Imaging Of Β-amyloid Plaques Research Articles

GFP-based red-emissive fluorescent probes for dual imaging of β-amyloid plaques and mitochondrial viscosity

Alzheimer’s disease (AD), with incurable neurodegenerative damage, has attracted growing interest in exploration of better AD biomarkers in its early diagnosis. Among various biomarkers, amyloid-β (Aβ) aggregates and mitochondrial viscosity are closely related to AD and their dual imaging might provide a potential and feasible strategy. In this work, five GFP-based red-emissive fluorescent probes were rationally designed and synthesized for selective detection of β-amyloid plaques and viscosity, among which C25e exhibited superior properties and could successfully image β-amyloid plaques and mitochondrial viscosity with different fluorescence wavelength signals “turn-on” at around 624 and 640 nm, respectively. Moreover, the staining of brain sections from a transgenic AD mouse showed that probe C25e showed higher selectivity and signal-to-noise ratio towards Aβ plaques than commercially-available Thio-S. In addition, the probe C25e was, for the first time, employed for monitoring amyloid-β induced mitochondrial viscosity changes. Therefore, this GFP-based red-emissive fluorescent probe C25e could serve as a dual-functional tool for imaging β-amyloid plaques and mitochondrial viscosity, which might provide a unique strategy for the early diagnosis of Alzheimer’s disease.

A New Highly Deuterated [18F]AV-45, [18F]D15FSP, for Imaging β-Amyloid Plaques in the Brain.

[18F]AV-45 (florbetapir f18, Amyvid) is an FDA-approved PET imaging agent targeting Aβ plaques in the brain for diagnosis of Alzheimer's disease (AD). Its metabolites led to a high background in the brain and large bone uptake of [18F]F-, produced from dealkylation of the PEG chain. To slow down the in vivo metabolism, we report the design, synthesis, and evaluation of a highly deuterated derivative, [18F]D15FSP, and compared it with N-methyl-deuterated [18F]D3FSP and nondeuterated [18F]AV-45. D15FSP displayed excellent binding affinity (K i = 7.52 nM) to Aβ aggregates. In vitro autoradiography of [18F]D15FSP, [18F]D3FSP, and [18F]AV-45 showed excellent binding to Aβ plaques in human AD brain sections. Biodistribution studies displayed lower bone uptake at 120 min for [18F]D15FSP compared to that for [18F]D3FSP and [18F]AV-45 (1.44 vs 4.23 and 4.03%ID/g, respectively). As the highly deuterated [18F]D15FSP displayed excellent Aβ binding affinity, high initial brain penetration, and lower bone retention, it might be suitable for PET imaging in detecting Aβ plaques.

Dual-functional AIE fluorescent probes for imaging β-amyloid plaques and lipid droplets

Alzheimer’s disease (AD) is a chronic neurodegenerative disease. Better imaging and early diagnosis of biomarkers of AD is extremely important for therapeutic interventions. The amyloid cascade hypothesis and its revised version identify insoluble β-amyloid deposition as a good diagnostic biomarker for AD. Moreover, lipid droplets may also act as an auxiliary biomarker related to AD pathology based on recent studies. Herein, two quinoline-based AIE probes were designed and synthesized for the imaging of Aβ plaques and lipid droplets. The probes exhibited remarkable turn-on fluorescence enhancements with the Aβ aggregates. The lipid droplets-targeting probe FB exhibited high selectivity and binding affinity towards the Aβ aggregates with a detection limit as low as 26.9 nM. Furthermore, FB was capable of readily imaging Aβ plaques and lipid droplets at the cellular level and in brain sections of transgenic AD mice. The probe FB can serve as a promising tool for developing early diagnosis and innovative therapeutics of AD.

β-淀粉样蛋白斑块的无标记成像及光动力降解

β-淀粉样蛋白斑块的无标记成像及光动力降解

Label-free multiphoton imaging of β-amyloid plaques in Alzheimer's disease mouse models.

