Beta-amyloid Plaque Formation Research Articles

Particulate matter constituents trigger the formation of extracellular amyloid β and Tau -containing plaques and neurite shortening in vitro

Air pollution is an environmental factor associated with an increased risk of neurodegenerative diseases, such as Alzheimer’s and Parkinson’s, characterized by decreased cognitive abilities and memory. The limited models of sporadic Alzheimer’s disease fail to replicate all pathological hallmarks of the disease, making it challenging to uncover potential environmental causes. Environmentally driven models of Alzheimer’s disease are thus timely and necessary. We used live-cell confocal fluorescent imaging combined with high-resolution stimulated emission depletion (STED) microscopy to follow the response of retinoic acid-differentiated human neuroblastoma SH-SY5Y cells to nanomaterial exposure. Here, we report that exposure of the cells to some particulate matter constituents reproduces a neurodegenerative phenotype, including extracellular amyloid beta-containing plaques and decreased neurite length. Consistent with the existing in vivo research, we observed detrimental effects, specifically a substantial reduction in neurite length and formation of amyloid beta plaques, after exposure to iron oxide and diesel exhaust particles. Conversely, after exposure to engineered cerium oxide nanoparticles, the lengths of neurites were maintained, and almost no extracellular amyloid beta plaques were formed. Although the exact mechanism behind this effect remains to be explained, the retinoic acid differentiated SH-SY5Y cell in vitro model could serve as an alternative, environmentally driven model of neurodegenerative diseases, including Alzheimer’s disease.

Protective Effect of Ferulic Acid on Acetylcholinesterase and Amyloid Beta Peptide Plaque Formation in Alzheimer's Disease: An In Vitro Study.

Aim This study aims to comprehensively evaluate the effects of ferulic acid (FA) on acetylcholinesterase (AChE) enzyme activity and amyloid beta (Aβ) peptide plaque formation in an in vitro model of Alzheimer's disease (AD). Background ADis a progressive neurological condition marked by disrupted cholinergic signaling, accumulation of Aβ peptide, and tau protein hyperphosphorylation. Currently, no direct anti-Alzheimer drug that effectively prevents the cognitive decline from AD has been reported. To combat this, a multi-target drug addressing several molecular aspects would be ideal for AD. Natural compounds are preferred over synthetic drugs due to their accessibility, cost-efficiency, and lower toxicity The proven association between polyphenolconsumption and the prevention of AD has led to the investigation of the effect of FA, a polyphenolic compound, on acetylcholinesterase enzyme activity and Aβ peptide formation, the key targets of AD. Materials and method The free radical scavenging ability of FA was assessed by xanthine oxidase inhibitory activity. Furthermore, FA was also evaluated for its inhibitory activity against AChE enzyme and amyloid beta peptide formation to evaluate the neuroprotective potential of FA. Results The results showed that FA has the potential to be an AChE inhibitor, thus helping in blocking the activity of AChE and also reducing the incidence of amyloid beta plaque formation. Furthermore, the compound also exhibited a significant antioxidant property which was demonstrated by the xanthine oxidase enzyme inhibitory effect. Conclusion From the observed results, FA has significant antioxidant and neuroprotective effects which are compared with those of their respective standards. More research is required to determine the efficacy and safety of this compound as a treatment for neurodegenerative diseases like AD because the precise mechanism and degree of its AChE inhibitory effects in the brain are still elusive. A potent, selective, and effective drug is desperately needed to treat patients with AD and those at risk of developing the disease.

Ketogenic strategies for Alzheimer’s disease and other memory impairments: History, rationale, and 288 caregiver case reports

