). In addition, compound 1 displayed good metal chelating properties and had anti-Aβ aggregation activities. Therefore, compound 1 might be the potential anti-AD agent for further developments.

From Kinase Inhibitors to Multitarget Ligands as Powerful Drug Leads for Alzheimer's Disease using Protein-Templated Synthesis

Multitarget directed ligands (MTDLs) are arising as promising tools to tackle complex diseases. The main goal of this work is to create powerful modulating agents for neurodegenerative disorders. To achieve this aim, we have combined fragments that inhibit key protein kinases involved in the main pathomolecular pathways of Alzheimer's disease (AD) such as tau aggregation, neuroinflammation and decreased neurogenesis, whilst looking for a third action in beta-secretase (BACE1), responsible of β-amyloid production. We obtained well-balanced MTDLs with in vitro activity in three different relevant targets and efficacy in two cellular models of AD. Furthermore, computational studies confirmed how these compounds accommodate adequately into the long and rather narrow BACE1 catalytic site. Finally, we employed in situ click chemistry using BACE1 as protein template as a versatile synthetic tool that allowed us to obtain further MTDLs.

Therapeutic potential of ferulic acid and its derivatives in Alzheimer's disease-A systematic review

Alzheimer's disease (AD) is a progressive neurodegenerative disorder primarily caused by accumulation of amyloid-beta (Aβ) peptide extracellularly and neurofibrillary tangles intracellularly. Recently, it has been shown that oxidative stress and mitochondrial dysregulation play an important role in pathology of AD. Therefore, modulating various targets such as Aβ aggregation, neuro-inflammation, and oxidative stress, genetic factors such as Apolipoprotein E gene (ApoE) are some of the ways to manage AD. Studying the natural products which can act as multifunctional agents could be key toward discovering new therapeutics. Ferulic acid (FA) represents one such natural product, which has exhibited great potential in this regard. Found in the plant cell walls, FA is an antioxidant, free radical scavenger with anti-inflammatory activity. Taking this into consideration, over the years, various derivatives have been reported as anti-AD molecules based on structure of FA. The present review explores the role of FA and its derivatives as therapeutic agents in AD.

Phenothiazine-Tacrine Heterodimers: Pursuing Multitarget Directed Approach in Alzheimer's Disease

Since 2002, no clinical candidate against Alzheimer's disease has reached the market; hence, an effective therapy is urgently needed. We followed the so-called "multitarget directed ligand" approach and designed 36 novel tacrine-phenothiazine heterodimers which were in vitro evaluated for their anticholinesterase properties. The assessment of the structure-activity relationships of such derivatives highlighted compound 1dC as a potent and selective acetylcholinesterase inhibitor with IC₅₀ = 8 nM and 1aA as a potent butyrylcholinesterase inhibitor with IC₅₀ = 15 nM. Selected hybrids, namely, 1aC, 1bC, 1cC, 1dC, and 2dC, showed a significant inhibitory activity toward τ_(306-336) peptide aggregation with percent inhibition ranging from 50.5 to 62.1%. Likewise, 1dC and 2dC exerted a remarkable ability to inhibit self-induced Aβ_1-42 aggregation. Notwithstanding, in vitro studies displayed cytotoxicity toward HepG2 cells and cerebellar granule neurons; no pathophysiological abnormality was observed when 1dC was administered to mice at 14 mg/kg (i.p.). 1dC was also able to permeate to the CNS as shown by in vitro and in vivo models. The maximum brain concentration was close to the IC₅₀ value for acetylcholinesterase inhibition with a relatively slow elimination half-time. 1dC showed an acceptable safety and good pharmacokinetic properties and a multifunctional biological profile.

