Combining Blood-Based Biomarkers and Structural MRI Measurements to Distinguish Persons with and without Significant Amyloid Plaques.

Background: Amyloid-ß (Aß) plaques play a pivotal role in Alzheimer's disease. The current positron emission tomography (PET) is expensive and limited in availability. In contrast, blood-based biomarkers (BBBMs) show potential for characterizing Aß plaques more affordably. We have previously proposed an MRI-based hippocampal morphometry measure to be an indicator of Aß plaques. Objective: To develop and validate an integrated model to predict brain amyloid PET positivity combining MRI feature and plasma Aß42/40 ratio. Methods: We extracted hippocampal multivariate morphometry statistics from MR images and together with plasma Aß42/40 trained a random forest classifier to perform a binary classification of participant brain amyloid PET positivity. We evaluated the model performance using two distinct cohorts, one from the Alzheimer's Disease Neuroimaging Initiative (ADNI) and the other from the Banner Alzheimer's Institute (BAI), including prediction accuracy, precision, recall rate, F1 score, and AUC score. Results: Results from ADNI (mean age 72.6, Aß+ rate 49.5%) and BAI (mean age 66.2, Aß+ rate 36.9%) datasets revealed the integrated multimodal (IMM) model's superior performance over unimodal models. The IMM model achieved prediction accuracies of 0.86 in ADNI and 0.92 in BAI, surpassing unimodal models based solely on structural MRI (0.81 and 0.87) or plasma Aß42/40 (0.73 and 0.81) predictors. CONCLUSIONS: Our IMM model, combining MRI and BBBM data, offers a highly accurate approach to predict brain amyloid PET positivity. This innovative multiplex biomarker strategy presents an accessible and cost-effective avenue for advancing Alzheimer's disease diagnostics, leveraging diverse pathologic features related to Aß plaques and structural MRI.

Noninvasive Visualization of Amyloid-Beta Deposits in Alzheimer's Amyloidosis Mice via Fluorescence Molecular Tomography Using Contrast Agent.

Alzheimer's disease is pathologically featured by the accumulation of amyloid-beta (Aß) plaque and neurofibrillary tangles. Compared to small animal positron emission tomography, optical imaging features nonionizing radiation, low cost, and logistic convenience. Optical detection of Aß deposits is typically implemented by 2D macroscopic imaging and various microscopic techniques assisted with Aß-targeted contrast agents. Here, we introduce fluorescence molecular tomography (FMT), a macroscopic 3D fluorescence imaging technique, convenient for in vivo longitudinal monitoring of the animal brain without the involvement of cranial window opening operation. This chapter aims to provide the protocols for FMT in vivo imaging of Aß deposits in the brain of rodent model of Alzheimer's disease. The materials, stepwise method, notes, limitations of FMT, and emerging opportunities for FMT techniques are presented.

Timing of Biomarker Changes in Sporadic Alzheimer's Disease in Estimated Years from Symptom Onset.

OBJECTIVE: A clock relating amyloid positron emission tomography (PET) to time was used to estimate the timing of biomarker changes in sporadic Alzheimer disease (AD). METHODS: Research participants were included who underwent cerebrospinal fluid (CSF) collection within 2 years of amyloid PET. The ages at amyloid onset and AD symptom onset were estimated for each individual. The timing of change for plasma, CSF, imaging, and cognitive measures was calculated by comparing restricted cubic splines of cross-sectional data from the amyloid PET positive and negative groups. RESULTS: The amyloid PET positive sub-cohort (n = 118) had an average age of 70.4 ± 7.4 years (mean ± standard deviation) and 16% were cognitively impaired. The amyloid PET negative sub-cohort (n = 277) included individuals with low levels of amyloid plaque burden at all scans who were cognitively unimpaired at the time of the scans. Biomarker changes were detected 15-19 years before estimated symptom onset for CSF Aß42/Aß40, plasma Aß42/Aß40, CSF pT217/T217, and amyloid PET; 12-14 years before estimated symptom onset for plasma pT217/T217, CSF neurogranin, CSF SNAP-25, CSF sTREM2, plasma GFAP, and plasma NfL; and 7-9 years before estimated symptom onset for CSF pT205/T205, CSF YKL-40, hippocampal volumes, and cognitive measures. INTERPRETATION: The use of an amyloid clock enabled visualization and analysis of biomarker changes as a function of estimated years from symptom onset in sporadic AD. This study demonstrates that estimated years from symptom onset based on an amyloid clock can be used as a continuous staging measure for sporadic AD and aligns with findings in autosomal dominant AD. ANN NEUROL 2024;95:951-965.

