Amyloid β-interacting partners in Alzheimer's disease: From accomplices to possible therapeutic targets

How Can We Use Mathematical Modeling of Amyloid-β in Alzheimer's Disease Research and Clinical Practices?

The accumulation of amyloid-β (Aβ) plaques in the brain is considered a hallmark of Alzheimer's disease (AD). Mathematical modeling, capable of predicting the motion and accumulation of Aβ, has obtained increasing interest as a potential alternative to aid the diagnosis of AD and predict disease prognosis. These mathematical models have provided insights into the pathogenesis and progression of AD that are difficult to obtain through experimental studies alone. Mathematical modeling can also simulate the effects of therapeutics on brain Aβ levels, thereby holding potential for drug efficacy simulation and the optimization of personalized treatment approaches. In this review, we provide an overview of the mathematical models that have been used to simulate brain levels of Aβ (oligomers, protofibrils, and/or plaques). We classify the models into five categories: the general ordinary differential equation models, the general partial differential equation models, the network models, the linear optimal ordinary differential equation models, and the modified partial differential equation models (i.e., Smoluchowski equation models). The assumptions, advantages and limitations of these models are discussed. Given the popularity of using the Smoluchowski equation models to simulate brain levels of Aβ, our review summarizes the history and major advancements in these models (e.g., their application to predict the onset of AD and their combined use with network models). This review is intended to bring mathematical modeling to the attention of more scientists and clinical researchers working on AD to promote cross-disciplinary research.

The 3-(3-oxoisoindolin-1-yl)pentane-2,4-dione (ISOAC1) as a new molecule able to inhibit Amyloid β aggregation and neurotoxicity

Amyloid β 1-42 (Aβ1-42) protein aggregation is considered one of the main triggers of Alzheimer's disease (AD). In this study, we examined the in vitro anti-amyloidogenic activity of the isoindolinone derivative 3-(3-oxoisoindolin-1-yl)pentane-2,4-dione (ISOAC1) and its neuroprotective potential against the Aβ1-42 toxicity. By performing the Thioflavin T fluorescence assay, Western blotting analyses, and Circular Dichroism experiments, we found that ISOAC1 was able to reduce the Aβ1-42 aggregation and conformational transition towards β-sheet structures. Interestingly, in silico studies revealed that ISOAC1 was able to bind to both the monomer and a pentameric protofibril of Aβ1-42, establishing a hydrophobic interaction with the PHE19 residue of the Aβ1-42 KLVFF motif. In vitro analyses on primary cortical neurons showed that ISOAC1 counteracted the increase of intracellular Ca2+ levels and decreased the Aβ1-42-induced toxicity, in terms of mitochondrial activity reduction and increase of reactive oxygen species production. In addition, confocal microscopy analyses showed that ISOAC1 was able to reduce the Aβ1-42 intraneuronal accumulation. Collectively, our results clearly show that ISOAC1 exerts a neuroprotective effect by reducing the Aβ1-42 aggregation and toxicity, hence emerging as a promising compound for the development of new Aβ-targeting therapeutic strategies for AD treatment.

Flanking regions, amyloid cores, and polymorphism: the potential interplay underlying structural diversity

The β-sheet-rich amyloid core is the defining feature of protein aggregates associated with neurodegenerative disorders. Recent investigations have revealed that there exist multiple examples of the same protein, with the same sequence, forming a variety of amyloid cores with distinct structural characteristics. These structural variants, termed as polymorphs, are hypothesized to influence the pathological profile and the progression of different neurodegenerative diseases, giving rise to unique phenotypic differences. Thus, identifying the origin and properties of these structural variants remain a focus of studies, as a preliminary step in the development of therapeutic strategies. Here, we review the potential role of the flanking regions of amyloid cores in inducing polymorphism. These regions, adjacent to the amyloid cores, show a preponderance for being structurally disordered, imbuing them with functional promiscuity. The dynamic nature of the flanking regions can then manifest in the form of conformational polymorphism of the aggregates. We take a closer look at the sequences flanking the amyloid cores, followed by a review of the polymorphic aggregates of the well-characterized proteins amyloid-β, α-synuclein, Tau, and TDP-43. We also consider different factors that can potentially influence aggregate structure and how these regions can be viewed as novel targets for therapeutic strategies by utilizing their unique structural properties.

The QPLEX™ Plus Assay Kit for the Early Clinical Diagnosis of Alzheimer's Disease

We recently developed a multiplex diagnostic kit, QPLEX™ Alz plus assay kit, which captures amyloid-β1-40, galectin-3 binding protein, angiotensin-converting enzyme, and periostin simultaneously using microliters of peripheral blood and utilizes an optimized algorithm for screening Alzheimer's disease (AD) by correlating with cerebral amyloid deposition. Owing to the demand for early AD detection, we investigate the potential of our kit for the early clinical diagnosis of AD. A total of 1395 participants were recruited, and their blood samples were analyzed with the QPLEX™ kit. The average of QPLEX™ algorithm values in each group increased gradually in the order of the clinical progression continuum of AD: cognitively normal (0.382 ± 0.150), subjective cognitive decline (0.452 ± 0.130), mild cognitive impairment (0.484 ± 0.129), and AD (0.513 ± 0.136). The algorithm values between each group showed statistically significant differences among groups divided by Mini-Mental State Examination and Clinical Dementia Rating. The QPLEX™ algorithm values could be used to distinguish the clinical continuum of AD or cognitive function. Because blood-based diagnosis is more accessible, convenient, and cost- and time-effective than cerebral spinal fluid or positron emission tomography imaging-based diagnosis, the QPLEX™ kit can potentially be used for health checkups and the early clinical diagnosis of AD.

Paclitaxel induces cognitive impairment via necroptosis, decreased synaptic plasticity and M1 polarisation of microglia

CONTEXT

Paclitaxel (PTX) leads to chemotherapy brain (chemo-brain) which is characterised by cognitive impairment. It has been reported that necroptosis is associated with cognitive impairment in some neurodegenerative diseases, but it is not clear whether it is related to the development of chemo-brain.

OBJECTIVE

To investigate the role of necroptosis and related changes in PTX-induced cognitive impairment.

MATERIALS AND METHODS

C57bl/6n mice were randomly divided into five groups: control, vehicle, and different concentrations of PTX (6, 8, 10 mg/kg). Two additional groups received pre-treatment with Gdcl3 or PBS through Intracerebroventricular (ICV) injection before PTX-treatment. Cognitive function, necroptosis, synaptic plasticity and microglia polarisation were analysed.

RESULTS

PTX (10 mg/kg) induced significant cognitive impairment, accompanied by changes in synaptic plasticity, including decreased density of PSD95 (0.65-fold), BDNF (0.44-fold) and dendritic spines (0.57-fold). PTX induced necroptosis of 53.41% (RIP3) and 61.91% (MLKL) in hippocampal neurons, with high expression of RIP3 (1.58-fold) compared with the control group. MLKL (1.87-fold) exhibited the same trend, reaching a peak on the 14th day. The increased expression of iNOS (1.63-fold) and inflammatory factors such as TNF-α (1.85-fold) and IL-β (1.89-fold) compared to the control group suggests that M1 polarisation of microglia is involved in the process of cognitive impairment. Pre-treatment with Gdcl3 effectively reduced the number of microglia (0.50-fold), inhibited the release of TNF-α (0.73-fold) and IL-β (0.56-fold), and improved cognitive impairment.

CONCLUSION

We established a stable animal model of PTX-induced cognitive impairment and explored the underlying pathophysiological mechanism. These findings can guide the future treatment of chemo-brain.

Synthetic amyloid beta does not induce a robust transcriptional response in innate immune cell culture systems

BACKGROUND

Alzheimer's disease (AD) is a progressive neurodegenerative disease that impacts nearly 400 million people worldwide. The accumulation of amyloid beta (Aβ) in the brain has historically been associated with AD, and recent evidence suggests that neuroinflammation plays a central role in its origin and progression. These observations have given rise to the theory that Aβ is the primary trigger of AD, and induces proinflammatory activation of immune brain cells (i.e., microglia), which culminates in neuronal damage and cognitive decline. To test this hypothesis, many in vitro systems have been established to study Aβ-mediated activation of innate immune cells. Nevertheless, the transcriptional resemblance of these models to the microglia in the AD brain has never been comprehensively studied on a genome-wide scale.

