Comprehensive assessment of blood-brain barrier opening and sterile inflammatory response: unraveling the therapeutic window.

Microbubbles (MBs) combined with focused ultrasound (FUS) has emerged as a promising noninvasive technique to permeabilize the blood-brain barrier (BBB) for drug delivery into the brain. However, the safety and biological consequences of BBB opening (BBBO) remain incompletely understood. This study aims to investigate the effects of two parameters mediating BBBO: microbubble volume dose (MVD) and mechanical index (MI). High-resolution MRI-guided FUS was employed in mouse brains to assess BBBO by manipulating these two parameters. Afterward, the sterile inflammatory response (SIR) was studied 6 h post-FUS treatment. Results demonstrated that both MVD and MI significantly influenced the extent of BBBO, with higher MVD and MI leading to increased permeability. Moreover, RNA sequencing revealed upregulation of major inflammatory pathways and immune cell infiltration after BBBO, indicating the presence and extent of SIR. Gene set enrichment analysis identified 12 gene sets associated with inflammatory responses that were significantly upregulated at higher MVD or MI. A therapeutic window was established between therapeutically relevant BBBO and the onset of SIR, providing operating regimes to avoid damage from stimulation of the NFκB pathway via TNFɑ signaling to apoptosis. These results contribute to the optimization and standardization of BBB opening parameters for safe and effective drug delivery to the brain and further elucidate the underlying molecular mechanisms driving sterile inflammation.

Introduction

Purpose Drug delivery with BBB opening

Study Objective To determine how microbubble volume dose (MVD) and mechanical index (MI) influence focused ultrasound–induced blood–brain barrier opening and the resulting sterile inflammatory response, and to define safe therapeutic windows.

Animal model / Human subject Mouse (Mus musculus); strain: None; age: None; sex: None

Disease model Healthy

MRI or image guidance method High-resolution MRI-guided

Outcomes and Safety

Summary of Outcomes Focused ultrasound with microbubbles produced dose-dependent blood–brain barrier opening (BBBO), with higher microbubble volume dose (MVD) and mechanical index (MI) increasing permeability and, at higher doses, eliciting a sterile inflammatory response (upregulation of TNFα/NFκB, JAK/STAT, interferon, complement, hypoxia and apoptosis pathways). Significant BBBO without acute SIR was observed for these tested parameter combinations: 10 and 40 µL/kg MVD at 0.2 MI; 1 and 10 µL/kg MVD at 0.4 MI; and 1 µL/kg MVD at 0.6 MI (onset thresholds noted as >1 µL/kg at 0.2 MI and >0.1 µL/kg at 0.4/0.6 MI).

Duration of biological effect 6 h

Safety-related matter The study found dose-dependent adverse effects: MB+FUS induced a sterile inflammatory response (SIR) with upregulation of NFκB/TNFα pathways and immune cell infiltration, and at higher MVD/MI doses observed signs of cellular damage including hypoxia, apoptosis pathway activation, irregular MRI tissue morphology and potential microhemorrhages. The authors therefore define therapeutic windows to achieve significant BBB opening while avoiding these inflammatory and damage-related safety endpoints.

Brain Region

Visualization unavailable

Ultrasound Parameters

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

Treatment frequency single session

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