Combination of deep learning and 2D CARS figures for identification of amyloid-ß plaques.

In vivo imaging and accurate identification of amyloid-ß (Aß) plaque are crucial in Alzheimer's disease (AD) research. In this work, we propose to combine the coherent anti-Stokes Raman scattering (CARS) microscopy, a powerful detection technology for providing Raman spectra and label-free imaging, with deep learning to distinguish Aß from non-Aß regions in AD mice brains in vivo. The 1D CARS spectra is firstly converted to 2D CARS figures by using two different methods: spectral recurrence plot (SRP) and spectral Gramian angular field (SGAF). This can provide more learnable information to the network, improving the classification precision. We then devise a cross-stage attention network (CSAN) that automatically learns the features of Aß plaques and non-Aß regions by taking advantage of the computational advances in deep learning. Our algorithm yields higher accuracy, precision, sensitivity and specificity than the results of conventional multivariate statistical analysis method and 1D CARS spectra combined with deep learning, demonstrating its competence in identifying Aß plaques. Last but not least, the CSAN framework requires no prior information on the imaging modality and may be applicable to other spectroscopy analytical fields.

Two-Photon Fluorescent Probes for Amyloid-ß Plaques Imaging In Vivo.

Amyloid-ß (Aß) peptide deposition, hyperphosphorylated tau proteins, reactive astrocytes, high levels of metal ions, and upregulated monoamine oxidases are considered to be the primary pathological markers of Alzheimer's disease (AD). Among them, Aß peptide deposition or Aß plaques, is regarded as the initial factor in the pathogenesis of AD and a critical pathological hallmark in AD. This review highlights recently Aß-specific fluorescent probes for two-photon imaging of Aß plaques in vivo. It includes the synthesis and detection mechanism of probes, as well as their application to two-photon imaging of Aß plaques in vivo.

3D dynamic tracking Aß plaques in live brains using vinyl-bridged dyes with two-photon excitation/NIR emission and large Stokes shifts.

Real-time studies of biomarkers for neurological disorders present significant opportunities for diagnosing and treating related diseases, and fluorescent probes offer a promising approach to brain imaging. However, intracerebral fluorescence imaging is often limited by blood-brain barrier permeability and penetration depth. Moreover, only very few probes have rapid intracerebral metabolic properties, which are critical for in vivo imaging. Here, we developed a novel class of fluorescent dyes with two-photon excitation and near-infrared (NIR) emission (920/705 nm). The representative WAPP-4 probe exhibits a large Stokes shift (Δλ = 324 nm in ethanol) and excellent blood-brain barrier permeability. Notably, using WAPP-4, we achieved in vivo 3D dynamic imaging of Aß plaques in the brains of living mice with Alzheimer's disease (AD). In addition, super-resolution imaging showed that WAPP-4 could effectively characterize the distribution and shape of Aß plaques in isolated brain slices. This study demonstrates that newly developed fluorescent dyes with large Stokes shifts and blood-brain barrier permeability enable real-time imaging of amyloid plaques, which will contribute to the development of other valuable tools for near-infrared imaging and super-resolution imaging in the brain.

Virtual histology of Alzheimer's disease: Biometal entrapment within amyloid-ß plaques allows for detection via X-ray phase-contrast imaging.

