Iminodiacetic Acid-Modified Human Serum Albumin: A Multifunctional Agent against Metal-Associated Amyloid β-Protein Aggregation and Cytotoxicity

Homeostasis and metabolism of iron and other metal ions in neurodegenerative diseases

As essential micronutrients, metal ions such as iron, manganese, copper, and zinc, are required for a wide range of physiological processes in the brain. However, an imbalance in metal ions, whether excessive or insufficient, is detrimental and can contribute to neuronal death through oxidative stress, ferroptosis, cuproptosis, cell senescence, or neuroinflammation. These processes have been found to be involved in the pathological mechanisms of neurodegenerative diseases. In this review, the research history and milestone events of studying metal ions, including iron, manganese, copper, and zinc in neurodegenerative diseases such as Parkinson's disease (PD), Alzheimer's disease (AD), amyotrophic lateral sclerosis (ALS), and Huntington's disease (HD), will be introduced. Then, the upstream regulators, downstream effector, and crosstalk of mental ions under both physiologic and pathologic conditions will be summarized. Finally, the therapeutic effects of metal ion chelators, such as clioquinol, quercetin, curcumin, coumarin, and their derivatives for the treatment of neurodegenerative diseases will be discussed. Additionally, the promising results and limitations observed in clinical trials of these metal ion chelators will also be addressed. This review will not only provide a comprehensive understanding of the role of metal ions in disease development but also offer perspectives on their modulation for the prevention or treatment of neurodegenerative diseases.

Multifunctional Nanocarriers for Alzheimer's Disease: Befriending the Barriers

Neurodegenerative diseases (NDDs) have been increasing in incidence in recent years and are now widespread worldwide. Neuronal death is defined as the progressive loss of neuronal structure or function which is closely associated with NDDs and represents the intrinsic features of such disorders. Amyotrophic lateral sclerosis, frontotemporal dementia, Alzheimer's, Parkinson's, and Huntington's diseases (AD, PD, and HD, respectively) are considered neurodegenerative diseases that affect a large number of people worldwide. Despite the testing of various drugs, there is currently no available therapy that can remedy or effectively slow the progression of these diseases. Nanomedicine has the potential to revolutionize drug delivery for the management of NDDs. The use of nanoparticles (NPs) has recently been developed to improve drug delivery efficiency and is currently subjected to extensive studies. Nanoengineered particles, known as nanodrugs, can cross the blood-brain barrier while also being less invasive compared to the most treatment strategies in use. Polymeric, magnetic, carbonic, and inorganic NPs are examples of NPs that have been developed to improve drug delivery efficiency. Primary research studies using NPs to cure AD are promising, but thorough research is needed to introduce these approaches to clinical use. In the present review, we discussed the role of metal-based NPs, polymeric nanogels, nanocarrier systems such as liposomes, solid lipid NPs, polymeric NPs, exosomes, quantum dots, dendrimers, polymersomes, carbon nanotubes, and nanofibers and surfactant-based systems for the therapy of neurodegenerative diseases. In addition, we highlighted nanoformulations such as N-butyl cyanoacrylate, poly(butyl cyanoacrylate), D-penicillamine, citrate-coated peptide, magnetic iron oxide, chitosan (CS), lipoprotein, ceria, silica, metallic nanoparticles, cholinesterase inhibitors, an acetylcholinesterase inhibitors, metal chelators, anti-amyloid, protein, and peptide-loaded NPs for the treatment of AD.

Inhibition of Aβ peptide aggregation by ruthenium(II) polypyridyl complexes through copper chelation

Alzheimer's disease (AD) is known as a complex multifactorial syndrome and both metal chelators and amyloid β peptide (Aβ) inhibitors show promise against AD. Herein, four small hybrid compounds have been designed and synthesized utilizing 8-hydroxyquinoline, pyridine or imidazole as chelators and benzimidazole as the recognition moiety for AD treatment. These conjugates can capture Cu²⁺ from Aβ and become dimers upon Cu²⁺ coordination and show high efficiency for both Cu²⁺ elimination and Aβ assembly inhibition. Besides, these designed complexes can inhibit the production of Aβ-induced reactive oxygen species (ROS), protect mitochondria from damage, and improve the survival rate of neuron cells. Our work provides a new strategy to combine hydrophobic interaction and metal ion chelation to design amyloid inhibitors.

