Beta Amyloid ~In Vitro and Mechanistic Studies of an Anti-Amyloidogenic Self-Assembled Cyclic D,L-α-Peptide Architecture.

Misfolding of the Aβ protein and its subsequent aggregation into toxic oligomers are related to Alzheimer's disease. Although peptides of various sequences can self-assemble into amyloid structures, these structures share common three-dimensional features that may promote their cross-reaction. Given the significant similarities between amyloids and the architecture of self-assembled cyclic D,L-α-peptide, we hypothesized that the latter may bind and stabilize a non-toxic form of Aβ, so preventing its aggregation into toxic forms. By screening a focused library of six-residue cyclic D,L-α-peptides and optimizing the activity of a lead peptide, we found one cyclic D,L-α-peptide (CP-2) that interacts strongly with Aβ and inhibits its aggregation. In transmission electron microscopy and optimized thioflavin T assays, CP-2 inhibits the formation of Aβ aggregates, entirely disassembles pre-formed aggregated and fibrillar Aβ, and protects rat pheochromocytoma PC12 cells from Aβ toxicity, without inducing any toxicity by itself. Using various immunoassays, circular dichroism spectroscopy, photo-induced cross-linking of unmodified proteins (PICUP) combined with SDS/PAGE, and NMR, we probed the mechanisms underlying CP-2's anti-amyloidogenic activity. NMR spectroscopy indicates that CP-2 interacts with Aβ through its self-assembled conformation and induces weak secondary structure in Aβ. Upon co-incubation, CP-2 changes the aggregation pathway of Aβ and alters its oligomer distribution by stabilizing low-molecular-weight species. Our results support studies suggesting that toxic early oligomeric states of Aβ may be composed of antiparallel β-peptide structures and that the interaction of Aβ with CP-2 promotes formation of more benign parallel β-structures. Further studies will show whether these kinds of abiotic cyclic D,L-α-peptides are also beneficial as an intervention in related in vivo models.