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.

Circularly Polarized Light Can Override and Amplify Asymmetry in Supramolecular Helices.

Circularly polarized light (CPL) is an inherently chiral entity and is considered one of the possible deterministic signals that led to the evolution of homochirality. While accumulating examples indicate that chirality beyond the molecular level can be induced by CPL, not much is yet known about circumstances where the spin angular momentum of light competes with existing molecular chiral information during the chirality induction and amplification processes. Here we present a light-triggered supramolecular polymerization system where chiral information can both be transmitted and nonlinearly amplified in a "sergeants-and-soldiers" manner. While matching handedness with CPL resulted in further amplification, we determined that opposite handedness could override molecular information at the supramolecular level when the enantiomeric excess was low. The presence of a critical chiral bias suggests a bifurcation point in the homochirality evolution under random external chiral perturbation. Our results also highlight opportunities for the orthogonal control of supramolecular chirality decoupled from molecular chirality preexisting in the system.

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-ß (Aß) 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 Aß, metal-bound Aß, reactive oxygen species (ROS), and acetylcholinesterase (AChE). Aß peptides are partially folded and aggregate into oligomers, protofibrils, and fibrils. Aß 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 Aß aggregates, which indicates that metal ions can directly interact with Aß. Metal binding to Aß 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 Aß, metal-bound Aß, 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 Aß can be modulated by modifying amino acid residues responsible for self-assembling Aß or disassembling preformed fibrils. To alter the aggregation and cytotoxicity profiles of metal-bound Aß, 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.

N,N'-Diacetyl-p-phenylenediamine restores microglial phagocytosis and improves cognitive defects in Alzheimer's disease transgenic mice.

As a central feature of neuroinflammation, microglial dysfunction has been increasingly considered a causative factor of neurodegeneration implicating an intertwined pathology with amyloidogenic proteins. Herein, we report the smallest synthetic molecule (N,N'-diacetyl-p-phenylenediamine [DAPPD]), simply composed of a benzene ring with 2 acetamide groups at the para position, known to date as a chemical reagent that is able to promote the phagocytic aptitude of microglia and subsequently ameliorate cognitive defects. Based on our mechanistic investigations in vitro and in vivo, 1) the capability of DAPPD to restore microglial phagocytosis is responsible for diminishing the accumulation of amyloid-ß (Aß) species and significantly improving cognitive function in the brains of 2 types of Alzheimer's disease (AD) transgenic mice, and 2) the rectification of microglial function by DAPPD is a result of its ability to suppress the expression of NLRP3 inflammasome-associated proteins through its impact on the NF-κB pathway. Overall, our in vitro and in vivo investigations on efficacies and molecular-level mechanisms demonstrate the ability of DAPPD to regulate microglial function, suppress neuroinflammation, foster cerebral Aß clearance, and attenuate cognitive deficits in AD transgenic mouse models. Discovery of such antineuroinflammatory compounds signifies the potential in discovering effective therapeutic molecules against AD-associated neurodegeneration.

A Glycosylated Prodrug to Attenuate Neuroinflammation and Improve Cognitive Deficits in Alzheimer's Disease Transgenic Mice.

We report a prodrug, Glu-DAPPD, to overcome the shortcomings of an anti-neuroinflammatory molecule, N,N'-diacetyl-p-phenylenediamine (DAPPD), in biological applicability for potential therapeutic applications. We suspect that Glu-DAPPD can release DAPPD through endogenous enzymatic bioconversion. Consequently, Glu-DAPPD exhibits in vivo efficacies in alleviating neuroinflammation, reducing amyloid-ß aggregate accumulation, and improving cognitive function in Alzheimer's disease transgenic mice. Our studies demonstrate that the prodrug approach is suitable and effective toward developing drug candidates against neurodegeneration.

Complexation of C-Functionalized Cyclams with Copper(II) and Zinc(II): Similarities and Changes When Compared to Parent Cyclam Analogues.

Herein, we report a comprehensive coordination study of the previously reported ligands cyclam, CB-cyclam, TMC, DMC, and CB-DMC and of their C-functional analogues, cyclam-E, CB-cyclam-E, TMC-E, DMC-E, and CB-DMC-E. This group of ligands includes cyclam, cross-bridged cyclams, their di- or tetramethylated derivatives, and the analogues bearing an additional hydroxyethyl group on one ß-N position of the ring. The Cu(II) and Zn(II) complexes of these macrocycles have been highlighted previously for the biological interest, but the details of their structures in the solid state and in solution remained largely unexplored. In particular, we analyzed the impact that adding noncoordinating N-methyl and C-hydroxyethyl functionalities has in the structures of the complexes. All the Cu(II) and Zn(II) complexes were synthesized and investigated using single crystal X-ray diffraction and NMR, electronic absorption, and EPR spectroscopies, along with DFT studies. Dissociation kinetics experiments in acidic conditions and electrochemical studies were also performed. Special attention was paid to analyze the different configurations present in solution and in the solid state, as well as the impact of the C-appended hydroxyethyl group on the coordination behavior. Various ratios of the trans-I, trans-III, and cis-V configurations have been observed depending on the degree of N-methylation and the presence of the ethylene cross-bridge.