Amyloid-ß (Aß) plaques from Alzheimer's Disease (AD) can be visualized ex vivo in label-free brain samples using synchrotron X-ray phase-contrast tomography (XPCT). However, for XPCT to be useful as a screening method for amyloid pathology, it is essential to understand which factors drive the detection of Aß plaques. The current study was designed to test the hypothesis that Aß-related contrast in XPCT could be caused by Aß fibrils and/or by metals trapped in the plaques. Fibrillar and elemental compositions of Aß plaques were probed in brain samples from different types of AD patients and AD models to establish a relationship between XPCT contrast and Aß plaque characteristics. XPCT, micro-Fourier-Transform Infrared spectroscopy and micro-X-Ray Fluorescence spectroscopy were conducted on human samples (one genetic and one sporadic case) and on four transgenic rodent strains (mouse: APPPS1, ArcAß, J20; rat: TgF344). Aß plaques from the genetic AD patient were visible using XPCT, and had higher ß-sheet content and higher metal levels than those from the sporadic AD patient, which remained undetected by XPCT. Aß plaques in J20 mice and TgF344 rats appeared hyperdense on XPCT images, while they were hypodense with a hyperdense core in the case of APPPS1 and ArcAß mice. In all four transgenic strains, ß-sheet content was similar, while metal levels were highly variable: J20 (zinc and iron) and TgF344 (copper) strains showed greater metal accumulation than APPPS1 and ArcAß mice. Hence, a hyperdense contrast formation of Aß plaques in XPCT images was associated with biometal entrapment within plaques. STATEMENT OF SIGNIFICANCE: The role of metals in Alzheimer's disease (AD) has been a subject of continuous interest. It was already known that amyloid-ß plaques (Aß), the earliest hallmark of AD, tend to trap endogenous biometals like zinc, iron and copper. Here we show that this metal accumulation is the main reason why Aß plaques are detected with a new technique called X-ray phase contrast tomography (XPCT). XPCT enables to map the distribution of Aß plaques in the whole excised brain without labeling. In this work we describe a unique collection of four transgenic models of AD, together with a human sporadic and a rare genetic case of AD, thus exploring the full spectrum of amyloid contrast in XPCT.

GFP-based red-emissive fluorescent probes for dual imaging of ß-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-ß (Aß) 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 ß-amyloid plaques and viscosity, among which C25e exhibited superior properties and could successfully image ß-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 Aß plaques than commercially-available Thio-S. In addition, the probe C25e was, for the first time, employed for monitoring amyloid-ß induced mitochondrial viscosity changes. Therefore, this GFP-based red-emissive fluorescent probe C25e could serve as a dual-functional tool for imaging ß-amyloid plaques and mitochondrial viscosity, which might provide a unique strategy for the early diagnosis of Alzheimer's disease.

Radiolabeled Chalcone Derivatives as Potential Radiotracers for ß-Amyloid Plaques Imaging.

Natural products often provide a pool of pharmacologically relevant precursors for the development of various drug-related molecules. In this review, the research performed on some radiolabeled chalcone derivatives characterized by the presence of the α-ß unsaturated carbonyl functional group as potential radiotracers for the imaging of ß-amyloids plaques will be summarized. Chalcones' structural modifications and chemical approaches which allow their radiolabeling with the most common SPECT (Single Photon Emission Computed Tomography) and PET (Positron Emission Tomography) radionuclides will be described, as well as the state of the art regarding their in vitro binding affinity and in vivo biodistribution and pharmacokinetics in preclinical studies. Moreover, an explanation of the rationale behind their potential utilization as probes for Alzheimer's disease in nuclear medicine applications will be provided.

Tetramodal Chemical Imaging Delineates the Lipid-Amyloid Peptide Interplay at Single Plaques in Transgenic Alzheimer's Disease Models.

