Background: Despite the great potential of FUS-BBB disruption (FUS-BBBD), it is still controversial whether FUS-BBBD acts as an inducing factor of neuro-inflammation or not, and the biological responses after FUS-BBBD triggers the inflammatory process are poorly understood. The aim of this study is to investigate the safety window for FUS levels based on a comprehensive safety assessment. Methods: The mice were treated with two different ultrasound parameters (0.25 MPa and 0.42 MPa) in the thalamus region of brain. The efficacy of BBB opening was verified by dynamic contrast-enhanced MRI (DCE-MRI) and the cavitation monitoring. The transcriptome analysis was performed to investigate the molecular response for the two BBBD conditions after FUS-mediated BBB opening in time-dependent manners. Histological analysis was used for evaluation of the tissue damage, neuronal degeneration, and activation of glial cells induced by FUS-BBBD. Results: The BBBD, as quantified by the K_trans, was approximately threefold higher in 0.42 MPa-treated group than 0.25 MPa-treated group. While the minimal tissue/cellular damage was found in 0.25 MPa-treated group, visible damages containing microhemorrhages and degenerating neurons were detected in 0.42 MPa-treated group in accordance with the extent of BBBD. In transcriptome analysis, 0.42 MPa-treated group exhibited highly dynamic changes in the expression levels of an inflammatory response or NF-κB pathway-relative genes in a time-dependent manner whereas, 0.25 MPa was not altered. Interestingly, although it is clear that 0.42 MPa induces neuroinflammation through glial activation, neuroprotective properties were evident by the expression of A2-type astrocytes. Conclusions: Our findings propose that a well-defined BBBD parameter of 0.25 MPa could ensure the safety without cellular/tissue damage or sterile inflammatory response in the brain. Furthermore, the fact that the excessive sonication parameters at 0.42 MPa could induce a sterile inflammation response via glial activation suggested the possibility that could lead to tissue repair toward the homeostasis of the brain microenvironment through A2-type reactive astrocytes.

Alzheimer’s disease (AD) is the most prevalent neurodegenerative disease worldwide, causing progressive cognitive decline, memory impairment, and neurological deficits. Methylene blue (MB), an antioxidant, has emerged as a potential drug for the treatment of AD owing to its cognitive improvement and neuroprotective functions. Despite the small molecular size of MB, which can cross the BBB, the therapeutic effective dosage using a BBB-permeable delivery system in a specific brain localization remains unclear. In this study, we presented magnetic resonance–guided focused ultrasound (MRgFUS) as a delivery system to enhance BBB permeability for the effective treatment of AD. MRgFUS using two ultrasound intensities (0.25 and 0.32 MPa) was used to intravenously deliver MB to the hippocampal region. Compared with treatment with 0.25 MPa FUS, treatment with 0.32 MPa FUS significantly enhanced MB brain accumulation. Deposition of amyloid-β (Aβ) plaques and neural cell damage was significantly reduced in 0.32 MPa FUS/MB-treated APP/PS1 mice. Furthermore, aquaporin-4 expression increased significantly in the 0.32 MPa FUS and 0.32 MPa FUS/MB groups without glial fibrillary acidic protein activation. The results from this study demonstrate that FUS improved MB delivery to the brain, and FUS/MB combination treatment reduced the number of Aβ plaques. This study revealed the potential of FUS-BBBD as an effective strategy to enhance the efficacy of therapeutic drugs for AD.

Focused ultrasound (FUS) has emerged as a promising technique for temporarily disrupting the blood-brain barrier (BBB) and blood-tumor barrier (BTB) to enhance the delivery of therapeutic agents. Despite its potential, optimizing FUS to maximize drug delivery while minimizing adverse effects remains a significant challenge. In this study, we evaluated a novel FUS protocol that incorporates additional FUS stimulation without microbubbles (MBs) (“FUS protocol”) prior to conventional BBB disruption with MBs (“BBBD protocol”) in a rat brain tumor model (n = 35). This approach aimed to validate its effectiveness in enhancing BBB/BTB disruption and facilitating doxorubicin delivery. T1-weighted contrast-enhanced and dynamic contrast-enhanced (DCE) MRI demonstrated significant increases in signal intensity and permeability (K_trans) in the tumor region under the “FUS + BBBD protocol”, with 2.65-fold and 2.08-fold increases, respectively, compared to the non-sonicated contralateral region. These values were also elevated compared to the conventional “BBBD protocol” by 1.45-fold and 1.25-fold, respectively. Furthermore, doxorubicin delivery in the targeted region increased by 1.91-fold under the “FUS + BBBD protocol”, compared to a 1.44-fold increase using the conventional “BBBD protocol”. This novel FUS approach offers a promising, cost-effective strategy for enhancing drug delivery to brain tumors. While further studies are required to assess its applicability with different chemotherapeutics and tumor types, it holds significant potential for improving brain tumor treatment in both preclinical and clinical settings.