Clearance of amyloid plaque via focused ultrasonication in a mouse model of Alzheimer's disease

Abstract

Background: The success of anti-amyloid-β (Aβ) monoclonal antibodies in recent clinical trials validates the promising approach of clearing amyloid-β in Alzheimer's therapy. Building on these successes, focused ultrasound (FUS), a non-invasive therapeutic modality that delivers acoustic energy to targeted brain regions with high precision, has emerged as a potential technique to modulate Aβ pathology, either in combination with drugs or as a standalone treatment. This study focused on the standalone potential of FUS to reduce Aβ plaques without accompanying drugs.

Methods: Synthetic Aβ42 aggregates were prepared and exposed to FUS. The changes in fibril and oligomer levels were analyzed using Thioflavin T (ThT) fluorescence, gel electrophoresis combined with photo-induced cross-linking of unmodified protein (PICUP) chemistry, transmission electron microscopy (TEM), and immunoblotting. The effect of FUS on Aβ42-induced cytotoxicity was evaluated in SH-SY5Y human neuroblastoma cells. FUS-mediated dissociation of Aβ plaques was performed by ex vivo and in vivo methods on the 5XFAD mouse model. In the ex vivo experiment, FUS was applied to brain slices, specifically targeting the hippocampal region. In the in vivo experiment, the left hippocampus of awake animals was sonicated in a transcranial manner ten times over two weeks using a miniature ultrasound transducer affixed to the skull. For both ex vivo and in vivo experiments, immunohistochemistry was performed on brain sections for measuring Aβ plaques after sonication. Blood was collected from animals before and after in vivo stimulation for plasma analysis.

Results: In vitro, FUS treatment reduced the β-sheet structure of synthetic Aβ42 aggregates by up to 55.28% in the ThT assay, and fibrillar Aβ42 levels by up to 62.27% in the gel electrophoresis, as further confirmed by TEM imaging, which showed disrupted fibrillar structures. The level of oligomeric Aβ42 was also reduced by up to 65.02% following FUS exposure. SH-SY5Y cells treated with FUS-treated Aβ42 aggregates exhibited improved viability from 81.56% to 90.48%, showing a tendency of attenuated Aβ42-induced cytotoxicity by FUS. Ex vivo FUS stimulation significantly reduced the number of Aβ plaques in the hippocampal region compared to untreated brain slices. In vivo transcranial FUS reduced both the number and size of plaques in the FUS-treated hippocampal and thalamic region compared to the contralateral side. Plasma analysis with Aβ42 enzyme-linked immunosorbent assay revealed a 65.91% increase in Aβ levels following FUS treatment compared to pre-treatment levels, suggesting that Aβ plaques dissociated by FUS were released into the bloodstream.

Conclusions: FUS exposure effectively reduced amyloid plaques in both ex vivo and in vivo models by disrupting fibrillar and oligomeric Aβ, demonstrating its potential as a non-invasive strategy for Aβ clearance.