EGCG Nanoparticles Attenuate Aluminum Chloride Induced Neurobehavioral Deficits, Beta Amyloid and Tau Pathology in a Rat Model of Alzheimer's Disease

The influence of vinpocetine alone or in combination with Epigallocatechin-3-gallate, Coenzyme COQ10, Vitamin E and Selenium as a potential neuroprotective combination against aluminium-induced Alzheimer's disease in Wistar Albino Rats

Alzheimer's disease (AD) is one of such diseases that represent the most prominent cause of dementia in elderly people. To explore the possible neuroprotective effect as well as mechanism of action of Vinpocetine either alone or in combination with EGCG, CoQ10, or VE & Se in ameliorating aluminum chloride-induced AD in rats. Rats were received AlCl₃ (70 mg/kg) intraperitoneal daily dose for 30 days along with EGCG (10 mg/kg, I.P), CoQ10 (200 mg/kg, P.O), VE (100 mg/kg, P.O) & Se (1 mg/kg, P.O) as well as Vinpocetine (20 mg/kg, P.O) either alone or in combination. Results revealed that the combination of Vinpocetine with EGCG showed the best neuroprotection. This protection in the brain was indicated by the significant decrease in Aβ and ACHE. The same pattern of results were shown in the levels of monoamines and BDNF. In addition, the combination of Vinpocetine with EGCG showed more pronounced anti-inflammatory (TNF-α, IL-1β) and antioxidant (MDA, SOD, TAC) effects in comparison to other combinations. These results were confirmed using histopathological examinations as well as DNA fragmentation assays. Vinpocetine with EGCG showed pronounced protection on neurons against AD induced by AlCl₃ in rats.

Green Tea Polyphenol Epigallocatechin-Gallate in Amyloid Aggregation and Neurodegenerative Diseases

The accumulation of protein aggregates in human tissues is a hallmark of more than 40 diseases called amyloidoses. In seven of these disorders, the aggregation is associated with neurodegenerative processes in the central nervous system such as Alzheimer’s disease (AD), Parkinson’s disease (PD), and Huntington’s disease (HD). The aggregation occurs when certain soluble proteins lose their physiological function and become toxic amyloid species. The amyloid assembly consists of protein filament interactions, which can form fibrillar structures rich in β-sheets. Despite the frequent incidence of these diseases among the elderly, the available treatments are limited and at best palliative, and new therapeutic approaches are needed. Among the many natural compounds that have been evaluated for their ability to prevent or delay the amyloidogenic process is epigallocatechin-3-gallate (EGCG), an abundant and potent polyphenolic molecule present in green tea that has extensive biological activity. There is evidence for EGCG’s ability to inhibit the aggregation of α-synuclein, amyloid-β, and huntingtin proteins, respectively associated with PD, AD, and HD. It prevents fibrillogenesis (in vitro and in vivo), reduces amyloid cytotoxicity, and remodels fibrils to form non-toxic amorphous species that lack seed propagation. Although it is an antioxidant, EGCG in an oxidized state can promote fibrils’ remodeling through formation of Schiff bases and crosslinking the fibrils. Moreover, microparticles to drug delivery were synthesized from oxidized EGCG and loaded with a second anti-amyloidogenic molecule, obtaining a synergistic therapeutic effect. Here, we describe several pre-clinical and clinical studies involving EGCG and neurodegenerative diseases and their related mechanisms.

Computational and Experimental Assessments of Magnolol as a Neuroprotective Agent and Utilization of UiO-66(Zr) as Its Drug Delivery System

The phenolic natural product magnolol exhibits neuroprotective properties through β-amyloid toxicity in PC-12 cells and ameliorative effects against cognitive deficits in a TgCRND8 transgenic mice model. Its bioavailability and blood-brain barrier crossing ability have been significantly improved using the metal-organic framework (MOF) UiO-66(Zr) as a drug delivery system (DDS). To investigate the neuroprotective effects of the Zr-based DDS, magnolol and magnolol-loaded-UiO-66(Zr) (Mag@UiO-66(Zr)) were evaluated for inhibitory activity against β-secretase and AlCl₃-induced neurotoxicity. Due to the moderate inhibition observed for magnolol in vitro, in silico binding studies were explored against β-secretase along with 11 enzymes known to affect Alzheimer's disease (AD). Favorable binding energies against CDK2, CKD5, MARK, and phosphodiesterase 3B (PDE3B) and dynamically stable complexes were noted through molecular docking and molecular dynamic simulation experiments, respectively. The magnolol-loaded DDS UiO-66(Zr) also showed enhanced neuroprotective activity against two pathological indices, namely, neutrophil infiltration and apoptotic neurons, in addition to damage reversal compared to magnolol. Thus, MOFs are promising drug delivery platforms for poorly bioavailable drugs.

Taurine and Camel Milk Modulate Neurobehavioral and Biochemical Changes in Aluminum Chloride-Induced Alzheimer's Disease in Rats

BACKGROUND

Alzheimer's disease (AD) is a neurodegenerative disease associated with deficiency in motor coordination, cognitive impairment, and excessive reactive oxygen species production in the brain.

OBJECTIVE

The study evaluated effects of taurine and camel milk (CM) on neurobehavior, amyloid-beta peptide 1-42 (Aβ) expression, acetylcholinesterase, and superoxide dismutase activities in aluminum chloride (AlCl3) model of Alzheimer's disease in rats.

METHODS

Thirty-five female Wistar rats were divided into seven groups (n = 5): Normal saline (0.2 mL/kg body weight); AlCl3 (100 mg/kg) (AD); CM (33 mL/kg); Taurine (50 mg/kg); AlCl3 (100 mg/kg) + CM (33 mL/kg); AlCl3 (100 mg/kg) + Taurine (50 mg/kg); and AlCl3 (100 mg/kg) + CM (33 mL/kg) + Taurine (50 mg/kg). The administration lasted for eight weeks via oral gavage. After the eighth week, neurobehavior assessments were performed. Rats were sacrificed, and brain and blood samples collected for analysis.

