Natural products and their derivatives as multifunctional ligands against Alzheimer's disease

Harnessing the Therapeutic Potential of Peptides for Synergistic Treatment of Alzheimer's Disease by Targeting Aβ Aggregation, Metal-Mediated Aβ Aggregation, Cholinesterase, Tau Degradation, and Oxidative Stress

Alzheimer's disease (AD) is a progressive multifaceted neurodegenerative disease and remains a formidable global health challenge. The current medication for AD gives symptomatic relief and, thus, urges us to look for alternative disease-modifying therapies based on a multitarget directed approach. Looking at the remarkable progress made in peptide drug development in the last decade and the benefits associated with peptides, they offer valuable chemotypes [multitarget directed ligands (MTDLs)] as AD therapeutics. This review recapitulates the current developments made in harnessing peptides as MTDLs in combating AD by targeting multiple key pathways involved in the disease's progression. The peptides hold immense potential and represent a convincing avenue in the pursuit of novel AD therapeutics. While hurdles remain, ongoing research offers hope that peptides may eventually provide a multifaceted approach to combat AD.

Protective effects of myricetin and morin on neurological damage in Aβ1-42/Al3+ -induced Alzheimer's disease model of rats

Alzheimer's disease (AD) is a degenerative neurological disorder with unclear pathogenesis. Single-target drugs have very limited efficacy in treating AD, but synthetic multi-target drugs have poor efficacy and safety. Therefore, finding suitable natural multi-target drugs against AD is of great interest for research studies. We chose two flavonols, myricetin and morin, for the relevant study. In this study, we used microinjection of Aβ1-42 oligomers into the CA1 region of rat hippocampus, combined with gavage of Aluminum chloride hexahydrate (AlCl3·6H2O) solution to establish AD rat models, and myricetin and morin were selected as intervening drugs to explore the protective effects against neurological impairment. Experimental results showed that myricetin or morin could reduce the production of Aβ, Tubulin-associated unit (Tau), and Phosphorylated tubulin-associated unit (p-Tau), down-regulate the expression of relevant inflammatory factors, reduce hippocampal cell apoptosis in rats. There was a significant increase in the activity of adenosine triphosphatase, catalase, total superoxide dismutase, and the content of glutathione in the brain tissue. However, the content of malondialdehyde, inducible nitric oxide synthase, and the activity of acetylcholinesterase were decreased in the brain tissue. These two flavonols can regulate the imbalance of monoamine and amino acid neurotransmitter levels. In conclusion, Myricetin or morin can effectively improve learning and memory dysfunction in AD rats induced by Aβ1-42/Al3+ through anti-oxidative stress and anti-apoptotic features.

Exploring the Therapeutic Potential of Phytoconstituents for Addressing Neurodegenerative Disorders

Neurodegenerative disorder is a serious condition that is caused by abnormal or no neurological function. Neurodegenerative disease is a major growing cause of mortality and morbidity worldwide, especially in the elderly. After World War Ⅱ, eugenics term was exterminated from medicines. Neurodegenerative disease is a genetically inherited disease. Lifestyle changes, environmental factors, and genetic modification, together or alone, are involved in the occurrence of this disorder. The major examples of neurodegenerative disorders are Alzheimer's and Parkinson's disease, in which apoptosis and necrosis are the two major death pathways for neurons. It has been determined from various studies that the etiology of the neurodegenerative disease involves the role of oxidative stress and anti-oxidant defence system, which are prime factors associated with the activation of signal transduction pathway that is responsible for the formation of synuclein in the brain and manifestation of toxic reactions in the form of functional abnormality, which ultimately leads to the dysfunction of neuronal pathway or cell. There has not been much success in the discovery of effective therapy to treat neurodegenerative diseases because the main cause of abnormal functioning or death of neurons is not well known. However, the use of natural products that are derived from plants has effective therapeutic potential against neurodegenerative disease. The natural compounds with medicinal properties to prevent neurological dysfunction are curcumin, wolfberry, ginseng, and Withania somnifera. The selection and use of natural compounds are based on their strong anti-inflammatory and anti-oxidant properties against neurodegenerative disease. Herbal products have active constituents that play an important role in the prevention of communication errors between neurons and neurotransmitters and their respective receptors in the brain, which influence their function. Considering this, natural products have great potential against neurodegenerative diseases. This article reviews the natural compounds used to treat neurodegenerative diseases and their mechanisms of action.

Role of multi-targeted bioactive natural molecules and their derivatives in the treatment of Alzheimer's disease: an insight into structure-activity relationship

Alzheimer's disease (AD) is a complex neurodegenerative disorder involving cognitive dysfunction like short-term memory and behavioral changes as the disease progresses due to other unaltered physiological factors. The solution for this problem is Multi-targeted Drugs (MTDs), which can affect multiple determinants to realize the multifunctional effects. Acetylcholinesterase (AChE) inhibitors donepezil, rivastigmine, galantamine, and N-methyl-D-aspartate (NMDA) receptor antagonist memantine are FDA-approved drugs used to treat AD symptomatically. The key objective of this review is to understand multitargeted bioactive natural molecules that could be considered as leads for further development as effective drugs for treating AD, along with understanding its pharmacology and structure-activity relationship (SAR). Understanding the molecular mechanism of the AD pathophysiology, the role of existing drugs, treatment of AD via amyloid beta (Aβ) plaque, and neurofibrillary tangle (NFT) inhibition by natural bioactive molecules were also discussed in the review. The current quest and recent advancements with natural bioactive compounds like physostigmine, resveratrol, curcumin, and catechins, along with the study of in silico SAR, were reported in the present study. This review summarises the structural properties required for bioactive natural molecules to show anti-Alzheimer's activity by emphasizing on SAR of several bioactive natural molecules targeting various AD pathologies, their key molecular interactions that are critical for target specificity, their role as multitargeted ligands, used with adjunctive therapy for AD followed by related US patents granted recently. This article highlights the significance of the structural features of natural bioactive molecules in the treatment of AD and establishes a connection between them.Communicated by Ramaswamy H. Sarma.