Glucose hypometabolism predates Alzheimer’s disease symptoms by at least one to two decades. Ketones are an alternative fuel to glucose and are taken up normally in affected regions of the Alzheimer’s brain and could address certain pathologies that are common in the aging brain and exaggerated in Alzheimer’s disease including insulin resistance, a brain-energy deficit, mitochondrial dysfunction, oxidative stress, and neuroinflammation. Ketones have also been shown to reduce formation of beta-amyloid plaques and neurofibrillary tangles in animal models. Experts have estimated that at least 30 percent of Alzheimer’s and other dementias could be avoided by adopting a healthy diet, increasing physical activity, and correcting other modifiable lifestyle risk factors. Mild to moderate ketosis can be achieved through consumption of a healthy whole food low-carbohydrate ketogenic diet, ketogenic oils containing medium-chain triglycerides, or exogenous ketone supplements as well as intermittent or overnight fasting, and moderately vigorous aerobic exercise. An analysis was performed of 288 anecdotal reports about people with Alzheimer’s, other dementias, Parkinson’s disease with dementia, mild cognitive impairment, and other diagnosed or subjective memory impairments consuming coconut oil and/or medium-chain triglyceride oil. Improvement was reported by 89.2 percent, no improvement by 7.3 percent, and no improvement but stabilization for at least 3 months by 2.4 percent. One or more improvements were reported in the areas of memory/cognition (65.3%), social/behavior/ mood/personality (32.6%), speech/language/conversation (33%), resumption of self-care/other activities (24.7%), physical symptoms (18.4%), sleep (3.5%), appetite (2.4%), vision (1.4%), and improvement that was otherwise unspecified (8%). Certain fatty acids found in medium-chain triglyceride oil and coconut oil are ketogenic but also have other important biological effects which, along with polyphenols and other bioactive substances in virgin coconut oil, could explain these results. Adopting a personalized ketogenic lifestyle plan using one or more ketogenic strategies could address certain pathological processes that occur in the aging brain while potentially improving symptoms in people with Alzheimer’s disease. In addition, this approach could possibly prevent or delay the onset of cognitive impairment during aging, though larger long-term studies would be needed to confirm this.

Immunohistochemical detection of amyloid beta and tau proteins in the Monodelphis domestica brain

AbstractBackgroundAnimal models have been important for the understanding of Alzheimer’s disease and related dementias (ADRD). However, most of the research involving these diseases has been with rodents. Researchers have raised awareness about the need for alternative and feasible animal models in order to understand these types of diseases. To increase the knowledge of alternative animal models for the study of ADRD, the current study proposed the use of the Monodelphis domestica animal model to detect the presence of amyloid beta and tau proteins.MethodFixed brains from young adult Monodelphis were used in the present study. A standard immunohistochemistry (ABC‐DAB) staining protocol was used to detect amyloid beta and tau proteins. To detect the presence of amyloid beta, a 1:100 anti‐amyloid primary dilution was used; for tau protein, a 1:1000 anti‐tau primary dilution was utilized. Only the hippocampal region was selected for description and quantification. An Axioscan Z.1 microscope system was utilized to capture images, and image analysis was performed using ImageJ software.ResultThe area of the hippocampus of the first coronal section was 30262602.934 um2. The results from an amyloid‐beta dilution of 1:100 detected amyloid beta in a number of neurons in the hippocampus. Amyloid beta was also detected in the hippocampus of another brain section (total area: 7048008 um2). The negative control tissue did not reveal positive signal in neurons in the hippocampal area, suggesting low levels of non‐specific binding. The results for tau antibody are pending.ConclusionOur study revealed that in Monodelphis domestica animal model brain tissue, a 1:100 dilution resulted in identification of positive amyloid beta protein. However, no abnormal amyloid beta plaque formation was found with this animal model. A possible explanation was that a natural, non‐induced animal model was used in the study.

Pincer Ligands as Multifunctional Agents for Alzheimer's Copper Dysregulation and Oxidative Stress: A Computational Evaluation.

Alzheimer's disease (AD) is the most common form of dementia worldwide, affecting millions of people around the globe. AD is characterized by different pathologies being beta-amyloid (Aβ) plaque formation, metal ion dysregulation, and oxidative stress (OS) central topics under investigation. Copper-Aβ complexes have been shown to induce catalytic hydrogen peroxide formation and increase OS in the brain leading to neuronal death. Pincer-type compounds are tridentate ligands that coordinate metals in a planar fashion whose properties can be tuned via group substitutions, giving rise to many possibilities in catalysis and drug discovery. In this work we evaluated the potential pharmaceutical activity of 26 pincer compounds in AD's copper ion-related oxidative stress framework. In this sense, four key aspects were considered: 1) Lipinski's rule of five, 2) blood-brain barrier permeation, 3) standard reduction potential (SRP) of the formed copper complexes, and 4) the ligand's affinity towards copper cations. The evaluation of these criteria was performed by means of bioinformatic tools and electronic structure calculations at the DFT level of theory. Our results suggest that two compounds from this set are potential antioxidant agents, whereas five of them are promissory distributor-like compounds in the context of AD.

