Switchable photooxygenation catalysts that sense higher-order amyloid structures

Unravelling the antioxidant behaviour of self-assembly β-Sheet in silk fibroin

Local oxidative stress in diseases or injury severely hinders cell homeostasis and organ regeneration. Antioxidant therapy is an effective strategy for oxidative stress treatment. Biomaterials with good biocompatibility and reactive oxygen species (ROS) scavenging ability are good choices for antioxidant therapeutics. However, there are few natural biomaterials that are identified with both biocompatibility and strong antioxidant activity. Here, we show, for the first time, that silk fibroin (SF) is a strong antioxidant, which can eliminate ROS in both cells and zebrafish. We further demonstrate that the β-sheet structures turn into a random coiled structure when SF is treated with hydrogen peroxide. The content of β-sheet structures can be increased by heating, thus enhancing the antioxidation properties of SF. Therefore, SF can serve as a good antioxidant biomaterial for therapeutics, and its β-sheet structure-based antioxidation mechanism provides a novel theoretical basis, which could be a new cue for more antioxidant biomaterial discovery and identification.

A Biocompatible Hydrogen-Bonded Organic Framework (HOF) as Sonosensitizer and Artificial Enzyme for In-Depth Treatment of Alzheimer's Disease

Current phototherapeutic approaches for Alzheimer's disease (AD) exhibit restricted clinical outcomes due to the limited physical penetration and comprised brain microenvironment of noninvasive nanomedicine. Herein, a hydrogen-bonded organic framework (HOF) based sonosensitizer is designed and synthesized. Mn-TCPP, a planar molecule where Mn2+ ion is chelated in the core with a large p-conjugated system and 4 carboxylate acid groups, has been successfully used as building blocks to construct an ultrasound-sensitive HOF (USI-MHOF), which can go deep in the brain of AD animal models. The both in vitro and in vivo studies indicate that USI-MHOF can generate singlet oxygen (1O2) and oxidize β-amyloid (Aβ) to inhibit aggregation, consequently attenuating Aβ neurotoxicity. More intriguingly, USI-MHOF exhibits catalase (CAT)- and superoxide dismutase (SOD)-like activities, mitigating neuron oxidative stress and reprograming the brain microenvironment. For better crossing the blood-brain barrier (BBB), the peptide KLVFFAED (KD8) has been covalently grafted to USI-MHOF for improving BBB permeability and Aβ selectivity. Further, in vivo experiments demonstrate a significant reduction of the craniocerebral Aβ plaques and improvement of the cognition deficits in triple-transgenic AD (3×Tg-AD) mice models following deep-penetration ultrasound treatment. The work provides the first example of an ultrasound-responsive biocompatible HOF as non-invasive nanomedicine for in-depth treatment of AD.

Leuco Ethyl Violet as Self-Activating Prodrug Photocatalyst for In Vivo Amyloid-Selective Oxygenation

Aberrant aggregates of amyloid-β (Aβ) and tau protein (tau), called amyloid, are related to the etiology of Alzheimer disease (AD). Reducing amyloid levels in AD patients is a potentially effective approach to the treatment of AD. The selective degradation of amyloids via small molecule-catalyzed photooxygenation in vivo is a leading approach; however, moderate catalyst activity and the side effects of scalp injury are problematic in prior studies using AD model mice. Here, leuco ethyl violet (LEV) is identified as a highly active, amyloid-selective, and blood-brain barrier (BBB)-permeable photooxygenation catalyst that circumvents all of these problems. LEV is a redox-sensitive, self-activating prodrug catalyst; self-oxidation of LEV through a hydrogen atom transfer process under photoirradiation produces catalytically active ethyl violet (EV) in the presence of amyloid. LEV effectively oxygenates human Aβ and tau, suggesting the feasibility for applications in humans. Furthermore, a concept of using a hydrogen atom as a caging group of a reactive catalyst functional in vivo is postulated. The minimal size of the hydrogen caging group is especially useful for catalyst delivery to the brain through BBB.

Redesign of a thioflavin-T-binding protein with a flat β-sheet to evaluate a thioflavin-T-derived photocatalyst with enhanced affinity

Amyloids, proteinous aggregates with β-sheet-rich fibrils, are involved in several neurodegenerative diseases such as Alzheimer's disease; thus, their detection is critically important. The most common fluorescent dye for amyloid detection is thioflavin-T (ThT), which shows on/off fluorescence upon amyloid binding. We previously reported that an engineered globular protein with a flat β-sheet, peptide self-assembly mimic (PSAM), can be used as an amyloid binding model. In this study, we further explored the residue-specific properties of ThT-binding to the flat β-sheet by introducing systematic mutations. We found that site-specific mutations at the ThT-binding channel enhanced affinity. We also evaluated the binding of a ThT-based photocatalyst, which showed the photooxygenation activity on the amyloid fibril upon light radiation. Upon binding of the photocatalyst to the PSAM variant, singlet oxygen-generating activity was observed. The results of this study expand our understanding of the detailed binding mechanism of amyloid-specific molecules.

Theranostic Fluorescent Probes

The ability to gain spatiotemporal information, and in some cases achieve spatiotemporal control, in the context of drug delivery makes theranostic fluorescent probes an attractive and intensely investigated research topic. This interest is reflected in the steep rise in publications on the topic that have appeared over the past decade. Theranostic fluorescent probes, in their various incarnations, generally comprise a fluorophore linked to a masked drug, in which the drug is released as the result of certain stimuli, with both intrinsic and extrinsic stimuli being reported. This release is then signaled by the emergence of a fluorescent signal. Importantly, the use of appropriate fluorophores has enabled not only this emerging fluorescence as a spatiotemporal marker for drug delivery but also has provided modalities useful in photodynamic, photothermal, and sonodynamic therapeutic applications. In this review we highlight recent work on theranostic fluorescent probes with a particular focus on probes that are activated in tumor microenvironments. We also summarize efforts to develop probes for other applications, such as neurodegenerative diseases and antibacterials. This review celebrates the diversity of designs reported to date, from discrete small-molecule systems to nanomaterials. Our aim is to provide insights into the potential clinical impact of this still-emerging research direction.

Molecularly generated light and its biomedical applications

Molecularly generated light, referred to here as "molecular light", mainly includes bioluminescence, chemiluminescence, and Cerenkov luminescence. Molecular light possesses unique dual features of being both a molecule and a source of light. Its molecular nature enables it to be delivered as molecules to regions deep within the body, overcoming the limitations of natural sunlight and physically generated light sources like lasers and LEDs. Simultaneously, its light properties make it valuable for applications such as imaging, photodynamic therapy, photo-oxidative therapy, and photobiomodulation. In this review article, we provide an updated overview of the diverse applications of molecular light and discuss the strengths and weaknesses of molecular light across various domains. Lastly, we present forward-looking perspectives on the potential of molecular light in the realms of molecular imaging, photobiological mechanisms, therapeutic applications, and photobiomodulation. While some of these perspectives may be considered bold and contentious, our intent is to inspire further innovations in the field of molecular light applications.