Tryptamine: A privileged scaffold for the management of Alzheimer's disease

Alzheimer's disease (AD) is a chronic and irreversible neurodegenerative disease associated with aging. It is characterized by the progressive loss of memory and other cognitive functions. Although the exact etiology of AD is not well explored, several factors, such as the deposition of amyloid-β (Aβ) plaques, hyperphosphorylation of tau protein, presence of low levels of acetylcholine, and generation of oxidative stress, are key mediators in the progression of AD. Currently, the clinical treatment options for AD are limited and are based on cholinesterase (ChE) inhibitors (e.g., donepezil, rivastigmine, and galantamine), N-methyl- d-aspartic acid receptor antagonists (e.g., memantine), and the recently approved Aβ modulator (e.g., aducanumab). Tryptamine (2-(1H-indol-3-yl)ethan-1-amine) is a small molecule that contains an indole nucleus and an ethylamine side chain. It is also the active metabolite of tryptophan. It possesses a wide range of biological activities related to neurodegenerative disorders, such as ChE inhibition, Aβ aggregation inhibition, antioxidant effects, monoamine-oxidase inhibition, and neuroprotection. Several tryptamine-based hybrid analogs are currently being investigated as multifunctional agents for the development of novel hybrids for AD treatment. Thus, this review article aims to provide in-depth insights into the research progress and strategies for designing multifunctional agents used in Alzheimer's therapy.

Synthetic and Natural Bioactive Molecules in Balancing the Crosstalk among Common Signaling Pathways in Alzheimer's Disease: Understanding the Neurotoxic Mechanisms for Therapeutic Intervention

The structure and function of the brain greatly rely on different signaling pathways. The wide variety of biological processes, including neurogenesis, axonal remodeling, the development and maintenance of pre- and postsynaptic terminals, and excitatory synaptic transmission, depends on combined actions of these molecular pathways. From that point of view, it is important to investigate signaling pathways and their crosstalk in order to better understand the formation of toxic proteins during neurodegeneration. With recent discoveries, it is established that the modulation of several pathological events in Alzheimer's disease (AD) due to the mammalian target of rapamycin (mTOR), Wnt signaling, 5'-adenosine monophosphate activated protein kinase (AMPK), peroxisome proliferator-activated receptor gamma coactivator 1α (PGC-1α), and sirtuin 1 (Sirt1, silent mating-type information regulator 2 homologue 1) are central to the key findings. These include decreased amyloid formation and inflammation, mitochondrial dynamics control, and enhanced neural stability. This review intends to emphasize the importance of these signaling pathways, which collectively determine the fate of neurons in AD in several ways. This review will also focus on the role of novel synthetic and natural bioactive molecules in balancing the intricate crosstalk among different pathways in order to prolong the longevity of AD patients.

New Hybrid Compounds Incorporating Natural Products as Multifunctional Agents against Alzheimer's Disease

A series of new hybrid derivatives 1a-c, 2a-c, 3a-c, 4a-c, 5a-c, inspired by nature, were synthesized and studied as multifunctional agents for the treatment of Alzheimer's disease (AD). These compounds were designed to merge together the trifluoromethyl benzyloxyaminic bioactive moiety, previously identified, with different acids available in nature. The ability of the synthesized compounds to chelate biometals, such as Cu2+, Zn2+ and Fe2+, was studied by UV-Vis spectrometer, and through a preliminary screening their antioxidant activity was evaluated by DPPH. Then, selected compounds were tested by in vitro ABTS free radical method and ex vivo rat brain TBARS assay. Compounds 2a-c, combining the strongest antioxidant and biometal chelators activities, were studied for their ability to contrast Aβ1-40 fibrillization process. Finally, starting from the promising profile obtained for compound 2a, we evaluated if it could be able to induce a positive cross-interaction between transthyretin (TTR) and Aβ in presence and in absence of Cu2+.

From gut to skin: exploring the potential of natural products targeting microorganisms for atopic dermatitis treatment

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease. Recent studies have revealed that interactions between pathogenic microorganisms, which have a tendency to parasitize the skin of AD patients, play a significant role in the progression of the disease. Furthermore, specific species of commensal bacteria in the human intestinal tract can have a profound impact on the immune system by promoting inflammation and pruritogenesis in AD, while also regulating adaptive immunity. Natural products (NPs) have emerged as promising agents for the treatment of various diseases. Consequently, there is growing interest in utilizing natural products as a novel therapeutic approach for managing AD, with a focus on modulating both skin and gut microbiota. In this review, we discuss the mechanisms and interplay between the skin and gut microbiota in relation to AD. Additionally, we provide a comprehensive overview of recent clinical and fundamental research on NPs targeting the skin and gut microbiota for AD treatment. We anticipate that our work will contribute to the future development of NPs and facilitate research on microbial mechanisms, based on the efficacy of NPs in treating AD.

A Multilevel Study of Eupatorin and Scutellarein as Anti-Amyloid Agents in Alzheimer's Disease

Today, Alzheimer's disease (AD)-the most common neurodegenerative disorder, which affects 50 million people-remains incurable. Several studies suggest that one of the main pathological hallmarks of AD is the accumulation of abnormal amyloid beta (Aβ) aggregates; therefore, many therapeutic approaches focus on anti-Aβ aggregation inhibitors. Taking into consideration that plant-derived secondary metabolites seem to have neuroprotective effects, we attempted to assess the effects of two flavones-eupatorin and scutellarein-on the amyloidogenesis of Aβ peptides. Biophysical experimental methods were employed to inspect the aggregation process of Aβ after its incubation with each natural product, while we monitored their interactions with the oligomerized Aβ through molecular dynamics simulations. More importantly, we validated our in vitro and in silico results in a multicellular organismal model-namely, Caenorhabditis elegans-and we concluded that eupatorin is indeed able to delay the amyloidogenesis of Aβ peptides in a concentration-dependent manner. Finally, we propose that further investigation could lead to the exploitation of eupatorin or its analogues as potential drug candidates.

