Ultrasound-targeted microbubble cavitation increases paracellular gaps in an in vitro blood brain barrier model

Abstract

Background: Ultrasound-targeted microbubble cavitation (UTMC) can transiently open the blood brain barrier (BBB). We sought to determine the timeline of paracellular gap formation after UTMC in an in vitro model of the BBB. Methods: We utilized a transwell model with murine brain endothelial cells (EC) and astrocytes on opposite sides of a support membrane. Ultrasound (1 MHz, 10 μs duration, 10 ms pulse interval) at 250 kPa was applied to lipid microbubbles in contact with ECs for 20 s. Z-stacks of transwells acquired by confocal microscopy were converted to maximum intensity projections to quantify number and size of paracellular gaps (NIS-Elements). Endothelial barrier function was assessed using transendothelial electrical resistance (TEER). One-way ANOVA with post-hoc t-testing was performed. Results: Compared to no UTMC, there was an increase in the number and size of paraceullar gaps two minutes after UTMC that lasted at least 60 min (p < 0.05). The increase in gaps was associated with a decrease in TEER (p < 0.05). The number of gaps started to decrease 15 min after UTMC, and total gap area started to decrease 30 min after UTMC (p < 0.05). Conclusions: In our model of the BBB, UTMC induces endothelial hyperpermeability, which appears mediated by dynamic paracellular gap formation.