Beta-amyloid (Aß) plaque pathology is one of the most prominent histopathological feature of Alzheimer's disease (AD). The exact pathogenic mechanisms linking Aß to AD pathogenesis remain however not fully understood. Recent advances in amyloid-targeting pharmacotherapies highlight the critical relevance of Aß aggregation for understanding the molecular basis of AD pathogenesis. We developed a novel, integrated, tetramodal chemical imaging paradigm for acquisition of trimodal mass spectrometry imaging (MSI) and interlaced fluorescent microscopy from a single tissue section. We used this approach to comprehensively investigate lipid-Aß correlates at single plaques in two different mouse models of AD (tgAPPSwe and tgAPPArcSwe) with varying degrees of intrinsic properties affecting amyloid aggregation. Integration of the multimodal imaging data and multivariate data analysis identified characteristic patterns of plaque-associated lipid- and peptide localizations across both mouse models. Correlative fluorescence microscopy using structure-sensitive amyloid probes identified intra-plaque structure-specific lipid- and Aß patterns, including Aß 1-40 and Aß 1-42 along with gangliosides (GM), phosphoinositols (PI), conjugated ceramides (CerP and PE-Cer), and lysophospholipids (LPC, LPA, and LPI). Single plaque correlation analysis across all modalities further revealed how these distinct lipid species were associated with Aß peptide deposition across plaque heterogeneity, indicating different roles for those lipids in plaque growth and amyloid fibrillation, respectively. Here, conjugated ceramide species correlated with Aß core formation indicating their involvement in initial plaque seeding or amyloid maturation. In contrast, LPI and PI were solely correlated with general plaque growth. In addition, GM1 and LPC correlated with continuous Aß deposition and maturation. The results highlight the potential of this comprehensive multimodal imaging approach and implement distinct lipids in amyloidogenic proteinopathy.

Independent study demonstrates amyloid probability score accurately indicates amyloid pathology.

BACKGROUND: The amyloid probability score (APS) is the model read-out of the analytically validated mass spectrometry-based PrecivityAD® blood test that incorporates the plasma Aß42/40 ratio, ApoE proteotype, and age to identify the likelihood of brain amyloid plaques among cognitively impaired individuals being evaluated for Alzheimer's disease. PURPOSE: This study aimed to provide additional independent evidence that the pre-established APS algorithm, along with its cutoff values, discriminates between amyloid positive and negative individuals. METHODS: The diagnostic performance of the PrecivityAD test was analyzed in a cohort of 200 nonrandomly selected Australian Imaging, Biomarker & Lifestyle Flagship Study of Aging (AIBL) study participants, who were either cognitively impaired or healthy controls, and for whom a blood sample and amyloid PET imaging were available. RESULTS: In a subset of the dataset aligned with the Intended Use population (patients aged 60 and older with CDR ≥0.5), the pre-established APS algorithm predicted amyloid PET with a sensitivity of 84.9% (CI: 72.9-92.1%) and specificity of 96% (CI: 80.5-99.3%), exclusive of 13 individuals for whom the test was inconclusive. INTERPRETATION: The study shows individuals with a high APS are more likely than those with a low APS to have abnormal amounts of amyloid plaques and be on an amyloid accumulation trajectory, a dynamic and evolving process characteristic of progressive AD pathology. Exploratory data suggest APS retains its diagnostic performance in healthy individuals, supporting further screening studies in the cognitively unimpaired.

Synthesis and In Vitro and In Vivo Evaluation of 18F-Labeled Positron Emission Tomography Tracers for Imaging Aß Plaques.

Accurate quantification of amyloid beta (Aß) plaques is an important indicator for Alzheimer's disease diagnosis and treatment. For this purpose, new highly sensitive Aß tracers were designed by regulating the position and number of nitrogen atoms. A series of derivatives of florbetapir (AV45) containing different numbers and positions of N atoms were synthesized and evaluated for in vitro affinity and in vivo biodistribution. Preliminary study results showed that [18F]BIBD-124 and [18F]BIBD-127 had better clearance rates and less in vivo defluorination than AV45 in ICR (ICR = Institute of Cancer Research) mice. Autoradiography and molecular docking indicated that the binding sites of [18F]BIBD-124/127 were similar to that of [18F]AV45. Micro-positron emission tomography-computed tomography imaging further demonstrated that [18F]BIBD-124 could monitor Aß plaques similar to [18F]AV45. Besides, the imaging contrast of [18F]BIBD-124 is better than that of [18F]AV45. Mass spectrometric metabolic analysis showed that BIBD-124 was less demethylated than AV45 without subsequent acetylation, which might explain its less non-specific uptake and higher imaging contrast. Gauss calculations further confirmed that the introduction of N5 in [18F]BIBD-124 decreased demethylation. Considering imaging contrast and in vivo defluorination, [18F]BIBD-124 is expected to be a promising radiotracer of Aß plaques for further clinical trials.

