Soluble amyloid β-protein (Aβ) oligomers, the main neurotoxic species, are predominantly formed from monomers through a fibril-catalyzed secondary nucleation. Herein, we virtually screened an in-house library of natural compounds and discovered brazilin as a dual functional compound in both Aβ42 fibrillogenesis inhibition and mature fibril remodeling, leading to significant reduction in Aβ42 cytotoxicity. The potent inhibitory effect of brazilin was proven by an IC50 of 1.5 ± 0.3 μM, which was smaller than that of (-)-epigallocatechin gallate in Phase III clinical trials and about one order of magnitude smaller than those of curcumin and resveratrol. Most importantly, it was found that brazilin redirected Aβ42 monomers and its mature fibrils into unstructured Aβ aggregates with some β-sheet structures, which could prevent both the primary nucleation and the fibril-catalyzed secondary nucleation. Molecular simulations demonstrated that brazilin inhibited Aβ42 fibrillogenesis by directly binding to Aβ42 species via hydrophobic interactions and hydrogen bonding and remodeled mature fibrils by disrupting the intermolecular salt bridge Asp23-Lys28 via hydrogen bonding. Both experimental and computational studies revealed a different working mechanism of brazilin from that of known inhibitors. These findings indicate that brazilin is of great potential as a neuroprotective and therapeutic agent for Alzheimer's disease.

Amyloid-β (Aβ) and islet amyloid polypeptide (IAPP) are small peptides, classified as amyloids, that have the potential to self-assemble and form cytotoxic species, such as small soluble oligomers and large insoluble fibrils. The formation of Aβ aggregates facilitates the progression of Alzheimer's disease (AD), while IAPP aggregates induce pancreatic β-cell apoptosis, leading to exacerbation of type 2 diabetes (T2D). Cross-amyloid interactions between Aβ and IAPP have been described both in vivo and in vitro, implying the role of Aβ or IAPP as modulators of cytotoxic self-aggregation of each species, and suggesting that Aβ-IAPP interactions are a potential molecular link between AD and T2D. Using molecular dynamics (MD) simulations, "hotspot" regions of the two peptides were studied to understand the formation of hexamers in a heterogeneous and homogeneous peptide-containing environment. Systems of only Aβ(16-22) peptides formed antiparallel, β-barrel-like structures, while systems of only IAPP(20-29) peptides formed stacked, parallel β-sheets and had relatively unstable aggregation structures after 2 μs of simulation time. Systems containing both Aβ and IAPP (1:1 ratio) hexamers showed antiparallel, β-barrel-like structures, with an interdigitated arrangement of Aβ(16-22) and IAPP(20-29). These β-barrel structures have features of cytotoxic amyloid species identified in previous literature. Ultimately, this work seeks to provide atomistic insight into both the mechanism behind cross-amyloid interactions and structural morphologies of these toxic amyloid species.

The gut-brain axis has attracted increasing attention in recent years, fueled by accumulating symptomatic, physiological, and pathological findings. In this study, the aggregation and toxicity of amyloid beta (Aβ), the pathogenic peptide associated with Alzheimer's disease (AD), seeded by FapC amyloid fragments (FapCS) of Pseudomonas aeruginosa that colonizes the gut microbiome through infections are examined. FapCS display favorable binding with Aβ and a catalytic capacity in seeding the peptide amyloidosis. Upon seeding, twisted Aβ fibrils assume a much-shortened periodicity approximating that of FapC fibrils, accompanied by a 37% sharp rise in the fibrillar diameter, compared with the control. The robust seeding capacity for Aβ by FapCS and the biofilm fragments derived from P. aeruginosa entail abnormal behavior pathology and immunohistology, as well as impaired cognitive function of zebrafish. Together, the data offer the first concrete evidence of structural integration and inheritance in peptide cross-seeding, a crucial knowledge gap in understanding the pathological correlations between different amyloid diseases. The catalytic role of infectious bacteria in promoting Aβ amyloidosis may be exploited as a potential therapeutic target, while the altered mesoscopic signatures of Aβ fibrils may serve as a prototype for molecular assembly and a biomarker for screening bacterial infections in AD.