MTOR signaling and Alzheimer's disease: What we know and where we are?

Despite the great body of research done on Alzheimer's disease, the underlying mechanisms have not been vividly investigated. To date, the accumulation of amyloid-beta plaques and tau tangles constitutes the hallmark of the disease; however, dysregulation of the mammalian target of rapamycin (mTOR) seems to be significantly involved in the pathogenesis of the disease as well. mTOR, as a serine-threonine protein kinase, was previously known for controlling many cellular functions such as cell size, autophagy, and metabolism. In this regard, mammalian target of rapamycin complex 1 (mTORC1) may leave anti-aging impacts by robustly inhibiting autophagy, a mechanism that inhibits the accumulation of damaged protein aggregate and dysfunctional organelles. Formation and aggregation of neurofibrillary tangles and amyloid-beta plaques seem to be significantly regulated by mTOR signaling. Understanding the underlying mechanisms and connection between mTOR signaling and AD may suggest conducting clinical trials assessing the efficacy of rapamycin, as an mTOR inhibitor drug, in managing AD or may help develop other medications. In this literature review, we aim to elaborate mTOR signaling network mainly in the brain, point to gaps of knowledge, and define how and in which ways mTOR signaling can be connected with AD pathogenesis and symptoms.

Beta-Secretase 1 Recruits Amyloid-Beta Precursor Protein to ROCK2 Kinase, Resulting in Erroneous Phosphorylation and Beta-Amyloid Plaque Formation.

The amyloidogenic processing of APP depends on two events: its phosphorylation by ROCK2 (at Thr654) and the phosphorylation of the APP-cleaving enzyme BACE1 (at Ser498). However, the mechanisms and structural details of APP-ROCK2 and BACE1-ROCK2 binding are unknown. Using direct physical methods in combination with an in silico approach, we found that BACE1 binds into the substrate-binding groove of ROCK2 with a low affinity (Kd = 18 µM), while no binding of APP to ROCK2 alone could be detected. On the other hand, a strong association (Kd = 3.5 nM) of APP to the weak ROCK2-BACE1 complex was observed, although no stable ternary complex was detected, i.e., BACE1 was displaced by APP. We constructed a sequential functional model: (1) BACE1 weakly binds to ROCK2 and induces an allosteric conformational change in ROCK2; (2) APP strongly binds to the ROCK2-BACE1 complex, and BACE1 is released; and (3) ROCK2 phosphorylates APP at Thr654 (leading to a longer stay in the early endosome during APP processing). Direct fluorescence titration experiments showed that the APP646-664 or APP665-695 fragments did not bind separately to the ROCK2-BACE1 complex. Based on these observations, we conclude that two binding sites are involved in the ROCK2-APP interaction: (1) the substrate-binding groove, where the APP646-664 sequence containing Thr654 sits and (2) the allosteric binding site, where the APP665-695 sequence binds. These results open the way to attack the allosteric site to prevent APP phosphorylation at Thr654 by ROCK2 without inhibiting the activity of ROCK2 towards its other substrates.

The cognitive dysfunction of claustrum on Alzheimer's disease: A mini-review.

Alzheimer's disease (AD) is one of the most common neurodegenerative diseases characterized by cognitive deficits and dementia. AD entails predominant pathological characteristics including amyloid beta (Aβ) plaque formation, neurofibrillary entanglements, and brain atrophy, which gradually result in cognitive dysfunctions. Studies showed that these pathological changes are found in a myriad of brain structures, including the claustrum (CLA), a nucleus that penetrates deeply into the brain and is extensively interconnected to various brain structures. The CLA modulates many aspects of cognitive functions, with attention, executive function, visuospatial ability, language, and memory in particular. It is also implicated in multiple neuropsychiatric disorders, of which one worthy of particular attention is AD-related cognitive impairments. To inspire novel AD treatment strategies, this review has summarized the CLA functionality in discriminative cognitive dysfunctions in AD. And then propose an array of potential mechanisms that might contribute to the cognitive impairments caused by an abnormal CLA physiology. We advocate that the CLA might be a new promising therapeutic target in combination with existing anti-AD drugs and brain stimulation approaches for future AD treatment.