An ongoing journey of chalcone analogues as single and multi-target ligands in the field of Alzheimer's disease: A review with structural aspects

Alzheimer's disease (AD) is a chronic and irreversible neurodegenerative disorder with progressive dementia and cognitive impairment. AD poses severe health challenge in elderly people and become one of the leading causes of death worldwide. It possesses complex pathophysiology with several hypotheses (cholinergic hypothesis, amyloid hypothesis, tau hypothesis, oxidative stress, mitochondrial dysfunction etc.). Several attempts have been made for the management of multifactorial AD. Acetylcholinesterase is the only target has been widely explored in the management of AD to the date. The current review set forth the chalcone based natural, semi-synthetic and synthetic compounds in the search of potential anti-Alzheimer's agents. The main highlights of current review emphasizes on chalcone target different enzymes and pathways like Acetylcholinesterase, β-secretase (BACE1), tau proteins, MAO, free radicals, Advanced glycation end Products (AGEs) etc. and their structure activity relationships contributing in the inhibition of above mentioned various targets of AD.

Nature's Toolbox Against Tau Aggregation: An Updated Review of Current Research

Tau aggregation is a hallmark of several neurodegenerative disorders, such as Alzheimer's disease (AD), frontotemporal dementia, and progressive supranuclear palsy. Hyperphosphorylated tau is believed to contribute to the degeneration of neurons and the development of these complex diseases. Therefore, one potential treatment for these illnesses is to prevent or counteract tau aggregation. In recent years, interest has been increasing in developing nature-derived tau aggregation inhibitors as a potential treatment for neurodegenerative disorders. Researchers have become increasingly interested in natural compounds with multifunctional features, such as flavonoids, alkaloids, resveratrol, and curcumin, since these molecules can interact simultaneously with the various targets of AD. Recent studies have demonstrated that several natural compounds can inhibit tau aggregation and promote the disassembly of pre-formed tau aggregates. Nature-derived tau aggregation inhibitors hold promise as a potential treatment for neurodegenerative disorders. However, it is important to note that more research is needed to fully understand the mechanisms by which these compounds exert their effects and their safety and efficacy in preclinical and clinical studies. Nature-derived inhibitors of tau aggregation are a promising new direction in the research of neurodegenerative complexities. This review focuses on the natural products that have proven to be a rich supply for inhibitors in tau aggregation and their uses in neurodegenerative complexities, including AD.

Role of Metal Cations of Copper, Iron, and Aluminum and Multifunctional Ligands in Alzheimer's Disease: Experimental and Computational Insights

Alzheimer's disease (AD) is the most common form of dementia, affecting millions of people around the world. Even though the causes of AD are not completely understood due to its multifactorial nature, some neuropathological hallmarks of its development have been related to the high concentration of some metal cations. These roles include the participation of these metal cations in the production of reactive oxygen species, which have been involved in neuronal damage. In order to avoid the increment in the oxidative stress, multifunctional ligands used to coordinate these metal cations have been proposed as a possible treatment to AD. In this review, we present the recent advances in experimental and computational works aiming to understand the role of two redox active and essential transition-metal cations (Cu and Fe) and one nonbiological metal (Al) and the recent proposals on the development of multifunctional ligands to stop or revert the damaging effects promoted by these metal cations.

Anti-Neuroinflammatory Potential of Natural Products in the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is an age-related chronic progressive neurodegenerative disease, which is the main cause of dementia in the elderly. Much evidence shows that the onset and late symptoms of AD are caused by multiple factors. Among them, aging is the main factor in the pathogenesis of AD, and the most important risk factor for AD is neuroinflammation. So far, there is no cure for AD, but the relationship between neuroinflammation and AD may provide a new strategy for the treatment of AD. We herein discussed the main etiology hypothesis of AD and the role of neuroinflammation in AD, as well as anti-inflammatory natural products with the potential to prevent and alleviate AD symptoms, including alkaloids, steroids, terpenoids, flavonoids and polyphenols, which are available with great potential for the development of anti-AD drugs.

Isoxazole/Isoxazoline Skeleton in the Structural Modification of Natural Products: A Review

Isoxazoles and isoxazolines are five-membered heterocyclic molecules containing nitrogen and oxygen. Isoxazole and isoxazoline are the most popular heterocyclic compounds for developing novel drug candidates. Over 80 molecules with a broad range of bioactivities, including antitumor, antibacterial, anti-inflammatory, antidiabetic, cardiovascular, and other activities, were reviewed. A review of recent studies on the use of isoxazoles and isoxazolines moiety derivative activities for natural products is presented here, focusing on the parameters that affect the bioactivity of these compounds.

Recent Progress in Cyclic Aryliodonium Chemistry: Syntheses and Applications

Hypervalent aryliodoumiums are intensively investigated as arylating agents. They are excellent surrogates to aryl halides, and moreover they exhibit better reactivity, which allows the corresponding arylation reactions to be performed under mild conditions. In the past decades, acyclic aryliodoniums are widely explored as arylation agents. However, the unmet need for acyclic aryliodoniums is the improvement of their notoriously low reaction economy because the coproduced aryl iodides during the arylation are often wasted. Cyclic aryliodoniums have their intrinsic advantage in terms of reaction economy, and they have started to receive considerable attention due to their valuable synthetic applications to initiate cascade reactions, which can enable the construction of complex structures, including polycycles with potential pharmaceutical and functional properties. Here, we are summarizing the recent advances made in the research field of cyclic aryliodoniums, including the nascent design of aryliodonium species and their synthetic applications. First, the general preparation of typical diphenyl iodoniums is described, followed by the construction of heterocyclic iodoniums and monoaryl iodoniums. Then, the initiated arylations coupled with subsequent domino reactions are summarized to construct polycycles. Meanwhile, the advances in cyclic aryliodoniums for building biaryls including axial atropisomers are discussed in a systematic manner. Finally, a very recent advance of cyclic aryliodoniums employed as halogen-bonding organocatalysts is described.