Epidemiological studies support a connection between the two common disorders, type-2 diabetes and Alzheimer's disease. Both conditions have local amyloid formation in their pathogenesis, and cross-seeding between islet amyloid polypeptide (IAPP) and amyloid β (Aβ) could constitute the link. The bimolecular fluorescence complementation (BiFC) assay was used to investigate the occurrence of heterologous interactions between IAPP and Aβ and to compare the potential toxic effects of IAPP/Aβ, IAPP/IAPP, and Aβ/Aβ expression in living cells. Microscopy was used to confirm the fluorescence and determine the lysosomal, mitochondrial areas and mitochondrial membrane potential, and a FACS analysis was used to determine ROS production and the role for autophagy. Drosophila melanogaster expressing IAPP and Aβ was used to study their co-deposition and effects on longevity. We showed that the co-expression of IAPP and Aβ resulted in fluorophore reconstitution to the same extent as determined for homologous IAPP/IAPP or Aβ/Aβ expression. The BiFC(+)/BiFC(-) ratio of lysosomal area calculations increased in transfected cells independent of the vector combinations, while only Aβ/Aβ expression increased mitochondrial membrane potential. Expression combinations containing Aβ were necessary for the formation of a congophilic amyloid. In Drosophila melanogaster expressing IAPP/Aβ, co-deposition of the amyloid-forming peptides caused reduced longevity. The BiFC results confirmed a heterologous interaction between IAPP and Aβ, while co-deposits in the brain of Drosophila suggest mixed amyloid aggregates.

Pyroglutamate-modified amyloid β (AβpE3) could be a biomarker for Aβ plaque pathology in the brain. An ultra-high-sensitive assay is needed for detecting AβpE3-40.

Individuals with Down syndrome (DS) show enhanced amyloid beta (Aβ) deposition in the brain. A new positron emission tomography (PET) index of amyloid load (AβL ) was recently developed as an alternative to standardized uptake value ratios (SUVrs) to quantify Aβ burden with high sensitivity for detecting and tracking Aβ change.1.

Aberrant misfolding and amyloid aggregation, which result in amyloid fibrils, are frequent and critical pathological incidents in various neurodegenerative disorders. Multiple drugs or inhibitors have been investigated to avert amyloid aggregation in individual peptides, exhibiting sequence-dependent inhibition mechanisms. Establishing or inventing inhibitors capable of preventing amyloid aggregation in a wide variety of amyloid peptides is quite a daunting task. Bleomycin (BLM), a complex glycopeptide, has been widely used as an antibiotic and antitumor drug due to its ability to inhibit DNA metabolism, and as an antineoplastic, especially for solid tumors. In this study, we investigated the dual inhibitory effects of BLM on Aβ aggregation, associated with Alzheimer's disease and hIAPP, which is linked to type 2 diabetes, using both computational and experimental techniques. Combined results from drug repurposing and replica exchange molecular dynamics simulations demonstrate that BLM binds to the β-sheet region considered a hotspot for amyloid fibrils of Aβ and hIAPP. BLM was also found to be involved in β-sheet destabilization and, ultimately, in its reduction. Further, experimental validation through in vitro amyloid aggregation assays was obtained wherein the fibrillar load was decreased for the BLM-treated Aβ and hIAPP peptides in comparison to controls. For the first time, this study shows that BLM is a dual inhibitor of Aβ and hIAPP amyloid aggregation. In the future, the conformational optimization and processing of BLM may help develop various efficient sequence-dependent inhibitors against amyloid aggregation in various amyloid peptides.

Amyloid-β (Aβ) is a peptide deposited in the brain parenchyma in Alzheimer's disease and in cerebral blood vessels, causing cerebral amyloid angiopathy (CAA). Aβ pathology is transmissible experimentally in animals and through medical procedures in humans, such as contaminated growth hormone or dura mater transplantation in the context of iatrogenic prion disease. Here, we present four patients who underwent neurosurgical procedures during childhood or teenage years and presented with intracerebral haemorrhage approximately three decades later, caused by severe CAA. None of these patients carried pathogenic mutations associated with early Aβ pathology development. In addition, we identified in the literature four patients with a history of neurosurgical intervention and subsequent development of CAA. These findings raise the possibility that Aβ pathology may be transmissible, as prion disease is, through neurosurgical procedures.

