In situ fibrillizing amyloid-beta 1-42 induces neurite degeneration and apoptosis of differentiated SH-SY5Y cells

BDNF/proBDNF Interplay in the Mediation of Neuronal Apoptotic Mechanisms in Neurodegenerative Diseases

The neurotrophic system includes neurotrophins, such as brain-derived neurotrophic factor (BDNF) and its precursor proBDNF, which play conflicting roles in neuronal survival and apoptosis, with their balance having a significant impact on neurodegenerative outcomes. While BDNF is widely acknowledged as a potent neurotrophin that promotes neuronal survival and differentiation, its precursor, proBDNF, has the opposite effect, promoting apoptosis and neuronal death. This review highlights the new and unique aspects of BDNF/proBDNF interaction in the modulation of neuronal apoptotic pathways in neurodegenerative disorders. It systematically discusses the cross-talk in apoptotic signaling at the molecular level, whereby BDNF activates survival pathways such as PI3K/Akt and MAPK/ERK, whereas proBDNF activates p75NTR and sortilin to induce neuronal apoptosis via JNK, RhoA, NFkB, and Rac-GTPase pathways such as caspase activation and mitochondrial injury. Moreover, this review emphasizes the factors that affect the balance between proBDNF and BDNF levels within the context of neurodegeneration, including proteolytic processing, the expression of TrkB and p75NTR receptors, and extrinsic gene transcription regulators. Cellular injury, stress, or signaling pathway alterations can disrupt the balance of BDNF/proBDNF, which may be involved in apoptotic-related neurodegenerative diseases like Alzheimer's, Parkinson's, and Huntington's diseases. This review provides a comprehensive framework for targeting neurotrophin signaling in the development of innovative therapies for neuronal survival and managing apoptotic-related neurodegenerative disorders, addressing the mechanistic complexity and clinical feasibility of BDNF/proBDNF interaction.

Nootropic foods in neurodegenerative diseases: mechanisms, challenges, and future

Neurodegenerative diseases (NDDs) such as Alzheimer's and Parkinson's disease are increasing globally and represent a significant cause of age-related death in the population. Recent studies emphasize the strong association between environmental stressors, particularly dietary factors, and brain health and neurodegeneration unsatisfactory outcomes. Despite ongoing efforts, the efficiency of current treatments for NDDs remains wanting. Considering this, nootropic foods with neuroprotective effects are of high interest as part of a possible long-term therapeutic strategy to improve brain health and alleviate NDDs. However, since it is a new and emerging area in food and neuroscience, there is limited information on mechanisms and challenges to consider for this to be a successful intervention. Here, we seek to address these gaps by presenting a comprehensive review of possible pathways or mechanisms including mutual interactions governing nootropic food metabolism, linkages of the pathways with NDDs, intake, and neuroprotective properties of nootropic foods. We also discuss in-depth intervention with nootropic compounds and dietary patterns in NDDs, providing a detailed exploration of their mechanisms of action. Additionally, we analyze the demand, challenges, and future directions for successful development of nootropic foods targeting NDDs.

From protective enzyme to facilitator of amyloid propagation: Cathepsin D-mediated amyloid fibril fragmentation

Amyloid fibrils, linked to severe pathologies such as neurodegenerative diseases, pose a significant challenge to modern medicine. Lysosomal proteases, particularly cathepsins, have attracted attention for their potential role in modulating amyloid pathologies, especially in the context of immunotherapy. However, the impact of these proteases on mature amyloids remains poorly understood. This study investigates the effects of cathepsin D (CTSD), a lysosomal aspartyl protease, on mature amyloid fibrils associated with local insulin and systemic lysozyme amyloidoses, as well as neurodegenerative Alzheimer's and Parkinson's diseases. Our results demonstrate that CTSD induces fragmentation of all examined fibril types, presumably by disrupting hydrogen bonds between the beta-strands forming the fibril backbone. This fragmentation occurs without depolymerizing or destructuring the amyloids and does not reduce their toxic effects on immortalized and primary cell lines. Furthermore, the size, structure, and properties of CTSD-induced amyloid degradation products suggest that the enzyme may contribute to the rapid accumulation and propagation of pathological amyloids at both intercellular and tissue levels in mammals. This finding is valuable for understanding physiological processes and developing immunotherapeutic strategies, as artificially stimulating the immune response may exacerbate pathological conditions.

Disruption of Copper Redox Balance and Dysfunction under In Vivo and In Vitro Alzheimer's Disease Models

Alzheimer's disease (AD) is a neurodegenerative disorder disease mainly caused by extracellular senile plaques (SP) formed by β-amyloid (Aβ1-42) protein deposits. Copper (Cu) is an essential metal involved in neural system, and its homeostasis is the key to maintain its proper function. Herein, the subcellular locations of Cu(I) and Cu(II) in human neurodegenerative disease SH-SY5Y cells and AD mouse brains were imaged. We found that the content of Cu(II) decreased while that of Cu(I) increased under Aβ exposure, which were further verified in the brain tissues of the AD mouse model, strongly suggesting the disruption of Cu homeostasis under Aβ exposure or AD. Remarkably, the mitochondrial and lysosomal Cu(II) decreased significantly, whereas Cu(I) decreased in mitochondria but increased in lysosome. Lysosomes digested the damaged mitochondria via mitophagy to remove excess Cu(I) and maintain Cu homeostasis. The Aβ induced Cu(I) in mitochondria resulted in an overformation of reactive oxygen species and altered the morphology of this organelle. Due to the oxidative stress, glutathione (GSH) was converted into glutathione disulfide (GSSG), and Cu(I) bound with GSH was further released into the cytoplasm and absorbed by the lysosome. Transcriptomic analysis showed that genes (ATP7A/B) related to Cu transportation were upregulated, whereas genes related to mitochondrial complex were down-regulated, representing the damage of this organelle. This study demonstrated that Aβ exposure caused the disruption of intracellular homeostasis by reducing Cu(II) to Cu(I) and damaging the mitochondria, which further triggered detoxification by the lysosome. Our finding provided new insights in Aβ and AD induced Cu redox transformation and toxicity.

Targeting necroptosis in Alzheimer's disease: can exercise modulate neuronal death?

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by cognitive decline and neuronal degeneration. Emerging evidence implicates necroptosis in AD pathogenesis, driven by the RIPK1-RIPK3-MLKL pathway, which promotes neuronal damage, inflammation, and disease progression. Exercise, as a non-pharmacological intervention, can modulate key inflammatory mediators such as TNF-α, HMGB1, and IL-1β, thereby inhibiting necroptotic signaling. Additionally, exercise enhances O-GlcNAc glycosylation, preventing Tau hyperphosphorylation and stabilizing neuronal integrity. This review explores how exercise mitigates necroptosis and neuroinflammation, offering novel therapeutic perspectives for AD prevention and management.

Neuroprotective Effects of Dehydroepiandrosterone Sulphate Against Aβ Toxicity and Accumulation in Cellular and Animal Model of Alzheimer's Disease

Background/Objectives: Beneficial effects of neurosteroid dehydroepiandrosterone sulphate (DHEAS) on cognition, emotions and behavior have been previously reported, suggesting its potential in the prevention and treatment of various neuropsychiatric and neurodegenerative disorders, including Alzheimer's disease (AD). This study aimed to investigate the potential neuroprotective actions of DHEAS against Aβ toxicity in both cellular and animal models of AD. Methods: After optimizing the AD model in vitro, we investigated the DHEAS effects on the viability and death of primary mouse neurons exposed to toxic Aβ42 oligomers for 24 h. In order to extend our research to an in vivo study, we further tested the acute effects of intraperitoneal DHEAS administration on the Aβ plaque density in different brain regions of 3xTg-AD mice, an animal model of AD. Results: In cell culture, DHEAS hampered the decrease in the neuronal viability caused by toxic Aβ oligomers, primarily by influencing mitochondrial function and apoptosis. DHEAS also counteracted the increase in the mRNA expression of selected genes (PI3K, Akt, Bcl2, Bax), induced in neuronal culture by treatment with Aβ42 oligomers. Obtained data suggested the involvement of mitochondria, caspases 3 and 7, as well as the PI3K/Akt and Bcl2 signaling network in the antiapoptotic properties of DHEAS in neurons. Forty-eight hours after DHEAS treatment, a significantly lower number of Aβ plaques was observed in the motor cortex but not in other brain areas of 3xTg-AD mice. Conclusions: Results indicated potential neuroprotective effects of DHEAS against Aβ toxicity and accumulation, suggesting that DHEAS supplementation should be further studied as a novel option for AD prevention and/or treatment.