The cocrystal of 3-((4-(3-isocyanobenzyl) piperazine-1-yl) methyl) benzonitrile with 5-hydroxy isophthalic acid prevents protofibril formation of serum albumin

The formation of amyloid-like fibrils is a central problem in biophysical chemistry and medicine. Fibril formation and their deposition in various tissues and organs are associated with many human diseases. Searching for molecules able to prevent the formation of fibrils is, therefore, necessary. In this work, we examined the potential of a cocrystal (SS3) of 3-((4-(3-isocyanobenzyl) piperazine-1-yl) methy) benzonitrile with 5-hydroxy isophthalic acid, to prevent fibrillation of human serum albumin. We found that the cocrystal strongly bound to human serum albumin (HSA) with association constant (K_a) of 5.8 ± 0.7 × 10⁵ M^-1. The SS3 binding was found to cause small alterations in both secondary and tertiary structure of the protein. Transmission electron microscopy showed that the cocrystal completely prevented the formation of worm-like protofibrils by HSA at SS3/HSA molar ratio of 1:1. The molecule was found to prevent the aggregation in a concentration dependent manner. It was also observed that most of protein in the presence of SS3 remained in soluble state and the secondary structure contained native-like α-helical structure. Therefore, we conclude that the cocrystal effectively prevented conversion of HSA into worm-like protofibril. These finding suggest that combination of molecules in the form of cocrystal or other stable combination could pave a way for the development of drugs against amyloidosis.Communicated by Ramaswamy H. Sarma.

Near-Infrared Light-Powered Janus Nanomotor Significantly Facilitates Inhibition of Amyloid-β Fibrillogenesis

Inspired by the natural motors, artificial nanomotors (NMs) have emerged as intelligent, advanced, and multifunctional nanoplatforms that can perform complex tasks in living environments. However, the functionalization of these fantastic materials is in its infancy, hindering the success of this booming field. Herein, an inhibitor-conjugated near-infrared (NIR) laser-propelled Janus nanomotor (JNM-I) was constructed and first applied in the modulation of amyloid-β protein (Aβ) aggregation which is highly associated with Alzheimer's disease (AD). Under NIR light illumination, JNM-I exhibited efficient propulsion through the "self-thermophoresis" effect, and the active motion of JNM-I increased the opportunity of the contacts between the immobilized inhibitors and Aβ species, leading to an intensification of JNM-I on modulating the on-pathway Aβ aggregation, as evidenced by the distinct changes of the amyloid morphology, conformation, and cytotoxicity. For example, with a NIR irradiation, 200 μg/mL of JNM-I increased the cultured SH-SY5Y cell viability from 68% to nearly 100%, but it only protected the cells to 89% viability without an NIR irradiation. Meanwhile, the NIR irradiation effectively improved the blood-brain barrier (BBB) penetration of JNM-I. Such a JNM-I has connected artificial nanomotors with protein aggregation and provided new insight into the potential applications of various nanomotors in the prevention and treatment of AD.

Conjugation of RTHLVFFARK to human lysozyme creates a potent multifunctional modulator for Cu2+-mediated amyloid β-protein aggregation and cytotoxicity

Conjugation of alkaline decapeptide (RTHLVFFARK) to lysozyme creates a potent multifunctional modulator (R-hLys) for Cu²⁺-mediated amyloid β-protein aggregation and cytotoxicity.

d-Enantiomeric RTHLVFFARK-NH2: A Potent Multifunctional Decapeptide Inhibiting Cu2+-Mediated Amyloid β-Protein Aggregation and Remodeling Cu2+-Mediated Amyloid β Aggregates

