Development of Multifunctional Molecules as Potential Therapeutic Candidates for Alzheimer’s Disease, Parkinson’s Disease, and Amyotrophic Lateral Sclerosis in the Last Decade

Autophagy Regulation Influences β-Amyloid Toxicity in Transgenic Caenorhabditis elegans

Alzheimer’s disease (AD) is a progressive, neurodegenerative disease characterized by the accumulation of amyloid-beta (Aβ) proteins in the form of plaques that cause a proteostasis imbalance in the brain. Several studies have identified autophagy deficits in both AD patients and AD animal models. Here, we used transgenic Caenorhabditis elegans to study the relationship between autophagy flux and Aβ. We labeled autophagosomes with an advanced fluorescence reporter system, and used this to observe that human Aβ expression caused autophagosome accumulation in C. elegans muscle. The autophagy-related drugs chloroquine and 3-MA were employed to investigate the relationship between changes in autophagic flux and the toxicity of Aβ expression. We found that reducing autophagosome accumulation delayed Aβ-induced paralysis in the CL4176 strain of C. elegans, and alleviated Aβ-induced toxicity, thus having a neuroprotective effect. Finally, we used RNA-sequencing and proteomics to identify genes whose expression was affected by Aβ aggregation in C. elegans. We identified a series of enriched autophagy-related signal pathways, suggesting that autophagosome accumulation impairs Aβ protein homeostasis in nematodes. Thus, maintaining normal autophagy levels appears to be important in repairing the protein homeostasis imbalance caused by Aβ expression.

Composite of gold nanoclusters and basified human serum albumin significantly boosts the inhibition of Alzheimer's β-amyloid by photo-oxygenation

Photo-oxygenation has become an effective way to inhibit Alzheimer's β-amyloid protein (Aβ) fibrillogenesis, which involves oxidative modification of Aβ by photo-oxidants. However, limitations of the current photo-oxidants, such as low biocompatibility and low affinity for Aβ, hinder the progression of the photo-oxygenation strategy. Herein, using human serum albumins (HSA) with binding affinity for Aβ as a platform, we have fabricated HSA-stabilized gold nanoclusters (AuNCs@HSA) and further modified the AuNCs@HSA with ethylenediamine to create basified HSA (HSA-B)-stabilized AuNCs. The basified composite, AuNCs@HSA-B, showed significantly higher potency on the inhibition of β-amyloid formation and capability of reactive oxidative species generation than AuNCs@HSA. In addition to the inhibition effect, under near-infrared (NIR) laser irradiation, AuNCs@HSA-B generated singlet oxygen to oxygenate Aβ monomers, distinctly alleviating Aβ-mediated neurotoxicity at a low concentration. In vivo studies demonstrated that NIR-activated AuNCs@HSA-B promoted the lifespan extension of transgenic C. elegans strain CL2006 by decreasing the Aβ burden. This well-designed AuNCs@HSA-B integrates inhibition, Aβ targeting, and photo-oxygenation, providing new insights into the development of protein-based photo-oxidant against Alzheimer's β-amyloid. STATEMENT OF SIGNIFICANCE: Alzheimer's disease (AD) has been threatening human health for more than 100 years. Recently, researchers have focused on inhibiting β-amyloid protein (Aβ) aggregation by exploring photo-excited biomaterials, which enable modulation of Aβ fibrillization with high spatiotemporal controllability. The present work demonstrates the fabrication of basified human serum albumins (HSA-B)-stabilized gold nanoclusters (AuNCs@HSA-B), and shows the potential of this near-infrared (NIR) laser-activated AuNCs@HSA-B as a photo-oxidant against Aβ aggregation by photo-oxygenation. Our work should open a new horizon in the design of protein-based photo-oxidant for treating AD in the future.

Advancements in the development of multi-target directed ligands for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial irreversible neurological disorder which results in cognitive impairment, loss of cholinergic neurons in synapses of the basal forebrain and neuronal death. Exact pathology of the disease is not yet known however, many hypotheses have been proposed for its treatment. The available treatments including monotherapies and combination therapies are not able to combat the disease effectively because of its complex pathological mechanism. A multipotent drug for AD has the potential to bind or inhibit multiple targets responsible for the progression of the disease like aggregated Aβ, hyperphosphorylated tau proteins, cholinergic and adrenergic receptors, MAO enzymes, overactivated N-methyl-d-aspartate (NMDA), α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptor etc. The traditional approach of one disease-one target-one drug has been rationalized to one drug-multi targets for the chronic diseases like AD and cancer. Thus, over the last decade research focus has been shifted towards the development of multi target directed ligands (MTDLs) which can simultaneously inhibit multiple targets and stop or slow the progression of the disease. The MTDLs can be more effective against AD and eliminate any possibility of drug-drug interactions. Many important active pharmacophore units have been fused, merged or incorporated into different scaffolds to synthesize new potent drugs. In the current article, we have described various hypothesis for AD and effectiveness of the MTDLs treatment strategy is discussed in detail. Different chemical scaffolds and their synthetic strategies have been described and important functionalities are identified in the chemical scaffold that have the potential to bind to the multiple targets. The important leads identified in this study with MTDL characteristics have the potential to be developed as drug candidates for the effective treatment of AD.

Oxidative stress: The core pathogenesis and mechanism of Alzheimer's disease

As the number of patients with Alzheimer's disease (AD) increases, it brings great suffering to their families and causes a heavy socioeconomic burden to society. A vast amount of funds and a mass of research have been devoted to elucidating the pathology of AD. However, the main pathogenesis is still elusive, and its mechanism is not completely clear. Research on the mechanisms of AD mainly focuses on the amyloid cascade, tau protein, neuroinflammation, metal ions, and oxidative stress hypotheses. Oxidative stress is as a bridge that connects the different hypotheses and mechanisms of AD. It is a process that causes neuronal damage and occurs in various pathways. Oxidative stress plays a critical role in AD and can even be considered a crucial central factor in the pathogenesis of AD. Previous reviews have also summarized the role of oxidative stress in AD, but these mainly review a specific signaling pathway. Taking oxidative stress as the central point, this review comprehensively expands on the roles of oxidative stress that are involved in the pathogenesis of AD. The vivid and easy-to-understand figures systematically clarify the connected roles of oxidative stress in AD and allow readers to further understand oxidative stress and AD.

Fluorescent probes for the detection of disease-associated biomarkers

Fluorescent probes have emerged as indispensable chemical tools to the field of chemical biology and medicine. The ability to detect intracellular species and monitor physiological processes has not only advanced our knowledge in biology but has provided new approaches towards disease diagnosis. In this review, we detail the design criteria and strategies for some recently reported fluorescent probes that can detect a wide range of biologically important species in cells and in vivo. In doing so, we highlight the importance of each biological species and their role in biological systems and for disease progression. We then discuss the current problems and challenges of existing technologies and provide our perspective on the future directions of the research area. Overall, we hope this review will provide inspiration for researchers and prove as useful guide for the development of the next generation of fluorescent probes.

