Toward the Noninvasive Diagnosis of Alzheimer's Disease: Molecular Basis for the Specificity of Curcumin for Fibrillar Amyloid-β.
Ontology highlight
ABSTRACT:
SUBMITTER: Khurshid B
PROVIDER: S-EPMC9245119 | biostudies-literature |
REPOSITORIES: biostudies-literature
Similar Datasets
Project description:High levels of homocysteine are reported as a risk factor for Alzheimer's disease (AD). Correspondingly, inborn hyperhomocysteinemia is associated with an increased predisposition to the development of dementia in later stages of life. Yet, the mechanistic link between homocysteine accumulation and the pathological neurodegenerative processes is still elusive. Furthermore, despite the clear association between protein aggregation and AD, attempts to develop therapy that specifically targets this process have not been successful. It is envisioned that the failure in the development of efficacious therapeutic intervention may lie in the metabolomic state of affected individuals. We recently demonstrated the ability of metabolites to self-assemble and cross-seed the aggregation of pathological proteins, suggesting a role for metabolite structures in the initiation of neurodegenerative diseases. Here, we provide a report of homocysteine crystal structure and self-assembly into amyloid-like toxic fibrils, their inhibition by polyphenols, and their ability to seed the aggregation of the AD-associated β-amyloid polypeptide. A yeast model of hyperhomocysteinemia indicates a toxic effect, correlated with increased intracellular amyloid staining that could be rescued by polyphenol treatment. Analysis of AD mouse model brain sections indicates the presence of homocysteine assemblies and the interplay between β-amyloid and homocysteine. This work implies a molecular basis for the association between homocysteine accumulation and AD pathology, potentially leading to a paradigm shift in the understanding of AD initial pathological processes.
| S-EPMC8214689 | biostudies-literature
Project description:Amyloid ?-protein (A?42) oligomerization is an early event in Alzheimer's disease (AD). Current diagnostic methods using sequence-specific antibodies against less toxic fibrillar and monomeric A?42 run the risk of overdiagnosis. Hence, conformation-specific antibodies against neurotoxic A?42 oligomers have garnered much attention for developing more accurate diagnostics. Antibody 24B3, highly specific for the toxic A?42 conformer that has a turn at Glu22 and Asp23, recognizes a putative A?42 dimer, which forms stable and neurotoxic oligomers more potently than the monomer. 24B3 significantly rescues A?42-induced neurotoxicity, whereas sequence-specific antibodies such as 4G8 and 82E1, which recognizes the N-terminus, do not. The ratio of toxic to total A?42 in the cerebrospinal fluid of AD patients is significantly higher than in control subjects as measured by sandwich ELISA using antibodies 24B3 and 82E1. Thus, 24B3 may be useful for AD diagnosis and therapy.
| S-EPMC4931470 | biostudies-literature
Project description:Development of a rapid and sensitive method for Aβ(1-42) aggregation detection is of great importance to overcome the limitations of conventional techniques. In this study, we developed a label-free paper-based electrochemiluminescence sensor for amyloid-β aggregation detection toward potential diagnosis of Alzheimer's disease (AD). The paper-based chip used in the system serves as a low-cost and disposable detection method. In this detection platform, the bonding of [Ru(phen)2dppz]2+ to Aβ(1-42) aggregates results in enhanced electrochemiluminescence due to the change in the polarity of the microenvironment when [Ru(phen)2dppz]2+ intercalated into the β-sheets during oligomerization. The oligomerization process of Aβ(1-42) can be monitored in real time by the novel method, and as low as 100 pM equivalent monomer concentration of Aβ(1-42) could be detected simultaneously. In addition, the cerebrospinal fluid of transgenic AD model mice was tested by this method, which is highly consistent with genetic identification. In addition, we demonstrated that this detection platform could be a potential new method for the screening of Aβ(1-42) aggregation inhibitors, highlighting the practical application capacity of this platform. The platform is label free, low cost and sensitive. Therefore, the proposed platform holds great promise for the diagnosis of AD.
| S-EPMC5928890 | biostudies-literature
Project description:We describe a full structural model for amyloid fibrils formed by the 40-residue beta-amyloid peptide associated with Alzheimer's disease (Abeta(1-40)), based on numerous constraints from solid state NMR and electron microscopy. This model applies specifically to fibrils with a periodically twisted morphology, with twist period equal to 120 +/- 20 nm (defined as the distance between apparent minima in fibril width in negatively stained transmission electron microscope images). The structure has threefold symmetry about the fibril growth axis, implied by mass-per-length data and the observation of a single set of (13)C NMR signals. Comparison with a previously reported model for Abeta(1-40) fibrils with a qualitatively different, striated ribbon morphology reveals the molecular basis for polymorphism. At the molecular level, the 2 Abeta(1-40) fibril morphologies differ in overall symmetry (twofold vs. threefold), the conformation of non-beta-strand segments, and certain quaternary contacts. Both morphologies contain in-register parallel beta-sheets, constructed from nearly the same beta-strand segments. Because twisted and striated ribbon morphologies are also observed for amyloid fibrils formed by other polypeptides, such as the amylin peptide associated with type 2 diabetes, these structural variations may have general implications.