METHODS

We used bulk RNA-seq to assess the transcriptional differences between in vitro cell types used to model neuroinflammation in AD, including several established, primary and iPSC-derived immune cell lines (macrophages, microglia and astrocytes) and their similarities to primary cells in the AD brain. We then analyzed the transcriptional response of these innate immune cells to synthetic Aβ or LPS and INFγ.

RESULTS

We found that human induced pluripotent stem cell (hIPSC)-derived microglia (IMGL) are the in vitro cell model that best resembles primary microglia. Surprisingly, synthetic Aβ does not trigger a robust transcriptional response in any of the cellular models analyzed, despite testing a wide variety of Aβ formulations, concentrations, and treatment conditions. Finally, we found that bacterial LPS and INFγ activate microglia and induce transcriptional changes that resemble many, but not all, aspects of the transcriptomic profiles of disease associated microglia (DAM) present in the AD brain.

CONCLUSIONS

These results suggest that synthetic Aβ treatment of innate immune cell cultures does not recapitulate transcriptional profiles observed in microglia from AD brains. In contrast, treating IMGL with LPS and INFγ induces transcriptional changes similar to those observed in microglia detected in AD brains.

Human serum albumin in neurodegeneration

Serum albumin (SA) exists in relatively high concentrations, in close contact with most cells. However, in the adult brain, except for cerebrospinal fluid (CSF), SA concentration is relatively low. It is mainly produced in the liver to serve as the main protein of the blood plasma. In the plasma, it functions as a carrier, chaperon, antioxidant, source of amino acids, osmoregulator, etc. As a carrier, it facilitates the stable presence and transport of the hydrophobic and hydrophilic molecules, including free fatty acids, steroid hormones, medicines, and metal ions. As a chaperon, SA binds to and protects other proteins. As an antioxidant, thanks to a free sulfhydryl group (-SH), albumin is responsible for most antioxidant properties of plasma. These functions qualify SA as a major player in, and a mirror of, overall health status, aging, and neurodegeneration. The low concentration of SA is associated with cognitive deterioration in the elderly and negative prognosis in multiple sclerosis (MS) and amyotrophic lateral sclerosis (ALS). SA has been shown to be structurally modified in neurological conditions such as Alzheimer's disease (AD). During blood-brain barrier damage albumin enters the brain tissue and could trigger epilepsy and neurodegeneration. SA is able to bind to the precursor agent of the AD, amyloid-beta (Aβ), preventing its toxic effects in the periphery, and is being tested for treating this disease. SA therapy may also be effective in brain rejuvenation. In the current review, we will bring forward the prominent properties and roles of SA in neurodegeneration.

Application of Programmable Tetrahedral Framework Nucleic Acid-Based Nanomaterials in Neurological Disorders: Progress and Prospects

Tetrahedral framework nucleic acid (tFNA), a special DNA nanodevice, is widely applied in diverse biomedical fields. Due to its high programmability, biocompatibility, tissue permeability as well as its capacity for cell proliferation and differentiation, tFNA presents a powerful tool that could overcome potential barriers in the treatment of neurological disorders. This review evaluates recent studies on the use and progress of tFNA-based nanomaterials in neurological disorders.

Pharmacological implications of ipriflavone against environmental metal-induced neurodegeneration and dementia in rats

Long-term exposure to environmental neurotoxic metals is implicated in the induction of dementia and cognitive decline. The present study aims to illustrate the therapeutic role of ipriflavone as a synthetic isoflavone against environmental metal-induced cognitive impairment in rats. Dementia was induced by a mixture of aluminum, cadmium, and fluoride for 90 days followed by ipriflavone for a further 30 days.  Metal-treated animals exhibited abnormal behaviors in the Morris water maze task. Neuropathological biomarkers including oxidative stress (TBARS, NO, SOD, GPX, GST, and GSH), inflammation (TNF- α, IL-6, and IL-1β), neurotransmission (AChE and MAO), and insulin resistance (insulin, insulin receptor, and insulin-degrading enzyme) were altered, which consequently elevated the level of amyloid-β42 and tau protein in the hippocampus tissues inducing neuronal injury. Ipriflavone significantly (P < 0.05) ameliorated the neurobehavioral abnormalities and the cognitive dysfunction biomarkers via antioxidant/anti-inflammatory mechanism. Moreover, ipriflavone downregulated the mRNA expression level of amyloid precursor protein and tau protein, preventing amyloid plaques and neurofibrillary tangle aggregation at P < 0.05. A molecular docking study revealed that ipriflavone has a potent binding affinity towards AChE more than donepezil and acts as a strong AChE inhibitor. Our data concluded that the therapeutic potential of ipriflavone against dementia could provide a new strategy in AD treatment.

microRNA-425 loss mediates amyloid plaque microenvironment heterogeneity and promotes neurodegenerative pathologies

Different cellular and molecular changes underlie the pathogenesis of Alzheimer's disease (AD). Among these, neuron‐specific dysregulation is a necessary event for accumulation of classic pathologies including amyloid plaques. Here, we show that AD‐associated pathophysiology including neuronal cell death, inflammatory signaling, and endolysosomal dysfunction is spatially colocalized to amyloid plaques in regions with abnormal microRNA‐425 (miR‐425) levels and this change leads to focal brain microenvironment heterogeneity, that is, an amyloid plaque‐associated microenvironment (APAM). APAM consists of multiple specific neurodegenerative signature pathologies associated with senile plaques that contribute to the heterogeneity and complexity of AD. Remarkably, miR‐425, a neuronal‐specific regulator decreased in AD brain, maintains a normal spatial transcriptome within brain neurons. We tested the hypothesis that miR‐425 loss correlates with enhanced levels of mRNA targets downstream, supporting APAM and AD progression. A miR‐425‐deficient mouse model has enhanced APP amyloidogenic processing, neuroinflammation, neuron loss, and cognitive impairment. In the APP/PS1 mouse model, intervening with miR‐425 supplementation ameliorated APAM changes and memory deficits. This study reveals a novel mechanism of dysregulation of spatial transcriptomic changes in AD brain, identifying a probable neuronal‐specific microRNA regulator capable of staving off amyloid pathogenesis. Moreover, our findings provide new insights for developing AD treatment strategies with miRNA oligonucleotide(s).

Extracellular protein components of amyloid plaques and their roles in Alzheimer's disease pathology

Alzheimer's disease (AD) is pathologically defined by the presence of fibrillar amyloid β (Aβ) peptide in extracellular senile plaques and tau filaments in intracellular neurofibrillary tangles. Extensive research has focused on understanding the assembly mechanisms and neurotoxic effects of Aβ during the last decades but still we only have a brief understanding of the disease associated biological processes. This review highlights the many other constituents that, beside Aβ, are accumulated in the plaques, with the focus on extracellular proteins. All living organisms rely on a delicate network of protein functionality. Deposition of significant amounts of certain proteins in insoluble inclusions will unquestionably lead to disturbances in the network, which may contribute to AD and copathology. This paper provide a comprehensive overview of extracellular proteins that have been shown to interact with Aβ and a discussion of their potential roles in AD pathology. Methods that can expand the knowledge about how the proteins are incorporated in plaques are described. Top-down methods to analyze post-mortem tissue and bottom-up approaches with the potential to provide molecular insights on the organization of plaque-like particles are compared. Finally, a network analysis of Aβ-interacting partners with enriched functional and structural key words is presented.

Multipronged Regulatory Functions of Serum Albumin in Early Stages of Amyloid-β Aggregation

Human serum albumin (HSA) is a major interacting-partner of Alzheimer's amyloid-β (Aβ) peptide in the plasma and has emerged as a promising therapeutic target. HSA inhibits Aβ fibrillization, but the underlying molecular mechanism is not well elucidated. In this work, we investigated the role of HSA in the early stages of Aβ aggregation by simulating the binding process of multiple Aβ monomers and protofibrils to HSA with extensive molecular dynamics simulations. HSA could simultaneously trap multiple Aβ monomers and accommodate the formation of nonfibrillar Aβ oligomers after binding. In particular, domains I and III show stronger binding capacities and hold preferable interaction sites for oligomers. Consequently, HSA prevents the formation of fibrillar oligomers in water, thus interfering with the nucleation process. On the other aspect, when protofibrils are preformed, HSA tends to block the β-strand spanning the central hydrophobic core located at the protofibril end, preventing the addition of monomers to protofibrils. Furthermore, Aβ protofibril structures are severely disrupted both globally and locally. Thus, further growth of protofibrils to fibrils is impeded by HSA. Our results collectively indicate that HSA performs multipronged regulatory functions in the early stages of Aβ aggregation. Our work advances the understanding of the amyloid inhibition of Aβ by HSA and provides theoretical guidance for developing rational therapies of Alzheimer's disease.