A role for bioinorganic chemistry in the reactivation of mutant p53 in cancer

Metal ion dysregulation has been implicated in a number of diseases from neurodegeneration to cancer. While defective metal ion transport mechanisms are known to cause specific diseases of genetic origin, the role of metal dysregulation in many diseases has yet to be elucidated due to the complicated function (both good and bad!) of metal ions in the body. A breakdown in metal ion speciation can manifest in several ways from increased reactive oxygen species (ROS) generation to an increase in protein misfolding and aggregation. In this review, we will discuss the role of Zn in the proper function of the p53 protein in cancer. The p53 protein plays a critical role in the prevention of genome mutations via initiation of apoptosis, DNA repair, cell cycle arrest, anti-angiogenesis, and senescence pathways to avoid propagation of damaged cells. p53 is the most frequently mutated protein in cancer and almost all cancers exhibit malfunction along the p53 pathway. Thus, there has been considerable effort dedicated to restoring normal p53 expression and activity to mutant p53. This includes understanding the relative populations of the Zn-bound and Zn-free p53 in wild-type and mutant forms, and the development of metallochaperones to re-populate the Zn binding site to restore mutant p53 activity. Parallels will be made to the development of multifunctional metal binding agents for modulating the aggregation of the amyloid-beta peptide in Alzheimer's Disease (AD).

A K+-sensitive AND-gate dual-mode probe for simultaneous tumor imaging and malignancy identification

Although molecular imaging probes have the potential to non-invasively diagnose a tumor, imaging probes that can detect a tumor and simultaneously identify tumor malignancy remain elusive. Here, we demonstrate a potassium ion (K⁺) sensitive dual-mode nanoprobe (KDMN) for non-invasive tumor imaging and malignancy identification, which operates via a cascaded ‘AND’ logic gate controlled by inputs of magnetic resonance imaging (MRI) and fluorescence imaging (FI) signals. We encapsulate commercial K⁺ indicators into the hollow cavities of magnetic mesoporous silica nanoparticles, which are subsequently coated with a K⁺-selective membrane that exclusively permits the passage of K⁺ while excluding other cations. The KDMN can readily accumulate in tumors and enhance the MRI contrast after systemic administration. Spatial information of the tumor lesion is thus accessible via MRI and forms the first layer of the ‘AND’ gate. Meanwhile, the KDMN selectively captures K⁺ and prevents interference from other cations, triggering a K⁺-activated FI signal as the second layer of the ‘AND’ gate in the case of a malignant tumor with a high extracellular K⁺ level. This dual-mode imaging approach effectively eliminates false positive or negative diagnostic results and allows for non-invasive imaging of tumor malignancy with high sensitivity and accuracy.

Bioactive Compounds and Their Derivatives: An Insight into Prospective Phytotherapeutic Approach against Alzheimer’s Disease

Alzheimer's disease (AD) is a common neurodegenerative brain disorder that causes cellular response alterations, such as impaired cholinergic mechanism, amyloid-beta (Aβ) AD aggregation, neuroinflammation, and several other pathways. AD is still the most prevalent form of dementia and affects many individuals across the globe. The exact cause of the disorder is obscure. There are yet no effective medications for halting, preventing, or curing AD's progress. Plenty of natural products are isolated from several sources and analyzed in preclinical and clinical settings for neuroprotective effects in preventing and treating AD. In addition, natural products and their derivatives have been promising in treating and preventing AD. Natural bioactive compounds play an active modulatory role in the pathological molecular mechanisms of AD development. This review focuses on natural products from plant sources and their derivatives that have demonstrated neuroprotective activities and maybe promising to treat and prevent AD. In addition, this article summarizes the literature pertaining to natural products as agents in the treatment of AD. Rapid metabolism, nonspecific targeting, low solubility, lack of BBB permeability, and limited bioavailability are shortcomings of most bioactive molecules in treating AD. We can use nanotechnology and nanocarriers based on different types of approaches.

Site-Directed Chemical Modification of Amyloid by Polyoxometalates for Inhibition of Protein Misfolding and Aggregation

Post-translational modification (PTM) of protein can significantly change protein conformation and function. Inspired by the natural PTM, we present a new approach to inhibit amyloid aggregation by chemical PTM modification. Polyoxometalates (POMs) were used as examples of inhibitors of β-amyloid peptide (Aβ) aggregation to illustrate the chemical PTM method. After the POMs were modified with thiazolidinethione (TZ), the resulting POMD-TZ acted as a chemical PTM agent and could covalently modify Aβ site-selectively at Lys16. Multiple biophysical techniques and biochemical assays have been employed to show the superiority of the chemical PTM method compared to traditional Aβ inhibitors. Since Aβ oligomers are more cytotoxic, we further functionalized POMD-TZ with an Aβ-targeted peptide and a fluorescent probe to obtain an "Aβ oligomer sensitive" probe. The use of PTM agents for the site-directed chemical modification of proteins provides a new way to regulate amyloid aggregation.

Fluorescence "Turn-Off" and Colorimetric Sensor for Fe2+, Fe3+, and Cu2+ Ions Based on a 2,5,7-Triarylimidazopyridine Scaffold

Two cyanoimidazopyridine-based sensors (SS1 and SS2) were explored for the colorimetric and fluorometric detection of Fe2+, Fe3+, and Cu2+ ions in the semi-aqueous medium. The "turn-off" fluorescence response of both sensors to these ions was due to the restriction in internal charge transfer. Job's plot and semi-empirical calculations revealed that SS1 and SS2 complexed with Cu2+ ions in a 1:1 ratio and Fe2+/3+ ions in a 2:1 ratio, respectively. The sensors were found to have high binding constant (K a) values and low detection limit values. FMO analysis using the semi-empirical quantum mechanics method revealed the decrease in energy gap after complexation with metal ions. Sensor-coated filter paper strips were prepared and analyzed, where the color changes in the strips could be utilized for the real-time detection of Fe2+, Fe3+, and Cu2+ ions.

Discovery and In Vivo Proof of Concept of a Highly Potent Dual Inhibitor of Soluble Epoxide Hydrolase and Acetylcholinesterase for the Treatment of Alzheimer's Disease

With innumerable clinical failures of target-specific drug candidates for multifactorial diseases, such as Alzheimer's disease (AD), which remains inefficiently treated, the advent of multitarget drug discovery has brought a new breath of hope. Here, we disclose a class of 6-chlorotacrine (huprine)-TPPU hybrids as dual inhibitors of the enzymes soluble epoxide hydrolase (sEH) and acetylcholinesterase (AChE), a multitarget profile to provide cumulative effects against neuroinflammation and memory impairment. Computational studies confirmed the gorge-wide occupancy of both enzymes, from the main site to a secondary site, including a so far non-described AChE cryptic pocket. The lead compound displayed in vitro dual nanomolar potencies, adequate brain permeability, aqueous solubility, human microsomal stability, lack of neurotoxicity, and it rescued memory, synaptic plasticity, and neuroinflammation in an AD mouse model, after low dose chronic oral administration.