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.

Early experience of pump-controlled retrograde trial off for weaning from veno-arterial extracorporeal membrane oxygenation in adult patients with cardiogenic shock.

INTRODUCTION: Pump-controlled retrograde trial off has recently been introduced as an effective method for weaning from veno-arterial extracorporeal membrane oxygenation in pediatric patients. However, studies on pump-controlled retrograde trial off in adults are still lacking. Thus, this study aimed to examine the outcomes of pump-controlled retrograde trial off for weaning from veno-arterial extracorporeal membrane oxygenation in adult patients. METHODS: Between January 2018 and July 2019, 87 consecutive adult patients underwent veno-arterial extracorporeal membrane oxygenation support, of whom 47 (54.0%) underwent pump-controlled retrograde trial off for weaning from extracorporeal membrane oxygenation and were enrolled in this study. The pump-controlled retrograde trial off results, extracorporeal membrane oxygenation reapplication rate, and clinical outcomes were analyzed. RESULTS: Of the 47 patients, 38 (80.9%) were weaned from veno-arterial extracorporeal membrane oxygenation on the first attempt of pump-controlled retrograde trial off, 5 (10.6%) on the second attempt, and 4 (8.5%) on the third attempt. Three patients were converted to venovenous extracorporeal membrane oxygenation by desaturation but had stable blood pressure during pump-controlled retrograde trial off. No extracorporeal membrane oxygenation reapplication was performed within 3 days after removal, and two patients underwent veno-arterial extracorporeal membrane oxygenation during follow-up. No complications associated with pump-controlled retrograde trial off occurred during the weaning process, including thromboembolic events. Five in-hospital deaths (10.6%) occurred after weaning from extracorporeal membrane oxygenation. CONCLUSION: Pump-controlled retrograde trial off is an effective method to safely wean from veno-arterial extracorporeal membrane oxygenation in adult patients. It is simple and can be easily implemented without additional invasive procedures and may help prevent deterioration of the cardiovascular system after weaning from veno-arterial extracorporeal membrane oxygenation.

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.

Sequential Connection of Mutually Exclusive Catalytic Reactions by a Method Controlling the Presence of an MOF Catalyst: One-Pot Oxidation of Alcohols to Carboxylic Acids.

A functionalized metal-organic framework (MOF) catalyst applied to the sequential one-pot oxidation of alcohols to carboxylic acids controls the presence of a heterogeneous catalyst. The conversion of alcohols to aldehydes was acquired through aerobic oxidation using a well-known amino-oxy radical-functionalized MOF. In the same flask, a simple filtration of the radical MOF with mild heating of the solution completely altered the reaction media, providing radical scavenger-free conditions suitable for the autoxidation of the aldehydes formed in the first step to carboxylic acids. The mutually exclusive radical-catalyzed aerobic oxidation (the first step with MOF) and radical-inhibited autoxidation (the second step without MOF) are sequentially achieved in a one-pot manner. Overall, we demonstrate a powerful and efficient method for the sequential oxidation of alcohols to carboxylic acids by employing a readily functionalizable heterogeneous MOF. In addition, our MOF in-and-out method can be utilized in an environmentally friendly way for the oxidation of alcohols to carboxylic acids of industrial and economic value with broad functional group tolerance, including 2,5-furandicarboxylic acid and 1,4-benzenedicarboxylic acid, with good yield and reusability. Furthermore, MOF-TEMPO, as an antioxidative stabilizer, prevents the undesired oxidation of aldehydes, and the perfect "recoverability" of such a reactive MOF requires a re-evaluation of the advantages of MOFs from heterogeneity in catalytic and related applications.

A multiple target chemosensor for the sequential fluorescence detection of Zn2+ and S2- and the colorimetric detection of Fe3+/2+ in aqueous media and living cells.

