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

<b>Background:</b> 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. <b>Methods:</b> 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 <i>ex vivo</i> and <i>in vivo</i> methods on the 5XFAD mouse model. In the <i>ex vivo</i> experiment, FUS was applied to brain slices, specifically targeting the hippocampal region. In the <i>in vivo</i> 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 <i>ex vivo</i> and <i>in vivo</i> experiments, immunohistochemistry was performed on brain sections for measuring Aβ plaques after sonication. Blood was collected from animals before and after <i>in vivo</i> stimulation for plasma analysis. <b>Results:</b> <i>In vitro</i>, 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. <i>Ex vivo</i> FUS stimulation significantly reduced the number of Aβ plaques in the hippocampal region compared to untreated brain slices. <i>In vivo</i> 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. <b>Conclusions:</b> FUS exposure effectively reduced amyloid plaques in both <i>ex vivo</i> and <i>in vivo</i> models by disrupting fibrillar and oligomeric Aβ, demonstrating its potential as a non-invasive strategy for Aβ clearance.