Curcumin inhibits formation of amyloid beta oligomers and fibrils, binds plaques, and reduces amyloid in vivo

A Galantamine-Curcumin Hybrid Decreases the Cytotoxicity of Amyloid-Beta Peptide on SH-SY5Y Cells

Misfolded amyloid beta (Aβ) peptides aggregate and form neurotoxic oligomers. Membrane and mitochondrial damages, calcium dysregulation, oxidative stress, and fibril deposits are among the possible mechanisms of Aβ cytotoxicity. Galantamine (GAL) prevents apoptosis induced by Aβ mainly through the ability to stimulate allosterically the α7 nAChRs and to regulate the calcium cytosolic concentration. Here, we examined the cytoprotective effects of two GAL derivatives, namely compounds 4b and 8, against Aβ cytotoxicity on the human neuroblastoma cell line SH-SY5Y. The protective effects were tested at simultaneous administration, pre-incubation and post-incubation, with Aβ. GAL and curcumin (CU) were used in the study as reference compounds. It was found that 4b protects cells in a similar mode as GAL, while compound 8 and CU potentiate the toxic effects of Aβ. Allosteric stimulation of α7 nAChRs is suggested as a possible mechanism of the cytoprotectivity of 4b. These and previous findings characterize 4b as a prospective non-toxic multi-target agent against neurodegenerative disorders with inhibitory activity on acetylcholinesterase, antioxidant, and cytoprotective properties.

An insight into the in vivo imaging potential of curcumin analogues as fluorescence probes

Curcumin and its derivatives have good electrical and optical properties due to the highly symmetric structure of delocalized π electrons. Apart from that, curcumin and its derivatives can interact with numerous molecular targets, thereby exerting less side effects on human body. The fluorescence emission wavelength and fluorescence intensity of curcumin can be enhanced by modifying its π-conjugated system and ß-diketone structure. Some curcumin-based fluorescent probes have been utilized to detect soluble/insoluble amyloid-ß protein, intracranial reactive oxygen species, cysteine, cancer cells, etc. Based on the binding characteristics of curcumin-based fluorescent probes with various target molecules, the factors affecting the fluorescence intensity and emission wavelength of the probes are analyzed, in order to obtain a curcumin probe with higher sensitivity and selectivity. Such an approach will be greatly applicable to in vivo fluorescence imaging.

Curcumin: A small molecule with big functionality against amyloid aggregation in neurodegenerative diseases and type 2 diabetes

Amyloidosis is a concept that implicates disorders and complications that are due to abnormal protein accumulation in different cells and tissues. Protein aggregation-associated diseases are classified according to the type of aggregates and deposition sites, such as neurodegenerative disorders and type 2 diabetes mellitus. Polyphenolic phytochemicals such as curcumin and its derivatives have anti-amyloid effects both in vitro and in animal models; however, the underlying mechanisms are not understood. In this review, we summarized possible mechanisms by which curcumin could interfere with self-assembly processes and reduce amyloid aggregation in amyloidosis. Furthermore, we discuss clinical trials in which curcumin is used as a therapeutic agent for the treatment of diseases linking to protein aggregates.

The Pathogenesis Mechanism, Structure Properties, Potential Drugs and Therapeutic Nanoparticles against the Small Oligomers of Amyloid-β

Alzheimer's Disease (AD) is a devastating neurodegenerative disease that affects millions of people in the world. The abnormal aggregation of amyloid β protein (Aβ) is regarded as the key event in AD onset. Meanwhile, the Aβ oligomers are believed to be the most toxic species of Aβ. Recent studies show that the Aβ dimers, which are the smallest form of Aβ oligomers, also have the neurotoxicity in the absence of other oligomers in physiological conditions. In this review, we focus on the pathogenesis, structure and potential therapeutic molecules against small Aβ oligomers, as well as the nanoparticles (NPs) in the treatment of AD. In this review, we firstly focus on the pathogenic mechanism of Aβ oligomers, especially the Aβ dimers. The toxicity of Aβ dimer or oligomers, which attributes to the interactions with various receptors and the disruption of membrane or intracellular environments, were introduced. Then the structure properties of Aβ dimers and oligomers are summarized. Although some structural information such as the secondary structure content is characterized by experimental technologies, detailed structures are still absent. Following that, the small molecules targeting Aβ dimers or oligomers are collected; nevertheless, all of these ligands have failed to come into the market due to the rising controversy of the Aβ-related "amyloid cascade hypothesis". At last, the recent progress about the nanoparticles as the potential drugs or the drug delivery for the Aβ oligomers are present.

ARCAM-1 Facilitates Fluorescence Detection of Amyloid-Containing Deposits in the Retina

Purpose

To investigate the use of an amyloid-targeting fluorescent probe, ARCAM-1, to identify amyloid-containing deposits in the retina of a transgenic mouse model of Alzheimer's disease (AD) and in human postmortem AD patients.

Methods

Aged APP/PS1 transgenic AD and wild-type (WT) mice were given an intraperitoneal (IP) injection of ARCAM-1 and their retinas imaged in vivo using a fluorescence ophthalmoscope. Eyes were enucleated and dissected for ex vivo inspection of retinal amyloid deposits. Additionally, formalin-fixed eyes from human AD and control patients were dissected, and the retinas were stained using ARCAM-1 or with an anti-amyloid-β antibody. Confocal microscopy was used to image amyloid-containing deposits stained with ARCAM-1 or with immunostaining.

Results

Four out of eight APP/PS1 mice showed the presence of amyloid aggregates in the retina during antemortem imaging. Retinas from three human AD patients stained with ARCAM-1 showed an apparent increased density of fluorescently labeled amyloid-containing deposits compared to the retinas from two healthy, cognitively normal (CN) patients. Immunolabeling confirmed the presence of amyloid deposits in both the retinal neuronal layers and in retinal vasculature.

Conclusions

ARCAM-1 facilitates antemortem detection of amyloid aggregates in the retina of a mouse model for AD, and postmortem detection of amyloid-containing deposits in human retinal tissues from AD patients. These results support the hypothesis of AD pathology manifesting in the eye and highlight a novel area for fluorophore development for the optical detection of retinal amyloid in AD patients.

Translational Relevance

This paper represents an initial examination for potential translation of an amyloid-targeting fluorescent probe to a retinal imaging agent for aiding in the diagnosis of Alzheimer's disease.

Surface Plasmon Resonance Assay for Identification of Small Molecules Capable of Inhibiting Aβ Aggregation

Toxic aggregates of amyloid-beta (Aβ) have importance in the pathology of Alzheimer's disease, and inhibition of aggregate formation is considered to be a promising strategy for drug development. Here, we report a simple and rapid surface plasmon resonance (SPR) assay method that can identify potential Aβ aggregation inhibitors. Our assay is based on the SPR shifting of the Aβ-gold nanoparticle (Aβ-GNP) aggregates by size under the influence of an Aβ aggregation inhibitor. This user-friendly assay features a short assay time with a low reagent consumption that can be easily adapted as a high-throughput screen. We demonstrated that an effective Aβ aggregation inhibitor induces the blue-shifted SPR peaks of the Aβ-GNP aggregates by hindering the formation of long fibrillar aggregates. Moreover, the blue shifting was correlated to the efficacy and concentrations of an Aβ aggregation inhibitor. Overall, our findings suggest that our simple SPR assay can be a powerful tool to screen small molecules targeting Aβ aggregation.

An Insight in Pathophysiological Mechanism of Alzheimer's Disease and its Management Using Plant Natural Products

Alzheimer's disease (AD) is an age-associated nervous system disorder and a leading cause of dementia worldwide. Clinically, it is described by cognitive impairment and pathophysiologically by deposition of amyloid plaques and neurofibrillary tangles in the brain and neurodegeneration. This article reviews the pathophysiology, course of neuronal degeneration, and the various possible hypothesis of AD progression. These hypotheses include amyloid cascade, tau hyperphosphorylation, cholinergic disruption, metal dysregulation, vascular dysfunction, oxidative stress, and neuroinflammation. There is an exponential increase in the occurrence of AD in the recent few years that indicate an urgent need to develop some effective treatment. Currently, only 2 classes of drugs are available for AD treatment, namely acetylcholinesterase inhibitor and NMDA receptor antagonist. Since AD is a complex neurological disorder and these drugs use a single target approach, alternatives are needed due to limited effectiveness and unpleasant side-effects of these drugs. Currently, plants have been used for drug development research especially because of their multiple sites of action and fewer side effects. Uses of some herbs and phytoconstituents for the management of neuronal disorders like AD have been documented in this article. Phytochemical screening of these plants shows the presence of many beneficial constituents like flavonoids, triterpenes, alkaloids, sterols, polyphenols, and tannins. These compounds show a wide array of pharmacological activities, such as anti-amyloidogenic, anticholinesterase, and antioxidants. This article summarizes the present understanding of AD progression and gathers biochemical evidence from various works on natural products that can be useful in the management of this disease.

