Department of Radiology, Stanford University, Stanford, California 94305, USA.
Department of Electrical Engineering, Stanford University, Stanford, California 94305, USA.
Nanotheranostics. 2020 Jul 14;4(4):210-223. doi: 10.7150/ntno.49898. eCollection 2020.
Localized blood-brain barrier (BBB) opening can be achieved with minimal to no tissue damage by applying pulsed focused ultrasound alongside a low microbubble (MB) dose. However, relatively little is known regarding how varying treatment parameters affect the degree of neuroinflammation following BBB opening. The goal of this study was to evaluate the activation of an inflammatory response following BBB opening as a function of applied acoustic pressure using two different microbubble doses. Mice were treated with 650 kHz ultrasound using varying acoustic peak negative pressures (PNPs) using two different MB doses, and activation of an inflammatory response, in terms of microglial and astrocyte activation, was assessed one hour following BBB opening using immunohistochemical staining. Harmonic and subharmonic acoustic emissions (AEs) were monitored for all treatments with a passive cavitation detector, and contrast-enhanced magnetic resonance imaging (CE-MRI) was performed following BBB opening to quantify the degree of opening. Hematoxylin and eosin-stained slides were assessed for the presence of microhemorrhage and edema. For each MB dose, BBB opening was achieved with minimal activation of microglia and astrocytes using a PNP of 0.15 MPa. Higher PNPs were associated with increased activation, with greater increases associated with the use of the higher MB dose. Additionally, glial activation was still observed in the absence of histopathological findings. We found that CE-MRI was most strongly correlated with the degree of activation. While acoustic emissions were not predictive of microglial or astrocyte activation, subharmonic AEs were strongly associated with marked and severe histopathological findings. Our study demonstrated that there were mild histologic changes and activation of the acute inflammatory response using PNPs ranging from 0.15 MPa to 0.20 MPa, independent of MB dose. However, when higher PNPs of 0.25 MPa or above were applied, the same applied PNP resulted in more severe and widespread histological findings and activation of the acute inflammatory response when using the higher MB dose. The potential activation of the inflammatory response following ultrasound-mediated BBB opening should be considered when treating patients to maximize therapeutic benefit.
局部血脑屏障（BBB）开放可以通过施加脉冲聚焦超声和低剂量微泡（MB）来实现，几乎没有组织损伤。然而，对于治疗参数如何影响 BBB 开放后的神经炎症程度，我们知之甚少。本研究的目的是评估在两种不同 MB 剂量下，应用不同声压强度对 BBB 开放后炎症反应激活的影响。使用 650 kHz 超声，通过不同的声压峰值（PNP）对小鼠进行处理，采用两种不同的 MB 剂量，在 BBB 开放后 1 小时，通过免疫组化染色评估炎症反应的激活程度，即小胶质细胞和星形胶质细胞的激活。采用被动式空化探测器监测所有处理的谐波和次谐波声发射（AE），并在 BBB 开放后进行对比增强磁共振成像（CE-MRI）以定量评估开放程度。苏木精和伊红染色的载玻片评估微出血和水肿的存在。对于每种 MB 剂量，当 PNP 为 0.15 MPa 时，BBB 开放仅伴有小胶质细胞和星形胶质细胞的轻度激活。更高的 PNP 与更高的激活程度相关，更高的 MB 剂量与更高的激活程度相关。此外，即使在没有组织病理学发现的情况下，仍观察到神经胶质细胞的激活。我们发现，CE-MRI 与激活程度相关性最强。虽然声发射并不能预测小胶质细胞或星形胶质细胞的激活，但次谐波 AE 与明显和严重的组织病理学发现密切相关。我们的研究表明，在 MB 剂量独立的情况下，当 PNP 范围在 0.15 MPa 至 0.20 MPa 之间时，存在轻微的组织学变化和急性炎症反应的激活。然而，当施加更高的 PNP（0.25 MPa 或更高）时，当使用更高的 MB 剂量时，相同的施加 PNP 会导致更严重和更广泛的组织学发现和急性炎症反应的激活。在对患者进行治疗以最大程度地提高治疗效果时，应考虑超声介导的 BBB 开放后炎症反应的潜在激活。