The Aβ42:Aβ40 ratio modulates aggregation in beta-amyloid oligomers and drives metabolic changes and cellular dysfunction

The pathophysiological role of Aβ42 oligomers in the onset of Alzheimer's disease (AD) is heavily disputed, pivoting research toward investigating mixed oligomers composed of Aβ42 and Aβ40, which is more abundant but less aggregation-prone. This study investigates Aβ42:Aβ40 oligomers in different ratios, examining their adverse effects on endothelial cells, neurons, astroglia, and microglia, as well as in a human blood-brain barrier (BBB) model. Combining label-free Raman microscopy with complementary imaging techniques and biochemical assays, we show the prominent impact of Aβ40 on Aβ42 fibrillation, suggesting an inhibitory effect on aggregation. Mixed oligomers, especially with low proportions of Aβ42, were equally detrimental as pure Aβ42 oligomers regarding cell viability, functionality, and metabolism. They also differentially affected lipid droplet metabolism in BBB-associated microglia, indicating distinct pathophysiological responses. Our findings demonstrate the overarching significance of the Aβ42:Aβ40 ratio in Aβ oligomers, challenging the traditional focus on Aβ42 in AD research.

Effect of Low-Frequency, Low-Energy Pulsed Electromagnetic Fields in Neuronal and Microglial Cells Injured with Amyloid-Beta

Alzheimer's disease (AD) is a neurodegenerative pathology covering about 70% of all cases of dementia. It is associated with neuroinflammation and neuronal cell death, which are involved in disease progression. There is a lack of effective therapies, and halting this process represents a therapeutic challenge. Data in the literature suggest several neuroprotective effects of low-frequency, low-energy pulsed electromagnetic fields (PEMFs) on biological systems, and clinical studies report that PEMF stimulation is safe and well tolerated. The aim of this work is to investigate the effects of PEMF exposure on oxidative stress and cell death in in vitro-injured cellular models of neurons and microglia. SH-SY5Y cells were stimulated by hydrogen peroxide (H2O2) or amyloid-β (Aβ) peptide, and N9 microglial cells were activated with lipopolysaccharide (LPS) or Aβ peptide. Reactive oxygen production, mitochondrial integrity, and cell death modulation were investigated through 2',7'-dichlorodihydrofluorescein diacetate (H2DCFDA) and 5,5',6,6'-tetrachloro-1,1',3,3'-tetraethylbenzimidazolocarbo-cyanine iodide (JC-1) biochemical assays, fluorescence, and MTS experiments. Cells were exposed to PEMFs producing a pulsed signal with the following parameters: pulse duration of 1.3 ms and frequency of 75 Hz. The outcomes demonstrated that PEMFs defended SH-SY5Y cells against Aβ peptide- or H2O2-induced oxidative stress, mitochondrial damage, and cell death. Furthermore, in microglia activated by LPS or Aβ peptide, they reverted the reduction in mitochondrial potential, oxidative damage, and cell death. Overall, these findings imply that PEMFs influence the redox state of the cells by significantly boosting antioxidant levels in both injured microglia and neuronal in vitro cells mimicking in vitro AD.

Different amyloid β42 preparations induce different cell death pathways in the model of SH-SY5Y neuroblastoma cells

Amyloid β42 (Aβ42) plays a decisive role in the pathology of Alzheimer's disease. The Aβ42 peptide can aggregate into various supramolecular structures, with oligomers being the most toxic form. However, different Aβ species that cause different effects have been described. Many cell death pathways can be activated in connection with Aβ action, including apoptosis, necroptosis, pyroptosis, oxidative stress, ferroptosis, alterations in mitophagy, autophagy, and endo/lysosomal functions. In this study, we used a model of differentiated SH-SY5Y cells and applied two different Aβ42 preparations for 2 and 4 days. Although we found no difference in the shape and size of Aβ species prepared by two different methods (NaOH or NH4OH for Aβ solubilization), we observed strong differences in their effects. Treatment of cells with NaOH-Aβ42 mainly resulted in damage of mitochondrial function and increased production of reactive oxygen species, whereas application of NH4OH-Aβ42 induced necroptosis and first steps of apoptosis, but also caused an increase in protective Hsp27. Moreover, the two Aβ42 preparations differed in the mechanism of interaction with the cells, with the effect of NaOH-Aβ42 being dependent on monosialotetrahexosylganglioside (GM1) content, whereas the effect of NH4OH-Aβ42 was independent of GM1. This suggests that, although both preparations were similar in size, minor differences in secondary/tertiary structure are likely to strongly influence the resulting processes. Our work reveals, at least in part, one of the possible causes of the inconsistency in the data observed in different studies on Aβ-toxicity pathways.

Liposomal Formulations of Anti-Alzheimer Drugs and siRNA for Nose-to-Brain Delivery: Design, Safety and Efficacy In Vitro

β-site amyloid precursor protein cleaving enzyme (BACE1) represents a key target for Alzheimer's disease (AD) therapy because it is essential for producing the toxic amyloid β (Aβ) peptide that plays a crucial role in the disease's development. BACE1 inhibitors are a promising approach to reducing Aβ levels in the brain and preventing AD progression. However, systemic delivery of such inhibitors to the brain demonstrates limited efficacy because of the presence of the blood-brain barrier (BBB). Nose-to-brain (NtB) delivery has the potential to overcome this obstacle. Liposomal drug delivery systems offer several advantages over traditional methods for delivering drugs and nucleic acids from the nose to the brain. The current study aims to prepare, characterize, and evaluate in vitro liposomal forms of donepezil, memantine, BACE-1 siRNA, and their combination for possible treatment of AD via NtB delivery. All the liposomal formulations were prepared using the rotary evaporation method. Their cellular internalization, cytotoxicity, and the suppression of beta-amyloid plaque and other pro-inflammatory cytokine expressions were studied. The Calu-3 Transwell model was used as an in vitro system for mimicking the anatomical and physiological conditions of the nasal epithelium and studying the suitability of the proposed formulations for possible NtB delivery. The investigation results show that liposomes provided the effective intracellular delivery of therapeutics, the potential to overcome tight junctions in BBB, reduced beta-amyloid plaque accumulation and pro-inflammatory cytokine expression, supporting the therapeutic potential of our approach.

Neuroprotective Potential of Photobiomodulation Therapy: Mitigating Amyloid-Beta Accumulation and Modulating Acetylcholine Levels in an In Vitro Model of Alzheimer's Disease

Objective: To investigate the effects of photobiomodulation therapy (PBMT) at 660 and 810 nm on amyloid-beta (Aβ)42-induced toxicity in differentiated SH-SY5Y cells and to assess its impact on Aβ42 accumulation and cholinergic neurotransmission. Background: Alzheimer's disease (AD) is characterized by the accumulation of Aβ peptides, leading to neurodegeneration, cholinergic deficit, and cognitive decline. PBMT has emerged as a potential therapeutic approach to mitigate Aβ-induced toxicity and enhance cholinergic function. Methods: Differentiated neurons were treated with 1 μM Aβ42 for 1 day, followed by daily PBMT at wavelengths of 660 and 810 nm for 7 days. Treatments used LEDs emitting continuous wave light at a power density of 5 mW/cm2 for 10 min daily to achieve an energy density of 3 J/cm2. Results: Differentiated SH-SY5Y cells exhibited increased Aβ42 aggregation, neurite retraction, and reduced cell viability. PBMT at 810 nm significantly mitigated the Aβ42-induced toxicity in these cells, as evidenced by reduced Aβ42 aggregation, neurite retraction, and improved cell viability and neuronal morphology. Notably, this treatment also restored acetylcholine levels in the neurons exposed to Aβ42. Conclusions: PBMT at 810 nm effectively reduces Aβ42-induced toxicity and supports neuronal survival, highlighting its neuroprotective effects on cholinergic neurons. By shedding light on the impact of low-level light therapy on Aβ42 accumulation and cellular processes. These findings advocate for further research to elucidate the mechanisms of PBMT and validate its clinical relevance in AD management.