The clinical use of blood-test factors for Alzheimer's disease: improving the prediction of cerebral amyloid deposition by the QPLEXTM Alz plus assay kit

Alzheimer's disease (AD) is the leading cause of dementia, and many studies have focused on finding effective blood biomarkers for the accurate diagnosis of this disease. Predicting cerebral amyloid deposition is considered the key for AD diagnosis because a cerebral amyloid deposition is the hallmark of AD pathogenesis. Previously, blood biomarkers were discovered to predict cerebral amyloid deposition, and further efforts have been made to increase their sensitivity and specificity. In this study, we analyzed blood-test factors (BTFs) that can be commonly measured in medical health check-ups from 149 participants with cognitively normal, 87 patients with mild cognitive impairment, and 64 patients with clinically diagnosed AD dementia with brain amyloid imaging data available. We demonstrated that four factors among regular health check-up blood tests, cortisol, triglyceride/high-density lipoprotein cholesterol ratio, alanine aminotransferase, and free triiodothyronine, showed either a significant difference by or correlation with cerebral amyloid deposition. Furthermore, we made a prediction model for Pittsburgh compound B-positron emission tomography positivity, using BTFs and the previously discovered blood biomarkers, the QPLEXTM Alz plus assay kit biomarker panel, and the area under the curve was significantly increased up to 0.845% with 69.4% sensitivity and 90.6% specificity. These results show that BTFs could be used as co-biomarkers and that a highly advanced prediction model for amyloid plaque deposition could be achieved by the combinational use of diverse biomarkers.

Plexin-A4 mediates amyloid-β-induced tau pathology in Alzheimer's disease animal model

Amyloid-β (Aβ) and tau are major pathological hallmarks of Alzheimer's disease (AD). Several studies have revealed that Aβ accelerates pathological tau transition and spreading during the disease progression, and that reducing tau can mitigate pathological features of AD. However, molecular links between Aβ and tau pathologies remain elusive. Here, we suggest a novel role for the plexin-A4 as an Aβ receptor that induces aggregated tau pathology. Plexin-A4, previously known as proteins involved in regulating axon guidance and synaptic plasticity, can bound to Aβ with co-receptor, neuropilin-2. Genetic downregulation of plexin-A4 in neurons was sufficient to prevent Aβ-induced activation of CDK5 and reduce tau hyperphosphorylation and aggregation, even in the presence of Aβ. In an AD mouse model that manifests both Aβ and tau pathologies, genetic downregulation of plexin-A4 in the hippocampus reduced tau pathology and ameliorated spatial memory impairment. Collectively, these results indicate that the plexin-A4 is capable of mediating Aβ-induced tau pathology in AD pathogenesis.

Tetrahydroxy Stilbene Glucoside Ameliorates Cognitive Impairments and Pathology in APP/PS1 Transgenic Mice

Cognitive impairment is the main clinical manifestation of Alzheimer's disease (AD), and amyloid-β (Aβ) deposition and senile plaques are the characteristic neuropathological hallmarks in AD brains. This study aimed to explore the effect and mechanism of tetrahydroxy stilbene glucoside (TSG) on cognitive function in APP/PS1 mice during long-term administration. Here, we treated APP/PS1 model mice of AD with different doses of TSG (50 mg/kg and 100 mg/kg) for 5 to 17 months by gavage, and we further observed whether TSG could ameliorate the cognitive decline in APP/PS1 mice using behavioral tests, and investigated the possible mechanisms by immunohistochemistry and Western blotting. Our results showed that TSG treatment rescued the spatial and non-spatial learning and memory impairments of APP/PS1 mice at Morris water maze test and novel object recognition test. Furthermore, Aβ40/42 deposition in the cortex and hippocampus of APP/PS1 mice treated with TSG was significantly reduced compared to the wild type mice using the immunohistochemical technique. Finally, Western blotting showed that TSG primarily decreased the APP expression to avoid the Aβ plaque deposition in the cortex and hippocampus of mice. These results reveal the beneficial effects of TSG in APP/PS1-AD mice, which may be associated with the reduction of Aβ deposits in the brain.

Albumin Alters the Conformational Ensemble of Amyloid-β by Promiscuous Interactions: Implications for Amyloid Inhibition

Human serum albumin (HSA) is a key endogenous inhibitor of amyloid-β (Αβ) aggregation. In vitro HSA inhibits Aβ fibrillization and targets multiple species along the aggregation pathway including monomers, oligomers, and protofibrils. Amyloid inhibition by HSA has both pathological implications and therapeutic potential, but the underlying molecular mechanism remains elusive. As a first step towards addressing this complex question, we studied the interactions of an Aβ42 monomer with HSA by molecular dynamics simulations. To adequately sample the conformational space, we adapted the replica exchange with solute tempering (REST2) method to selectively heat the Aβ42 peptide in the absence and presence of HSA. Aβ42 binds to multiple sites on HSA with a preference to domain III and adopts various conformations that all differ from the free state. The β-sheet abundances of H14-E22 and A30-M33 regions are significantly reduced by HSA, so are the β-sheet lengths. HSA shifts the conformational ensemble towards more disordered states and alters the β-sheet association patterns. In particular, the frequent association of Q15-V24 and N27-V36 regions into β-hairpin which is critical for aggregation is impeded. HSA primarily interacts with the latter β-region and the N-terminal charged residues. They form promiscuous interactions characterized by salt bridges at the edge of the peptide-protein interface and hydrophobic cores at the center. Consequently, intrapeptide interactions crucial for β-sheet formation are disrupted. Our work builds the bridge between the modification of Aβ conformational ensemble and amyloid inhibition by HSA. It also illustrates the potential of the REST2 method in studying interactions between intrinsically disordered peptides and globular proteins.

Stem Cell Therapies in Alzheimer's Disease: Applications for Disease Modeling

Alzheimer's disease (AD) is a neurodegenerative disease with complex pathologic and biologic characteristics. Extracellular β-amyloid deposits, such as senile plaques, and intracellular aggregation of hyperphosphorylated tau, such as neurofibrillary tangles, remain the main neuropathological criteria for the diagnosis of AD. There is currently no effective treatment of the disease, and many clinical trials have failed to prove any benefits of new therapeutics. More recently, there has been increasing interest in harnessing the potential of stem cell technologies for drug discovery, disease modeling, and cell therapies, which have been used to study an array of human conditions, including AD. The recently developed and optimized induced pluripotent stem cell (iPSC) technology is a critical platform for screening anti-AD drugs and understanding mutations that modify AD. Neural stem cell (NSC) transplantation has been investigated as a new therapeutic approach to treat neurodegenerative diseases. Mesenchymal stem cells (MSCs) also exhibit considerable potential to treat neurodegenerative diseases by secreting growth factors and exosomes, attenuating neuroinflammation. This review highlights recent progress in stem cell research and the translational applications and challenges of iPSCs, NSCs, and MSCs as treatment strategies for AD. Even though these treatments are still in relative infancy, these developing stem cell technologies hold considerable promise to combat AD and other neurodegenerative disorders. SIGNIFICANCE STATEMENT: Alzheimer's disease (AD) is a neurodegenerative disease that results in learning and memory defects. Although some drugs have been approved for AD treatment, fewer than 20% of patients with AD benefit from these drugs. Therapies based on stem cells, including induced pluripotent stem cells, neural stem cells, and mesenchymal stem cells, provide promising therapeutic strategies for AD.