The aggregation or misfolding of amyloid-β (Aβ) is a major pathological hallmark of Alzheimer's disease (AD). The regulation of Aβ aggregation is thought to be an effective strategy for AD treatment. The capability of a water-soluble porphyrin, 5,10,15,20-tetrakis(N-methyl-4-pyridyl)porphyrin (TMPyP), to inhibit Aβ aggregation and to lower Aβ-induced toxicity was demonstrated. As evidenced by surface plasmon resonance and circular dichroism, TMPyP can not only disrupt Aβ aggregation but also disassemble the preformed Aβ aggregates. The atomic force microscopy imaging proves that TMPyP inhibits the formation of both oligomers and fibrils. Molecular dynamic simulations provide an insight into the interaction between TMPyP and Aβ at the molecular level. The half-maximal inhibitory concentrations of TMPyP acting on the oligomers and fibrils were determined to be 0.6 and 0.43 μM, respectively. As a member of porphyrin family, TMPyP is of rather low cytotoxicity, and the cytotoxicity of the Aβ aggregates was also relieved upon coincubation with TMPyP. The excellent performance of TMPyP thus makes it a potential drug candidate for AD therapy.

Beta amyloid (Aβ) is a key component of parenchymal Aβ plaques and vascular Aβ fibrils, which lead to cerebral amyloid angiopathy (CAA) in Alzheimer's disease (AD). Recent studies have revealed that Aβ contained in the cerebrospinal fluid (CSF) can re-enter into brain through paravascular spaces. However, whether Aβ in CSF may act as a constant source of pathogenic Aβ in AD is still unclear. This study aimed to examine whether Aβ pathology could be worsened when CSF Aβ level was enhanced by intra-cisternal infusion of aged brain extract containing abundant Aβ in TgCRND8 host mice. TgCRND8 mouse is an AD animal model which develops predominant parenchymal Aβ plaques in the brain at as early as 3 months of age. Here, we showed that single intracisternal injection of Aβ seeds into TgCRND8 mice before the presence of Aβ pathology induced robust prion-like propagation of CAA within 90 days. The induced CAA is mainly distributed in the cerebral cortex, hippocampus and thalamus of TgCRND8 mice. Surprisingly, despite the robust increase in CAA levels, the TgCRND8 mice had a marked decrease in parenchymal Aβ plaques and the plaques related neuroinflammation in the brains compared with the control mice. These results amply indicate that Aβ in CSF may act as a source of Aβ contributing to the growth of vascular Aβ deposits in CAA. Our findings provide experimental evidence to unravel the mechanisms of CAA formation and the potential of targeting CSF Aβ for CAA.

The driving theoretical framework of Alzheimer's disease (AD) has been built around the amyloid-β (Aβ) cascade in which amyloid pathology precedes and drives tau pathology. Other evidence has suggested that tau and amyloid pathology may arise independently. Both lines of research suggest that there may be epistatic relationships between genes involved in amyloid and tau pathophysiology. In the current study, we hypothesized that genes coding glycogen synthase kinase 3 (GSK-3) and comparable tau kinases would modify genetic risk for amyloid plaque pathology. Quantitative amyloid positron emission tomography data from the Alzheimer's Disease Neuroimaging Initiative served as the quantitative outcome in regression analyses, covarying for age, gender, and diagnosis. Three interactions reached statistical significance, all involving the GSK3β single nucleotide polymorphism rs334543-2 with APBB2 (rs2585590, rs3098914) and 1 with APP (rs457581). These interactions explained 1.2%, 1.5%, and 1.5% of the variance in amyloid deposition respectively. Our results add to a growing literature on the role of GSK-3 activity in amyloid processing and suggest that combined variation in GSK3β and APP-related genes may result in increased amyloid burden.

