Inhibition of amyloid β fibrosis by stereocomplex formation with D-peptide Haruhiko Miwa 1 , Shiho Seguchi 1 , Ayaka Hayashi 1 , Eri Chatani 2 , Kenta Morita 1 , Tatsuo Maruyama 1 1 Graduate School of Engineering, Kobe University, 2 Graduate School of Science, Kobe University Alzheimer's disease (AD) is the most common form of dementia worldwide. Conventional medicines today for AD can only "delay" the progression of dementia. Hence, therapeutics that can fully cure AD is required as our society keeps aging. However, the development of a medicine for AD has been difficult, since the mechanism of AD is still unclear. The amyloid cascade is the most supported hypothesis for the onset of AD, in which amyloid β(Aβ) monomers aggregate to form Aβ-oligomers, ultimately resulting in insoluble Aβ-fibrils. These Aβaggregates are toxic and are thought to be responsible for neuronal cell death, leading to dementia. We thought that the inhibition of the aggregation of Aβmolecules would prevent the progression of AD. In this study, we attempted to inhibit Aβaggregation using peptides consisted of D-amino acid residues (D-peptides) by forming a stereocomplex between Aβ and the D-peptides.Stereocomplex is a complex formed by a stereoselective interaction between two complementing stereoregular polymers. Our group recently found that short L- and D-peptides could also form a stereocomplex with hydrophobic and electrostatic interactions enhanced by stereochemistry. We here designed D-peptides to interact with Aβto form stereocomplexes and to give electrostatic repulsion between the complexes. We evaluated the effect of the designed D-peptides on the inhibition of Aβ aggregation. The D-peptides consisted of D-phenylalanine (f) and D-arginine (r) or D-lysine (l) with the N-termini acetylated and C-termini amidated (Ac-f 4 r 6 -Am and Ac-f 4 k 6 -Am). The L-peptide complementary with the D-peptide was also prepared (Ac-F 4 R 6 -Am). To investigate the inhibitory effect of the peptides, we conducted the thioflavin T (ThT) fluorescence assays to observe Aβaggregation. The ThT assays revealed Ac-f 4 r 6 -Am had the highest inhibitory effect among the peptides tested. Although the L-peptide also inhibited the aggregation, the D-peptide was more effective. It was considered that the interactions between Aβand Ac-f 4 r 6 -Am was remarkably strong, which resulted in the effective inhibition of the Aβaggregation. The TEM observation revealed that the addition of the D-peptide (Ac-f 4 r 6 -Am) gave the morphology of the Aβ aggregates that was obviously different from the original Aβaggregates. We then evaluated the cytotoxicity of the Aβaggregates to neuronal cells in the presence and absence of the peptides. In the absence of the peptides, the Aβaggregates showed the remarkable cytotoxicity. When the L-peptide (Ac-F 4 R 6 -Am) was added to Aβ, the Aβaggregates still showed the cytotoxicity. When the D-peptide (Ac-f 4 r 6 -Am) was added, the resultant Aβaggregates did not show the cytotoxicity. The present study suggested that Ac-f 4 r 6 -Am had the highest inhibitory effect against the Aβaggregation and suppressed the cytotoxicity of the Aβaggregates, probably because of forming a stereocomplex with Aβ.
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© The Author(s), 2023
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