A novel multiple target sensor, (E)-5-((4-(diethylamino)-2-hydroxybenzyldene)amino)-1H-imidazole-4-carboxamide (DHIC), was synthesized for fluorescence detection of Zn2+ and S2- and colorimetric detection of Fe3+/2+ in aqueous media. DHIC can operate as a turn "on-off" sequential fluorescent sensor for Zn2+ and S2-. Detection limits (1.59 µM and 8.03 µM) for Zn2+ and S2- are below the WHO standards (76.0 µM and 14.7 µM). The DHIC-Zn2+ complex could be reversibly reused with ethylenediaminetetraacetic acid. Importantly, DHIC could image sequentially Zn2+ and S2- in living cells. Moreover, DHIC displayed a discriminatory color change from pale yellow to orange yellow to Fe3+/2+. The detection limit of DHIC for Fe3+/2+ (0.73 µM and 1.11 µM) is far below the EPA drinking water standard (5.37 µM). The sensor DHIC could be applied to analyze Fe3+ in real samples.

Strategies Employing Transition Metal Complexes To Modulate Amyloid-ß Aggregation.

Aggregation of amyloid-ß (Aß) peptides is implicated in the development of Alzheimer's disease (AD), the most common type of dementia. Thus, numerous efforts to identify chemical tactics to control the aggregation pathways of Aß peptides have been made. Among them, transition metal complexes as a class of chemical modulators against Aß aggregation have been designed and utilized. Transition metal complexes are able to carry out a variety of chemistry with Aß peptides (e.g., coordination chemistry and oxidative and proteolytic reactions for peptide modifications) based on their tunable characteristics, including the oxidation state of and coordination geometry around the metal center. This Viewpoint illustrates three strategies employing transition metal complexes toward modulation of Aß aggregation pathways (i.e., oxidation and hydrolysis of Aß as well as coordination to Aß), along with some examples of such transition metal complexes. In addition, proposed mechanisms for three reactivities of transition metal complexes with Aß peptides are discussed. Our greater understanding of how transition metal complexes have been engineered and used for alteration of Aß aggregation could provide insight into the new discovery of chemical reagents against Aß peptides found in AD.

Incidence and Distribution of Cerebral Embolism After Cardiac Surgery According to the Systemic Perfusion Strategy　- A Diffusion-Weighted Magnetic Resonance Imaging Study.

BACKGROUND: Stroke is a major concern in minimally invasive cardiac surgery, so we investigated the incidence and risk factors of cerebral embolism according to the systemic perfusion strategy under thorough imaging assessment.Methods and Results:Between November 2011 and May 2015, 315 cardiac surgery patients who underwent preoperative computed tomography angiography (CTA) as a routine evaluation were enrolled. The incidence and distribution of cerebral embolism were analyzed with routine postoperative brain diffusion-weighted magnetic resonance imaging (DW-MRI) examination. Anterograde perfusion was used in 103 patients (group A), and retrograde perfusion was performed in 212 patients (group R). Operative deaths, incidence of clinical stroke (group A: 0%, group R: 0.5%, P=0.77), and rate of cerebral embolism (group A: 35.9%, group R: 26.4%, P=0.08) were comparable. The median number of new embolic lesions detected by MRI per patient (group A: 2, group R: 2, P=0.16), maximal diameter of the lesion (group A: 6.5 mm, group R: 6.0 mm, P=0.97), and anatomic distribution of the lesion were similar between groups. In the multivariate analysis, hypertension, emergency status, atherosclerosis grade 3 or 4 (intimal thickening >4 mm), and cardiopulmonary bypass time were independent risk factors for postoperative cerebral embolism, but retrograde perfusion was not. CONCLUSIONS: According to the results of postoperative DW-MRI, retrograde perfusion itself might not increase the incidence of postoperative cerebral embolism in properly selected cardiac surgery patients undergoing routine preoperative CTA examination.

A Novel Thiophene-Based Fluorescent Chemosensor for the Detection of Zn2+ and CN-: Imaging Applications in Live Cells and Zebrafish.

A novel fluorescent turn-on chemosensor DHADC ((E)-3-((4-(diethylamino)-2-hydroxybenzylidene)amino)-2,3-dihydrothiophene-2-carboxamide) has been developed and used to detect Zn2+ and CN-. Compound DHADC displayed a notable fluorescence increase with Zn2+. The limit of detection (2.55 ± 0.05 µM) for zinc ion was far below the standard (76 µM) of the WHO (World Health Organization). In particular, compound DHADC could be applied to determine Zn2+ in real samples, and to image Zn2+ in both HeLa cells and zebrafish. Additionally, DHADC could detect CN- through a fluorescence enhancement with little inhibition with the existence of other types of anions. The detection processes of compound DHADC for Zn2+ and CN- were demonstrated with various analytical methods like Job plots, 1H NMR titrations, and ESI-Mass analyses.

Reduced Lipid Bilayer Thickness Regulates the Aggregation and Cytotoxicity of Amyloid-ß.