RESULTS

There was a significant (p < 0.0001) increase in the duration of motor endurance in AD + CM rats, compared to AD rats. Duration of forced swimming time was lowest (p < 0.0001) in AlCl3 + Taurine rats, compared to that of AD rats. Concentration of Aβ peptide decreased (p < 0.05) in AD rats, treated with CM and/or combination. In taurine-treated rats, superoxide dismutase activity was significantly (p < 0.05) higher than in AD rats. Treatment with taurine + CM increased (p < 0.05) acetylcholinesterase activity compared to controls.

CONCLUSION

Taurine and CM enhanced cognition and sensorimotor activity by decreasing Aβ peptide concentration and increasing superoxide dismutase and acetylcholinesterase activities in AD rats.

Formaldehyde-Crosslinked Nontoxic Aβ Monomers to Form Toxic Aβ Dimers and Aggregates: Pathogenicity and Therapeutic Perspectives

Alzheimer's disease (AD) is characterized by the presence of senile plaques in the brain. However, medicines targeting amyloid-beta (Aβ) have not achieved the expected clinical effects. This review focuses on the formation mechanism of the Aβ dimer (the basic unit of oligomers and fibrils) and its tremendous potential as a drug target. Recently, age-associated formaldehyde and Aβ-derived formaldehyde have been found to crosslink the nontoxic Aβ monomer to form the toxic dimers, oligomers and fibrils. Particularly, Aβ-induced formaldehyde accumulation and formaldehyde-promoted Aβ aggregation form a vicious cycle. Subsequently, formaldehyde initiates Aβ toxicity in both the early-and late-onset AD. These facts also explain why AD drugs targeting only Aβ do not have the desired therapeutic effects. Development of the nanoparticle-based medicines targeting both formaldehyde and Aβ dimer is a promising strategy for improving the drug efficacy by penetrating blood-brain barrier and extracellular space into the cortical neurons in AD patients.

Optimization of cerebral organoids: a more qualified model for Alzheimer's disease research

Alzheimer's disease (AD) is a neurodegenerative disease that currently cannot be cured by any drug or intervention, due to its complicated pathogenesis. Current animal and cellular models of AD are unable to meet research needs for AD. However, recent three-dimensional (3D) cerebral organoid models derived from human stem cells have provided a new tool to study molecular mechanisms and pharmaceutical developments of AD. In this review, we discuss the advantages and key limitations of the AD cerebral organoid system in comparison to the commonly used AD models, and propose possible solutions, in order to improve their application in AD research. Ethical concerns associated with human cerebral organoids are also discussed. We also summarize future directions of studies that will improve the cerebral organoid system to better model the pathological events observed in AD brains.

[Constructing Brain Aβ-Targeting Nanoparticles Loaded with EGCG for Treating Alzheimer's Disease in Mice]

OBJECTIVE

To construct a nanodelivery system surface-modified with RD2 peptide (polypeptide sequence PTLHTHNRRRRR) for brain tissue penetration and β-amyloid (Aβ) binding. Epigallocatechin-3-gallate (EGCG) was selected for encapsulation in the targeted delivery system and its therapeutic potential for Alzheimer's disease (AD) was investigated.

METHODS

EGCG-load nanoparticles (NP/EGCG), NP/EGCG with RD2 peptide surface modification (RD2-NP/EGCG), as well as RD2 peptide-modified blank nanoparticles (RD2-NP) were prepared and characterized. Thioflavin T assay was done to assess the ability of RD2-NP to bind with Aβ and ex vivo imaging was conducted to evaluate the distribution of RD2-NP in brain lesion sites. The AD mice model was established by injecting oligomeric Aβ 42 in the bilateral hippocampi of ICR mice. Then AD mice were administered intravenously through the tail vein with normal saline, EGCG solution, NP/EGCG or RD2-NP/EGCG for 28 d, respectively, and the Morris water maze tests were performed to assess the spatial memory of mice. Subsequently, RT-PCR method was used to determine the mRNA levels of tumor necrosis factor-α (TNF-α) and interleukin-1β (IL-1β) in the hippocampus of the mice, and the morphological changes of hippocampal neurons were observed with Nissl staining. Additionally, the pathological changes of heart, liver, spleen, lung, and kidney were characterized by hematoxylin-eosin (HE) staining.

RESULTS

The particle diameter of the prepared RD2-NP/EGCG was (204.83±2.80) nm and the zeta potential was -23.88 mV. The encapsulation efficiency and drug loading capacity were 94.39% and 5.90%, respectively. The RD2 peptide modification has no significant effect on the physiochemical properties of the nanoparticles. RD2-NP had good Aβ binding ability, and it could be concentrated in hippocampus and cerebral cortex, the most common Aβ deposition sites. The four-week RD2-NP/EGCG treatment significantly decreased the expression of the pro-inflammatory cytokine TNF-α and IL-1β, restored neuronal losses and hippocampal damage, and ameliorated spatial memory impairment in AD model mice. Moreover, treatment with the RD2-NP/EGCG did not present organ toxicity.

CONCLUSION

Surface modified RD2 peptide nanodelivery system can efficiently deliver drugs to AD lesions and improve the therapeutic effect of EGCG on AD.

Microenvironment-tailored nanoassemblies for the diagnosis and therapy of neurodegenerative diseases

Neurodegenerative disorder is an illness involving neural dysfunction/death attributed to complex pathological processes, which eventually lead to the mortality of the host. It is generally recognized through features such as mitochondrial dysfunction, protein aggregation, oxidative stress, metal ions dyshomeostasis, membrane potential change, neuroinflammation and neurotransmitter impairment. The aforementioned neuronal dysregulations result in the formation of a complex neurodegenerative microenvironment (NME), and may interact with each other, hindering the performance of therapeutics for neurodegenerative disease (ND). Recently, smart nanoassemblies prepared from functional nanoparticles, which possess the ability to interfere with different NME factors, have shown great promise to enhance the diagnostic and therapeutic efficacy of NDs. Herein, this review highlights the recent advances of stimuli-responsive nanoassemblies that can effectively combat the NME for the management of ND. The first section outlined the NME properties and their interrelations that are exploitable for nanoscale targeting. The discussion is then extended to the controlled assembly of functional nanoparticles for the construction of stimuli-responsive nanoassemblies. Further, the applications of stimuli-responsive nanoassemblies for the enhanced diagnosis and therapy of ND are introduced. Finally, perspectives on the future development of NME-tailored nanomedicines are given.

