Inhibition of amyloid β aggregation and protective effect on SH-SY5Y cells by triterpenoid saponins from the cactus Polaskia chichipe

Inhibition of amyloid β aggregation and BACE1, and protective effect on SH-SY5Y cells, by p-terphenyl compounds from mushroom Thelephora aurantiotincta

The number of patients with Alzheimer's disease (AD) is expected to increase as the population ages. The amyloid cascade hypothesis is proposed as the pathogenic mechanism of AD. We report the isolation and structural determination of three new p-terphenyl compounds, thelephantin P (1), thelephantin Q (2), and thelephantin R (3), with four known compounds (4-7), from the fruiting bodies of Thelephora aurantiotincta Corner. We evaluated Aβ aggregation and BACE1 inhibitory activities and neuroprotective activities of these isolated compounds. Compound 1 was shown to be multi-inhibitors for AD. Compound 1 had an IC50 = 12.9 μM (Aβ), 6.3 μM (BACE1), and EC50 = 8.0 μM (neuroprotection), respectively. Therefore, these compounds are potential therapeutic agents for AD.

The mechanistic interaction, aggregation and neurotoxicity of α-synuclein after interaction with glycyrrhizic acid: Modulation of synucleinopathies

This article reveals the binding mechanism between glycyrrhizic acid (GA) and α-synuclein to may provide further information for the modulation of synucleinopathies using bioactive compounds. Therefore, the inhibitory activities of GA against α-synuclein aggregation and induced neurotoxicity were evaluated using different assays. Results showed that α-synuclein-GA binding was mediated by intermolecular hydrogen bonds leading to the formation of a slightly folded complex. Theoretical studies revealed that GA binds to the N-terminal domain of α-synuclein and triggers a compact structure around a major part of the N-terminal and the NAC regions along with fluctuations in the C-terminal domain, which are prerequisites for the inhibition of α-synuclein aggregation. Then, the cellular assays showed that GA as a potential small molecule can inhibit the oligomerization of α-synuclein and relevant neurotoxicity through modulation of neural viability, membrane leakage, and ROS formation in a concentration-dependent manner. As a result, the primary mechanism of GA's anti-aggregation and neuroprotective activities is the reorganized α-synuclein structure and fluctuating C-terminal domain, which promotes long-range transient intramolecular contacts between the N-terminal and the C-terminal domain.

Therapeutic Candidates for Alzheimer's Disease: Saponins

Drug development for Alzheimer's disease, the leading cause of dementia, has been a long-standing challenge. Saponins, which are steroid or triterpenoid glycosides with various pharmacological activities, have displayed therapeutic potential in treating Alzheimer's disease. In a comprehensive review of the literature from May 2007 to May 2023, we identified 63 references involving 40 different types of saponins that have been studied for their effects on Alzheimer's disease. These studies suggest that saponins have the potential to ameliorate Alzheimer's disease by reducing amyloid beta peptide deposition, inhibiting tau phosphorylation, modulating oxidative stress, reducing inflammation, and antiapoptosis. Most intriguingly, ginsenoside Rg1 and pseudoginsenoside-F11 possess these important pharmacological properties and show the best promise for the treatment of Alzheimer's disease. This review provides a summary and classification of common saponins that have been studied for their therapeutic potential in Alzheimer's disease, showcasing their underlying mechanisms. This highlights the promising potential of saponins for the treatment of Alzheimer's disease.

