Alzheimer's Disease: From Pathology to Therapeutic Approaches

Mind how you go : The current strategies for the development of therapies for Alzheimer's disease are very diverse. Particular attention is given to the search for inhibitors (see picture for two examples) of the proteolytic enzyme β‐ and γ‐secretase, which inhibits the cleavage of the amyloid precursor proteins into amyloid β peptides, from which the disease‐defining deposits of plaque in the brains of Alzheimer's patients originates.

     

Amyloid Aggregates,Presenilins, and Alzheimer's Disease

The cooperative action of three proteases is required to process the APP protein (695–770 amino acids) into small β-amyloid peptides (Aβ, 40–42 amino acids). Aβ aggregates are found in the senile plaques of patients with Alzheimer's disease and play a major role in the onset of this disorder. The functional analysis of several factors that contribute to the production and aggregation of Aβ has enhanced our knowledge of the mechanism of amyloid formation and increased the potential for effective therapeutic treatment.     

Development of Tau Aggregation Inhibitors for Alzheimer's Disease

Small molecules against Alzheimer's : The pathological aggregation of the tau protein is a major hallmark of neurodegenerative diseases such as Alzheimer's disease. The inhibition or reversal of tau aggregation is a potential therapeutic strategy that is currently undergoing clinical trials. The image shows pathological fibers assembled from tau protein, which are the main components of the neurofibrillary tangles of Alzheimer's disease.

     

Extracellular Matrix Proteins Involved in Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases and characterized by cognitive and memory impairments. Emerging evidence suggests that the extracellular matrix (ECM) in the brain plays an important role in the etiology of AD. It has been detected that the levels of ECM proteins have changed in the brains of AD patients and animal models. Some ECM components, for example, elastin and heparan sulfate proteoglycans, are considered to promote the upregulation of extracellular amyloid-beta (Aβ) proteins. In addition, collagen VI and laminin are shown to have interactions with Aβ peptides, which might lead to the clearance of those peptides. Thus, ECM proteins are involved in both amyloidosis and neuroprotection in the AD process. However, the molecular mechanism of neuronal ECM proteins on the pathophysiology of AD remains elusive. More investigation of ECM proteins with AD pathogenesis is needed, and this may lead to novel therapeutic strategies and biomarkers for AD.     

Monomer Dynamics of Alzheimer Peptides and Kinetic Control of Early Aggregation in Alzheimer's Disease

The rate of reconfiguration—or intramolecular diffusion—of monomeric Alzheimer (Aβ) peptides is measured and, under conditions that aggregation is more likely, peptide diffusion slows down significantly, which allows bimolecular associations to be initiated. By using the method of Trp–Cys contact quenching, the rate of reconfiguration is observed to be about five times faster for Aβ₄₀, which aggregates slowly, than that for Aβ₄₂, which aggregates quickly. Furthermore, the rate of reconfiguration for Aβ₄₂ speeds up at higher pH, which slows aggregation, and in the presence of the aggregation inhibitor curcumin. The measured reconfiguration rates are able to predict the early aggregation behavior of the Aβ peptide and provide a kinetic basis for why Aβ₄₂ is more prone to aggregation than Aβ₄₀, despite a difference of only two amino acids.     

A simple, rapid and sensitive method for simultaneous determination of rivastigmine and its major metabolite NAP 226-90 in rat brain and plasma by reversed-phase liquid chromatography coupled to electrospray ionization mass spectrometry

