Natural Scaffolds with Multi-Target Activity for the Potential Treatment of Alzheimer's Disease

Targeting Biometals in Alzheimer's Disease with Metal Chelating Agents Including Coumarin Derivatives

Numerous physiological processes happening in the human body, including cerebral development and function, require the participation of biometal ions such as iron, copper, and zinc. Their dyshomeostasis may, however, contribute to the onset of Alzheimer's disease (AD) and potentially other neurodegenerative diseases. Chelation of biometal ions is therefore a therapeutic strategy against AD. This review provides a survey of natural and synthetic chelating agents that are or could potentially be used to target the metal hypothesis of AD. Since metal dyshomeostasis is not the only pathological aspect of AD, and the nature of this disorder is very complex and multifactiorial, the most efficient therapeutics should target as many neurotoxic factors as possible. Various coumarin derivatives match this description and apart from being able to chelate metal ions, they exhibit the capacity to inhibit cholinesterases (ChEs) and monoamine oxidase B (MAO-B) while also possessing antioxidant, anti-inflammatory, and numerous other beneficial effects. Compounds based on the coumarin scaffold therefore represent a desirable class of anti-AD therapeutics.

Tenuazonic acid alters immune and physiological reactions and susceptibility to pathogens in Galleria mellonella larvae

Tenuazonic acid (TeA) is synthesized by phytopathogenic and opportunistic fungi and is detected in a broad range of foods. This natural compound is of interest in terms of toxicity to animals, but its mechanisms of action on insects are poorly understood. We administered TeA orally at different concentrations (0.2-5.0 mg/[gram of a growth medium]) to the model insect Galleria mellonella, with subsequent estimation of physiological, histological, and immunological parameters in different tissues (midgut, fat body, and hemolymph). Susceptibility of the TeA-treated larvae to pathogenic microorganisms Beauveria bassiana and Bacillus thuringiensis was also analyzed. The feeding of TeA to the larvae led to a substation delay of larval growth, apoptosis-like changes in midgut cells, and an increase in midgut bacterial load. A decrease in activities of detoxification enzymes and downregulation of genes Nox, lysozyme, and cecropin in the midgut and/or hemocoel tissues were detected. By contrast, genes gloverin, gallerimycin, and galiomycin and phenoloxidase activity proved to be upregulated in the studied tissues. Hemocyte density did not change under the influence of TeA. TeA administration increased susceptibility of the larvae to B. bassiana but diminished their susceptibility to B. thuringiensis. The results indicate that TeA disturbs wax moth gut physiology and immunity and also exerts a systemic action on this insect. Mechanisms underlying the observed changes in wax moth susceptibility to the pathogens are discussed.

Antimicrobial Natural Products from Plant Pathogenic Fungi

Isolates of a variety of fungal plant pathogens (Alternaria radicina ICMP 5619, Cercospora beticola ICMP 15907, Dactylonectria macrodidyma ICMP 16789, D. torresensis ICMP 20542, Ilyonectria europaea ICMP 16794, and I. liriodendra ICMP 16795) were screened for antimicrobial activity against the human pathogenic bacteria Acinetobacter baumannii, Pseudomonas aeruginosa, Escherichia coli, Mycobacterium abscessus, and M. marinum and were found to have some activity. Investigation of the secondary metabolites of these fungal isolates led to the isolation of ten natural products (1-10) of which one was novel, (E)-4,7-dihydroxyoct-2-enoic acid (1). Structure elucidation of all natural products was achieved by a combination of NMR spectroscopy and mass spectrometry. We also investigated the antimicrobial activity of a number of the isolated natural products. While we did not find (E)-4,7-dihydroxyoct-2-enoic acid (1) to have any activity against the bacteria and fungi in our assays, we did find that cercosporin (7) exhibited potent activity against Methicillin resistant Staphylococcus aureus (MRSA), dehydro-curvularin (6) and radicicol (10) exhibited antimycobacterial activity against M. marinum, and brefeldin A (8) and radicicol (10) exhibited antifungal activity against Candida albicans. Investigation of the cytotoxicity and haemolytic activities of these natural products (6-8 and 10) found that only one of the four active compounds, radicicol (10), was non-cytotoxic and non-haemolytic.

