A fluorescent molecular imaging probe with selectivity for soluble tau aggregated protein

Visualization of Oxidative Stress in the Early Stage of Alzheimer's Disease with a NIR-IIb Probe

Alzheimer's disease (AD), a progressive neurodegenerative disorder, is associated with the complete loss of cognition, and its pathogenesis has been suggested to be closely linked to oxidative stress in the early stage. However, there is currently a lack of effective methods to provide direct evidence for dynamic development of the oxidative stress status during AD progression. Herein, through manipulating the multiple energy transfer between 4f electronic levels of lanthanide ions (Ln3+), we proposed an energy interception strategy to construct activatable NIR-IIb nanoprobe for visualizing oxidative stress level. By utilizing an organic molecule, A1094 that absorbs light at wavelength matching the emission of Nd3+ and Yb3+, NIR-IIb emission from Er3+ can be modulated upon the response of A1094 to oxidative species. This nanoprobe can not only clearly outline and distinguish oxidative stress regions in AD brains with adjacent age but also provide fast feedback on the efficacy of early interventional treatment for AD.

PET Imaging of a Transgenic Tau Rat Model SHR24 with [18F]AV1451

PURPOSE

Positron Emission Tomography (PET) scans with radioligands targeting tau neurofibrillary tangles (NFT) have accelerated our understanding of the role of misfolded tau in neurodegeneration. While intended for human research, applying these radioligands to small animals establishes a vital translational link. Transgenic animal models of dementia, such as the tau rat SHR24, play a crucial role in enhancing our understanding of these disorders. This study aims to evaluate the utility of SHR24 rat model for PET studies.

PROCEDURES

Dynamic PET scans were conducted in male SHR24 rats and their wild-type SHR (SHRwt) littermates using [18F]AV1451. Rapid blood sampling and metabolite analysis were performed to acquire input curves. Time activity curves were obtained from various brain regions over 60 min. Blood-based, 2-Tissue Compartment Model (2-TCM) and Logan graphical analysis were used to obtain kinetic modelling parameters. The ability of reference tissue models to predict the binding potential (BPND) were assessed. Autoradiography studies were performed to corroborate the scan data.

RESULTS

Total distribution volume (VT) was the best predicted parameter which revealed significantly higher uptake of [18F]AV1451 in the cortex (5.8 ± 1.1 vs 4.6 ± 0.7, P < 0.05) of SHR24 rats compared to SHRwt rats. Binding potential obtained from 2-TCM was variable, however BPND from reference tissue models detected significantly higher binding in cortex (0.28 ± 0.07 vs 0.20 ± 0.04, P < 0.01 by SRTM) and brainstem (0.14 ± 0.04 vs 0.08 ± 0.02, P < 0.01, by SRTM).

CONCLUSIONS

With the ability to detect binding of established radioligand [18F]AV1451 in these rats, we have demonstrated the utility of this model for assessing aggregated tau neurobiology by PET, with reference tissue models providing potential for longitudinal studies.

Optical molecular imaging technology and its application in precise surgical navigation of liver cancer

Recent innovations in medical imaging technology have placed molecular imaging techniques at the forefront of diagnostic advancements. The current research trajectory in this field aims to integrate personalized molecular data of patients and diseases with traditional anatomical imaging data, enabling more precise, non-invasive, or minimally invasive diagnostic options for clinical medicine. This article provides an in-depth exploration of the basic principles and system components of optical molecular imaging technology. It also examines commonly used targeting mechanisms of optical probes, focusing especially on indocyanine green-the FDA-approved optical dye widely used in clinical settings-and its specific applications in diagnosing and treating liver cancer. Finally, this review highlights the advantages, limitations, and future challenges facing optical molecular imaging technology, offering a comprehensive overview of recent advances, clinical applications, and potential impacts on liver cancer treatment strategies.