Ameliorative Role of Nutraceuticals on Neurodegenerative Diseases Using the Drosophila melanogaster as a Discovery Model to Define Bioefficacy

Neurodegeneration is the destruction of neurons, and once the neurons degenerate they can't revive. This is one of the most concerned health conditions among aged population, more than ∼70% of the elderly people are suffering from neurodegeneration. Among all of the neurodegenerative diseases, Alzheimer's disease (AD), Parkinson's disease (PD) and Poly-glutamine disease (Poly-Q) are the major one and affecting most of the people around the world and posing excessive burden on the society. In order to understand this disease in non-human animal models it is pertinent to examine in model organism and various animal model are being used for such diseases like rat, mice and non-vertebrate model like Drosophila. Drosophila melanogaster is one of the best animal proven by several eminent scientist and had received several Nobel prizes for uncovering mechanism of human related genes and highly efficient model for studying neurodegenerative diseases due to its great affinity with human disease-related genes. Another factor is also employed to act as therapeutic or preventive method that is nutraceuticals. Nutraceuticals are functional natural compounds with antioxidant properties and had extensively showed the neuroprotective effect in different organisms. These nutraceuticals having antioxidant properties act through scavenging free radicals or by increasing endogenous cellular antioxidant defense molecules. For the best benefit, we are trying to utilize these nutraceuticals, which will have no or negligible side effects. In this review, we are dealing with various types of such nutraceuticals which have potent value in the prevention and curing of the diseases related to neurodegeneration.HighlightsNeurodegeneration is the silently progressing disease which shows its symptoms when it is well rooted.Many chemical drugs (almost all) have only symptomatic relief with side effects.Potent mechanism of neurodegeneration and improvement effect by nutraceuticals is proposed.Based on the Indian Cuisine scientists are trying to find the medicine from the food or food components having antioxidant properties.The best model to study the neurodegenerative diseases is Drosophila melanogaster.Many nutraceuticals having antioxidant properties have been studied and attenuated various diseases are discussed.

Novel concept of exosome-like liposomes for the treatment of Alzheimer's disease

Exosomes are cell-derived vesicles that act as carriers for proteins and nucleic acids, with therapeutic potential and high biocompatibility. We propose a new concept of exosome-like liposomes for controlled delivery. The goal of this work was to develop a new type of liposomes with a unique mixture of phospholipids, similar to naturally occurring exosomes but overcoming their limitations of heterogeneity and low productivity, for therapeutic delivery of bioactive compounds. Curcumin was chosen as model compound, as it is a phytochemical molecule known to have antioxidant and anti-inflammatory properties, which can protect the brain against oxidative stress and reduce β-amyloid accumulation, major hallmarks of Alzheimer's disease (AD). These new liposomes can efficiently encapsulate hydrophobic curcumin, yielding particles with a size smaller than 200 nm, and a polydispersity index lower than 0.20, which make them ideal for crossing the blood-brain barrier. These particles have a long shelf life, being stable up to 6 months. The curcumin encapsulation efficiency was higher than 85% (up to approximately 94%). Curcumin-loaded liposomes were not cytotoxic (up to 20 μM curcumin, and 200 μM of exo-liposomes), and significantly reduced oxidative stress induced in SH-SY5Y neuronal cells, indicating their potential for neuroprotection. They also do not show any toxicity and are internalized in zebrafish embryos, concentrating in lipid enriched areas, as the brain and the yolk sac. Such innovative carriers are a new effective approach to deliver drugs into the brain, as these are stable, protect the cargo and are uptaken by neuronal cells. Upon internalization, liposomes release the therapeutic biomolecules, resulting in successful neuroprotection, being a positive alternative strategy for AD therapy.

Formulated Chinese medicine Shaoyao Gancao Tang reduces NLRP1 and NLRP3 in Alzheimer's disease cell and mouse models for neuroprotection and cognitive improvement

Amyloid β (Aβ) plays a major role in the neurodegeneration of Alzheimer’s disease (AD). The accumulation of misfolded Aβ causes oxidative stress and inflammatory damage leading to apoptotic cell death. Traditional Chinese herbal medicine (CHM) has been widely used in treating neurodegenerative diseases by reducing oxidative stress and neuroinflammation. We examined the neuroprotective effect of formulated CHM Shaoyao Gancao Tang (SG-Tang, made of Paeonia lactiflora and Glycyrrhiza uralensis at 1:1 ratio) in AD cell and mouse models. In Aβ-GFP SH-SY5Y cells, SG-Tang reduced Aβ aggregation and reactive oxygen species (ROS) production, as well as improved neurite outgrowth. When the Aβ-GFP-expressing cells were stimulated with conditioned medium from interferon (IFN)-γ-activated HMC3 microglia, SG-Tang suppressed expressions of inducible nitric oxide synthase (iNOS), NLR family pyrin domain containing 1 (NLRP1) and 3 (NLRP3), tumor necrosis factor (TNF)-α, interleukin (IL)-1β and IL-6, attenuated caspase-1 activity and ROS production, and promoted neurite outgrowth. In streptozocin-induced hyperglycemic APP/PS1/Tau triple transgenic (3×Tg-AD) mice, SG-Tang also reduced expressions of NLRP1, NLRP3, Aβ and Tau in hippocampus and cortex, as well as improved working and spatial memories in Y maze and Morris water maze. Collectively, our results demonstrate the potential of SG-Tang in treating AD by moderating neuroinflammation.

Ferulic acid amide derivatives with varying inhibition of amyloid-β oligomerization and fibrillization

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized, in part, by the misfolding, oligomerization and fibrillization of amyloid-β (Aβ). Evidence suggests that the mechanisms underpinning Aβ oligomerization and subsequent fibrillization are distinct, and may therefore require equally distinct therapeutic approaches. Prior studies have suggested that amide derivatives of ferulic acid, a natural polyphenol, may combat multiple AD pathologies, though its impact on Aβ aggregation is controversial. We designed and synthesized a systematic library of amide derivatives of ferulic acid and evaluated their anti-oligomeric and anti-fibrillary capacities independently. Azetidine tethered, triphenyl derivatives were the most potent anti-oligomeric agents (compound 2i: IC₅₀ = 1.8 µM ± 0.73 µM); notably these were only modest anti-fibrillary agents (20.57% inhibition of fibrillization), and exemplify the poor correlation between anti-oligomeric/fibrillary activities. These data were subsequently codified in an in silico QSAR model, which yielded a strong predictive model of anti-Aβ oligomeric activity (κ = 0.919 for test set; κ = 0.737 for validation set).

Inflammation: A Major Target for Compounds to Control Alzheimer's Disease

Several hypotheses have been postulated to explain how Alzheimer's disease is triggered, but none of them provide a unified view of its pathogenesis. The dominant hypothesis based on build-ups of the amyloid-β peptide has been around for longer than three decades; however, up to today, numerous clinical trials based on the amyloid postulates have been attempted, but all of them have failed. Clearly, the revisited tau hypothesis provides a better explanation of the clinical observations of patients, but it needs to integrate the cumulative observations on the onset of this disease. In this context, the neuroimmuno modulation theory, based on the involvement of inflammatory events in the central nervous system, accounts for all these observations. In this review we intend to emphasize the idea that neuroinflammation is a main target for the search of new therapeutic strategies to control Alzheimer's disease. Beyond mono-targeting approaches using synthetic drugs that control only specific pathophysiological events, emerging therapeutics views based on multi targeting compounds appear to provide a new pathway for Alzheimer's disease treatment.