| S-EPMC2587602 | biostudies-literature
Project description:Although amyloid fibers are found in neurodegenerative diseases, evidence points to soluble oligomers of amyloid-forming proteins as the cytotoxic species. Here, we establish that our preparation of toxic amyloid-β(1-42) (Abeta42) fibrillar oligomers (TABFOs) shares with mature amyloid fibrils the cross-β structure, in which adjacent β-sheets adhere by interpenetration of protein side chains. We study the structure and properties of TABFOs by powder X-ray diffraction, EM, circular dichroism, FTIR spectroscopy, chromatography, conformational antibodies, and celluar toxicity. In TABFOs, Abeta42 molecules stack into short protofilaments consisting of pairs of helical β-sheets that wrap around each other to form a superhelix. Wrapping results in a hole along the superhelix axis, providing insight into how Abeta may form pathogenic amyloid pores. Our model is consistent with numerous properties of Abeta42 fibrillar oligomers, including heterogenous size, ability to seed new populations of fibrillar oligomers, and fiber-like morphology.
| S-EPMC3356606 | biostudies-literature
Project description:Glial activation plays an important role in the pathogenesis of various neurodegenerative disorders including Alzheimer's disease. However, molecular mechanisms by which activated glia could kill neurons are poorly understood. The present study underlines the importance of neutral sphingomyelinase (N-SMase) in mediating the damaging effect of fibrillar amyloid-? 1-42 (A?1-42) peptide-activated astroglia on neurons. In transwell experiments, soluble products released from activated primary human astroglia induced the activation of neutral sphingomyelinase (N-SMase), production of ceramide, and cell death in primary human neurons. Protection of neurons from cytotoxic effects of activated astroglia by antisense knockdown of N-SMase, but not acidic sphingomyelinase (A-SMase), suggests that soluble products released from activated astroglia kill neurons via N-SMase but not A-SMase. Next we examined the role of N-SMase in the activation of human astroglia. Interestingly, knockdown of N-SMase, but not A-SMase, by either antisense oligonucleotides or chemical inhibitor, prevented the induction of proinflammatory molecules [tumor necrosis factor-?, inducible nitric oxide synthase, interleukin-1? (IL-1?), and IL-6] and the activation of nuclear factor-?B in A?1-42-activated astroglia. Subsequently, fibrillar A? peptides also induced the activation of N-SMase and ceramide in vivo in mouse cortex. Most importantly, antisense knockdown of N-SMase, but not A-SMase, decreased the activation of astroglia and protected neurons from fibrillar A? toxicity in vivo in the cortex. Together, it is apparent that both the activation of astroglia by A? and that the cytotoxicity of activated astroglia on neurons depend on N-SMase.
| S-EPMC3020912 | biostudies-literature
Project description:Having a parent affected with late-onset Alzheimer's disease (LOAD) is a major risk factor among cognitively normal (NL) individuals. This (11)C-Pittsburgh Compound B (PiB)-PET study examines whether NL individuals with LOAD parents show increased fibrillar amyloid-beta (Abeta) deposition, a hallmark of Alzheimer's disease (AD) pathology and whether there are parent-of-origin effects. Forty-two 50- to 80-year-old NL persons were examined with PiB-PET. These individuals included 14 NL subjects with a maternal family history (FH) of LOAD (FHm), 14 NL subjects with a paternal FH (FHp), and 14 NL subjects with a negative family history of any dementia (FH-). Statistical parametric mapping and automated regions-of-interest were used to compare cerebral-to-cerebellar PiB standardized uptake value ratios, reflecting fibrillar Abeta burden, across groups. FH groups did not differ in age, gender, education, and apolipoprotein E (ApoE) status. NL FHm subjects showed higher PiB retention in AD-affected anterior and posterior cingulate cortex (PCC), precuneus, parietal, temporal, occipital, and frontal cortices, right basal ganglia, and thalamus, compared with FH- and FHp subjects. FHp subjects showed increased PiB retention in the PCC and frontal cortex, intermediate between FHm and FH- subjects. Results remained significant after controlling for age, gender, education, and ApoE status. Children of parents with LOAD, particularly those with affected mothers, have increased fibrillar Abeta load in AD-vulnerable regions compared with controls, perhaps accounting for the known increased risk for AD. Present findings may motivate further research on familial transmission and parent-of-origin effects in LOAD.
