Mechanistic approaches for chemically modifying the coordination sphere of copper-amyloid-ß complexes.

Neurotoxic implications of the interactions between Cu(I/II) and amyloid-ß (Aß) indicate a connection between amyloid cascade hypothesis and metal ion hypothesis with respect to the neurodegeneration associated with Alzheimer's disease (AD). Herein, we report a mechanistic strategy for modifying the first coordination sphere of Cu(II) bound to Aß utilizing a rationally designed peptide modifier, L1. Upon reacting with L1, a metal-binding histidine (His) residue, His14, in Cu(II)-Aß was modified through either covalent adduct formation, oxidation, or both. Consequently, the reactivity of L1 with Cu(II)-Aß was able to disrupt binding of Cu(II) to Aß and result in chemically modified Aß with altered aggregation and toxicity profiles. Our molecular-level mechanistic studies revealed that such L1-mediated modifications toward Cu(II)-Aß could stem from the molecule's ability to 1) interact with Cu(II)-Aß and 2) foster copper-O2 chemistry. Collectively, our work demonstrates the development of an effective approach to modify Cu(II)-Aß at a metal-binding amino acid residue and consequently alter Aß's coordination to copper, aggregation, and toxicity, supplemented with an in-depth mechanistic perspective regarding such reactivity.

Metal Complexes as Promising Matrix Metalloproteinases Regulators.

Nowadays, cancers and dementia, such as Alzheimer's disease, are the most fatal causes of death. Many studies tried to understand the pathogenesis of those diseases clearly and develop a promising way to treat the diseases. Matrix metalloproteinases (MMPs) have been reported to be involved in the pathology of cancers and AD through tumor cell movement and amyloid degradation. Therefore, control of the levels and actions of MMPs, especially MMP-2 and MMP-9, is necessary to care for and/or cure cancer and AD. Various molecules have been examined for their potential application as regulators of MMPs expression and activity. Among the molecules, multiple metal complexes have shown advantages, including simple synthesis, less toxicity and specificity toward MMPs in cancer cells or in the brain. In this review, we summarize the recent studies and knowledge of metal complexes (e.g., Pt-, Ru-, Au-, Fe-, Cu-, Ni-, Zn-, and Sn-complexes) targeting MMPs and their potentials for treating and/or caring the most fatal human diseases, cancers and AD.

Vitamin A, D, E, and K as Matrix Metalloproteinase-2/9 Regulators That Affect Expression and Enzymatic Activity.

Fat-soluble vitamins (vitamin A, D, E, and K) assume a pivotal role in maintaining human homeostasis by virtue of their enzymatic functions. The daily inclusion of these vitamins is imperative to the upkeep of various physiological processes including vision, bone health, immunity, and protection against oxidative stress. Current research highlights fat-soluble vitamins as potential therapeutics for human diseases, especially cancer. Fat-soluble vitamins exert their therapeutic effects through multiple pathways, including regulation of matrix metalloproteinases' (MMPs) expression and enzymatic activity. As MMPs have been reported to be involved in the pathology of various diseases, such as cancers, cardiovascular diseases, and neurological disorders, regulating the expression and/or activity of MMPs could be considered as a potent therapeutic strategy. Here, we summarize the properties of fat-soluble vitamins and their potential as promising candidates capable of effectively modulating MMPs through multiple pathways to treat human diseases.

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

Neurodegenerative diseases pose a substantial socioeconomic burden on society. Unfortunately, the aging world population and lack of effective cures foreshadow a negative outlook. Although a large amount of research has been dedicated to elucidating the pathologies of neurodegenerative diseases, their principal causes remain elusive. Metal ion dyshomeostasis, proteopathy, oxidative stress, and neurotransmitter deficiencies are pathological features shared across multiple neurodegenerative disorders. In addition, these factors are proposed to be interrelated upon disease progression. Thus, the development of multifunctional compounds capable of simultaneously interacting with several pathological components has been suggested as a solution to undertake the complex pathologies of neurodegenerative diseases. In this review, we outline and discuss possible therapeutic targets in Alzheimer's disease, Parkinson's disease, and amyotrophic lateral sclerosis and molecules, previously designed or discovered as potential drug candidates for these disorders with emphasis on multifunctionality. In addition, underrepresented areas of research are discussed to indicate new directions.