Design and biological evaluation of Repaglinide loaded polymeric nanocarriers for diabetes linked neurodegenerative disorder: QbD-driven optimization, in situ, in vitro and in vivo investigation

Diabetes mellitus is a metabolic disorder characterized by inadequate insulin secretion and signaling dysfunction, leading to a vast spectrum of systemic complications. These complications trigger cascades of events that result in amyloid-beta plaque formation and lead to neurodegenerative disorders such as Alzheimer’s. Repaglinide (REP) an insulinotropic agent, suppresses the down regulatory element antagonist modulator (DREAM) and enhances the ATF6 expression to provide neuroprotection following the DREAM/ATF6/apoptotic pathway. However, oral administration of REP for brain delivery becomes more complicated due to its physicochemical characteristics (high protein binding (>98%), low permeability, short half-life (∼1 h), low bioavailability). Therefore, to circumvent these problems, we develop a polymeric nanocarrier system (PNPs) by in-house synthesized di-block copolymer (PEG-PCL). PNPs were optimized using quality by design approach response surface methodology and characterized by particle size (112.53 ± 5.91 nm), PDI (0.157 ± 0.08), and zeta potential (−6.20 ± 0.82 mV). In vitro release study revealed that PNPs (∼70% in 48 h) followed the Korsmeyer-Peppas model with a Fickian diffusion release pattern, and in intestinal absorption assay PNPs showed increment of ∼1.3 folds compared of REP. Moreover, cellular studies confirmed that REP-loaded PNPs significantly enhance the cellular viability, uptake and reduce the peroxide-induced stress in neuroblastoma SHSY-5Y cells. Further, pharmacokinetic parameters of PNPs showed an increment in tmax (2.46-fold), and Cmax (1.25-fold) associated with REP. In the brain biodistribution study, REP loaded PNPs was sustained for 24 h whereas free REP sustained only for12 h. In DM induced neurodegenerative murine model, a significantly (p < 0.01) enhanced pharmacodynamic was observed in PNP treated group by estimating biochemical and behavioral parameters. Hence, oral administration of REP-loaded PNPs promotes efficient brain uptake and improved efficacy of REP in the diseased model.

Long-Term Administration of Vespa velutina nigrithorax Venom Ameliorates Alzheimer's Phenotypes in 5xFAD Transgenic Mice.

Alzheimer's disease (AD), the most prevalent neurodegenerative disease, is characterized by progressive and irreversible impairment of cognitive functions. However, its etiology is poorly understood, and therapeutic interventions are limited. Our preliminary study revealed that wasp venom (WV) from Vespa velutina nigrithorax can prevent lipopolysaccharide-induced inflammatory signaling, which is strongly implicated in AD pathogenesis. Therefore, we examined whether WV administration can ameliorate major AD phenotypes in the 5xFAD transgenic mouse model. Adult 5xFAD transgenic mice (6.5 months of age) were treated with WV by intraperitoneal injection at 250 or 400 μg/kg body weight once weekly for 14 consecutive weeks. This administration regimen improved procedural, spatial, and working memory deficits as assessed by the passive avoidance, Morris water maze, and Y-maze tasks, respectively. It also attenuated histological damage and amyloid-beta plaque formation in the hippocampal region and decreased expression levels of pro-inflammatory factors in the hippocampus and cerebrum, while it reduced oxidative stress markers (malondialdehyde in the brain and liver and 8-hydroxy-2'-deoxyguanosine in the plasma). Overall, these findings suggest that long-term administration of WV may alleviate AD-related symptoms and pathological phenotypes.

The Protective Effects of Policosanol on Learning and Memory Impairments in a Male Rat Model of Alzheimer's Disease.