Brain Slice Derived Nerve Fibers Grow along Microcontact Prints and are Stimulated by Beta-Amyloid(42)

BACKGROUND

Alzheimer's disease is characterized by extracellular beta-amyloid plaques, intraneuronal tau neurofibrillary tangles and excessive neurodegeneration. The mechanisms of neuron degeneration and the potential of these neurons to form new nerve fibers for compensation remain elusive. The present study aimed to evaluate the impact of beta-amyloid and tau on new formations of nerve fibers from mouse organotypic brain slices connected to collagen-based microcontact prints.

METHODS

Organotypic brain slices of postnatal day 8-10 wild-type mice were connected to established collagen-based microcontact prints loaded with polyornithine to enhance nerve fiber outgrowth. Human beta-amyloid(42) or P301S mutated aggregated tau was co-loaded to the prints. Nerve fibers were immunohistochemically stained with neurofilament antibodies. The physiological activity of outgrown neurites was tested with neurotracer MiniRuby, voltage-sensitive dye FluoVolt, and calcium-sensitive dye Rhod-4.

RESULTS

Immunohistochemical staining revealed newly formed nerve fibers extending along the prints derived from the brain slices. While collagen-only microcontact prints stimulated nerve fiber growth, those loaded with polyornithine significantly enhanced nerve fiber outgrowth. Beta-amyloid(42) significantly increased the neurofilament-positive nerve fibers, while tau had only a weak effect. MiniRuby crystals, retrogradely transported along these newly formed nerve fibers, reached the hippocampus, while FluoVolt and Rhod-4 monitored electrical activity in newly formed nerve fibers.

CONCLUSIONS

Our data provide evidence that intact nerve fibers can form along collagen-based microcontact prints from mouse brain slices. The Alzheimer's peptide beta-amyloid(42) stimulates this growth, hinting at a neuroprotective function when physiologically active. This "brain-on-chip" model may offer a platform for screening bioactive factors or testing drug effects on nerve fiber growth.

Identification of a novel oligopeptide from defatted walnut meal hydrolysate as a potential neuroprotective agent

Free radical damage and oxidative stress are thought to play a crucial role in the development of neurodegenerative diseases. Walnut peptides, especially walnut oligopeptides, have been shown to protect nerve cells from oxidative stress and inflammatory damage, as well as improve memory function. In this study, walnut peptides were obtained from walnut meal through enzymatic hydrolysis, ultrafiltration, and gel filtration chromatography. A novel oligopeptide called AQ was successfully isolated and its chemical structure was identified as AASCDQ using ESI-MS/MS. AQ demonstrated remarkable scavenging activity against O2- free radicals (81.00%), DPPH free radicals (79.40%), and ABTS free radicals (67.09%) at a concentration of 1 mg mL-1. Furthermore, AQ exhibited strong neuroprotective effects against hydrogen peroxide-induced damage in SH-SY5Y cells, reducing cell injury and apoptosis. AQ also effectively inhibited the secretion of pro-inflammatory factors NO (IC50 = 46.03 ± 0.32 μM) and suppressed the expression of IL-6 and TNF-α in RAW264.7 cells stimulated by LPS. In vivo experiments demonstrated that AQ promoted angiogenesis in the quail chick chorioallantoic membrane assay and reduced ROS accumulation in Caenorhabditis elegans, thereby extending its lifespan. The anti-inflammatory mechanism of AQ was further confirmed by western blotting. In summary, the novel oligopeptide AQ possesses potential neuroprotective effects, including antioxidant, anti-inflammatory, angiogenic, and anti-aging properties, making it a promising candidate for the development of functional foods and pharmaceutical products.

Death Induced by Survival gene Elimination (DISE) correlates with neurotoxicity in Alzheimer's disease and aging

Alzheimer's disease (AD) is characterized by progressive neurodegeneration, but the specific events that cause cell death remain poorly understood. Death Induced by Survival gene Elimination (DISE) is a cell death mechanism mediated by short (s) RNAs acting through the RNA-induced silencing complex (RISC). DISE is thus a form of RNA interference, in which G-rich 6mer seed sequences in the sRNAs (position 2-7) target hundreds of C-rich 6mer seed matches in genes essential for cell survival, resulting in the activation of cell death pathways. Here, using Argonaute precipitation and RNAseq (Ago-RP-Seq), we analyze RISC-bound sRNAs to quantify 6mer seed toxicity in several model systems. In mouse AD models and aging brain, in induced pluripotent stem cell-derived neurons from AD patients, and in cells exposed to Aβ42 oligomers, RISC-bound sRNAs show a shift to more toxic 6mer seeds compared to controls. In contrast, in brains of "SuperAgers", humans over age 80 who have superior memory performance, RISC-bound sRNAs are shifted to more nontoxic 6mer seeds. Cells depleted of nontoxic sRNAs are sensitized to Aβ42-induced cell death, and reintroducing nontoxic RNAs is protective. Altogether, the correlation between DISE and Aβ42 toxicity suggests that increasing the levels of nontoxic miRNAs in the brain or blocking the activity of toxic RISC-bound sRNAs could ameliorate neurodegeneration.

APPI-Derived Cyclic Peptide Enhances Aβ42 Aggregation and Reduces Aβ42-Mediated Membrane Destabilization and Cytotoxicity

An amyloid precursor protein inhibitor (APPI) and amyloid beta 42 (Aβ42) are both subdomains of the human transmembrane amyloid precursor protein (APP). In the brains of patients with Alzheimer's disease (AD), Aβ42 oligomerizes into aggregates of various sizes, with intermediate, low-molecular-weight Aβ42 oligomers currently being held to be the species responsible for the most neurotoxic effects associated with the disease. Strategies to ameliorate the toxicity of these intermediate Aβ42 oligomeric species include the use of short, Aβ42-interacting peptides that either inhibit the formation of the Aβ42 oligomeric species or promote their conversion to high-molecular-weight aggregates. We therefore designed such an Aβ42-interacting peptide that is based on the β-hairpin amino acid sequence of the APPI, which exhibits high similarity to the β-sheet-like aggregation site of Aβ42. Upon tight binding of this 20-mer cyclic peptide to Aβ42 (in a 1:1 molar ratio), the formation of Aβ42 aggregates was enhanced, and consequently, Aβ42-mediated cell toxicity was ameliorated. We showed that in the presence of the cyclic peptide, interactions of Aβ42 with both plasma and mitochondrial membranes and with phospholipid vesicles that mimic these membranes were inhibited. Specifically, the cyclic peptide inhibited Aβ42-mediated mitochondrial membrane depolarization and reduced Aβ42-mediated apoptosis and cell death. We suggest that the cyclic peptide modulates Aβ42 aggregation by enhancing the formation of large aggregates─as opposed to low-molecular-weight intermediates─and as such has the potential for further development as an AD therapeutic.