Inhibitory Effects of Sulfated Polysaccharides from the Sea Cucumber Cucumaria Frondosa against Aβ40 Aggregation and Cytotoxicity

Abnormal aggregation and deposition of Aβ is one of the causative agents for Alzheimer's disease. The development of inhibitors for Aβ aggregation has been considered a possible method to prevent and treat Alzheimer's disease. Edible sea cucumbers contain many bioactive molecules, including saponins, phospholipids, peptides, and polysaccharides. Herein, we report that polysaccharides extracted from sea cucumber Cucumaria frondosa could reduce the aggregation and cytotoxicity of Aβ40. By utilizing multiple biochemical and biophysical instruments, we found that the polysaccharides could inhibit the aggregation of Aβ40. A chemical kinetics analysis further suggested that the major inhibitory effects of the polysaccharides were achieved by disassembling mature fibrils, which in turn reduced the cytotoxicity of Aβ. These results suggested that the polysaccharides extracted from sea cucumber could be used as an effective inhibitor for Aβ.

From Small Molecules to Synthesized Polymers: Potential Role in Combating Amyloidogenic Disorders

The concept of developing novel anti-amyloid inhibitors in the scientific community has engrossed remarkable research interests and embraced significant potential to resolve numerous pathological conditions including neurological as well as non-neuropathic disorders associated with amyloid protein aggregation. These pathological conditions have harmful effects on cellular activities which include malfunctioning of organs and tissue, cellular impairment, etc. To date, different types of small molecular probes like polyphenolic compounds, nanomaterials, surfactants, etc. have been developed to address these issues. Recently synthetic polymeric materials are extensively investigated to explore their role in the protein aggregation pathway. On the basis of these perspectives, in this review article, we have comprehensively summarized the current perspectives on protein misfolding and aggregation and importance of therapeutic approaches in designing novel effective inhibitors. The main purpose of this review article is to provide a detailed perspective of the current landscape as well as trailblazing voyage of various inhibitors ranging from small molecular probes to polymeric scaffolds in the field of protein misfolding and aggregation. A particular emphasis is given on the structural role and molecular mechanistic pathway involved in modulating the aggregation pathway to further inspire the researchers and shed light in this bright research field.

Investigation of therapeutic effect of curcumin α and β glucoside anomers against Alzheimer's disease by the nose to brain drug delivery

Alzheimer's disease (AD) is one of the greatest geriatric medicinal challenges of our century and is the main disease leading to dementia. Despite extensive scientific research advances, available disease-modifying treatment strategies remained limited; thus, increasing demand for new drugs. In recent years, medicinal plants attracted attention due to their potential role in dementia. In the present study, α and β anomers of curcumin glucosides (CGs) were synthesized and evaluated for Alzheimer's treatment. CGs were synthesized by fusion reaction as a novel and easy method with more advantages (high yield, short reaction time, and low chemicals), and the products were characterized using HNMR. Wistar male rats were used to administer different treatments. They divided into control, sham, Alzheimer, and test groups (Alzheimer + α anomer and Alzheimer + β anomer). Animals received normal saline, Scopolamine (1 mg/kg), high dose anomers, scopolamine, and two doses (12.5 and 25 mg/kg) of anomers, respectively, for 10 days. Then the Morris Water Maze (MWM) test was performed on all animals. Finally, the animals' brains were extracted and homogenized for glutathione, acetylcholine esterase activity, protein carbonyl, and lipid peroxide level detection. The escape latency and the distance towards the hidden platform in Morris water maze in the Alzheimer group were significantly higher than both the control and test groups. Besides, there were no significant differences between sham and control groups in all tests. Both anomers led to a significant increase in glutathione, and acetylcholine levels while they caused a decrease in lipid peroxidation and protein carbonyl levels in brain tissue. It seems that intranasal administration of both anomers positively influenced maze learning in scopolamine receiving subjects. Although both anomers resulted in similar biochemistry tests, a higher dose of β anomer indicated better results than α anomer not only in behavioral tests but also in biochemical tests.

Some Candidate Drugs for Pharmacotherapy of Alzheimer's Disease

Alzheimer’s disease (AD; progressive neurodegenerative disorder) is associated with cognitive and functional impairment with accompanying neuropsychiatric symptoms. The available pharmacological treatment is of a symptomatic nature and, as such, it does not modify the cause of AD. The currently used drugs to enhance cognition include an N-methyl-d-aspartate receptor antagonist (memantine) and cholinesterase inhibitors. The PUBMED, Medical Subject Heading and Clinical Trials databases were used for searching relevant data. Novel treatments are focused on already approved drugs for other conditions and also searching for innovative drugs encompassing investigational compounds. Among the approved drugs, we investigated, are intranasal insulin (and other antidiabetic drugs: liraglitude, pioglitazone and metformin), bexarotene (an anti-cancer drug and a retinoid X receptor agonist) or antidepressant drugs (citalopram, escitalopram, sertraline, mirtazapine). The latter, especially when combined with antipsychotics (for instance quetiapine or risperidone), were shown to reduce neuropsychiatric symptoms in AD patients. The former enhanced cognition. Procognitive effects may be also expected with dietary antioxidative and anti-inflammatory supplements—curcumin, myricetin, and resveratrol. Considering a close relationship between brain ischemia and AD, they may also reduce post-brain ischemia neurodegeneration. An investigational compound, CN-105 (a lipoprotein E agonist), has a very good profile in AD preclinical studies, and its clinical trial for postoperative dementia is starting soon.

Effects of Curcumin and Ferulic Acid on the Folding of Amyloid-β Peptide

The polyphenols curcumin (CU) and ferulic acid (FA) are able to inhibit the aggregation of amyloid-β (Aβ) peptide with different strengths. CU is a strong inhibitor while FA is a weaker one. In the present study, we examine the effects of CU and FA on the folding process of an Aβ monomer by 1 µs molecular dynamics (MD) simulations. We found that both inhibitors increase the helical propensity and decrease the non-helical propensity of Aβ peptide. They prevent the formation of a dense bulk core and shorten the average lifetime of intramolecular hydrogen bonds in Aβ. CU makes more and longer-lived hydrogen bonds, hydrophobic, π–π, and cation–π interactions with Aβ peptide than FA does, which is in a good agreement with the observed stronger inhibitory activity of CU on Aβ aggregation.

Leveraging hallmark Alzheimer's molecular targets using phytoconstituents: Current perspective and emerging trends

Alzheimer's disease (AD), a type of dementia, severely distresses different brain regions. Characterized by various neuropathologies, it interferes with cognitive functions and neuropsychiatrical controls. This progressive deterioration has negative impacts not only on an individual's daily activity but also on social and occupational life. The pharmacological approach has always remained in the limelight for the treatment of AD. However, this approach is condemned with several side effects. Henceforth, a change in treatment approach has become crucial. Plant-based natural products are garnering special attention due to lesser side effects associated with their use. The current review emphasizes the anti-AD properties of phytoconstituents, throws light on those under clinical trials, and compiles information on their specific mode of actions against AD-related different neuropathologies. The phytoconstituents alone or in combinations will surely help discover new potent drugs for the effective treatment of AD with lesser side effects than the currently available pharmacological treatment.

Curcuma Longa, the "Golden Spice" to Counteract Neuroinflammaging and Cognitive Decline-What Have We Learned and What Needs to Be Done

Due to the global increase in lifespan, the proportion of people showing cognitive impairment is expected to grow exponentially. As target-specific drugs capable of tackling dementia are lagging behind, the focus of preclinical and clinical research has recently shifted towards natural products. Curcumin, one of the best investigated botanical constituents in the biomedical literature, has been receiving increased interest due to its unique molecular structure, which targets inflammatory and antioxidant pathways. These pathways have been shown to be critical for neurodegenerative disorders such as Alzheimer's disease and more in general for cognitive decline. Despite the substantial preclinical literature on the potential biomedical effects of curcumin, its relatively low bioavailability, poor water solubility and rapid metabolism/excretion have hampered clinical trials, resulting in mixed and inconclusive findings. In this review, we highlight current knowledge on the potential effects of this natural compound on cognition. Furthermore, we focus on new strategies to overcome current limitations in its use and improve its efficacy, with attention also on gender-driven differences.