Therapeutic Potential of Phytoconstituents in Management of Alzheimer's Disease

Since primitive times, herbs have been extensively used in conventional remedies for boosting cognitive impairment and age-associated memory loss. It is mentioned that medicinal plants have a variety of dynamic components, and they have become a prominent choice for synthetic medications for the care of cognitive and associated disorders. Herbal remedies have played a major role in the progression of medicine, and many advanced drugs have already been developed. Many studies have endorsed practicing herbal remedies with phytoconstituents, for healing Alzheimer's disease (AD). All the information in this article was collated from selected research papers from online scientific databases, such as PubMed, Web of Science, and Scopus. The aim of this article is to convey the potential of herbal remedies for the prospect management of Alzheimer's and related diseases. Herbal remedies may be useful in the discovery and advancement of drugs, thus extending new leads for neurodegenerative diseases such as AD. Nanocarriers play a significant role in delivering herbal medicaments to a specific target. Therefore, many drugs have been described for the management of age-linked complaints such as dementia, AD, and the like. Several phytochemicals are capable of managing AD, but their therapeutic claims are restricted due to their lower solubility and metabolism. These limitations of natural therapeutics can be overcome by using a targeted nanocarrier system. This article will provide the primitive remedies as well as the development of herbal remedies for AD management.

New insights in drug development for Alzheimer's disease based on microglia function

One of the biggest challenges in drug development for Alzheimer's disease (AD) is how to effectively remove deposits of amyloid-beta (Aβ). Recently, the relationship between microglia and Aβ has become a research hotspot. Emerging evidence suggests that Aβ-induced microglia-mediated neuroinflammation further aggravates the decline of cognitive function, while microglia are also involved in the process of Aβ clearance. Hence, microglia have become a potential therapeutic target for the treatment or prevention of AD. An in-depth understanding of the role played by microglia in the development of AD will help us to broaden therapeutic strategies for AD. In this review, we provide an overview of the dual roles of microglia in AD progression: the positive effect of phagocytosis of Aβ and its negative effect on neuroinflammation after over-activation. With the advantages of novel structure, high efficiency, and low toxicity, small-molecule compounds as modulators of microglial function have attracted considerable attention in the therapeutic areas of AD. In this review, we also summarize the therapeutic potential of small molecule compounds (SMCs) and their structure-activity relationship for AD treatment through modulating microglial phagocytosis and inhibiting neuroinflammation. For example, the position and number of phenolic hydroxyl groups on the B ring are the key to the activity of flavonoids, and the substitution of hydroxyl groups on the benzene ring enhances the anti-inflammatory activity of phenolic acids. This review is expected to be useful for developing effective modulators of microglial function from SMCs for the amelioration and treatment of AD.

Green Tea Epigallocatechin-3-gallate (EGCG) Targeting Protein Misfolding in Drug Discovery for Neurodegenerative Diseases

The potential to treat neurodegenerative diseases (NDs) of the major bioactive compound of green tea, epigallocatechin-3-gallate (EGCG), is well documented. Numerous findings now suggest that EGCG targets protein misfolding and aggregation, a common cause and pathological mechanism in many NDs. Several studies have shown that EGCG interacts with misfolded proteins such as amyloid beta-peptide (Aβ), linked to Alzheimer's disease (AD), and α-synuclein, linked to Parkinson's disease (PD). To date, NDs constitute a serious public health problem, causing a financial burden for health care systems worldwide. Although current treatments provide symptomatic relief, they do not stop or even slow the progression of these devastating disorders. Therefore, there is an urgent need to develop effective drugs for these incurable ailments. It is expected that targeting protein misfolding can serve as a therapeutic strategy for many NDs since protein misfolding is a common cause of neurodegeneration. In this context, EGCG may offer great potential opportunities in drug discovery for NDs. Therefore, this review critically discusses the role of EGCG in NDs drug discovery and provides updated information on the scientific evidence that EGCG can potentially be used to treat many of these fatal brain disorders.

Alendronate reduces the cognitive and neurological disturbances induced by combined doses of d-galactose and aluminum chloride in mice

Neurological disturbances including cholinergic dysfunction, oxidative stress, neuroinflammation, and cognitive impairments are the well-reported consequences of old age-related disorders like Alzheimer's disease (AD) or dementia. Bisphosphonates were shown to ameliorate dementia in osteoporotic patients, neuroinflammation, and cholinesterase activity in rodents. Thus, the present study has been designed to examine the role of alendronate against cognitive and neurological disturbances in mice induced by a combined oral dose of d-galactose and aluminum chloride (AlCl₃ ) for 6 weeks. d-galactose acts as a senescence agent, whereas AlCl₃ is a neurotoxin and in combination generates neuropathologies and cognitive depletion resembling aging and AD. It was found that memory was markedly impaired in d-galactose + AlCl₃ -treated mice as assessed in different behavioral paradigms. Additionally, d-galactose + AlCl₃ led to neurotoxicity assessed on the basis of neuroinflammation, oxidative stress, glial cell activation, neuronal damage, and augmented GSK-3β level in mice hippocampus. Consequently, alendronate administration orally for 15 days in d-galactose + AlCl₃ -exposed mice prominently reversed all these behavioral and neuropathological changes. These findings show that alendronate can be a potential therapeutic molecule with multiple targets for the management of age-related neurological disorders such as AD.