Detecting and Tracking β-Amyloid Oligomeric Forms and Dynamics In Vitro by a High-Sensitivity Fluorescent-Based Assay

Aggregation of β-amyloid protein is a hallmark pathology of the neurodegenerative disorder Alzheimer's disease and proceeds from monomers to insoluble misfolded fibril forms via soluble and highly toxic oligomeric intermediates. Given the dual feature of being the most toxic form of the Aβ aggregate proteome and an early marker of pathogenesis, there is a need for sensitive methods that can be used to detect Aβ oligomers and investigate the dynamics of aggregation. Herein, we describe a method based on the application of an oligomer-sensitive fluorescent chemical probe pTP-TFE combined with the use of a QIAD (Quantitative determination of Interference with Aβ Aggregate Size Distribution) assay to correctly identify Aβ oligomers in high sensitivity. pTP-TFE was evaluated and compared to thioflavin T and pFTAA, the two most widely used amyloid fibril dyes, and shown to be the only probe capable of detecting significant differences across all oligomeric species of β-amyloid. Furthermore, by observing changes in pTP-TFE fluorescence emission over time, we could track the dynamics of oligomer populations and thereby obtain kinetic information on the Aβ42 dynamic aggregation model. Therefore, we have established a highly sensitive, readily available, and simple method for studying β-amyloid protein aggregation dynamics.

Design, Synthesis, and Characterization of Novel Styryl Dyes as Fluorescent Probes for Tau Aggregate Detection in Vitro and in Cells

A series of novel styryl dye derivatives incorporating indolium and quinolinium core structures were successfully synthesized to explore their interacting and binding capabilities with tau aggregates in vitro and in cells. The synthesized dyes exhibited enhanced fluorescence emission in viscous environments due to the rotatable bond confinement in the core structure. Dye 4, containing a quinolinium moeity and featuring two cationic sites, demonstrated a 28-fold increase in fluorescence emission upon binding to tau aggregates. This dye could also stain tau aggregates in living cells, confirmed by cell imaging using confocal fluorescence microscopy. A molecular docking study was conducted to provide additional visualization and support for binding interactions. This work offers novel and non-cytotoxic fluorescent probes with desirable photophysical properties, which could potentially be used for studying tau aggregates in living cells, prompting further development of new fluorescent probes for early Alzheimer's disease detection.

A closer look at amyloid ligands, and what they tell us about protein aggregates

The accumulation of amyloid fibrils is characteristic of neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease. Detecting these fibrils with fluorescent or radiolabelled ligands is one strategy for diagnosing and better understanding these diseases. A vast number of amyloid-binding ligands have been reported in the literature as a result. To obtain a better understanding of how amyloid ligands bind, we have compiled a database of 3457 experimental dissociation constants for 2076 unique amyloid-binding ligands. These ligands target Aβ, tau, or αSyn fibrils, as well as relevant biological samples including AD brain homogenates. From this database significant variation in the reported dissociation constants of ligands was found, possibly due to differences in the morphology of the fibrils being studied. Ligands were also found to bind to Aβ(1-40) and Aβ(1-42) fibrils with similar affinities, whereas a greater difference was found for binding to Aβ and tau or αSyn fibrils. Next, the binding of ligands to fibrils was shown to be largely limited by the hydrophobic effect. Some Aβ ligands do not fit into this hydrophobicity-limited model, suggesting that polar interactions can play an important role when binding to this target. Finally several binding site models were outlined for amyloid fibrils that describe what ligands target what binding sites. These models provide a foundation for interpreting and designing site-specific binding assays.

Early Diagnosis of Neurodegenerative Diseases: What Has Been Undertaken to Promote the Transition from PET to Fluorescence Tracers

Alzheimer's Disease (AD) and Parkinson's Disease (PD) represent two among the most frequent neurodegenerative diseases worldwide. A common hallmark of these pathologies is the misfolding and consequent aggregation of amyloid proteins into soluble oligomers and insoluble β-sheet-rich fibrils, which ultimately lead to neurotoxicity and cell death. After a hundred years of research on the subject, this is the only reliable histopathological feature in our hands. Since AD and PD are diagnosed only once neuronal death and the first symptoms have appeared, the early detection of these diseases is currently impossible. At present, there is no effective drug available, and patients are left with symptomatic and inconclusive therapies. Several reasons could be associated with the lack of effective therapeutic treatments. One of the most important factors is the lack of selective probes capable of detecting, as early as possible, the most toxic amyloid species involved in the onset of these pathologies. In this regard, chemical probes able to detect and distinguish among different amyloid aggregates are urgently needed. In this article, we will review and put into perspective results from ex vivo and in vivo studies performed on compounds specifically interacting with such early species. Following a general overview on the three different amyloid proteins leading to insoluble β-sheet-rich amyloid deposits (amyloid β1-42 peptide, Tau, and α-synuclein), a list of the advantages and disadvantages of the approaches employed to date is discussed, with particular attention paid to the translation of fluorescence imaging into clinical applications. Furthermore, we also discuss how the progress achieved in detecting the amyloids of one neurodegenerative disease could be leveraged for research into another amyloidosis. As evidenced by a critical analysis of the state of the art, substantial work still needs to be conducted. Indeed, the early diagnosis of neurodegenerative diseases is a priority, and we believe that this review could be a useful tool for better investigating this field.