Redox-Active Metal Ions and Amyloid-Degrading Enzymes in Alzheimer's Disease.

Redox-active metal ions, Cu(I/II) and Fe(II/III), are essential biological molecules for the normal functioning of the brain, including oxidative metabolism, synaptic plasticity, myelination, and generation of neurotransmitters. Dyshomeostasis of these redox-active metal ions in the brain could cause Alzheimer's disease (AD). Thus, regulating the levels of Cu(I/II) and Fe(II/III) is necessary for normal brain function. To control the amounts of metal ions in the brain and understand the involvement of Cu(I/II) and Fe(II/III) in the pathogenesis of AD, many chemical agents have been developed. In addition, since toxic aggregates of amyloid-ß (Aß) have been proposed as one of the major causes of the disease, the mechanism of clearing Aß is also required to be investigated to reveal the etiology of AD clearly. Multiple metalloenzymes (e.g., neprilysin, insulin-degrading enzyme, and ADAM10) have been reported to have an important role in the degradation of Aß in the brain. These amyloid degrading enzymes (ADE) could interact with redox-active metal ions and affect the pathogenesis of AD. In this review, we introduce and summarize the roles, distributions, and transportations of Cu(I/II) and Fe(II/III), along with previously invented chelators, and the structures and functions of ADE in the brain, as well as their interrelationships.

Minimalistic Principles for Designing Small Molecules with Multiple Reactivities against Pathological Factors in Dementia.

Multiple pathogenic elements, including reactive oxygen species, amyloidogenic proteins, and metal ions, are associated with the development of neurodegenerative disorders. We report minimalistic redox-based principles for preparing compact aromatic compounds by derivatizing the phenylene moiety with various functional groups. These molecular agents display enhanced reactivities against multiple targets such as free radicals, metal-free amyloid-ß (Aß), and metal-bound Aß that are implicated in the most common form of dementia, Alzheimer's disease (AD). Mechanistic studies reveal that the redox properties of these reagents are essential for their function. Specifically, they engage in oxidative reactions with metal-free and metal-bound Aß, leading to chemical modifications of the Aß peptides to form covalent adducts that alter the aggregation of Aß. Moreover, the administration of the most promising candidate significantly attenuates the amyloid pathology in the brains of AD transgenic mice and improves their cognitive defects. Our studies demonstrate an efficient and effective redox-based strategy for incorporating multiple functions into simple molecular reagents.

Towards an understanding of amyloid-ß oligomers: characterization, toxicity mechanisms, and inhibitors.

Alzheimer's disease (AD) is characterized by an imbalance between production and clearance of amyloid-ß (Aß) species. Aß peptides can transform structurally from monomers into ß-stranded fibrils via multiple oligomeric states. Among the various Aß species, structured oligomers are proposed to be more toxic than fibrils; however, the identification of Aß oligomers has been challenging due to their heterogeneous and metastable nature. Multiple techniques have recently helped us gain a better understanding of oligomers' assembly details and structural properties. Moreover, some progress on elucidating the mechanisms of oligomer-triggered toxicity has been made. Based on the collection of current findings, there is growing consensus that control of toxic Aß oligomers could be a valid approach to regulate Aß-associated toxicity, which could advance development of new diagnostics and therapeutics for amyloid-related diseases. In this review, we summarize the recent understanding of Aß oligomers' assembly, structural properties, and toxicity, along with inhibitors against Aß aggregation, including oligomerization.

Molecular Insights into Human Serum Albumin as a Receptor of Amyloid-ß in the Extracellular Region.