Design, Synthesis, and Molecular Docking of Some Novel Tacrine Based Cyclopentapyranopyridine- and Tetrahydropyranoquinoline-Kojic Acid Derivatives as Anti-Acetylcholinesterase Agents

A novel series of tacrine based cyclopentapyranopyridine- and tetrahydropyranoquinoline-kojic acid derivatives were designed, synthesized, and evaluated as anti-cholinesterase agents. The chemical structures of all target compounds were characterized by ¹ H-NMR, ¹³ C-NMR, and elemental analyses. The synthesized compounds mostly inhibited acetylcholinesterase enzyme (AChE) with IC₅₀ values of 4.18-48.71 μM rather than butyrylcholinesterase enzyme (BChE) with IC₅₀ values of >100 μM. Among them, cyclopentapyranopyridine-kojic acid derivatives showed slightly better AChE inhibitory activity compared to tetrahydropyranoquinoline-kojic acid. The compound 10-amino-2-(hydroxymethyl)-11-(4-isopropylphenyl)-7,8,9,11-tetrahydro-4H-cyclopenta[b]pyrano[2',3' : 5,6]pyrano[3,2-e]pyridin-4-one (6f) bearing 4-isopropylphenyl moiety and cyclopentane ring exhibited the highest anti-AChE activity with IC₅₀ value of 4.18 μM. The kinetic study indicated that the compound 6f acts as a mixed inhibitor and the molecular docking studies also illustrated that the compound 6f binds to both the catalytic site (CS) and peripheral anionic site (PAS) of AChE. The compound 6f showed moderate neuroprotective properties against H₂ O₂ -induced cytotoxicity in PC12 cells. The theoretical ADME study also predicted good drug-likeness for the compound 6f. Based on these results, the compound 6f seems to be a very promising AChE inhibitor for the treatment of Alzheimer's disease.

Neuropeptides: Roles and Activities as Metal Chelators in Neurodegenerative Diseases

Neurodegenerative diseases, such as Alzheimer's disease (AD) and Parkinson's disease (PD), are characterized by deposits of amyloid proteins. The homeostasis of metal ions is crucial for the normal biological functions in the brain. However, in AD and PD, the imbalance of metal ions leads to formation of amyloid deposits. In the past four decades, there has been extensive effort to design compound agents than can chelate metal ions with the aim of preventing the formation of the amyloid deposits. Unfortunately, the compounds to date that were designed were not successful candidates to be used in clinical trials. Neuropeptides are small molecules that are produced and released by neurons. It has been shown that neuropeptides have neuroprotective effects in the brain and reduce the formation of amyloid deposits. This Review Article is focused on the function of neuropeptides as metal chelators. Experimental and computational studies demonstrated that neuropeptides could bind metal ions, such as Cu²⁺ and Zn²⁺. This Review Article provides perspectives and initiates future studies to investigate the role of neuropeptides as metal chelators in neurodegenerative diseases.

NEUROTOXICITY OF METAL MIXTURES

Environmental exposures and/or alterations in the homeostasis of essential transition metals (ETM), such as Fe, Cu, Zn or Mn, are known to contribute to neurodegenerative diseases (ND), such as Alzheimer's Disease (AD) and Parkinson's Disease (PD). Aberrant ETM homeostasis leads to altered distributions, as significant amounts may accumulate in specific brain areas, while causing metal deficiency in others. The disruption of processes reliant on the interplay between these ETM, may lead to loss of metal balance and the ensuing neurotoxicity via shared mechanisms, such as the induction of oxidative stress (OS). Both ETM imbalance and OS may play a role, via complex positive loop processes, in primary neuropathological signatures of AD, such as the accumulation of amyloid plaques and neurofibrillary tangles (NTF), and in PD, α-Syn aggregation and loss of dopamine(DA)rgic neurons. The association between ETM imbalance and ND is rarely approached under the view that metals such as Fe, Cu, Zn and Mn, can act as dangerous endogenous neurotoxic mixtures when their control mechanisms became disrupted. In fact, their presence as mixtures implies intricacies, which should be kept in mind when developing therapies for complex disorders of metal dyshomeostasis, which commonly occur in ND.

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.

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.

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.

