Enhanced macromolecular substance extravasation through the blood-brain barrier via acoustic bubble-cell interactions

The blood-brain barrier (BBB) maintains brain homeostasis, regulates influx and efflux transport, and provides protection to the brain tissue. Ultrasound (US) and microbubble (MB)-mediated blood-brain barrier opening is an effective and safe technique for drug delivery in-vitro and in-vivo. However, the exact mechanism underlying this technique is still not fully elucidated. The aim of the study is to explore the contribution of transcytosis in the BBB transient opening using an in-vitro model of BBB. Utilizing a diverse set of techniques, including Ca²⁺ imaging, electron microscopy, and electrophysiological recordings, our results showed that the combined use of US and MBs triggers membrane deformation within the endothelial cell membrane, a phenomenon primarily observed in the US + MBs group. This deformation facilitates the vesicles transportation of 500 kDa fluorescent Dextran via dynamin-/caveolae-/clathrin- mediated transcytosis pathway. Simultaneously, we observed increase of cytosolic Ca²⁺ concentration, which is related with increased permeability of the 500 kDa fluorescent Dextran in-vitro. This was found to be associated with the Ca²⁺-protein kinase C (PKC) signaling pathway. The insights provided by the acoustically-mediated interaction between the microbubbles and the cells delineate potential mechanisms for macromolecular substance permeability.