Role of natural products for the treatment of Alzheimer's disease

Negative psychological and physiological consequences of neurodegenerative disorders represent a high social and health cost. Among the neurodegenerative disorders Alzheimer's disease (AD) is recognized as a leading neurodegenerative condition and a primary cause of dementia in the elderlys. AD is considered as neurodegenerative disorder that progressively impairs cognitive function and memory. According to current epidemiological data, about 50 milLion people worldwide are suffering from AD. The primary symptoms of AD are almost inappreciable and usually comprise forgetfulness of recent events. Numerous processes are involved in the development of AD, for example oxidative stress (OS) mainly due to mitochondrial dysfunction, intracellular the accumulation of hyperphosphorylated tau (τ) proteins in the form of neurofibrillary tangles, excessive the accumulation of extracellular plaques of beta-amyloid (Aβ), genetic and environmental factors. Running treatments only attenuate symptoms and temporarily reduce the rate of cognitive progression associated with AD. This means that most treatments focus only on controlLing symptoms, particularly in the initial stages of the disease. In the past, the first choice of treatment was based on natural ingredients. In this sense, diverse natural products (NPs) are capable to decrease the symptoms and alleviate the development of several diseases including AD attracting the attention of the scientific community and the pharmaceutical industry. Specifically, numerous NPs including flavonoids, gingerols, tannins, anthocyanins, triterpenes and alkaloids have been shown anti-inflammatory, antioxidant, anti-amyloidogenic, and anti-choLinesterase properties. This review provide a summary of the pathogenesis and the therapeutic goals of AD. It also discusses the available data on various plants and isolated natural compounds used to prevent and diminish the symptoms of AD.

Quercetin-Conjugated Superparamagnetic Iron Oxide Nanoparticles Protect AlCl3-Induced Neurotoxicity in a Rat Model of Alzheimer's Disease via Antioxidant Genes, APP Gene, and miRNA-101

Alzheimer's disease (AD) is a neurodegenerative disease with cognitive impairment. Oxidative stress in neurons is considered as a reason for development of AD. Antioxidant agents such as quercetin slow down AD progression, but the usage of this flavonoid has limitations because of its low bioavailability. We hypothesized that quercetin-conjugated superparamagnetic iron oxide nanoparticles (QT-SPIONs) have a better neuroprotective effect on AD than free quercetin and regulates the antioxidant, apoptotic, and APP gene, and miRNA-101. In this study, male Wistar rats were subjected to AlCl3, AlCl3 + QT, AlCl3 + SPION, and AlCl3 + QT-SPION for 42 consecutive days. Behavioral tests and qPCR were used to evaluate the efficiency of treatments. Results of behavioral tests revealed that the intensity of cognitive impairment was decelerated at both the middle and end of the treatment period. The effect of QT-SPIONs on learning and memory deficits were closely similar to the control group. The increase in expression levels of APP gene and the decrease in mir101 led to the development of AD symptoms in rats treated with AlCl3 while these results were reversed in the AlCl3 + QT-SPIONs group. This group showed similar results with the control group. QT-SPION also decreased the expression levels of antioxidant enzymes along with increases in expression levels of anti-apoptotic genes. Accordingly, the antioxidant effect of QT-SPION inhibited progression of cognitive impairment via sustaining the balance of antioxidant enzymes in the hippocampus of AD model rats.

Flavonoid-Based Nanomedicines in Alzheimer's Disease Therapeutics: Promises Made, a Long Way To Go

Alzheimer's disease (AD) is characterized by the continuous decline of the cognitive abilities manifested due to the accumulation of large aggregates of amyloid-beta 42 (Aβ42), the formation of neurofibrillary tangles of hyper-phosphorylated forms of microtubule-associated tau protein, which may lead to many alterations at the cellular and systemic level. The current therapeutic strategies primarily focus on alleviating pathological symptoms rather than providing a possible cure. AD is one of the highly studied but least understood neurological problems and remains an unresolved condition of human brain degeneration. Over the years, multiple naturally derived small molecules, including plant products, microbial isolates, and some metabolic byproducts, have been projected as supplements reducing the risk or possible treatment of the disease. However, unfortunately, none has met the expected success. One major challenge for most medications is their ability to cross the blood-brain barrier (BBB). In past decades, nanotechnology-based interventions have offered an alternative platform to address the problem of the successful delivery of the drugs to the specific targets. Interestingly, the exciting interface of natural products and nanomedicine is delivering promising results in AD treatment. The potential applications of flavonoids, the plant-derived compounds best known for their antioxidant activities, and their amalgamation with nanomedicinal approaches may lead to highly effective therapeutic strategies for treating well-known neurodegenerative diseases. In the present review, we explore the possibilities and recent developments on an exciting combination of flavonoids and nanoparticles in AD.

In vitro and in vivo models for anti-amyloidosis nanomedicines

Amyloid diseases are global epidemics characterized by the accumulative deposits of cross-beta amyloid fibrils and plaques. Despite decades of intensive research, few solutions are available for the diagnosis, treatment, and prevention of these debilitating diseases. Since the early work on the interaction of human β₂-microglobulin and nanoparticles by Linse et al. in 2007, the field of amyloidosis inhibition has gradually evolved into a new frontier in nanomedicine offering numerous interdisciplinary research opportunities, especially for materials, chemistry and biophysics. In this review we summarise, for the first time, the in vitro and in vivo models employed thus far in the field of anti-amyloidosis nanomedicines. Based on this systematic summary, we bring forth the notion that, due to the complex and often overlapping physiopathologies of amyloid diseases, there is a crucial need for the appropriate use of in vitro and in vivo models for validating novel anti-amyloidosis nanomedicines, and there is a crucial need for the development of new animal models that reflect the behavioural, symptomatic and cross-talk hallmarks of amyloid diseases such as Alzheimer's (AD), Parkinson's (PD) diseases and type 2 diabetes (T2DM).

Nanotechnology Therapy for Alzheimer's Disease Memory Impairment Attenuation

Currently, there is no cure for Alzheimer's disease (AD) in humans; treatment is symptomatic only. Aging of the population, together with an unhealthy diet and lifestyle, contribute to the steady, global increase of AD patients. This increase creates significant health, societal and economical challenges even for the most developed countries. AD progresses from an asymptomatic stage to a progressively worsening cognitive impairment. The AD cognitive impairment is underpinned by progressive memory impairment, an increasing inability to recall recent events, to execute recently planned actions, and to learn. These changes prevent the AD patient from leading an independent and fulfilling life. Nanotechnology (NT) enables a new, alternative pathway for development of AD treatment interventions. At present, the NT treatments for attenuation of AD memory impairment are at the animal model stage. Over the past four years, there has been a steady increase in publications of AD animal models with a wide variety of original NT treatment interventions, able to attenuate memory impairment. NT therapy development, in animal models of AD, is faced with the twin challenges of the nature of AD, a chronic impairment, unique to human, of the tau protein and A β peptides that regulate several key physiological brain processes, and the incomplete understanding of AD's aetiology. This paper reviews the state-of-the-art in NT based treatments for AD memory impairment in animal models and discusses the future work for translation to the successful treatment of AD cognitive impairment in human.

