Molecular Imaging of Fluorinated Probes for Tau Protein and Amyloid-β Detection

TSPO in pancreatic beta cells and its possible involvement in type 2 diabetes

Amyloidosis forms a large family of pathologies associated with amyloid deposit generated by the formation of amyloid fibrils or plaques. The amyloidogenic proteins and peptides involved in these processes are targeted against almost all organs. In brain they are associated with neurodegenerative disease, and the Translocator Protein (TSPO), overexpressed in these inflammatory conditions, is one of the target for the diagnostic. Moreover, TSPO ligands have been described as promising therapeutic drugs for neurodegenerative diseases. Type 2 diabetes, another amyloidosis, is due to a beta cell mass decrease that has been linked to hIAPP (human islet amyloid polypeptide) fibril formation, leading to the reduction of insulin production. In the present study, in a first approach, we link overexpression of TSPO and inflammation in potentially prediabetic patients. In a second approach, we observed that TSPO deficient rats have higher level of insulin secretion in basal conditions and more IAPP fibrils formation compared with wild type animals. In a third approach, we show that diabetogenic conditions also increase TSPO overexpression and IAPP fibril formation in rat beta pancreatic cell line (INS-1E). These data open the way for further studies in the field of type 2 diabetes treatment or prevention.

Combined use of Donepezil and Memantine increases the probability of five-year survival of Alzheimer's disease patients

BACKGROUND

Alzheimer's disease (AD) is the most common neurodegenerative disease. Studying the effects of drug treatments on multiple health outcomes related to AD could be beneficial in demonstrating which drugs reduce the disease burden and increase survival.

METHODS

We conducted a comprehensive causal inference study implementing doubly robust estimators and using one of the largest high-quality medical databases, the Oracle Electronic Health Records (EHR) Real-World Data. Our work was focused on the estimation of the effects of the two common Alzheimer's disease drugs, Donepezil and Memantine, and their combined use on the five-year survival since initial diagnosis of AD patients. Also, we formally tested for the presence of interaction between these drugs.

RESULTS

Here, we show that the combined use of Donepezil and Memantine significantly elevates the probability of five-year survival. In particular, their combined use increases the probability of five-year survival by 0.050 (0.021, 0.078) (6.4%), 0.049 (0.012, 0.085), (6.3%), 0.065 (0.035, 0.095) (8.3%) compared to no drug treatment, the Memantine monotherapy, and the Donepezil monotherapy respectively. We also identify a significant beneficial additive drug-drug interaction effect between Donepezil and Memantine of 0.064 (0.030, 0.098).

CONCLUSIONS

Based on our findings, adopting combined treatment of Memantine and Donepezil could extend the lives of approximately 303,000 people with AD living in the USA to be beyond five-years from diagnosis. If these patients instead have no drug treatment, Memantine monotherapy or Donepezil monotherapy they would be expected to die within five years.

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.

A causal inference study: The impact of the combined administration of Donepezil and Memantine on decreasing hospital and emergency department visits of Alzheimer's disease patients

Alzheimer's disease is the most common type of dementia that currently affects over 6.5 million people in the U.S. Currently there is no cure and the existing drug therapies attempt to delay the mental decline and improve cognitive abilities. Two of the most commonly prescribed such drugs are Donepezil and Memantine. We formally tested and confirmed the presence of a beneficial drug-drug interaction of Donepezil and Memantine using a causal inference analysis. We applied doubly robust estimators to one of the largest and high-quality medical databases to estimate the effect of two commonly prescribed Alzheimer's disease (AD) medications, Donepezil and Memantine, on the average number of hospital or emergency department visits per year among patients diagnosed with AD. Our results show that, compared to the absence of medication scenario, the Memantine monotherapy, and the Donepezil monotherapy, the combined use of Donepezil and Memantine treatment significantly reduces the average number of hospital or emergency department visits per year by 0.078 (13.8%), 0.144 (25.5%), and 0.132 days (23.4%), respectively. The assessed decline in the average number of hospital or emergency department visits per year is consequently associated with a substantial reduction in medical costs. As of 2022, according to the Alzheimer's Disease Association, there were over 6.5 million individuals aged 65 and older living with AD in the US alone. If patients who are currently on no drug treatment or using either Donepezil or Memantine alone were switched to the combined used of Donepezil and Memantine therapy, the average number of hospital or emergency department visits could decrease by over 613 thousand visits per year. This, in turn, would lead to a remarkable reduction in medical expenses associated with hospitalization of AD patients in the US, totaling over 940 million dollars per year.