Microhemorrhages are strongly associated with advanced cerebral amyloid angiopathy (CAA). Although it has been frequently proposed that the deposition of Aβ in the walls of cortical vessels directly causes microhemorrhages, this has not been studied in great detail, mainly because the ruptured vessels are often missed on routine histopathologic examination. Here, we examined histopathological data from studies targeting microhemorrhages with high-resolution ex vivo 7 T MRI in nine cases with moderate-to-severe CAA, and assessed the presence of Aβ in the walls of involved vessels. We also assessed the density of Aβ positive cortical vessels in areas surrounding microhemorrhages compared to control areas. In seven out of 19 microhemorrhages, the presumed involved vessel could be identified on the histopathological section. Only one of these vessels was positive for Aβ at the site of rupture. Moreover, the density of Aβ positive cortical vessels was lower (1.0 per mm2) within a range of 315 µm surrounding the microhemorrhage, compared to control areas (2.0 per mm2; p < 0.05). These findings question the widely held assumption that the deposition of Aβ in the walls of cortical vessels directly causes microhemorrhages.

Eugenol has attracted considerable attention because of its potential for many pharmaceutical applications including anti-inflammatory, anti-tumorigenic and anti-oxidant properties. Here, we have investigated the effect of eugenol on amyloid formation of selected globular proteins. We find that both spontaneous and seed-induced aggregation processes of insulin and serum albumin (BSA) are significantly suppressed in the presence of eugenol. Isothermal titration calorimetric data predict a single binding site for eugenol-insulin complex confirming the affinity of eugenol for native soluble insulin species. We also find that eugenol suppresses amyloid-induced hemolysis. Our findings reveal the inherent ability of eugenol to stabilize native proteins and to delay the conversion of protein species of native conformation into β-sheet assembled mature fibrils, which seems to be crucial for its inhibitory effect.

Seeding and spread of beta-amyloid (Aβ) pathologies have been considered to be based on prion-like mechanisms. However, limited transmissibility of Aβ seeding activity upon peripheral exposure would represent a key difference to prions, not only in terms of pathogenesis but also in terms of potential transmission of disease. We partially characterized the seeded Aβ amyloidosis after intracerebral injection of various brain homogenates in APP/PS1 mice. One particularly seed-laden homogenate was selected to investigate the development of Aβ pathologies after intravenous exposure. We report here that a single intravenous injection of an Alzheimer disease patient's-brain extract into APP/PS1 recipient mice led to cerebral amyloid angiopathy within 180 days post injection. Thus, vascular proteinopathies such as CAA are transmissible in mice via the intravenous route of peripheral exposure.

Protein aggregation into amyloid fibrils is a ubiquitous phenomenon across the spectrum of neurodegenerative disorders and type 2 diabetes. A common strategy against amyloidogenesis is to minimize the populations of toxic oligomers and protofibrils by inhibiting protein aggregation with small molecules or nanoparticles. However, melanin synthesis in nature is realized by accelerated protein fibrillation to circumvent accumulation of toxic intermediates. Accordingly, we designed and demonstrated the use of star-shaped poly(2-hydroxyethyl acrylate) (PHEA) nanostructures for promoting aggregation while ameliorating the toxicity of human islet amyloid polypeptide (IAPP), the peptide involved in glycemic control and the pathology of type 2 diabetes. The binding of PHEA elevated the β-sheet content in IAPP aggregates while rendering a new morphology of "stelliform" amyloids originating from the polymers. Atomistic molecular dynamics simulations revealed that the PHEA arms served as rodlike scaffolds for IAPP binding and subsequently accelerated IAPP aggregation by increased local peptide concentration. The tertiary structure of the star nanoparticles was found to be essential for driving the specific interactions required to impel the accelerated IAPP aggregation. This study sheds new light on the structure-toxicity relationship of IAPP and points to the potential of exploiting star polymers as a new class of therapeutic agents against amyloidogenesis.

To assess whether global or regional changes in amyloid burden over 4 years predict early declines in episodic memory in initially amyloid-negative adults.

