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Aggregation of α-synuclein (α-syn) into amyloid fibrils is closely associated with Parkinson's disease (PD). Familial mutations or posttranslational truncations in α-syn are known as risk factor for PD. Here, we examined the effects of the PD-related A30P or A53T point mutation and C-terminal 123–140 or 104–140 truncation on the aggregating property of α-syn based on the kinetic and thermodynamic analyses. Thioflavin T fluorescence measurements indicated that A53T, Δ123‒140, and Δ104–140 variants aggregated faster than WT α-syn, in which the A53T mutation markedly increases nucleation rate whereas the Δ123‒140 or Δ104‒140 truncation significantly increases both nucleation and fibril elongation rates. Ultracentrifugation and western blotting analyses demonstrated that these mutations or truncations promote the conversion of monomer to aggregated forms of α-syn. Analysis of the dependence of aggregation reaction of α-syn variants on the monomer concentration suggested that the A53T mutation enhances conversion of monomers to amyloid nuclei whereas the C-terminal truncations, especially the Δ104–140, enhance autocatalytic aggregation on existing fibrils. In addition, thermodynamic analysis of the kinetics of nucleation and fibril elongation of α-syn variants indicated that both nucleation and fibril elongation of WT α-syn are enthalpically and entropically unfavorable. Interestingly, the unfavorable activation enthalpy of nucleation greatly decreases for the A53T and becomes reversed in sign for the C-terminally truncated variants. Taken together, our results indicate that the A53T mutation and the C-terminal truncation enhance α-syn aggregation by reducing unfavorable activation enthalpy of nucleation, and the C-terminal truncation further triggers the autocatalytic fibril elongation on the fibril surfaces. [ABSTRACT FROM AUTHOR]

Senile plaques that is characterized as an amyloid deposition found in Alzheimer's disease are composed primarily of fibrils of an aggregated peptide, amyloid β (Aβ). The ability to monitor senile plaque formation on a neuronal membrane under physiological conditions provides an attractive model. In this study, the growth behavior of amyloid Aβ fibrils in the presence of liposomes incorporating β-cholesteryl-D-glucose (β-CG) was examined using total internal reflection fluorescence microscopy, transmittance electron microscopy, and other spectroscopic methods. We found that β-CG on the liposome membrane induced the spontaneous formation of spherulitic Aβ fibrillar aggregates. The β-CG cluster formed on liposome membranes appeared to induce the accumulation of Aβ, followed by the growth of the spherulitic Aβ aggregates. In contrast, DMPC and DMPC incorporated cholesterol-induced fibrils that are laterally associated with each other. A comparison study using three types of liposomes implied that the induction of glucose contributed to the agglomeration of Aβ fibrils and liposomes. This agglomeration required the spontaneous formation of spherulitic Aβ fibrillary aggregates. This action can be regarded as a counterbalance to the growth of fibrils and their toxicity, which has great potential in the study of amyloidopathies. • β-CG on liposomes induced a spontaneous formation of spherulitic fibrillary aggregatie of Aβ. • β-CG enhanced the accumulation of Aβ on liposome membranes to accelerate its nucleation. • Spherulite formation of Aβ resulted from a synergetic effect of glucoside group and cholesterol in β-CG. [ABSTRACT FROM AUTHOR]

The adsorption behaviour of amyloid beta (Aβ), thought to be a key peptide for understanding Alzheimer's disease, was investigated by means of time-of-flight secondary ion mass spectrometry (ToF-SIMS). Aβ aggregates depending on the lipid membrane condition though it has not been fully understood yet. In this study, Aβ samples on different lipid membranes, 1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DPPC), 1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPC) and 1,2-dioleoyl- sn-glycero-3-phosphocholine (DOPC), were observed with ToF-SIMS and the complex ToF-SIMS data of the Aβ samples was interpreted using data analysis techniques such as principal component analysis (PCA), gentle-SIMS (G-SIMS) and g-ogram. DOPC and DMPC are liquid crystal at room temperature, while DPPC is gel at room temperature. As primary ion beams, Bi and Ar cluster ion beams were used and the effect of an Ar cluster ion for evaluating biomolecules was also studied. The secondary ion images of the peptide fragment ions indicated by G-SIMS and g-ogram were consistent with the PCA results. It is suggested that Aβ is adsorbed homogeneously on the liquid-crystalline-phase lipid membranes, while it aggregates along the lipid on the gel-phase lipid membrane. Moreover, in the results using the Ar cluster, the influence of contamination was reduced. [ABSTRACT FROM AUTHOR]