.-Amyloid () plaque, representing the progressive accumulation of the protein that mainly consists of , is one of the prominent pathological hallmarks of Alzheimer’s disease (AD). Label-free imaging of plaques holds the potential to be a histological examination tool for diagnosing AD. We applied label-free multiphoton microscopy to identify extracellular plaque as well as intracellular accumulation for the first time from AD mouse models. We showed that a two-photon-excited fluorescence signal is a sensitive optical marker for revealing the spatial–temporal progression and the surrounding morphological changes of deposition, which demonstrated that both extracellular and intracellular accumulations play an important role in the progression of AD. Moreover, combined with a custom-developed image-processing program, we established a rapid method to visualize different degrees of deposition by color coding. These results provide an approach for investigating pathophysiology of AD that can complement traditional biomedical procedures.

Development of novel theranostic agents for in vivo amyloid imaging and protective effects on human neuroblastoma cells

Brain amyloid deposits have been identified as the main neuropathological hallmarks of Alzheimer's diseases (AD) and intensive efforts have been devoted to develop aggregation inhibitors preventing the formation of toxic oligomeric Aβ for therapeutic. In addition, evidence indicates that the formation and accumulation of β−amyloid plaques probably precede clinical symptoms by around 20 years and imaging of such plaques would be beneficial for early-stage AD detection. In this study, we investigated phenothiazine-based compounds as novel promising theranostic agents for AD. These multifunctional agents exhibited BBB permeability, low neurotoxicity, good bio-stability as well as strong turn-on fluorescence with a Stokes shift upon binding to Aβ aggregates. They had metal-chelating property which could delay Aβ aggregation and displayed high binding affinity for β−amyloid aggregates. Moreover, they have been simultaneously applied to perform in vivo near-infrared fluorescence imaging of β-amyloid plaques in double transgenic AD mouse model, to prevent self-aggregation of Aβ monomer from forming toxic oligomers and to protect human neuroblastoma SH-SY5Y cells against Aβ-induced toxicity and oxidative stress.

Phenothiazine-based theranostic compounds for in vivo near-infared fluorescence imaging of β-amyloid plaques and inhibition of Aβ aggregation

A global burden of Alzheimer's disease (AD) has been growing over last decades. Evidence indicates that β-amyloid (Aβ) production and senile plaque deposition in the brain is causative in the onset of AD pathogenesis. It appears much earlier than cognitive decline and plays a key role in initiating and developing AD neuropathology. As such, there is an intense passion with discovering theranostic agents which make a significant impact in diagnostic and therapy. Herein, we report an investigation of novel phenothiazine-based compounds as promising potential theranostic agents for AD. Remarkably, they have exhibited a high binding affinity toward Aβ aggregates, a good biostability and a strong increase in their fluorescence intensity with blue shift when interacting with Aβ aggregates. Furthermore, they have been simultaneously applied to perform NIR in vivo imaging of β-amyloid plaques in double transgenic AD mouse model, to prevent self-aggregation of Aβ monomer from forming toxic oligmers and to reduce Aβ-induced toxicity of human neuroblastoma cells (SH-SY5Y).

A hemicyanine derivative for near-infrared imaging of β-amyloid plaques in Alzheimer's disease

The formation of amyloid-β (Aβ) plaques in the brain is one of the main pathological features of Alzheimer's disease (AD). The imaging probes, capable of detecting Aβ deposition, are important tools for early diagnosis of AD. In this article, we designed, synthesized and evaluated a cyanine-based near-infrared fluorescence (NIRF) probe ZT-1 for the detection of Aβ deposits in the brain. The probe had excellent fluorescent properties with an emission maximum above 720 nm upon binding to Aβ aggregates with affinity of 445.0 nM (Kd). Furthermore, ZT-1 exhibited good biostability, photostability, and binding selectivity toward Aβ1-42 aggregates by in vitro fluorescence staining experiments. In vivo NIRF imaging result also revealed that our probe could efficiently differentiate transgenic and wild-type mice. All these studies indicated that ZT-1 is a promising fluorescent probe for Aβ plaques in the AD brains.

Early Detection of Aβ Deposition in the 5xFAD Mouse by Amyloid PET.