Butenolide derivatives from Aspergillus terreus selectively inhibit butyrylcholinesterase

Two undescribed butenolide derivatives, asperteretal J (1) and K (2), together with 13 known ones (3-15) were isolated from an endophytic fungus Aspergillus terreus SGP-1, the fermentation product of which exhibited selective inhibitory activity toward butyrylcholinesterase. The structures of the new compounds were elucidated based on HRMS and NMR data, and the absolute configurations were determined by specific optical rotation comparison. All compounds were evaluated for cholinesterase inhibitory effects with galantamine as a positive control. Compounds 4-8 selectively inhibited butyrylcholinesterase with IC₅₀ values of 18.4-45.8 µM in a competitive manner, with Ki values of 12.3-38.2 µM. The structure-activity relationship was discussed. Molecular docking and dynamic simulation of the inhibitor-enzyme complex were performed to better understand the interactions.

Fenugreek Extract-Loaded Polycaprolacton/Cellulose Acetate Nanofibrous Wound Dressings for Transplantation of Unrestricted Somatic Stem Cells: An In Vitro and In Vivo Evaluation

Complex pathophysiology of diabetic wounds causes a delayed wound healing response. Advanced wound dressing materials that deliver biochemical cues are of particular interest in wound healing research. Here, we developed a dual-function delivery vehicle for drug and cell delivery applications to treat diabetic wounds. The delivery system was developed via electrospinning of polycaprolacton/cellulose acetate solution containing fenugreek extract. The produced delivery vehicle was characterized using microstructural studies, cell viability assay, cytoprotection assay, cell migration assay, In Vitro anti-inflammatory assay, free radical scavenging assay, tensile strength studies, swelling studies, and protein adsorption test. Scaffolds were then seeded with 30000 unrestricted somatic stem cells and transplanted into the rat model of excisional diabetic wound. Wound healing assay showed that the co-delivery of fenugreek extract and unrestricted somatic stem cells led to a substantial improvement in the healing activity of electrospun dressings, as evidenced by higher wound contraction, epithelial thickness, and collagen deposition in this group compared with other experimental groups. Gene expression analysis showed that dual-function delivery system could increase the expression level of VEGF, b-FGF, and collagen type II genes. Furthermore, the tissue expression level of IL-1β and glutathione peroxidase genes was significantly reduced in this group compared with other groups. This study shows that the developed system may be considered as a potential treatment modality for diabetic wounds in the clinic.

Recent advance on pleiotropic cholinesterase inhibitors bearing amyloid modulation efficacy

Due to the hugely important roles of neurotransmitter acetylcholine (ACh) and amyloid-β (Aβ) in the pathogenesis of Alzheimer's disease (AD), the development of multi-target directed ligands (MTDLs) focused on cholinesterase (ChE) and Aβ becomes one of the most attractive strategies for combating AD. To date, numerous preclinical studies toward multifunctional conjugates bearing ChE inhibition and anti-Aβ aggregation have been reported. Noteworthily, most of the reported multifunctional cholinesterase inhibitors are carbamate-based compounds due to the initial properties of carbamate moiety. However, because their easy hydrolysis in vivo and the instability of the compound-enzyme conjugate, the mechanism of action of these compounds is rare. Thus, non-carbamate compounds are of great need for developing novel cholinesterase inhibitors. Besides, given that Aβ accumulation begins to occur 10-15 years before AD onset, modulating Aβ is ineffective only in inhibiting its aggregation but not eliminate the already accumulated Aβ if treatment is started when the patient has been diagnosed as AD. Considering the limitation of current Aβ accumulation modulators in ameliorating cognitive deficits and ineffectiveness of ChE inhibitors in blocking disease progression, the development of a practically valuable strategy with multiple pharmaceutical properties including ChE inhibition and Aβ modulation for treating AD is indispensable. In this review, we focus on summarizing the scaffold characteristics of reported non-carbamate cholinesterase inhibitors with Aβ modulation since 2020, and understanding the ingenious multifunctional drug design ideas to accelerate the pace of obtaining more efficient anti-AD drugs in the future.

