Characterization of Different Microbubbles in Assisting Focused Ultrasound-Induced Blood-Brain Barrier Opening.

Microbubbles (MBs) serve as a critical catalyst to amplify local cavitation in CNS capillary lumen to facilitate focused ultrasound (FUS) to transiently open the blood-brain barrier (BBB). However, limited understanding is available regarding the effect of different microbubbles to induce BBB opening. The aim of this study is to characterize different MBs on their effect in FUS-induced BBB opening. Three MBs, SonoVue, Definity, and USphere, were tested, with 0.4-MHz FUS exposure at 0.62-1.38 of mechanical index (MI) on rats. Evans blue, dynamic contrast-enhanced (DCE) MRI and small-animal ultrasound imaging were used as surrogates to allow molecule-penetrated quantification, BBB-opened observation, and MBs circulation/persistence. Cavitation activity was measured via the passive cavitation detection (PCD) setup to correlate with the exposure level and the histological effect. Under given and identical MB concentrations, the three MBs induced similar and equivalent BBB-opening effects and persistence. In addition, a treatment paradigm by adapting exposure time is proposed to compensate MB decay to retain the persistence of BBB-opening efficiency in multiple FUS exposures. The results potentially improve understanding of the equivalence among MBs in focused ultrasound CNS drug delivery, and provide an effective strategy for securing persistence in this treatment modality.

Introduction

Purpose Drug delivery with BBB opening

Study Objective To characterize and compare the effects of three microbubble formulations (SonoVue, Definity, USphere) on focused ultrasound–induced blood–brain barrier opening in rats.

Animal model / Human subject Rat (Rattus norvegicus); strain None; age None; sex None

Disease model Healthy

Cargo name and characteristics Evans blue (small-molecule dye used as a tracer to quantify BBB permeability)

Outcomes and Safety

Summary of Outcomes All three microbubbles (SonoVue, Definity, USphere) enabled focused‑ultrasound (FUS)–induced blood–brain barrier (BBB) opening at matched doses with broadly comparable efficacy and persistence; SonoVue produced stronger stable cavitation and greater BBB opening at low MI (0.62) while higher MIs (≥0.85) produced similar effects across MBs and 1.38 MI caused erythrocyte extravasation/damage. Successful FUS parameters tested: ~0.4–0.5 MHz FUS at mechanical indices 0.62, 0.85 and 1.38 with 2‑min single exposures (MB dose 4×10^7 bubbles/kg) produced BBB opening, and persistence across multiple targets was maintained by adapting exposure times (sequentially 15, 30, 60, 120 s) at 0.62 MI.

Duration of biological effect SonoVue: 1.04 ± 0.15 min; Definity: 6.88 ± 4.88 min; USphere: 4.98 ± 0.83 min

Safety-related matter At higher FUS exposure levels (notably 1.38 MI and to a lesser extent 0.85 MI) the study observed apparent and large-scale erythrocyte extravasation and some histological damage, attributed to inertial cavitation, indicating a need to carefully control exposure for safety; by contrast, at the low exposure level (0.62 MI) no obvious damage was found and the exposure-time adaptation scheme did not induce noticeable erythrocyte extravasations.

Brain Region

Visualization unavailable

Ultrasound Parameters

FUS Frequency 0.4 MHz

FUS Pressure ParseError

Focal Characteristics focal depth: None; focal length: None; aperture size: None

Treatment frequency multiple sessions

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