Regulation of amyloid-ß (Aß) aggregation by metal ions and proteins is essential for understanding the pathology of Alzheimer's disease (AD). Human serum albumin (HSA), a regulator of metal and protein transportation, can modulate metal-Aß interactions and Aß aggregation in human fluid; however, the molecular mechanisms for such activities remain unclear. Herein, we report the molecular-level complexation between Zn(II), Cu(II), Aß, and HSA, which is able to alter the aggregation and cytotoxicity of Aß peptides and induce their cellular transportation. In addition, a single Aß monomer-bound HSA is observed with the structural change of Aß from a random coil to an α-helix. Small-angle X-ray scattering (SAXS) studies indicate that Aß-HSA complexation causes no structural variation of HSA in solution. Conversely, ion mobility mass spectrometry (IM-MS) results present that Aß prevents the shrinkage of the V-shaped groove of HSA in the gas phase. Consequently, for the first time, HSA is demonstrated to predominantly capture a single Aß monomer at the groove using the phase transfer of a protein heterodimer from solution to the gas phase. Moreover, HSA sequesters Zn(II) and Cu(II) from Aß while maintaining Aß-HSA interaction. Therefore, HSA is capable of controlling metal-free and metal-bound Aß aggregation and aiding the cellular transportation of Aß via Aß-HSA complexation. The overall results and observations regarding HSA, Aß, and metal ions advance our knowledge of how protein-protein interactions associated with Aß and metal ions could be linked to AD pathogenesis.

Structural and Mechanistic Insights into Development of Chemical Tools to Control Individual and Inter-Related Pathological Features in Alzheimer's Disease.

To elucidate the involvement of individual and inter-related pathological factors [i.e., amyloid-ß (Aß), metals, and oxidative stress] in the pathogenesis of Alzheimer's disease (AD), chemical tools have been developed. Characteristics required for such tool construction, however, have not been clearly identified; thus, the optimization of available tools or new design has been limited. Here, key structural properties and mechanisms that can determine tools' regulatory reactivities with multiple pathogenic features found in AD are reported. A series of small molecules was built up through rational structural selection and variations onto the framework of a tool useful for in vitro and in vivo metal-Aß investigation. Variations include: (i) location and number of an Aß interacting moiety; (ii) metal binding site; and (iii) denticity and structural flexibility. Detailed biochemical, biophysical, and computational studies were able to provide a foundation of how to originate molecular formulas to devise chemical tools capable of controlling the reactivities of various pathological components through distinct mechanisms. Overall, this multidisciplinary investigation illustrates a structure-mechanism-based strategy of tool invention for such a complicated brain disease.

An Iridium(III) Complex as a Photoactivatable Tool for Oxidation of Amyloidogenic Peptides with Subsequent Modulation of Peptide Aggregation.

Aggregates of amyloidogenic peptides are involved in the pathogenesis of several degenerative disorders. Herein, an iridium(III) complex, Ir-1, is reported as a chemical tool for oxidizing amyloidogenic peptides upon photoactivation and subsequently modulating their aggregation pathways. Ir-1 was rationally designed based on multiple characteristics, including 1) photoproperties leading to excitation by low-energy radiation; 2) generation of reactive oxygen species responsible for peptide oxidation upon photoactivation under mild conditions; and 3) relatively easy incorporation of a ligand on the IrIII center for specific interactions with amyloidogenic peptides. Biochemical and biophysical investigations illuminate that the oxidation of representative amyloidogenic peptides (i.e., amyloid-ß, α-synuclein, and human islet amyloid polypeptide) is promoted by light-activated Ir-1, which alters the conformations and aggregation pathways of the peptides. Additionally, their potential oxidation sites are identified as methionine, histidine, or tyrosine residues. Overall, our studies on Ir-1 demonstrate the feasibility of devising metal complexes as chemical tools suitable for elucidating the nature of amyloidogenic peptides at the molecular level, as well as controlling their aggregation.

Strategic Design of 2,2'-Bipyridine Derivatives to Modulate Metal-Amyloid-ß Aggregation.