Detection of Small-Molecule Interactions with Fibrillar Tau Protein Aggregates Using Microscale Thermophoresis

Aggregated fibrillar tau protein is a pathological hallmark of several neurodegenerative diseases. Small molecules that bind to tau fibrils may be applied for their detection and quantification. This is of great importance as they can potentially be used for earlier diagnosis of disease and disease progression. Microscale thermophoresis (MST) enables the detection of biomolecular interactions in an aqueous environment in which no immobilization of either reaction partner is required. Here, an MST assay methodology is described for the detection of the interaction between a variety of small molecules and tau fibrils. The results of this study demonstrate that MST is a practical methodology to quantify interactions between small molecules and tau fibrillar aggregates.

Development of fluorophores for the detection of oligomeric aggregates of amyloidogenic proteins found in neurodegenerative diseases

Alzheimer's disease and Parkinson's disease are the two most common neurodegenerative diseases globally. These neurodegenerative diseases have characteristic late-stage symptoms allowing for differential diagnosis; however, they both share the presence of misfolded protein aggregates which appear years before clinical manifestation. Historically, research has focused on the detection of higher-ordered aggregates (or amyloids); however, recent evidence has shown that the oligomeric state of these protein aggregates plays a greater role in disease pathology, resulting in increased efforts to detect oligomers to aid in disease diagnosis. In this review, we summarize some of the exciting new developments towards the development of fluorescent probes that can detect oligomeric aggregates of amyloidogenic proteins present in Alzheimer's and Parkinson's disease patients.

TMSCF3-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism

As reported by Zhao, the TBAT ([Ph3SiF2]-[Bu4N]+)-initiated reaction of ethyl salicylate with TMSCF3 in THF generates α,α-difluoro-3-coumaranones via the corresponding O-silylated ethoxy ketals. The mechanism has been investigated by in situ 19F and 29Si NMR spectroscopy, CF2-trapping, competition, titration, and comparison of the kinetics with the 3-, 4-, 5-, and 6-fluoro ethyl salicylate analogues and their O-silylated derivatives. The process evolves in five distinct stages, each arising from a discrete array of anion speciations that modulate a sequence of silyl-transfer chain reactions. The deconvolution of coupled equilibria between salicylate, [CF3]-, and siliconate [Me3Si(CF3)2]- anions allowed the development of a kinetic model that accounts for the first three stages. The model provides valuable practical insights. For example, it explains how the initial concentrations of the TMSCF3 and salicylate and the location of electron-withdrawing salicylate ring substituents profoundly impact the overall viability of the process, how stoichiometric CF3H generation can be bypassed by using the O-silylated salicylate, and how the very slow liberation of the α,α-difluoro-3-coumaranone can be rapidly accelerated by evaporative or aqueous workup.

Fluorene-based tau fibrillation sensor and inhibitor with fluorogenic and photo-crosslinking properties

Tau protein aggregation into neurofibrillary tangles often causes tauopathies. Herein, we report fluorene based sensors with fluorogenicity upon binding to tau proteins. Intriguingly, these sensors possess triplet state properties to inhibit tau fibrillation upon photo-induced crosslinking.

