Amentoflavone: A Bifunctional Metal Chelator that Controls the Formation of Neurotoxic Soluble Aβ42 Oligomers

Alzheimer's disease (AD) is the most common neurodegenerative disorder, yet the cause and progression of this disorder are not completely understood. While the main hallmark of AD is the deposition of amyloid plaques consisting of the β-amyloid (Aβ) peptide, transition metal ions are also known to play a significant role in disease pathology by expediting the formation of neurotoxic soluble β-amyloid (Aβ) oligomers, reactive oxygen species (ROS), and oxidative stress. Thus, bifunctional metal chelators that can control these deleterious properties are highly desirable. Herein, we show that amentoflavone (AMF) – a natural biflavonoid compound, exhibits good metal-chelating properties, especially for chelating Cu²⁺ with very high affinity (pCu_7.4 = 10.44). In addition, AMF binds to Aβ fibrils with a high affinity (K_i = 287 ± 20 nM) – as revealed by a competition thioflavin T (ThT) assay, and specifically labels the amyloid plaques ex vivo in the brain sections of transgenic AD mice – as confirmed via immunostaining with an Ab antibody. The effect of AMF on Aβ₄₂ aggregation and disaggregation of Aβ₄₂ fibrils was also investigated, to reveal that AMF can control the formation of neurotoxic soluble Aβ₄₂ oligomers, both in absence and presence of metal ions, and as confirmed via cell toxicity studies. Furthermore, an ascorbate consumption assay shows that AMF exhibits potent antioxidant properties and can chelate Cu²⁺ and significantly diminish the Cu²⁺-ascorbate redox cycling and reactive oxygen species (ROS) formation. Overall, these studies strongly suggest that AMF acts as a bifunctional chelator that can interact with various Aβ aggregates and reduce their neurotoxicity, can also bind Cu²⁺ and mediate its deleterious redox properties, and thus AMF has the potential to be a lead compound for further therapeutic agent development for AD.