Design, Synthesis, Calculation and Biological Activity Studies Based on Privileged Coumarin Derivatives as Multifunctional Anti-AD Lead Compound

Coumarins and their derivatives possessed a variety of biological activities and some of coumarin-based drugs have been approved by the US Food and Drug Administration. Alzheimer's disease (AD) has caused great losses to human society. However, due to its complex pathogenesis, the ideal therapeutic approach has not been found yet. Free radical scavenging activity which is one of the main activities of coumarin core structure is closely related to other anti-AD activities. Therefore, in this work coumarins were chosen as privileged lead compounds for the development of anti-AD drugs based on strategy of multi-target directed ligands (MTDLs). Derivatives 1-3 which could modulate multiple targets simultaneously, including ROS, cholinesterase, βamyloid (Aβ) aggregation, and metal dyshomeostasis were designed and for the first time synthesized. Their anti-AD activities were studied both in vitro and in silico. Results showed that 1-3 possessed potent antioxidant activities and 7-OH group did change the electron distribution of the molecule and enhance the antioxidant activities. They also have good inhibition activities on acetylcholinesterase (AChE) and Aβ aggregation and compound 1 had the strongest AChE inhibitory effect among the three compounds (AChE IC₅₀ =11.15 μM). Compound 1-3 could also selectively chelate with Cu²⁺ and Al³⁺ to regulate the metal homeostasis. In silico simulations, including molecular docking and prediction of ADMET performance, indicated that 1-3 could interact with target proteins and cross the blood brain barrier. In conclusion, 1-3 could be promising MTDLs applied as anti-AD candidate drugs.

Natural product-based pharmacological studies for neurological disorders

Central nervous system (CNS) disorders and diseases are expected to rise sharply in the coming years, partly because of the world's aging population. Medicines for the treatment of the CNS have not been successfully made. Inadequate knowledge about the brain, pharmacokinetic and dynamic errors in preclinical studies, challenges with clinical trial design, complexity and variety of human brain illnesses, and variations in species are some potential scenarios. Neurodegenerative diseases (NDDs) are multifaceted and lack identifiable etiological components, and the drugs developed to treat them did not meet the requirements of those who anticipated treatments. Therefore, there is a great demand for safe and effective natural therapeutic adjuvants. For the treatment of NDDs and other memory-related problems, many herbal and natural items have been used in the Ayurvedic medical system. Anxiety, depression, Parkinson's, and Alzheimer's diseases (AD), as well as a plethora of other neuropsychiatric disorders, may benefit from the use of plant and food-derived chemicals that have antidepressant or antiepileptic properties. We have summarized the present level of knowledge about natural products based on topological evidence, bioinformatics analysis, and translational research in this review. We have also highlighted some clinical research or investigation that will help us select natural products for the treatment of neurological conditions. In the present review, we have explored the potential efficacy of phytoconstituents against neurological diseases. Various evidence-based studies and extensive recent investigations have been included, which will help pharmacologists reduce the progression of neuronal disease.

Development of new donepezil analogs: synthesis, biological screening and in silico study rational

Fifteen new benzothiophene-based compounds were designed, synthesized, and evaluated as potential anti-Alzheimer agents. Most of the synthesized compounds exhibited remarkable AChE inhibitory activity and effectively inhibited self-mediated β-amyloid protein in vitro. Compound 3g (IC50 = 72.488 ± 3.69 μM) showed a significant β-amyloid inhibitory effect exceeding that of donepezil (IC50 = 87.414 ± 4.46 μM). Furthermore, compound 3j (IC50 = 0.498 ± 0.02 μM) showed the best inhibitory activity comparable to that of donepezil (IC50 = 0.404 ± 0.03 μM). The in vivo evaluation of the promising compounds (3g and 3j) confirmed a significant memory improvement in scopolamine-induced memory impairment model in mice. The molecular docking simulation of compounds 3g and 3j in Torpedo californica-AChE (TcAChE) active site showed a good agreement with the obtained screening results. The in silico ADMET and other physicochemical parameters were also reported.

Synthesis and Biological Evaluation of Flavonoid‐Cinnamic Acid Amide Hybrids with Distinct Activity against Neurodegeneration in Vitro and in Vivo

Flavonoids are polyphenolic natural products and have shown significant potential as disease‐modifying agents against neurodegenerative disorders like Alzheimer's disease (AD), with activities even in vivo. Hybridization of the natural products taxifolin and silibinin with cinnamic acid led to an overadditive effect of these compounds in several phenotypic screening assays related to neurodegeneration and AD. Therefore, we have exchanged the flavonoid part of the hybrids with different flavonoids, which show higher efficacy than taxifolin or silibinin, to improve the activity of the respective hybrids. Chemical connection between the flavonoid and cinnamic acid was realized by an amide instead of a labile ester bond to improve stability towards hydrolysis. To investigate the influence of a double bond at the C‐ring of the flavonoid, the dehydro analogues of the respective hybrids were also synthesized. All compounds obtained show neuroprotection against oxytosis, ferroptosis and ATP‐depletion, respectively, in the murine hippocampal cell line HT22. Interestingly, the taxifolin and the quercetin derivatives are the most active compounds, whereby the quercetin derivate shows even more pronounced activity than the taxifolin one in all assays applied. As aimed for, no hydrolysis product was found in cellular uptake experiments after 4 h whereas different metabolites were detected. Furthermore, the quercetin‐cinnamic acid amide showed pronounced activity in an in vivo AD mouse model at a remarkably low dose of 0.3 mg/kg.