A simple and sensitive reversed-phase liquid chromatography coupled with electrospray-mass spectrometry was developed and validated for the simultaneous determination of rivastigmine, a cholinesterase inhibitor, and its major metabolite NAP 226-90 in rat plasma and brain homogenates. Rivastigmine and NAP 226-90 were extracted from plasma and brain by ethyl acetate and, after drying under nitrogen, re-dissolved in acetonitrile and separated isocratic by HPLC on a C(18) column and quantified by single ion monitoring mass spectrometer. The mean (+/-SD) extraction efficiency for rivastigmine in plasma and brain was 93 +/- 2 and 95 +/- 2% (n = 5) of NAP 226-90 in a drug range of 10-100 pmol/mL or pmol/g. The method proved to be linear within the tested range (regression coefficient, r = 0.9999, n = 5). Intra- and inter-day precision coefficients of variation and accuracy bias were acceptable (within 15%, n = 5) over the entire range for both compounds using plasma or brain samples. The limits of quantification were 0.5 pmol/mL plasma and 2.5 pmol/g brain for rivastigmine and 1 pmol/mL plasma and 5 pmol/g brain for NAP 226-90, respectively. The analytical technique was used to determine the concentrations of rivastigmine and its metabolite NAP 226-90 in rat plasma and brain after oral drug administration. The concentrations of the parent drug and its major metabolite were compared to a pharmacodynamic parameter, the ex vivo inhibition of acetylcholinesterase.     

Repurposing FDA-Approved Compounds for the Discovery of Glutaminyl Cyclase Inhibitors as Drugs Against Alzheimer's Disease

Alzheimer's disease (AD) is one of the most common neurodegenerative causes of dementia, the pathology of which is still not much clear. It′s challenging to discover the disease modifying agents for the prevention and treatment of AD over the years. Emerging evidence has been accumulated to reveal the crucial role of up-regulated glutaminyl cyclase (QC) in the initiation of AD. In the current study, the QC inhibitory potency of a library consisting of 1621 FDA-approved compounds was assessed. A total of 54 hits, 3.33 % of the pool, exhibited QC inhibitory activities. The Ki of the top 5 compounds with the highest QC inhibitory activities were measured. Among these selected hits, compounds affecting neuronal signaling pathways and other mechanisms were recognized. Moreover, several polyphenol derivatives with QC inhibitory activities were also identified. Frameworks and subsets contained in these hits were analyzed. Taken together, our results may contribute to the discovery and development of novel QC inhibitors as potential anti-AD agents.     

Peptide-derived from Seahorse Exerts a Protective Effect against Cholinergic Neuronal Death in in vitro Model of Alzheimer's Disease

Hippocampus trimaculatus are highly valued and the most heavily traded seahorse species for traditional medicine purposes in many Asian countries. One of the main interesting features in H.trimaculatus is their richness in protein which can be hydrolyzed into bioactive peptides. In the previous study, H. trimaculatus was hydrolyzed using commercial enzymes, the peptides responsible for neuroprotective activity was identified as HTP-1. In the present study, in vitro co-culture system of neuronal (PC12) cells and Aβ₄₂ oligomer-stimulated murine microglia cells (BV2 cells) were used to test neuroprotective effects of HTP-1. The co-culture system showed that HTP-1 protected PC12 cells from BV2 neurotoxic responses. In addition, the activation of PI3K/Akt signaling pathway by HTP-1 were confirmed. The PI3K/Akt activation was found to be mediated through transforming growth factor-β (TGF-β) induction by HTP-1. Furthermore, this signaling pathway was found to up-regulate the expression of pro survival protein expression in PC12 cells. Collectively, HTP-1 has potent protective effect against neuronal cells death in in vitro model of Alzheimer's disease.     

Tacrines as Therapeutic Agents for Alzheimer's Disease. V. Recent Developments

Herein we have reviewed our recent developments for the identification of new tacrine analogues for Alzheimer's disease (AD) therapy. Tacrine, the first cholinesterase inhibitor approved for AD treatment, did not stop the progression of AD, producing only some cognitive improvements, but exhibited secondary effects mainly due to its hepatotoxicity. Thus, the drug was withdrawn from the clinics administration. Since then, many publications have described non‐hepatotoxic tacrines, and in addition, important efforts have been made to design multitarget tacrines by combining their cholinesterase inhibition profile with the modulation of other biological targets involved in AD.     