Novel Phenothiazine/Donepezil-like Hybrids Endowed with Antioxidant Activity for a Multi-Target Approach to the Therapy of Alzheimer’s Disease

Alzheimer’s disease (AD) is a complex multi-factorial neurodegenerative disorder for which only few drugs (including donepezil, DPZ) are available as symptomatic treatments; thus, researchers are focusing on the development of innovative multi-target directed ligands (MTDLs), which could also alter the course of the disease. Among other pathological factors, oxidative stress has emerged as an important factor in AD that could affect several pathways involved in the onset and progression of the pathology. Herein, we propose a new series of hybrid molecules obtained by linking a phenothiazine moiety, known for its antioxidant properties, with N-benzylpiperidine or N-benzylpiperazine fragments, mimicking the core substructure of DPZ. The investigation of the resulting hybrids showed, in addition to their antioxidant properties, their activity against some AD-related targets, such as the inhibition of cholinesterases (both AChE and BChE) and in vitro Aβ1-40 aggregation, as well as the inhibition of the innovative target fatty acid amide hydrolase (FAAH). Furthermore, the drug-likeness properties of these compounds were assessed using cheminformatic tools. Compounds 11d and 12d showed the most interesting multi-target profiles, with all the assayed activities in the low micromolar range. In silico docking calculations supported the obtained results. Compound 13, on the other hand, while inactive in the DPPH assay, showed the best results in the in vitro antioxidant cell assays conducted on both HepG2 and SHSY-5Y cell lines. These results, paired with the low or absent cytotoxicity of these compounds at tested concentrations, allow us to aim our future research at the study of novel and effective drugs and pro-drugs with similar structural characteristics.

Entomotoxic Activity of the Extracts from the Fungus, Alternaria tenuissima and Its Major Metabolite, Tenuazonic Acid

The study of fungal antibiotics in their competitive interactions with arthropods may lead to the development of novel biorational insecticides. Extracts of Alternaria tenuissima MFP253011 obtained using various methods showed a wide range of biological activities, including entomotoxic properties. Analysis of their composition and bioactivity allowed us to reveal several known mycotoxins and unidentified compounds that may be involved in the entomotoxic activity of the extracts. Among them, tenuazonic acid (TeA), which was the major component of the A. tenuissima extracts, was found the most likely to have larvicidal activity against Galleria mellonella. In the intrahaemocoel injection bioassay, TeA was toxic to G. mellonella and of Zophobas morio with an LT50 of 6 and 2 days, respectively, at the level of 50 µg/larva. Administered orally, TeA inhibited the growth of G. mellonella larvae and caused mortality of Acheta domesticus adults (LT50 7 days) at a concentration of 250 µg/g of feed. TeA showed weak contact intestinal activity against the two phytophages, Tetranychus urticae and Schizaphis graminum, causing 15% and 27% mortality at a concentration of 1 mg/mL, respectively. TeA was cytotoxic to the Sf9 cell line (IC50 25 µg/mL). Thus, model insects such as G. mellonella could be used for further toxicological characterization of TeA.

