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.

ABSTRACT: Identifying agents that inhibit amyloid beta peptide (A?) aggregation is the ultimate goal for slowing Alzheimer's disease (AD) progression. This study investigated whether the glycoside asiaticoside inhibits A?1-42 fibrillation in vitro.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 A?1-42 fibrillation steps, more A?s would remain free and rapidly diffuse in the confocal volume. In contrast, "weaker or no inhibition" permits a greater number of A?s to polymerize into oligomers, leading to fibers and gives rise to slow diffusion times in the solution. Trace amounts of 5-carboxytetramethylrhodamine (TAMRA)-labeled A?1-42 in the presence of excess unlabeled A?1-42 (10 ?M) 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 A?1-42 at the atomic level was computationally examined using the Molegro Virtual Docker and PatchDock.With 1 h of incubation time for aggregation, FCS data analysis revealed that the diffusion time of TAMRA-A?1-42 was 208 ± 4 ?s, which decreased to 164 ± 8.0 ?s in the presence of asiaticoside, clearly indicating that asiaticoside inhibited the early stages A?1-42 of fibrillation, leaving more free A?s 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 A?1-42 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 ?-sheet formation and longitudinal extension of fibrils.Finally, asiaticoside prevents amyloidogenesis that precedes neurodegeneration in patients with Alzheimer's disease.

SUBMITTER: Hossain S 

PROVIDER: S-EPMC4422550 | biostudies-literature | 2015

REPOSITORIES: biostudies-literature