Table 1.

Amyloid beta (Aβ) species and their characteristics.

Aβ Species	Properties	Study Models	Refs.
Amyloid fibrils	Stable and filamentous Aβ aggregates with fibrillar structure and common structural features	In vitro; patients with AD; mouse models	[34-36]
Aβ protofibrils	Flexible, short, rod-like structure; <200 nm in length; 6-8 nm in diameter; toxic; precursor of mature fibrils	In vitro	[37-40]
Aβ Plaques	Mainly composed of fibrils; not toxic; large extracellular Aβ deposits; surrounded by reactive astrocytes, activated microglia, axons, and dystrophic dendrites	In vivo; patients with AD; mouse models	[41, 42]
Aβ derived diffusible ligands (ADDLs)	Neurotoxic; nonfibrillar; an estimated mass of 17-42 kDa; trimers to 24 mers	In vitro; brain extracts of humans and murine models	[43, 44]
Small oligomers	Toxic; mostly unstable and transient; comprised of 3-50 monomers; heteromorphous	In vivo; AD individuals; mouse models	[6, 9, 45-48]
Annular Aβ oligomers	Play significant roles in membrane-disrupting ion channels or pores	In vitro; cell culture	[49-53]
Aβ Monomers	Mainly α-helical and random coil in structure; produced from APP; soluble amphipathic molecule	In vitro; in vivo; human brain extracts	[54-56]
Aβ Dimers	Diameter of around 35 nm; hydrophobic core	In vitro; in vivo; human brain extracts	[57-59]
Aβ Trimers	Act as a subunit of toxic oligomers	In vivo; mouse models	[6, 60]