The pharmacological activity of epigallocatechin-3-gallate (EGCG) on Alzheimer's disease animal model: A systematic review

BACKGROUND

Alzheimer's disease (AD) is currently incurable and there is an urgent need to develop new AD drugs. Many studies have revealed the potential neuroprotective effect of Epigallocatechin-3-O-gallate (EGCG), the main antioxidant in green tea, on animal models of AD. However, a systematic review of these reports is lacking.

PURPOSE

To assess the effectiveness of EGCG for AD treatment using systematic review and meta-analysis of pre-clinical trials.

METHODS

We conducted a systematic search of all available randomized controlled trials (RCTs) performed up to November 2019 in the following electronic databases: ScienceDirect, Web of Science, and PubMed. 17 preclinical studies assessing the effect of EGCG on animal AD models have been identified. Meta-analysis and subgroup analysis was performed to evaluate cognition improvement of various types of AD models. The study quality was assessed using the CAMARADES checklist and the criteria of published studies.

RESULTS

Our analysis shows that the methodological quality ranges from 3 to 5, with a median score of 4. According to meta-analysis of random-effects method, EGCG showed a positive effect in AD with shorter escape latency (SMD= -9.24, 95%CI= -12.05 to -6.42) and decreased Aβ₄₂ level (SD= -25.74,95%CI= -42.36 to -9.11). Regulation of α-, β-, γ-secretase activity, inhibition of tau phosphorylation, anti-oxidation, anti-inflammation, anti-apoptosis, and inhibition of AchE activity are reported as the main neuroprotective mechanisms. Though more than 100 clinical trials have been registered on the ClinicalTrials.gov, only one clinical trial has been conducted to test the therapeutic effects of EGCG on the AD progression and cognitive performance.

CONCLUSION

Here, we conducted this review to systematically describe the therapeutic potential of EGCG in animal models of AD and hope to provide a more comprehensive assessment of the effects in order to design future clinical trials. Besides, the safety, blood-brain barrier (BBB) penetration and bioavailability issues in conducting clinical trials were also discussed.

Sildenafil ameliorates Alzheimer disease via the modulation of vascular endothelial growth factor and vascular cell adhesion molecule-1 in rats

Alzheimer disease (AD) is a chronic neurodegenerative disease with multi-pathways pathogenesis. Sildenafil is a selective phosphodiesterase-5 inhibitor with a potential benefit in the treatment of AD. This study investigated the possible mechanisms underlying the effect of sildenafil in AD with emphasis on vascular endothelial growth factor (VEGF), and vascular cell adhesion molecule-1 (VCAM-1). Twenty-four adult male rats were classified into four groups; control group: received vehicles, sildenafil-control: received sildenafil (15 mg/kg/day, p.o.), AD group received Aluminum (25 mg/kg/day, p.o.), AD-treated group: received sildenafil (15 mg/kg/day, p.o.) for 6 weeks. AD was assessed by memory performance test and confirmed by histopathological examination and immunostaining of, neurogenesis marker nestin and α-synuclein. The levels of VEGF-A, VCAM-1, oxidative stress markers and TNF-α in brain tissue were evaluated. AD rats showed histopathological evidences of AD; along with increased latency time in the memory test. There was a decrease in VEGF-A, and an increase in VCAM-1, TNF-α, and oxidative stress markers. Immunohistochemical study showed a significant increase in α-synuclein and a significant decrease in nestin expressions in brain tissues. Sildenafil administration ameliorated the histopathological changes and decreased latency time. Such effect was associated with a decrease in VCAM-1, TNF-α and oxidative stress as well as an increase in VEGF-A. Sildenafil caused a significant increase in nestin and a decrease in α-synuclein immunostaining. These findings suggested a protective effect of sildenafil via modulation of VEGF-A, and VCAM-1.

Biotin, coenzyme Q10, and their combination ameliorate aluminium chloride-induced Alzheimer's disease via attenuating neuroinflammation and improving brain insulin signaling

Insulin is important for brain function and neuronal survival. Insulin signaling is initiated by the phosphorylation of insulin receptor substrate-1 (IRS-1) at tyrosine (pTyr) residue. However, IRS-1 is inhibited by phosphorylation at serine (pSer). In Alzheimer's disease (AD), oxidative stress and accumulation of amyloid beta (Aβ) induce neuroinflammation, which augments pSer-IRS-1 and reduces pTyr-IRS-1 disturbing insulin signaling pathway. Coenzyme Q10 (CoQ10) and biotin possess antioxidant and anti-inflammatory properties, and, in this study, their impact on insulin signaling is investigated in an aluminium chloride (AlCl3 ) model of AD. AD was induced by oral administration of AlCl3 (75 mg/kg) for 60 days. Biotin (2 mg/kg), CoQ10 (10 mg/kg), and their combination were supplemented concomitantly with AlCl3 for 60 days. Memory test and histological examination were performed. Brain levels of lipid peroxides, antioxidants (reduced glutathione and superoxide dismutase), inflammatory markers (tumor necrosis factor-α, interleukin-6 [IL-6], IL-1, and nuclear factor κB), and phosphorylated Akt (survival kinase) as well as protein levels of Aβ, IRS-1 (pTyr and pSer), and caspase-3 (apoptotic marker) were determined. AlCl3 resulted in impaired memory, significant increase in Aβ, lipid peroxides, inflammatory markers, caspase-3, and pSer-IRS-1, with significant reduction of the antioxidants, pTyr-IRS-1, and p-Akt reflecting Aβ-induced inflammation and defective insulin signaling. Histological examination revealed focal aggregations of inflammatory cells and neuronal degeneration. The biochemical deviations and histological changes were attenuated by the concomitant treatment with biotin and, to greater extent, with CoQ10 and the combination. In conclusion, biotin and CoQ10 could protect against AD via attenuating inflammatory response and enhancing insulin signaling.