Thioflavin T indicates mitochondrial membrane potential in mammalian cells

The fluorescent benzothiazole dye thioflavin T (ThT) is widely used as a marker for protein aggregates, most commonly in the context of neurodegenerative disease research and diagnosis. Recently, this same dye was shown to indicate membrane potential in bacteria due to its cationic nature. This finding prompted a question whether ThT fluorescence is linked to the membrane potential in mammalian cells, which would be important for appropriate utilization of ThT in research and diagnosis. Here, we show that ThT localizes into the mitochondria of HeLa cells in a membrane-potential-dependent manner. Specifically, ThT colocalized in cells with the mitochondrial membrane potential indicator tetramethylrhodamine methyl ester (TMRM) and gave similar temporal responses as TMRM to treatment with a protonophore, carbonyl cyanide-4-(trifluoromethoxy) phenylhydrazone (FCCP). Additionally, we found that presence of ThT together with exposure to blue light (λ = 405 nm), but neither factor alone, caused depolarization of mitochondrial membrane potential. This additive effect of the concentration and blue light was recapitulated by a mathematical model implementing the potential-dependent distribution of ThT and its effect on mitochondrial membrane potential through photosensitization. These results show that ThT can act as a mitochondrial membrane potential indicator in mammalian cells, when used at low concentrations and with low blue light exposure. However, it causes dissipation of the mitochondrial membrane potential depending additively on its concentrations and blue light exposure. This conclusion motivates a re-evaluation of ThT's use at micromolar range in live-cell analyses and indicates that this dye can enable future studies on the potential connections between mitochondrial membrane potential dynamics and protein aggregation.

Noninvasive Treatment of Alzheimer's Disease with Scintillating Nanotubes

Effective and accessible treatments for Alzheimer's disease (AD) are urgently needed. Soluble Aβ oligomers are identified as neurotoxic species in AD and targeted in antibody-based drug development to mitigate cognitive decline. However, controversy exists concerning their efficacy and safety. In this study, an alternative strategy is proposed to inhibit the formation of Aβ oligomers by selectively oxidizing specific amino acids in the Aβ sequence, thereby preventing its aggregation. Targeted oxidation is achieved using biocompatible and blood-brain barrier-permeable multicomponent nanoscintillators that generate singlet oxygen upon X-ray interaction. Surface-modified scintillators interact selectively with Aβ and, upon X-ray irradiation, inhibit the formation of neurotoxic aggregates both in vitro and in vivo. Feeding transgenic Caenorhabditis elegans expressing human Aβ with the nanoscintillators and subsequent irradiation with soft X-ray reduces Aβ oligomer levels, extends lifespan, and restores memory and behavioral deficits. These findings support the potential of X-ray-based therapy for AD and warrant further development.

Photo-oxygenation of histidine residue inhibits α-synuclein aggregation

Aggregation of α-synuclein (α-syn) into amyloid is the pathological hallmark of several neurodegenerative disorders, including Parkinson disease, dementia with Lewy bodies, and multiple system atrophy. It is widely accepted that α-syn aggregation is associated with neurodegeneration, although the mechanisms are not yet fully understood. Therefore, the inhibition of α-syn aggregation is a potential therapeutic approach against these diseases. This study used the photocatalyst for α-syn photo-oxygenation, which selectively adds oxygen atoms to fibrils. Our findings demonstrate that photo-oxygenation using this photocatalyst successfully inhibits α-syn aggregation, particularly by reducing its seeding ability. Notably, we also discovered that photo-oxygenation of the histidine at the 50th residue in α-syn aggregates is responsible for the inhibitory effect. These findings indicate that photo-oxygenation of the histidine residue in α-syn is a potential therapeutic strategy for synucleinopathies.

A Photolabile Curcumin-Diazirine Analogue Enables Phototherapy with Physically and Molecularly Produced Light for Alzheimer's Disease Treatment

The development of Alzheimer's disease (AD) drugs has recently witnessed substantial achievement. To further enhance the pool of drug candidates, it is crucial to explore non-traditional therapeutic avenues. In this study, we present the use of a photolabile curcumin-diazirine analogue, CRANAD-147, to induce changes in properties, structures (sequences), and neurotoxicity of amyloid beta (Aβ) species both in cells and in vivo. This manipulation was achieved through irradiation with LED light or molecularly generated light, dubbed as "molecular light", emitted by the chemiluminescence probe ADLumin-4. Next, aided by molecular chemiluminescence imaging, we demonstrated that the combination of CRANAD-147/LED or CRANAD-147/ADLumin-4 (molecular light) could effectively slow down the accumulation of Aβs in transgenic 5xFAD mice in vivo. Leveraging the remarkable tissue penetration capacity of molecular light, phototherapy employing the synergistic effect of a photolabile Aβ ligand and molecular light emerges as a promising alternative to conventional AD treatment interventions.

Design of aggregation-induced emission-active fluorogen-based nanoparticles for imaging and scavenging Alzheimer's β-amyloid by photo-oxygenation

Photo-oxygenation has emerged as an effective modality for scavenging Alzheimer's amyloid-β (Aβ) plaques. However, limitations of the current photo-oxidants, such as low Aβ-targeting and single functionality, hinder the scavenging of Aβ plaques via photo-oxygenation. Herein, based on an aggregation-induced emission (AIE)-active fluorogen (named TPMD), we designed AIE photo-oxidant nanoparticles (T-LD NPs) for Aβ imaging, inhibition, and disaggregation. The T-LD NPs were prepared by the assembly of hydrophobic TPMD with an Aβ-targeting peptide (LPPFD, L) conjugated amphiphilic polymer (DSPE-PEG). Such T-LD NPs could specifically label Aβ plaques for image-guided therapy. Under laser irradiation, T-LD NPs generated a plethora of reactive oxygen species (ROS), including 1O2, ˙OH, and O2˙-, to oxygenate Aβ species, leading to the potent inhibition of Aβ fibrillization, and significant alleviation of Aβ-mediated neurotoxicity (36% to 10% at 20 μg mL-1). Notably, T-LD NPs could rapidly disaggregate mature Aβ fibrils into fractured β-sheet rich aggregates via photo-oxygenation, resulting in alleviated cytotoxicity. In vivo studies revealed that the photo-activated T-LD NPs scavenged amyloid plaques in the transgenic C. elegans strain CL2006 and extended the lifespan by 4 days. Taken together, this multifunctional T-LD NP integrated Aβ-targeting, near-infrared fluorescence imaging, and photo-oxygenation, provides a new strategy for the development of multifunctional AIE photo-oxidants for the treatment of Alzheimer's disease.

Attenuation of α-synuclein aggregation by catalytic photo-oxygenation

We developed catalyst 11 to promote selective photo-oxygenation of α-synuclein amyloid and attenuate its aggregation. Catalyst 11 effectively oxygenated both small and large aggregates. The oxygenated α-synuclein exhibited lower seeding activity than intact α-synuclein. This study corroborates the feasibility of catalytic photo-oxygenation as an anti-synucleinopathy strategy.