The complexity of Alzheimer's disease (AD) stems from the inter-relation of multiple pathological factors upon initiation and progression of the disease. To identify the involvement of metal-bound amyloid-ß (metal-Aß) aggregation in AD pathology, among the pathogenic features found in the AD-affected brain, small molecules as chemical tools capable of controlling metal-Aß aggregation were developed. Herein, we report a new class of 2,2'-bipyridine (bpy) derivatives (1-4) rationally designed to be chemical modulators toward metal-Aß aggregation over metal-free Aß analogue. The bpy derivatives were constructed through a rational design strategy employing straightforward structural variations onto the backbone of a metal chelator, bpy: (i) incorporation of an Aß interacting moiety; (ii) introduction of a methyl group at different positions. The newly prepared bpy derivatives were observed to bind to metal ions [i.e., Cu(II) and Zn(II)] and interact with metal-Aß over metal-free Aß to varying degrees. Distinguishable from bpy, the bpy derivatives (1-3) were indicated to noticeably modulate the aggregation pathways of Cu(II)-Aß and Zn(II)-Aß over metal-free Aß. Overall, our studies of the bpy derivatives demonstrate that the alteration of metal binding properties as well as the installation of an Aß interacting capability onto a metal chelating framework, devised via the rational structure-based design, were able to achieve evident modulating reactivity against metal-Aß aggregation. Obviating the need for complicated structures, our design approach, presented in this work, could be appropriately utilized for inventing small molecules as chemical tools for studying desired metal-related targets in biological systems.

A Redox-Active, Compact Molecule for Cross-Linking Amyloidogenic Peptides into Nontoxic, Off-Pathway Aggregates: In Vitro and In Vivo Efficacy and Molecular Mechanisms.

Chemical reagents targeting and controlling amyloidogenic peptides have received much attention for helping identify their roles in the pathogenesis of protein-misfolding disorders. Herein, we report a novel strategy for redirecting amyloidogenic peptides into nontoxic, off-pathway aggregates, which utilizes redox properties of a small molecule (DMPD, N,N-dimethyl-p-phenylenediamine) to trigger covalent adduct formation with the peptide. In addition, for the first time, biochemical, biophysical, and molecular dynamics simulation studies have been performed to demonstrate a mechanistic understanding for such an interaction between a small molecule (DMPD) and amyloid-ß (Aß) and its subsequent anti-amyloidogenic activity, which, upon its transformation, generates ligand-peptide adducts via primary amine-dependent intramolecular cross-linking correlated with structural compaction. Furthermore, in vivo efficacy of DMPD toward amyloid pathology and cognitive impairment was evaluated employing 5xFAD mice of Alzheimer's disease (AD). Such a small molecule (DMPD) is indicated to noticeably reduce the overall cerebral amyloid load of soluble Aß forms and amyloid deposits as well as significantly improve cognitive defects in the AD mouse model. Overall, our in vitro and in vivo studies of DMPD toward Aß with the first molecular-level mechanistic investigations present the feasibility of developing new, innovative approaches that employ redox-active compounds without the structural complexity as next-generation chemical tools for amyloid management.

Cholesterol and metal ions in Alzheimer's disease.

Cholesterol and metal ions have been suggested to be associated with the onset and progression of Alzheimer's disease (AD). Moreover, recent findings have demonstrated a potential interconnection between these two factors. For example, (a) cholesterol has been shown to be misregulated in AD-afflicted brains, and the aberrant activity of proteins (particularly, apolipoprotein E (ApoE) and 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (HMGR)) has been linked to cholesterol-related AD exacerbation; (b) dyshomeostasis of metal ions associated with misfolded proteins (i.e., amyloid-ß (Aß) aggregates) found in the brains of AD patients is shown to promote oxidative stress leading to the malfunction of multiple proteins, including cytochrome c oxidase (CcO), and Cu/Zn superoxide dismutase (SOD1); (c) metal ion misregulation has also been observed to disrupt the activity of proteins (e.g., HMGR, low-density lipoproteins (LDL)), required for cholesterol production and regulation. Herein, we briefly discuss the potential involvement of cholesterol and metal ions in AD neuropathogenesis in both individual and interrelated manners.

Rational design of a structural framework with potential use to develop chemical reagents that target and modulate multiple facets of Alzheimer's disease.