| S-EPMC2851906 | biostudies-other
Project description:PurposeAmyloid PET tracers have been developed for in vivo detection of brain fibrillar amyloid deposition in Alzheimer's disease (AD). To serve as an early biomarker in AD the amyloid PET tracers need to be analysed in multicentre clinical studies.MethodsIn this study 238 [(11)C]Pittsburgh compound-B (PIB) datasets from five different European centres were pooled. Of these 238 datasets, 18 were excluded, leaving [(11)C]PIB datasets from 97 patients with clinically diagnosed AD (mean age 69?±?8 years), 72 patients with mild cognitive impairment (MCI; mean age 67.5?±?8 years) and 51 healthy controls (mean age 67.4?±?6 years) available for analysis. Of the MCI patients, 64 were longitudinally followed for 28?±?15 months. Most participants (175 out of 220) were also tested for apolipoprotein E (ApoE) genotype.Results[(11)C]PIB retention in the neocortical and subcortical brain regions was significantly higher in AD patients than in age-matched controls. Intermediate [(11)C]PIB retention was observed in MCI patients, with a bimodal distribution (64 % MCI PIB-positive and 36 % MCI PIB-negative), which was significantly different the pattern in both the AD patients and controls. Higher [(11)C]PIB retention was observed in MCI ApoE ?4 carriers compared to non-ApoE ?4 carriers (p?<?0.005). Of the MCI PIB-positive patients, 67 % had converted to AD at follow-up while none of the MCI PIB-negative patients converted.ConclusionThis study demonstrated the robustness of [(11)C]PIB PET as a marker of neocortical fibrillar amyloid deposition in brain when assessed in a multicentre setting. MCI PIB-positive patients showed more severe memory impairment than MCI PIB-negative patients and progressed to AD at an estimated rate of 25 % per year. None of the MCI PIB-negative patients converted to AD, and thus PIB negativity had a 100 % negative predictive value for progression to AD. This supports the notion that PIB-positive scans in MCI patients are an indicator of prodromal AD.
| S-EPMC3510420 | biostudies-literature
Project description:BackgroundReactive microglia are associated with ?-amyloid (A?) deposit and clearance in Alzhiemer's Disease (AD). Paradoxically, entocranial resident microglia fail to trigger an effective phagocytic response to clear A? deposits although they mainly exist in an "activated" state. Oligomeric A? (oA?), a recent target in the pathogenesis of AD, can induce more potent neurotoxicity when compared with fibrillar A? (fA?). However, the role of the different A? forms in microglial phagocytosis, induction of inflammation and oxidation, and subsequent regulation of phagocytic receptor system, remain unclear.ResultsWe demonstrated that A?(1-42) fibrils, not A?(1-42) oligomers, increased the microglial phagocytosis. Intriguingly, the pretreatment of microglia with oA?(1-42) not only attenuated fA?(1-42)-triggered classical phagocytic response to fluorescent microspheres but also significantly inhibited phagocytosis of fluorescent labeled fA?(1-42). Compared with the fA?(1-42) treatment, the oA?(1-42) treatment resulted in a rapid and transient increase in interleukin 1? (IL-1?) level and produced higher levels of tumor necrosis factor-? (TNF-?), nitric oxide (NO), prostaglandin E2 (PGE2) and intracellular superoxide anion (SOA). The further results demonstrated that microglial phagocytosis was negatively correlated with inflammatory mediators in this process and that the capacity of phagocytosis in fA?(1-42)-induced microglia was decreased by IL-1?, lippolysaccharide (LPS) and tert-butyl hydroperoxide (t-BHP). The decreased phagocytosis could be relieved by pyrrolidone dithiocarbamate (PDTC), a nuclear factor-?B (NF-?B) inhibitor, and N-acetyl-L-cysteine (NAC), a free radical scavenger. These results suggest that the oA?-impaired phagocytosis is mediated through inflammation and oxidative stress-mediated mechanism in microglial cells. Furthermore, oA?(1-42) stimulation reduced the mRNA expression of CD36, integrin ?1 (Itgb1), and Ig receptor Fc?RIII, and significantly increased that of formyl peptide receptor 2 (FPR2) and scavenger receptor class B1 (SRB1), compared with the basal level. Interestingly, the pre-stimulation with oA?(1-42) or the inflammatory and oxidative milieu (IL-1?, LPS or t-BHP) significantly downregulated the fA?(1-42)-induced mRNA over-expression of CD36, CD47 and Itgb1 receptors in microglial cells.ConclusionThese results imply that A? oligomers induce a potent inflammatory response and subsequently disturb microglial phagocytosis and clearance of A? fibrils, thereby contributing to an initial neurodegenerative characteristic of AD. Antiinflammatory and antioxidative therapies may indeed prove beneficial to delay the progression of AD.
| S-EPMC3149591 | biostudies-literature
Project description:Noninvasive brain stimulation techniques (NiBS) have gathered substantial interest in the study of dementia, considered their possible role in help defining diagnostic biomarkers of altered neural activity for early disease detection and monitoring of its pathophysiological course, as well as for their therapeutic potential of boosting residual cognitive functions. Nevertheless, current approaches suffer from some limitations. In this study, we review and discuss experimental NiBS applications that might help improve the efficacy of future NiBS uses in Alzheimer's Disease (AD), including perturbation-based biomarkers for early diagnosis and disease tracking, solutions to enhance synchronization of oscillatory electroencephalographic activity across brain networks, enhancement of sleep-related memory consolidation, image-guided stimulation for connectome control, protocols targeting interneuron pathology and protein clearance, and finally hybrid-brain models for in-silico modeling of AD pathology and personalized target selection. The present work aims to stress the importance of multidisciplinary, translational, model-driven interventions for precision medicine approaches in AD.
| S-EPMC8858588 | biostudies-literature