Attenuation Aβ1-42-induced neurotoxicity in neuronal cell by 660nm and 810nm LED light irradiation

Oligomeric amyloid-β 1-42 (Aβ1-42) has a close correlation with neurodegenerative disorder especially Alzheimer's disease (AD). It induces oxidative stress and mitochondrial damage in neurons. Therefore, it is used to generate AD-like in vitro model for studying neurotoxicity and neuroprotection against amyloid-β. A low-level light therapy (LLLT) is a non-invasive method that has been used to treat several neurodegenerative disorders. In this study, the red wavelength (660nm) and near infrared wavelength (810nm) at energy densities of 1, 3, and 5 J/cm2 were used to modulate biochemical processes in the neural cells. The exposure of Aβ1-42 resulted in cell death, increased intracellular reactive oxygen species (ROS), and retracted neurite outgrowth. We showed that both of LLLT wavelengths could protect neurons form Aβ1-42-induced neurotoxicity in a biphasic manner. The treatment of LLLT at 3 J/cm2 potentially alleviated cell death and recovered neurite outgrowth. In addition, the treatment of LLLT following Aβ1-42 exposure could attenuate the intracellular ROS generation and Ca2+ influx. Interestingly, both wavelengths could induce minimal level of ROS generation. However, they did not affect cell viability. In addition, LLLT also stimulated Ca2+ influx, but not altered mitochondrial membrane potential. This finding indicated LLLT may protect neurons through the stimulation of secondary signaling messengers such as ROS and Ca2+. The increase of these secondary messengers was in a functional level and did not harmful to the cells. These results suggested the use of LLLT as a tool to modulate the neuronal toxicity following Aβ1-42 accumulation in AD's brain.

Ganglioside GM1 produces stable, short, and cytotoxic Aβ40 protofibrils

Monosialoganglioside GM1-bound amyloid β-peptides have been found in patients' brains exhibiting early pathological changes of Alzheimer's disease. Herein, we report the ability of non-micellar GM1 to modulate Aβ40 aggregation resulting in the formation of stable, short, rod-like, and cytotoxic Aβ40 protofibrils with the ability to potentiate both Aβ40 and Aβ42 aggregation.

Probing differences among Aβ oligomers with two triangular trimers derived from Aβ

The assembly of the β-amyloid peptide (Aβ) to form oligomers and fibrils is closely associated with the pathogenesis and progression of Alzheimer's disease. Aβ is a shape-shifting peptide capable of adopting many conformations and folds within the multitude of oligomers and fibrils the peptide forms. These properties have precluded detailed structural elucidation and biological characterization of homogeneous, well-defined Aβ oligomers. In this paper, we compare the structural, biophysical, and biological characteristics of two different covalently stabilized isomorphic trimers derived from the central and C-terminal regions Aβ. X-ray crystallography reveals the structures of the trimers and shows that each trimer forms a ball-shaped dodecamer. Solution-phase and cell-based studies demonstrate that the two trimers exhibit markedly different assembly and biological properties. One trimer forms small soluble oligomers that enter cells through endocytosis and activate capase-3/7-mediated apoptosis, while the other trimer forms large insoluble aggregates that accumulate on the outer plasma membrane and elicit cellular toxicity through an apoptosis-independent mechanism. The two trimers also exhibit different effects on the aggregation, toxicity, and cellular interaction of full-length Aβ, with one trimer showing a greater propensity to interact with Aβ than the other. The studies described in this paper indicate that the two trimers share structural, biophysical, and biological characteristics with oligomers of full-length Aβ. The varying structural, assembly, and biological characteristics of the two trimers provide a working model for how different Aβ trimers can assemble and lead to different biological effects, which may help shed light on the differences among Aβ oligomers.

Protective Role of an Extract Waste Product from Citrus bergamia in an In Vitro Model of Neurodegeneration

A balanced diet, rich in fruits and vegetables and ensuring the intake of natural products, has been shown to reduce or prevent the occurrence of many chronic diseases. However, the choice to consume large quantities of fruits and vegetables leads to an increase in the amount of waste, which can cause an alteration in environmental sustainability. To date, the concept of a "byproduct" has evolved, now being understood as a waste product from which it is still possible obtain useful compounds. Byproducts in the agricultural sector are a rich source of bioactive compounds, capable of possessing a second life, decreasing the amount of waste products, the disposal costs, and environmental pollution. A promising and well-known citrus of the Mediterranean diet is the bergamot (Citrus bergamia, Risso et Poiteau). The composition of bergamot is known, and the rich presence of phenolic compounds and essential oils has justified the countless beneficial properties found, including anti-inflammatory, antioxidant, anti-cholesterolemic, and protective activity for the immune system, heart failure, and coronary heart diseases. The industrial processing of bergamot fruits leads to the formation of bergamot juice and bergamot oil. The solid residues, referred to as "pastazzo", are normally used as feed for livestock or pectin production. The fiber of bergamot (BF) can be obtained from pastazzo and could exert an interesting effect thanks to its content of polyphenols. The aims of this work were twofold: (a) to have more information (composition, polyphenol and flavonoid content, antioxidant activity, etc.) on BF powder and (b) to verify the effects of BF on an in vitro model of neurotoxicity induced by treatment with amyloid beta protein (Aβ). In particular, a study of cell lines was carried out on both neurons and oligodendrocytes, to measure the involvement of the glia and compare it with that of the neurons. The results obtained showed that BF powder contains polyphenols and flavonoids and that it is able to exercise an antioxidant property. Moreover, BF exerts a protective action on the damage induced by treatment with Aβ, and this defense is found in experiments on the cell viability, on the accumulation of reactive oxygen species, on the involvement of the expression of caspase-3, and on necrotic or apoptotic death. In all these results, oligodendrocytes were always more sensitive and fragile than neurons. Further experiments are needed, and if this trend is confirmed, BF could be used in AD; at the same time, it could help to avoid the accumulation of waste products.

GLUT inhibitor WZB117 induces cytotoxicity with increased production of amyloid-beta peptide in SH-SY5Y cells preventable by beta-hydroxybutyrate: implications in Alzheimer's disease

BACKGROUND

Inhibitors of glucose transporters are being explored as potential anti-cancer drugs. Decreased cerebral glucose utilization with reduced levels of several glucose transporters is also an important pathogenic signature of neurodegeneration of Alzheimer's disease, but its exact role in the pathogenesis of this disease is not established. We explored in an experimental model if inhibitors of glucose transporters could lead to altered amyloid-beta homeostasis, mitochondrial dysfunction, and neuronal death, which are relevant in the pathogenesis of Alzheimer's disease.

METHODS

SH-SY5Y cells (human neuroblastoma cell line) were exposed to an inhibitor (WZB117) of several types of glucose transporters. We examined the effects of glucose hypometabolism on SH-SY5Y cells in terms of mitochondrial functions, production of reactive oxygen species, amyloid-beta homeostasis, and neural cell death. The effect of β-hydroxybutyrate in ameliorating the effects of WZB117 on SH-SY5Y cells was also examined.

RESULTS

We observed that exposure of SH-SY5Y cells to WZB117 caused mitochondrial dysfunction, increased production of reactive oxygen species, loss of cell viability, increased expression of BACE 1, and intracellular accumulation of amyloid β peptide (Aβ42). All the effects of WZB117 could be markedly prevented by co-treatment with β-hydroxybutyrate. Cyclosporine A, a blocker of mitochondrial permeability transition pore (mPTP) activation, could not prevent cell death caused by WZB117.

CONCLUSION

Results in this neuroblastoma model have implications for the pathogenesis of Alzheimer's disease and warrant further explorations of WZB117 in primary cultures of neurons and experimental animal models.

Identification of a Novel Wnt Antagonist Based Therapeutic and Diagnostic Target for Alzheimer's Disease Using a Stem Cell-Derived Model

Currently, all the existing treatments for Alzheimer's disease (AD) fail to stall progression due to longer duration of time between onset of the symptoms and diagnosis of the disease, raising the necessity of effective diagnostics and novel treatment. Specific molecular regulation of the onset and progression of disease is not yet elucidated. This warranted investigation of the role of Wnt signaling regulators which are thought to be involved in neurogenesis. The AD model was established using amyloid beta (Aβ) in human mesenchymal stem cells derived from amniotic membranes which were differentiated into neuronal cell types. In vivo studies were carried out with Aβ or a Wnt antagonist, AD201, belonging to the sFRP family. We further created an AD201-knockdown in vitro model to determine the role of Wnt antagonism. BACE1 upregulation, ChAT and α7nAChR downregulation with synapse and functionality loss with increases in ROS confirmed the neurodegeneration. Reduced β-catenin and increased AD201 expression indicated Wnt/canonical pathway inhibition. Similar results were exhibited in the in vivo study along with AD-associated behavioural and molecular changes. AD201-knockdown rescued neurons from Aβ-induced toxicity. We demonstrated for the first time a role of AD201 in Alzheimer's disease manifestation, which indicates a promising disease target and biomarker.