Alzheimer's disease (AD), the most common form of dementia, is characterized by a progressive decline in cognitive performance and memory formation. The present study was designed to investigate the effect of policosanol (PCO) on cognitive function, oxidative-antioxidative status, and amyloid-beta (Aβ) plaque formation in an AD rat model induced by intracerebroventricular (ICV) injection of Aβ1-40. Healthy adult male Wistar rats were randomly divided into seven groups: control, sham (5 μL, ICV injection of phosphate-buffered saline), AD model (5 μL, ICV injection of Aβ), acacia gum (50mg/kg, 8weeks, gavage), PCO (50mg/kg, 8weeks, gavage), AD + acacia gum (50mg/kg, 8weeks, gavage), and AD + PCO (50mg/kg, 8weeks, gavage). During the ninth and tenth weeks of the study, the cognitive function of the rats was assessed by commonly used behavioral paradigms. Subsequently, oxidative-antioxidative status was examined in the serum. Moreover, compact Aβ plaques were detected by Congo red staining. The results showed that injection of Aβ impaired recognition memory in the novel object recognition test, reduced the spatial cognitive ability in the Morris water maze, and alleviated retention and recall capability in the passive avoidance task. Additionally, injection of Aβ resulted in increased total oxidant status, decreased total antioxidant capacity, and enhanced Aβ plaque formation in the rats. Intriguingly, PCO treatment improved all the above-mentioned neuropathological changes in the Aβ-induced AD rats. The results suggest that PCO improves Aβ-induced cognitive decline, possibly through modulation of oxidative-antioxidative status and inhibition of Aβ plaque formation.

Exploring the Associations between Alzheimer's Disease and GBM Mediated by Microglia Based on Network Analysis.

Previous studies have revealed that there existed epidemic associations between Alzheimer's disease (AD) and many types of tumors, however, the inner biological mechanism connecting these diseases was not clear currently. In this study, we explored the transcriptome associations between AD and glioblastoma multiforme (GBM) that both originate in the brain, using microglia as a bridge, from gene and network levels. Firstly, we extracted human scRNA sequencing datasets from Gene Expression Omnibus (GEO) database, and identified differentially expressed genes within microglia after cell annotation. It was observed that there were 11 common genes shared by AD and GBM dys-regulated genes. Next, we utilized DIAMOnD and Flow Centrality algorithms to identify microglia modules and mediating pathways connecting these two diseases based on global network topology. Among these candidate pathways, the mediating genes FURIN and BACE1 (from SPIKN5 to CSNK1A1) were not only related to the formation of amyloid beta plaques that accumulate in the brain of AD patients, but also involved in cancer biology. Furthermore, the biological explorations of mediating pathways connecting AD and GBM modules reveal inflammatory response, lipid metabolism disorder, and cell proliferation terms. Finally, novel signatures for early AD detection as well as risk models for glioma prognosis were identified based on mediating genes involved in these pathways. In conclusion, this study provided a novel network-based strategy for exploring microglia mediation between AD and GBM and identified candidate signatures for disease detection and prognosis.

Concentration Effect, Structural Properties, and Driving Force on Aβ28 Dimerization with and without Zn2+ Cooperation: Learning from Replica Exchange Sampling.

Zn2+ is a very important factor in promoting the formation of amyloid beta (Aβ) aggregates and amyloid plaques. The Zn2+ -bound Aβ species generate amorphous or low molecular-weight oligomers. However, it is a lack of studies to approach the starting structural features (dimerization) in Aβ nucleation processes with and without Zn2+ , which is the key point in understanding Zn2+ -induced nucleation mechanisms. To better understand the effect of concentration, structural properties, and the driving force, 14 independent replica exchange molecular dynamics simulations were performed in Aβ28 dimerization with and without Zn2+ (zAβ28 ) cooperation. Our scanning results show that the aggregation propensity is easier in Aβ28 -Aβ28 and Aβ28 -zAβ28 systems than zAβ28 -zAβ28 system. In binding property, the Aβ28 -Aβ28 model (-61.5 kcal mol-1 ) is stronger than zAβ28 -zAβ28 (-26.6 kcal mol-1 ) and Aβ28 -zAβ28 (-7.24 kcal mol-1 ) models. Further analysis confirmed that H13 and H14 residues play specific roles in the three systems. The key point is the orientation of N atom of the imidazole ring in histidine residues. Furthermore, we discovered different driving forces for each system. Our current study contributes to the understanding of how the Aβ28 dimer interacts with Zn2+ , which could lead to new insights into Zn2+ -induced nucleation mechanisms.