Near-Infrared Aggregation-Induced Emission Luminogens for In Vivo Theranostics of Alzheimer's Disease

Optimized theranostic strategies for Alzheimer's disease (AD) remain almost absent from bench to clinic. Current probes and drugs attempting to prevent β-amyloid (Aβ) fibrosis encounter failures due to the blood–brain barrier (BBB) penetration challenge and blind intervention time window. Herein, we design a near-infrared (NIR) aggregation-induced emission (AIE) probe, DNTPH, via balanced hydrophobicity-hydrophilicity strategy. DNTPH binds selectively to Aβ fibrils with a high signal-to-noise ratio. In vivo imaging revealed its excellent BBB permeability and long-term tracking ability with high-performance AD diagnosis. Remarkably, DNTPH exhibits a strong inhibitory effect on Aβ fibrosis and promotes fibril disassembly, thereby attenuating Aβ-induced neurotoxicity. DNTPH treatment significantly reduced Aβ plaques and rescued learning deficits in AD mice. Thus, DNTPH serves as the first AIE in vivo theranostic agent for real-time NIR imaging of Aβ plaques and AD therapy simultaneously.     

Acetylcholinesterase Sensor Based on Polyelectrolyte Complexes with DNA Inclusion for the Determination of Reversible Inhibitors

The acetylcholinesterase (AChE) biosensor has been developed for the determination of reversible inhibitors applied in the Alzheimer's disease therapy, i. e., Huperzine A (HupA) and galantamine (Gal). For this purpose, glassy carbon electrode (GCE) was first modified with carbon black (CB) and Co phthalocyanine and then polyelectrolyte complex was self‐assembled on its surface by drop casting of reactants and washing. To extend the stability and improve biosensor performance, it was proposed for the first time to use DNA as polyanion in the complex assembly. The DNA showed higher charge density than conventional polyelectrolytes and stabilized the surface coating by adsorption of higher enzyme amount and prevention of its leaching during the biosensor operation. Complex formation and the influence of structural factors were monitored with surface plasmon resonance. Kinetic study showed mixed inhibition of the enzyme within micro‐ and nanomolar range of inhibitor concentrations. The AChE biosensor showed limit of detection of HupA equal to 0.9 and that of Gal to 70 nM. The sensitivity of drug determination was found to be close or better than that of the AChE biosensors previously reported in the literature. The biosensor was tested on the sample of artificial urine and showed 102 % recovery of the drugs determination.     

Label‐free Electrochemical Sensor for Ex‐vivo Monitoring of Alzheimer's Disease Biomarker

The beta‐amyloid (Aβ) peptide was used as an important biomarker for Alzheimer's disease (AD) diagnosis. The development of an accurate, selective, rapid, and highly sensitive technique for detecting of Aβ level is an important issue in biology, and medicine to assess human health risks. Here, gold nanoparticles (Au NPs) with different size were electrochemically deposited onto the indium tin oxide (ITO) substrate in the presence of different molecular weights of surfactants. The modified substrates were used as a high sensitive electrochemical sensor of in‐vitro as well as ex‐vivo monitoring of Aβ based on cyclic voltammetry and square wave voltammetry techniques. Our findings revealed that the modification of ITO electrode with Au NPs could enhance its sensor performance with high sensitivity for low concentration levels of Aβ over a wide linear range with a detection limit of about 20.7 ng/g, which is less than the concentration of insoluble Aβ40 (105.4±40.2 μg/g) in brain of AD induced. In addition, Au NPs/ITO modified electrodes have demonstrated ability to monitor Aβ in the brain extracted samples without any potential interference with other components. Raman spectroscopy has been used to confirm the presence of Aβ in the AD‐induced samples. Thus, it is applicable for analyzing ex‐vivo samples.     

