Design of LVFFARK and LVFFARK-functionalized nanoparticles for inhibiting amyloid β-protein fibrillation and cytotoxicity.

Aggregation of amyloid β-protein (Aβ) into amyloid oligomers and fibrils is pathologically linked to Alzheimer's disease (AD). Hence, the inhibition of Aβ aggregation is essential for the prevention and treatment of AD, but the development of potent agents capable of inhibiting Aβ fibrillogenesis has posed significant challenges. Herein, we designed Ac-LVFFARK-NH2 (LK7) by incorporating two positively charged residues, R and K, into the central hydrophobic fragment of Aβ17-21 (LVFFA) and examined its inhibitory effect on Aβ42 aggregation and cytotoxicity by extensive physical, biophysical, and biological analyses. LK7 was observed to inhibit Aβ42 fibrillogenesis in a dose-dependent manner, but its strong self-assembly characteristic also resulted in high cytotoxicity. In order to prevent the cytotoxicity that resulted from the self-assembly of LK7, the peptide was then conjugated to the surface of poly(lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) to fabricate a nanosized inhibitor, LK7@PLGA-NPs. It was found that LK7@PLGA-NPs had little cytotoxicity because the self-assembly of the LK7 conjugated on the NPs was completely inhibited. Moreover, the NPs-based inhibitor showed remarkable inhibitory capability against Aβ42 aggregation and significantly alleviated its cytotoxicity at a low LK7@PLGA-NPs concentration of 20 μg/mL. At the same peptide concentration, free LK7 showed little inhibitory effect. It is considered that several synergetic effects contributed to the strong inhibitory ability of LK7@PLGA-NPs, including the enhanced interactions between Aβ42 and LK7@PLGA-NPs brought on by inhibiting LK7 self-assembly, restricting conformational changes of Aβ42, and thus redirecting Aβ42 aggregation into unstructured, off-pathway aggregates. The working mechanisms of the inhibitory effects of LK7 and LK7@PLGA-NPs on Aβ42 aggregation were proposed based on experimental observations. This work provides new insights into the design and development of potent NPs-based inhibitors against Aβ aggregation and cytotoxicity.