Performance of the QPLEX™ Alz plus assay, a novel multiplex kit for screening cerebral amyloid deposition

Background

Alzheimer’s disease (AD) is an irreversible neurodegenerative disease characterized by the hallmark finding of cerebral amyloid deposition. Many researchers have tried to predict the existence of cerebral amyloid deposition by using easily accessible blood plasma samples, but the effectiveness of such strategies remains controversial.

Methods

We developed a new multiplex kit, the QPLEX™ Alz plus assay kit, which uses proteomics-based blood biomarkers to prescreen for cerebral amyloid deposition. A total of 300 participants who underwent Pittsburgh compound B (PiB)-positron emission tomography (PET) which allows imaging of cerebral amyloid deposition were included in this study. We compared the levels of QPLEX™ biomarkers between patients who were classified as PiB-negative or PiB-positive, regardless of their cognitive function. Logistic regression analysis followed by receiver operating characteristic (ROC) curve analysis was performed. The kit accuracy was tested using a randomized sample selection method.

Results

The results obtained using our assay kit reached 89.1% area under curve (AUC) with 80.0% sensitivity and 83.0% specificity. Further validation of the QPLEX™ Alz plus assay kit using a randomized sample selection method showed an average accuracy of 81.5%.

Conclusions

Our QPLEX™ Alz plus assay kit provides preliminary evidence that it can be used as blood marker to predict cerebral amyloid deposition but independent validation is needed.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13195-020-00751-x.

The Neuroprotective and Neurodegeneration Effects of Heme Oxygenase-1 in Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disease characterized by complex pathological and biological features. Notably, extracellular amyloid-β deposits as senile plaques and intracellular aggregation of hyperphosphorylated tau as neurofibrillary tangles remain the primary premortem criterion for the diagnosis of AD. Currently, there exist no disease-modifying therapies for AD, and many clinical trials have failed to show its benefits for patients. Heme oxygenase 1 (HO-1) is a 32 kDa enzyme, which catalyzes the degradation of cellular heme to free ferrous iron, biliverdin, and carbon monoxide under stressful conditions. Several studies highlight the crucial pathological roles of HO-1 in the molecular processes of AD. The beneficial roles of HO-1 overexpression in AD brains are widely accepted due to its ability to convert pro-oxidant heme to biliverdin and bilirubin (antioxidants), which promote restoration of a suitable tissue redox microenvironment. However, the intracellular oxidative stress might be amplified by metabolites of HO-1 and exacerbate the progression of AD under certain circumstances. Several lines of evidence have demonstrated that upregulated HO-1 is linked to tauopathies, neuronal damage, and synapse aberrations in AD. Here, we review the aspects of the molecular mechanisms by which HO-1 regulates AD and the latest information on the pathobiology of AD. We further highlight the neuroprotective and neurodystrophic actions of HO-1 and the feasibility of HO-1 as a therapeutic target for AD.

Shenzao jiannao oral liquid, an herbal formula, ameliorates cognitive impairments by rescuing neuronal death and triggering endogenous neurogenesis in AD-like mice induced by a combination of Aβ42 and scopolamine

ETHNOPHARMACOLOGICAL RELEVANCE

According to the theory of traditional Chinese medicine (TCM), Alzheimer's disease (AD) is identified as "forgetfulness" or "dementia", and is mainly caused by "kidney essence deficiency" which ultimately induces "encephala reduction". Therefore, herbal formulas possessing the efficacy of nourishing kidney essence or replenishing brain marrow are commonly served as effective strategies for AD treatment. Shenzao jiannao oral liquid (SZJN), a traditional Chinese preparation approved by the China Food and Drug Administration (CFDA), is used for the treatment of insomnia and mind fatigue at present for its efficacy of nourishing kidneys. In present study, we found that SZJN could improve cognitive function of AD-like mice.

AIMS OF STUDY

This study aims to investigate the effects of SJZN on ameliorating cognitive deficits of AD-like mouse model, and to illuminate the underlying mechanisms from the perspective of neuroprotection and neurogenesis.

MATERIALS AND METHODS

Kunming mice (28 ± 2 g) were randomly allocated into seven groups: control, sham, model, donepezil and SZJN groups (low, middle and high). The AD mouse model was established by Aβ42 combined with scopolamine. SZJN were intragastrically administrated at doses of 0.3, 1.5 and 7.5 g/kg for 28 days. Morris water maze (MWM) test was applied to determine the cognitive function. Hematoxylin eosin (HE) and Nissl staining were carried out to evaluate pathological damages in the cortex and hippocampal tissues. To explore the protective effects of SZJN on multiple pathogenic factors of AD, protein levels of Aβ42, glial fibrillary acidic protein (GFAP), Bax, Bcl-2, Caspase-3, synaptophysin (SYP), brain-derived neurotrophic factor (BDNF), and neurogenesis related proteins were assessed using Immunofluorescence (IF) and western blot analysis. In vitro, the AD cell model was established by transduction of APP_695swe genes into Neural stem cells (NSCs) isolated from the hippocampal tissues of neonatal C57BL/6 mice. Cell viability assay and neurosphere formation assay were carried out to verify the efficacy of SZJN on proliferation of NSCs.

RESULTS

Our results demonstrated that SZJN (1.5 g/kg and 7.5 g/kg) treatment significantly ameliorated cognitive deficits of AD-like mice. SZJN (7.5 g/kg) treatment significantly retarded the pathological damages including neuronal degeneration, neuronal apoptosis, Aβ peptides aggregation and reaction of astrocytes in AD-like mice. In addition, SZJN (7.5 g/kg) increased the expression of BDNF and SYP, and restored the abnormal level of MDA and SOD in the brain of AD-like mice. Furthermore, SZJN treatment for 28 days remarkably increased the proliferation of NSCs evidenced by more Nestin⁺ and BrdU⁺ cells in the hippocampal DG regions, and increased the amount of mature neurons marked by NeuN both in the cortex and hippocampal DG regions. In vitro, SZJN treatement (16, 32, 64 mg/ml) promoted the proliferation of NSCs evidenced by the increased amount and enlarged size of the neurospheres (p < 0.05).

CONCLUSIONS

Our findings indicated that SZJN could ameliorate cognitive deficits by protecting neurons from death and triggering endogenous neurogenesis. Therefore, SZJN may be considered as a promising agent to restore neuronal loss and deter the deterioration in AD patients.

Amyloid Beta Peptide (Aβ1-42) Reverses the Cholinergic Control of Monocytic IL-1β Release

Amyloid-β peptide (Aβ_1-42), the cleavage product of the evolutionary highly conserved amyloid precursor protein, presumably plays a pathogenic role in Alzheimer's disease. Aβ_1-42 can induce the secretion of the pro-inflammatory cytokine intereukin-1β (IL-1β) in immune cells within and out of the nervous system. Known interaction partners of Aβ_1-42 are α7 nicotinic acetylcholine receptors (nAChRs). The physiological functions of Aβ_1-42 are, however, not fully understood. Recently, we identified a cholinergic mechanism that controls monocytic release of IL-1β by canonical and non-canonical agonists of nAChRs containing subunits α7, α9, and/or α10. Here, we tested the hypothesis that Aβ_1-42 modulates this inhibitory cholinergic mechanism. Lipopolysaccharide-primed monocytic U937 cells and human mononuclear leukocytes were stimulated with the P2X7 receptor agonist 2'(3')-O-(4-benzoylbenzoyl)adenosine-5'-triphosphate triethylammonium salt (BzATP) in the presence or absence of nAChR agonists and Aβ_1-42. IL-1β concentrations were measured in the supernatant. Aβ_1-42 dose-dependently (IC₅₀ = 2.54 µM) reversed the inhibitory effect of canonical and non-canonical nicotinic agonists on BzATP-mediated IL-1β-release by monocytic cells, whereas reverse Aβ_42-1 was ineffective. In conclusion, we discovered a novel pro-inflammatory Aβ_1-42 function that enables monocytic IL-1β release in the presence of nAChR agonists. These findings provide evidence for a novel physiological function of Aβ_1-42 in the context of sterile systemic inflammation.