The amyloid fibrils of amyloid β protein (Aβ) from Alzheimer's disease are likely to show the cytotoxicity, depending on their morphology. The relationship between the nucleation kinetics of the Aβ fibrils and their morphology has been investigated. From the perspective of a crystallization technique assuming primary/secondary nucleation steps and an elongation step, the secondary nucleation rate B [# m−3 s−1], was experimentally and coarsely determined by using total internal reflection fluorescence microscopy combined with thioflavin T. In an aqueous solution, linear and rigid fibrils were formed with a relatively smaller B value ((2.83 ± 0.55) × 105 # m−3 s−1), whereas spherulitic amyloid assemblies were formed in the presence of negatively charged liposome including oxidized lipids, with a larger B value ((7.65 ± 0.47) × 105 # m−3 s−1). Those findings should lead to a better understanding of the mechanism for the formation of fibrils and senile plaques in Alzheimer's disease. © 2012 American Institute of Chemical Engineers AIChE J, 2012 [ABSTRACT FROM AUTHOR]

Abstract: The inhibition of fibril formation of amyloid β proteins (Aβ) would be attractive therapeutic targets for the treatment of Alzheimer''s disease (AD). Dopamine (DA) and other catechol derivatives were used as inhibitory factors for Aβ fibril formation. The fibril formation of Aβ was monitored by Thioflavin T fluorescence, a transmission electron microscopy (TEM) and a total internal reflection fluorescence microscopy (TIRFM). Catechol and its derivatives showed the dose-dependent inhibitory effects on the spontaneous Aβ fibril formation. The inhibitory activity depended on the chemical structure of catechol derivatives both in the presence and absence of the liposome a model of biomembrane. Formation of catechol quinone-conjugated-Aβ adduct by a Schiff-base is a key step for the inhibition effect of Aβ fibril formation. [Copyright &y& Elsevier]

The liposome immobilized on indium tin-oxide electrode was prepared as a "Membrane Chip" to evaluate the liposome-liposome interaction. Three kinds of neutral liposomes entrapping the fluorescence probe, calcein, were utilized as a sensory liposome. Twenty four kinds of liposomes were used to construct a membrane library based on the calcein release behavior. The loading of liposome including the unsaturated phospholipid into the dialyzer induced the variation of surface state of liposome membrane. We analyzed the above liposome by a comparison of it with the membrane library constructed by Membrane Chip. The liposome after its dialysis treatment was found to show the membrane property of the liposome with domain-like structure prior to the interaction with amyloid β protein. Also the above liposome showed the oxidized liposome-like membrane property. In conclusion, we demonstrated a membrane library-based method to evaluate the surface state of the model biomembranes with unclear surface property. [ABSTRACT FROM AUTHOR]

Abstract: The amyloid β protein with 42 amino acid residues (Aβ), which is a causative protein of Alzheimer''s disease (AD), forms the complex with copper (II) to induce the cholesterol oxidase-like activity by the proton transfer from the cholesterol. In this study, the oxidation of cholesterol by Aβ/Cu complex was investigated on the surface of the zwitterionic phospholipid liposome including the bound water advantageous for the enhancement of the proton transfer. The bound water was pooled by the formation of cholesterol-rich domain within liposomes. The resulting reactivity was enhanced by the proton transfer mediated by the bound water. [Copyright &y& Elsevier]

The amyloid deposition of amyloid β (Aβ) peptides is a critical pathological event in Alzheimer disease (AD). Preventing the formation of amyloid deposits and removing preformed fibrils in tissues are important therapeutic strategies against AD. Previously, we reported the destruction of amyloid fibrils of β2-microglobulin K3 fragments by laser irradiation coupled with the binding of amyloid-specific thioflavin T. Here, we studied the effects of a laser beam on Aβ fibrils. As was the case for K3 fibrils, extensive irradiation destroyed the preformed Aβ fibrils. However, irradiation during spontaneous fibril formation resulted in only the partial destruction of growing fibrils and a subsequent explosive propagation of fibrils. The explosive propagation was caused by an increase in the number of active ends due to breakage. The results not only reveal a case of fragmentation-induced propagation of fibrils but also provide insights into therapeutic strategies for AD. [ABSTRACT FROM AUTHOR]