Purpose. 18F-FC119S is a positron emission tomography (PET) tracer for imaging β-amyloid (Aβ) plaques in Alzheimer's disease (AD). The aim of this study is to evaluate the efficacy of 18F-FC119S in quantitating Aβ deposition in a mouse model of early amyloid deposition (5xFAD) by PET. Method. Dynamic 18F-FC119S PET images were obtained in 5xFAD (n = 5) and wild-type (WT) mice (n = 7). The brain PET images were spatially normalized to the M. Mirrione T2-weighted mouse brain MR template, and the volumes of interest were then automatically drawn on the cortex, hippocampus, thalamus, and cerebellum. The specific binding of 18F-FC119S to Aβ was quantified as the distribution volume ratio using Logan graphical analysis with the cerebellum as a reference tissue. The Aβ levels in the brain were also confirmed by immunohistochemical analysis. Result. For the 5xFAD group, radioactivity levels in the cortex, the hippocampus, and the thalamus were higher than those for the WT group. In these regions, specific binding was approximately 1.2-fold higher in 5xFAD mice than in WT. Immunohistochemistry supported these findings; the 5xFAD showed severe Aβ deposition in the cortex and hippocampus in contrast to the WT group. Conclusion. These results demonstrated that 18F-FC119S PET can successfully distinguish Aβ depositions in 5xFAD mice from WT.

Design and synthesis of new theranostic agents for near-infrared imaging of β-amyloid plaques and inhibition of β-amyloid aggregation in Alzheimer's disease

The presence of amyloid plaques predisposes clinical symptoms of cognitive impairment, which occurs much earlier than other clinical symptoms and plays a crucial role in the neuropathology of AD. Thus, developing probes for Aβ species imaging could be used for early diagnosis of AD, and blocking the initial steps of Aβ aggregation with small molecules has emerged as a valid disease-modifying therapy for Aβ. Herein, we report the design, synthesis and evaluation of a series of new theranostic agents, which can simultaneously perform near infra-red imaging of Aβ plaques, prevent self-aggregation of Aβ monomer, disaggregate preformed Aβ fibrils and play a protective effect on the toxicity of human neuroblastoma cells (SHSY5Y) induced by Aβ1–42. Most of these probes displayed maximum emission in PBS (>650 nm), which falls in the good range for NIRF probes. Importantly, these probes are found to have a high binding affinity toward Aβ aggregates, to exhibit a large fluorescence enhancement upon interaction with Aβ aggregates accompanied by a blueshift in the emission spectra of 20–40 nm and to show an excellent targeting ability for Aβ plaques in slices of brain and eye containing retina tissue from double transgenic mice. These molecules show a promising potential as theranostic agents for the diagnosis and therapy of AD.

6-Methoxy-indanone derivatives as potential probes for β-amyloid plaques in Alzheimer's disease

A series of 6-methoxy indanone derivatives was synthesized and evaluated as potential probes for β-amyloid plaque imaging in Alzheimer's disease (AD). Two derivatives (5d and 5k) displayed significant binding abilities in fluorescent staining experiments using the brain sections of AD patients. Two derivatives showed high binding affinities to β-amyloid aggregates (5j, Ki = 5.82 ± 0.19 nM) and brain homogenates of AD patients (5j, Ki = 18.96 ± 0.28 nM) in in vitro binding assay. With a log P value of 3.45, [125I]5k exhibited an excellent initial brain uptake (5.29%ID g−1, 2 min after i.v.) and a fast clearance from the brain in biodistribution experiments in normal mice. In autoradiography, [125I]5k exhibited an obvious binding ability to β-amyloid plaques and a relatively low nonspecific binding in the brain sections of AD patients (in vitro) and APP/PS1 transgenic mice (in vitro and ex vivo). Results suggest that 5k is a potential probe for detecting β-amyloid plaques in vivo.

Preliminary Characterization and In Vivo Studies of Structurally Identical (18)F- and (125)I-Labeled Benzyloxybenzenes for PET/SPECT Imaging of β-Amyloid Plaques.