Multipronged diagnostic and therapeutic strategies for Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurodegenerative disorder and a major contributor to dementia cases worldwide. AD is clinically characterized by learning, memory, and cognitive deficits. The accumulation of extracellular amyloid β (Aβ) plaques and neurofibrillary tangles (NFTs) of tau are the pathological hallmarks of AD and are explored as targets for clinical diagnosis and therapy. AD pathology is poorly understood and there are no fully approved diagnosis and treatments. Notwithstanding the gap, decades of research in understanding disease mechanisms have revealed the multifactorial nature of AD. As a result, multipronged and holistic approaches are pertinent to targeting multiple biomarkers and targets for developing effective diagnosis and therapeutics. In this perspective, recent developments in Aβ and tau targeted diagnostic and therapeutic tools are discussed. Novel indirect, combination, and circulating biomarkers as potential diagnostic targets are highlighted. We underline the importance of multiplexing and multimodal detection of multiple biomarkers to generate biomarker fingerprints as a reliable diagnostic strategy. The classical therapeutics targeting Aβ and tau aggregation pathways are described with bottlenecks in the strategy. Drug discovery efforts targeting multifaceted toxicity involving protein aggregation, metal toxicity, oxidative stress, mitochondrial damage, and neuroinflammation are highlighted. Recent efforts focused on multipronged strategies to rationally design multifunctional modulators targeting multiple pathological factors are presented as future drug development strategies to discover potential therapeutics for AD.

Non-invasive imaging of tau-targeted probe uptake by whole brain multi-spectral optoacoustic tomography

PURPOSE

Abnormal tau accumulation within the brain plays an important role in tauopathies such as Alzheimer's disease and frontotemporal dementia. High-resolution imaging of tau deposits at the whole-brain scale in animal disease models is highly desired.

METHODS

We approached this challenge by non-invasively imaging the brains of P301L mice of 4-repeat tau with concurrent volumetric multi-spectral optoacoustic tomography (vMSOT) at ~ 115 μm spatial resolution using the tau-targeted pyridinyl-butadienyl-benzothiazole derivative PBB5 (i.v.). In vitro probe characterization, concurrent vMSOT and epi-fluorescence imaging of in vivo PBB5 targeting (i.v.) was performed in P301L and wild-type mice, followed by ex vivo validation using AT-8 antibody for phosphorylated tau.

RESULTS

PBB5 showed specific binding to recombinant K18 tau fibrils by fluorescence assay, to post-mortem Alzheimer's disease brain tissue homogenate by competitive binding against [11C]PBB3 and to tau deposits (AT-8 positive) in post-mortem corticobasal degeneration and progressive supranuclear palsy brains. Dose-dependent optoacoustic and fluorescence signal intensities were observed in the mouse brains following i.v. administration of different concentrations of PBB5. In vivo vMSOT brain imaging of P301L mice showed higher retention of PBB5 in the tau-laden cortex and hippocampus compared to wild-type mice, as confirmed by ex vivo vMSOT, epi-fluorescence, multiphoton microscopy, and immunofluorescence staining.

CONCLUSIONS

We demonstrated non-invasive whole-brain imaging of tau in P301L mice with vMSOT system using PBB5 at a previously unachieved ~ 115 μm spatial resolution. This platform provides a new tool to study tau spreading and clearance in a tauopathy mouse model, foreseeable in monitoring tau targeting putative therapeutics.

Visualizing the Interplay of Lipid Droplets and Protein Aggregates During Aging via a Dual-Functional Fluorescent Probe

Fluorescence imaging the interplay between lipid droplets (LDs) and protein aggregates (PAs) is extremely valuable for elucidating molecular mechanisms of aging. Here, we describe the first dual-functional fluorescent probe, LW-1, for simultaneously imaging LDs and PAs in distinct fluorescence channels to dissect interplaying roles between LDs and PAs during aging. Notably, based on an intriguing mechanism of hydrogen bonds regulating single bond rotation, LW-1 selectively detected LDs in a red channel. Meanwhile, based on another mechanism of the hydrogen bond regulating intramolecular charge transfer efficiency, probe LW-1 further detected PAs in an NIR channel. Practical applications showed that LW-1 was capable of concurrently detecting LDs and PAs in living cells. Moreover, simultaneously imaging LDs and PAs in intestine tissues of mice at different aging degrees was conducted. The results denoted that the PAs level in the intestine tissue increased dramatically with aging, accompanying the buildup of LDs. Significantly, the interplay between LDs and PAs during aging was observed. These evidences demonstrated that the PAs level was closely related with aging processes in intestine tissues, while LDs were formed correspondingly to interact with PAs, suggesting that excessive PAs can be loaded into LDs and then be removed by lipophagy.