Neutral Ligands as Potential 64Cu Chelators for Positron Emission Tomography Imaging Applications in Alzheimer's Disease

Positron emission tomography (PET), which uses positron-emitting radionuclides to visualize and measure processes in the human body, is a useful noninvasive diagnostic tool for Alzheimer's disease (AD). The development of longer-lived radiolabeled compounds is essential for further expansion of the use of PET imaging in healthcare, and diagnostic agents employing longer-lived radionuclides such as ⁶⁴Cu (t_1/2 = 12.7 h, β⁺ = 17%, β^- = 39%, electron capture EC = 43%, and E_max = 0.656 MeV) can accomplish this task. One limitation of ⁶⁴Cu PET agents for neuroimaging applications is their limited lipophilicity due to the presence of several anionic groups needed to ensure strong Cu chelation. Herein, we evaluate a series of neutral chelators containing the 1,4,7-triazacyclononane or 2,11-diaza[3.3](2,6)pyridinophane macrocycles that have pyridyl-containing arms incorporating Aβ-peptide-interacting fragments. The crystal structures of the corresponding Cu complexes confirm that the pyridyl N atoms are involved in binding to Cu. Radiolabeling and autoradiography studies show that the compounds efficiently chelate ⁶⁴Cu, and the resulting complexes exhibit specific binding to the amyloid plaques in the AD mouse brain sections versus wild-type controls.

Chemical Design of Activatable Photoacoustic Probes for Precise Biomedical Applications

Photoacoustic (PA) imaging technology, a three-dimensional hybrid imaging modality that integrates the advantage of optical and acoustic imaging, has great application prospects in molecular imaging due to its high imaging depth and resolution. To endow PA imaging with the ability for real-time molecular visualization and precise biomedical diagnosis, numerous activatable molecular PA probes which can specifically alter their PA intensities upon reacting with the targets or biological events of interest have been developed. This review highlights the recent developments of activatable PA probes for precise biomedical applications including molecular detection of the biotargets and imaging of the biological events. First, the generation mechanism of PA signals will be given, followed by a brief introduction to contrast agents used for PA probe design. Then we will particularly summarize the general design principles for the alteration of PA signals and activatable strategies for developing precise PA probes. Furthermore, we will give a detailed discussion of activatable PA probes in molecular detection and biomedical imaging applications in living systems. At last, the current challenges and outlooks of future PA probes will be discussed. We hope that this review will stimulate new ideas to explore the potentials of activatable PA probes for precise biomedical applications in the future.

Pathological mechanisms and therapeutic strategies for Alzheimer's disease

Alzheimer's disease is a rather complex neurodegenerative disease, which is attributed to a combination of multiple factors. Among the many pathological pathways, synaptic dysfunctions, such as synapses loss and deficits in synaptic plasticity, were thought to be strongly associated with cognitive decline. The deficiencies in various sorts of neurotransmissions are responsible for the multifarious neurodegenerative symptoms in Alzheimer's disease, for example, the cholinergic and glutamatergic deficits for cognitive decline, the excitatory and inhibitory neurotransmission dyshomeostasis for synaptic plasticity deficits and epileptiform symptoms, and the monoamine neurotransmission for neuropsychiatric symptoms. Amyloid cascade hypothesis is the most popular pathological theory to explain Alzheimer's disease pathogenesis and attracts considerable attention. Multiple lines of genetic and pathological evidence support the predominant role of amyloid beta in Alzheimer's disease pathology. Neurofibrillary tangles assembled by microtubule-associated protein tau are other important histopathological characteristics in Alzheimer's disease brains. Cascade of tau toxicity was proved to lead to neuron damage, neuroinflammation and oxidative stress in brain. Ageing is the main risk factor of neurodegenerative diseases, and is associated with inflammation, oxidative stress, reduced metabolism, endocrine insufficiencies and organ failures. These aging related risk factors were also proved to be some of the risk factors contributing to Alzheimer's disease. In Alzheimer's disease drug development, many good therapeutic strategies have been investigated in clinical evaluations. However, complex mechanism of Alzheimer's disease and the interplay among different pathological factors call for the come out of all-powerful therapies with multiple curing functions. This review seeks to summarize some of the representative treatments targeting different pathological pathways currently under clinical evaluations. Multi-target therapies as an emerging strategy for Alzheimer's disease treatment will be highlighted.

Simultaneous visualization and quantification of copper (II) ions in Alzheimer's disease by a near-infrared fluorescence probe

The abnormal accumulation of copper ions (Cu²⁺) is considered to be one of the pathological factors of Alzheimer's disease (AD), but the internal relationship between Cu²⁺ and AD progression is still not fully clear. In this work, a sensitive and selective near-infrared fluorescent copper ion probe (DDP-Cu) was designed for quantification and visualization of Cu²⁺ level in lysates, living cells, living zebrafish and brain tissues of drosophila and mice with AD. By using this probe, we demonstrated that the content of Cu²⁺ in the brains of AD mice and drosophila enhanced nearly 3.5-fold and 4-fold than that of normal mice and drosophila, respectively. More importantly, pathogenesis analysis revealed that elevated Cu²⁺ led to changes in factors closely associated with AD, such as the increasing of reactive oxygen species(ROS), the aggregation of amyloid-β protein (Aβ) and nerve cell cytotoxicity. These findings could promote the understanding of the roles between Cu²⁺ and AD.

Phosphinate-benzoindocyanin fluorescent probe for endogenous mitochondrial peroxynitrite detection in living cells and gallbladder access in inflammatory zebrafish animal models

Potent oxidants such as peroxynitrite (ONOO^-) play important roles in the regulation of different physiopathological processes; their overproduction is thought to potentially cause several diseases in living organisms. Hence, the precise and selective monitoring of ONOO^- is imperative for elucidating its interplay and roles in pathological and physiological processes. Herein, we present a novel diphenyl phosphinate-masked benzoindocyanin "turn-on" fluorogenic probe to help detect mitochondrial ONOO^- in living cells and zebrafish models. A pale yellow color solution of BICBzDP turns rose-red upon the addition of ONOO^-_, selectively, contrary to that of other competitive bioactive molecules. BICBzDP displays an ultra-sensitivity detection limit (47.8 nM) with outstanding selectivity and sensitivity towards mitochondrial ONOO^- and possesses a notable 68-fold fluorescence enhancement involving a large redshift of 91 nm. Importantly, further biological experimental investigations with BICBzDP indicate specific sensitivity and reliability of the probe to track the ONOO^- level, not only in live cells, but also demonstrates dynamic fluctuations in the inflammatory zebrafish animal models. Thus, BICBzDP could be employed as a future potential biological tool for exploiting the role of ONOO^- in a variety of different physiological systems.