Peripheral inflammatory biomarkers in Alzheimer's disease: a brief review

Alzheimer’s disease (AD) is a chronic neurodegenerative disease characterized by the accumulation of amyloid plaques and neurofibrillary tangles in the brain. The AD pathophysiology entails chronic inflammation involving innate immune cells including microglia, astrocytes, and other peripheral blood cells. Inflammatory mediators such as cytokines and complements are also linked to AD pathogenesis. Despite increasing evidence supporting the association between abnormal inflammation and AD, no well-established inflammatory biomarkers are currently available for AD. Since many reports have shown that abnormal inflammation precedes the outbreak of the disease, non-invasive and readily available peripheral inflammatory biomarkers should be considered as possible biomarkers for early diagnosis of AD. In this mini-review, we introduce the peripheral biomarker candidates related to abnormal inflammation in AD and discuss their possible molecular mechanisms. Furthermore, we also summarize the current state of inflammatory biomarker research in clinical practice and molecular diagnostics. We believe this review will provide new insights into biomarker candidates for the early diagnosis of AD with systemic relevance to inflammation during AD pathogenesis.

APOE-amyloid interaction: Therapeutic targets

Alzheimer's disease (AD) is a devastating neurodegenerative disorder that is growing in prevalence globally. It is the only major cause of death without any effective pharmacological means to treat or slow progression. Inheritance of the ε4 allele of the Apolipoprotein (APO) E gene is the strongest genetic risk factor for late-onset AD. The interaction between APOE and amyloid β (Aβ) plays a key role in AD pathogenesis. The APOE-Aβ interaction regulates Aβ aggregation and clearance and therefore directly influences the development of amyloid plaques, congophilic amyloid angiopathy and subsequent tau related pathology. Relatively few AD therapeutic approaches have directly targeted the APOE-Aβ interaction thus far. Here we review the critical role of APOE in the pathogenesis of AD and some of the most promising therapeutic approaches that focus on the APOE-Aβ interaction.

The role of cell type-specific mitochondrial dysfunction in the pathogenesis of Alzheimer's disease

The decrease of metabolism in the brain has been observed as the important lesions of Alzheimer’s disease (AD) from the early stages of diagnosis. The cumulative evidence has reported that the failure of mitochondria, an organelle involved in diverse biological processes as well as energy production, maybe the cause or effect of the pathogenesis of AD. Both amyloid and tau pathologies have an impact upon mitochondria through physical interaction or indirect signaling pathways, resulting in the disruption of mitochondrial function and dynamics which can trigger AD. In addition, mitochondria are involved in different biological processes depending on the specific functions of each cell type in the brain. Thus, it is necessary to understand mitochondrial dysfunction as part of the pathological phenotypes of AD according to each cell type. In this review, we summarize that 1) the effects of AD pathology inducing mitochondrial dysfunction and 2) the contribution of mitochondrial dysfunction in each cell type to AD pathogenesis.

Plasma tau/amyloid-β1-42 ratio predicts brain tau deposition and neurodegeneration in Alzheimer's disease

One of the hallmarks of Alzheimer's disease is abnormal deposition of tau proteins in the brain. Although plasma tau has been proposed as a potential biomarker for Alzheimer's disease, a direct link to brain deposition of tau is limited. Here, we estimated the amount of in vivo tau deposition in the brain by PET imaging and measured plasma levels of total tau (t-tau), phosphorylated tau (p-tau, T181) and amyloid-β1-42. We found significant correlations of plasma p-tau, t-tau, p-tau/amyloid-β1-42, and t-tau/amyloid-β1-42 with brain tau deposition in cross-sectional and longitudinal manners. In particular, t-tau/amyloid-β1-42 in plasma was highly predictive of brain tau deposition, exhibiting 80% sensitivity and 91% specificity. Interestingly, the brain regions where plasma t-tau/amyloid-β1-42 correlated with brain tau were similar to the typical deposition sites of neurofibrillary tangles in Alzheimer's disease. Furthermore, the longitudinal changes in cerebral amyloid deposition, brain glucose metabolism, and hippocampal volume change were also highly associated with plasma t-tau/amyloid-β1-42. These results indicate that combination of plasma tau and amyloid-β1-42 levels might be potential biomarkers for predicting brain tau pathology and neurodegeneration.

N2L, a novel lipoic acid-niacin dimer protects HT22 cells against β-amyloid peptide-induced damage through attenuating apoptosis

β-amyloid protein (Aβ) is thought to be the primary cause of the pathogenesis of Alzheimer's disease (AD). Niacin has been reported to have beneficial effects on AD. Previously, we synthesized a novel compound lipoicacid-niacin dimer (N2L) and revealed that it had potent blood-lipid regulation and antioxidative properties without aflushing effect. Given that lipid metabolism is also associated with AD, the present study aimed to investigate the neuroprotective effects of N2L on Aβ_1-42-induced cytotoxicity in HT22 cells. We found that N2L significantly attenuated cell apoptosis, MDA level, ROS content, and the mitochondrial membrane potential corruption induced by Aβ_1-42 in HT22 cells. In addition, the activities of SOD, GSH-px and CAT that were decreased by Aβ_1-42 were also restored by N2L. Furthermore, N2L reduced proapoptotic signaling by increasing the expression of anti-apoptotic Bcl-2 and decreasing the protein expression of both pro-apoptotic Bax and cleaved Caspase-3. Together, these findings indicate that N2L holds great potential for neuroprotection against Aβ_1-42-induced cytotoxicity via inhibition of oxidative stress and cell apoptosis, suggesting that N2L may be a promising agent for AD therapy.

Protofibrillar and Fibrillar Amyloid-β Binding Proteins in Cerebrospinal Fluid

Aggregation and deposition of misfolded amyloid-β (Aβ) peptide in the brain is central to Alzheimer's disease (AD). Oligomeric, protofibrillar, and fibrillar forms of Aβ are believed to be neurotoxic and cause neurodegeneration in AD, but the toxicity mechanisms are not well understood and may involve Aβ-interacting molecular partners. In a previous study, we identified potential Aβ42 protofibrillar-binding proteins in serum and cerebrospinal fluid (CSF) using an engineered version of Aβ42 (Aβ42CC) that forms protofibrils, but not fibrils. Here we studied binding of proteins to Aβ42 fibrils in AD and non-AD CSF and compared these with protofibrillar Aβ42CC-binding partners. Aβ42 fibrils sequestered 2.4-fold more proteins than Aβ42CC protofibrils. Proteins with selective binding to fibrillar aggregates with low nanomolar affinity were identified. We also found that protofibrillar and fibrillar Aβ-binding proteins represent distinct functional categories. Aβ42CC protofibrils triggered interactions with proteins involved in catalytic activities, like transferases and oxidoreductases, while Aβ42 fibrils were more likely involved in binding to proteoglycans, growth factors and neuron-associated proteins, e.g., neurexin-1, -2, and -3. Interestingly, 10 brain-enriched proteins were identified among the fibril-binding proteins, while protofibril-extracted proteins had more general expression patterns. Both types of Aβ aggregates bound several extracellular proteins. Additionally, we list a set of CSF proteins that might have potential to discriminate between AD and non-AD CSF samples. The results may be of relevance both for biomarker studies and for studies of Aβ-related toxicity mechanisms.

Therapeutic Potential of Multifunctional Tacrine Analogues

Abstract: Tacrine is a potent inhibitor of cholinesterases (acetylcholinesterase and butyrylcholinesterase) that shows limiting clinical application by liver toxicity. In spite of this, analogues of tacrine are considered as a model inhibitor of cholinesterases in the therapy of Alzheimer’s disease. The interest in these compounds is mainly related to a high variety of their structure and biological properties. In the present review, we have described the role of cholinergic transmission and treatment strategies in Alzheimer’s disease as well as the synthesis and biological activity of several recently developed classes of multifunctional tacrine analogues and hybrids, which consist of a new paradigm to treat Alzheimer’s disease. We have also reported potential of these analogues in the treatment of Alzheimer’s diseases in various experimental systems.