Partial Destabilization of Amyloid-β Protofibril by Methionine Photo-Oxidation: A Molecular Dynamic Simulation Study

Selective photosensitized oxidation of amyloid protein aggregates is being investigated as a possible therapeutic strategy for treating Alzheimer's disease (AD). Photo-oxidation has been shown to degrade amyloid-β (Aβ) aggregates and ameliorate aggregate toxicity in vitro and reduce aggregate levels in the brains of AD animal models. To shed light on the mechanism by which photo-oxidation induces fibril destabilization, we carried out an all-atom molecular dynamics (MD) simulation to examine the effect of methionine (Met35) oxidation on the conformation and stability of a β-sheet-rich Aβ9-40 protofibril. Analyses of up to 1 μs simulations showed that the oxidation of the Met35 residues, which resulted in the addition of hydrophilic oxygens in the fibril core, reduced the overall conformational stability of the protofibril. Specifically, Met35 disrupted the hydrophobic interface that stabilizes the stacking of the two hexamers that comprise the protofibril. The oxidized protofibril is more solvent exposed and exhibits more backbone flexibility. However, the protofibril retained the underlying U-shaped architecture of each peptide upon oxidation, and although some loss of β-sheets occurred, a significant portion remained. Our simulation results are thus consistent with our experimental observation that photo-oxidation of Aβ40 fibril resulted in the dis-agglomeration and fragmentation of Aβ fibrils but did not cause complete disruption of the fibrillar morphology or β-sheet structures. The partial destabilization of Aβ aggregates supports the further development of photosensitized platforms for the targeting and clearing of Aβ aggregates as a therapeutic strategy for treating AD.

NIR-excited upconversion nanoparticles used for targeted inhibition of Aβ42 monomers and disassembly of Aβ42 fibrils

Much attention has been paid to oxidising amyloid-β peptides (Aβ) for inhibiting their aggregation using photosensitive materials. However, the low penetration of ultraviolet/visible light into biological tissues and low targeting properties of the materials hinder their application. Here, we constructed a novel platform for attenuating the neurotoxicity of Aβ through functional upconversion nanoparticles (UCNPs@SiO₂-ThS). UCNPs@SiO₂-ThS can not only inhibit the aggregation of Aβ₄₂ monomers, but also disassemble Aβ₄₂ fibrils by its selective photooxidative capacity under the irradiation of near-infrared (NIR) light. Moreover, based on the enhancement of ThS fluorescence after attaching to Aβ₄₂ fibrils, only Aβ₄₂ fibrils exposed to both UCNPs@SiO₂-ThS and light can be oxidized rather than other normal proteins. To further enhance Aβ-target photooxygenation, we introduced the Aβ-target peptide (KLVFF) on the surface. Compared to traditional chemotherapies and radiotherapies, this novel PDT strategy shows remarkably reduced side effects and improved targeting.

In vivo visualization of enantioselective targeting of amyloid and improvement of cognitive function by clickable chiral metallohelices

The pathogenesis of Alzheimer's disease (AD) is closely related to several contributing factors, especially amyloid-β (Aβ) aggregation. Bioorthogonal reactions provide a general, facile, and robust route for the localization and derivatization of Aβ-targeted agents. Herein, a pair of chiral alkyne-containing metallohelices (ΛA and ΔA) were demonstrated to enantioselectively target and modulate Aβ aggregation, which has been monitored in triple-transgenic AD model mice and proved to improve cognitive function. Compared with its enantiomer ΔA, ΛA performed better in blocking Aβ fibrillation, relieving Aβ-triggered toxicity, and recovering memory deficits in vivo. Moreover, clickable ΛA could act as a functional module for subsequent visualization and versatile modification of amyloid via bioorthogonal reaction. As a proof-of-concept, thioflavin T, tacrine, and magnetic nanoparticles were conjugated with ΛA to realize Aβ photo-oxygenation, acetylcholinesterase inhibition, and Aβ clearance, respectively. This proof-of-principle work provided new insights into the biolabeling and bioconjugation of multifunctional metallosupramolecules through click reactions for AD therapy.

Transcranial deep-tissue phototherapy for Alzheimer's disease using low-dose X-ray-activated long-afterglow scintillators

Non-invasive phototherapy has been emerging as an ambitious tactic for suppression of amyloid-β (Aβ) self-assembly against Alzheimer's disease (AD). However, it remains a daunting challenge to develop efficient photosensitizers for Aβ oxygenation that are activatable in a deep brain tissue through the scalp and skull, while reducing side effects on normal tissues. Here, we report an Aβ targeted, low-dose X-ray-excitable long-afterglow scintillator (ScNPs@RB/Ab) for efficient deep-brain phototherapy. We demonstrate that the as-synthesized ScNPs@RB/Ab is capable of converting X-rays into visible light to activate the photosensitizers of rose bengal (RB) for Aβ oxygenation through the scalp and skull. We show that the ScNPs@RB/Ab persistently emitting visible luminescence can substantially minimize the risk of excessive X-ray exposure dosage. Importantly, peptide KLVFFAED-functionalized ScNPs@RB/Ab shows a blood-brain barrier permeability. In vivo experimental results validated that ScNPs@RB/Ab alleviated Aβ burden and slowed cognitive decline in triple-transgenic AD model mice at extremely low X-ray doses without side effects. Our study paves a new pathway to develop high-efficiency transcranial AD phototherapy. STATEMENT OF SIGNIFICANCE: Non-invasive phototherapy has been emerging as an ambitious tactic for suppression of amyloid-β (Aβ) self-assembly against Alzheimer's disease (AD). However, it remains a daunting challenge to develop efficient photosensitizers for Aβ oxygenation that are activatable in a deep brain tissue through the scalp and skull, while reducing side effects on normal tissues. Herein, we report an Aβ targeted, low-dose X-ray-excitable long-afterglow scintillators (ScNPs@RB/Ab) for efficient deep-brain phototherapy. In vivo experimental results validated that ScNPs@RB/Ab alleviated Aβ burden and slowed cognitive decline in triple-transgenic AD model mice at extremely low X-ray doses without side effects.

Excited-State Intramolecular Hydrogen Transfer of Compact Molecules Controls Amyloid Aggregation Profiles

Developing chemical methodologies to directly modify harmful biomolecules affords the mitigation of their toxicity by persistent changes in their properties and structures. Here we report compact photosensitizers composed of the anthraquinone (AQ) backbone that undergo excited-state intramolecular hydrogen transfer, effectively oxidize amyloidogenic peptides, and, subsequently, alter their aggregation pathways. Density functional theory calculations showed that the appropriate position of the hydroxyl groups in the AQ backbone and the consequent intramolecular hydrogen transfer can facilitate the energy transfer to triplet oxygen. Biochemical and biophysical investigations confirmed that these photoactive chemical reagents can oxidatively vary both metal-free amyloid-β (Aβ) and metal-bound Aβ, thereby redirecting their on-pathway aggregation into off-pathway as well as disassembling their preformed aggregates. Moreover, the in vivo histochemical analysis of Aβ species produced upon photoactivation of the most promising candidate demonstrated that they do not aggregate into oligomeric or fibrillar aggregates in the brain. Overall, our combined computational and experimental studies validate a light-based approach for designing small molecules, with minimum structural complexity, as chemical reagents targeting and controlling amyloidogenic peptides associated with neurodegenerative disorders.