Inhibition of Aβ aggregation by naphtho-γ-pyrone derivatives from a marine-derived fungus, Aspergillus sp. MPUC239

Alzheimer's disease (AD) is an important human disease that mainly causes cognitive impairments. Growing evidence has shown that amyloid-β (Aβ) peptide plays a key role in AD pathogenesis in what is known as the Aβ cascade hypothesis. This hypothesis suggests the importance of suppressing Aβ aggregation and Aβ production. The latter process is governed by β-site APP Cleaving Enzyme1 (BACE1) and γ-secretase. We, therefore, focused on Aβ aggregation inhibitory activity, initially assessing numerous extracts derived from our marine-derived fungus collections. One EtOAc extract derived from an Aspergillus sp. exhibited Aβ aggregation inhibitory activity. Eleven known compounds (1-11) were isolated from CHCl₃ and EtOAc extracts derived from the fungus, and the structures were identified based on MS, NMR, and ECD spectra. Compounds 2, 6, and 10 inhibited Aβ aggregation with IC₅₀ values of 2.8, 3.9, and 8.1 μM, respectively. The protective effect on SH-SY5Y cells against Aβ toxicity was also evaluated, and compounds 6 and 10 significantly alleviated Aβ toxicity. BACE1 inhibitory activity was also examined, and compounds 4, 5, 7, 10, and 11 inhibited BACE1 activity with IC₅₀ values of 14.9, 70.0, 36.5, 28.0, and 72.8 μM, respectively. These data suggest that compound 10 could be useful in AD treatment.

Triterpenoids impede the fibrillation and cytotoxicity of human islet amyloid polypeptide

The inhibition of human islet amyloid polypeptide (hIAPP) deposition to block its toxicity is an important strategy for the prevention and treatment of type II diabetes mellitus (T2DM).Natural compounds with pharmacological properties and low toxicity can serve as a good point to discover potential inhibitors of protein misfolding, which may be useful for the treatment of various amyloidosis-related diseases. Previous studies have reported that triterpenoids, such as maslinic acid (MA) and momordicin I (MI), can modulate glucose metabolism partially by reducing insulin resistance. However, the internal antidiabetic mechanism of these triterpenoids remains unclear. In this study, we examined the inhibition and disaggregation of MAandits isomer MI on the fibrillation of hIAPP using various experimental and computational approaches. The assembly behaviors and peptide-induced cytotoxicity of hIAPP could be effectively resisted by MA and MI. Moreover, the interaction of the two triterpenoids with hIAPP displayed a spontaneous and exothermic process. Moreover, molecular dynamics simulation results of different peptides revealed that MA and MI could bind to Asn and other non-polar residues near the core C-terminal region and reduce the oligomerization of hIAPP. The binding affinity was predominantly contributed by hydrophobic, electrostatic and hydrogen bonding interactions. The present work provides valuable data for MA and MI to treat T2DM and amyloidosis-related diseases.

Inhibition of BACE1 and amyloid β aggregation by polyketide from Streptomyces sp

Alzheimer's disease (AD) causes cognitive impairment in the elderly and is a severe problem worldwide. One of the major reasons for the pathogenesis of AD is thought to be due to the accumulation of amyloid beta (Aβ) peptides that result in neuronal cell death in the brain. In this study, bioassay-guided fractionation was performed to develop seed compounds for anti-AD drugs that can act as dual inhibitors of BACE1 and Aβ aggregation from secondary metabolites produced by Streptomyces sp. To improve the solubility, the crude extracts were methylated with trimethylsilyl (TMS) diazomethane and then purified to yield polyketides 1-5, including the new compound 1. We synthesized the compounds 6 and 7 (original compounds 2 and 3, respectively), and their activities were evaluated. KS-619-1, the demethylated form of 4 and 5, was isolated and evaluated for its inhibitory activity. The IC₅₀ values for BACE1 and Aβ aggregation were found to be 0.48 and 1.1 μM, respectively, indicating that KS-619-1 could be a lead compound for the development of therapeutic agents for AD.