With the assistance of molecular docking and 3D-QSAR models established previously, structurally identical 18F- and 125I-labeled benzyloxybenzene derivatives were designed to achieve the early detection of Aβ plaques by PET/SPECT imaging. In competition binding assay, ligands 7a and 12a displayed high binding affinities to Aβ42 aggregates with Ki values of 19.5 nM and 23.9 nM, respectively. Specific plaque labeling was observed on the in vitro autoradiography of brain sections from AD patients and Tg mice. In biodistribution, [125I]7a, [18F]7a, [125I]12a and [18F]12a all exhibited high initial brain uptakes (>5% ID/g at 2 min). [125I]7a and [125I]12a cleared fast from the normal brain regions, while corresponding [18F]7a and [18F]12a showed slow washout rates. Dynamic microPET/CT and microSPECT/CT imaging data in normal ICR mice were in accordance with in vivo biodistribution results. In vivo metabolism results indicated that the different clearance profiles between the structurally identical 18F- and 125I-labeled tracers could be attributed to different biochemical characteristics of the radiometabolites. Radioiodinated benzyloxybenzene derivatives exhibited good in vivo biostability in brain. Ex vivo autoradiography further confirmed the strong in vivo Aβ labeling ability of [125I]7a. These new fluorinated and iodinated benzyloxybenzenes can develop into PET/SPECT dual imaging agents targeting Aβ plaques.

Imaging of β-amyloid plaques by near infrared fluorescent tracers: a new frontier for chemical neuroscience

Brain amyloid depositions are the main hallmarks of Alzheimer's and other protein misfolding diseases. Since they are believed to precede clinical symptoms by several years, imaging of such fibrillar aggregates is particularly suitable to diagnose the onset of the disease in its early stage and monitor its progression. In this context, near infrared (NIR) imaging has been proposed as a promising and non-invasive method to visualize amyloid plaques in vivo because of its acceptable depth of penetration and minimal degree of tissue damage. In this tutorial review, we describe the main chemical and physicochemical features of probes associated with fluorescence emission in the NIR region. The review focuses on the recent progress and improvements in the development of small-molecule NIR fluorescent probes and their in vivo application in living animals. In addition, the possible therapeutic application of NIR probes to block the pathological aggregation process will be discussed, raising the fascinating possibility of their exploitation as theranostic agents.

In vivo fluorescence imaging of β-amyloid plaques with push-pull dimethylaminothiophene derivatives.

In vivo fluorescence imaging of β-amyloid (Aβ) plaques in the brain is expected to be used as a new method for detecting Alzheimer's disease (AD). We synthesized novel push-pull dimethylaminothiophenyl (DTM) derivatives and evaluated their utility as in vivo fluorescence imaging probes targeting Aβ plaques. As a result, we found that DTM-2 is a promising fluorescent probe for Aβ plaques in the AD brains.

Synthesis and biological evaluation of 123I-labeled pyridyl benzoxazole derivatives: novel β-amyloid imaging probes for single-photon emission computed tomography

The result in the present study suggested that [123I]9 may be a potential SPECT probe for imaging β-amyloid plaques in the brains of patient with Alzheimer's disease.

Radiolabeled bioactive benzoheterocycles for imaging β-amyloid plaques in Alzheimer's disease.

Alzheimer's disease (AD) is a debilitating neurodegenerative dementia that involves substantial neuronal loss. Extracellular deposition of neurotoxic β-amyloid (Aβ) plaques in the brain has been recognized as the central histological characteristic of AD. In the past decade, precise detection of the Aβ plaques at preclinical AD with positron emission tomography (PET) or single photon emission computed tomography (SPECT) has achieved continued development. A big category of Aβ imaging agents was benzoheterocycles which derived from Thioflavin-T (ThT), a traditional amyloid binding dye. This review summarizes the past and current status of radioactive benzoheterocycles designed to selectively bind to Aβ plaques. Separate sections discuss the chemical synthesis, invitro and invivo investigations of radiolabeled benzothiazole, benzoxazole, benzofuran, benzothiophene, indole, imidazopyridine and quinoxaline analogs to act as PET/SPECT candidates for imaging Aβ plaques.