Evaluation of heptelidic acid as a potential inhibitor for tau aggregation-induced Alzheimer's disease and associated neurotoxicity

Tau is a major component of protein plaques in tauopathies, especially Alzheimer's disease (AD). The purpose of the present study is to explore the inhibitory effects of heptelidic acid as a bioactive compound from fungus T. koningii on tau fibrillization and associated neurotoxicity. The influences of various concentrations of heptelidic acid on tau fibrillization and underlying neurotoxicity were explored by assessment of the biophysical (ThT/Nile red fluorescence, CR absorbance, CD, and TEM) and cellular (MTT, LDH, and caspase-3) assays. It was shown that heptelidic acid inhibited tau fibrillization in a concentration-dependent manner. On the other hand, cellular assays indicated that the viability, LDH release, and caspase-3 activity were regulated when neurons were exposed to tau samples co-incubated with heptelidic acid. In conclusion, it may be indicated that heptelidic acid inhibited tau fibrillization which was accompanied by formation of amorphous aggregated species of tau with much less neurotoxicity than tau amyloid alone. Thus, heptelidic acid can be considered as a potential candidate in preventive care studies to inhibit the formation of tau plaques as neurotoxic species.

Derivatives of Tenuazonic Acid as Potential New Multi-Target Anti-Alzheimer's Disease Agents

Alzheimer's disease (AD) is generally recognized as a multifactorial neurodegenerative pathology with an increasing impact on society. Tenuazonic acid (TA) is a natural compound that was recently identified as a potential multitarget ligand with anti-cholinesterase, anti-amyloidogenic and antioxidant activities. Using its structure as a chemical scaffold, we synthesized and evaluated new derivatives (1-5), including tenuazonic-donepezil (TA-DNP) hybrids (4 and 5) due to the clinical importance of the anti-AD drug donepezil. These novel compounds all achieved activity in the micromolar range towards all selected targets and demonstrated to be potentially orally absorbed. Moreover, a selected compound (1) was further investigated as a chelating agent towards copper (II), zinc (II) and iron (III) and showed good chelating ability (pFe = 16.6, pCu = 11.6, pZn = 6.0 at pH 7.4). Therefore, the TA motif can be considered an interesting building block in the search for innovative multi-functional anti-neurodegenerative drugs, as exemplified by hybrid 5, a promising non-cytotoxic lead compound adequate for the early stages of AD, and capable of ameliorating the oxidative status of SH-SY5Y human neuroblastoma cells.

Advances in deep eutectic solvents and water: applications in metal- and biocatalyzed processes, in the synthesis of APIs, and other biologically active compounds

This review highlights recent advances in metal- and biocatalyzed transformations, in the synthesis of APIs and other biologically active compounds, when employing deep eutectic solvents and water as environmentally responsible solvents.

Natural Compounds for the Prevention and Treatment of Cardiovascular and Neurodegenerative Diseases

Secondary metabolites from plants and fungi are stimulating growing interest in consumers and, consequently, in the food and supplement industries. The beneficial effects of these natural compounds are being thoroughly studied and there are frequent updates about the biological activities of old and new molecules isolated from plants and fungi. In this article, we present a review of the most recent literature regarding the recent discovery of secondary metabolites through isolation and structural elucidation, as well as the in vitro and/or in vivo evaluation of their biological effects. In particular, the possibility of using these bioactive molecules in the prevention and/or treatment of widely spread pathologies such as cardiovascular and neurodegenerative diseases is discussed.

Chemical Composition and Anti-Alzheimer's Disease-Related Activities of a Functional Oil from the Edible Seaweed Hizikia fusiforme