Key Peptides and Proteins in Alzheimer's Disease

Alzheimer's Disease (AD) is a form of progressive dementia involving cognitive impairment, loss of learning and memory. Different proteins (such as amyloid precursor protein (APP), β- amyloid (Aβ) and tau protein) play a key role in the initiation and progression of AD. We review the role of the most important proteins and peptides in AD pathogenesis. The structure, biosynthesis and physiological role of APP are shortly summarized. The details of trafficking and processing of APP to Aβ, the cytosolic intracellular Aβ domain (AICD) and small soluble proteins are shown, together with other amyloid-forming proteins such as tau and α-synuclein (α-syn). Hypothetic physiological functions of Aβ are summarized. The mechanism of conformational change, the formation and the role of neurotoxic amyloid oligomeric (oAβ) are shown. The fibril formation process and the co-existence of different steric structures (U-shaped and S-shaped) of Aβ monomers in mature fibrils are demonstrated. We summarize the known pathogenic and non-pathogenic mutations and show the toxic interactions of Aβ species after binding to cellular receptors. Tau phosphorylation, fibrillation, the molecular structure of tau filaments and their toxic effect on microtubules are shown. Development of Aβ and tau imaging in AD brain and CSF as well as blood biomarkers is shortly summarized. The most probable pathomechanisms of AD including the toxic effects of oAβ and tau; the three (biochemical, cellular and clinical) phases of AD are shown. Finally, the last section summarizes the present state of Aβ- and tau-directed therapies and future directions of AD research and drug development.

Regulation of the alternative β-secretase meprin β by ADAM-mediated shedding

Alzheimer's Disease (AD) is the sixth-leading cause of death in industrialized countries. Neurotoxic amyloid-β (Aβ) plaques are one of the pathological hallmarks in AD patient brains. Aβ accumulates in the brain upon sequential, proteolytic processing of the amyloid precursor protein (APP) by β- and γ-secretases. However, so far disease-modifying drugs targeting β- and γ-secretase pathways seeking a decrease in the production of toxic Aβ peptides have failed in clinics. It has been demonstrated that the metalloproteinase meprin β acts as an alternative β-secretase, capable of generating truncated Aβ2-x peptides that have been described to be increased in AD patients. This indicates an important β-site cleaving enzyme 1 (BACE-1)-independent contribution of the metalloprotease meprin β within the amyloidogenic pathway and may lead to novel drug targeting avenues. However, meprin β itself is embedded in a complex regulatory network. Remarkably, the anti-amyloidogenic α-secretase a disintegrin and metalloproteinase domain-containing protein 10 (ADAM10) is a direct competitor for APP at the cell surface, but also a sheddase of inactive pro-meprin β. Overall, we highlight the current cellular, molecular and structural understanding of meprin β as alternative β-secretase within the complex protease web, regulating APP processing in health and disease.

Potential Novel Approaches to Understand the Pathogenesis and Treat Alzheimer's Disease

There is growing genetic and proteomic data highlighting the complexity of Alzheimer's disease (AD) pathogenesis. Greater use of unbiased "omics" approaches is being increasingly recognized as essential for the future development of effective AD research, that need to better reflect the multiple distinct pathway abnormalities that can drive AD pathology. The track record of success in AD clinical trials thus far has been very poor. In part, this high failure rate has been related to the premature translation of highly successful results in animal models that mirror only limited aspects of AD pathology to humans. We highlight our recent efforts to increase use of human tissue to gain a better understanding of the AD pathogenesis subtype variety and to develop several distinct therapeutic approaches tailored to address this diversity. These therapeutic approaches include the blocking of the Aβ/apoE interaction, stimulation of innate immunity, and the simultaneous blocking of Aβ/tau oligomer toxicity. We believe that future successful therapeutic approaches will need to be combined to better reflect the complexity of the abnormal pathways triggered in AD pathogenesis.

Unravelling the interaction mechanism between clioquinol and bovine serum albumin by multi-spectroscopic and molecular docking approaches

Clioquinol has recently been proposed for the treatment of Alzheimer's disease. It is able to diminish β-amyloid protein aggregation and to restore cognition of Alzheimer's mice. However, its therapeutic benefits for Alzheimer's disease in human remain controversy and need further confirmation. Herein, we have explored the interaction mechanism of clioquinol toward bovine serum albumin (BSA) by means of multi-spectroscopic and docking simulation approaches. Clioquinol interacts with BSA by a combined mechanism of static and dynamic processes. Application of the Hill's equation to fluorescence quenching experiment revealed that the binding constant of the BSA-clioquinol complex is extremely high at 10⁸ M^-1 level. Competitive displacement and docking analysis consistently suggested that there are the multiple binding modes of clioquinol toward BSA. Competitive binding study showed that clioquinol shares the binding sites with ibuprofen and digitoxin on albumin, referring to be site II and site III binding compounds. Besides, partial binding in site I was also observed. Docking simulation confirmed that clioquinol favors to bind in site I, site II, site III, fatty acid binding site 5, and the protein cleft between subdomain IB and IIIB of the BSA. Due to its small size and electric dipole property, clioquinol may easily fit in multiple pockets of the BSA. Our finding suggests the potential role of BSA as a clioquinol carrier in the vascular system. Nonetheless, clioquinol-induced BSA aggregation has been observed by the three-dimensional fluorescence technique. This phenomenon may not only impair the BSA, but may also affect other endogenous proteins, which eventually causes adverse effects to human. Therefore, the redesigned or modified molecular structure of clioquinol may reduce its toxicity and improve its bioavailability.

Modification of Serum Albumin by High Conversion of Carboxyl to Amino Groups Creates a Potent Inhibitor of Amyloid β-Protein Fibrillogenesis

Fibrillogenesis of amyloid β-protein (Aβ) has been thought to be implicated in the progression of Alzheimer's disease (AD). Therefore, development of high-efficiency inhibitors is one of the strategies for the prevention and treatment of AD. Serum albumin has been found to capture Aβ monomers through its hydrophobic groove and suppress amyloid formation, but the inhibition efficiency is limited. Inspired by the strong inhibition potency of a basic protein, human lysozyme, we have herein proposed to develop a basified serum albumin by converting carboxyl groups into amino groups with ethylenediamine conjugated on the protein surface. The idea was verified with both bovine and human serum albumins (BSA/HSA). Four basified BSA (BSA-B) preparations with amino modification degrees (MDs) from 8.0 to 41.5 were first synthesized. Extensive biophysical and biological analyses revealed that the inhibition potency significantly increased with increasing amino MD. BSA-B of the highest MD (41.5), BSA-B4, which had an isoelectric point of 9.7, presented strong inhibition on Aβ₄₂ fibrillation at a concentration as low as 0.5 μM, at which it functioned similarly with 25 μM native BSA to impede 25 μM Aβ fibrillation. Cell viability assays also confirmed that the detoxification of 5 μM BSA-B4 was superior over 25 μM native BSA by increasing cell viability from 60.6% to 96.0%. Fluorescence quenching study unveiled the decrease of the binding affinity between Aβ₄₂ and the hydrophobic pocket region of BSA-B4, while quartz crystal microbalance experiments demonstrated that the binding constant of BSA-B4 to Aβ₄₂ increased nearly 5 times. Therefore, the increase of electrostatic interactions between BSA-B4 and Aβ₄₂ was the main reason for its high potency. Hence, aminated BSA achieved a conversion of binding way to Aβ from a mainly single-site hydrophobic binding to multiregional electrostatic interactions. Similar results were obtained with basified HSA preparations on inhibiting the amyloid formation and cytotoxicity. This work has thus provided new insights into the development of more efficient protein-based inhibitors against Aβ fibrillogenesis.

Future horizons in Alzheimer's disease research

There are growing genetic, transcriptomic and proteomic data pointing to the complexity of Alzheimer's disease (AD) pathogenesis. Unbiased "omics" approaches are essential for the future development of effective AD research, which will need to be combined and personalized, given that multiple distinct pathways can drive AD pathology. It is essential to gain a better understanding of the AD pathogenesis subtype variety and to develop several distinct therapeutic approaches tailored to address this diversity, as well as the common presence of mixed pathologies. These nonmutually exclusive therapeutic approaches include the targeting of multiple toxic oligomeric species concurrently, targeting the apolipoprotein E/amyloid β interaction and the modulation of innate immunity, as well as more "out of the box" ideas such as targeting infectious agents that may play a role in AD.