Syntheses of Two Potential Ligands for Tc－99m Labeling as Diagnosis Agents of Alzheimer‘s Disease

Two types of ligands-biphenyl and stilbene derivatives, which can be labeled with Tc-99m for the diagnosis of Alzheimer‘ s disease (AD) have been synthesized successfully. The key steps in these two syntheses involved Suzuki reaction and Wittig reaction respectively. The new discovered debromination reaction may be expanded to the compounds with double or triple bond adjacent to the carbon atom bearing the bromine atoms. These types of syntheses provide a route to a series of biphenyl and stilbene derivatives that will benefit the search of new lmaging agents for AD.     

Recent Electrokinetic and Microfluidic Strategies for Detection of Amyloid Beta Peptide Biomarkers: Towards Molecular Diagnosis of Alzheimer's Disease

Among all neurodegenerative diseases, Alzheimer's Disease (AD) is the most prevalent worldwide, with a huge burden to the society and no efficient AD treatment so far. Continued efforts have been being made towards early and powerful diagnosis of AD, in the hope for a successful set of clinical trials and subsequently AD curative treatment. Towards this aim, detection and quantification of amyloid beta (Aβ) peptides in cerebrospinal fluid (CSF) and other biofluids, which are established and validated biomarkers for AD, have drawn attention of the scientific community and industry over almost two decades. In this work, an overview on our major contributions over 15 years to develop different electrokinetic and microfluidic strategies for Aβ peptides detection and quantification is reported. Accordingly, discussions and viewpoints on instrumental and methodological developments for microscale electrophoresis, microfluidic designs and immuno‐enrichment / assays on magnetic beads in microchannels for tracing Aβ peptides in CSF are given in this review.     

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.     

Extraction and isolation of acetylcholinesterase inhibitors from Citrus limon peel using an in vitro method

A simple and efficient ultrafiltration–liquid chromatography–mass spectrometry–based method was developed for the rapid screening and identification of ligands from Citrus limon peel, which are suitable acetylcholinesterase inhibitors. Subsequently, the anti‐Alzheimer's activity of these compounds was assessed using a PC12 cell model. Six major compounds, viz. neoeriocitrin, isonaringin, naringin, hesperidin, neohesperidin, and limonin, were identified as potent acetylcholinesterase inhibitors. A continuous and efficient online method, which involved the use of a microwave‐assisted extraction device, solvent concentration tank, and centrifugal partition chromatography column, was developed for the scale‐up of these compounds, and the obtained compounds presented high purity. Next, their bioactivity was evaluated using a PC12 cell model. This novel approach, which was based on ultrafiltration–liquid chromatography–mass spectrometry, microwave‐assisted extraction online coupled with solvent concentration tank, and centrifugal partition chromatography along with in vitro evaluation, could represent a powerful tool for the screening and extraction of acetylcholinesterase inhibitors from complex matrices, and could be a useful platform for the large‐scale production of bioactive and nutraceutical ingredients.     

丙交酯合成过程的理论及实验研究

采用密度泛函方法研究了丙交酯的合成过程, 优化了合成过程中可能出现的化合物的几何构型, 分析了各化合物的振动频率和偶极矩. 在B3LYP/6-31G*和B3LYP/6-311＋G*水平上进行了各化合物的能量计算, 得到了所设计的各模型反应的焓变和吉布斯自由能变. 结果表明, 所选择的各模型反应为吸热反应且近似可逆, 水的控制对丙交酯的形成很重要. 根据量化计算结果与丙交酯合成实验中不同阶段反应体系红外谱图的变化, 提出了丙交酯合成的可能机理.     

Mycoepoxydiene核磁共振谱的理论研究

用密度泛涵理论(Density Functional Theory,DFT)的B3PW 91方法在6-311G**基组下优化了标题化合物mycoepoxyd iene的几何构型,同时计算了红外光谱.并用规范不变原子轨道(gauge independent atom ic orb ital)G IAO/B3PW 91以及G IAO/HF方法分别在6-311G**,6-311++G**等基组进行了核磁共振谱研究,计算结果与实验结果吻合很好.