Evaluation of Dimercaptosuccinic Acid-Coated Iron Nanoparticles Immunotargeted to Amyloid Beta as MRI Contrast Agents for the Diagnosis of Alzheimer's Disease

Nanoparticle-based magnetic contrast agents have opened the potential for magnetic resonance imaging (MRI) to be used for early non-invasive diagnosis of Alzheimer's disease (AD). Accumulation of amyloid pathology in the brain has shown association with cognitive decline and tauopathy; hence, it is an effective biomarker for the early detection of AD. The aim of this study was to develop a biocompatible magnetic nanoparticle targeted to amyloid beta (Aβ) plaques to increase the sensitivity of T2-weighted MRI for imaging of amyloid pathology in AD. We presented novel iron core-iron oxide nanoparticles stabilized with a dimercaptosuccinic acid coating and functionalized with an anti-Aβ antibody. Nanoparticle biocompatibility and cellular internalization were evaluated in vitro in U-251 glioblastoma cells using cellular assays, proteomics, and transmission electron microscopy. Iron nanoparticles demonstrated no significant in vitro cytotoxicity, and electron microscopy results showed their movement through the endocytic cycle within the cell over a 24 h period. In addition, immunostaining and bio-layer interferometry confirmed the targeted nanoparticle's binding affinity to amyloid species. The iron nanoparticles demonstrated favourable MRI contrast enhancement; however, the addition of the antibody resulted in a reduction in the relaxivity of the particles. The present work shows promising preliminary results in the development of a targeted non-invasive method of early AD diagnosis using contrast-enhanced MRI.

Molecular Design of Magnetic Resonance Imaging Agents Binding to Amyloid Deposits

The ability to detect and monitor amyloid deposition in the brain using non-invasive imaging techniques provides valuable insights into the early diagnosis and progression of Alzheimer's disease and helps to evaluate the efficacy of potential treatments. Magnetic resonance imaging (MRI) is a widely available technique offering high-spatial-resolution imaging. It can be used to visualize amyloid deposits with the help of amyloid-binding diagnostic agents injected into the body. In recent years, a number of amyloid-targeted MRI probes have been developed, but none of them has entered clinical practice. We review the advances in the field and deduce the requirements for the molecular structure and properties of a diagnostic probe candidate. These requirements make up the base for the rational design of MRI-active small molecules targeting amyloid deposits. Particular attention is paid to the novel cryo-EM structures of the fibril aggregates and their complexes, with known binders offering the possibility to use computational structure-based design methods. With continued research and development, MRI probes may revolutionize the diagnosis and treatment of neurodegenerative diseases, ultimately improving the lives of millions of people worldwide.

Fluorescent Sensing Platforms for Detecting and Imaging the Biomarkers of Alzheimer's Disease

Alzheimer's disease (AD) is an irreversible neurodegenerative disease with clinical symptoms of memory loss and cognitive impairment. Currently, no effective drug or therapeutic method is available for curing this disease. The major strategy used is to identify and block AD at its initial stage. Thus, early diagnosis is very important for intervention of the disease and assessment of drug efficacy. The gold standards of clinical diagnosis include the measurement of AD biomarkers in cerebrospinal fluid and positron emission tomography imaging of the brain for amyloid-β (Aβ) deposits. However, these methods are difficult to apply to the general screening of a large aging population because of their high cost, radioactivity and inaccessibility. Comparatively, blood sample detection is less invasive and more accessible for the diagnosis of AD. Hence, a variety of assays based on fluorescence analysis, surface-enhanced Raman scattering, electrochemistry, etc., were developed for the detection of AD biomarkers in blood. These methods play significant roles in recognizing asymptomatic AD and predicting the course of the disease. In a clinical setting, the combination of blood biomarker detection with brain imaging may enhance the accuracy of early diagnosis. Fluorescence-sensing techniques can be used not only to detect the levels of biomarkers in blood but also to image biomarkers in the brain in real time due to their low toxicity, high sensitivity and good biocompatibility. In this review, we summarize the newly developed fluorescent sensing platforms and their application in detecting and imaging biomarkers of AD, such as Aβ and tau in the last five years, and discuss their prospects for clinical applications.