Inhibition of BACE1 and Amyloid-β Aggregation by Meroterpenoids from the Mushroom Albatrellus yasudae

To develop drugs to treat Alzheimer's disease (AD) on the basis of the amyloid cascade hypothesis, the amyloid-β (Aβ) aggregation inhibitory activities of 110 extracts from mushrooms were evaluated by thioflavin T (Th-T) assays. The MeOH extract of Albatrellus yasudae inhibited Aβ aggregation, and the bioactivity-guided fractionation of the extract afforded four novel meroterpenoids, named scutigeric acid (1), albatrelactone methyl ester (2), albatrelactone (3), and 10',11'-dihydroxygrifolic acid (4), together with two known compounds, grifolin (5) and grifolic acid (6). The structures of 1-4 were elucidated using NMR, MS, UV, IR, and induced ECD spectral data. The structure of 1 was determined as a methyl ester (1a) by 2D NMR spectroscopy. Th-T assays showed that compounds 1-4 and 1a possessed inhibitory activities against Aβ aggregation, with IC₅₀ values of 6.6, 40.7, 51.4, 53.3, and 50.3 μM, respectively. Notably, 1 possessed an inhibitory activity against Aβ aggregation comparable to that of myricetin as a positive control. Moreover, 1-6 exhibited inhibitory activities against BACE1, with IC₅₀ values of 1.6, 10.9, 10.5, 34.4, 6.1, and 1.4 μM, respectively.

Amyloid β aggregation inhibitory activity of triterpene saponins from the cactus Stenocereus pruinosus

Six new triterpene saponins (1-5,7) and 3 known saponins (6,8,9) were isolated from MeOH extracts of the cactus Stenocereus pruinosus. The structures of the isolated saponins were elucidated using MS, IR, and comprehensive NMR measurements. To develop drugs for treating Alzheimer's disease (AD) on the basis of the amyloid cascade hypothesis, the isolated saponins were evaluated for inhibition of BACE1 activity and amyloid beta (Aβ) aggregation using thioflavin-T assay, and triterpenes as an aglycone moiety and an alkaline hydrolysate of the saponins were also evaluated. One saponin, stenoside A (7), exhibited inhibitory activity related to Aβ aggregation and its degree of Aβ aggregation was 40.6% at 100 μM.

Natural Products as Potential Anti-Alzheimer Agents

Medicinal plants have curative properties due to the presence of various complex chemical substances of different composition, which are found as secondary metabolites in one or more parts of the plant. The diverse secondary metabolites play an important role in the prevention and cure of various diseases including neurodegenerative diseases like Alzheimer's disease. Naturally occurring compounds such as flavonoids, polyphenols, alkaloids, and glycosides found in various parts of the plant and/or marine sources may potentially protect neurodegeneration as well as improve memory and cognitive function. Many natural compounds show anti-Alzheimer activity through specific pharmacological mechanisms like targeting β-amyloid, Beta-secretase 1 and Acetylcholinesterase. In this review, we have compiled more than 130 natural products with a broad diversity in the class of compounds, which were isolated from different sources showing anti- Alzheimer properties.

Non-polyphenolic natural inhibitors of amyloid aggregation

Protein misfolding diseases (PMDs) are chronic and progressive, with no effective therapy so far. Aggregation and misfolding of amyloidogenic proteins are closely associated with the onset and progression of PMDs, such as amyloid-β (Aβ) in Alzheimer's disease, α-Synuclein (α-Syn) in Parkinson's disease and human islet amyloid polypeptide (hIAPP) in type 2 diabetes. Inhibiting toxic aggregation of amyloidogenic proteins is regarded as a promising therapeutic approach in PMDs. The past decade has witnessed the rapid progresses of this field, dozens of inhibitors have been screened and verified in vitro and in vivo, demonstrating inhibitory effects against the aggregation and misfolding of amyloidogenic proteins, together with beneficial effects. Natural products are major sources of small molecule amyloid inhibitors, a number of natural derived compounds have been identified with great bioactivities and translational prospects. Here, we review the non-polyphenolic natural inhibitors that potentially applicable for PMDs treatment, along with their working mechanisms. Future directions are proposed for the development and clinical applications of these inhibitors.