Mitochondria and lipid peroxidation in the mechanism of neurodegeneration: Finding ways for prevention

The world's population aging progression renders age-related neurodegenerative diseases to be one of the biggest unsolved problems of modern society. Despite the progress in studying the development of pathology, finding ways for modifying neurodegenerative disorders remains a high priority. One common feature of neurodegenerative diseases is mitochondrial dysfunction and overproduction of reactive oxygen species, resulting in oxidative stress. Although lipid peroxidation is one of the markers for oxidative stress, it also plays an important role in cell physiology, including activation of phospholipases and stimulation of signaling cascades. Excessive lipid peroxidation is a hallmark for most neurodegenerative disorders including Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and many other neurological conditions. The products of lipid peroxidation have been shown to be the trigger for necrotic, apoptotic, and more specifically for oxidative stress-related, that is, ferroptosis and neuronal cell death. Here we discuss the involvement of lipid peroxidation in the mechanism of neuronal loss and some novel therapeutic directions to oppose it.

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.

A Perspective on Multi-target Drugs for Alzheimer's Disease

Alzheimer's disease (AD) has a complex pathophysiology that includes aggregation of pathological proteins, impaired neurotransmission, increased oxidative stress, or microglia-mediated neuroinflammation. Therapeutics targeting only one of these AD-related subpathologies have not yet been successful in the search for a disease-modifying treatment. Therefore, multi-target drugs (MTDs) aiming simultaneously at several subpathologies are expected to be a better approach. However, the concept of MTD is inherently connected with several limitations, which are often ignored during MTD design and development. Here, we provide an overview of the MTD approach and discuss its potential pitfalls in the context of AD treatment. We also put forward ideas to be used in the rational design of MTDs to obtain drugs that are effective against AD.

Rational design, synthesis and biological evaluation of novel multitargeting anti-AD iron chelators with potent MAO-B inhibitory and antioxidant activity

A series of (3-hydroxypyridin-4-one)-coumarin hybrids were developed and investigated as potential multitargeting candidates for the treatment of Alzheimer's disease (AD) through the incorporation of iron-chelating and monoamine oxidase B (MAO-B) inhibition. This combination endowed the hybrids with good capacity to inhibit MAO-B as well as excellent iron-chelating effects. The pFe³⁺ values of the compounds were ranging from 16.91 to 20.16, comparable to more potent than the reference drug deferiprone (DFP). Among them, compound 18d exhibited the most promising activity against MAO-B, with an IC₅₀ value of 87.9 nM. Moreover, compound 18d exerted favorable antioxidant activity, significantly reversed the amyloid-β_1-42 (Aβ_1-42) induced PC12 cell damage. More importantly, 18d remarkably ameliorated the cognitive dysfunction in a scopolamine-induced mice AD model. In brief, a series of hybrids with potential anti-AD effect were successfully obtained, indicating that the design of iron chelators with MAO-B inhibitory and antioxidant activities is an attractive strategy against AD progression.

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.

Bifunctional ligand design for modulating mutant p53 aggregation in cancer

Protein misfolding and aggregation contributes to the development of a wide range of diseases. In cancer, over 50% of diagnoses are attributed to p53 malfunction due to missense mutations, many of which result in protein misfolding and accelerated aggregation. p53 mutations also frequently result in alteration or loss of zinc at the DNA-binding site, which increases aggregation via nucleation with zinc-bound p53. Herein, we designed two novel bifunctional ligands, LI and LH , to modulate mutant p53 aggregation and restore zinc binding using a metallochaperone approach. Interestingly, only the incorporation of iodine function in LI resulted in modulation of mutant p53 aggregation, both in recombinant and cellular environments. Native mass spectrometry shows a protein-ligand interaction for LI , as opposed to LH , which is hypothesized to lead to the distinct difference in the p53 aggregation profile for the two ligands. Incorporation of a di-2-picolylamine binding unit into the ligand design provided efficient intracellular zinc uptake, resulting in metallochaperone capability for both LI and LH . The ability of LI to reduce mutant p53 aggregation results in increased restoration of p53 transcriptional function and mediates both caspase-dependent and -independent cell death pathways. We further demonstrate that LI exhibits minimal toxicity in non-cancerous organoids, and that it is well tolerated in mice. These results demonstrate that iodination of our ligand framework restores p53 function by interacting with and inhibiting mutant p53 aggregation and highlights LI as a suitable candidate for comprehensive in vivo anticancer preclinical evaluations.