Curcumin and Homotaurine Suppress Amyloid-β25-35 Aggregation in Synthetic Brain Membranes

Amyloid-β (Aβ) peptides spontaneously aggregate into β- and cross-β-sheets in model brain membranes. These nanometer sized can fuse into larger micrometer sized clusters and become extracellular and serve as nuclei for further plaque and fibril growth. Curcumin and homotaurine represent two different types of Aβ aggregation inhibitors. While homotaurine is a peptic antiaggregant that binds to amyloid peptides, curcumin is a nonpeptic molecule that can inhibit aggregation by changing membrane properties. By using optical and fluorescent microscopy, X-ray diffraction, and UV-vis spectroscopy, we study the effect of curcumin and homotaurine on Aβ_25-35 aggregates in synthetic brain membranes. Both molecules partition spontaneously and uniformly in membranes and do not lead to observable membrane defects or disruption in our experiments. Both curcumin and homotaurine were found to significantly reduce the number of small, nanoscopic Aβ aggregates and the corresponding β- and cross-β-sheet signals. While a number of research projects focus on potential drug candidates that target Aβ peptides directly, membrane-lipid therapy explores membrane-mediated pathways to suppress peptide aggregation. Based on the results obtained, we conclude that membrane active drugs can be as efficient as peptide targeting drugs in inhibiting amyloid aggregation in vitro.

Brain regional pharmacokinetics following the oral administration of curcumagalactomannosides and its relation to cognitive function

OBJECTIVE

Though a number of bioavailable formulations of curcuminoids have been reported and available commercially as nutraceuticals for brain health, systematic informations on their blood-brain-barrier permeability and brain tissue distribution have not been reported. The present study was aimed to investigate the brain regional pharmacokinetics of curcuminoids following both single dose and repeated dose oral administration of a self-emulsifying food-grade formulation of curcuminoids using fenugreek galactomannan hydrogel scaffold as 'curcumagalactomannosides' (CGM), and its influence on cognitive functions in comparison with unformulated natural curcuminoids (NC) in Wistar rats.

METHODS

CGM was given to animals in single dose (100 mg curcuminoids/kg b. wt.) and repeated dose (100 mg curcuminoids/kg b. wt. for 28 days) and the concentration of total curcuminoids at various parts of brain was evaluated at different time points using Ultra-performance liquid chromatography/electrospray ionization triple quadruple tandem mass spectroscopy (UPLC-ESI-MS/MS) system. Another set of animals were also fed with CGM at single dose (100 mg curcuminoids/kg b. wt.) and repeated dose (100 mg curcuminoids/kg b. wt. for 28 days) and the behavioural studies were conducted using open field test and radial arm maze.

RESULTS

UPLC-ESI-MS/MS analyses of plasma revealed significant absorption of unconjugated (free) curcuminoids upon both single and repeated dose administration of CGM with maximum concentrations of 173.34 ± 27.12 ng/mL and 223.22 ± 32.73 ng/mL, respectively. Further analysis of brain tissues demonstrated significant blood-brain-barrier permeability. Brain regional pharmacokinetics (AUC, C_max and t_1/2) indicated a relative distribution order of hippocampus > striatum > cerebellum > cerebral cortex > brain stem. Supplementation of CGM for 28 days also offered significant (p  <  0.05) improvement in locomotor activity and reduction in spatial memory errors as compared to NC. The NC treatment also improved the behaviour better than the vehicle-treated group.

CONCLUSION

CGM could distribute significant amount of free curcuminoids, in brain especially in the hippocampus at both single and repeated dose administration with an elimination half-life of 2.6 h. CGM also showed a positive impact in behaviour of animals in comparison with normal unformulated curcuminoids.

Curcumin activates Nrf2 through PKCδ-mediated p62 phosphorylation at Ser351

Curcumin, a phytochemical extracted from Curcuma longa rhizomes, is known to be protective in neurons via activation of Nrf2, a master regulator of endogenous defense against oxidative stress in cells. However, the exact mechanism by which curcumin activates Nrf2 remains controversial. Here, we observed that curcumin induced the expression of genes downstream of Nrf2 such as HO-1, NQO1, and GST-mu1 in neuronal cells, and increased the level of Nrf2 protein. Notably, the level of p62 phosphorylation at S351 (S349 in human) was significantly increased in cells treated with curcumin. Additionally, curcumin-induced Nrf2 activation was abrogated in p62 knockout (−/−) MEFs, indicating that p62 phosphorylation at S351 played a crucial role in curcumin-induced Nrf2 activation. Among the kinases involved in p62 phosphorylation at S351, PKCδ was activated in curcumin-treated cells. The phosphorylation of p62 at S351 was enhanced by transfection of PKCδ expression plasmid; in contrast, it was inhibited in cells treated with PKCδ-specific siRNA. Together, these results suggest that PKCδ is mainly involved in curcumin-induced p62 phosphorylation and Nrf2 activation. Accordingly, we demonstrate for the first time that curcumin activates Nrf2 through PKCδ-mediated p62 phosphorylation at S351.

Nanomedicine: A Promising Way to Manage Alzheimer's Disease

Alzheimer's disease (AD) is a devastating disease of the aging population characterized by the progressive and slow brain decay due to the formation of extracellular plaques in the hippocampus. AD cells encompass tangles of twisted strands of aggregated microtubule binding proteins surrounded by plaques. Delivering corresponding drugs in the brain to deal with these clinical pathologies, we face a naturally built strong, protective barrier between circulating blood and brain cells called the blood-brain barrier (BBB). Nanomedicines provide state-of-the-art alternative approaches to overcome the challenges in drug transport across the BBB. The current review presents the advances in the roles of nanomedicines in both the diagnosis and treatment of AD. We intend to provide an overview of how nanotechnology has revolutionized the approaches used to manage AD and highlight the current key bottlenecks and future perspective in this field. Furthermore, the emerging nanomedicines for managing brain diseases like AD could promote the booming growth of research and their clinical availability.

Neuroprotective Herbs for the Management of Alzheimer's Disease

Background—Alzheimer’s disease (AD) is a multifactorial, progressive, neurodegenerative disease that is characterized by memory loss, personality changes, and a decline in cognitive function. While the exact cause of AD is still unclear, recent studies point to lifestyle, diet, environmental, and genetic factors as contributors to disease progression. The pharmaceutical approaches developed to date do not alter disease progression. More than two hundred promising drug candidates have failed clinical trials in the past decade, suggesting that the disease and its causes may be highly complex. Medicinal plants and herbal remedies are now gaining more interest as complementary and alternative interventions and are a valuable source for developing drug candidates for AD. Indeed, several scientific studies have described the use of various medicinal plants and their principal phytochemicals for the treatment of AD. This article reviews a subset of herbs for their anti-inflammatory, antioxidant, and cognitive-enhancing effects. Methods—This article systematically reviews recent studies that have investigated the role of neuroprotective herbs and their bioactive compounds for dementia associated with Alzheimer’s disease and pre-Alzheimer’s disease. PubMed Central, Scopus, and Google Scholar databases of articles were collected, and abstracts were reviewed for relevance to the subject matter. Conclusions—Medicinal plants have great potential as part of an overall program in the prevention and treatment of cognitive decline associated with AD. It is hoped that these medicinal plants can be used in drug discovery programs for identifying safe and efficacious small molecules for AD.

Non-invasive optical imaging of retinal Aβ plaques using curcumin loaded polymeric micelles in APPswe/PS1ΔE9 transgenic mice for the diagnosis of Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disease clinically characterized by impaired memory and progressive cognitive decline. Despite the advances in AD research, an effective method to timely diagnose AD has remained elusive, and until now, most AD patients receive the available symptomatic treatments late. Although the pathological hallmarks of AD have been traditionally described in the brain, recent studies have shown similar pathological changes in the retina which is developmentally an extension of the forebrain. Interestingly, retinal beta-amyloid (Aβ) accumulation preceded that of the brain in a transgenic mouse model of AD. In the quest of finding an early reliable biomarker for AD, researchers have targeted the optical imaging of retinal Aβ plaques as a method of diagnosing AD. One promising polyphenol compound that has found application in this area is curcumin due to its natural binding affinity to Aβ fibrils and oligomers while giving out a strong fluorescence signal. However, the clinical applications of curcumin have been difficult due to problems related to its bioavailability and retention in the body since it is a hydrophobic molecule. To address these limitations, we herein report the development of anionic and water-soluble DSPE-PEG2000 curcumin polymeric micelles (also referred to as curcumin micelles) that can label both brain and retinal Aβ plaques ex vivo. Following their intravitreal injection in the APPswe/PS1ΔE9 transgenic mouse model of AD, green-labeled retinal deposits were optically imaged live using a rodent retinal microscope. Furthermore, these micelles had excellent intraocular biocompatibility, low hemolytic ratio, and were safe for use in two key retinal cell lines (ARPE-19 and 661W cells). Taken together, these findings provide an alternative insight into the optical imaging of Aβ plaques for the diagnosis of AD using the eyes. More importantly, this study can be translated to humans in the future to improve on early diagnosis and timely management of the disease.