Effects of pharmacological modulators of α-synuclein and tau aggregation and internalization

Parkinson's disease (PD) and Alzheimer's disease (AD) are common neurodegenerative disorders of the elderly and, therefore, affect a growing number of patients worldwide. Both diseases share, as a common hallmark, the accumulation of characteristic protein aggregates, known as Lewy bodies (LB) in PD, and neurofibrillary tangles in AD. LBs are primarily composed of misfolded α-synuclein (aSyn), and neurofibrillary tangles are primarily composed of tau protein. Importantly, upon pathological evaluation, most AD and PD/Lewy body dementia cases exhibit mixed pathology, with the co-occurrence of both LB and neurofibrillary tangles, among other protein inclusions. Recent studies suggest that both aSyn and tau pathology can spread and propagate through neuronal connections. Therefore, it is important to investigate the mechanisms underlying aggregation and propagation of these proteins for the development of novel therapeutic strategies. Here, we assessed the effects of different pharmacological interventions on the aggregation and internalization of tau and aSyn. We found that anle138b and fulvic acid decrease aSyn and tau aggregation, that epigallocatechin gallate decreases aSyn aggregation, and that dynasore reduces tau internalization. Establishing the effects of small molecules with different chemical properties on the aggregation and spreading of aSyn and tau will be important for the development of future therapeutic interventions.

Clopidogrel combats neuroinflammation and enhances learning behavior and memory in a rat model of Alzheimer's disease

BACKGROUND AND AIM

Alzheimer's disease (AD) is a progressive neurodegenerative disease. Multiple molecular mechanisms have been employed in its pathogenesis such as Amyloid β (Aβ) formation, tau protein hyperphosphorylation, reduced acetylcholine (ACh) level, and neuroinflammation. This study aimed to assess the possible neuroprotective effect of clopidogrel in AD model induced by aluminum chloride (AlCl₃) in rats.

METHODS

Sixty adult male Sprague-Dawley rats were divided into four different groups: Control, AlCl₃, AlCl₃ + donepezil, and AlCl₃ + Clopidogrel. AlCl₃ and the drugs were given orally once/day for 42 days. The spatial learning and memory and recognition memory were evaluated using Morris Water Maze (MWM) and Novel Object Recognition (NOR) tests, respectively. After euthanasia, hippocampal acetylcholinesterase (AChE) activity, tumor necrosis factor-alpha (TNF-α), and interleukin-1β (IL-1β) levels were biochemically assessed. Moreover, amyloid precursor protein (APP) mRNA gene expression was analyzed in the hippocampi of all rats. Histopathology for amyloid plaques was done.

RESULTS

Clopidogrel co-treatment significantly ameliorated the cognitive deficits induced by AlCl₃ in rats. Besides, clopidogrel significantly reduced AChE activity, TNF-α and IL-1β concentrations, and APP mRNA gene expression in the hippocampi of rats compared to AlCl₃ rats. The decrease of hippocampal TNF-α and IL-1β concentrations by clopidogrel was significant compared to donepezil co-treated rats. Clopidogrel co-treatment lessened amyloid plaque deposition in the hippocampal tissues of rats compared to AlCl₃ rats.

CONCLUSION

These findings demonstrate that clopidogrel could alleviate learning and memory deficit induced by AlCl₃ in rats and significantly reduced AChE activity. The neuroprotective outcome of clopidogrel might be assigned to its anti-inflammatory effect.

Neuroinflammation in pathogenesis of Alzheimer's disease: Phytochemicals as potential therapeutics

Accumulation of neurotoxic forms of amyloid-β proteins in senile plaques and hyperphosphorylated tau proteins in neurofibrillary tangles is a well-known pathophysiological hallmark of Alzheimer's disease (AD). However, clinical trials with drugs targeting amyloid-β and tau have failed to demonstrate efficacy in treating AD. All currently FDA-approved anti-AD drugs have symptomatic effects only and are not able to cure this disease. This makes necessary to search for alternative therapeutic targets. Accumulating evidence suggests that systemic inflammation and related vascular dysfunction play important etiological roles in AD and precede its clinical manifestation. Therefore, novel therapeutic modalities targeted at these pathophysiological components of AD are intensively developed now. Phytochemicals such as resveratrol, curcumin, quercetin, genistein and catechins are promising anti-AD therapeutics due to their ability to affect major pathogenetic mechanisms of AD, including oxidative stress, neuroinflammation and mitochondrial dysfunction. The implementation of innovative approaches for phytochemical delivery, including the nanotechnology-based ones which enable to significantly enhance their oral bioavailability, would likely provide an opportunity to address many challenges of conventional anti-AD therapies. In this review, roles of inflammation and vascular dysregulation in AD are described and phytobioactive compound-based treatment strategies for AD are discussed.

Cassia tora extract alleviates Aβ1-42 aggregation processes in vitro and protects against aluminium-induced neurodegeneration in rats

OBJECTIVES

To examine the ability of Cassia tora extract to produce, in vitro and in vivo, beneficial effects with respect to events occurring during Alzheimer's disease.

METHODS

Previously characterised methanol extract of C. tora was tested for its ability to lessen Aβ₄₂ aggregation processes in vitro and to alleviate aluminium-induced impairments in vivo in rats.

KEY FINDINGS

Cassia tora extract prevents the aggregation of monomeric, oligomeric and fibrillary Aβ_1-42 in vitro. Moreover, the daily ingestion of 100 and 400 milligrams of the extract per kilogram of body weight for 60 days ameliorates the neurobehavioral and cognitive abilities of aluminium-treated rats in vivo. Importantly, treatments with the extract trigger a significant recovery of antioxidant enzymes function, a diminution of lipid peroxidation and acetylcholinesterase activity, a decrease of pro-inflammatory cytokines expression and an increase of brain-derived neurotrophic factor levels in both the hippocampus and the frontal cortex. Finally, we evidence that the extract is able to ameliorate the aluminium-dependent loss of neuronal integrity in the CA1 and CA3 regions of the hippocampus.