Alzheimer's disease (AD) is characterized by multiple, intertwined pathological features, including amyloid-ß (Aß) aggregation, metal ion dyshomeostasis, and oxidative stress. We report a novel compound (ML) prototype of a rationally designed molecule obtained by integrating structural elements for Aß aggregation control, metal chelation, reactive oxygen species (ROS) regulation, and antioxidant activity within a single molecule. Chemical, biochemical, ion mobility mass spectrometric, and NMR studies indicate that the compound ML targets metal-free and metal-bound Aß (metal-Aß) species, suppresses Aß aggregation in vitro, and diminishes toxicity induced by Aß and metal-treated Aß in living cells. Comparison of ML to its structural moieties (i.e., 4-(dimethylamino)phenol (DAP) and (8-aminoquinolin-2-yl)methanol (1)) for reactivity with Aß and metal-Aß suggests the synergy of incorporating structural components for both metal chelation and Aß interaction. Moreover, ML is water-soluble and potentially brain permeable, as well as regulates the formation and presence of free radicals. Overall, we demonstrate that a rational structure-based design strategy can generate a small molecule that can target and modulate multiple factors, providing a new tool to uncover and address AD complexity.

Chemical Insights into Topical Agents in Intraocular Pressure Management: From Glaucoma Etiopathology to Therapeutic Approaches.

Glaucoma encompasses a group of optic neuropathies characterized by complex and often elusive etiopathology, involvihttng neurodegeneration of the optic nerve in conjunction with abnormal intraocular pressure (IOP). Currently, there is no cure for glaucoma, and treatment strategies primarily aim to halt disease progression by managing IOP. This review delves into the etiopathology, diagnostic methods, and treatment approaches for glaucoma, with a special focus on IOP management. We discuss a range of active pharmaceutical ingredients used in glaucoma therapy, emphasizing their chemical structure, pharmacological action, therapeutic effectiveness, and safety/tolerability profiles. Notably, most of these therapeutic agents are administered as topical formulations, a critical aspect considering patient compliance and drug delivery efficiency. The classes of glaucoma therapeutics covered in this review include prostaglandin analogs, beta blockers, alpha agonists, carbonic anhydrase inhibitors, Rho kinase inhibitors, and miotic (cholinergic) agents. This comprehensive overview highlights the importance of topical administration in glaucoma treatment, offering insights into the current state and future directions of pharmacological management in glaucoma.

Natural Products as Regulators against Matrix Metalloproteinases for the Treatment of Cancer.

Cancers are currently the major cause of mortality in the world. According to previous studies, matrix metalloproteinases (MMPs) have an impact on tumor cell proliferation, which could lead to the onset and progression of cancers. Therefore, regulating the expression and activity of MMPs, especially MMP-2 and MMP-9, could be a promising strategy to reduce the risk of cancers. Various studies have tried to investigate and understand the pathophysiology of cancers to suggest potent treatments. In this review, we summarize how natural products from marine organisms and plants, as regulators of MMP-2 and MMP-9 expression and enzymatic activity, can operate as potent anticancer agents.

Aconitine Neurotoxicity According to Administration Methods.

We evaluated the toxic effects of aconitine on the human nervous system and its associated factors, and the general clinical characteristics of patients who visited the emergency room due to aconitine intoxication between 2008 and 2017. We also analyzed the differences related to aconitine processing and administration methods (oral pill, boiled in water, and alcohol-soaked), and the clinical characteristics of consciousness deterioration and neurological symptoms. Of the 41 patients who visited the hospital due to aconitine intoxication, 23 (56.1%) were female, and most were older. Aconitine was mainly used for pain control (28 patients, 68.3%) and taken as oral pills (19 patients, 46%). The patients showed a single symptom or a combination of symptoms; neurological symptoms were the most common (21 patients). All patients who took aconitine after processing with alcohol showed neurological symptoms and a higher prevalence of consciousness deterioration. Neurological symptoms occurred most frequently in patients with aconitine intoxication. Although aconitine intoxication presents with various symptoms, its prognosis may vary with the processing method and prevalence of consciousness deterioration during the early stages. Therefore, the administration method and accompanying symptoms should be comprehensively investigated in patients who have taken aconitine to facilitate prompt and effective treatment and better prognoses.