Perphenazine-Macrocycle Conjugates Rapidly Sequester the Aβ42 Monomer and Prevent Formation of Toxic Oligomers and Amyloid

Alzheimer's disease is imposing a growing social and economic burden worldwide, and effective therapies are urgently required. One possible approach to modulation of the disease outcome is to use small molecules to limit the conversion of monomeric amyloid (Aβ42) to cytotoxic amyloid oligomers and fibrils. We have synthesized modulators of amyloid assembly that are unlike others studied to date: these compounds act primarily by sequestering the Aβ42 monomer. We provide kinetic and nuclear magnetic resonance data showing that these perphenazine conjugates divert the Aβ42 monomer into amorphous aggregates that are not cytotoxic. Rapid monomer sequestration by the compounds reduces fibril assembly, even in the presence of pre-formed fibrillar seeds. The compounds are therefore also able to disrupt monomer-dependent secondary nucleation, the autocatalytic process that generates the majority of toxic oligomers. The inhibitors have a modular design that is easily varied, aiding future exploration and use of these tools to probe the impact of distinct Aβ42 species populated during amyloid assembly.

Optical Nanosensor for Intracellular and Intracranial Detection of Amyloid-Beta

Amyloid-beta (Aβ) deposition occurs in the early stages of Alzheimer's disease (AD), but the early detection of Aβ is a persistent challenge. Herein, we engineered a near-infrared optical nanosensor capable of detecting Aβ intracellularly in live cells and intracranially in vivo. The sensor is composed of single-walled carbon nanotubes functionalized with Aβ wherein Aβ-Aβ interactions drive the response. We found that the Aβ nanosensors selectively responded to Aβ via solvatochromic modulation of the near-infrared emission of the nanotube. The sensor tracked Aβ accumulation in live cells and, upon intracranial administration in a genetic model of AD, signaled distinct responses in aged mice. This technology enables the interrogation of molecular mechanisms underlying Aβ neurotoxicity in the development of AD in living systems.

Passion fruit seed extract protects beta-amyloid-induced neuronal cell death in a differentiated human neuroblastoma SH-SY5Y cell model

Alzheimer's disease (AD) is a progressive neurodegenerative disease with accompanying perceptive disorder. We previously reported that decreasing levels of brain-derived neurotrophic factor (BDNF) promoted beta-amyloid (Aβ)-induced neuronal cell death in neuron-like differentiated SH-SY5Y (ndSH-SY5Y) human neuroblastoma cells in an AD mimic cell model. We investigated the neuroprotective effects of passion fruit seed extract (PFSE) and one of the main stilbene compounds, piceatannol, in an AD cell model using ndSH-SY5Y cells. Both PFSE and piceatannol were found to protect Aβ-induced neurite fragmentation in the cell model (protection efficacy; 34% in PFSE and 36% in piceatannol). In addition, both PFSE and piceatannol suppress Aβ-induced neuronal cell death in the cell model (inhibitory effect; 27% in PFSE and 32% in piceatannol). Our study is the first to report that piceatannol-rich PFSE can repress Aβ-induced neuronal cell death by protecting against neurite fragmentation in the AD human cell model. These findings suggest that piceatannol-rich PFSE can be considered a potentially neuroprotective functional food for both prevention and treatment of AD.

Cell models for Down syndrome-Alzheimer’s disease research

Down syndrome (DS) is the most common chromosomal abnormality and leads to intellectual disability, increased risk of cardiac defects, and an altered immune response. Individuals with DS have an extra full or partial copy of chromosome 21 (trisomy 21) and are more likely to develop early-onset Alzheimer’s disease (AD) than the general population. Changes in expression of human chromosome 21 (Hsa21)-encoded genes, such as amyloid precursor protein (APP), play an important role in the pathogenesis of AD in DS (DS-AD). However, the mechanisms of DS-AD remain poorly understood. To date, several mouse models with an extra copy of genes syntenic to Hsa21 have been developed to characterise DS-AD-related phenotypes. Nonetheless, due to genetic and physiological differences between mouse and human, mouse models cannot faithfully recapitulate all features of DS-AD. Cells differentiated from human-induced pluripotent stem cells (iPSCs), isolated from individuals with genetic diseases, can be used to model disease-related cellular and molecular pathologies, including DS. In this review, we will discuss the limitations of mouse models of DS and how these can be addressed using recent advancements in modelling DS using human iPSCs and iPSC-mouse chimeras, and potential applications of iPSCs in preclinical studies for DS-AD.

Quantification of Neurite Degeneration with Enhanced Accuracy and Efficiency in an In Vitro Model of Parkinson's Disease

Neurite degeneration is associated with early stages of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease (PD), and amyotrophic lateral sclerosis. One method that is commonly used to analyze neurite degeneration involves calculation of a Degeneration Index (DI) following utilization of the Analyze Particles tool of ImageJ to detect neurite fragments in micrographs of cultured cells. However, DI analyses are prone to several types of measurement error, can be time consuming to perform, and are limited in application. Here, we describe an improved method for performing DI analyses. Accuracy of measurements was enhanced through modification of selection criteria for detecting neurite fragments, removal of image artifacts and non-neurite materials from images, and optimization of image contrast. Such enhancements were implemented into an ImageJ macro that enables rapid and fully automated DI analysis of multiple images. The macro features operations for automated removal of cell bodies from micrographs, thus expanding the application of DI analyses to use in experiments involving dissociated cultures. We present experimental findings supporting that, compared with the conventional method, the enhanced analysis method yields measurements with increased accuracy and requires significantly less time to perform. Furthermore, we demonstrate the utility of the method to investigate neurite degeneration in a cell culture model of PD by conducting an experiment revealing the effects of c-Jun N-terminal kinase (JNK) on neurite degeneration induced by oxidative stress in human mesencephalic cells. This improved analysis method may be used to gain novel insight into factors underlying neurite degeneration and the progression of neurodegenerative disorders.

α-Lipoic Acid Has the Potential to Normalize Copper Metabolism, Which Is Dysregulated in Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is an age-dependent progressive neurodegenerative disorder and the most common cause of dementia. The treatment and prevention of AD present immense yet unmet needs. One of the hallmarks of AD is the formation of extracellular amyloid plaques in the brain, composed of amyloid-β (Aβ) peptides. Besides major amyloid-targeting approach there is the necessity to focus also on alternative therapeutic strategies. One factor contributing to the development of AD is dysregulated copper metabolism, reflected in the intracellular copper deficit and excess of extracellular copper.

OBJECTIVE

In the current study, we follow the widely accepted hypothesis that the normalization of copper metabolism leads to the prevention or slowing of the disease and search for new copper-regulating ligands.

METHODS

We used cell culture, ICP MS, and Drosophila melanogaster models of AD.

RESULTS

We demonstrate that the natural intracellular copper chelator, α-lipoic acid (LA) translocates copper from extracellular to intracellular space in an SH-SY5Y-based neuronal cell model and is thus suitable to alleviate the intracellular copper deficit characteristic of AD neurons. Furthermore, we show that supplementation with LA protects the Drosophila melanogaster models of AD from developing AD phenotype by improving locomotor activity of fruit fly with overexpression of human Aβ with Iowa mutation in the fly brain. In addition, LA slightly weakens copper-induced smooth eye phenotype when amyloid-β protein precursor (AβPP) and beta-site AβPP cleaving enzyme 1 (BACE1) are overexpressed in eye photoreceptor cells.