Identification of potential neuroprotective compound from Ganoderma lucidum extract targeting microtubule affinity regulation kinase 4 involved in Alzheimer's disease through molecular dynamics simulation and MMGBSA.

Alzheimer's disease (AD) is one of the most prevalent neurological ailments, affecting around 50 million individuals globally. The condition is characterized by nerve cell damage due to the formation of amyloid-beta plaques and neurofibrillary tangles. Only a few US Food and Drug Administration (FDA)-approved medications are available in the market which are devoid of side effects, thus, making it imperative to investigate new alternatives for countering this disease. According to a recent study, microtubule affinity regulation kinase 4 (MARK4) is attributed as one of the most promising drug targets for AD, thus, being selected for this study. Compounds from Ganoderma lucidum (Reishi mushroom) extracts were selected to be used as ligands for this study. In this study, the five most potent compounds from Ganoderma lucidum were selected and their absorption, distribution, metabolism, excretion, and toxicity (ADMET) analysis was performed, followed by molecular docking, and molecular dynamics simulation of each compound with MARK4 and supported by molecular mechanics generalized born surface area (MMGBSA) binding free energy calculations. The promising compounds were selected based on their ADMET profile and interactions with the active site residues of MARK4. Based on docking scores of -9.1 and -10.3kcal/ mol, respectively, stability assessment by molecular dynamics simulation, and MMGBSA calculations, ganoderic acid A and ganoderenic acid B were found to be the most promising compounds against MARK4 which will require further in vitro and in vivo validations. Through this study, it is suggested that ganoderic acid A and ganoderenic acid B might be a class of promising compounds against AD, based on computational research, and can be further studied for preclinical and clinical studies.

Role of calcium dysregulation in Alzheimer's disease and its therapeutic implications.

The increasing incidence of Alzheimer's disease (AD) coupled with the lack of therapeutics to address the underlying pathology of the disease has necessitated the need for exploring newer targets. Calcium dysregulation represents a relatively newer target associated with AD. Ca+2 serves as an important cellular messenger in neurons. The concentration of the Ca+2 ion needs to be regulated at optimal concentrations intracellularly for normal functioning of the neurons. This is achieved with the help of mitochondria, endoplasmic reticulum, and neuronal plasma membrane channel proteins. Disruption in normal calcium homeostasis can induce formation of amyloid beta plaques, accumulation of neurofibrillary tangles, and dysfunction of synaptic plasticity, which in turn can affect calcium homeostasis further, thus forming a vicious cycle. Hence, understanding calcium dysregulation can prove to be a key to develop newer therapeutics. This review provides detailed account of physiology of calcium homeostasis and its dysregulation associated with AD. Further, with an understanding of various receptors and organelles involved in these pathways, the review also discusses various calcium channel blockers explored in AD hand in hand with some multitarget molecules addressing calcium as one of the targets.

Recognizing novel drugs against Keap1 in Alzheimer's disease using machine learning grounded computational studies.