Bis-Amiridines as Acetylcholinesterase and Butyrylcholinesterase Inhibitors: N-Functionalization Determines the Multitarget Anti-Alzheimer’s Activity Profile

Using two ways of functionalizing amiridine—acylation with chloroacetic acid chloride and reaction with thiophosgene—we have synthesized new homobivalent bis-amiridines joined by two different spacers—bis-N-acyl-alkylene (3) and bis-N-thiourea-alkylene (5) —as potential multifunctional agents for the treatment of Alzheimer’s disease (AD). All compounds exhibited high inhibitory activity against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with selectivity for BChE. These new agents displayed negligible carboxylesterase inhibition, suggesting a probable lack of untoward drug–drug interactions arising from hydrolytic biotransformation. Compounds 3 with bis-N-acyl-alkylene spacers were more potent inhibitors of both cholinesterases compared to compounds 5 and the parent amiridine. The lead compounds 3a–c exhibited an IC₅₀(AChE) = 2.9–1.4 µM, IC₅₀(BChE) = 0.13–0.067 µM, and 14–18% propidium displacement at 20 μM. Kinetic studies of compounds 3a and 5d indicated mixed-type reversible inhibition. Molecular docking revealed favorable poses in both catalytic and peripheral AChE sites. Propidium displacement from the peripheral site by the hybrids suggests their potential to hinder AChE-assisted Aβ₄₂ aggregation. Conjugates 3 had no effect on Aβ₄₂ self-aggregation, whereas compounds 5c–e (m = 4, 5, 6) showed mild (13–17%) inhibition. The greatest difference between conjugates 3 and 5 was their antioxidant activity. Bis-amiridines 3 with N-acylalkylene spacers were nearly inactive in ABTS and FRAP tests, whereas compounds 5 with thiourea in the spacers demonstrated high antioxidant activity, especially in the ABTS test (TEAC = 1.2–2.1), in agreement with their significantly lower HOMO-LUMO gap values. Calculated ADMET parameters for all conjugates predicted favorable blood–brain barrier permeability and intestinal absorption, as well as a low propensity for cardiac toxicity. Thus, it was possible to obtain amiridine derivatives whose potencies against AChE and BChE equaled (5) or exceeded (3) that of the parent compound, amiridine. Overall, based on their expanded and balanced pharmacological profiles, conjugates 5c–e appear promising for future optimization and development as multitarget anti-AD agents.

Treatment of Acute Kidney Injury Using a Dual Enzyme Embedded Zeolitic Imidazolate Frameworks Cascade That Catalyzes In Vivo Reactive Oxygen Species Scavenging

Significant advances have been made in recent years for the utilization of natural enzymes with antioxidant properties to treat acute kidney injury (AKI). However, these enzymes have been of limited clinical utility because of their limited cellular uptake, poor pharmacokinetic properties, and suboptimal stability. We employed a novel biomimetic mineralization approach to encapsulate catalase (CAT) and superoxide dismutase (SOD) in a zeolitic imidazolate framework-8 (ZIF-8). Next, this SOD@CAT@ZIF-8 complex was anchored with MPEG₂₀₀₀-COOH to yield an MPEG₂₀₀₀-SOD@CAT@ZIF-8 (PSCZ) composite. The composite was then used as a stable tool with antioxidant properties for the integrated cascade-based treatment of AKI, remarkably improved intracellular enzyme delivery. This dual-enzyme-embedded metal-organic framework could effectively scavenge reactive oxygen species. In conclusion, the ZIF-8-based "armor plating" represents an effective means of shielding enzymes with improved therapeutic utility to guide the precision medicine-based treatment of AKI.

Computational Molecular Characterization of the Interaction of Acetylcholine and the NMDA Receptor to Explain the Direct Glycine-Competitive Potentiation of NMDA-Mediated Neuronal Currents

The activation of N-methyl-d-aspartate receptor (NMDAR) is triggered by the closure of bilobed (D1 and D2) clamshell-like clefts upon binding glycine (Gly) and glutamate. There is evidence that cholinergic compounds modulate NMDAR-mediated currents via direct receptor-ligand interactions; however, molecular bases are unknown. Here, we first propose a mechanistic structure-based explanation for the observed ACh-induced submaximal potentiation of NMDA-elicited currents in striatal neurons by predicting competitive inhibition with Gly. Then, the model was validated, in principle, by confirming that the coapplication of Gly and ACh significantly reduces these neuronal currents. Finally, we delineate the interplay of ACh with the NMDAR by a combination of computational strategies. Crystallographic ACh-bound complexes were studied, revealing a similar ACh binding environment on the GluN1 subunit of the NMDAR. We illustrate how ACh can occupy X-ray monomeric open, dimeric "semiopen" cleft conformations obtained by molecular dynamics and a full-active cryo-EM NMDAR structure, explaining the suboptimal NMDAR electrophysiological activity under the "Venus Flytrap model". At an evolutionary biology level, the binding mode of ACh coincides with that of the homologous ornithine-bound periplasmic LAO binding protein complex. Our computed results indicate an analogous mechanism of action, inasmuch as ACh may stabilize the GluN1 subunit "semiclosed" conformations by inducing direct and indirect D1-to-D2 interdomain bonds. Additionally, an alternative binding site was detected, shared by the known NMDAR allosteric modulators. Experimental and computed results strongly suggest that ACh acts as a Gly-competitive, submaximal potentiating agent of the NMDAR, possibly constituting a novel chemotype for multitarget-directed drug development, e.g., to treat Alzheimer's, and it may lead to a new understanding of glutamatergic neurotransmission.

Imidazolylacetophenone oxime-based multifunctional neuroprotective agents: Discovery and structure-activity relationships

Alzheimer's disease (AD) possesses a complex pathogenetic mechanism. Nowadays, multitarget agents are considered to have potential in effectively treating AD via triggering molecules in functionally complementary pathways at the same time. Here, based on the screening (∼1400 compounds) against neuroinflammation, an imidazolylacetophenone oxime ether (IOE) was discovered as a novel hit. In order to obtain SARs, a series of imidazolylacetophenone oxime derivatives were constructed, and their C=N bonds were confirmed as the Z configuration by single crystals. These derivatives exhibited potential multifunctional neuroprotective effects including anti-neuroinflammatory, antioxidative damage, metal-chelating, inhibition of acetylcholinesterase (AChE) properties. Among these derivatives, compound 12i displayed the most potent inhibitory activity against nitric oxide (NO) production with EC₅₀ value of 0.57 μM 12i can dose-dependently suppress the expression of iNOS and COX-2 but not change the expression of HO-1 protein. Moreover, 12i exhibited evidently neuroprotective effects on H₂O₂-induced PC12 cells damage and ferroptosis without cytotoxicity at 10 μM, as well as selectively metal chelating properties via chelating Cu²⁺. In addition, 12i showed a mixed-type inhibitory effect on AChE in vitro. The structure-activity relationships (SARs) analysis indicated that dioxolane groups on benzene ring and rigid oxime ester can improve the activity. Parallel artificial membrane permeation assay (PAMPA) also verified that 12i can overcome the blood-brain barrier (BBB). Overall, this is the first report on imidazolylacetophenone oxime-based multifunctional neuroprotective effects, suggesting that this type of compounds might be novel multifunctional agents against AD.