Aggregation of amyloid β-protein (Aβ) into β-sheet-rich plaques is a general feature of Alzheimer's disease (AD). Homeostasis dysregulation of Cu²⁺ mediates Aβ to form high cytotoxic aggregates, which causes cell damage by generation of reactive oxygen species (ROS). To improve the inhibitory potency and explore the multifaceted functions of our previously designed decapeptide, RTHLVFFARK-NH₂ (RK10), we have herein reformulated the decapeptide into its d-enantiomer, rk10, and the effects of chirality on Aβ aggregation, Cu²⁺-mediated Aβ aggregations, and aggregate-remodeling effects were investigated. The results revealed the following: (1) The d-enantiomer presented enhanced inhibitory potency on Aβ fibrillogenesis in comparison to RK10; rk10 and RK10 increased the cell viability from 60% to 91% and 71%, respectively, at an equimolar concentration to Aβ. (2) The enantiomers were chemically equivalent to Cu²⁺ chelation, ROS suppression and oxidative damage rescue. (3) The d-enantiomer exhibited higher performance to inhibit Cu²⁺-mediated Aβ aggregation, and more significantly attenuated the cytotoxicity caused by Aβ₄₂-Cu²⁺ complex than RK10. Cell viability was rescued from 51% to 89% and 74% by coincubating with rk10 and RK10 at 50 μM, respectively. Intracellular ROS levels generated by Aβ₄₂ and Aβ₄₂-Cu²⁺ species were also remarkably decreased by treating with rk10. (4) The enantiomers could remodel mature Aβ₄₂-Cu²⁺ aggregates by Cu²⁺ chelation, and rk10 showed higher performance than RK10, as evidenced by the enhanced cell viability from 57% to 86% by RK10 and to 96% by rk10. The d-enantiomer also showed higher ability than RK10 on protecting the disrupted species from reaggregation. Taken together, D-chiral derivatization of the decapeptide resulted in a potent multifunctional agent in inhibiting Cu²⁺-mediated Aβ aggregation and remodeling mature Aβ-Cu²⁺ species. To the best of our knowledge, this is the first investigation on the chirality effect of a multifunctional peptide inhibitor on Cu²⁺-mediated Aβ aggregation and on the remodeling effect of mature Aβ-Cu²⁺ aggregates. The work provides new insights into the critical role of chirality in the multifaceted functions of peptide inhibitors against amyloid formation and its toxicity.

Therapeutic strategies and nano-drug delivery applications in management of ageing Alzheimer's disease

In recent years, the incidental rate of neurodegenerative disorders has increased proportionately with the aging population. Alzheimer's disease (AD) is one of the most commonly reported neurodegenerative disorders, and it is estimated to increase by roughly 30% among the aged population. In spite of screening numerous drug candidates against various molecular targets of AD, only a few candidates - such as acetylcholinesterase inhibitors are currently utilized as an effective clinical therapy. However, targeted drug delivery of these drugs to the central nervous system (CNS) exhibits several limitations including meager solubility, low bioavailability, and reduced efficiency due to the impediments of the blood-brain barrier (BBB). Current advances in nanotechnology present opportunities to overcome such limitations in delivering active drug candidates. Nanodrug delivery systems are promising in targeting several therapeutic moieties by easing the penetration of drug molecules across the CNS and improving their bioavailability. Recently, a wide range of nano-carriers, such as polymers, emulsions, lipo-carriers, solid lipid carriers, carbon nanotubes, metal based carriers etc., have been adapted to develop successful therapeutics with sustained release and improved efficacy. Here, we discuss few recently updated nano-drug delivery applications that have been adapted in the field of AD therapeutics, and future prospects on potential molecular targets for nano-drug delivery systems.

Redox-Activated Near-Infrared-Responsive Polyoxometalates Used for Photothermal Treatment of Alzheimer's Disease

Adjustable structure, excellent physiochemical properties, and good biocompatibility render polyoxometalates (POMs) as a suitable drug agent for the treatment of Alzheimer's disease (AD). However, previous works using POMs against AD just focus on the inhibition of amyloid-β (Aβ) monomer aggregation. In consideration that both Aβ fibrils and reactive oxygen species (ROS) are closely associated with clinical development of AD symptoms, it would be more effective if POMs can disaggregate Aβ fibrils and eliminate ROS as well. Herein, a redox-activated near-infrared (NIR) responsive POMs-based nanoplaform (rPOMs@MSNs@copolymer) is developed with high photothermal effect and antioxidant activity. The rPOMs@MSNs@copolymer can generate local hyperthermia to disaggregate Aβ fibrils under NIR laser irradiation because of POMs (rPOMs) with strong NIR absorption. Furthermore, Aβ-induced ROS can be scavenged by the antioxidant activity of rPOMs. To the authors' knowledge, there is no report of using rPOMs for NIR photothermal treatment of AD. This work may promote the development of multifunctional inorganic agents for biomedical applications.

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

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