Alzheimer's disease (AD) is the most common neurodegenerative disorder in the world, affecting an estimated 50 million individuals. The nerve cells become impaired and die due to the formation of amyloid-beta (Aβ) plaques and neurofibrillary tangles (NFTs). Dementia is one of the most common symptoms seen in people with AD. Genes, lifestyle, mitochondrial dysfunction, oxidative stress, obesity, infections, and head injuries are some of the factors that can contribute to the development and progression of AD. There are just a few FDA-approved treatments without side effects in the market, and their efficacy is restricted due to their narrow target in the etiology of AD. Therefore, our aim is to identify a safe and potent treatment for Alzheimer's disease. We chose the ursolic acid (UA) and its similar compounds as a compounds' library. And the ChEMBL database was adopted to obtain the active and inactive chemicals against Keap1. The best Quantitative structure-activity relationship (QSAR) model was created by evaluating standard machine learning techniques, and the best model has the lowest RMSE and greatest R2 (Random Forest Regressor). We chose pIC50 of 6.5 as threshold, where the top five potent medicines (DB06841, DB04310, DB11784, DB12730, and DB12677) with the highest predicted pIC50 (7.091184, 6.900866, 6.800155, 6.768965, and 6.756439) based on QSAR analysis. Furthermore, the top five medicines utilize as ligand molecules were docked in Keap1's binding region. The structural stability of the nominated medications was then evaluated using molecular dynamics simulations, RMSD, RMSF, Rg, and hydrogen bonding. All models are stable at 20 ns during simulation, with no major fluctuations observed. Finally, the top five medications are shown as prospective inhibitors of Keap1 and are the most promising to battle AD.

Upregulation of Ca2+-binding proteins contributes to VTA dopamine neuron survival in the early phases of Alzheimer’s disease in Tg2576 mice

BackgroundRecent clinical and experimental studies have highlighted the involvement of Ventral Tegmental Area (VTA) dopamine (DA) neurons for the early pathogenesis of Alzheimer’s Disease (AD). We have previously described a progressive and selective degeneration of these neurons in the Tg2576 mouse model of AD, long before amyloid-beta plaque formation. The degenerative process in DA neurons is associated with an autophagy flux impairment, whose rescue can prevent neuronal loss. Impairments in autophagy can be the basis for accumulation of damaged mitochondria, leading to disturbance in calcium (Ca2+) homeostasis, and to functional and structural deterioration of DA neurons.MethodsIn Tg2576 mice, we performed amperometric recordings of DA levels and analysis of dopaminergic fibers in the Nucleus Accumbens – a major component of the ventral striatum precociously affected in AD patients – together with retrograde tracing, to identify the most vulnerable DA neuron subpopulations in the VTA. Then, we focused on these neurons to analyze mitochondrial integrity and Apoptosis-inducing factor (AIF) localization by electron and confocal microscopy, respectively. Stereological cell count was also used to evaluate degeneration of DA neuron subpopulations containing the Ca2+-binding proteins Calbindin-D28K and Calretinin. The expression levels for these proteins were analyzed by western blot and confocal microscopy. Lastly, using electrophysiology and microfluorometry we analyzed VTA DA neuron intrinsic properties and cytosolic free Ca2+ levels.ResultsWe found a progressive degeneration of mesolimbic DA neurons projecting to the ventral striatum, located in the paranigral nucleus and parabrachial pigmented subnucleus of the VTA. At the onset of degeneration (3 months of age), the vulnerable DA neurons in the Tg2576 accumulate damaged mitochondria, while AIF translocates from the mitochondria to the nucleus. Although we describe an age-dependent loss of the DA neurons expressing Calbindin-D28K or Calretinin, we observed that the remaining cells upregulate the levels of Ca2+-binding proteins, and the free cytosolic levels of Ca2+ in these neurons are significantly decreased. Coherently, TUNEL-stained Tg2576 DA neurons express lower levels of Calbindin-D28K when compared with non-apoptotic cells.ConclusionOverall, our results suggest that the overexpression of Ca2+-binding proteins in VTA DA neurons might be an attempt of cells to survive by increasing their ability to buffer free Ca2+. Exploring strategies to overexpress Ca2+-binding proteins could be fundamental to reduce neuronal suffering and improve cognitive and non-cognitive functions in AD.

The effect of ghrelin on antioxidant status in the rat's model of Alzheimer's disease induced by amyloid-beta.