Copper Ion Uptake by Chitosan in the Presence of Amyloid-β and Histidine

Alzheimer's disease (AD) is related to the anomalous binding that occurs between amyloid-β peptide (Aβ) and copper ion, through imidazole ring of histidine (His), as stated in the literature. It is also known that high-affinity metal ion chelators can be pharmacologically used as a possible therapeutic approach. In this work, we tested the ability "in vitro" of chitosan (Chi) to reduce Aβ aggregation and Thioflavin T binding assay indicated that chitosan has affinity for Aβ and interferes in its aggregation. We also tested the ability of Chi to uptake copper ions in the presence of Aβ or His. Equilibrium data reveals that chitosan acted as an effective chelating agent competing with Aβ and histidine for copper binding. The addition of histidine or Aβ in the system promotes an unfolding of chitosan chains, as verified by small-angle X-ray scattering. Extended X-ray absorption fine structure and XPS spectra show that new copper interactions with groups containing nitrogen in the presence of histidine may occur. These results can help understanding fundamental chemical interactions among species detected in AD and biopolymers, opening up possibilities for new treatment approaches for this disease.

Preparation and in vitro evaluation of multi-target-directed selenium-chondroitin sulfate nanoparticles in protecting against the Alzheimer's disease

The purpose of this study was to ascertain the effect of selenium-chondroitin sulfate nanoparticles (CS@Se) on multi-target-directed therapy for the treatment of Alzheimer's disease (AD). CS@Se nanoparticles were successfully synthesized, and their therapeutic effects were studied in in vitro AD models. CS@Se effectively inhibited amyloid-β (Aβ) aggregation and protected SH-SY5Y cells from Aβ_1-42-induced cytotoxicity. Moreover, CS@Se significantly decreased okadaic acid-induced actin cytoskeleton instability in SH-SY5Y cells. In addition, CS@Se decreased the levels of reactive oxygen species (ROS) and malondialdehyde (MDA) and increased the levels of glutathione peroxidase (GSH-Px). The Western blot results indicated that CS@Se attenuated the hyperphosphorylation of tau (Ser396/Ser404) by regulating the expression of GSK-3β. In summary, this study demonstrated that CS@Se could inhibit the aggregation of Aβ, reduce damage to the cytoskeleton, mitigate oxidative stress and attenuate the hyperphosphorylation of tau protein. CS@Se might be a potent multi-functional agent for the treatment of AD and thus warrants further research and evaluation.

Rebalancing metal dyshomeostasis for Alzheimer's disease therapy

Alzheimer's disease (AD) is a type of neurodegenerative malady that is associated with the accumulation of amyloid plaques. Metal ions are critical for the development and upkeep of brain activity, but metal dyshomeostasis can contribute to the development of neurodegenerative diseases, including AD. This review highlights the association between metal dyshomeostasis and AD pathology, the feasibility of rebalancing metal homeostasis as a therapeutic strategy for AD, and a survey of current drugs that action via rebalancing metal homeostasis. Finally, we discuss the challenges that should be overcome by researchers in the future to enable the practical use of metal homeostasis rebalancing agents for clinical application.

Natural products and their derivatives as multifunctional ligands against Alzheimer's disease

Alzheimer's disease (AD), a complex neurodegenerative disorder causing multiple cellular changes including impaired cholinergic system, beta-amyloid (βA) aggregation, tau hyperphosphorylation, metal dyshomeostasis, neuroinflammation, and many other pathways are involved in the pathogenesis of the disease. However, the exact cause of the disease is not known. Natural products such as flavonoids, alkaloids, resveratrol, and curcumin have multifunctional properties, and have drawn the attention of the researchers because these molecules are capable of interacting concurrently with the multiple targets of AD. Therefore, natural products and their derivatives with proven efficacy could be used in the management of the neurodegenerative disorders. This review focuses on the natural product based multitarget directed ligands like tacrine-coumarin, tacrine-huperzine A, harmine-isoxazoline, berberine-thiophenyl, galantamine-indole, pyridoxine-resveratrol, donepezil-curcumin and their mode of action.