Pharmacological exploration of triazole based therapeutics for Alzheimer disease: An overview

Abstract:

Alzheimer`s disease (AD) is an irreversible progressive neurodegenerative disorder which may account for approximately 60-70% cases of dementia worldwide. AD is characterized by impaired behavioural and cognitive functions including memory, language, conception, attentiveness, judgment, and reasoning problems. The two important hallmarks of AD are the appearance of plaques and tangles of amyloid beta (Aβ) and tau proteins, respectively, in the brain based on the etiology of the disease including cholinergic impairment, metal dyshomeostasis, oxidative stress, and degradation of neurotransmitters. Currently, the used medication only provides alleviation of symptoms but not effective in curing the disease that is creating by an urge to develop new molecules to treat AD. Heterocyclic compounds have proven their ability to be developed as drugs for the treatment of various diseases. The five-membered heterocyclic compound triazole has received foremost fascination for the discovery of new drugs due to the possibility of structural variation and proved its significance in various drug categories. Therefore, this review summarizes mainly the recent advancements in the development of novel 1,2,3-triazole and 1,2,4-triazole based molecules in the drug discovery process for targeting various AD targets such as phosphodiesterase 1 (PDE1) Inhibitors, Apoptosis signal-regulating kinase 1 (ASK1) inhibitors, Somatostatin receptor subtype-4 (SSTR4) agonist, many other druggable targets, molecular modelling studies as well as various methodology for the synthesis of triazoles containing molecules such as Click reaction, Pellizzari and Einhorn-Brunner Reaction.

Development of oxoisoaporphine derivatives with topoisomerase I inhibition and reversal of multidrug resistance in breast cancer MCF-7/ADR cells

A series of oxoisoaporphine derivatives with topoisomerase I inhibition and cytotoxic activities. Among them, compound 14 showed the most potent cytotoxic activity against all cancer cell lines tested, and substantially lower cytotoxicity to LO2 cells. Molecular docking studies, dynamics simulation and a follow-up enzyme inhibition assay indicated that 14 could interfere with DNA and significantly inhibit the activity of topoisomerase I. Further mechanistic studies revealed that 14 could arrest cell cycle at the G1 phase, and finally killed MCF-7 cells via apoptosis. In addition, 14 exhibited remarkable chemoreversal ability on multidrug-resistant MCF-7/ADR breast cancer cells. Some of its mechanisms may be related to inhibition of MCF-7/ADR P-gp-mediated Rhodamine (Rh123) efflux function and expression level, as well as inhibition of ROS, increase of ADR accumulation in MCF7/ADR cells, and enhancement of ADR in inducing apoptosis of MCF7/ADR cells. As 14 has little toxic and side effects, it may have the potential for further research.

Role of Cholinergic Signaling in Alzheimer's Disease

Acetylcholine, a neurotransmitter secreted by cholinergic neurons, is involved in signal transduction related to memory and learning ability. Alzheimer’s disease (AD), a progressive and commonly diagnosed neurodegenerative disease, is characterized by memory and cognitive decline and behavioral disorders. The pathogenesis of AD is complex and remains unclear, being affected by various factors. The cholinergic hypothesis is the earliest theory about the pathogenesis of AD. Cholinergic atrophy and cognitive decline are accelerated in age-related neurodegenerative diseases such as AD. In addition, abnormal central cholinergic changes can also induce abnormal phosphorylation of ttau protein, nerve cell inflammation, cell apoptosis, and other pathological phenomena, but the exact mechanism of action is still unclear. Due to the complex and unclear pathogenesis, effective methods to prevent and treat AD are unavailable, and research to explore novel therapeutic drugs is various and active in the world. This review summaries the role of cholinergic signaling and the correlation between the cholinergic signaling pathway with other risk factors in AD and provides the latest research about the efficient therapeutic drugs and treatment of AD.

Therapeutic approaches employing natural compounds and derivatives for treating bipolar disorder: emphasis on experimental models of the manic phase

Bipolar disorder (BD) is a complex psychiatric disease characterized by mood swings that include episodes of mania and depression. Given its cyclical nature, BD is especially hard to model; however, the standard practice has been to mimic manic episodes in animal models. Despite scientific advances, the pathophysiology of BD is not fully understood, and treatment remains limited. In the last years, natural products have emerged as potential neuroprotective agents for the treatment of psychiatric diseases. Thus, the aim of this review was to explore the therapeutic potential of natural compounds and derivatives against BD, taking into account preclinical and clinical studies. Reliable articles indexed in databases such as PubMed, Web of Science and Science Direct were used. In clinical studies, treatment with herbal plants extracts, omega-3, inositol, n-acetylcysteine and vitamin D has been associated with a clinical improvement in symptoms of mania and depression in BD patients. In animal models, it has been shown that red fruits extracts, curcumin, quercetin, gallic acid, alpha-lipoic acid and carvone can modulate many neurochemical pathways involved in the pathophysiology of manic episodes. Thus, this review appointed the advances in the consumption of natural compounds and derivatives as an important therapeutic strategy to mitigate the symptoms of BD.

Anti-inflammatory Activity of a Polypeptide Fraction From Achyranthes bidentate in Amyloid β Oligomers Induced Model of Alzheimer's Disease

Neuroinflammation plays a crucial role in neurodegenerative diseases such as Alzheimer's disease (AD) and Parkinson's disease (PD), and anti-inflammation has been considered as a potential therapeutic strategy. Achyranthes bidentate polypeptide fraction k (ABPPk) was shown to protect neurons from death and suppress microglia and astrocyte activation in PD model mice. However, how ABPPk regulates neuroinflammation to exert a neuroprotective role remains unclear. Toxic Aβ oligomers (AβOs) can trigger inflammatory response and play an important role in the pathogenesis of AD. In the present study, for the first time, we investigated the effects and underlying mechanisms of ABPPk on neuroinflammation in AβOs-induced models of AD. In vitro, ABPPk pretreatment dose-dependently inhibited AβOs-induced pro-inflammatory cytokines mRNA levels in BV2 and primary microglia. ABPPk pretreatment also reduced the neurotoxicity of BV2 microglia-conditioned media on primary hippocampal neurons. Furthermore, ABPPk down-regulated the AβOs-induced phosphorylation of IκBα and NF-κB p65 as well as the expression of NLRP3 in BV2 microglia. In vivo, ABPPk pre-administration significantly improved locomotor activity, alleviated memory deficits, and rescued neuronal degeneration and loss in the hippocampus of AβOs-injected mice. ABPPk inhibited the activation of microglia in hippocampal CA3 region and suppressed the activation of NF-κB as well as the expression of NLRP3, cleaved caspase-1, and ASC in the brain after AβOs injection. ABPPk hindered the release of pro-inflammatory cytokines and promoted the release of anti-inflammatory cytokines in the brain. Notably, the polarization experiment on BV2 microglia demonstrated that ABPPk inhibited M1-phenotype polarization and promoted M2-phenotype polarization by activating the LPS- or AβOs-impaired autophagy in microglia. Taken together, our observations indicate that ABPPk can restore the autophagy of microglia damaged by AβOs, thereby promoting M2-phenotype polarization and inhibiting M1-phenotype polarization, thus playing a role in regulating neuroinflammation and alleviating neurotoxicity.