Near-Infrared Photothermally Enhanced Photo-Oxygenation for Inhibition of Amyloid-β Aggregation Based on RVG-Conjugated Porphyrinic Metal-Organic Framework and Indocyanine Green Nanoplatform

Amyloid aggregation is associated with many neurodegenerative diseases such as Alzheimer's disease (AD). The current technologies using phototherapy for amyloid inhibition are usually photodynamic approaches based on evidence that reactive oxygen species can inhibit Aβ aggregation. Herein, we report a novel combinational photothermally assisted photo-oxygenation treatment based on a nano-platform of the brain-targeting peptide RVG conjugated with the 2D porphyrinic PCN-222 metal-organic framework and indocyanine green (PCN-222@ICG@RVG) with enhanced photo-inhibition in Alzheimer's Aβ aggregation. A photothermally assisted photo-oxygenation treatment based on PCN@ICG could largely enhance the photo-inhibition effect on Aβ₄₂ aggregation and lead to much lower neurotoxicity upon near-infrared (NIR) irradiation at 808 nm compared with a single modality of photo-treatment in both cell-free and in vitro experiments. Generally, local photothermal heat increases the instability of Aβ aggregates and keeps Aβ in the status of monomers, which facilitates the photo-oxygenation process of generating oxidized Aβ monomers with low aggregation capability. In addition, combined with the brain-targeting peptide RVG, the PCN-222@ICG@RVG nanoprobe shows high permeability of the human blood-brain barrier (BBB) on a human brain-on-a-chip platform. The ex vivo study also demonstrates that NIR-activated PCN-222@ICG@RVG could efficiently dissemble Aβ plaques. Our work suggests that the combination of photothermal treatment with photo-oxygenation can synergistically enhance the inhibition of Aβ aggregation, which may boost NIR-based combinational phototherapy of AD in the future.

Recent advance on pleiotropic cholinesterase inhibitors bearing amyloid modulation efficacy

Due to the hugely important roles of neurotransmitter acetylcholine (ACh) and amyloid-β (Aβ) in the pathogenesis of Alzheimer's disease (AD), the development of multi-target directed ligands (MTDLs) focused on cholinesterase (ChE) and Aβ becomes one of the most attractive strategies for combating AD. To date, numerous preclinical studies toward multifunctional conjugates bearing ChE inhibition and anti-Aβ aggregation have been reported. Noteworthily, most of the reported multifunctional cholinesterase inhibitors are carbamate-based compounds due to the initial properties of carbamate moiety. However, because their easy hydrolysis in vivo and the instability of the compound-enzyme conjugate, the mechanism of action of these compounds is rare. Thus, non-carbamate compounds are of great need for developing novel cholinesterase inhibitors. Besides, given that Aβ accumulation begins to occur 10-15 years before AD onset, modulating Aβ is ineffective only in inhibiting its aggregation but not eliminate the already accumulated Aβ if treatment is started when the patient has been diagnosed as AD. Considering the limitation of current Aβ accumulation modulators in ameliorating cognitive deficits and ineffectiveness of ChE inhibitors in blocking disease progression, the development of a practically valuable strategy with multiple pharmaceutical properties including ChE inhibition and Aβ modulation for treating AD is indispensable. In this review, we focus on summarizing the scaffold characteristics of reported non-carbamate cholinesterase inhibitors with Aβ modulation since 2020, and understanding the ingenious multifunctional drug design ideas to accelerate the pace of obtaining more efficient anti-AD drugs in the future.

Photo-Oxygenation as a New Therapeutic Strategy for Neurodegenerative Proteinopathies by Enhancing the Clearance of Amyloid Proteins

Alzheimer disease (AD) is associated with the aggregation of two amyloid proteins: tau and amyloid-β (Aβ). The results of immunotherapies have shown that enhancing the clearance and suppressing the aggregation of these two proteins are effective therapeutic strategies for AD. We have developed photocatalysts that attach oxygen atoms to Aβ and tau aggregates via light irradiation. Photo-oxygenation of these amyloid aggregates reduced their neurotoxicity by suppressing their aggregation both in vitro and in vivo. Furthermore, photo-oxygenation enhanced the clearance of Aβ in the brain and microglial cells. Here, we describe the effects of photo-oxygenation on tau and Aβ aggregation, and the potential of photo-oxygenation as a therapeutic strategy for AD, acting via microglial clearance.

Mouse Models of Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by memory loss and personality changes, eventually leading to dementia. The pathological hallmarks of AD are senile plaques and neurofibrillary tangles, which comprise abnormally aggregated β-amyloid peptide (Aβ) and hyperphosphorylated tau protein. To develop preventive, diagnostic, and therapeutic strategies for AD, it is essential to establish animal models that recapitulate the pathophysiological process of AD. In this review, we will summarize the advantages and limitations of various mouse models of AD, including transgenic, knock-in, and injection models based on Aβ and tau. We will also discuss other mouse models based on neuroinflammation because recent genetic studies have suggested that microglia are crucial in the pathogenesis of AD. Although each mouse model has its advantages and disadvantages, further research on AD pathobiology will lead to the establishment of more accurate mouse models, and accelerate the development of innovative therapeutics.

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.

Controlled and Selective Photo-oxidation of Amyloid-β Fibrils by Oligomeric p-Phenylene Ethynylenes

Photodynamic therapy (PDT) has been explored as a therapeutic strategy to clear toxic amyloid aggregates involved in neurodegenerative disorders such as Alzheimer's disease. A major limitation of PDT is off-target oxidation, which can be lethal for the surrounding cells. We have shown that a novel class of oligo-p-phenylene ethynylenes (OPEs) exhibit selective binding and fluorescence turn-on in the presence of prefibrillar and fibrillar aggregates of disease-relevant proteins such as amyloid-β (Aβ) and α-synuclein. Concomitant with fluorescence turn-on, OPE also photosensitizes singlet oxygen under illumination through the generation of a triplet state, pointing to the potential application of OPEs as photosensitizers in PDT. Herein, we investigated the photosensitizing activity of an anionic OPE for the photo-oxidation of Aβ fibrils and compared its efficacy to the well-known but nonselective photosensitizer methylene blue (MB). Our results show that, while MB photo-oxidized both monomeric and fibrillar conformers of Aβ40, OPE oxidized only Aβ40 fibrils, targeting two histidine residues on the fibril surface and a methionine residue located in the fibril core. Oxidized fibrils were shorter and more dispersed but retained the characteristic β-sheet rich fibrillar structure and the ability to seed further fibril growth. Importantly, the oxidized fibrils displayed low toxicity. We have thus discovered a class of novel theranostics for the simultaneous detection and oxidization of amyloid aggregates. Importantly, the selectivity of OPE's photosensitizing activity overcomes the limitation of off-target oxidation of traditional photosensitizers and represents an advancement of PDT as a viable strategy to treat neurodegenerative disorders.