Development of [124/125I]IAZA as a New Proteinopathy Imaging Agent for Alzheimer's Disease.

Radioiodinated imaging agents for Aß amyloid plaque imaging in Alzheimer's disease (AD) patients have not been actively pursued. Our previous studies employed the "diaza" derivatives [11C]TAZA and [18F]flotaza in order to develop successful positron emission tomography (PET) imaging agents for Aß plaques. There is a need for radioiodinated imaging agents for Aß plaques for single photon emission computed tomography (SPECT) and PET imaging. We report our findings on the preparation of [124/125I]IAZA, a "diaza" analog of [11C]TAZA and [18F]flotaza, and the evaluation of binding to Aß plaques in the postmortem human AD brain. The binding affinity of IAZA for Aß plaques was Ki = 10.9 nM with weak binding affinity for neurofibrillary tangles (Ki = 3.71 µM). Both [125I]IAZA and [124I]IAZA were produced in >25% radiochemical yield and >90% radiochemical purity. In vitro binding of [125I]IAZA and [124I]IAZA in postmortem human AD brains was higher in gray matter containing Aß plaques compared to white matter (ratio of gray to white matter was >7). Anti-Aß immunostaining strongly correlated with [124/125I]IAZA in postmortem AD human brains. The binding of [124/125I]IAZA in postmortem human AD brains was displaced by the known Aß plaque imaging agents. Thus, radiolabeled [124/123I]IAZA may potentially be a useful PET or SPECT radioligand for Aß plaques in brain imaging studies.

Altered dynamics of glymphatic flow in a mature-onset Tet-off APP mouse model of amyloidosis.

BACKGROUND: Alzheimer's disease (AD) is an incurable neurodegenerative disorder characterised by the progressive buildup of toxic amyloid-beta (Aß) and tau protein aggregates eventually leading to cognitive decline. Recent lines of evidence suggest that an impairment of the glymphatic system (GS), a brain waste clearance pathway, plays a key role in the pathology of AD. Moreover, a relationship between GS function and neuronal network integrity has been strongly implicated. Here, we sought to assess the efficacy of the GS in a transgenic Tet-Off APP mouse model of amyloidosis, in which the expression of mutant APP was delayed until maturity, mimicking features of late-onset AD-the most common form of dementia in humans. METHODS: To evaluate GS function, we used dynamic contrast-enhanced MRI (DCE-MRI) in 14-month-old Tet-Off APP (AD) mice and aged-matched littermate controls. Brain-wide transport of the Gd-DOTA contrast agent was monitored over time after cisterna magna injection. Region-of-interest analysis and computational modelling were used to assess GS dynamics while characterisation of brain tissue abnormalities at the microscale was performed ex vivo by immunohistochemistry. RESULTS: We observed reduced rostral glymphatic flow and higher accumulation of the contrast agent in areas proximal to the injection side in the AD group. Clustering and subsequent computational modelling of voxel time courses revealed significantly lower influx time constants in AD relative to the controls. Ex vivo evaluation showed abundant amyloid plaque burden in the AD group coinciding with extensive astrogliosis and microgliosis. The neuroinflammatory responses were also found in plaque-devoid regions, potentially impacting brain-fluid circulation. CONCLUSIONS: In a context resembling late-onset AD in humans, we demonstrate the disruption of glymphatic function and particularly a reduction in brain-fluid influx in the AD group. We conjecture that the hindered circulation of cerebrospinal fluid is potentially caused by wide-spread astrogliosis and amyloid-related obstruction of the normal routes of glymphatic flow resulting in redirection towards caudal regions. In sum, our study highlights the translational potential of alternative approaches, such as targeting brain-fluid circulation as potential therapeutic strategies for AD.

Preparation of near-infrared AIEgen-active fluorescent probes for mapping amyloid-ß plaques in brain tissues and living mice.