Blood acetylcholinesterase level is a potential biomarker for the early detection of cerebral amyloid deposition in cognitively normal individuals

Cerebral β-amyloid (cAβ) deposition and cholinergic dysfunction have been considered as major pathological and functional hallmarks of Alzheimer's disease (AD). Acetylcholinesterase (AChE) is one of the major cholinergic enzymes, and there is no report to show the relationship between cAβ accumulation and peripheral AChE alteration in early stage of AD pathogenesis. Recent studies demonstrate that cAβ starts to deposit 15-20 years ahead of symptomatic appearance and this preclinical AD is important for early diagnosis of disease. In this study, we investigated the link between cAβ deposition and the peripheral AChE in cognitively normal (CN) individuals. A total of 407 individuals who underwent Pittsburgh compound B (PiB)-positron emission tomography participated in our study. Lower levels of plasma AChE and its enzymatic activity were detected in CN individuals with cAβ deposition than in those without cAβ. Plasma AChE levels and enzymatic activity were negatively correlated with the degree of cAβ deposition. Our results suggest that blood AChE can be used as a potential blood biomarker for the prediction of cAβ deposition in CN individuals.

Neuroprotective Effect of Tetrahedral DNA Nanostructures in a Cell Model of Alzheimer's Disease

Accumulating evidence supports the abnormal deposition of amyloid β-peptide (Aβ) as the main cause of Alzheimer's disease (AD). Therefore, fighting against the formation, deposition, and toxicity of Aβ is a basic strategy for the treatment of AD. In the process of in vitro nerve cell culture, screening out drugs that can antagonize a series of toxic reactions caused by β-amyloid deposition has become an effective method for the follow-up treatment of AD. Our previous studies showed that tetrahedral DNA nanostructures (TDNs) had good biocompatibility and had some positive effects on the biological behavior of cells. In this study, the main aim of our work was to explore the effects and potential mechanism of TDNs in protecting neuronal PC12 cells from the toxicity of Aβ. Our study demonstrated that TDNs can protect and rescue PC12 cell death through Aβ25-35-induced PC12 cell apoptosis. Further studies showed that TDNs significantly improved the apoptosis by affecting the abnormal cell cycle, restoring abnormal nuclear morphology and caspase activity. Western blot analysis showed that TDNs could prevent the damage caused by Aβ deposition by activating the ERK1/2 pathway and thus be a potential therapeutic agent with a neuroprotective effect in Alzheimer's disease. Our finding provides a potential application of TDNs in the prevention and treatment of AD.

Charge effects of self-assembled chitosan-hyaluronic acid nanoparticles on inhibiting amyloid β-protein aggregation

Amyloid β-protein (Aβ) aggregation is crucial for the pathogenesis of Alzheimer's disease, and surface charge of nanoparticles (NPs) has been recognized as an important factor influencing Aβ aggregation. Herein, we report a systematic study on the issue with a series of self-assembled chitosan-hyaluronic acid composite (CH) NPs of different surface charges (CH1 to CH7, zeta potentials from +38 to -35 mV). Both the positive and negative CH NPs inhibited Aβ aggregation and the inhibitory effect increased with increasing the surface charges density. Circular dichroism spectroscopy and atomic force microscopy revealed the difference in their working mechanisms. Studies at different pH values further confirmed the importance of electrostatic interactions in Aβ aggregation and presented that the effects of CH NPs changed due to the change of Aβ charge property with pH. This work has thus provided new insight into the surface charge effects on Aβ aggregation.

Nanogels of dual inhibitor-modified hyaluronic acid function as a potent inhibitor of amyloid β-protein aggregation and cytotoxicity

Inhibition of amyloid β-protein (Aβ) aggregation is considered as a promising strategy for the prevention and treatment of Alzheimer’s disease. Epigallocatechin-3-gallate (EGCG) and curcumin have been recognized as effective inhibitors of Aβ aggregation. Herein, we proposed dual-inhibitor modification of hyaluronic acid (HA) to explore the synergistic effect of the two inhibitors. EGCG-modified HA (EHA) formed dispersed hydrogel structures, while EGCG-curcumin bi-modified HA (CEHA) self-assembled into nanogels like curcumin-modified HA (CHA). Thioflavin T fluorescent assays revealed that the inhibitory effect of CEHA was 69% and 55% higher than EHA and CHA, respectively, and cytotoxicity assays showed that the viability of SH-SY5Y cells incubated with Aβ and CEHA was 28% higher than that with Aβ and the mixture of EHA and CHA. These results clearly indicate the synergism of the two inhibitors. It is considered that the difference in the hydrophobicities of the two inhibitors made the bi-modification of HA provide a favorable CEHA nanostructure that coordinated different inhibition effects of the two inhibitors. This research indicates that fabrication of dual-inhibitor nanosystem is promising for the development of potent agents against Aβ aggregation and cytotoxicity.

Prion Protein as a Toxic Acceptor of Amyloid-β Oligomers

The initial report that cellular prion protein (PrPC) mediates toxicity of amyloid-β species linked to Alzheimer's disease was initially treated with scepticism, but growing evidence supports this claim. That there is a high-affinity interaction is now clear, and its molecular basis is being unraveled, while recent studies have identified possible downstream toxic mechanisms. Determination of the clinical significance of such interactions between PrPC and disease-associated amyloid-β species will require experimental medicine studies in humans. Trials of compounds that inhibit PrP-dependent amyloid-β toxicity are commencing in humans, and although it is clear that only a fraction of Alzheimer's disease toxicity could be governed by PrPC, a partial, but still therapeutically useful, role in human disease may soon be testable.

Serum Albumin's Protective Inhibition of Amyloid-β Fiber Formation Is Suppressed by Cholesterol, Fatty Acids and Warfarin

Central to Alzheimer's disease (AD) pathology is the assembly of monomeric amyloid-β peptide (Aβ) into oligomers and fibers. The most abundant protein in the blood plasma and cerebrospinal fluid is human serum albumin. Albumin can bind to Aβ and is capable of inhibiting the fibrillization of Aβ at physiological (μM) concentrations. The ability of albumin to bind Aβ has recently been exploited in a phase II clinical trial, which showed a reduction in cognitive decline in AD patients undergoing albumin-plasma exchange. Here we explore the equilibrium between Aβ monomer, oligomer and fiber in the presence of albumin. Using transmission electron microscopy and thioflavin-T fluorescent dye, we have shown that albumin traps Aβ as oligomers, 9 nm in diameter. We show that albumin-trapped Aβ oligomeric assemblies are not capable of forming ion channels, which suggests a mechanism by which albumin is protective in Aβ-exposed neuronal cells. In vivo albumin binds a variety of endogenous and therapeutic exogenous hydrophobic molecules, including cholesterol, fatty acids and warfarin. We show that these molecules bind to albumin and suppress its ability to inhibit Aβ fiber formation. The interplay between Aβ, albumin and endogenous hydrophobic molecules impacts Aβ assembly; thus, changes in cholesterol and fatty acid levels in vivo may impact Aβ fibrillization, by altering the capacity of albumin to bind Aβ. These observations are particularly intriguing given that high cholesterol or fatty acid diets are well-established risk factors for late-onset AD.

Neuroprotective effect of berberine against environmental heavy metals-induced neurotoxicity and Alzheimer's-like disease in rats

Heavy metals are reported as neurodegenerative disorders progenitor. They play a role in the precipitation of abnormal β-amyloid protein and hyper-phosphorylated tau, the main hallmarks of Alzheimer's disease (AD). The present study aimed to validate the heavy metals-induced Alzheimer's-like disease in rats as an experimental model of AD and explore the therapeutic effect of berberine via tracking its effect on the oxidative stress-inflammatory pathway. Alzheimer's-like disease was induced in rats orally by a mixture of aluminium, cadmium and fluoride for three months, followed by berberine treatment for another one month. Berberine significantly improved the cognitive behaviors in Morris water maze test and offered a protective effect against heavy metals-induced memory impairment. Docking results showed that berberine inhibited AChE, COX-2 and TACE. Matching with in silico study, berberine downregulated the AChE expression and inhibited its activity in the brain tissues. Also, it normalized the production of TNF- α, IL-12, IL-6 and IL-1β. Moreover, it evoked the production of antioxidant Aβ40 and inhibited the formation of Aβ42, responsible for the aggregations of amyloid-β plaques. Histopathological examination confirmed the neuroprotective effect of berberine. The present data advocate the possible beneficial effect of berberine as therapeutic modality for Alzheimer's disease via its antiinflammatory/antioxidant mechanism.