Cognitive enhancement and neuroprotective effects of OABL, a sesquiterpene lactone in 5xFAD Alzheimer's disease mice model

Alzheimer's disease (AD) is a neurodegenerative disease in which oxidative stress and neuroinflammation were demonstrated to be associated with neuronal loss and cognitive deficits. However, there are still no specific treatments that can prevent the progression of AD. In this study, a screening of anti-inflammatory hits from 4207 natural compounds of two different molecular libraries indicated 1,6-O,O-diacetylbritannilactone (OABL), a 1,10-seco-eudesmane sesquiterpene lactone isolated from the herb Inula britannica L., exhibited strong anti-inflammatory activity in vitro as well as favorable BBB penetration property. OABL reduced LPS-induced neuroinflammation in BV-2 microglial cells as assessed by effects on the levels of inflammatory mediators including NO, PGE₂, TNF-α, iNOS, and COX-2, as well as the translocation of NF-κB. Besides, OABL also exhibited pronounced neuroprotective effects against oxytosis and ferroptosis in the rat pheochromocytoma PC12 cell line. For in vivo research, OABL (20 mg/kg B.W., i.p.) for 21 d attenuated the impairments in cognitive function observed in 6-month-old 5xFAD mice, as assessed with the Morris water maze test. OABL restored neuronal damage and postsynaptic density protein 95 (PSD95) expression in the hippocampus. OABL also significantly reduced the accumulation of amyloid plaques, the Aβ expression, the phosphorylation of Tau protein, and the expression of BACE1 in AD mice brain. In addition, OABL attenuated the overactivation of microglia and astrocytes by suppressing the expressions of inflammatory cytokines, and increased glutathione (GSH) and reduced malondialdehyde (MDA) and super oxide dismutase (SOD) levels in the 5xFAD mice brain. In conclusion, these results highlight the beneficial effects of the natural product OABL as a novel treatment with potential application for drug discovery in AD due to its pharmacological profile.

Multifunctional molecules with bipyridyl core ameliorate multifaceted amyloid toxicity

A series of 2,2’-bipyridine derivatives appended with structurally unique biomolecular auxiliaries were synthesized and investigated for their ability to ameliorate multifaceted amyloid toxicity. Our results highlight the roles of metal-chelating...

Systems Biology to Address Unmet Medical Needs in Neurological Disorders

Neurological diseases are highly prevalent and constitute a significant cause of mortality and disability. Neurological disorders encompass a heterogeneous group of neurodegenerative conditions, broadly characterized by injury to the peripheral and/or central nervous system. Although the etiology of neurological diseases varies greatly, they share several characteristics, such as heterogeneity of clinical presentation, non-cell autonomous nature, and diversity of cellular, subcellular, and molecular pathways. Systems biology has emerged as a valuable platform for addressing the challenges of studying heterogeneous neurological diseases. Systems biology has manifold applications to address unmet medical needs for neurological illness, including integrating and correlating different large datasets covering the transcriptome, epigenome, proteome, and metabolome associated with a specific condition. This is particularly useful for disentangling the heterogeneity and complexity of neurological conditions. Hence, systems biology can help in uncovering pathophysiology to develop novel therapeutic targets and assessing the impact of known treatments on disease progression. Additionally, systems biology can identify early diagnostic biomarkers, to help diagnose neurological disease preceded by a long subclinical phase, as well as define the exposome, the collection of environmental toxicants that increase risk of certain neurological diseases. In addition to these current applications, there are numerous potential emergent uses, such as precision medicine.

Hybrid Bis-Histidine Phenanthroline-Based Ligands to Lessen Aβ-Bound Cu ROS Production: An Illustration of Cu(I) Significance

We here report the synthesis of three new hybrid ligands built around the phenanthroline scaffold and encompassing two histidine-like moieties: phenHH, phenHGH and H'phenH', where H correspond to histidine and H' to histamine. These ligands were designed to capture Cu(I/II) from the amyloid-β peptide and to prevent the formation of reactive oxygen species produced by amyloid-β bound copper in presence of physiological reductant (e.g., ascorbate) and dioxygen. The amyloid-β peptide is a well-known key player in Alzheimer's disease, a debilitating and devasting neurological disorder the mankind has to fight against. The Cu-Aβ complex does participate in the oxidative stress observed in the disease, due to the redox ability of the Cu(I/II) ions. The complete characterization of the copper complexes made with phenHH, phenHGH and H'phenH' is reported, along with the ability of ligands to remove Cu from Aβ, and to prevent the formation of reactive oxygen species catalyzed by Cu and Cu-Aβ, including in presence of zinc, the second metal ions important in the etiology of Alzheimer's disease. The importance of the reduced state of copper, Cu(I), in the prevention and arrest of ROS is mechanistically described with the help of cyclic voltammetry experiments.

Characterization of copper(II) specific pyridine containing ligands: Potential metallophores for Alzheimer's disease therapy

Two amide group containing pyridine derivatives, N-(pyridin-2-ylmethyl)picolinamide (PMPA) and N-(pyridin-2-ylmethyl)-2-((pyridin-2-ylmethyl)amino)acetamide (DPMGA), have been investigated as potential metallo-phores in the therapy of Alzheimer's disease. Their complex formation with Cu(II) and Zn(II) were characterized in details. Unexpectedly not only the Cu(II) but also the Zn(II) was able to induce deprotonation of the amide-NH, however, it occurred only at higher pH or at higher metal ion concentrations than the biological conditions. At μM concentration level mono complexes (MLH_-1) dominate with both ligands. Direct fluorescence and reactive oxygen species (ROS) producing measurements prove that both ligands are able to remove Cu(II) from its amyloid-β complexes (CuAβ). Correlation was also established between the conditional stability constant of the Cu(II) complexes with different ligands and their ability of inhibition of ROS production by CuAβ.

Coassembled Chitosan-Hyaluronic Acid Nanoparticles as a Theranostic Agent Targeting Alzheimer's β-Amyloid

β-Amyloid (Aβ) fibrillogenesis is closely associated with the pathogenesis of Alzheimer's disease (AD), so detection and inhibition of Aβ aggregation are of significance for the theranostics of AD. In this work, the coassembled nanoparticles of chitosan and hyaluronic acid cross-linked with glutaraldehyde (CHG NPs) were found to work as a theranostic agent for imaging/probing and inhibition of Aβ fibrillization both in vitro and in vivo. The biomass-based CHG NPs of high stability exhibited a wide range of excitation/emission wavelengths and showed binding affinity toward Aβ aggregates, especially for soluble Aβ oligomers. CHG NPs displayed weak emission in the monodispersed state, while they remarkably emitted increased red fluorescence upon interacting with Aβ oligomers and fibrils, showing high sensitivity with a detection limit of 0.1 nM. By comparing the different fluorescence responses of CHG NPs and Thioflavin T to Aβ aggregation, the Aβ oligomerization rate during nucleation can be determined. Moreover, the fluorescence recognition behavior of CHG NPs was selective. CHG NPs specifically bind to negatively charged amyloid aggregates but not to positively charged amyloids and negatively charged soluble proteins. Such enhancement in fluorescence emission is attributed to the clustering-triggered emission effect of CHG NPs after interaction with Aβ aggregates via various electronic conjugations and hydrogen bonding, electrostatic, and hydrophobic interactions. Besides fluorescent imaging/probing, CHG NPs over 360 μg/mL could almost completely inhibit the formation of Aβ fibrils, exhibiting the capability of regulating Aβ aggregation. In-vivo assays with Caenorhabditis elegans CL2006 demonstrated the potency of CHG NPs as an effective theranostic nanoagent for imaging Aβ plaques and inhibiting Aβ deposition. The findings proved the potential of CHG NPs for development as a potent agent for the diagnosis and treatment of AD.