Alzheimer's disease (AD) is a neurodegenerative disorder associated with amyloid-beta (Aβ) plaque formation and oxidative stress in the brain. Ghrelin has been proven to exert antioxidant activity and neuroprotection in different neurological diseases. This study is going on to examine the effect of ghrelin on antioxidant status in the rat's model of AD induced by Aβ. Cognitive impairment was induced by intra-hippocampal administration of Aβ (10 μg) in Wistar rats and ghrelin (80 μg/kg) was administrated intraperitoneal for ten consecutive days. Behavior was assessed with Morris water maze and passive avoidance tests. Malondialdehyde (MDA) level as a marker of lipid peroxidation was assessed using the thiobarbituric acid. Catalase activity was assayed by the decomposition of H2O2. Antioxidant capacity was determined using the FRAP method. Treatment with ghrelin decreased the hippocampus and serum MDA levels in wild-type rodents and prevented an increase in hippocampal and serum MDA levels in animals receiving Aβ. There was no significant change in the serum catalase activity between the studied groups. Hippocampus catalase activity was reduced in the Aβ group and treatment with ghrelin increased it. The antioxidant capacity of the hippocampus and serum increased in the ghrelin-receiving control group. The hippocampus antioxidant capacity level decreased in the Aβ group, and treatment with ghrelin increased it, but there were no significant changes in the serum antioxidant capacity of animals receiving Aβ. These results provide evidence that the administration of ghrelin has antioxidant properties and protects against hippocampal lipid peroxidation in a rat model of AD.

Prevention of microgliosis halts early memory loss in a mouse model of Alzheimer’s disease

Alzheimer’s disease (AD) is a neurodegenerative disorder characterized by cognitive decline, the neuropathological formation of amyloid-beta (Aβ) plaques and neurofibrillary tangles. The best cellular correlates of the early cognitive deficits in AD patients are synapse loss and gliosis. In particular, it is unclear whether the activation of microglia (microgliosis) has a neuroprotective or pathological role early in AD. Here we report that microgliosis is an early mediator of synaptic dysfunction and cognitive impairment in APP/PS1 mice, a mouse model of increased amyloidosis. We found that the appearance of microgliosis, synaptic dysfunction and behavioral impairment coincided with increased soluble Aβ42 levels, and occurred well before the presence of Aβ plaques. Inhibition of microglial activity by treatment with minocycline (MC) reduced gliosis, synaptic deficits and cognitive impairments at early pathological stages and was most effective when provided preventive, i.e., before the onset of microgliosis. Interestingly, soluble Aβ levels or Aβ plaques deposition were not affected by preventive MC treatment at an early pathological stage (4 months) whereas these were reduced upon treatment at a later stage (6 months). In conclusion, this study demonstrates the importance of early-stage prevention of microgliosis on the development of cognitive impairment in APP/PS1 mice, which might be clinically relevant in preventing memory loss and delaying AD pathogenesis.

Proteomic analysis for the effects of non-saponin fraction with rich polysaccharide from Korean Red Ginseng on Alzheimer's disease in a mouse model

BackgroundThe most common type of dementia, Alzheimer's disease (AD), is marked by the formation of extracellular amyloid beta (Aβ) plaques. The impairments of axons and synapses appear in the process of Aβ plaques formation, and this damage could cause neurodegeneration. We previously reported that non-saponin fraction with rich polysaccharide (NFP) from Korean Red Ginseng (KRG) showed neuroprotective effects in AD. However, precise molecular mechanism of the therapeutic effects of NFP from KRG in AD still remains elusive. MethodsTo investigate the therapeutic mechanisms of NFP from KRG on AD, we conducted proteomic analysis for frontal cortex from vehicle-treated wild-type, vehicle-treated 5XFAD mice, and NFP-treated 5XFAD mice by using nano-LC-ESI-MS/MS. Metabolic network analysis was additionally performed as the effects of NFP appeared to be associated with metabolism according to the proteome analysis. ResultsStarting from 5,470 proteins, 2,636 proteins were selected for hierarchical clustering analysis, and finally 111 proteins were further selected for protein-protein interaction network analysis. A series of these analyses revealed that proteins associated with synapse and mitochondria might be linked to the therapeutic mechanism of NFP. Subsequent metabolic network analysis via genome-scale metabolic models that represent the three mouse groups showed that there were significant changes in metabolic fluxes of mitochondrial carnitine shuttle pathway and mitochondrial beta-oxidation of polyunsaturated fatty acids. ConclusionOur results suggested that the therapeutic effects of NFP on AD were associated with synaptic- and mitochondrial-related pathways, and they provided targets for further rigorous studies on precise understanding of the molecular mechanism of NFP.