In Vitro Antioxidant, Anti-Biofilm, and Solar Protection Activities of Melocactus zehntneri (Britton & Rose) Pulp Extract

Cactaceae plants are important due to their nutritional and therapeutic values. This study aimed to identify the phytochemical profile and biological activities of six Melocactus zehntneri pulp extracts: hexane extract (HE), chloroform extract (CE), ethanol extract (EE), methanol extract (ME), final water extract (FWE), and water extract (WE). Sugar, phenolic compounds, and protein content of the extracts were determined. Then thin layer chromatography (TLC) was performed to detect the presence of terpenes (ursolic and oleanolic acids), saponins, sugars, and glycoproteins. These extracts were analyzed for antioxidant activity via in vitro assay. HE showed 75% ferric chelating activity. All extracts showed 80-100% superoxide and hydroxyl radical-scavenging activities, respectively. Further, all extracts at 25 µg/mL showed 60% activity against DPPH. Moreover, in the 3T3 cells lines, no cytotoxicity was observed; however, therapeutic activity against the effects of the H₂O₂ treatment was exhibited. Finally, the polar extracts (EE, ME, FWE, and WE), particularly WE, elicited activity against the biofilms of Staphylococcus epidermidis, and HE and CE expressed a capacity for solar protection.

In vitro evaluation of the protective effects of plant extracts against amyloid-beta peptide-induced toxicity in human neuroblastoma SH-SY5Y cells

Alzheimer's disease (AD) is the most common form of dementia and has no cure. Therapeutic strategies focusing on the reduction of oxidative stress, modulation of amyloid-beta (Aβ) toxicity and inhibition of tau protein hyperphosphorylation are warranted to avoid the development and progression of AD. The aim of this study was to screen the crude extracts (CEs) and ethyl-acetate fractions (EAFs) of Guazuma ulmifolia, Limonium brasiliense, Paullinia cupana, Poincianella pluviosa, Stryphnodendron adstringens and Trichilia catigua using preliminary in vitro bioassays (acetylcholinesterase inhibition, antioxidant activity and total polyphenol content) to select extracts/fractions and assess their protective effects against Aβ25-35 toxicity in SH-SY5Y cells. The effect of the EAF of S. adstringens on mitochondrial membrane potential, lipid peroxidation, superoxide production and mRNA expression of 10 genes related to AD was also evaluated and the electropherogram fingerprints of EAFs were established by capillary electrophoresis. Chemometric tools were used to correlate the in vitro activities of the samples with their potential to be evaluated against AD and to divide extracts/fractions into four clusters. Pretreatment with the EAFs grouped in cluster 1 (S. adstringens, P. pluviosa and L. brasiliense) protected SH-SY5Y cells from Aβ25-35-induced toxicity. The EAF of S. adstringens at 15.62 μg/mL was able completely to inhibit the mitochondrial depolarization (69%), superoxide production (49%) and Aβ25-35-induced lipid peroxidation (35%). With respect to mRNA expression, the EAF of S. adstringens also prevented the MAPT mRNA overexpression (expression ratio of 2.387x) induced by Aβ25-35, which may be related to tau protein hyperphosphorylation. This is the first time that the neuroprotective effects of these fractions have been demonstrated and that the electropherogram fingerprints for the EAFs of G. ulmifolia, L. brasiliense, P. cupana, P. pluviosa and S. adstringens have been established. The study expands knowledge of the in vitro protective effects and quality control of the evaluated fractions.

Lignans from the seeds of Chinese hawthorn (Crataegus pinnatifida var. major N.E.Br.) against β-amyloid aggregation

Phytochemical investigation on the seeds of hawthorn (Crataegus spp.) led to the isolation of a new compound, (7'R, 8'R, 8S)-isolariciresinol (1), along with six known compounds (2-7). The structures of all compounds were determined based on spectroscopic data interpretation. The Aβ_1-42 inhibition activity of all isolated compounds was evaluated in vitro. As a result, compounds 5 and 6 showed stronger inhibition of Aβ_1-42 aggregation than curcumin, with inhibition rates of 70.59 and 68.14% at 20 μM. The possible mechanism of interaction between Aβ_1-42 and the active compounds 5 and 6 was also investigated by molecular docking.