CONCLUSION

Collectively, these results provide evidence that LA has the potential to normalize copper metabolism in AD.

Probing Amyloid β Interactions with Synthetic Heparan Sulfate Oligosaccharides

Heparan sulfate (HS) can play important roles in the biology and pathology of amyloid β (Aβ), a hallmark of Alzheimer's disease. To better understand the structure-activity relationship of HS/Aβ interactions, synthetic HS oligosaccharides ranging from tetrasaccharides to decasaccharides have been utilized to study Aβ interactions. Surface plasmon resonance experiments showed that the highly sulfated HS tetrasaccharides bearing full 2-O, 6-O, and N-sulfations exhibited the strongest binding with Aβ among the tetrasaccharides investigated. Elongating the glycan length to hexa- and deca-saccharides significantly enhanced Aβ affinity compared to the corresponding HS tetrasaccharide. Solid state NMR studies of the complexes of Aβ with HS hexa- and deca-saccharides showed most significant chemical shift perturbation in the C-terminus residues of Aβ. The strong binding HS oligosaccharides could reduce the cellular toxicities induced by Aβ. This study provides new insights into HS/Aβ interactions, highlighting how synthetic structurally well-defined HS oligosaccharides can assist in biological understanding of Aβ.

Myricetin prevents high molecular weight Aβ1-42 oligomer-induced neurotoxicity through antioxidant effects in cell membranes and mitochondria

Excessive accumulation of amyloid β-protein (Aβ) is one of the primary mechanisms that leads to neuronal death with phosphorylated tau in the pathogenesis of Alzheimer's disease (AD). Protofibrils, one of the high-molecular-weight Aβ oligomers (HMW-Aβo), are implicated to be important targets of disease modifying therapy of AD. We previously reported that phenolic compounds such as myricetin inhibit Aβ1-40, Aβ1-42, and α-synuclein aggregations, including their oligomerizations, which may exert protective effects against AD and Parkinson's disease. The purpose of this study was to clarify the detailed mechanism of the protective effect of myricetin against the neurotoxicity of HMW-Aβo in SH-SY5Y cells. To assess the effect of myricetin on HMW-Aβo-induced oxidative stress, we systematically examined the level of membrane oxidative damage by measuring cell membrane lipid peroxidation, membrane fluidity, and cell membrane potential, and the mitochondrial oxidative damage was evaluated by mitochondrial permeability transition (MPT), mitochondrial reactive oxygen species (ROS), and manganese-superoxide dismutase (Mn-SOD), and adenosine triphosphate (ATP) assay in SH-SY5Y cells. Myricetin has been found to increased cell viability by suppression of HMW-Aβo-induced membrane disruption in SH-SY5Y cells, as shown in reducing membrane phospholipid peroxidation and increasing membrane fluidity and membrane resistance. Myricetin has also been found to suppress HMW-Aβo-induced mitochondria dysfunction, as demonstrated in decreasing MPT, Mn-SOD, and ATP generation, raising mitochondrial membrane potential, and increasing mitochondrial-ROS generation. These results suggest that myricetin preventing HMW-Aβo-induced neurotoxicity through multiple antioxidant functions may be developed as a disease-modifying agent against AD.

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

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

Rapid Conversion of Amyloid-Beta 1-40 Oligomers to Mature Fibrils through a Self-Catalytic Bimolecular Process

The formation of fibrillar aggregates of the amyloid beta peptide (Aβ) in the brain is one of the hallmarks of Alzheimer's disease (AD). A clear understanding of the different aggregation steps leading to fibrils formation is a keystone in therapeutics discovery. In a recent study, we showed that Aβ40 and Aβ42 form dynamic micellar aggregates above certain critical concentrations, which mediate a fast formation of more stable oligomers, which in the case of Aβ40 are able to evolve towards amyloid fibrils. Here, using different biophysical techniques we investigated the role of different fractions of the Aβ aggregation mixture in the nucleation and fibrillation steps. We show that both processes occur through bimolecular interplay between low molecular weight species (monomer and/or dimer) and larger oligomers. Moreover, we report here a novel self-catalytic mechanism of fibrillation of Aβ40, in which early oligomers generate and deliver low molecular weight amyloid nuclei, which then catalyze the rapid conversion of the oligomers to mature amyloid fibrils. This fibrillation catalytic activity is not present in freshly disaggregated low-molecular weight Aβ40 and is, therefore, a property acquired during the aggregation process. In contrast to Aβ40, we did not observe the same self-catalytic fibrillation in Aβ42 spheroidal oligomers, which could neither be induced to fibrillate by the Aβ40 nuclei. Our results reveal clearly that amyloid fibrillation is a multi-component process, in which dynamic collisions between different interacting species favor the kinetics of amyloid nucleation and growth.

The modulator action of thiamine against pentylenetetrazole-induced seizures, apoptosis, nitric oxide, and oxidative stress in rats and SH-SY5Y neuronal cell line

Accumulating evidences indicate that thiamine plays a vital role in the nervous system. However, questions exist as to how it causes epilepsy, neuronal damage, and antiepileptic mechanisms. The study looked at how the thiamine supplement impacted pentylenetetrazole (PTZ)-induced seizures in rats and pentylenetetrazole-induced neurotoxicity in the SH-SY5Y cell line. We used twenty-four male rats and they were randomly divided into 4 groups as control, saline (1 mL/kg/day serum physiologic) + PTZ, thiamine (50 mg/kg/day) + PTZ, and thiamine (50 mg/kg/day) for 10 days. PTZ (45 mg/kg) was given to activate the seizure on day 10. Memory efficiency was measured by using passive avoidance. The brain levels of 8-hydroxy-2'-deoxyguanosine (8-OHdG), caspase-3, nitric oxide (NO), and cyclic guanosine monophosphate (cGMP) were analyzed by using ELISA kits. SH-SY5Y cells were treated with/without thiamine for 1 h, followed by PTZ (30 μm) at a medium level to trigger neurotoxicity. Cell viability, total antioxidant status, total oxidant status, and apoptosis were assayed in the SH-SY5Y cells. Thiamine delayed the initiation of epileptic seizures and increased memory damage. In addition, 8-OHdG, caspase-3, NO, and cGMP levels were significantly reduced in the brain and prevented pentylenetetrazole-induced neurotoxicity, apoptosis, enhanced antioxidant, and reduced oxidant in SH-SY5Y cells. Thiamine dramatically altered seizures, memory loss, oxidative stress, and apoptosis. Thiamine has a preventative effect on PTZ-induced seizures in rats and PTZ-induced neurotoxicity in SH-SY5Y neuroblastoma cells. It could prevent oxidative stress and signaling of NO/cGMP. Thiamine supplement could be used as an additional therapeutic agent in epilepsy.

An Analysis of the Neurological and Molecular Alterations Underlying the Pathogenesis of Alzheimer's Disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by amyloid beta (Aβ) plaques, neurofibrillary tangles, and neuronal loss. Unfortunately, despite decades of studies being performed on these histological alterations, there is no effective treatment or cure for AD. Identifying the molecular characteristics of the disease is imperative to understanding the pathogenesis of AD. Furthermore, uncovering the key causative alterations of AD can be valuable in developing models for AD treatment. Several alterations have been implicated in driving this disease, including blood–brain barrier dysfunction, hypoxia, mitochondrial dysfunction, oxidative stress, glucose hypometabolism, and altered heme homeostasis. Although these alterations have all been associated with the progression of AD, the root cause of AD has not been identified. Intriguingly, recent studies have pinpointed dysfunctional heme metabolism as a culprit of the development of AD. Heme has been shown to be central in neuronal function, mitochondrial respiration, and oxidative stress. Therefore, dysregulation of heme homeostasis may play a pivotal role in the manifestation of AD and its various alterations. This review will discuss the most common neurological and molecular alterations associated with AD and point out the critical role heme plays in the development of this disease.