Target Enzymes Considered for the Treatment of Alzheimer's Disease and Parkinson's Disease.

Various amyloidogenic proteins have been suggested to be involved in the onset and progression of neurodegenerative diseases (ND) such as Alzheimer's disease (AD) and Parkinson's disease (PD). Particularly, the aggregation of misfolded amyloid-ß and hyperphosphorylated tau and α-synuclein are linked to the pathogenesis of AD and PD, respectively. In order to care the diseases, multiple small molecules have been developed to regulate the aggregation pathways of these amyloid proteins. In addition to controlling the aggregation of amyloidogenic proteins, maintaining the levels of the proteins in the brain by amyloid degrading enzymes (ADE; neprilysin (NEP), insulin-degrading enzyme (IDE), asparagine endopeptidase (AEP), and ADAM10) is also essential to cure AD and PD. Therefore, numerous biological molecules and chemical agents have been investigated as either inducer or inhibitor against the levels and activities of ADE. Although the side effect of enhancing the activity of ADE could occur, the removal of amyloidogenic proteins could result in a relatively good strategy to treat AD and PD. Furthermore, since the causes of ND are diverse, various multifunctional (multitarget) chemical agents have been designed to control the actions of multiple risk factors of ND, including amyloidogenic proteins, metal ions, and reactive oxygen species. Many of them, however, were invented without considerations of regulating ADE levels and actions. Incorporation of previously created molecules with the chemical agents handling ADE could be a promising way to treat AD and PD. This review introduces the ADE and molecules capable of modulating the activity and expression of ADE.

Multiple reactivities of flavonoids towards pathological elements in Alzheimer's disease: structure-activity relationship.

Amyloid-ß (Aß) accumulation, metal ion dyshomeostasis, oxidative stress, and cholinergic deficit are four major characteristics of Alzheimer's disease (AD). Herein, we report the reactivities of 12 flavonoids against four pathogenic elements of AD: metal-free and metal-bound Aß, free radicals, and acetylcholinesterase. A series of 12 flavonoids was selected based on the molecular structures that are responsible for multiple reactivities including hydroxyl substitution and transfer of the B ring from C2 to C3. Our experimental and computational studies reveal that the catechol moiety, the hydroxyl groups at C3 and C7, and the position of the B ring are important for instilling multiple functions in flavonoids. We establish a structure-activity relationship of flavonoids that should be useful for designing chemical reagents with multiple reactivities against the pathological factors of AD.

Impact of sphingosine and acetylsphingosines on the aggregation and toxicity of metal-free and metal-treated amyloid-ß.

Pathophysiological shifts in the cerebral levels of sphingolipids in Alzheimer's disease (AD) patients suggest a link between sphingolipid metabolism and the disease pathology. Sphingosine (SP), a structural backbone of sphingolipids, is an amphiphilic molecule that is able to undergo aggregation into micelles and micellar aggregates. Considering its structural properties and cellular localization, we hypothesized that SP potentially interacts with amyloid-ß (Aß) and metal ions that are found as pathological components in AD-affected brains, with manifesting its reactivity towards metal-free Aß and metal-bound Aß (metal-Aß). Herein, we report, for the first time, that SP is capable of interacting with both Aß and metal ions and consequently affects the aggregation of metal-free Aß and metal-Aß. Moreover, incubation of SP with Aß in the absence and presence of metal ions results in the aggravation of toxicity induced by metal-free Aß and metal-Aß in living cells. As the simplest acyl derivatives of SP, N-acetylsphingosine and 3-O-acetylsphingosine also influence metal-free Aß and metal-Aß aggregation to different degrees, compared to SP. Such slight structural modifications of SP neutralize its ability to exacerbate the cytotoxicity triggered by metal-free Aß and metal-Aß. Notably, the reactivity of SP and the acetylsphingosines towards metal-free Aß and metal-Aß is determined to be dependent on their formation of micelles and micellar aggregates. Our overall studies demonstrate that SP and its derivatives could directly interact with pathological factors in AD and modify their pathogenic properties at concentrations below and above critical aggregation concentrations.