Inhibitory Effect of Hexahydrocurcumin on Memory Impairment and Amyloidogenesis in Dexamethasone-Treated Mice

A high dose of dexamethasone induces neurodegeneration by initiating the inflammatory processes that lead to neural apoptosis. A dexamethasone administration model induces overproduction of amyloid-β (Aβ) and tau protein hyperphosphorylation and shows abnormalities of cholinergic function similar to Alzheimer's disease (AD). This study aimed to investigate the protective effect of hexahydrocurcumin on the brain of dexamethasone-induced mice. The results showed that hexahydrocurcumin and donepezil attenuated the levels of amyloid precursor protein and β-secretase mRNA by reverse transcription polymerase chain reaction, decreased the expression of hyperphosphorylated tau, and improved synaptic function. Moreover, we found that hexahydrocurcumin treatment could decrease interleukin-6 levels by attenuating p65 of nuclear factor kappa-light-chain-enhancer (NF-κB) of activated beta cells. In addition, hexahydrocurcumin also decreased oxidative stress, as demonstrated by the expression of 4-hydroxynonenal and thereby prevented apoptosis. Therefore, our finding suggests that hexahydrocurcumin prevents dexamethasone-induced AD-like pathology and improves memory impairment.

Azobioisosteres of Curcumin with Pronounced Activity against Amyloid Aggregation, Intracellular Oxidative Stress, and Neuroinflammation

Many (poly-)phenolic natural products, for example, curcumin and taxifolin, have been studied for their activity against specific hallmarks of neurodegeneration, such as amyloid-β 42 (Aβ42) aggregation and neuroinflammation. Due to their drawbacks, arising from poor pharmacokinetics, rapid metabolism, and even instability in aqueous medium, the biological activity of azobenzene compounds carrying a pharmacophoric catechol group, which have been designed as bioisoteres of curcumin has been examined. Molecular simulations reveal the ability of these compounds to form a hydrophobic cluster with Aβ42, which adopts different folds, affecting the propensity to populate fibril-like conformations. Furthermore, the curcumin bioisosteres exceeded the parent compound in activity against Aβ42 aggregation inhibition, glutamate-induced intracellular oxidative stress in HT22 cells, and neuroinflammation in microglial BV-2 cells. The most active compound prevented apoptosis of HT22 cells at a concentration of 2.5 μm (83 % cell survival), whereas curcumin only showed very low protection at 10 μm (21 % cell survival).

Modeling the Inhibition Kinetics of Curcumin, Orange G, and Resveratrol with Amyloid-β Peptide

The β-amyloid (Aβ) protein aggregation into toxic forms is one of the major factors in the Alzheimer's disease (AD) pathology. Screening compound libraries as inhibitors of Aβ-aggregation is a common strategy to discover novel molecules as potential therapeutics in AD. In this regard, thioflavin T (ThT)-based fluorescence spectroscopy is a widely used in vitro method to identify inhibitors of Aβ aggregation. However, conventional data processing of the ThT assay experimental results generally provides only qualitative output and lacks inhibitor-specific quantitative data, which can offer a number of advantages such as identification of critical inhibitor-specific parameters required to design superior inhibitors and reduce the need to conduct extensive in vitro kinetic studies. Therefore, we carried out mathematical modeling based on logistic equation and power law (PL) model to correlate the experimental results obtained from the ThT-based Aβ40 aggregation kinetics for small-molecule inhibitors curcumin, orange G, and resveratrol and quantitatively fit the data in a logistic equation. This approach provides important inhibitor-specific parameters such as lag time λ, inflection point τ, maximum slope v _m, and apparent rate constant k _app, which are particularly useful in comparing the effectiveness of potential Aβ40 aggregation inhibitors and can be applied in drug discovery campaigns to compare and contrast Aβ40 inhibition data for large compound libraries.

In Vivo Brain Imaging of Amyloid-β Aggregates in Alzheimer's Disease with a Near-Infrared Fluorescent Probe

Abnormal accumulation of amyloid-β (Aβ) has been determined to be a critical factor for the progression of Alzheimer's disease (AD), which has motivated the development of new chemical approaches for early sensing and imaging of these Aβ aggregates. Herein, we report a new near-infrared (NIR) fluorescent probe for the selective monitoring of Aβ aggregates in vivo. This novel fluorophore, named CAQ, was based on the curcumin scaffold and was designed by introducing an intramolecular rotation donor and a quinoline functional group. CAQ was an environment-sensitive fluorescent probe that can be used as a reliable chemical tool for NIR imaging of amyloid plaques in a live Caenorhabditis elegans model of AD and in 5× FAD transgenic mice of early amyloid deposition. Our observations indicate that CAQ is promising for providing comprehensive information on neurodegenerative research, thereby promoting a deeper understanding of Alzheimer's pathological processes.

Polyphenol-Peptide Interactions in Mitigation of Alzheimer's Disease: Role of Biosurface-Induced Aggregation

Alzheimer's disease (AD) is the most common age-related neurodegenerative disorder, responsible for nearly two-thirds of all dementia cases. In this review, we report the potential AD treatment strategies focusing on natural polyphenol molecules (green chemistry) and more specifically on the inhibition of polyphenol-induced amyloid aggregation/disaggregation pathways: in bulk and on biosurfaces. We discuss how these pathways can potentially alter the structure at the early stages of AD, hence delaying the aggregation of amyloid-β (Aβ) and tau. We also discuss multidisciplinary approaches, combining experimental and modelling methods, that can better characterize the biochemical and biophysical interactions between proteins and phenolic ligands. In addition to the surface-induced aggregation, which can occur on surfaces where protein can interact with other proteins and polyphenols, we suggest a new concept referred as "confinement stability". Here, on the contrary, the adsorption of Aβ and tau on biosurfaces other than Aβ- and tau-fibrils, e.g., red blood cells, can lead to confinement stability that minimizes the aggregation of Aβ and tau. Overall, these mechanisms may participate directly or indirectly in mitigating neurodegenerative diseases, by preventing protein self-association, slowing down the aggregation processes, and delaying the progression of AD.

Insight into Inhibitory Mechanism of PDE4D by Dietary Polyphenols Using Molecular Dynamics Simulations and Free Energy Calculations

Phosphodiesterase 4 (PDE4), mainly present in immune, epithelial, and brain cells, represents a family of key enzymes for the degradation of cyclic adenosine monophosphate (cAMP), which modulates inflammatory response. In recent years, the inhibition of PDE4 has been proven to be an effective therapeutic strategy for the treatment of neurological disorders. PDE4D constitutes a high-interest therapeutic target primarily for the treatment of Alzheimer's disease, as it is highly involved in neuroinflammation, learning ability, and memory dysfunctions. In the present study, a thorough computational investigation consisting of molecular docking, molecular dynamics (MD) simulations, and binding free energy calculations based on the linear response approximation (LRA) method was performed to study dietary polyphenols as potential PDE4D inhibitors. The obtained results revealed that curcumin, 6-gingerol, capsaicin, and resveratrol represent potential PDE4D inhibitors; however, the predicted binding free energies of 6-gingerol, capsaicin, and resveratrol were less negative than in the case of curcumin, which exhibited the highest inhibitory potency in comparison with a positive control rolipram. Our results also revealed that the electrostatic component through hydrogen bonding represents the main driving force for the binding and inhibitory activity of curcumin, 6-gingerol, and resveratrol, while the van der Waals component through shape complementarity plays the most important role in capsaicin's inhibitory activity. All investigated compounds form hydrophobic interactions with residues Gln376 and Asn602 as well as hydrogen bonds with nearby residues Asp438, Met439, and Ser440. The binding mode of the studied natural compounds is consequently very similar; however, it significantly differs from the binding of known PDE4 inhibitors. The uncovered molecular inhibitory mechanisms of four investigated natural polyphenols, curcumin, 6-gingerol, capsaicin, and resveratrol, form the basis for the design of novel PDE4D inhibitors for the treatment of Alzheimer's disease with a potentially wider therapeutic window and fewer adverse side effects.