Caveolin-1: A promising therapeutic target for diverse diseases

The plasma membrane of eukaryotic cells contains small flask-shaped invaginations known as caveolae that are involved in the regulation of cellular signaling. Caveolin-1 is a 21-24kDa protein localized in the caveolar membrane. Caveolin-1 (Cav-1) has been considered as a master regulator among the various signaling molecules. It has been emerging as a chief protein regulating cellular events associated with homeostasis, caveolae formation, and caveolae trafficking. In addition to the physiological role of cav-1, it has a complex role in the progression of various diseases. Caveolin-1 has been identified as a prognosticator in patients with cancer and has a dual role in tumorigenesis. The expression of Cav-1 in hippocampal neurons and synapses is related to neurodegeneration, cognitive decline, and aging. Despite the ubiquitous association of caveolin-1 in various pathological processes, the mechanisms associated with these events are still unclear. Caveolin-1 has a significant role in various events of the viral cycle, such as viral entry. This review will summarize the role of cav-1 in the development of cancer, neurodegeneration, glaucoma, cardiovascular diseases, and infectious diseases. The therapeutic perspectives involving clinical applications of Caveolin-1 have also been discussed. The understanding of the involvement of caveolin-1 in various diseased states provides insights into how it can be explored as a novel therapeutic target.

Neurodegenerative Diseases and Cholesterol: Seeing the Field Through the Players

Neurodegenerative diseases, namely Alzheimer’s (AD), Parkinson’s (PD), and Huntington’s disease (HD) together with amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS), devastate millions of lives per year worldwide and impose an increasing socio-economic burden across nations. Consequently, these diseases occupy a considerable portion of biomedical research aiming to understand mechanisms of neurodegeneration and to develop efficient treatments. A potential culprit is cholesterol serving as an essential component of cellular membranes, as a cofactor of signaling pathways, and as a precursor for oxysterols and hormones. This article uncovers the workforce studying research on neurodegeneration and cholesterol using the TeamTree analysis. This new bibliometric approach reveals the history and dynamics of the teams and exposes key players based on citation-independent metrics. The team-centered view reveals the players on an important field of biomedical research.

Dual-Channel Imaging of Amyloid-β Plaques and Peroxynitrite To Illuminate Their Correlations in Alzheimer's Disease Using a Unimolecular Two-Photon Fluorescent Probe

Alzheimer's disease (AD) involves multiple pathological factors that mutually cooperate and closely contact to form interaction networks for jointly promoting the AD progression. Therefore, the comonitoring of different factors is particularly valuable for elucidating their level dynamics and complex interactions. However, such significant investigations remain a major challenge due to the lack of unimolecular fluorescent probes capable of simultaneous and discriminative visualization of multiple targets. To address this concern, as proof of principle, we rationally designed a unimolecular fluorescent probe to discriminate and simultaneously profile amyloid-β (Aβ) plaques and peroxynitrite (ONOO^-), which are both the pronounced AD pathological factors. Herein, a novel ONOO^- reaction trigger was installed onto an Aβ plaque binding fluorophore to generate a dual functional fluorescent probe, displaying completely separate spectral responses to Aβ plaques and ONOO^- with high selectivity and sensitivity. With this probe, for the first time, we comonitored the distribution and variation of Aβ plaques and ONOO^- through two independent fluorescence channels, demonstrating their close apposition and tight correlation during AD course in live cell and mouse models through two-photon imaging mode. Notably, Aβ aggregates induce the neuronal ONOO^- generation, which conversely facilitates Aβ aggregation. The two critical events, ONOO^- stress and Aβ aggregation, mutually amplify each other through positive feedback mechanisms and jointly promote the AD onset and progression. Furthermore, by coimaging of the level dynamics of Aβ plaques and ONOO^-, we found that the cerebral ONOO^- is a potential biomarker, which emerges earlier than Aβ plaques in transgenic mouse models. Overall, the dual-channel responsive performance renders this probe as a powerful imaging tool to decipher Aβ plaque-ONOO^- interactions, which will facilitate AD-associated molecular pathogenesis elucidation and multitarget drug discovery.

Dual monoamine oxidase B and acetylcholine esterase inhibitors for treating movement and cognition deficits in a C. elegans model of Parkinson's disease

Parkinson's disease (PD) is an age-associated neurodegenerative movement disorder that leads to loss of dopaminergic neurons and motor deficits. Approaches to neuroprotection and symptom management in PD include use of monoamine oxidase B (MAO-B) inhibitors. Many patients with PD also exhibit memory loss in the later stages of disease progression, which is treated with acetylcholine esterase (AChE) inhibitors. We sought to identify a dual-mechanism compound that would inhibit both MAO-B and AChE enzymes. Our screen identified a promising compound (7) with balanced MAO-B (IC₅₀ of 16.83 μM) and AChE inhibition activity (AChE IC₅₀ of 22.04 μM). Application of this compound 7 increased short-term associative memory and significantly prevented 6-hydroxy-dopamine toxicity in dopaminergic neurons in the Caenorhabditis elegans nematode. These findings present a platform for future development of dual-mechanism drugs to treat neurodegenerative diseases such as PD.

A Water-Soluble Peptoid Chelator that Can Remove Cu2+ from Amyloid-β Peptides and Stop the Formation of Reactive Oxygen Species Associated with Alzheimer's Disease

Cu bound to amyloid-β (Aβ) peptides can act as a catalyst for the formation of reactive oxygen species (ROS), leading to neuropathologic degradation associated with Alzheimer's disease (AD). An excellent therapeutic approach is to use a chelator that can selectively remove Cu from Cu-Aβ. This chelator should compete with Zn²⁺ ions (Zn) that are present in the synaptic cleft while forming a nontoxic Cu complex. Herein we describe P3, a water-soluble peptidomimetic chelator that selectively removes Cu²⁺ from Cu-Aβ in the presence of Zn and prevent the formation of ROS even in a reductive environment. We demonstrate, based on extensive spectroscopic analysis, that although P3 extracts Zn from Cu,Zn-Aβ faster than it removes Cu, the formed Zn complexes are kinetic products that further dissociate, while CuP3 is formed as an exclusive stable thermodynamic product. Our unique findings, combined with the bioavailability of peptoids, make P3 an excellent drug candidate in the context of AD.