Stephapierrines A-H, new tetrahydroprotoberberine and aporphine alkaloids from the tubers of Stephania pierrei Diels and their anti-cholinesterase activities

Eight new alkaloids, which are four new tetrahydroprotoberberine alkaloids, stephapierrines A-D (1-4), and four new aporphine alkaloids, stephapierrines E-H (5-8), together with three new naturally occurring alkaloids (9-11) and thirty-four known alkaloids (12-45) were isolated from the tubers of Stephania pierrei Diels. The structures of the new compounds were elucidated by spectroscopic analysis and physical properties. The structures of the known compounds were characterized by comparison of their spectroscopic data with those previously reported. Compound 42 exhibited the strongest acetylcholinesterase (AChE) inhibitory activity, which was more active than galanthamine, the reference drug. Compound 23 showed the highest butyrylcholinesterase (BuChE) inhibitory activity, which was also more active than galanthamine. Molecular docking studies are in good agreement with the experimental results.

Current Quest in Natural Bioactive Compounds for Alzheimer's Disease: Multi-Targeted-Designed-Ligand Based Approach with Preclinical and Clinical Based Evidence

Alzheimer's disease is a common and most chronic neurological disorder (NDs) associated with cognitive dysfunction. Pathologically, Alzheimer's disease (AD) is characterized by the presence of β-amyloid (Aβ) plaques, hyper-phosphorylated tau proteins, and neurofibrillary tangles, however, persistence oxidative-nitrative stress, endoplasmic reticulum stress, mitochondrial dysfunction, inflammatory cytokines, pro-apoptotic proteins along with altered neurotransmitters level are common etiological attributes in its pathogenesis. Rivastigmine, memantine, galantamine, and donepezil are FDA approved drugs for symptomatic management of AD, whereas tacrine has been withdrawn because of hepatotoxic profile. These approved drugs only exert symptomatic relief and exhibit poor patient compliance. In the current scenario, the number of published evidence shows the neuroprotective potential of naturally occurring bioactive molecules via their antioxidant, anti-inflammatory, antiapoptotic and neurotransmitter modulatory properties. Despite their potent therapeutic implications, concerns have arisen in context to their efficacy and probable clinical outcome. Thus, to overcome these glitches, many heterocyclic and cyclic hydrocarbon compounds inspired by natural sources have been synthesized and showed improved therapeutic activity. Computational studies (molecular docking) have been used to predict the binding affinity of these natural bioactive as well as synthetic compounds derived from natural sources for the acetylcholine esterase, α/β secretase Nuclear Factor kappa- light-chain-enhancer of activated B cells (NF-kB), Nuclear factor erythroid 2-related factor 2(Nrf2) and other neurological targets. Thus, in this review, we have discussed the molecular etiology of AD, focused on the pharmacotherapeutics of natural products, chemical and pharmacological aspects and multi-targeted designed ligands (MTDLs) of synthetic and semisynthetic molecules derived from the natural sources along with some important on-going clinical trials.

Potential of Naturally Derived Alkaloids as Multi-Targeted Therapeutic Agents for Neurodegenerative Diseases

Alkaloids are a class of secondary metabolites that can be derived from plants, fungi and marine sponges. They are widely known as a continuous source of medicine for the management of chronic disease including cancer, diabetes and neurodegenerative diseases. For example, galanthamine and huperzine A are alkaloid derivatives currently being used for the symptomatic management of neurodegenerative disease. The etiology of neurodegenerative diseases is polygenic and multifactorial including but not limited to inflammation, oxidative stress and protein aggregation. Therefore, natural-product-based alkaloids with polypharmacology modulation properties are potentially useful for further drug development or, to a lesser extent, as nutraceuticals to manage neurodegeneration. This review aims to discuss and summarise recent developments in relation to naturally derived alkaloids for neurodegenerative diseases.

Design and synthesis of benzyl aminocoumarin and its anti-Alzheimer's activity

Benzylaminocoumarin is a kind of compound with coumarin skeleton and benzylamino side chain structure at positions 3 and 4.

Structural alterations in the catalytic core of hSIRT2 enzyme predict therapeutic benefits of Garcinia mangostana derivatives in Alzheimer's disease: molecular dynamics simulation study

Recent studies have shown that inhibition of the hSIRT2 enzyme provides favorable effects in neurodegenerative diseases such as Alzheimer's disease. Prenylated xanthone phytochemicals including α-mangostin, β-mangostin and γ-mangostin obtained from Garcinia mangostana, a well-established tropical plant, have been shown experimentally to inhibit sirtuin enzymatic activity. However, the molecular mechanism of this sirtuin inhibition has not been reported. Using comprehensive integrated computational techniques, we provide molecular and timewise dynamical insights into the structural alterations capable of facilitating therapeutically beneficial effects of these phytochemicals at the catalytic core of the hSIRT2 enzyme. Findings revealed the enhanced conformational stability and compactness of the hSIRT2 catalytic core upon binding of γ-mangostin relative to the apoenzyme and better than α-mangostin and β-mangostin. Although thermodynamic calculations revealed favorable binding of all the phytochemicals to the hSIRT2 enzyme, the presence of only hydroxy functional groups on γ-mangostin facilitated the occurrence of additional hydrogen bonds involving Pro115, Phe119, Asn168 and His187 which are absent in α-mangostin- and β-mangostin-bound systems. Per-residue energy contributions showed that van der Waals and more importantly electrostatic interactions are involved in catalytic core stability with Phe96, Tyr104 and Phe235 notably contributing π–π stacking, π–π T shaped and π–sigma interactions. Cumulatively, our study revealed the structural alterations leading to inhibition of hSIRT2 catalysis and findings from this study could be significantly important for the future design and development of sirtuin inhibitors in the management of Alzheimer's disease.