Essential Oils as a Potential Neuroprotective Remedy for Age-Related Neurodegenerative Diseases: A Review

Despite the improvements in life expectancy, neurodegenerative conditions have arguably become the most dreaded maladies of older people. The neuroprotective and anti-ageing potentials of essential oils (EOs) are widely evaluated around the globe. The objective of this review is to analyse the effectiveness of EOs as neuroprotective remedies among the four common age-related neurodegenerative diseases. The literature was extracted from three databases (PubMed, Web of Science and Google Scholar) between the years of 2010 to 2020 using the medical subject heading (MeSH) terms "essential oil", crossed with "Alzheimer's disease (AD)", "Huntington's disease (HD)", "Parkinson's disease (PD)" or "amyotrophic lateral sclerosis (ALS)". Eighty three percent (83%) of the studies were focused on AD, while another 12% focused on PD. No classifiable study was recorded on HD or ALS. EO from Salvia officinalis has been recorded as one of the most effective acetylcholinesterase and butyrylcholinesterase inhibitors. However, only Cinnamomum sp. has been assessed for its effectiveness in both AD and PD. Our review provided useful evidence on EOs as potential neuroprotective remedies for age-related neurodegenerative diseases.

Residue Interaction Network Analysis Predicts a Val24-Ile31 Interaction May be Involved in Preventing Amyloid-Beta (1-42) Primary Nucleation

Alzheimer's disease (AD) patients could benefit from a more effective treatment than the current FDA-approved options. Because amyloid-beta (Aβ) is thought to play a central role in AD pathogenesis, many experimental drugs attempt to reduce Aβ-induced pathology. Preventing amyloid accumulation may be a more effective strategy than clearing Aβ plaques after they form. If preventing Aβ accumulation can treat or prevent AD, then understanding Aβ primary nucleation may aid rational drug design. This study examines Aβ residue interaction networks and reports network and structural observations that may provide insight into primary nucleation. While many studies identify structural features of Aβ that promote aggregation, this study reports features that may resist primary nucleation by examining Aβ42 studies in more and less polar solvents. In Aβ42 in a less polar solvent (PDB ID: 1IYT), Val24 and Ile31 have higher betweenness and residue centrality values. This may be due to a predicted interaction between Val24 and Ile31. Residues in the central hydrophobic cluster (CHC) of Aβ40 and Aβ42 had significantly higher betweenness values compared to the average betweenness of the structures, highlighting the CHC's reported role in oligomerization. The predicted interaction between Val24 and Ile31 may reduce the likelihood of primary nucleation of Aβ.

Low Levels of Brain-Derived Neurotrophic Factor Trigger Self-aggregated Amyloid β-Induced Neuronal Cell Death in an Alzheimer's Cell Model

Alzheimer's disease (AD) is pathologically characterized by accumulation of amyloid β (Aβ) and hyperphosphorylated tau, and thereby induction of neuronal cell death. The Aβ-induced neuronal cell death has been shown to occur by several modes, such as apoptosis, necrosis, and necroptosis. Interestingly, in AD patients, the brain and serum levels of brain-derived neurotrophic factor (BDNF) have been reported to be significantly decreased. However, the relationship between Aβ and BDNF in the onset of AD remains to be fully understood. Here, we used neuron-like differentiated human neuroblastoma SH-SY5Y (ndSH-SY5Y) cells to study the neurotoxicity of self-aggregated Aβ_1-42 peptide under different concentrations of BDNF in the culture medium. Importantly, decreasing levels of BDNF caused a considerable suppression in the extension of neurite length. Furthermore, only under low levels of BDNF, the aggregated Aβ was revealed to induce neurite fragmentation and neuronal cell death in ndSH-SY5Y cells. Notably, the aggregated Aβ and low levels of BDNF-induced neuronal cell death was characterized at least as caspase-6 dependent cell death and necroptosis. These results indicate that our ndSH-SY5Y cell system, cultured under decreasing levels of BDNF and aggregated Aβ, has the potential to be applied in the analysis of the molecular mechanisms of the progressive neurodegenerative processes of AD and the discovery of neuroprotective drug candidates.

Toxicity of Amyloid-β Peptides Varies Depending on Differentiation Route of SH-SY5Y Cells

Alzheimer's disease (AD) is a currently incurable neurodegenerative disorder being the major form of dementia worldwide. AD pathology is initiated by cerebral aggregation of amyloid-β (Aβ) peptides in the form of amyloid plaques; however, the mechanism how Aβ peptide aggregates participate in the disease progression and neurodegeneration is still under debate. Human neuroblastoma cell line SH-SY5Y is a convenient cellular model, which is widely used in biochemical and toxicological studies of neurodegenerative diseases. This model can be further improved by differentiation of the cells toward more neuron-like culture using different protocols. In the current study, dbcAMP, retinoic acid with TPA, or BDNF were used for differentiation of SH-SY5Y cells, and the resulting cultures were tested for the toxicity toward the Aβ42 peptide. The toxicity of Aβ42 peptide depended on the type of differentiated cells: RA and TPA- differentiated cells were most resistant, whereas dbcAMP and RA/BDNF- differentiated cells were more sensitive to Aβ toxicity as compared with non-differentiated cells. The differentiated cultures provide more appropriate cellular models of human origin that can be used for studies of the mechanism of Aβ pathogenesis and for a screening of compounds antagonistic to the toxicity of Aβ peptides.

Assessing Reproducibility in Amyloid β Research: Impact of Aβ Sources on Experimental Outcomes

The difficulty of synthesizing and purifying the amyloid β (Aβ) peptide, combined with its high aggregation propensity and low solubility under physiological conditions, leads to a wide variety of experimental results from kinetic assays to biological activity. Thus, it becomes challenging to reproduce outcomes, and this limits our ability to rely on reported results as the foundation for new research. This article examines variability of the Aβ peptide from different sources, comparing purity, and oligomer and fibril formation propensity side by side. The results highlight the importance of performing rigorous controls so that meaningful biophysical, biochemical, and neurobiological results can be obtained to improve our understanding on Aβ.

Identification and characterization of cytotoxic amyloid-like regions in human Pbx-regulating protein-1

The ability of many proteins to fold into well-defined structures has been traditionally considered a prerequisite for fulfilling their functions. Protein folding is also regarded as a valuable loophole to escape uncontrolled and harmful aggregations. Here we show that the PBX-regulating protein-1 (PREP1), an important homeodomain transcription factor involved in cell growth and differentiation during embryogenesis, is endowed with an uncommon thermostability. Indeed, circular dichroism analyses indicate that it retains most of its secondary structure at very high temperatures. These findings have important implications for PREP1 functions since it is a stabilizing factor of its partner PBX1. Predictive analyses suggest that the observed PREP1 thermostability could be related to the presence of aggregation-prone regions. Interestingly, synthetic peptides corresponding to these regions exhibit a remarkable propensity to form toxic β-rich amyloid-like aggregates in physiological conditions. On this basis, we suggest that PREP1 stability is an effective way to prevent or limit the formation of harmful aggregates. Notably, one of these PREP1 fragments (residues 117-132) is able to reversibly switch from α-helical to β-rich states depending on the environmental conditions. The chameleon conformational behavior of this peptide makes it an ideal system to study this intriguing and widespread structural transition.

Anticholinergic Drugs Interact With Neuroprotective Chaperone L-PGDS and Modulate Cytotoxicity of Aβ Amyloids

Anticholinergic drugs can be used as a treatment for many diseases. However, anticholinergic drugs are also known for their cognition-related side effects. Recently, there has been an increasing number of reports indicating a positive association between exposure to anticholinergic drugs and Alzheimer's disease (AD). Our novel study provides evidence of interactions between two representative anticholinergic drugs [Chlorpheniramine (CPM), a common antihistamine, and Trazodone (TRD), an antidepressant] with neuroprotective amyloid-beta (Aβ) chaperone, lipocalin-type prostaglandin D synthase (L-PGDS) and the amyloid beta-peptide (1–40). Here, we demonstrate that CPM and TRD bind to L-PGDS with high affinity where chlorpheniramine exhibited higher inhibitory effects on L-PGDS as compared to Trazodone. We also show that the interactions between the drug molecules and Aβ(1–40) peptides result in a higher fibrillar content of Aβ(1–40) fibrils with altered fibril morphology. These altered fibrils possess higher cytotoxicity compared to Aβ(1–40) fibrils formed in the absence of the drugs. Overall, our data suggest a mechanistic link between exposure to anticholinergic drugs and increased risk of Alzheimer's disease via inhibition of the neuroprotective chaperone L-PGDS and direct modification of Aβ amyloid morphology and cytotoxicity.