Degradation of amyloid peptide aggregates by targeted singlet oxygen delivery from a benzothiazole functionalized naphthalene endoperoxide

Aggregate structures formed by amyloid-β (Aβ) are correlated with the progression of pathogenesis in Alzheimer's disease. Previous works have shown that photodynamic photosensitizers were effective in oxidatively degrading amyloid-β aggregates and thus decreasing their cytotoxicity under various conditions. In this work, we designed and synthesized a benzothiazole-naphthalene conjugate, with high level of structural analogy to Thioflavin T which is known to have high affinities for the amyloid peptide aggregates. The endoperoxide form (BZTN-O2) of this compound, which releases singlet oxygen with a half-life of 77 minutes at 37 °C, successfully inhibited and/or reversed amyloid aggregation. The endoperoxide is capable of singlet oxygen release without any need for light, and its charge-neutral form could allow blood-brain barrier (BBB) permeability. The therapeutic potential of such endoperoxide compounds with amyloid binding affinity is exciting.

Site-Selective Itaconation of Complex Peptides by Photoredox Catalysis

Site-selective peptide functionalization provides a straightforward and cost-effective access to diversify peptides for biological studies. Among many existing non-invasive peptide conjugations methodologies, photoredox catalysis has emerged as one of the powerful approaches for site-specific manipulation on native peptides. Herein, we report a highly N-termini-specific method to rapidly access itaconated peptides and their derivatives through a combination of transamination and photoredox conditions. This strategy exploits the facile reactivity of peptidyl-dihydropyridine in the complex peptide settings, complementing existing approaches for bioconjugations with excellent selectivity under mild conditions. Distinct from conventional methods, this method utilizes the highly reactive carbamoyl radical derived from a peptidyl-dihydropyridine. In addition, this itaconated peptide can be further functionalized as a Michael acceptor to access the corresponding peptide-protein conjugate.

Photo-Oxygenation: An Innovative New Therapeutic Approach Against Amyloidoses

Many types of amyloidoses are pathologically characterized by the deposition of amyloid, which is comprised of fibrils formed by abnormally aggregated proteins, in various peripheral tissues and the central nervous system (CNS). Neurodegenerative disorders, such as Alzheimer disease (AD), Parkinson disease (PD), frontotemporal dementia (FTD), and amyotrophic lateral sclerosis (ALS), are well-known CNS amyloidoses that are characterized by amyloid deposition both inside and outside of cells. The amyloidogenic proteins of each disease have distinct primary sequences, and they normally function as soluble proteins. However, these proteins all aggregate and form amyloid with a common intermolecular tertiary structure, namely, a cross-β-sheet structure, finally leading to the onset of each disease. Therefore, inhibition of the aggregation of amyloid proteins or efficient clearance of the already formed amyloids are thought to be promising therapeutic strategies against amyloidoses.

NIR-II Hydrogen-Bonded Organic Frameworks (HOFs) Used for Target-Specific Amyloid-β Photooxygenation in an Alzheimer's Disease Model

Phototherapy has emerged as a powerful approach for interrupting β-amyloid (Aβ) self-assembly. However, deeper tissue penetration and safer photosensitizers are urgent to be exploited for avoiding damaging nearby normal tissues and improving therapeutic effectiveness. A hydrogen-bonded organic framework (HOF)-based NIR-II photooxygenation catalyst is presented here to settle the abovementioned challenges. By encapsulating the pyridinium hemicyanine dye DSM with a large two-photon absorption (TPA) cross-section in NIR-II window into the porphyrin-based HOF, the resultant DSM@n-HOF-6 exhibits significant two-photon NIR-II-excited Fluorescence Resonance Energy Transfer (FRET) to generate singlet oxygen (1 O2 ) for Aβ oxidation. Further, the target peptides of KLVFFAED (KD8) are covalently grafted on DSM@n-HOF-6 to enhance the blood-brain barrier (BBB) permeability and Aβ selectivity. The HOF-based photooxygenation catalyst shows an outstanding inhibitory effect of Aβ aggregation upon the NIR-II irradiation. Further in vivo studies demonstrate the obvious decrease of craniocerebral Aβ plaques and recovery of memory deficits in triple-transgenic AD (3×Tg-AD) model mice.

Chemical catalyst-promoted photooxygenation of amyloid proteins

Misfolded proteins produce aberrant fibrillar aggregates, called amyloids, which contain cross-β-sheet higher order structures. The species generated in the aggregation process (i.e., oligomers, protofibrils, and fibrils) are cytotoxic and can cause various diseases. Interfering with the amyloid formation of proteins could be a drug development target for treating diseases caused by aberrant protein aggregation. In this review, we introduce a variety of chemical catalysts that oxygenate amyloid proteins under light irradiation using molecular oxygen as the oxygen atom donor (i.e., photooxygenation catalysts). Catalytic photooxygenation strongly inhibits the aggregation of amyloid proteins due to covalent installation of hydrophilic oxygen atoms and attenuates the neurotoxicity of the amyloid proteins. Recent in vivo studies in disease model animals using photooxygenation catalysts showed promising therapeutic effects, such as memory improvement and lifespan extension. Moreover, photooxygenation catalysts with new modes of action, including interference with the propagation of amyloid core seeds and enhancement in the metabolic clearance of amyloids in the brain, have begun to be identified. Manipulation of catalytic photooxygenation with secured amyloid selectivity is indispensable for minimizing the side effects in clinical application. Here we describe several strategies for designing catalysts that selectively photooxygenate amyloids without reacting with other non-amyloid biomolecules.

Synthesis of D-π-A type benzothiazole-pyridinium salt composite and its application as photo-degradation agent for amyloid fibrils

We have synthesized a cyan fluorescent benzothiazole-pyridinium salt composite based on D-π-A architecture. This salt was found to work as not only a two- and three-photon excitable fluorophore but also a degradation agent against amyloid fibrils under LED irradiation conditions.

Selective Heavy Atom Effect Forming Photosensitizing Hot Spots in Double-Stranded DNA Matrix

Triplet exciton formation is essential for photosensitization-based photochemistry and photobiology. The heavy atom effect (HAE), in the form of either external or internal mode, is a basic mechanism for increasing the triplet exciton yield of photosensitizers. Herein, we report a new HAE mode by noncovalent cohosting of heavy atoms and photosensitizers in a double-stranded DNA (dsDNA) matrix. With dsDNA bearing several thymine (T) or cytosine (C) mismatches, heavy atoms (e.g., Hg²⁺ or Ag⁺) and dsDNA-staining dyes (photosensitizers) were spatially adjoined in close proximity, thus resulting in enhanced phosphorescence and ¹O₂ generation from the photosensitizers. The dsDNA-hosted HAE provides highly selective recognition for the heavy atoms, which is not applicable in either the external or the internal mode. Considering the simpleness and efficiency of the spatially adjoined HAE, as well as the functionality of DNA, the proposed HAE mode is appealing for various singlet oxygen- and phosphorescence-related applications.