Recent studies have shown that inhibition of the hSIRT2 enzyme provides favorable effects in neurodegenerative diseases such as Alzheimer's disease.

An α-helix mimetic oligopyridylamide, ADH-31, modulates Aβ42 monomer aggregation and destabilizes protofibril structures: insights from molecular dynamics simulations

Alzheimer's disease (AD), an epidemic growing worldwide due to no effective medical aid available in the market, is a neurological disorder. AD is known to be directly associated with the toxicity of amyloid-β (Aβ) aggregates. In search of potent inhibitors of Aβ aggregation, Hamilton and co-workers reported an α-helix mimetic, ADH-31, which acts as a powerful antagonist of Aβ42 aggregation. To identify the key interactions between protein-ligand complexes and to gain insights into the inhibitory mechanism of ADH-31 against Aβ42 aggregation, molecular dynamics (MD) simulations were performed in the present study. The MD simulations highlighted that ADH-31 showed distinct binding capabilities with residues spanning from the N-terminal to the central hydrophobic core (CHC) region of Aβ42 and restricted the conformational transition of the helix-rich structure of Aβ42 into another form of secondary structures (coil/turn/β-sheet). Hydrophobic contacts, hydrogen bonding and π-π interaction contribute to the strong binding between ADH-31 and Aβ42 monomer. The Dictionary of Secondary Structure of Proteins (DSSP) analysis highlighted that the probability of helical content increases from 38.5% to 50.2% and the turn content reduces from 14.7% to 6.2% with almost complete loss of the β-sheet structure (4.5% to 0%) in the Aβ42 monomer + ADH-31 complex. The per-residue binding free energy analysis demonstrated that Arg5, Tyr10, His14, Gln15, Lys16, Val18, Phe19 and Lys28 residues of Aβ42 are responsible for the favourable binding free energy in Aβ42 monomer + ADH-31 complex, which is consistent with the 2D HSQC NMR of the Aβ42 monomer that depicted a change in the chemical shift of residues spanning from Glu11 to Phe20 in the presence of ADH-31. The MD simulations highlighted the prevention of sampling of amyloidogenic β-strand conformations in Aβ42 trimer in the presence of ADH-31 as well as the ability of ADH-31 to destabilize Aβ42 trimer and protofibril structures. The lower binding affinity between Aβ42 trimer chains in the presence of ADH-31 highlights the destabilization of the Aβ42 trimer structure. Overall, MD results highlighted that ADH-31 inhibited Aβ42 aggregation by constraining Aβ peptides into helical conformation and destabilized Aβ42 trimer as well as protofibril structures. The present study provides a theoretical insight into the atomic level details of the inhibitory mechanism of ADH-31 against Aβ42 aggregation as well as protofibril destabilization and could be implemented in the structure-based drug design of potent therapeutic agents for AD.

Synthesis and Biological Evaluation of Halogenated E-Stilbenols as Promising Antiaging Agents

The increased risk of illness and disability is related to the age inevitable biological changes. Oxidative stress is a proposed mechanism for many age-related diseases. The crucial importance of polyphenol pharmacophore for aging process is largely described thanks to its effects on concentrations of reactive oxygen species. Resveratrol (3,5,4'-trihydroxy-trans-stilbene, RSV) plays a critical role in slowing the aging process but has a poor bioavailabity after oral intake. In this present work, a series of RSV derivatives was designed, synthesized, and evaluated as potential antioxidant agents. These derivatives contain substituents with different electronic and steric properties in different positions of aromatic rings. This kind of substituents affects the activity and the bioavailability of these compounds compared with RSV used as reference compound. Studies of Log P values demonstrated that the introduction of halogens gives the optimum lipophilicity to be considered promising active agents. Among them, compound 6 showed the higher antioxidant activity than RSV. The presence of trifluoromethyl group together with a chlorine atom increased the antioxidant activity compared to RSV.

Small molecule therapeutics for tauopathy in Alzheimer's disease: Walking on the path of most resistance

Alzheimer's disease (AD) is the most common form of dementia characterized by presence of extracellular amyloid plaques and intracellular neurofibrillary tangles composed of tau protein. Currently there are close to 50 million people living with dementia and this figure is expected to increase to 75 million by 2030 putting a huge burden on the economy due to the health care cost. Considering the effects on quality of life of patients and the increasing burden on the economy, there is an enormous need of new disease modifying therapies to tackle this disease. The current therapies are dominated by only symptomatic treatments including cholinesterase inhibitors and N-methyl-D-aspartate receptor blockers but no disease modifying treatments exist so far. After several failed attempts to develop drugs against amyloidopathy, tau targeting approaches have been in the main focus of drug development against AD. After an overview of the tauopathy in AD, this review summarizes recent findings on the development of small molecules as therapeutics targeting tau modification, aggregation, and degradation, and tau-oriented multi-target directed ligands. Overall, this work aims to provide a comprehensive and critical overview of small molecules which are being explored as a lead candidate for discovering drugs against tauopathy in AD.

