Composite of KLVFF-Transthyretin-Penetratin and Manganese Dioxide Nanoclusters: A Multifunctional Agent against Alzheimer's β-Amyloid Fibrillogenesis.

Design of amyloid β-protein (Aβ) inhibitors is considered an effective strategy for the prevention and treatment of Alzheimer's disease (AD). However, the limited blood-brain barrier (BBB) penetration and poor Aβ-targeting capability restricts the therapeutic efficiency of candidate drugs. Herein, we have proposed to engineer transthyretin (TTR) by fusion of the Aβ-targeting peptide KLVFF and cell-penetrating peptide Penetratin to TTR, and derived a fusion protein, KLVFF-TTR-Penetratin (KTP). Moreover, to introduce the scavenging activity for reactive oxygen species (ROS), a nanocomposite of KTP and manganese dioxide nanoclusters (KTP@MnO2) was fabricated by biomineralization. Results revealed that KTP@MnO2 demonstrated significantly enhanced inhibition on Aβ aggregation as compared to TTR. The inhibitory effect was increased from 18%, 33%, and 49% (10, 25, and 50 μg/mL TTR, respectively) to 52%, 81%, and 100% (10, 25, and 50 μg/mL KTP@MnO2). In addition, KTP@MnO2 could penetrate the BBB and target amyloid plaques. Moreover, multiple ROS, including hydroxyl radicals, superoxide radicals, hydrogen peroxide, and Aβ-induced-ROS, which cannot be scavenged by TTR, were scavenged by KTP@MnO2, thus resulting in the mitigation of cellular oxidative damages. More importantly, cell culture and in vivo experiments with AD nematodes indicated that KTP@MnO2 at 50 μg/mL increased the viability of Aβ-treated cells from 66% to more than 95%, and completely cleared amyloid plaques in AD nematodes and extended their lifespan by 7 d. Overall, despite critical aspects such as the stability, metabolic distribution, long-term biotoxicity, and immunogenicity of the nanocomposites in mammalian models remaining to be investigated, this work has demonstrated the multifunctionality of KTP@MnO2 for targeting Aβ in vivo, and provided new insights into the design of multifunctional nanocomposites of protein-metal clusters against AD.