Protein glycation, also known as nonenzymatic glycosylation, is a spontaneous post-translational modification that would change the structure and stability of proteins or hormone peptides. Recent studies have indicated that glycation plays a role in type 2 diabetes (T2D) and neurodegenerative diseases. Over the last two decades, many types of advanced glycation end products (AGEs), formed through the reactions of an amino group of proteins with reducing sugars, have been identified and detected in vivo. However, the effect of glycation on protein aggregation has not been fully investigated. In this study, we aim to elucidate the impact of protein glycation on islet amyloid polypeptide (IAPP, also known as amylin) aggregation, which was strongly associated with T2D. We chemically synthesized glycated IAPP (AGE-IAPP) to mimic the consequence of this hormone peptide in a hyperglycemia (high blood sugar) environment. Our data revealed that AGE-IAPP formed amyloid faster than normal IAPP, and higher-molecular-weight AGE-IAPP oligomers were also observed in the early stage of aggregation. Circular dichroism spectra also indicated that AGE-IAPP exhibited faster conformational changes from random coil to its β-sheet fibrillar states. Moreover, AGE-IAPP can induce normal IAPP to expedite its aggregation process, and its fibrils can also act as templates to promote IAPP aggregation. AGE-IAPP, like normal IAPP, is capable of interacting with synthetic membranes and also exhibits cytotoxicity. Our studies demonstrated that glycation modification of IAPP promotes the amyloidogenic properties of IAPP, and it may play a role in accumulating additional amyloid during T2D progression.

Endoplasmic reticulum (ER) degradation-enhancing α-mannosidase-like protein 1 (EDEM1) is a quality control factor directly involved in the endoplasmic reticulum-associated degradation (ERAD) process. It recognizes terminally misfolded proteins and directs them to retrotranslocation which is followed by proteasomal degradation in the cytosol. The amyloid-β precursor protein (APP) is synthesized and N-glycosylated in the ER and transported to the Golgi for maturation before being delivered to the cell surface. The amyloidogenic cleavage pathway of APP leads to production of amyloid-β (Aβ), deposited in the brains of Alzheimer's disease (AD) patients. Here, using biochemical methods applied to human embryonic kidney, HEK293, and SH-SY5Y neuroblastoma cells, we show that EDEM1 is an important regulatory factor involved in APP metabolism. We find that APP cellular levels are significantly reduced after EDEM1 overproduction and are increased in cells with downregulated EDEM1. We also report on EDEM1-dependent transport of APP from the ER to the cytosol that leads to proteasomal degradation of APP. EDEM1 directly interacts with APP. Furthermore, overproduction of EDEM1 results in decreased Aβ40 and Aβ42 secretion. These findings indicate that EDEM1 is a novel regulator of APP metabolism through ERAD.

Amyloid-β (Aβ) and cerebral small vessel disease (CSVD) commonly coexist. They can occur independently by chance, or may interact with each other. We aimed to determine whether the distribution of Aβ in subcortical vascular cognitive impairments (SVCI) patients can be classified by the underlying pathobiologies. A total of 45 11C-Pittsburgh compound B PET positive (PiB(+)) SVCI patients were included in this study. They were classified using a new cluster analysis method which adopted the Louvain method, which finds optimal decomposition of the participants based on similarity of relative Aβ deposition pattern. We measured atherosclerotic cerebral small vessel disease (CSVD) markers and cerebral amyloid angiopathy (CAA) markers. Forty-five PiB(+) SVCI patients were classified into two groups: 17 patients with the characteristic Alzheimer's disease like Aβ uptake with sparing of occipital region (OccSp) and 28 patients with occipital predominant Aβ uptake (OccP). Compared to OccSp group, OccP group had more postive association of atherosclerotic CSVD score (p for interaction = 0.044), but not CAA score with occipital/global ratio of PiB uptake. Our findings suggested that Aβ positive SVCI patients might consist of heterogeneous groups with combined CSVD and Aβ resulting from various pathobiologies. Furthermore, atherosclerotic CSVD might explain increased occipital Aβ uptakes.

Amyloid precursor protein (APP) and its family members amyloid precursor-like protein 1 (APLP1) and amyloid precursor-like protein 2 (APLP2) are type 1 transmembrane glycoproteins that are highly conserved across species. The transcriptional regulation of APP and APLP2 is similar but not identical, and the cleavage of both proteins is regulated by phosphorylation. APP has been implicated in Alzheimer's disease causation, and in addition to its importance in neurology, APP is deregulated in cancer cells. APLP2 is likewise overexpressed in cancer cells, and APLP2 and APP are linked to increased tumor cell proliferation, migration, and invasion. In this present review, we discuss the unfolding account of these APP family members' roles in cancer progression and metastasis.