Transferrin-functionalized lipid nanoparticles for curcumin brain delivery

Curcumin is an anti-inflammatory and antioxidant compound with potent neuroprotective activity. Due to its poor water solubility, low bioavailability, rapid elimination and the challenges for crossing and transposing the blood-brain barrier (BBB), solid lipid nanoparticles (SLNs) and nanostructured lipid carriers (NLCs) loaded with curcumin were successfully produced and functionalized with transferrin, in order to mediate the transport of these particles through the BBB endothelium to the brain. The nanosystems revealed Z-averages under 200 nm, polydispersity index below 0.2 and zeta potential around -30 mV. Curcumin encapsulation around 65 % for SLNs and 80 % for NLCs was accomplished, while the functionalized nanoparticles presented a value around 70-75 %. A stability study revealed these characteristics remained unchanged for at least 3 months. hCMEC/D3 cells viability was firstly analysed by MTT and LDH assays, respectively, and a concentration of 10 μM of curcumin-loaded nanoparticles were then selected for the subsequent permeability assay. The permeability study was conducted using transwell devices with hCMEC/D3 cells monolayers and a 1.5-fold higher permeation of curcumin through the BBB was verified. Both SLNs and NLCs are promising for curcumin brain delivery, protecting the incorporated curcumin and targeting to the brain by the addition of transferrin to the nanoparticles surface.

Stem cell in neurodegenerative disorders; an emerging strategy

Neurodegenerative disorders are a diversity of disorders, surrounding Alzheimer's (AD), Parkinson's (PD), Huntington's diseases (HD), and amyotrophic lateral sclerosis (ALS) accompanied by some other less common diseases generally characterized by either developed deterioration of central or peripheral nervous system structurally or functionally. Today, with the viewpoint of an increasingly aging society, the number of patients with neurodegenerative diseases and sociomedical burdens will spread intensely. During the last decade, stem cell technology has attracted great attention for treating neurodegenerative diseases worldwide because of its unique attributes. As acknowledged, there are several categories of stem cells being able to proliferate and differentiate into various cellular lineages, highlighting their significance in the context of regenerative medicine. In preclinical models, stem cell therapy using mesenchymal stem/stromal cells (MSCs), hematopoietic stem cells (HSCs), and neural progenitor or stem cells (NPCs or NSCs) along with pluripotent stem cells (PSCs)-derived neuronal cells could elicit desired therapeutic effects, enabling functional deficit rescue partially. Regardless of the noteworthy progress in our scientific awareness and understanding of stem cell biology, there still exist various challenges to defeat. In the present review, we provide a summary of the therapeutic potential of stem cells and discuss the current status and prospect of stem cell strategy in neurodegenerative diseases, in particular, AD, PD, ALS, and HD.

A Placebo-Controlled, Pseudo-Randomized, Crossover Trial of Botanical Agents for Gulf War Illness: Curcumin (Curcuma longa), Boswellia (Boswellia serrata), and French Maritime Pine Bark (Pinus pinaster)

This report is part of a larger study designed to rapidly and efficiently screen potential treatments for Gulf War Illness (GWI) by testing nine different botanicals. In this placebo-controlled, pseudo-randomized, crossover clinical trial of 20 men with GWI, we tested three botanical agents with putative peripheral and central anti-inflammatory actions: curcumin (Curcuma longa), boswellia (Boswellia serrata), and French maritime pine bark extract (Pinus pinaster). Participants completed 30 +/− 3 days of baseline symptom reports, followed by 30 +/− 3 days of placebo, 30 +/− 3 days of lower-dose botanical, and 30 +/− 3 days of higher-dose botanical. Participants then repeated the process with a new botanical until completing up to three botanical cycles. Data were analyzed using linear mixed models. Curcumin reduced GWI symptom severity significantly more than placebo at both the lower (p < 0.0001) and higher (p = 0.0003) dosages. Boswellia was not more effective than placebo at reducing GWI symptoms at either the lower (p = 0.726) or higher (p = 0.869) dosages. Maritime pine was not more effective than placebo at the lower dosage (p = 0.954) but was more effective than placebo at the higher dosage (p = 0.006). This study provides preliminary evidence that curcumin and maritime pine may help alleviate symptoms of GWI. As a screening study, a final determination of the efficacy of these compounds for all individuals with GWI cannot be made, and further studies will need to be conducted to determine strength and durability of effects, as well as optimal dosage. These results suggest that GWI may, at least in part, involve systemic inflammatory processes. This trial was registered on ClinicalTrials.gov (NCT02909686) on 13 September 2016.

Targeting Alzheimer's disease with multimodal polypeptide-based nanoconjugates

Alzheimer's disease (AD), the most prevalent form of dementia, remains incurable mainly due to our failings in the search for effective pharmacological strategies. Here, we describe the development of targeted multimodal polypeptide-based nanoconjugates as potential AD treatments. Treatment with polypeptide nanoconjugates bearing propargylamine moieties and bisdemethoxycurcumin or genistein afforded neuroprotection and displayed neurotrophic effects, as evidenced by an increase in dendritic density of pyramidal neurons in organotypic hippocampal culture. The additional conjugation of the Angiopep-2 targeting moiety enhanced nanoconjugate passage through the blood-brain barrier and modulated brain distribution with nanoconjugate accumulation in neurogenic areas, including the olfactory bulb. Nanoconjugate treatment effectively reduced neurotoxic β amyloid aggregate levels and rescued impairments to olfactory memory and object recognition in APP/PS1 transgenic AD model mice. Overall, this study provides a description of a targeted multimodal polyglutamate-based nanoconjugate with neuroprotective and neurotrophic potential for AD treatment.

Chalcone and its analogs: Therapeutic and diagnostic applications in Alzheimer's disease

Chalcone [(E)-1,3-diphenyl-2-propene-1-one], a small molecule with α, β unsaturated carbonyl group is a precursor or component of many natural flavonoids and isoflavonoids. It is one of the privileged structures in medicinal chemistry. It possesses a wide range of biological activities encouraging many medicinal chemists to study this scaffold for its usefulness to oncology, infectious diseases, virology and neurodegenerative diseases including Alzheimer's disease (AD). Small molecular size, convenient and cost-effective synthesis, and flexibility for modifications to modulate lipophilicity suitable for blood brain barrier (BBB) permeability make chalcones a preferred candidate for their therapeutic and diagnostic potential in AD. This review summarizes and highlights the importance of chalcone and its analogs as single target small therapeutic agents, multi-target directed ligands (MTDLs) as well as molecular imaging agents for AD. The information summarized here will guide many medicinal chemist and researchers involved in drug discovery to consider chalcone as a potential scaffold for the development of anti-AD agents including theranostics.

Natural Products Targeting Amyloid Beta in Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disease characterized by severe brain damage and dementia. There are currently few therapeutics to treat this disease, and they can only temporarily alleviate some of the symptoms. The pathogenesis of AD is mainly preceded by accumulation of abnormal amyloid beta (Aβ) aggregates, which are toxic to neurons. Therefore, modulation of the formation of these abnormal aggregates is strongly suggested as the most effective approach to treat AD. In particular, numerous studies on natural products associated with AD, aiming to downregulate Aβ peptides and suppress the formation of abnormal Aβ aggregates, thus reducing neural cell death, are being conducted. Generation of Aβ peptides can be prevented by targeting the secretases involved in Aβ-peptide formation (secretase-dependent). Additionally, blocking the intra- and intermolecular interactions of Aβ peptides can induce conformational changes in abnormal Aβ aggregates, whereby the toxicity can be ameliorated (structure-dependent). In this review, AD-associated natural products which can reduce the accumulation of Aβ peptides via secretase- or structure-dependent pathways, and the current clinical trial states of these products are discussed.

