Anti-amyloidogenic effects of soybean isoflavones in vitro: Fluorescence spectroscopy demonstrating direct binding to Aβ monomers, oligomers and fibrils

• Published in: Biochimica et biophysica acta 2012-08, Vol.1822 (8), p.1316-1324
• Main Authors: Hirohata, Mie, Ono, Kenjiro, Takasaki, Jun-ichi, Takahashi, Ryoichi, Ikeda, Tokuhei, Morinaga, Akiyoshi, Yamada, Masahito
• Format: Article
• Language: English
• Subjects: Alzheimer's disease; Amyloid beta-Peptides - chemistry; Amyloid beta-Peptides - metabolism; Amyloid β-protein oligomer; Benzothiazoles; Fragment; Glycine max - chemistry; Glycitein; Humans; Isoflavones - metabolism; Isoflavones - pharmacology; Microscopy, Atomic Force; Microscopy, Electron - methods; Peptide Fragments - chemistry; Peptide Fragments - metabolism; Photo-induced cross-linking of unmodified proteins (PICUP); Spectrometry, Fluorescence - methods; Thiazoles - chemistry; Three-dimensional fluorescence spectroscopy
• ISSN: 0925-4439; 0006-3002; 1879-260X
• DOI: 10.1016/j.bbadis.2012.05.006

Alzheimer's disease is characterized by the presence of extracellular deposits of amyloid, primarily composed of the amyloid β-protein (Aβ). A growing body of evidence indicates that oligomeric forms of Aβ play a critical role in disease causation. Soybean isoflavones are flavonoids with an isoflavone backbone. Isoflavones have been reported to protect against Aβ-induced neurotoxicity in cultured cell systems, the molecular mechanisms remain unclear. Our previous studies demonstrated that red wine-related flavonoids with a flavone backbone are able to inhibit Aβ assembly and destabilize preformed Aβ aggregates. Here, we show that isoflavones, especially glycitein and genistein, have anti-fibrillization, anti-oligomerization and fibril-destabilizing effects on Aβ1–40 and Aβ1–42in vitro at physiological pH and temperature, by using nucleation-dependent polymerization monitored by thioflavin T fluorescence, atomic force microscopy, electron microscopy, and photo-induced cross-linking of unmodified proteins followed by SDS-PAGE. Our three-dimensional fluorescence spectroscopic analyses demonstrated that glycitein interacted with Aβ monomers, oligomers and fibrils, indicating specific binding of glycitein to these Aβ species. Glycitein also interacted with different Aβ fragments (Aβ1–42, Aβ1–40, Aβ1–16 and Aβ25–35), exhibiting the highest fluorescence enhancement with Aβ25–35. We speculated that glycitein's anti-amyloidogenic properties are specifically mediated by its binding to Aβ monomers, oligomers and fibrils. Isoflavones may hold promise as a treatment option for preventative strategies targeting amyloid formation in Alzheimer's disease. ► Isoflavones inhibited the fibrillization and oligomerization of amyloid β-proteins (Aβs). ► Isoflavones destabilized preformed amyloid β-protein (Aβ) fibrils. ► Glycitein bound to Aβ monomers, oligomers and fibrils, leading the anti-amyloidogenic effects. ► Glycitein bound to Aβ1–42, Aβ1–40, Aβ1–16 and Aβ25–35, having the most potent affinity for Aβ25–35.