Spherical aggregates of [beta]-amyloid (amylospheroid) show high neurotoxicity and activate tau protein kinase I/glycogen synthase kinase-3[beta]

[beta]-Amyloid (A[beta]) acquires toxicity by self-aggregation. To identify and characterize the toxic form(s) of A[beta] aggregates, we examined in vitro aggregation conditions by using large quantities of homogenous, chemically synthesized A[[beta].sub.1-40] peptide. We found that slow rotation of A[[beta].sub.1-40] solution reproducibly gave self-aggregated A[[beta].sub.1-40] containing a stable and highly toxic moiety. Examination of the aggregates purified by glycerol-gradient centrifugation by atomic force microscopy and transmission electron microscopy revealed that the toxic moiety is a perfect sphere, which we call amylospheroid (ASPD). Other A[[beta].sub.1-40] aggregates, including fibrils, were nontoxic. Correlation studies between toxicity and sphere size indicate that 10- to 15-nm ASPD was highly toxic, whereas ASPD 10 nm also appeared to exist when A[[beta].sub.1-42] formed ASPD by slow rotation. However, A[[beta].sub.1-42]-ASPD formed more rapidly, killed neurons at lower concentrations, and showed [approximately equal to] 100-fold-higher toxicity than A[[beta].sub.1-40]-ASPD. The toxic ASPD was associated with SDS-resistant oligomeric bands in immunoblotting, which were absent in nontoxic ASPD. Because the formation of ASPD was not disturbed by pentapeptides that break [beta]-sheet interactions, A[beta] may form ASPD through a pathway that is at least partly distinct from that of fibril formation. Inhibition experiments with lithium suggest the involvement of tau protein kinase I/glycogen synthase kinase-3[beta] in the early stages of ASPD-induced neurodegeneration, Here we describe the identification and characterization of ASPD and discuss its possible role in the neurodegeneration in Alzheimer's disease.