Three-dimensional real time imaging of amyloid β aggregation on living cells

Alzheimer’s disease (AD) is a progressive disorder of the brain that gradually decreases thinking, memory, and language abilities. The aggregation process of amyloid β (Aβ) is a key step in the expression of its neurocytotoxicity and development of AD because Aβ aggregation and accumulation around neuronal cells induces cell death. However, the molecular mechanism underlying the neurocytotoxicity and cell death by Aβ aggregation has not been clearly elucidated. In this study, we successfully visualized real-time process of Aβ₄₂ aggregation around living cells by applying our established QD imaging method. 3D observations using confocal laser microscopy revealed that Aβ₄₂ preferentially started to aggregate at the region where membrane protrusions frequently formed. Furthermore, we found that inhibition of actin polymerization using cytochalasin D reduced aggregation of Aβ₄₂ on the cell surface. These results indicate that actin polymerization-dependent cell motility is responsible for the promotion of Aβ₄₂ aggregation at the cell periphery. 3D observation also revealed that the aggregates around the cell remained in that location even if cell death occurred, implying that amyloid plaques found in the AD brain grew from the debris of dead cells that accumulated Aβ₄₂ aggregates.

Association of Aβ with ceramide-enriched astrosomes mediates Aβ neurotoxicity

Amyloid-β (Aβ) associates with extracellular vesicles termed exosomes. It is not clear whether and how exosomes modulate Aβ neurotoxicity in Alzheimer's disease (AD). We show here that brain tissue and serum from the transgenic mouse model of familial AD (5xFAD) and serum from AD patients contains ceramide-enriched and astrocyte-derived exosomes (termed astrosomes) that are associated with Aβ. In Neuro-2a cells, primary cultured neurons, and human induced pluripotent stem cell-derived neurons, Aβ-associated astrosomes from 5xFAD mice and AD patient serum were specifically transported to mitochondria, induced mitochondrial clustering, and upregulated the fission protein Drp-1 at a concentration corresponding to 5 femtomoles Aβ/L of medium. Aβ-associated astrosomes, but not wild type or control human serum exosomes, mediated binding of Aβ to voltage-dependent anion channel 1 (VDAC1) and subsequently, activated caspases. Aβ-associated astrosomes induced neurite fragmentation and neuronal cell death, suggesting that association with astrosomes substantially enhances Aβ neurotoxicity in AD and may comprise a novel target for therapy.

Near-Infrared Responsive Dopamine/Melatonin-Derived Nanocomposites Abrogating in Situ Amyloid β Nucleation, Propagation, and Ameliorate Neuronal Functions

Alzheimer's disease (AD) is one of the common causes of dementia and mild cognitive impairments, which is progressively expanding among the elderly population worldwide. A short Amyloid-β (Aβ) peptide generated after amyloidogenic processing of amyloid precursor protein exist as intermolecular β-sheet rich oligomeric, protofibriler, and fibrillar structures and believe to be toxic species which instigate neuronal pathobiology in the brain and deposits as senile plaque. Enormous efforts are being made to develop an effective anti-AD therapy that can target Aβ processing, aggregation, and propagation and provide a synergistic neuroprotective effect. However, a nanodrug prepared from natural origin can confer a multimodal synergistic chemo/photothermal inhibition of Aβ pathobiology is not yet demonstrated. In the present work, we report a dopamine-melatonin nanocomposite (DM-NC), which possesses a synergistic near-infrared (NIR) responsive photothermal and pharmacological modality. The noncovalent interaction-mediated self-assembly of melatonin and dopamine oxidative intermediates leads to the evolution of DM-NCs that can withstand variable pH and peroxide environment. NIR-activated melatonin release and photothermal effect collectively inhibit Aβ nucleation, self-seeding, and propagation and can also disrupt the preformed Aβ fibers examined using in vitro Aβ aggregation and Aβ-misfolding cyclic amplification assays. The DM-NCs display a higher biocompatibility to neuroblastoma cells, suppress the AD-associated generation of intracellular reactive oxygen species, and are devoid of any negative impact on the axonal growth process. In okadaic acid-induced neuroblastoma and ex vivo midbrain slice culture-based AD model, DM-NCs exposure suppresses the intracellular Aβ production, aggregation, and accumulation. Therefore, this nature-derived nanocomposite demonstrates a multimodal NIR-responsive synergistic photothermal and pharmacological modality for effective AD therapy.

Estrogen protects neuroblastoma cell from amyloid-β 42 (Aβ42)-induced apoptosis via TXNIP/TRX axis and AMPK signaling

Alzheimer's disease (AD), a massive challenge to global health, is featured with the extracellular plaques made up of amyloid-β 42 (Aβ42) and the intracellular neurofibrillary pathology composed of the microtubule-associated protein tau. Women seem to have a higher vulnerability to AD. In the present study, we identified Thioredoxin-interacting protein (TXNIP) as a specifically highly-expressed gene in the hippocampus in female AD patients by bioinformatics analysis. Consistently, in the hippocampus in female AD mice, apoptosis and TXNIP expression were enhanced while TRX expression was suppressed. In Aβ42-stimulated SH-SY5Y cells, the administration of estradiol significantly rescued Aβ42-suppressed cell viability and protein level of TRX while inhibited Aβ42-induced increases in ROS production, cell apoptosis, ΔΨm, and the protein levels of PERK, IREα, and TXNIP, further confirming the potential role of estrogen in AD progression and the involvement of TXNIP/TRX axis. Furthermore, the protective effects of estradiol against Aβ42-induced in vitro neurotoxicity on SH-SY5Y cells could be significantly reversed by AMPK inhibitor, Compound C, indicating that estradiol could improve Aβ42-induced AD via TXNIP/TRX and AMPK signaling. In summary, we demonstrated the cellular function of estradiol on Aβ42-induced in vitro neurotoxicity on SH-SY5Y cells and a novel mechanism of TXNIP/TRX axis involved in estradiol function via AMPK signaling.

Exploring the Multi-Target Performance of Mitochondriotropic Antioxidants against the Pivotal Alzheimer's Disease Pathophysiological Hallmarks

Alzheimer disease (AD) is the most common neurodegenerative disease featuring progressive and degenerative neurological impairments resulting in memory loss and cognitive decline. The specific mechanisms underlying AD are still poorly understood, but it is suggested that a deficiency in the brain neurotransmitter acetylcholine, the deposition of insoluble aggregates of fibrillar β-amyloid 1–42 (Aβ₄₂), and iron and glutamate accumulation play an important role in the disease progress. Despite the existence of approved cholinergic drugs, none of them demonstrated effectiveness in modifying disease progression. Accordingly, the development of new chemical entities acting on more than one target is attracting progressively more attention as they can tackle intricate network targets and modulate their effects. Within this endeavor, a series of mitochondriotropic antioxidants inspired on hydroxycinnamic (HCA’s) scaffold were synthesized, screened toward cholinesterases and evaluated as neuroprotectors in a differentiated human SH-SY5Y cell line. From the series, compounds 7 and 11 with a 10-carbon chain can be viewed as multi-target leads for the treatment of AD, as they act as dual and bifunctional cholinesterase inhibitors and prevent the neuronal damage caused by diverse aggressors related to protein misfolding and aggregation, iron accumulation and excitotoxicity.