CONCLUSIONS

Altogether, our results reveal that methanol extract of C. tora is able to prevent typical AD-related events and therefore stands as a promising mild and natural anti-AD multitarget compound.

miR-34a-5p and miR-125b-5p attenuate Aβ-induced neurotoxicity through targeting BACE1

BACKGROUND

Accumulation of β-amyloid (Aβ) could induce neurotoxicity in Alzheimer's disease (AD). microRNA (miR)-34a-5p and miR-125b-5p have been reported to be aberrantly expressed in AD patients. However, the roles and mechanisms of these two miRNAs in AD remain poorly understood.

METHODS

Serum samples of 27 AD patients were collected. Primary mouse cortical neurons (MCN) and Neuro2a (N2a) cells were incubated with Aβ. The expression levels of miR-34a-5p, miR-125b-5p and β-site amyloid precursor protein cleaving enzyme 1 (BACE1) were detected by quantitative real-time polymerase chain reaction and western blot. The effect of miRNAs or epigallocatechin-3-gallate (EGCG) on Aβ-induced neurotoxicity was investigated by cell viability, Caspase 3 activity, apoptosis and intracellular ROS production. The interaction between BACE1 and miR-34a-5p or miR-125b-5p was analyzed by luciferase reporter assay.

RESULTS

miR-34a-5p and miR-125b-5p levels were decreased and BACE1 mRNA expression was increased in AD patients and Aβ-treated MCN and N2a cells. Addition of miR-34a-5p or miR-125b-5p attenuated Aβ-induced apoptosis and oxidative stress. BACE1 acted as a target of miR-34a-5p and miR-125b-5p and its restoration weakened the effect of miR-34a-5p or miR-125b-5p on Aβ-induced neurotoxicity. Moreover, EGCG could mitigate Aβ-induced neurotoxicity, which might be associated with miR-34a-5p and miR-125b-5p.

CONCLUSION

miR-34a-5p and miR-125b-5p inhibited Aβ-induced neurotoxicity by decreasing apoptosis and oxidative stress via targeting BACE1, providing novel targets for treatment of AD.

Alzheimer's disease: review of current nanotechnological therapeutic strategies

Introduction: Alzheimer's Disease (AD) is a progressive neurodegenerative pathology characterized by the presence of neuritic plaques and neurofibrillary tangles. The most important markers in AD pathology include excessive accumulation of amyloid beta (Aβ₄₂) and phosphorylated tau (P-tau) proteins. One of the possible therapeutic strategies entails the elimination of such deposits by inhibiting Aβ aggregation. For years, one of the major problems in the treatment of AD has been the limited ability to deliver drugs to the brain for reasons related to poor solubility, low bioavailability, and the impact of the blood-brain barrier (BBB).Areas covered: In recent years, the authors have observed an increasing scientific interest in nanotechnological solutions as the factors potentially capable of facilitating the treatment of neurodegenerative diseases. The authors discuss recent reports regarding the use of nanotechnology in the therapy and treatment of AD.Expert opinion: The current advances in nanotechnology promise a chance to overcome the obstacles posed by said limitations. The size and diversity of nanoparticles in terms of both composition and shape create new possibilities for a variety of therapeutic applications, also in the context of the treatment and diagnostics of neurodegenerative diseases, for instance in combination with magnetic resonance imaging.

Nanodelivery of Natural Antioxidants: An Anti-aging Perspective

The aging process is known to be associated with heightened oxidative stress and related systemic inflammation. Therefore, antioxidant supplementation is regarded as a promising strategy to combat aging and associated pathological conditions. Food-grade antioxidants from plant-derived extracts are the most common ingredients of these supplements. Phyto-bioactive compounds such as curcumin, resveratrol, catechins, quercetin are among the most commonly applied natural compounds used as potential modulators of the free radical-induced cellular damages. The therapeutic potential of these compounds is, however, restricted by their low bioavailability related to poor solubility, stability, and absorbance in gastrointestinal tract. Recently, novel nanotechnology-based systems were developed for therapeutic delivery of natural antioxidants with improved bioavailability and, consequently, efficacy in clinical practice. Such systems have provided many benefits in preclinical research over the conventional preparations, including superior solubility and stability, extended half-life, improved epithelium permeability and bioavailability, enhanced tissue targeting, and minimized side effects. The present review summarizes recent developments in nanodelivery of natural antioxidants and its application to combat pathological conditions associated with oxidative stress.

Nanodelivery of phytobioactive compounds for treating aging-associated disorders

Aging population presents a major challenge for many countries in the world and has made the development of efficient means for healthspan extension a priority task for researchers and clinicians worldwide. Anti-aging properties including antioxidant, anti-inflammatory, anti-tumor, and cardioprotective activities have been reported for various phytobioactive compounds (PBCs) including resveratrol, quercetin, curcumin, catechin, etc. However, the therapeutic potential of orally administered PBCs is limited by their poor stability, bioavailability, and solubility in the gastrointestinal tract. Recently, innovative nanotechnology-based approaches have been developed to improve the bioactivity of PBCs and enhance their potential in preventing and/or treating age-associated disorders, primarily those caused by aging-related chronic inflammation. PBC-loaded nanoparticles designed for oral administration provide many benefits over conventional formulations, including enhanced stability and solubility, prolonged half-life, improved epithelium permeability and bioavailability, enhanced tissue targeting, and minimized side effects. The present review summarizes recent advances in this rapidly developing research area.

Ferric-Tannic Nanoparticles Increase Neuronal Cellular Clearance

Targeting cellular clearance function in brain cells provides new opportunities for the prevention of dementia by clearance of potentially dangerous molecules. Herein, we present a new approach to enhancing neuroactive and neuroprotective activities in a neuronal cell line using ferric-tannic nanoparticles (FTs). Major biological functions mediated by FTs were clearly found to promote neuronal tube growth through the activation of axon guidance pathways. A number of neuronal tubes were found to increase under stimulation of amyloid beta-peptides, oxidative stress, and serum deprivation. The neuronal tubes generated play a role in clearing debris and amyloid beta-peptides. Another key function in cellular clearance mediated by FTs was their capability of inducing autophagy with the activation of lysosomes. Therefore, FTs are a promising new strategy for brain cell protection through the activation of the cellular clearance function. Hopefully, our findings will pave the way for the development of new methods for the prevention and therapy of dementia.