Radiolabeled Chalcone Derivatives as Potential Radiotracers for β-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-β unsaturated carbonyl functional group as potential radiotracers for the imaging of β-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.

Multi-fluorine labeled indanone derivatives as potential MRI imaging probes for β-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 β-amyloid (Aβ). 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 Aβ plaques with high affinity. In the in vitro binding assay, 7d showed a balanced affinity with Aβ1-40 (K_d = 367 ± 13) and Aβ1-42 (K_d = 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.

Fluorinated Human Serum Albumin as Potential 19F Magnetic Resonance Imaging Probe

Fluorinated human serum albumin conjugates were prepared and tested as potential metal-free probes for ¹⁹F magnetic resonance imaging (MRI). Each protein molecule was modified by several fluorine-containing compounds via the N-substituted natural acylating reagent homocysteine thiolactone. Albumin conjugates retain the protein's physical and biological properties, such as its 3D dimensional structure, aggregation ability, good solubility, proteolysis efficiency, biocompatibility, and low cytotoxicity. A dual-labeled with cyanine 7 fluorescence dye and fluorine reporter group albumin were synthesized for simultaneous fluorescence imaging and ¹⁹F MRI. The preliminary in vitro studies show the prospects of albumin carriers for multimodal imaging.

Fluorine-19 Magnetic Resonance Imaging for Detection of Amyloid β Oligomers Using a Keto Form of Curcumin Derivative in a Mouse Model of Alzheimer's Disease

Recent evidence suggests that the formation of soluble amyloid β (Aβ) aggregates with high toxicity, such as oligomers and protofibrils, is a key event that causes Alzheimer's disease (AD). However, understanding the pathophysiological role of such soluble Aβ aggregates in the brain in vivo could be difficult due to the lack of a clinically available method to detect, visualize, and quantify soluble Aβ aggregates in the brain. We had synthesized a novel fluorinated curcumin derivative with a fixed keto form, named as Shiga-Y51, which exhibited high selectivity to Aβ oligomers in vitro. In this study, we investigated the in vivo detection of Aβ oligomers by fluorine-19 (¹⁹F) magnetic resonance imaging (MRI) using Shiga-Y51 in an APP/PS1 double transgenic mouse model of AD. Significantly high levels of ¹⁹F signals were detected in the upper forebrain region of APP/PS1 mice compared with wild-type mice. Moreover, the highest levels of Aβ oligomers were detected in the upper forebrain region of APP/PS1 mice in enzyme-linked immunosorbent assay. These findings suggested that ¹⁹F-MRI using Shiga-Y51 detected Aβ oligomers in the in vivo brain. Therefore, ¹⁹F-MRI using Shiga-Y51 with a 7 T MR scanner could be a powerful tool for imaging Aβ oligomers in the brain.

Cyclodextrin-Based Contrast Agents for Medical Imaging

Cyclodextrins (CDs) are naturally occurring cyclic oligosaccharides consisting of multiple glucose subunits. CDs are widely used in host–guest chemistry and biochemistry due to their structural advantages, biocompatibility, and ability to form inclusion complexes. Recently, CDs have become of high interest in the field of medical imaging as a potential scaffold for the development of a large variety of the contrast agents suitable for magnetic resonance imaging, ultrasound imaging, photoacoustic imaging, positron emission tomography, single photon emission computed tomography, and computed tomography. The aim of this review is to summarize and highlight the achievements in the field of cyclodextrin-based contrast agents for medical imaging.