Fibrillar aggregates of the amyloid-ß protein (Aß) are the main component of the senile plaques found in brains of patients with Alzheimer's disease (AD). Development of probes allowing the noninvasive and high-fidelity mapping of Aß plaques in vivo is critical for AD early detection, drug screening and biomedical research. QM-FN-SO3 (quinoline-malononitrile-thiophene-(dimethylamino)phenylsulfonate) is a near-infrared aggregation-induced-emission-active fluorescent probe capable of crossing the blood-brain barrier (BBB) and ultrasensitively lighting up Aß plaques in living mice. Herein, we describe detailed procedures for the two-stage synthesis of QM-FN-SO3 and its applications for mapping Aß plaques in brain tissues and living mice. Compared with commercial thioflavin (Th) derivatives ThT and ThS (the gold standard for detection of Aß aggregates) and other reported Aß plaque fluorescent probes, QM-FN-SO3 confers several advantages, such as long emission wavelength, large Stokes shift, ultrahigh sensitivity, good BBB penetrability and miscibility in aqueous biological media. The preparation of QM-FN-SO3 takes ~2 d, and the confocal imaging experiments for Aß plaque visualization, including the preparation for mouse brain sections, take ~7 d. Notably, acquisition and analyses for in vivo visualization of Aß plaques in mice can be completed within 1 h and require only a basic knowledge of spectroscopy and chemistry.

Design and synthesis of astatinated benzothiazole compounds for their potential use in Targeted Alpha Therapy (TAT) strategies to treat Alzheimer's disease-associated amyloid plaques.

PURPOSE: Alzheimer's disease (AD) is a terminal neurodegenerative disease characterized by the buildup of amyloid fibrils, amorphous aggregates and tauopathies. Several treatment modalities, which rely on various biological processes to reduce disease burden, have been largely ineffective at treating Alzheimer's disease. Targeted alpha therapy (TAT) has demonstrated positive results in the treatment of cancer. Benzothiazole derivatives have been successfully shown to target these plaques and are used in several imaging applications. One such derivative, Flutemetamol (VizamylTM) is an FDA approved diagnostic tool for PET imaging of AD-associated plaques. We report the radiolabeling of benzothiazole derivatives with 211At, a 7.2 h alpha emitting radionuclide, using a copper catalyzed reaction with a boronic acid precursor molecule. Our final compound [211At]3'-At-PIB-OMe had a radiochemical yield of 55% and was found to be stable for at least 3 h in phosphate buffered saline.

Multi-fluorine labeled indanone derivatives as potential MRI imaging probes for ß-Amyloid plaques.

In order to realize the early diagnosis of Alzheimer's disease (AD), we designed and synthesized a series of multi-fluorine labeled indanone derivatives based on indanone which could target ß-amyloid (Aß). Through the in vitro staining experiment and affinity experiment, we selected 7d out, and then evaluated it through other in vivo and in vitro experiments. The staining of AD human brain adjacent sections revealed that compound 7d could bind to Aß plaques with high affinity. In the in vitro binding assay, 7d showed a balanced affinity with Aß1-40 (Kd = 367 ± 13) and Aß1-42 (Kd = 384 ± 56). Also, 7d exhibited a low toxicity (LD50 > 50 mg/kg) and an excellent ability to pass through the blood-brain barrier (Log p = 3.87). The biodistribution experiment in mice showed that 7d reached the highest brain uptake after 1 h of tail vein injection and cleared after 24 h. A low concentration of 7d (1.875 mg/ml) showed a strong imaging ability (19F-weighted mode), and the imaging capability increased with the increasing of concentration. All the results showed that 7d could provide a feasible solution for the early diagnosis of AD under non-radioactive condition.

Bis-iodine-labeled Curcumin as a Potential CT Imaging Agent for ß-amyloid Plaques in the Brain.

