Hossain S, Hashimoto M, Katakura M, Al Mamun A, Shido O. Medicinal value of asiaticoside for Alzheimer's disease as assessed using single-molecule-detection fluorescence correlation spectroscopy, laser-scanning microscopy, transmission electron microscopy, and in silico docking.
Altern Ther Health Med 2015;
15:118. [PMID:
25880304 PMCID:
PMC4422550 DOI:
10.1186/s12906-015-0620-9]
[Citation(s) in RCA: 14] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2014] [Accepted: 03/16/2015] [Indexed: 01/09/2023]
Abstract
BACKGROUND
Identifying agents that inhibit amyloid beta peptide (Aβ) aggregation is the ultimate goal for slowing Alzheimer's disease (AD) progression. This study investigated whether the glycoside asiaticoside inhibits Aβ1-42 fibrillation in vitro.
METHODS
Fluorescence correlation spectroscopy (FCS), evaluating the Brownian diffusion times of moving particles in a small confocal volume at the single-molecule level, was used. If asiaticoside inhibits early Aβ1-42 fibrillation steps, more Aβs would remain free and rapidly diffuse in the confocal volume. In contrast, "weaker or no inhibition" permits a greater number of Aβs to polymerize into oligomers, leading to fibers and gives rise to slow diffusion times in the solution. Trace amounts of 5-carboxytetramethylrhodamine (TAMRA)-labeled Aβ1-42 in the presence of excess unlabeled Aβ1-42 (10 μM) was used as a fluorescent probe. Steady-state and kinetic-Thioflavin T (ThT) fluorospectroscopy, laser-scanning fluorescence microscopy (LSM), and transmission electron microscopy (TEM) were also used to monitor fibrillation. Binding of asiaticoside with Aβ1-42 at the atomic level was computationally examined using the Molegro Virtual Docker and PatchDock.
RESULTS
With 1 h of incubation time for aggregation, FCS data analysis revealed that the diffusion time of TAMRA-Aβ1-42 was 208 ± 4 μs, which decreased to 164 ± 8.0 μs in the presence of asiaticoside, clearly indicating that asiaticoside inhibited the early stages Aβ1-42 of fibrillation, leaving more free Aβs in the solution and permitting their rapid diffusion in the confocal volume. The inhibitory effects were also evidenced by reduced fiber formation as assessed by steady-state and kinetic ThT fluorospectroscopy, LSM, and TEM. Asiaticoside elongated the lag phase of Aβ1-42 fibrillation, indicating the formation of smaller amyloid species were impaired in the presence of asiaticoside. Molecular docking revealed that asiaticoside binds with amyloid intra- and inter-molecular amino acid residues, which are responsible for β-sheet formation and longitudinal extension of fibrils.
CONCLUSION
Finally, asiaticoside prevents amyloidogenesis that precedes neurodegeneration in patients with Alzheimer's disease.
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