Photo-induced inhibition of Alzheimer's β-amyloid aggregation in vitro by rose bengal.

The abnormal aggregation of β-amyloid (Aβ) peptides in the brain is a major pathological hallmark of Alzheimer's disease (AD). The suppression (or alteration) of Aβ aggregation is considered to be an attractive therapeutic intervention for treating AD. We report on visible light-induced inhibition of Aβ aggregation by xanthene dyes, which are widely used as biomolecule tracers and imaging markers for live cells. Among many xanthene dyes, rose bengal (RB) under green LED illumination exhibited a much stronger inhibition effect upon photo-excitation on Aβ aggregation than RB under dark conditions. We found that RB possesses high binding affinity to Aβ; it exhibits a remarkable red shift and a strong enhancement of fluorescence emission in the presence of Aβ. Photo-excited RB interfered with an early step in the pathway of Aβ self-assembly and suppressed the conformational transition of Aβ monomers into β-sheet-rich structures. Photo-excited RB is not only effective in the inhibition of Aβ aggregation, but also in the reduction of Aβ-induced cytotoxicity.