Visible-Light-Mediated Modification and Manipulation of Biomacromolecules

Chemically modified biomacromolecules-i.e., proteins, nucleic acids, glycans, and lipids-have become crucial tools in chemical biology. They are extensively used not only to elucidate cellular processes but also in industrial applications, particularly in the context of biopharmaceuticals. In order to enable maximum scope for optimization, it is pivotal to have a diverse array of biomacromolecule modification methods at one's disposal. Chemistry has driven many significant advances in this area, and especially recently, numerous novel visible-light-induced photochemical approaches have emerged. In these reactions, light serves as an external source of energy, enabling access to highly reactive intermediates under exceedingly mild conditions and with exquisite spatiotemporal control. While UV-induced transformations on biomacromolecules date back decades, visible light has the unmistakable advantage of being considerably more biocompatible, and a spectrum of visible-light-driven methods is now available, chiefly for proteins and nucleic acids. This review will discuss modifications of native functional groups (FGs), including functionalization, labeling, and cross-linking techniques as well as the utility of oxidative degradation mediated by photochemically generated reactive oxygen species. Furthermore, transformations at non-native, bioorthogonal FGs on biomacromolecules will be addressed, including photoclick chemistry and DNA-encoded library synthesis as well as methods that allow manipulation of the activity of a biomacromolecule.

Boosting the inactivation of bacterial biofilms by photodynamic targeting of matrix structures with Thioflavin T

We report that Thioflavin T (ThT), the reference fluorogenic probe for amyloid detection, displays photodynamic activity against bacterial biofilms. ThT recognizes key structures of the biofilm matrix, disrupting the complex architecture and efficiently inactivating bacterial cells. We also show that ThT phototherapy synergistically boosts the activity of conventional antimicrobials.

Nanomaterials for Modulating the Aggregation of β-Amyloid Peptides

The aberrant aggregation of amyloid-β (Aβ) peptides in the brain has been recognized as the major hallmark of Alzheimer's disease (AD). Thus, the inhibition and dissociation of Aβ aggregation are believed to be effective therapeutic strategiesforthe prevention and treatment of AD. When integrated with traditional agents and biomolecules, nanomaterials can overcome their intrinsic shortcomings and boost their efficiency via synergistic effects. This article provides an overview of recent efforts to utilize nanomaterials with superior properties to propose effective platforms for AD treatment. The underlying mechanismsthat are involved in modulating Aβ aggregation are discussed. The summary of nanomaterials-based modulation of Aβ aggregation may help researchers to understand the critical roles in therapeutic agents and provide new insight into the exploration of more promising anti-amyloid agents and tactics in AD theranostics.

Visible-Light-Driven Redox Neutral Direct C-H Amination of Glycine Derivatives and Peptides with N-Acyloxyphthalimides

A room temperature, visible-light-promoted and redox neutral direct C-H amination of glycine and peptides has been firstly accomplished by using N-acyloxyphthalimide or -succinimide as nitrogen-radical precursor. The present strategy provides ways to introduce functionalities such as N-acyloxyphthalimide or -succinimide specifically to terminal glycine segment of peptides. Herein, mild conditions and high functional-group tolerance allow the preparation of non-natural α-amino acids and modification of corresponding peptides in this way.

Membrane Anchored Polymers Modulate Amyloid Fibrillation

The nucleating role of cellular membrane components, such as lipid moieties on amyloid beta (Aβ_1-40 ) fibrillation, has been reported in recent years. The influence of conjugates fabricated from lipid anchors (cholesterol, diacylglycerol) and hydrophilic polymers on Aβ_1-40 fibrillation is reported here, aiming to understand the impact of polymers cloud point temperature (T_cp ) and its hydrophobic tails on the amyloid fibrillation. Novel lipid-polymer conjugates, consisting of poly(oligo(ethylene glycol)_m acrylates) and hydrophobic groups (diacylglyceryl-, cholesteryl-, octyl-, decyl-, hexadecyl-) as anchors are synthesized using reversible addition-fragmentation chain transfer (RAFT) polymerization, allowing to tune the hydrophilic-hydrophobic profile of the conjugates by varying both, the degree of polymerization (n) and number of ethylene glycol units (m) in their side chain. The impact of these conjugates on Aβ_1-40 fibrillation is investigated via in vitro kinetic studies and transmission electron microscopy (TEM). Hydrophobic lipid-anchors are significantly delaying fibrillation (both lag- and half times), observing similar fibrillar structures via TEM when compared to native Aβ_1-40 . Other hydrophobic end groups are also delaying fibrillation of Aβ_1-40 , irrespective of their "n" and "m," whereas more hydrophilic polymers (both with longer ethylene glycol-sidechains, m = 3 for octyl, decyl and m = 5 for cholesterol) are only marginally inhibited fibrillation.

Current Strategies for Modulating Aβ Aggregation with Multifunctional Agents

Alzheimer's disease (AD), as the primary cause of dementia, has seriously affected millions of people worldwide and brought a very heavy financial and social burden. With the growth of population and aging, the situation will worsen unless efficacious drugs are found to reverse, stop, or even slow down disease progression. More and more evidence has demonstrated that amyloid-β (Aβ) aggregation is an upstream causative factor in AD pathogenesis and then triggers a slew of pathological events. Furthermore, the concentrated redox metal ions in the AD brain, especially Cu(II), can significantly exacerbate Aβ aggregation and contribute to the formation of neurotoxic reactive oxygen species (ROS). Therefore, the inhibition of Aβ aggregation and relief of amyloidosis-initiated neurotoxicity play a critical role in AD treatment. Until now, several methods have been proposed to modulate Aβ aggregation, such as developing aggregation inhibitors to interfere with Aβ assembly via noncovalent interactions, copper chelators to cut off metal-accelerated Aβ aggregation and concomitant cytotoxicity, photooxidation to reduce the hydrophobicity and aggregation tendency of Aβ, thermal dissociation to disrupt amyloid aggregates susceptible to temperature, degradation with artificial protease to fracture the Aβ peptide into small fragments, and the clearance of peripheral Aβ to bypass the obstruction of the BBB and reduce the Aβ burden.In this Account, we focus on our contributions to the development of Aβ-targeted multifunctional molecules and nanoparticles, emphasizing the diversified strategies and synergistic therapeutic effects. These therapeutic agents possess the following multifunctionalities: (1) compared with frequently used aggregation inhibitors restricted by intrinsically feeble and sensitive noncovalent interactions, multifunctional agents can efficiently block Aβ aggregation by exploiting two or more Aβ-specific inhibition strategies simultaneously; (2) apart from regulating Aβ aggregation, multipronged agents can also target and modulate other pathological factors in AD pathogenesis, such as increased oxidative stress, abnormal copper accumulation, and irreversible neuron loss; (3) multifunctional platforms with both diagnostic and therapeutic modalities through integrating in situ imaging, real-time diagnostics, a multitarget direction, stimuli-responsive drug release, and the blood-brain barrier (BBB) translocation features are instrumental in improving drug levels at trouble sites, diminishing off-target adverse reactions, evaluating therapeutic effects, and averting overtreatment.Given the fact that amyloid aggregation, local inflammation, and metal dyshomeostasis are universal biomarkers shared by various neurodegenerative disorders, this Account provides a perspective for the evolution of customized therapeutic agents with multiple reactivities for other neurodegenerative diseases. In addition, recent studies have indicated that Aβ aggregates can enter the nucleus and induce DNA damage and anomalous conformational transition. We also explore the influences of DNA on the biological effects of Aβ aggregates.

