Oligomeric and fibrillar species of amyloid-beta peptides differentially affect neuronal viability

Genetic evidence predicts a causative role for amyloid-beta (A beta) in Alzheimer's disease. Recent debate has focused on whether fibrils (amyloid) or soluble oligomers of A beta are the active species that contribute to neurodegeneration and dementia. We developed two aggregation protocols for the consistent production of stable oligomeric or fibrillar preparations of A beta-(1-42). Here we report that oligomers inhibit neuronal viability 10-fold more than fibrils and approximately 40-fold more than unaggregated peptide, with oligomeric A beta-(1-42)-induced inhibition significant at 10 nm. Under A beta-(1-42) oligomer- and fibril-forming conditions, A beta-(1-40) remains predominantly as unassembled monomer and had significantly less effect on neuronal viability than preparations of A beta-(1-42). We applied the aggregation protocols developed for wild type A beta-(1-42) to A beta-(1-42) with the Dutch (E22Q) or Arctic (E22G) mutations. Oligomeric preparations of the mutations exhibited extensive protofibril and fibril formation, respectively, but were not consistently different from wild type A beta-(1-42) in terms of inhibition of neuronal viability. However, fibrillar preparations of the mutants appeared larger and induced significantly more inhibition of neuronal viability than wild type A beta-(1-42) fibril preparations. These data demonstrate that protocols developed to produce oligomeric and fibrillar A beta-(1-42) are useful in distinguishing the structural and functional differences between A beta-(1-42) and A beta-(1-40) and genetic mutations of A beta-(1-42).