Cholinergic disorder, oxidative stress, and neuroinflammation play important roles in the pathology of Alzheimer's disease. To explore the healthy potential of the edible seaweed Hizikia fusiforme on this aspect, a functional oil (HFFO) was extracted from this alga and investigated on its constituents by gas chromatography-mass spectrometry (GC/MS) in this study. Its anti-Alzheimer's related bioactivities including acetylcholinesterase (AChE) inhibition, antioxidation, and anti-neuroinflammation were evaluated, traced, and simulated by in vitro and in silico methods. GC/MS analysis indicated that HFFO mainly contained arachidonic acid (ARA), 11,14,17-eicosatrienoic acid (ETrA), palmitic acid, phytol, etc. HFFO showed moderate AChE inhibition and antioxidant activity. Bioactivity tracing using commercial standards verified that AChE inhibition of HFFO mainly originated from ARA and ETrA, whereas antioxidant activity mainly from ARA. Lineweaver-Burk plots showed that both ARA and ETrA are noncompetitive AChE inhibitors. A molecular docking study demonstrated low CDOCKER interaction energy of -26.33 kcal/mol for ARA and -43.70 kcal/mol for ETrA when interacting with AChE and multiple interactions in the ARA (or ETrA)-AChE complex. In the anti-neuroinflammatory evaluation, HFFO showed no toxicity toward BV-2 cells at 20 μg/mL and effectively inhibited the production of nitroxide and reduced the level of reactive oxygen species in lipopolysaccharide-induced BV-2 cells. The results indicated that HFFO could be used in functional foods for its anti-Alzheimer's disease-related activities.

Novel Perspective on Alzheimer's Disease Treatment: Rosmarinic Acid Molecular Interplay with Copper(II) and Amyloid β

Alzheimer's disease is a severe disorder that affects millions of people worldwide. It is a very debilitating disease with no cure at the moment. The necessity of finding an effective treatment is very demanding, and the entire scientific community is putting in a lot of effort to address this issue. The major hallmark of Alzheimer's disease is the presence of toxic aggregated species in the brain, impaired metal homeostasis, and high levels of oxidative stress. Rosmarinic acid is a well-known potent antioxidant molecule, the efficacy of which has been proved both in vitro and in vivo. In this study, we investigated the possible role played by rosmarinic acid as a mediator of the copper(II)-induced neurotoxicity. Several spectroscopic techniques and biological assays were applied to characterize the metal complexes and to evaluate the cytotoxicity and the mutagenicity of rosmarinic acid and its Cu(II) complex. Our data indicate that rosmarinic acid is able to interfere with the interaction between amyloid β and Cu(II) by forming an original ternary association.

Importance of Biometals as Targets in Medicinal Chemistry: An Overview about the Role of Zinc (II) Chelating Agents

Zinc (II) is an important biometal in human physiology. Moreover, in the last two decades, it was deeply studied for its involvement in several pathological states. In particular, the regulation of its concentration in synaptic clefts can be fundamental for the treatment of neurodegenerative diseases, such as Alzheimer’s disease (AD). Zinc (II) is also a constituent of metalloenzymes (i.e., matrix metalloproteinases, MMPs, and carbonic anhydrases, CAs) with catalytic function; therefore, it can be an important target for the inhibition of these proteins, frequently involved in cancer onset. This review is focused on the significance of zinc (II) chelating agents in past and future medicinal chemistry research, and on the importance of selectivity in order to revamp the possibility of their use in therapy, often hindered by possible side effects.

A Review of Recent Patents (2016-2019) on Plant Food Supplements with Potential Application in the Treatment of Neurodegenerative and Metabolic Disorders

In the near future, it is expected that the prevalence of illnesses related to the increasing life expectancies and quality of life, such as neurodegenerative diseases and cardiovascular diseases related to metabolic disorders, will soar to unprecedented levels, leading to high socioeconomic costs. To address this rising threat, natural products are emerging as a novel strategy for the prevention and therapy of these ages- and lifestyle-related diseases, thanks to their high marketability and few side effects. In this patent review, we summarize selected patents for food supplements, functional and fortified foods, filed from 2016 to 2019, categorizing them based on the biological activity of their components.