Synthesis and evaluation of a phenylbenzothiazole-based 99mTc(CO)3-radiotracer for possible application in imaging of β-amyloid plaques in Alzheimer’s disease

The 2-phenyl benzothiazole pharmacophore is known to have high affinity for amyloid beta (Aβ) and is therefore derivatized, to [N-(4′-benzothiazol-pyridin-2-yl-methyl-amino)-acetic acid (BTPAA)] for radiolabeling with [99mTc(CO)3(H2O)3]+ precursor. The radiotracer, 99mTc(CO)3–BTPAA is evaluated in vitro and in vivo to determine its binding with the Aβ and ability to cross the blood brain barrier. The radiotracer prepared in >95 % radiochemical yield, showed ~25 % inhibition in presence of thioflavin-T, indicating its specificity towards aggregated Aβ protein. The radiotracer also showed brain uptake of 0.25 ± 0.04 % injected dose/g at 2 min post injection, indicating its ability to cross the blood brain barrier.

Novel 18F-labeled dibenzylideneacetone derivatives as potential positron emission tomography probes for in vivo imaging of β-amyloid plaques

A series of dibenzylideneacetones were synthesized and evaluated as imaging probes for β-amyloid plaques. They displayed high binding affinity to Aβ1–42 aggregates (Ki = 6.4 for 8, Ki = 3.0 for 9), and the high binding were confirmed by in vitro autoradiography with AD human and transgenic mouse brain sections. Two of them were selected for 18F-labeling directly on the benzene ring. In biodistribution experiments, [18F]8 and [18F]9 displayed high initial uptakes (9.29 ± 0.41 and 5.38 ± 0.68% ID/g) and rapid washouts from the normal brain (brain2 min/brain60 min ratios of 21.6 and 13.4). These preliminary results suggest that [18F]8 and [18F]9 may be used as potential PET imaging agents for the detection of Aβ plaques in the brain.

Synthesis and evaluation of a 18F-curcumin derivate for β-amyloid plaque imaging

IntroductionCurcumin is a neuroprotective compound that inhibits the formation of amyloid oligomers and fibrils and binds to β-amyloid plaques in Alzheimer’s disease (AD). We aimed to synthesize an 18F-labeled curcumin derivate ([18F]4) and to characterize its positron emission tomography (PET) tracer-binding properties to β-amyloid plaques in a transgenic APP23 mouse model of AD. MethodsWe utilized facile one-pot synthesis of [18F]4 using nucleophilic 18F-fluorination and click chemistry. Binding of [18F]4 to β-amyloid plaques in the transgenic APP23 mouse brain cryosections was studied in vitro using heterologous competitive binding against PIB. [18F]4 uptake was studied ex vivo in rodents and in vivo using PET/computed tomography of transgenic APP23 and wild-type control mice. ResultsThe radiochemical yield of [18F]4 was 21±11%, the specific activity exceeded 1TBq/μmol, and the radiochemical purity exceeded 99.3% at the end of synthesis. In vitro studies of [18F]4 with the transgenic APP23 mouse revealed high β-amyloid plaque binding. In vivo and ex vivo studies demonstrated that [18F]4 has fast clearance from the blood, moderate metabolism but low blood–brain barrier (BBB) penetration. Conclusions[18F]4 was synthesized in high yield and excellent quality. In vitro studies, metabolite profile, and fast clearance from the blood indicated a promising tracer for Aβ imaging. However, [18F]4 has low in vivo BBB penetration and thus further studies are needed to reveal the reason for this and to possibly overcome this issue.

Novel radioiodinated 1,3,4-oxadiazole derivatives with improved in vivo properties for SPECT imaging of β-amyloid plaques

We designed and synthesized a novel series of radioiodinated 3-(5-phenyl-1,3,4-oxadiazol-2-yl)pyridine (1,3,4-PODP) derivatives for imaging β-amyloid (Aβ) plaques in Alzheimer's disease (AD) brains using single photon emission computed tomography (SPECT). In binding experiments in vitro, 1,3,4-PODP derivatives (3 and 6) displayed high affinity for Aβ(1-42) aggregates (25 and 14 nM, respectively). In experiments in vivo, [123/125I]3 and [123/125I]6 displayed good initial uptake into and rapid washout from the brain in normal mice, and clearly labeled Aβ plaques in Tg2576 mice. Furthermore, specific labeling of Aβ plaques was observed in in vitro autoradiography of postmortem AD brain sections. These results suggested that 1,3,4-PODP derivatives may be useful SPECT probes for detecting Aβ plaques in AD brains.