Chemical Catalysis Intervening to Histone Epigenetics

Life emerges from complicated and sophisticated chemical networks comprising numerous biomolecules (e.g., nucleic acids, proteins, sugars, and lipids) and chemical reactions catalyzed by enzymes. Dysregulation of these chemical networks is linked to the emergence of diseases. Our research goal is to develop abiotic chemical catalysts that can intervene into life's chemical networks by complementing, surrogating, or exceeding enzymes in living cells or multicellular organisms such as animals or plants. Mending dysregulated networks in pathological states by the chemical catalysts will lead to a new medicinal strategy, catalysis medicine. This research direction will also advance catalysis science, because highly active and selective chemical catalysts must be developed to promote the intended reactions in a complex mixture of life in aqueous solution at body temperature.Epigenetics exists at the crossroads of chemistry, biology, and medicine and is a suitable field to pursue this idea. Post-translational modifications (PTMs) of histones epigenetically regulate chromatin functions and gene transcription and are intimately related to various diseases. Investigating the functions and cross-talk of histone PTMs is crucial for mechanistic elucidation of diseases and their treatments. We launched a program to develop chemical catalysts enabling endogenous histone modifications in living cells without relying on enzymes. We reported two types of chemical catalyst systems so far for synthetic histone acylation. The first system comprised a DNA-binding oligo-4-dimethylaminopyridine (DMAP) catalyst and a phenyl ester acyl donor, PAc-gly. This system promoted histone hyperacetylation in Xenopus laevis sperm chromatin. Using the thus-synthesized hyperacetylated sperm chromatin, we found a novel relationship between histone acetylation and DNA replication. The second system involved a histone-binding catalyst, LANA-DSH, composed of a catalytic motif (DSH) and a histone-binding peptide ligand (LANA), and thioester acyl donors, including endogenous acyl-CoA. This system regioselectively (i.e., selectively to a lysine residue at a specific position) acylated lysine 120 of histone H2B (H2BK120), a lysine residue proximal to the DSH motif defined by binding of the LANA ligand to a nucleosome substrate. This catalyst system was optimized to achieve H2BK120-selective acetylation in living cells without genetic manipulation. The synthetically introduced H2BK120Ac inhibited enzyme-catalyzed ubiquitination at the same lysine residue, acting as a protecting group. H2BK120Ub is a mark recognized by methyltransferase that plays an essential role in mixed-lineage leukemia (MLL)-rearranged leukemia, suggesting the potential of the catalyst system as an epigenetic tool and a cancer therapy. We also discuss the prospects of chemical catalyst-promoted synthetic epigenetics for future PTM studies and therapeutic uses.

Proximity Histidine Labeling by Umpolung Strategy Using Singlet Oxygen

While electrophilic reagents for histidine labeling have been developed, we report an umpolung strategy for histidine functionalization. A nucleophilic small molecule, 1-methyl-4-arylurazole, selectively labeled histidine under singlet oxygen (¹O₂) generation conditions. Rapid histidine labeling can be applied for instant protein labeling. Utilizing the short diffusion distance of ¹O₂ and a technique to localize the ¹O₂ generator, a photocatalyst in close proximity to the ligand-binding site, we demonstrated antibody Fc-selective labeling on magnetic beads functionalized with a ruthenium photocatalyst and Fc ligand, ApA. Three histidine residues located around the ApA binding site were identified as labeling sites by liquid chromatography-mass spectrometry analysis. This result suggests that ¹O₂-mediated histidine labeling can be applied to a proximity labeling reaction on the nanometer scale.

Photo-oxygenation by a biocompatible catalyst reduces amyloid-β levels in Alzheimer's disease mice

Amyloid formation and the deposition of the amyloid-β peptide are hallmarks of Alzheimer's disease pathogenesis. Immunotherapies using anti-amyloid-β antibodies have been highlighted as a promising approach for the prevention and treatment of Alzheimer's disease by enhancing microglial clearance of amyloid-β peptide. However, the efficiency of antibody delivery into the brain is limited, and therefore an alternative strategy to facilitate the clearance of brain amyloid is needed. We previously developed an artificial photo-oxygenation system using a low molecular weight catalytic compound. The photocatalyst specifically attached oxygen atoms to amyloids upon irradiation with light, and successfully reduced the neurotoxicity of aggregated amyloid-β via inhibition of amyloid formation. However, the therapeutic effect and mode of actions of the photo-oxygenation system in vivo remained unclear. In this study, we demonstrate that photo-oxygenation facilitates the clearance of aggregated amyloid-β from the brains of living Alzheimer's disease model mice, and enhances the microglial degradation of amyloid-β peptide. These results suggest that photo-oxygenation may represent a novel anti-amyloid-β strategy in Alzheimer's disease, which is compatible with immunotherapy.

Photoresponsive materials for intensified modulation of Alzheimer's amyloid-β protein aggregation: A review

The abnormal self-assembly of amyloid-β protein (Aβ) into toxic aggregates is a major pathological hallmark of Alzheimer's disease (AD). Modulation of Aβ fibrillization with pharmacological modalities has become an active field of research, which aims to mitigate Aβ-induced neurotoxicity and ameliorate impaired recognition. Among the various strategies for AD treatment, phototherapy, including photothermal therapy (PTT), photodynamic therapy (PDT), and photoresponsive release systems have attracted increased attention because of the spatiotemporal controllability. Under the irradiation of light, the heat or reactive oxygen species generated by photothermal or photodynamic processes significantly enhances the efficacy of the inhibitor or modulator, and the "caged" drug can be accurately released at the intended site, thus avoiding adverse effects. This review, from a viewpoint of materials, focuses on the recent advances in modulating Aβ aggregation by light that irradiates on the materials that function on modulating Aβ aggregation. Representative examples of PTT, PDT, and photoresponsive drug release systems are discussed in terms of inhibitory mechanism, the unique properties of materials, and the design of modulators. The major challenges of phototherapy against AD are addressed and the promising prospects are proposed. It is concluded that the noninvasive light-assisted approaches will become a promising strategy for intensifying the modulation of Aβ aggregation and thus facilitating AD treatment. STATEMENT OF SIGNIFICANCE: Alzheimer's disease (AD) with the hallmark of amyloid-β protein (Aβ) deposition is affecting more than 50 million people globally. It is urgent to explore intelligent materials to modulate Aβ aggregation. This review summarizes the intensified modulation of Aβ aggregation by a variety of photoresponsive materials including photothermal, photosensitizing and photoresponsive release materials, focusing on their characteristics and functionalities. We believe this review would arouse more interest in the research field of stimuli-responsive materials and promote their clinical applications in AD therapy.