Bionanoscale Recognition Underlies Cell Fate and Therapy

Understanding the bionanoscale recognition of nanostructured architectures is critical to the design and application of nanomaterials, but the related information is not well understood. In this study, it is found that bionanoscale recognition underlies cell fate and therapy. For example, 1T phase (octahedral coordination) monolayer MoS₂ exhibits a markedly stronger affinity for fibronectin than the 2H structure (triangular prism coordination) and promotes cell spreading and differentiation. The van der Waals energy and increased turn components contribute to the high adhesion of fibronectin onto the 1T-MoS₂ structure. 1T-MoS₂ exhibits a significantly stronger affinity (K_D , 6.59 × 10^-7 m) for liposomes than 2H-MoS₂ (1.21 × 10^-6 m) due to strong hydrophobic interactions. The existence of octahedrally coordinated atomic structures that improve cell viability by enhancing the neurite length is first proven by random forest and structural equation models. Consequently, octahedral coordination disaggregates α-synuclein (e.g., by decreasing β-sheets and increasing coil structures) and protects cells and hosts against Parkinson's disease. As a proof-of-principle demonstration, these findings indicate that bionanoscale recognition underlies the design of biomaterials and cell therapeutics.

Potentiating the Benefits of Melatonin through Chemical Functionalization: Possible Impact on Multifactorial Neurodegenerative Disorders

Although melatonin is an astonishing molecule, it is possible that chemistry will help in the discovery of new compounds derived from it that may exceed our expectations regarding antioxidant protection and perhaps even neuroprotection. This review briefly summarizes the significant amount of data gathered to date regarding the multiple health benefits of melatonin and related compounds. This review also highlights some of the most recent directions in the discovery of multifunctional pharmaceuticals intended to act as one-molecule multiple-target drugs with potential use in multifactorial diseases, including neurodegenerative disorders. Herein, we discuss the beneficial activities of melatonin derivatives reported to date, in addition to computational strategies to rationally design new derivatives by functionalization of the melatonin molecular framework. It is hoped that this review will promote more investigations on the subject from both experimental and theoretical perspectives.

Mechanistic Insight into the Design of Chemical Tools to Control Multiple Pathogenic Features in Alzheimer's Disease

Alzheimer's disease (AD) is the most common form of dementia and is characterized by memory loss and cognitive decline. Approximately 50 million people worldwide are suffering from AD and related dementias. Very recently, the first new drug targeting amyloid-β (Aβ) aggregates has been approved by the United States Food and Drug Administration, but its efficacy against AD is still debatable. Other available treatments temporarily relieve the symptoms of AD. The difficulty in discovering effective therapeutics for AD originates from its complicated nature, which results from the interrelated pathogenic pathways led by multiple factors. Therefore, to develop potent disease-modifying drugs, multiple pathological features found in AD should be fully elucidated.Our laboratory has been designing small molecules as chemical tools to investigate the individual and interrelated pathologies triggered by four pathogenic elements found in the AD-affected brain: metal-free Aβ, metal-bound Aβ, reactive oxygen species (ROS), and acetylcholinesterase (AChE). Aβ peptides are partially folded and aggregate into oligomers, protofibrils, and fibrils. Aβ aggregates are considered to be neurotoxic, causing membrane disruption, aberrant cellular signaling, and organelle dysfunction. In addition, highly concentrated metal ions accumulate in senile plaques mainly composed of Aβ aggregates, which indicates that metal ions can directly interact with Aβ. Metal binding to Aβ affects the aggregation and conformation of the peptide. Moreover, the impaired homeostasis of redox-active Fe(II/III) and Cu(I/II) induces the overproduction of ROS through Fenton chemistry and Fenton-like reactions, respectively. Dysregulated ROS prompt oxidative-stress-damaging biological components such as lipids, proteins, and nucleic acids and, consequently, lead to neuronal death. Finally, the loss of cholinergic transmission mediated by the neurotransmitter acetylcholine (ACh) contributes to cognitive deficits observed in AD.In this Account, we illustrate the design principles for small-molecule-based chemical tools with reactivities against metal-free Aβ, metal-bound Aβ, ROS, and AChE. More importantly, mechanistic details at the molecular level are highlighted with some examples of chemical tools that were developed by our group. The aggregation of metal-free Aβ can be modulated by modifying amino acid residues responsible for self-assembling Aβ or disassembling preformed fibrils. To alter the aggregation and cytotoxicity profiles of metal-bound Aβ, ternary complexation, metal chelation, and modifications onto metal-binding residues can be effective tactics. The presence and production of ROS are able to be controlled by small molecules with antioxidant and metal-binding properties. Finally, inhibiting substrate access or substrate binding at the active site of AChE can diminish its activity, which restores the levels of ACh. Overall, our rational approaches demonstrate the feasibility of developing small molecules as chemical tools that can target and modulate multiple pathological factors associated with AD and can be useful for gaining a greater understanding of the multifaceted pathology of the disease.

Salpyran: A Cu(II) Selective Chelator with Therapeutic Potential

We report the rational design of a tunable Cu(II) chelating scaffold, 2-(((2-((pyridin-2-ylmethyl)amino)ethyl)amino)methyl)phenol, Salpyran (HL). This tetradentate ligand is predicated to have suitable permeation, has an extremely high affinity for Cu compared to clioquinol (pCu_7.4 = 10.65 vs 5.91), and exhibits excellent selectivity for Cu(II) over Zn(II) in aqueous media. Solid and solution studies corroborate the formation of a stable [Cu(II)L]⁺ monocationic species at physiological pH values (7.4). Its action as an antioxidant was tested in ascorbate, tau, and human prion protein assays, which reveal that Salpyran prevents the formation of reactive oxygen species from the binary Cu(II)/H₂O₂ system, demonstrating its potential use as a therapeutic small molecule metal chelator.

Chemical characterization and multifunctional neuroprotective effects of sesquiterpenoid-enriched Inula britannica flowers extract

Dried flowers of Inula britannica commercially serve as pharmaceutical/nutraceutical herbs in the manufacture of medicinal products and functional tea that has been reported to possess extensive biological property. However, the neuroprotective constituents in I. britannica flowers are not known. In the current study, phytochemicals of sesquiterpenoid-enriched I. britannica flowers extract and their potential multifunctional neuroprotective effects were investigated. Nineteen structurally diverse sesquiterpenoids, including two new sesquiterpenoid dimers, namely, inubritanolides A and B (1, 2), and four new sesquiterpenoid monomers (3-6), namely, 1-O-acetyl-6-O-chloracetylbritannilactone (3), 6-methoxybritannilactone (4), 1-hydroxy-10β-methoxy-4αH-1,10-secoeudesma-5(6),11(13)-dien-12,8β-olide (5) and 1-hydroxy-4αH-1,10-secoeudesma-5(6),10(14),11(13)-trien-12,8β-olide (6), as well as 13 known congeners (7-19) were isolated from this source. The structures of compounds 1-6 were elucidated by 1D- and 2D- NMR and HR-ESI-MS data, and their absolute configurations were discerned by electronic circular dichroism (ECD) data analysis and single crystal X-ray diffraction. Interestingly, inubritannolide A (1) is a new type [4 + 2] Diels-Alder dimer featuring a hepta-membered cycloether skeleton. Most of the compounds showed potential multifunctional neuroprotective effects, including antioxidative, anti-neuroinflammatory, and microglial polarization properties. Specifically, 1 and 6 displayed slight strong neuroprotective potency against different types of neuronal cells mediated by various inducers including H₂O₂, 6-hydroxydopamine (6-OHDA), and lipopolysaccharide (LPS). Overall, this is the first report on multifunctional neuroprotective effects of sesquiterpenoid-enriched I. britannica flowers extract, which supports its potential pharmaceutical/nutraceutical application in neurodegenerative diseases.