Curcumin as Scaffold for Drug Discovery against Neurodegenerative Diseases

Neurodegenerative diseases (NDs) are one of major public health problems and their impact is continuously growing. Curcumin has been proposed for the treatment of several of these pathologies, such as Alzheimer's disease (AD) and Parkinson's disease (PD) due to the ability of this molecule to reduce inflammation and aggregation of involved proteins. Nevertheless, the poor metabolic stability and bioavailability of curcumin reduce the possibilities of its practical use. For these reasons, many curcumin derivatives were synthetized in order to overcome some limitations. In this review will be highlighted recent results on modification of curcumin scaffold in the search of new effective therapeutic agents against NDs, with particular emphasis on AD.

Preservation of dendritic spine morphology and postsynaptic signaling markers after treatment with solid lipid curcumin particles in the 5xFAD mouse model of Alzheimer's amyloidosis

BACKGROUND

Synaptic failure is one of the principal events associated with cognitive dysfunction in Alzheimer's disease (AD). Preservation of existing synapses and prevention of synaptic loss are promising strategies to preserve cognitive function in AD patients. As a potent natural anti-oxidant, anti-amyloid, and anti-inflammatory polyphenol, curcumin (Cur) shows great promise as a therapy for AD. However, hydrophobicity of natural Cur limits its solubility, stability, bioavailability, and clinical utility for AD therapy. We have demonstrated that solid lipid curcumin particles (SLCP) have greater therapeutic potential than natural Cur in vitro and in vivo models of AD. In the present study, we have investigated whether SLCP has any preservative role on affected dendritic spines and synaptic markers in 5xFAD mice.

METHODS

Six- and 12-month-old 5xFAD and age-matched wild-type mice received oral administration of SLCP (100 mg/kg body weight) or equivalent amounts of vehicle for 2 months. Neuronal morphology, neurodegeneration, and amyloid plaque load were investigated from prefrontal cortex (PFC), entorhinal cortex (EC), CA1, CA3, and the subicular complex (SC). In addition, the dendritic spine density from apical and basal branches was studied by Golgi-Cox stain. Further, synaptic markers, such as synaptophysin, PSD95, Shank, Homer, Drebrin, Kalirin-7, CREB, and phosphorylated CREB (pCREB) were studied using Western blots. Finally, cognitive and motor functions were assessed using open-field, novel object recognition (NOR) and Morris water maze (MWM) tasks after treatment with SLCP.

RESULTS

We observed an increased number of pyknotic and degenerated cells in all these brain areas in 5xFAD mice and SLCP treatment partially protected against those losses. Decrease in dendritic arborization and dendritic spine density from primary, secondary, and tertiary apical and basal branches were observed in PFC, EC, CA1, and CA3 in both 6- and 12-month-old 5xFAD mice, and SLCP treatments partially preserved the normal morphology of these dendritic spines. In addition, pre- and postsynaptic protein markers were also restored by SLCP treatment. Furthermore, SLCP treatment improved NOR and cognitive function in 5xFAD mice.

CONCLUSIONS

Overall, these findings indicate that use of SLCP exerts neuroprotective properties by decreasing amyloid plaque burden, preventing neuronal death, and preserving dendritic spine density and synaptic markers in the 5xFAD mice.

Recent advances in enzymeless-based electrochemical sensors to diagnose neurodegenerative diseases

The use of sensitive electrochemical sensors to detect biomarkers is an effective method for the early diagnosis of several neurodegenerative diseases (NDs), such as Alzheimer's disease, Parkinson's disease, Huntington's disease, amyotrophic lateral sclerosis, etc. However, the commercialization of enzyme/aptamer-based sensors is still hampered owing to the historic drawbacks of biorecognition elements including high cost, poor stability, and complex integration technology. Non-enzymatic electrochemical sensors are more attractive compared to their traditional counterparts and can be widely harnessed owing to their low cost, high stability, sensitivity, and ease of miniaturization. This review summarizes recent research progress focusing on the construction of non-enzymatic electrochemical sensors and analyzes their present use in the early diagnosis of NDs. Additionally, this review addresses the limitations and challenges of the use of current non-enzymatic electrochemical sensor technologies for the diagnosis of NDs and highlights the possible directions for future research.

Cognitive decline prevention in offspring of Pb+2 exposed mice by maternal aerobic training and Cur/CaCO3@Cur supplementations: In vitro and in vivo studies

Heavy metals are considered contaminants that hazardously influence the healthy life of humans and animals as they are widely used in industry. Contact of youngsters and women at ages of parturition with lead (Pb⁺²) is a main related concern, which passes through the placental barricade and its better absorption in the intestine leads to flaws in the fetal developfment. However, the metals threaten animal and human life, in particular throughout developmental stages. Products existing in the nature have a major contribution to innovating chemo-preventives. As a naturally available polyphenol and necessary curcuminoid, curcumin (Cur) is a derivative of the herb Curcuma longa (L.) rhizome, which globally recognized as "wonder drug of life"; however, Cur has a limited clinical use as it is poorly dissolved in water. Therefore, to enhance its clinically relevant parameters, curcumin-loaded calcium carbonate (CaCO₃@Cur) was synthesized by one step coprecipitation method as a newly introduced in this research. Initially, its structure was physio chemically characterized using FT-IR, FESEM and DLS equipment and then the cytotoxicity of lead when it was pretreated with Cur/CaCO₃@Cur were assessed by MTT assay. Both Cur and CaCO₃@Cur diminished the toxic effects of Pb⁺² while the most protective effect on the Pb⁺² cytotoxicity was achieved by pre-incubation of cells with CaCO₃@Cur. Besides, the morphological changes of Pb⁺²-treated cells that were pre-incubated with or without Cur/CaCO₃@Cur were observed by normal and florescent microscopes. A non-pharmacologic method that lowers the hazard of brain damage is exercise training that is capable of both improving and alleviating memory. In the current study, the role of regular aerobic training and CaCO₃@Cur was assessed in reducing the risk of brain damage induced by lead nitrate contact. To achieve the mentioned goal, pregnant Balb/C mice were assigned to five groups (six mice/group) at random: negative and positive controls, aerobic training group and Cur and CaCO₃@Cur treated (50 mg/kg/b.wt) trained groups that exposed to Pb⁺² (2 mg/kg) by drinking water during breeding and pregnancy. With the completion of study, offspring were subjected to the behavioral tasks that was tested by step-through ORT, DLB, MWM and YM tests. As a result, having regular aerobic training and CaCO₃@Cur co-administration with lead nitrate could reverse the most defected behavioral indicators; yet, this was not visible for both sexes and it seems that gender can also be a source of different effects in the animal's body. In fact, having regular aerobic training along with CaCO₃@Cur supplementation during pregnancy may be encouraging protecting potential agents towards the toxicity of Pb⁺² that could be recommended in the areas with high pollution of heavy metals.

Recent advances in dioxaborine-based fluorescent materials for bioimaging applications

Fluorescent materials are continuously contributing to important advances in the field of bioimaging. Among these materials, dioxaborine-based fluorescent materials (DBFM) are arousing growing interest. Due to their rigid structures conferred by a cyclic boron complex, DBFM possess appealing photophysical properties including high extinction coefficients and quantum yields as well as emission in the near infrared, enhanced photostability and high two-photon absorption. We herein discuss the recent advances of DBFM that found use in bioimaging applications. This review covers the development of fluorescent molecular probes for biomolecules (DNA, proteins), small molecules (cysteine, H₂O₂, oxygen), ions and the environment (polarity, viscosity) as well as polymers and nanomaterials used in bioimaging. This review aims at providing a comprehensive and critical insight on DBFM by highlighting the assets of these promising materials in bioimaging but also by pointing out their limitations that would require further developments.