BACKGROUND: Alzheimer's disease (AD) is one of the most common causes of dementia, affecting many old people. OBJECTIVES: By designing and synthesizing intracerebral imaging probes, we tried to provide a new solution for the early diagnosis of AD. METHODS: We designed and synthesized bis-iodine-labeled curcumin, and verified its performance through in vivo and in vitro experiments. RESULTS: In this study, bis-iodine-labeled curcumin (7, BICUR) was synthesized. In the in vitro mass spectrum binding assay, Kd values of BICUR with Aß1-40 and Aß1-42 aggregates were 46.29 nM and 64.29 nM, respectively. Aß plaques in AD brain adjacent sections were positively stained by BICUR, which was similar to some other curcumin derivatives. The Log P value of BICUR was 1.45. In the biodistribution experiment, BICUR showed the highest initial brain uptake (5.87% compared to the blood concentration) two minutes after the tail vein injection and rapid clearance from the mouse brain. In the acute toxicity experiment, BICUR showed low toxicity, and the LD50 was >100 mg/kg. Moreover, BICUR showed a high stability in vitro (86.68% unchanged BICUR after incubation for 120min in mouse brain homogenate). Besides, BICUR produced an enhanced CT imaging effect that could be sensitively detected in vitro, but it also showed an obvious differentiation from surrounding tissues after intracerebral injection. CONCLUSION: All results suggested that BICUR could probably act as a targeted CT imaging agent for Aß plaques in the brain.

Correlative Chemical Imaging Identifies Amyloid Peptide Signatures of Neuritic Plaques and Dystrophy in Human Sporadic Alzheimer's Disease.

Objective: Alzheimer's disease (AD) is the most common neurodegenerative disease. The predominantly sporadic form of AD is age-related, but the underlying pathogenic mechanisms remain not fully understood. Current efforts to combat the disease focus on the main pathological hallmarks, in particular beta-amyloid (Aß) plaque pathology. According to the amyloid cascade hypothesis, Aß is the critical early initiator of AD pathogenesis. Plaque pathology is very heterogeneous, where a subset of plaques, neuritic plaques (NPs), are considered most neurotoxic rendering their in-depth characterization essential to understand Aß pathogenicity. Methods: To delineate the chemical traits specific to NP types, we investigated senile Aß pathology in the postmortem, human sporadic AD brain using advanced correlative biochemical imaging based on immunofluorescence (IF) microscopy and mass spectrometry imaging (MSI). Results: Immunostaining-guided MSI identified distinct Aß signatures of NPs characterized by increased Aß1-42(ox) and Aß2-42. Moreover, correlation with a marker of dystrophy (reticulon 3 [RTN3]) identified key Aß species that both delineate NPs and display association with neuritic dystrophy. Conclusion: Together, these correlative imaging data shed light on the complex biochemical architecture of NPs and associated dystrophic neurites. These in turn are obvious targets for disease-modifying treatment strategies, as well as novel biomarkers of Aß pathogenicity.

Rational design synthesis and evaluation of a novel near-infrared fluorescent probe for selective imaging of amyloid-ß aggregates in Alzheimer's disease.

Alzheimer's disease (AD) is a degenerative neurological disorder that remains incurable to date, seriously affecting the quality of life and health of those affected. One of the key neuropathological hallmarks of AD is the formation of amyloid-ß (Aß) plaques. Near-infrared (NIR) probes that possess a large Stokes shift show great potential for imaging of Aß plaques in vivo and in vitro. Herein, we proposed a rational strategy for design and synthesis of a series of NIR fluorescent probes that incorporate a tricarbonitrile group as a strong electron-withdrawing group (EWG) to enable NIR emission and large Stokes shift for optimal imaging of Aß plaques. The probe TCM-UM exhibited remarkable in vitro performance, including strong NIR emission (λem = 670 nm), large Stokes shift (120-245 nm), and its affinity for Aß42 aggregates (Kd = 43.78 ± 4.09 nM) was superior to the commercially available probe Thioflavin T (ThT, Kd = 896.04 ± 33.43 nM). Further, TCM-UM was selected for imaging Aß plaques in brain tissue slices and APP/PS1 transgenic (AD) mice, the results indicated that TCM-UM had an excellent ability to penetrate the blood-brain barrier (BBB) compared with ThT, and it could effectively distinguish wild-type (Wt) mice and APP/PS1 transgenic (AD) mice.