Low Serum Phosphorus Correlates with Cerebral Aβ Deposition in Cognitively Impaired Subjects: Results from the KBASE Study

Alzheimer's disease (AD), characterized by progressive cognitive decline, is the most prevalent neurodegenerative disease in the elderly. Cerebral β-amyloid (Aβ) deposition is the major pathological hallmark of AD. Recent studies also have shown that the serum level of phosphorus correlates to the risk of incident dementia. To date, the linkage between cerebral Aβ deposition and the serum phosphorus level remains unknown. In this study, we analyzed the levels of serum phosphorus in 109 mild cognitive impairment (MCI) and 73 AD dementia (ADD) subjects. All subjects underwent Pittsburgh compound B positron emission tomography (PiB-PET) imaging to measure cerebral Aβ deposition. The results with Aβ deposition was compared with the serum levels of phosphorus. The subjects with cerebral Aβ deposition showed lower levels of serum phosphorus than those without Aβ deposition. Furthermore, multiple regression analyses showed that a low level of serum phosphorus correlated with cerebral Aβ deposition, even when age, sex, apolipoprotein E ε4 genotype, and MMSE z-score were controlled for. Serum levels of other ions, including calcium, iron, zinc, and copper, showed no such correlation. In conclusion, our results suggest that the serum level of phosphorus may be used as an easily accessible blood biomarker for cerebral Aβ deposition in a cognitively impaired population.

Brazilin inhibits the Zn2+-mediated aggregation of amyloid β-protein and alleviates cytotoxicity

Interactions of Zn²⁺ with amyloid β-protein (Aβ) and the subsequent induction of Aβ aggregation have been implicated in the pathogenesis of Alzheimer's disease (AD). The development of small-compound inhibitors against Zn²⁺-mediated Aβ aggregation is therefore greatly desired. In this study, brazilin was used to inhibit Zn²⁺-mediated Aβ aggregation and alleviate its cytotoxicity. The binding properties of brazilin and Zn²⁺ were first probed using Fourier transform infrared (FTIR) spectroscopy and isothermal titration calorimetry (ITC) assays. Both the FTIR and ITC results have shown that brazilin is able to bind Zn²⁺ in a physiologically suitable range of concentrations. The dissociation constant (K_d) between brazilin and Zn²⁺ was about 46.0±6.8μM, which makes brazilin a potential drug model for the chelation of free Zn²⁺. Moreover, the higher affinity of brazilin for Aβ₄₂ (K_d=2.5±1.6μM) than that of Zn²⁺ (K_d=6.2±0. 9μM), enables brazilin to sequester Zn²⁺ from the Aβ₄₂-Zn²⁺ complex. In addition, the inhibitory effects of brazilin on Zn²⁺-mediated Aβ aggregation were examined using the Thioflavin T fluorescence assay, transmission electron microscopy and cytotoxicity assays. It was found that brazilin showed remarkable inhibitory capability against Zn²⁺-induced aggregation of Aβ₄₂. Furthermore, the Zn²⁺-mediated cytotoxicity of Aβ₄₂ was also largely mitigated under the influence of brazilin. This study therefore provides further insights into the role of Zn²⁺ in the Aβ₄₂ aggregation pathway, indicating potential new strategies for the design of small compounds with therapeutic potential for AD.

Targeting Apolipoprotein E/Amyloid β Binding by Peptoid CPO_Aβ17-21 P Ameliorates Alzheimer's Disease Related Pathology and Cognitive Decline

Inheritance of the apolipoprotein E4 (apoE4) genotype has been identified as the major genetic risk factor for late onset Alzheimer's disease (AD). Studies have shown that apoE, apoE4 in particular, binds to amyloid-β (Aβ) peptides at residues 12-28 of Aβ and this binding modulates Aβ accumulation and disease progression. We have previously shown in several AD transgenic mice lines that blocking the apoE/Aβ interaction with Aβ12-28 P reduced Aβ and tau-related pathology, leading to cognitive improvements in treated AD mice. Recently, we have designed a small peptoid library derived from the Aβ12-28 P sequence to screen for new apoE/Aβ binding inhibitors with higher efficacy and safety. Peptoids are better drug candidates than peptides due to their inherently more favorable pharmacokinetic properties. One of the lead peptoid compounds, CPO_Aβ17-21 P, diminished the apoE/Aβ interaction and attenuated the apoE4 pro-fibrillogenic effects on Aβ aggregation in vitro as well as apoE4 potentiation of Aβ cytotoxicity. CPO_Aβ17-21 P reduced Aβ-related pathology coupled with cognitive improvements in an AD APP/PS1 transgenic mouse model. Our study suggests the non-toxic, non-fibrillogenic peptoid CPO_Aβ17-21 P has significant promise as a new AD therapeutic agent which targets the Aβ related apoE pathway, with improved efficacy and pharmacokinetic properties.

Proximate Mediators of Microvascular Dysfunction at the Blood-Brain Barrier: Neuroinflammatory Pathways to Neurodegeneration

Current projections are that by 2050 the numbers of people aged 65 and older with Alzheimer's disease (AD) in the US may increase threefold while dementia is projected to double every 20 years reaching ~115 million by 2050. AD is clinically characterized by progressive dementia and neuropathologically by neuronal and synapse loss, accumulation of amyloid plaques, and neurofibrillary tangles (NFTs) in specific brain regions. The preclinical or presymptomatic stage of AD-related brain changes may begin over 20 years before symptoms occur, making development of noninvasive biomarkers essential. Distinct from neuroimaging and cerebrospinal fluid biomarkers, plasma or serum biomarkers can be analyzed to assess (i) the presence/absence of AD, (ii) the risk of developing AD, (iii) the progression of AD, or (iv) AD response to treatment. No unifying theory fully explains the neurodegenerative brain lesions but neuroinflammation (a lethal stressor for healthy neurons) is universally present. Current consensus is that the earlier the diagnosis, the better the chance to develop treatments that influence disease progression. In this article we provide a detailed review and analysis of the role of the blood-brain barrier (BBB) and damage-associated molecular patterns (DAMPs) as well as coagulation molecules in the onset and progression of these neurodegenerative disorders.

Artemisinin protects PC12 cells against β-amyloid-induced apoptosis through activation of the ERK1/2 signaling pathway

Accumulating evidence displays that an abnormal deposition of amyloid beta-peptide (Aβ) is the primary cause of the pathogenesis of Alzheimer's disease (AD). And therefore the elimination of Aβ is regarded as an important strategy for AD treatment. The discovery of drug candidates using culture neuronal cells against Aβ peptide toxicity is believed to be an effective approach to develop drug for the treatment of AD patients. We have previously showed that artemisinin, a FDA-approved anti-malaria drug, has neuroprotective effects recently. In the present study, we aimed to investigate the effects and potential mechanism of artemisinin in protecting neuronal PC12 cells from toxicity of β amyloid peptide. Our studies revealed that artemisinin, in clinical relevant concentration, protected and rescued PC12 cells from Aβ25–35-induced cell death. Further study showed that artemisinin significantly ameliorated cell death due to Aβ25–35 insult by restoring abnormal changes in nuclear morphology, lactate dehydrogenase, intracellular ROS, mitochondrial membrane potential and activity of apoptotic caspase. Western blotting analysis demonstrated that artemisinin activated extracellular regulated kinase ERK1/2 but not Akt survival signaling. Consistent with the role of ERK1/2, preincubation of cells with ERK1/2 pathway inhibitor PD98059 blocked the effect of artemisinin while PI3K inhibitor LY294002 has no effect. Moreover, Aβ1-42 also caused cells death of PC12 cells while artemisinin suppressed Aβ1-42 cytotoxicity in PC12 cells. Taken together, these results, at the first time, suggest that artemisinin is a potential protectant against β amyloid insult through activation of the ERK1/2 pathway. Our finding provides a potential application of artemisinin in prevention and treatment of AD.

•

β-amyloid induced apoptosis in PC12 cells.

•

Artemisinin protected PC12 cells against β-amyloid-induced apoptosis.

•

Artemisinin activated ERK1/2 signaling pathway in PC12 cells.

•

Artemisinin protected PC12 cells against β-amyloid toxicity by ERK1/2 signaling pathway.