Neuroprotective Studies on Polygonum hydropiper L. Essential Oils Using Transgenic Animal Models

Polygonum hydropiper L. and related species are reported to possess neuroprotective potentials. In an attempt to validate its anti-Alzheimer's potentials, leaf oils (Ph. Lo) were extensively evaluated in this study against several in vitro and in vivo models of Alzheimer's disease. The Ph. Lo were tested against pathological targets of Alzheimer's diseases (ADs). The in vitro and in vivo assays were done for cholinesterase inhibition, anti-radical properties and cognitive assessments using transgenic animal models. In preliminary cholinesterase inhibition assays, Ph. Lo were more active against acetylcholinesterase (AChE), butyrylcholinesterase (BChE), 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2-azinobis (3-ethylbenzthiazoline)-6-sulfonic acid (ABTS), and hydrogen peroxide (H2O2) radicals. Subsequently, Ph. Lo was evaluated for its effects on special memory, exploratory behavior, and coordination using shallow water maze (SWM), Y-maze, open filed, and balance beam tests. Animal pre-genotyping was done via polymerase chain reaction (PCR) to confirm amyloid precursor protein (APP) transgene, and after completion of drug therapy, brain homogenates from the cortex and hippocampus were evaluated for cholinesterase and free radical studies. In SWM task, disease control animals treated with 10 mg/kg of Ph. Lo for 5 days exhibited significant improvement in cognitive performance indicated by low escape times on 5th day compared with normal animals. In the Y-maze test, transgenic animals showed higher spontaneous alternation behavior than disease control animals and standard control group animals. Ph. Lo therapy has improved the exploratory behavior and declined anxiety behavior in diseased animals as accessed via open field test. Ph. Lo administration significantly augmented the motor and coordination abilities of transgenic animals when compared to other groups of animals and declined AChE, BChE activities as well as free radicals load in the cortex and hippocampus tissues. Based on our finding, it is concluded that Ph. Lo exhibit significant neuroprotective potentials preliminary due to their anti-radicals and cholinesterase inhibitory activities. Ph. Lo need further detailed studies as potential aromatherapy against neurodegenerative disorders.

Plasmonic nanoparticle amyloid corona for screening Aβ oligomeric aggregate-degrading drugs

The generation of toxic amyloid β (Aβ) oligomers is a central feature of the onset and progression of Alzheimer's disease (AD). Drug discoveries for Aβ oligomer degradation have been hampered by the difficulty of Aβ oligomer purification and a lack of screening tools. Here, we report a plasmonic nanoparticle amyloid corona (PNAC) for quantifying the efficacy of Aβ oligomeric aggregate-degrading drugs. Our strategy is to monitor the drug-induced degradation of oligomeric aggregates by analyzing the colorimetric responses of PNACs. To test our strategy, we use Aβ-degrading proteases (protease XIV and MMP-9) and subsequently various small-molecule substances that have shown benefits in the treatment of AD. We demonstrate that this strategy with PNAC can identify effective drugs for eliminating oligomeric aggregates. Thus, this approach presents an appealing opportunity to reduce attrition problems in drug discovery for AD treatment.

Amyloid-β and tau aggregation dual-inhibitors: A synthetic and structure-activity relationship focused review

Alzheimer's disease (AD) is one of the most common types of dementia, especially in elderly, with an increasing number of people suffering from this disease worldwide. There are no available disease-modifying therapies and only four drugs are approved for the relief of symptoms. Currently, the therapeutic approach used for AD treatment is based on single target drugs, which are not capable to stop its progression. To address this issue, multi-target compounds, combining two or more pharmacophores in a single molecular entity, have gained increasing interest to deal with the multiple factors related to AD. The exact cause of AD is not yet completely disclosed, and several hallmarks have been associated to this neurodegenerative disease. Even though, the accumulation of both amyloid-β plaques (Aβ) and neurofibrillary tangles (NFTs) are fully accepted as the main AD hallmarks, being object of lots of research for early-stage diagnosis and pharmacological therapy. In this context, this review summarizes the state-of-the-art in the field of dual-target inhibitors of both Aβ and tau aggregation simultaneously, including the design and synthetic strategy of the dual-target compounds, as well as a brief structure-activity relationships (SAR) analysis.

Keto form of curcumin derivatives strongly binds to Aβ oligomers but not fibrils

The accumulation of β-amyloid (Aβ) aggregates in the brain occurs early in the progression of Alzheimer's disease (AD), and non-fibrillar soluble Aβ oligomers are particularly neurotoxic. During binding to Aβ fibrils, curcumin, which can exist in an equilibrium state between its keto and enol tautomers, exists predominantly in the enol form, and binding activity of the keto form to Aβ fibrils is much weaker. Here we described the strong binding activity the keto form of curcumin derivative Shiga-Y51 shows for Aβ oligomers and its scant affinity for Aβ fibrils. Furthermore, with imaging mass spectrometry we revealed the blood-brain barrier permeability of Shiga-Y51 and its accumulation in the cerebral cortex and the hippocampus, where Aβ oligomers were mainly localized, in a mouse model of AD. The keto form of curcumin derivatives like Shiga-Y51 could be promising seed compounds to develop imaging probes and therapeutic agents targeting Aβ oligomers in the brain.

Functional nanoassemblies for the diagnosis and therapy of Alzheimer's diseases

Alzheimer's disease (AD) is a progressive neurodegenerative disease that affects populations around the world. Many therapeutics have been investigated for AD diagnosis and/or therapy, but the efficacy is largely limited by the poor bioavailability of drugs and by the presence of the blood-brain barrier. Recently, the development of nanomedicines enables efficient drug delivery to the brain, but the complex pathological mechanism of AD prevents them from successful treatment. As a type of advanced nanomedicine, multifunctional nanoassemblies self-assembled from nanoscale imaging or therapeutic agents can simultaneously target multiple pathological factors, showing great potential in the diagnosis and therapy of AD. To help readers better understand this emerging field, in this review, we first introduce the pathological mechanisms and the potential drug candidates of AD, as well as the design strategies of nanoassemblies for improving AD targeting efficiency. Moreover, the progress of dynamic nanoassemblies that can diagnose and/or treat AD in response to the endogenous or exogenous stimuli will be described. Finally, we conclude with our perspectives on the future development in this field. The objective of this review is to outline the latest progress of using nanoassemblies to overcome the complex pathological environment of AD for improved diagnosis and therapy, in hopes of accelerating the future development of intelligent AD nanomedicines. This article is categorized under: Therapeutic Approaches and Drug Discovery > Nanomedicine for Neurological Disease Diagnostic Tools > in vivo Nanodiagnostics and Imaging.

Ellagic acid and pentagalloylglucose are potential inhibitors of prion protein fibrillization

Prion diseases are fatal neurodegenerative diseases caused by the conformational transition of the cellular prion protein (PrP^C) to the abnormal pathological prion protein (PrP^Sc). In this work, the effects of ellagic acid (EA) and pentagalloylglucose (PGG) on prion protein (PrP) fibrillization were investigated. Fluorescence quenching experiments indicated that both EA and PGG could specifically interact with native human PrP with binding affinities of 1.92 × 10⁵ and 2.36 × 10⁵ L·mol^-1, respectively. Thioflavin-T (ThT) fluorescence assays showed that the binding of EA or PPG could effectively inhibit the nucleation and elongation of PrP fibrilization and reduce the amount of PrP fibrils generated. EA and PGG could also lead to a significant disaggregation of PrP fibrils. Circular dichroism (CD) measurements suggested that EA- or PPG-bound PrP could preserve a higher content of α-helical structures than β-sheet-rich PrP fibrils. The PrP aggregates formed in the presence of EA or PGG showed lower resistance to proteinase K (PK) digestion. Overall, the present work reported the inhibitory effect of EA and PGG on PrP fibrillization. These two natural polyphenols could be potential prodrug molecules for the prevention and treatment of prion diseases.

Beneficial Effects of Epigallocatechin-3-O-Gallate, Chlorogenic Acid, Resveratrol, and Curcumin on Neurodegenerative Diseases

Many observational and clinical studies have shown that consumption of diets rich in plant polyphenols have beneficial effects on various diseases such as cancer, obesity, diabetes, cardiovascular diseases, and neurodegenerative diseases (NDDs). Animal and cellular studies have indicated that these polyphenolic compounds contribute to such effects. The representative polyphenols are epigallocatechin-3-O-gallate in tea, chlorogenic acids in coffee, resveratrol in wine, and curcumin in curry. The results of human studies have suggested the beneficial effects of consumption of these foods on NDDs including Alzheimer's and Parkinson's diseases, and cellular animal experiments have provided molecular basis to indicate contribution of these representative polyphenols to these effects. This article provides updated information on the effects of these foods and their polyphenols on NDDs with discussions on mechanistic aspects of their actions mainly based on the findings derived from basic experiments.