Catalytic photooxygenation degrades brain Aβ in vivo

Protein degradation induced by small molecules by recruiting endogenous protein degradation systems, such as ubiquitin-proteasome systems, to disease-related proteins is an emerging concept to inhibit the function of undruggable proteins. Protein targets without reliable ligands and/or existing outside the cells where ubiquitin-proteasome systems do not exist, however, are beyond the scope of currently available protein degradation strategies. Here, we disclose photooxygenation catalyst 7 that permeates the blood-brain barrier and selectively and directly degrades an extracellular Alzheimer's disease-related undruggable protein, amyloid-β protein (Aβ). Key was the identification of a compact but orange color visible light-activatable chemical catalyst whose activity can be switched on/off according to its molecular mobility, thereby ensuring high selectivity for aggregated Aβ. Chemical catalyst-promoted protein degradation can be applied universally for attenuating extracellular amyloids and various pathogenic proteins and is thus a new entry to induced protein degradation strategies.

Photomodulating Carbon Dots for Spatiotemporal Suppression of Alzheimer's β-Amyloid Aggregation

Extracellular deposition of β-amyloid (Aβ) peptide aggregates is a major characteristic of Alzheimer's disease (AD) brain. Because Aβ peptide aggregates aggravate neuropathy and cognitive impairment for AD patients, numerous efforts have been devoted to suppressing Aβ self-assembly as a prospective AD treatment option. Here, we report Aβ-targeting, red-light-responsive carbon dots (CDs), and their therapeutic functions as a light-powered nanomodulator to spatiotemporally suppress toxic Aβ aggregation both in vitro and in vivo. Our aptamer-functionalized carbon dots (Apta@CDs) showed strong targeting ability toward Aβ₄₂ species. Moreover, red LED irradiation induced Apta@CDs to irreversibly denature Aβ peptides, impeding the formation of β-sheet-rich Aβ aggregates and attenuating Aβ-associated cytotoxicity. Consequently, Apta@CDs-mediated photomodualtion modality achieved effective suppression of Aβ aggregation in vivo, which significantly reduced the Aβ burden at the targeted sites in the brain of 5xFAD mice by ∼40% and ∼25% according to imaging and ELISA analyses, respectively. Our work demonstrates the therapeutic potential of photomodulating CDs for light-driven suppression against Aβ self-assembly and related neurotoxicity.

Aggregation-induced photocatalytic activity and efficient photocatalytic hydrogen evolution of amphiphilic rhodamines in water

The development of photocatalysts is an essential task for clean energy generation and establishing a sustainable society. This paper describes the aggregation-induced photocatalytic activity (AI-PCA) of amphiphilic rhodamines and photocatalytic functions of the supramolecular assemblies. The supramolecular assemblies consisting of amphiphilic rhodamines with octadecyl alkyl chains exhibited significant photocatalytic activity under visible light irradiation in water, while the corresponding monomeric rhodamines did not exhibit photocatalytic activity. The studies on the photocatalytic mechanism by spectroscopic and microscopic analyses clearly demonstrated the AI-PCA of the rhodamines. Moreover, the supramolecular assemblies of the rhodamines exhibited excellent photocatalytic hydrogen evolution rates (up to 5.9 mmol g-1 h-1).

Target-driven supramolecular self-assembly for selective amyloid-β photooxygenation against Alzheimer's disease

Photo-oxygenation of β-amyloid (Aβ) has been considered an efficient way to inhibit Aβ aggregation in Alzheimer's disease (AD). However, current photosensitizers cannot simultaneously achieve enhanced blood-brain barrier (BBB) permeability and selective photooxygenation of Aβ, leading to poor therapeutic efficacy, severe off-target toxicity, and substandard bioavailability. Herein, an Aβ target-driven supramolecular self-assembly (PKNPs) with enhanced BBB penetrability and switchable photoactivity is designed and demonstrated to be effective in preventing Aβ aggregation in vivo. PKNPs are prepared by the self-assembly of the Aβ-targeting peptide KLVFF and an FDA-approved porphyrin derivative (5-(4-carboxyphenyl)-10,15,20-triphenylporphyrin). Due to the photothermal effect of PKNPs, the BBB permeability of PKNPs under irradiation is 8.5-fold higher than that of porphyrin alone. Moreover, upon selective interaction with Aβ, PKNPs undergo morphological change from the spherical to the amorphous form, resulting in a smart transformation from photothermal activity to photodynamic activity. Consequently, the disassembled PKNPs can selectively oxygenate Aβ without affecting off-target proteins (insulin, bovine serum albumin, and human serum albumin). The well-designed PKNPs exhibit not only improved BBB permeability but also highly selective Aβ photooxygenation. Furthermore, in vivo experiments demonstrate that PKNPs can alleviate Aβ-induced neurotoxicity and prolong the life span of the commonly used AD transgenic Caenorhabditis elegans CL2006. Our work may open a new path for using supramolecular self-assemblies as switchable phototheranostics for the selective and effective prevention of Aβ aggregation and related neurotoxicity in AD.

A Biocompatible Second Near-Infrared Nanozyme for Spatiotemporal and Non-Invasive Attenuation of Amyloid Deposition through Scalp and Skull

Phototherapy, such as photodynamic therapy and photothermal therapy, holds great potential for modulation of Alzheimer's β-amyloid (Aβ) self-assembly. Unfortunately, current works for phototherapy of Alzheimer's disease (AD) are just employing either visible or first near-infrared (NIR-I) light with limited tissue penetration, which can not avoid damaging nearby normal tissues of AD patients through the dense skull and scalp. To overcome the shortcomings of AD phototherapy, herein we report an amyloid targeting, N-doped three-dimensional mesoporous carbon nanosphere (KD8@N-MCNs) as a second near-infrared (NIR-II) PTT agent. This makes it possible for photothermal dissociation of Aβ aggregates through the scalp and skull in a NIR-II window without hurting nearby normal tissues. Besides, KD8@N-MCNs have both superoxide dismutase and catalase activities, which can scavenge intracellular superfluous reactive oxygen species and alleviate neuroinflammation in vivo. Furthermore, KD8@N-MCNs efficiently cross the blood-brain barrier owing to the covalently grafted target peptides of KLVFFAED on the nanosphere surface. In vivo studies demonstrate that KD8@N-MCNs decrease Aβ deposits, ameliorate memory deficits, and alleviate neuroinflammation in the 3xTg-AD mouse model. Our work provides a biocompatible and non-invasive way to attenuate AD-associated pathology.