Heavy metal toxicity: An update of chelating therapeutic strategies

AIM

This review illustrates heavy metals toxicity, currently available therapies and the role and efficacy of chelation therapy for its management.

SUMMARY

Heavy metals are necessary for various biological processes, but they become harmful in excess. Specifically, they induce oxidative stress by generating free radicals and reducing antioxidant levels. Heavy metals also alter the confirmation of protein and DNA and inhibit their function. Chelation therapy is commonly used to treat metals toxicity. Chelation is a chemical process that occurs when interaction between a central metal atom/ion and ligand leads to formation of a complex ring-like structure. The ligand has a donor ion/molecule, which has a lone pair of electrons and may be monodentate to polydentate. Each metal has a different reactivity with a ligand, so a specific chelation agent is required for each metal. Combination therapy with a chelating agent and an antioxidant led to improved outcome.

CONCLUSION

Heavy metal poisoning is a common health problem because of mining, smelting, industrial, agricultural and sewage waste. Heavy metals can be efficiently excreted from the body following treatment with proper chelation agents.

Unravelling the interaction mechanism between clioquinol and bovine serum albumin by multi-spectroscopic and molecular docking approaches

Clioquinol has recently been proposed for the treatment of Alzheimer's disease. It is able to diminish β-amyloid protein aggregation and to restore cognition of Alzheimer's mice. However, its therapeutic benefits for Alzheimer's disease in human remain controversy and need further confirmation. Herein, we have explored the interaction mechanism of clioquinol toward bovine serum albumin (BSA) by means of multi-spectroscopic and docking simulation approaches. Clioquinol interacts with BSA by a combined mechanism of static and dynamic processes. Application of the Hill's equation to fluorescence quenching experiment revealed that the binding constant of the BSA-clioquinol complex is extremely high at 10⁸ M^-1 level. Competitive displacement and docking analysis consistently suggested that there are the multiple binding modes of clioquinol toward BSA. Competitive binding study showed that clioquinol shares the binding sites with ibuprofen and digitoxin on albumin, referring to be site II and site III binding compounds. Besides, partial binding in site I was also observed. Docking simulation confirmed that clioquinol favors to bind in site I, site II, site III, fatty acid binding site 5, and the protein cleft between subdomain IB and IIIB of the BSA. Due to its small size and electric dipole property, clioquinol may easily fit in multiple pockets of the BSA. Our finding suggests the potential role of BSA as a clioquinol carrier in the vascular system. Nonetheless, clioquinol-induced BSA aggregation has been observed by the three-dimensional fluorescence technique. This phenomenon may not only impair the BSA, but may also affect other endogenous proteins, which eventually causes adverse effects to human. Therefore, the redesigned or modified molecular structure of clioquinol may reduce its toxicity and improve its bioavailability.

Developments with multi-target drugs for Alzheimer's disease: an overview of the current discovery approaches

Introduction: Alzheimer's disease (AD), the most common type of dementia among older adults, is a chronic neurodegenerative pathology that causes a progressive loss of cognitive functioning with a decline of rational skills. It is well known that AD is multifactorial, so there are many different pharmacological targets that can be pursued. Areas covered: The authors highlight the strategic value of privileged scaffolds in a multi-target lead compound generation against AD, exploring the concept of multi-target design, with a special emphasis on hybrid compounds. Hence, the most promising building blocks for designing and synthesizing hybrid anti-AD drugs are shown, while also presenting the more advanced hybrid compounds. Expert opinion: The available therapeutic arsenal for AD, designed under the traditional paradigm of 'one-drug/one target/one-disease', is based on the inhibition of brain acetylcholinesterase (AChE) to increase acetylcholine (ACh) levels. However, this classical approach has not been sufficiently effective when used to treat any multifactor-depending pathology (cancer, diabetes or AD). The multi-target drug concept has been quickly adopted by medicinal chemists. The basic research developments reported in recent years are a solid foundation that will pave the way for the construction of future AD therapeutics.