M. Pinto M, Sousa E. Marine Natural Products, Multitarget Therapy and Repurposed Agents in Alzheimer's Disease

Alzheimer's disease (AD) is a multifactorial disease characterized by the presence of amyloid plaques, neurofibrillary tangles, and nerve cell death that affects, mainly, older people. After decades of investigation, the search for an efficacious treatment for AD remains and several strategies can be and are being employed in this journey. In this review, four of the most promising strategies, alongside with its most promising agents under investigation or development are highlighted. Marine natural products (MNP) are a source of unique chemical structures with useful biological activities for AD treatment. One of the most promising compounds, a marine-derived acidic oligosaccharide (GV-971) just passed phase III clinical trials with a unique mechanism of action. Combination therapy and multitargeted-directed ligand therapy (MTDL) are also two important strategies, with several examples in clinical trials, based on the belief that the best approach for AD is a therapy capable of modulating multiple target pathways. Drug repurposing, a strategy that requires a smaller investment and is less time consuming, is emerging as a strong contender with a variety of pharmacological agents resurfacing in an attempt to identify a therapeutic candidate capable of modifying the course of this disease.

Alkaloids Modulate the Functioning of Ion Channels Produced by Antimicrobial Agents via an Influence on the Lipid Host

It is widely recognized that an alteration in membrane physical properties induced by the adsorption of various drugs and biologically active compounds might greatly affect the functioning of peptides and proteins embedded in the membrane, in particular various ion channels. This study aimed to obtain deep insight into the diversity of the molecular mechanisms of membrane action of one of the most numerous and extremely important class of phytochemicals, the alkaloids. Protoalkaloids (derivatives of β-phenylethylamine, benzylamines, and colchicines), heterocyclic alkaloids (derivatives of purine, quinolysidine, piperidine, pyridine, quinoline, and isoquinoline), and steroid alkaloids were tested. We evaluated the effects of 22 compounds on lipid packing by investigating the thermotropic behavior of membrane lipids and the leakage of a fluorescent marker from unilamellar lipid vesicles. The alteration in the transmembrane distribution of the electrical potential was estimated by measuring the alkaloid induced changes in the boundary potential of planar lipid bilayers. We found that benzylamines, the chili pepper active components, capsaicin and dihydrocapsaicin, strongly affect not only the elastic properties of the lipid host, but also its electrostatics by dramatic decrease in membrane dipole potential. We concluded that the increase in the conductance and lifetime of gramicidin A channels induced by benzylamines was related to alteration in membrane dipole potential not to decrease in membrane stiffness. A sharp decrease in the lifetime of single ion pores induced by the antifungal lipopeptide syringomycin E, after addition of benzylamines and black pepper alkaloid piperine, was also mainly due to the reduction in dipole potential. At the same time, we showed that the disordering of membrane lipids in the presence of benzylamines and piperine plays a decisive role in the regulation of the conductance induced by the antifungal polyene macrolide antibiotic nystatin, while the inhibition of steady-state transmembrane current produced by the antimicrobial peptide cecropin A was attributed to both the dipole potential drop and membrane lipid disordering in the presence of pepper alkaloids. These data might lead to a better understanding of the biological activity of alkaloids, especially their action on voltage-gated and mechanosensitive ion channels in cell membranes.

Discovery and Characterization of Novel Naphthalimide Analogs as Potent Multitargeted Directed Ligands against Alzheimer's Disease

Current therapeutic drugs for Alzheimer's disease (AD) can only offer limited symptomatic benefits and do not halt disease progression. Multitargeted directed ligands (MTDLs) have been considered to be a feasible way to treat AD due to the multiple neuropathological processes in AD. Previous studies proposed that compounds containing two aromatic groups connected by a carbon chain should act as effective amyloid β (Aβ) aggregation inhibitors although the optimal length of the carbon chain has not been explored. In the current study, a series of naphthalimide analogs were designed and synthesized based on the proposed structure and multiple bioactivities beneficial to the AD treatment were reported. In vitro studies showed that compound 8, which has two aromatic groups connected by a two-carbon chain, exhibited significant inhibition of Aβ aggregation through the prevention of elongation and association of Aβ fibril growth. Furthermore, this compound also displayed antioxidative activities and neuroprotection from Aβ monomer induced toxicity in primary cortical neurons. The results of the present study highlight a novel naphthalimide-based compound 8 as a promising MTDL against AD. Its structural elements can be further explored for enhanced therapeutic capabilities.

Curcumin in Health and Diseases: Alzheimer's Disease and Curcumin Analogues, Derivatives, and Hybrids

Worldwide, Alzheimer’s disease (AD) is the most common neurodegenerative multifactorial disease influencing the elderly population. Nowadays, several medications, among them curcumin, are used in the treatment of AD. Curcumin, which is the principal component of Curcuma longa, has shown favorable effects forsignificantly preventing or treating AD. During the last decade, the scientific community has focused their research on the optimization of therapeutic properties and on the improvement of pharmacokinetic properties of curcumin. This review summarizes bibliographical data from 2009 to 2019 on curcumin analogues, derivatives, and hybrids, as well as their therapeutic, preventic, and diagnostic applications in AD. Recent advances in the field have revealed that the phenolic hydroxyl group could contribute to the anti-amyloidogenic activity. Phenyl methoxy groups seem to contribute to the suppression of amyloid-β peptide (Aβ₄₂) and to the suppression of amyloid precursor protein (APP) andhydrophobic interactions have also revealed a growing role. Furthermore, flexible moieties, at the linker, are crucial for the inhibition of Aβ aggregation. The inhibitory activity of derivatives is increased with the expansion of the aromatic rings. The promising role of curcumin-based compounds in diagnostic imaging is highlighted. The keto-enol tautomerism seems to be a novel modification for the design of amyloid-binding agents. Molecular docking results, (Q)SAR, as well as in vitro and in vivo tests highlight the structures and chemical moieties that are correlated with specific activity. As a result, the knowledge gained from the existing research should lead to the design and synthesis ofinnovative and multitargetedcurcumin analogues, derivatives, or curcumin hybrids, which would be very useful drug and tools in medicine for both diagnosis and treatment of AD.