A diselenide bond-containing ROS-responsive ruthenium nanoplatform delivers nerve growth factor for Alzheimer's disease management by repairing and promoting neuron regeneration

Alzheimer's disease (AD) is an incurable neurodegenerative disease. Repairing damaged nerves and promoting nerve regeneration are key ways to relieve AD symptoms. However, due to the lack of effective strategies to deliver nerve growth factor (NGF) to the brain, achieving neuron regeneration is a major challenge for curing AD. Herein, a ROS-responsive ruthenium nanoplatform (R@NGF-Se-Se-Ru) drug delivery system for AD management by promoting neuron regeneration and Aβ clearance was investigated. Under near-infrared (NIR) irradiation, nanoclusters have good photothermal properties, which can effectively inhibit the aggregation of Aβ and disaggregate Aβ fibrils. Interestingly, the diselenide bond in the nanoclusters is broken, and the nanoclusters are degraded into small ruthenium nanoparticles in the high reactive oxygen species (ROS) environment of the diseased area. Besides, NGF can promote neuronal regeneration and repair damaged nerves. Furthermore, R@NGF-Se-Se-Ru efficiently crosses the blood-brain barrier (BBB) owing to the covalently grafted target peptides of RVG (R). In vivo studies demonstrate that R@NGF-Se-Se-Ru nanoclusters decrease Aβ deposits, inhibit Aβ-induced cytotoxicity, and promote neurite outgrowth. The study confirms that promoting both Aβ clearance and neuron regeneration is an important therapeutic target for anti-AD drugs and provides a novel insight for AD therapy.

Blood-Brain Barrier Permeable and NO-Releasing Multifunctional Nanoparticles for Alzheimer's Disease Treatment: Targeting NO/cGMP/CREB Signaling Pathways

The development of novel therapeutic strategies for combating Alzheimer's disease (AD) is challenging but imperative. Multifunctional nanoparticles are promising tools for regulating complex pathological dysfunctions for AD treatment. Herein, we constructed multifunctional nanoparticles consisting of regadenoson (Reg), nitric oxide (NO) donor, and YC-1 in a single molecular entity that can spontaneously self-assemble into nanoparticles and load donepezil to yield Reg-nanoparticles (Reg-NPs). The Reg moiety enabled the Reg-NPs to effectively regulate tight junction-associated proteins in the blood-brain barrier, thus facilitating the permeation of donepezil through the barrier and its accumulation in the brain. Moreover, the released NO and YC-1 activated the NO/cGMP/CREB signaling pathway by stimulating soluble guanylyl cyclase and inhibiting phosphodiesterase activity, which finally reduced cytotoxicity induced by aggregated Aβ in the neurons and was beneficial for synaptic plasticity and memory formation.

Drug repurposing: small molecules against Cu(II)-amyloid-β and free radicals

Alzheimer's disease (AD) presents a complex pathology entangling numerous pathological factors, including amyloid-β (Aβ), metal ions, and reactive oxygen species (ROS). Increasing evidence reveals pathological connections among these distinct components in AD. For instance, the association between the amyloid cascade and metal ion hypotheses has introduced a novel pathogenic target: metal-bound Aβ. Investigation of such interconnections requires substantial research and can be expedited by chemical reagents that are able to modify multiple pathogenic factors in AD. Drug repurposing is an efficient approach for rediscovering previously utilized molecules with desirable biological and pharmaceutical properties as chemical reagents. Herein, we report the evaluation of three pre-approved drug molecules, selected based on their chemical structure and properties, as chemical reagents that can be used for elucidating the complicated pathology of AD.

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.

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.

Amyloid β-Binding Bifunctional Chelators with Favorable Lipophilicity for 64Cu Positron Emission Tomography Imaging in Alzheimer's Disease

Herein, we report a new series of bifunctional chelators (BFCs) with a high affinity for amyloid aggregates, a strong binding affinity toward Cu(II), and favorable lipophilicity for potential blood-brain barrier penetration. The alkyl carboxylate ester pendant arms offer up to 3 orders of magnitude higher binding affinity toward Cu(II) and enable the BFCs to form stable ⁶⁴Cu-radiolabeled complexes. Among the five compounds tested, the ⁶⁴Cu-YW-7 and ⁶⁴Cu-YW-10 complexes exhibit strong and specific staining of amyloid plaques in ex vivo autoradiography studies. Importantly, these BFCs have promising partition coefficient (log D_oct) values of 0.91-1.26 and show some brain uptake in biodistribution studies using CD-1 mice. Overall, these BFCs could serve as lead compounds for the development of positron emission tomography imaging agents for AD diagnosis.

Near-infrared target enhanced peripheral clearance of amyloid-β in Alzheimer's disease model

Clearance of peripheral amyloid-β (Aβ) has been demonstrated particularly promising for overcoming the blood-brain barrier (BBB) hurdle to remove brain-derived Aβ associated with Alzheimer's disease (AD). However, currently used therapeutic agents targeting peripheral Aβ cannot simultaneously achieve plasma Aβ enrichment and enhanced clearance, which may result in poor bioavailability and rather low efficacy. Moreover, most of therapeutic agents usually promote the unfavorable aggregation of Aβ. Herein, we construct a near-infrared (NIR) regulated surface-transformable and target peptide-guided upconversion platform (UCNP/ONA-P/K), serving as a safe and effective way for Aβ clearance. Taking advantage of extended blood circulation, high selectivity toward Aβ, and surface-transformable property, such UCNP/ONA-P/K can address the challenges of peripheral Aβ clearance by a combination of enhancing the enrichment of plasma Aβ, preventing the unfavorable aggregation of Aβ and simultaneously facilitating the hepatic clearance of the captured Aβ. After verified by a series of systematic toxicity evaluation, cell uptake, deep tissue penetration, and hemolytic experiments, in vivo studies demonstrate that UCNP/ONA-P/K can efficiently decrease brain Aβ burden and reverse memory deficits in 3xTg-AD mice. Overall, this NIR multi-functional design provides a new biocompatible and efficient way for Aβ removal, which will promote the application of peripheral clearance of Aβ for AD treatment.