Biopharmaceutical Monotargeting versus 'Universal Targeting' of Late-Onset Alzheimer's Disease Using Mixtures of Pleiotropic Natural Compounds

A five-year close reading of the scientific literature on late-onset Alzheimer’s disease (AD) has prompted the invention of a novel therapeutic method that biomechanistically targets the targetable disease-process targets of AD with one or another mixture of non-toxic pleiotropic natural compounds. The featured mixture herein is comprised of curcumin, resveratrol, and EGCG. The mixture’s targets include central pathological elements of AD (including amyloid, tau, synaptic dysfunction, oxidative stress, mitochondrial dysfunction, and aberrant neuroinflammation), modifiable risk factors, comorbidities, and epigenetic elements. The featured mixture and other such mixtures are suitable for long-term use, and may be applied to any stage of AD, including primary and secondary prevention. Such mixtures also would be amenable for use as pre-treatment, co-treatment, and post-treatment applications with certain biopharmaceutical agents. The targeting focus here is the major credible hypotheses of AD. The focus of future such articles will include other AD-related targets, modifiable risk factors and comorbidities, APOE4, epigenetic factors, bioavailability, dose response, and implications for clinical testing. The “universal targeting” method described herein—that is, “targeting the targetable targets” of AD using certain mixtures of natural compounds—is reprogrammable and thus is applicable to other chronic neurological conditions, including Parkinson’s disease, vascular dementia, ischemic-stroke prevention and recovery, and sports-related head injuries and sequelae leading to chronic traumatic encephalopathy.

Encapsulation of epigallocatechin-3-gallate into albumin nanoparticles improves pharmacokinetic and bioavailability in rat model

In the present study, we fabricated epigallocatechin-3-gallate (EGCG) loaded albumin nanoparticles (Alb-NP-EGCG) to enhance bioavailability and improve pharmacokinetic parameters of EGCG. The physicochemical properties of the Alb-NP-EGCG were studied using scanning electron microscopy, differential scanning calorimetry, powder X-ray diffraction and in vitro release studies. Characterization of Alb-NP-EGCG indicated the formation of spherical nanoparticles with no drug and excipient interaction. Alb-NP-EGCG showed a high drug loading capacity of 92%. Further, in vitro study showed a sustained release of EGCG from Alb-NP-EGCG over a period of 48 h. Mathematical modeling and release kinetics indicated that the Alb-NP-EGCG followed zero order kinetic and EGCG was released via fickian diffusion method. In vivo bioavailability and distribution of Alb-NP-EGCG showed an enhanced plasma concentration of EGCG with 1.5 fold increase along with prolonged T 1/2 of 15.6 h in the system when compared with the free EGCG. All this study demonstrated the fabrication of EGCG loaded albumin nanoparticles which favored the slow and sustained release of EGCG with improved pharmacokinetics and bioavailability thereby prolonging the action of EGCG. Additional acute and sub-acute toxicity test of the Alb-NP-EGCG demonstrated the safety of the Alb-NP-EGCG. Therefore, the Alb-NP-EGCG could be a promising drug delivery system for EGCG.

Natural products as a potential modulator of microglial polarization in neurodegenerative diseases

Neurodegenerative diseases (NDs) are characterized by the progressive loss of structure and function of neurons most common in elderly population, mainly including Alzheimer's disease (AD), Parkinson's disease (PD), amyotrophic lateral sclerosis (ALS) and multiple sclerosis (MS). Neuroinflammation caused by microglia as the resident macrophages of the central nervous system (CNS) plays a contributory role in the onset and progression of NDs. Activated microglia, as in macrophages, to be heterogeneous, can polarize into M1 (pro-inflammatory) and M2 (anti-inflammatory) functional phenotypes. The former elaborate pro-inflammatory mediators promoting neuroinflammation and neuronal damage. In contrast, the latter generate anti-inflammatory mediators and neurotrophins that inhibit neuroinflammation and promote neuronal healing. Consistently, the regulation of microglial polarization from M1 to M2 phenotype appears as an outstanding therapeutic and preventive approach for NDs treatment. Although non-steroidal anti-inflammatory drugs (NSAIDs) currently used to alleviate M1 microglia-associated neuroinflammation responsible for the development of NDs, these drugs have different degrees of adverse effects and limited efficacy. As the advantages of novel structure, multi-target, high efficiency and low toxicity, natural products as the modulators of microglial polarization have attracted considerable concerns in the therapeutic areas of NDs. In this review, we mainly summarized the therapeutic potential of natural products and their various molecular mechanisms for NDs treatment through modulating microglial polarization. The aim of the current review is expected to be useful to develop innovative modulators of microglial polarization from natural products for the amelioration and treatment of NDs.

Regulation of Neprilysin Activity and Cognitive Functions in Rats After Prenatal Hypoxia

The amyloid-degrading enzyme neprilysin (NEP) is one of the therapeutic targets in prevention and treatment of Alzheimer's disease (AD). As we have shown previously NEP expression in rat parietal cortex (Cx) and hippocampus (Hip) decreases with age and is also significantly reduced after prenatal hypoxia. Following the paradigms for enhancement of NEP expression and activity developed in cell culture, we analysed the efficacy of various compounds able to upregulate NEP using our model of prenatal hypoxia in rats. In addition to the previous data demonstrating that valproic acid can upregulate NEP expression both in neuroblastoma cells and in rat Cx and Hip we have further confirmed that caspase inhibitors can also restore NEP expression in rat Cx reduced after prenatal hypoxia. Here we also report that administration of a green tea catechin epigallocatechin-3-gallate (EGCG) to adult rats subjected to prenatal hypoxia increased NEP activity in blood plasma, Cx and Hip as well as improved memory performance in the 8-arm maze and novel object recognition tests. Moreover, EGCG administration led to an increased number of dendritic spines in the hippocampal CA1 area which correlated with memory enhancement. The data obtained allowed us to conclude that the decrease in the activity of the amyloid-degrading enzyme NEP, as well as a reduction in the number of labile interneuronal contacts in the hippocampus, contribute to early cognitive deficits caused by prenatal hypoxia and that there are therapeutic avenues to restore these deficits via NEP activation which could also be used for designing preventive strategies in AD.