Multi-targeted ChEI-copper chelating molecules as neuroprotective agents

The identification of a valid therapeutic treatment for Alzheimer's disease (AD) represents nowadays an urgent and still unmet medical need, since currently available anti-AD drugs only relieve symptoms and show a modest efficacy. Recent evidence indicates that multi-target-directed ligands (MTDLs) can potentially provide an effective strategy to develop innovative therapies directed towards the onset and progression of this multifactorial neurodegenerative disorder. In this work we designed, synthesized and evaluated a new series of MTDLs bearing the rivastigmine skeleton (ChE-inhibitor) linked to known metal-chelating moieties with linkers of different length. For all the novel derivatives, AChE/BuChE inhibitory activity, ROS scavenging activity and potential cytotoxicity have been assessed. For the best compound (4), copper chelating properties and neuroprotective effects were also evaluated. Our data demonstrated that hybrid derivative 4 is able to effectively inhibit AChE and BuChE and to chelate copper, showing a protective action on neurons. These results, although preliminary, indicate that compound 4 can be considered as a possible hit molecule for the development of new anti-AD MTDLs.

Recent Developments in Metal-Based Drugs and Chelating Agents for Neurodegenerative Diseases Treatments

The brain has a unique biological complexity and is responsible for important functions in the human body, such as the command of cognitive and motor functions. Disruptive disorders that affect this organ, e.g. neurodegenerative diseases (NDDs), can lead to permanent damage, impairing the patients' quality of life and even causing death. In spite of their clinical diversity, these NDDs share common characteristics, such as the accumulation of specific proteins in the cells, the compromise of the metal ion homeostasis in the brain, among others. Despite considerable advances in understanding the mechanisms of these diseases and advances in the development of treatments, these disorders remain uncured. Considering the diversity of mechanisms that act in NDDs, a wide range of compounds have been developed to act by different means. Thus, promising compounds with contrasting properties, such as chelating agents and metal-based drugs have been proposed to act on different molecular targets as well as to contribute to the same goal, which is the treatment of NDDs. This review seeks to discuss the different roles and recent developments of metal-based drugs, such as metal complexes and metal chelating agents as a proposal for the treatment of NDDs.

A multifunctional bis-(-)-nor-meptazinol-oxalamide hybrid with metal-chelating property ameliorates Cu(II)-induced spatial learning and memory deficits via preventing neuroinflammation and oxido-nitrosative stress in mice

Excess copper exposure is a risk factor of neurodegeneration related to Alzheimer's disease (AD). Evidence indicates that, besides promoting amyloid β aggregation, activation of neuroinflammation and oxido-nitrosative stress (two key pathophysiological processes of AD) may also play important roles in Cu(II)-induced neuronal injury. Therefore, the copper-chelating strategy has gained attention in search for new anti-AD drugs. We previously reported a novel multifunctional compound N¹,N²-bis(3-(S)-meptazinol-propyl) oxalamide (ZLA), a bis-(-)-nor-meptazinol-oxalamide hybrid with properties of dual binding site acetylcholinesterase (AChE) inhibition and Cu(II)/Zn(II) chelation. The present study was aimed to explore its effect on cognitive deficits caused by intrahippocampal injection of Cu(II) in mice. Results showed that ZLA (2, 5 mg/kg; i.p.) treatment significantly ameliorated the Cu(II)-induced impairment of hippocampus-dependent learning and memory, whereas rivastigmine, an AChE inhibitor showing a similar potency of enzyme inhibition to ZLA, had no obvious effect. Immunohistochemical and Western blot analyses revealed that ZLA attenuated the decrease in hippocampal expression of microtubule-associated protein 2 (MAP2, a dendritic marker) in Cu(II)-challenged mice. Further analysis showed that ZLA suppressed the Cu(II)-evoked microglial activation. Moreover, it inhibited the Cu(II)-evoked production of pro-inflammatory cytokines such as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and IL-1β and expression of inducible nitric oxide synthase in the hippocampus. The Cu(II)-induced oxidative and nitrosative stress in the hippocampus was also attenuated after ZLA treatment. Collectively, these results suggest that ZLA ameliorates the Cu(II)-caused cognitive deficits. Inhibition of neuroinflammation and oxido-nitrosative stress, and thus ameliorating neuronal injury, may be the potential mechanism for the anti-amnesic effect of ZLA.