Deep Eutectic Solvents as Effective Reaction Media for the Synthesis of 2-Hydroxyphenylbenzimidazole-based Scaffolds en Route to Donepezil-Like Compounds

An unsubstituted 2-hydroxyphenylbenzimidazole has recently been included as a scaffold in a series of hybrids (including the hit compound PZ1) based on the framework of the acetylcholinesterase (AChE) inhibitor Donepezil, which is a new promising multi-target ligand in Alzheimer’s disease (AD) treatment. Building upon these findings, we have now designed and completed the whole synthesis of PZ1 in the so-called deep eutectic solvents (DESs), which have emerged as an unconventional class of bio-renewable reaction media in green synthesis. Under optimized reaction conditions, the preparation of a series of 2-hydroxyphenylbenzimidazole-based nuclei has also been perfected in DESs, and comparison with other routes which employ toxic and volatile organic solvents (VOCs) provided. The functionalization of the aromatic ring can have implications on some important biological properties of the described derivatives and will be the subject of future studies of structure-activity relationships (SARs).

Current and emerging therapeutic targets of alzheimer's disease for the design of multi-target directed ligands

Alzheimer's disease (AD) is the most prevalent neurodegenerative disease, and a major cause of death worldwide. The number of people suffering from this debilitating disorder is rising at an unprecedented rate, with a subsequent surge in healthcare costs. Only four drugs are clinically available for the treatment of AD symptoms, but they are not disease-modifying. Consequently, there is an urgent need for a cure. Although the cause of this debilitating condition remains poorly understood, it is believed that several factors may be involved in combination - including, health and lifestyle, environmental, and genetic factors. In recent years, a number of hallmarks of the disease have also been discovered, and it is believed that these factors may play an important role in the development of AD. Amyloid aggregation is one such factor which has been highly investigated, in addition to cholinesterase enzymes and tau aggregation. In the last decade, multi-target drugs have been increasingly investigated for their application to AD treatment. By combining two or more pharmacophores in a single compound, it is possible to synthesise a drug which can target several factors that are involved in AD development. This is a particularly attractive approach as it would avoid the use of combination therapies. As a result, it could reduce the burden on carers and families, and decrease healthcare and social care costs. Many active pharmacophores have been employed for the development of hybrid drugs, due to their abilities to inhibit the factors currently widely recognised to be involved in AD. These compounds have demonstrated promising results; however, research is still required to optimise the pharmacological profiles of the drugs, in addition to their potencies. Meanwhile, extensive research is continuously being performed into other potential targets for the treatment of AD. Based on the results obtained thus far, it is likely that multi-target compounds will continue to be increasingly studied in the future as potential treatments for AD.

Anti-Neuroinflammatory Property of Phlorotannins from Ecklonia cava on Aβ25-35-Induced Damage in PC12 Cells

Alzheimer disease (AD) is a neurodegenerative disorder characterized by excessive accumulation of amyloid-beta peptide (Aβ) and progressive loss of neurons. Therefore, the inhibition of Aβ-induced neurotoxicity is a potential therapeutic approach for the treatment of AD. Ecklonia cava is an edible brown seaweed, which has been recognized as a rich source of bioactive derivatives, mainly phlorotannins. In this study, phlorotannins including eckol, dieckol, 8,8'-bieckol were used as potential neuroprotective candidates for their anti-apoptotic and anti-inflammatory effects against Aβ25-35-induced damage in PC12 cells. Among the tested compounds, dieckol showed the highest effect in both suppressing intracellular oxidative stress and mitochondrial dysfunction and activation of caspase family. Three phlorotannins were found to inhibit TNF-α, IL-1β and PGE₂ production at the protein levels. These result showed that the anti-inflammatory properties of our compounds are related to the down-regulation of proinflammatory enzymes, iNOS and COX-2, through the negative regulation of the NF-κB pathway in Aβ25-35-stimulated PC12 cells. Especially, dieckol showed the strong anti-inflammatory effects via suppression of p38, ERK and JNK. However, 8,8'-bieckol markedly decreased the phosphorylation of p38 and JNK and eckol suppressed the activation of p38. Therefore, the results of this study indicated that dieckol from E. cava might be applied as a drug candidate for the development of new generation therapeutic agents against AD.