The aggregation of amyloid-ß (Aß) on lipid bilayers has been implicated as a mechanism by which Aß exerts its toxicity in Alzheimer's disease (AD). Lipid bilayer thinning has been observed during both oxidative stress and protein aggregation in AD, but whether these pathological modifications of the bilayer correlate with Aß misfolding is unclear. Here, we studied peptide-lipid interactions in synthetic bilayers of the short-chain lipid dilauroyl phosphatidylcholine (DLPC) as a simplified model for diseased bilayers to determine their impact on Aß aggregate, protofibril, and fibril formation. Aß aggregation and fibril formation in membranes composed of dioleoyl phosphatidylcholine (DOPC) or 1- palmitoyl-2-oleoyl phosphatidylcholine mimicking normal bilayers served as controls. Differences in aggregate formation and stability were monitored by a combination of thioflavin-T fluorescence, circular dichroism, atomic force microscopy, transmission electron microscopy, and NMR. Despite the ability of all three lipid bilayers to catalyze aggregation, DLPC accelerates aggregation at much lower concentrations and prevents the fibrillation of Aß at low micromolar concentrations. DLPC stabilized globular, membrane-associated oligomers, which could disrupt the bilayer integrity. DLPC bilayers also remodeled preformed amyloid fibrils into a pseudo-unfolded, molten globule state, which resembled on-pathway, protofibrillar aggregates. Whereas the stabilized, membrane-associated oligomers were found to be nontoxic, the remodeled species displayed toxicity similar to that of conventionally prepared aggregates. These results provide mechanistic insights into the roles that pathologically thin bilayers may play in Aß aggregation on neuronal bilayers, and pathological lipid oxidation may contribute to Aß misfolding.

Advanced Electron Paramagnetic Resonance Studies of a Ternary Complex of Copper, Amyloid-ß, and a Chemical Regulator.

Although there has been extensive effort to develop chemical regulators, progress has been static, in part because of these regulators' unclear mechanisms. Here, we report using advanced electron paramagnetic resonance (EPR) spectroscopy to obtain the first molecular-level structural information regarding a ternary complex of CuII-amyloid-ß (Aß) with a chemical regulator that can specifically modulate Cu-induced Aß aggregation. Our advanced EPR spectroscopic results revealed that a chemical regulator (1) for CuII-Aß1-16 disrupted the coordination environment of CuII in Aß, resulting in the detachment of the primary amine at the N-terminal and a carbonyl group between Asp1 and Ala2 from the CuII center and the subsequent formation of a ternary complex, chemical regulator-CuII-Aß1-16. Therefore, our results demonstrate how a chemical regulator interacts with metal-Aß at the molecular level. These findings provide novel insight into working mechanisms and thereby contribute to the establishment of a rational design for chemical regulators of metal-Aß complexes.

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.

Mechanistic Insights into Tunable Metal-Mediated Hydrolysis of Amyloid-ß Peptides.

An amyloidogenic peptide, amyloid-ß (Aß), has been implicated as a contributor to the neurotoxicity of Alzheimer's disease (AD) that continues to present a major socioeconomic burden for our society. Recently, the use of metal complexes capable of cleaving peptides has arisen as an efficient tactic for amyloid management; unfortunately, little has been reported to pursue this strategy. Herein, we report a novel approach to validate the hydrolytic cleavage of divalent metal complexes toward two major isoforms of Aß (Aß40 and Aß42) and tune their proteolytic activity based on the choice of metal centers (M = Co, Ni, Cu, and Zn) which could be correlated to their anti-amyloidogenic properties. Such metal-dependent tunability was facilitated employing a tetra-N-methylated cyclam (TMC) ligand that imparts unique geometric and stereochemical control, which has not been available in previous systems. Co(II)(TMC) was identified to noticeably cleave Aß peptides and control their aggregation, reporting the first Co(II) complex for such reactivities to the best of our knowledge. Through detailed mechanistic investigations by biochemical, spectroscopic, mass spectrometric, and computational studies, the critical importance of the coordination environment and acidity of the aqua-bound complexes in promoting amide hydrolysis was verified. The biological applicability of Co(II)(TMC) was also illustrated via its potential blood-brain barrier permeability, relatively low cytotoxicity, regulatory capability against toxicity induced by both Aß40 and Aß42 in living cells, proteolytic activity with Aß peptides under biologically relevant conditions, and inertness toward cleavage of structured proteins. Overall, our approaches and findings on reactivities of divalent metal complexes toward Aß, along with the mechanistic insights, demonstrate the feasibility of utilizing such metal complexes for amyloid control.

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.