Delivery of fluorescent dextrans through the ultrasound-induced blood-brain barrier opening in mice

The blood-brain barrier (BBB) is a specialized brain protection system consisting of endothelial cell, tight junctions and glial processes. BBB is the major limiting factor to therapeutic agents to the brain for disease treatment. Focused ultrasound (FUS) in the presence of microbubbles has the capability to deliver large molecules across BBB. In this study, we qualitatively and quantitatively analyzed the cellular impact, the size estimation of the opening and the amount delivered into the brain parenchyma in murine model. The method involved intravenously administration of a bolus of microbubbles at 1 mul/g body weight. Pulsed FUS was applied to the left hippocampus through the intact skin and skull at 0.75 MPa peak-negative pressure followed by a separate intravenously administration of fluorescence-conjugated dextrans at 3 kDa, 10 kDa and 70 kDa. Qualitative analysis was evaluated through the fluorescence imaging of sectioned brain slices. Smooth muscle cells engulfing the capillaries exhibited higher fluorescence in the case of 70 kDa dextran once the BBB was opened. The dextran dose delivered into the brain was analyzed by brain tissue homogenization and fluorescence intensity measurement. The concentration of 3 kDa, 10 kDa and 70 kDa dextrans delivered to the left hemisphere was quantified to be equal to 7.9plusmn4.9 mug/g, 2.4plusmn1.3 mug/g and 0.9plusmn0.47 mug/g of brain weight. In conclusion, significant drug delivery and the net deposition to the sonicated hippocampus, compared to the non-sonicated hippocampus, were determined. The delivered dosage and the spatial distribution provide useful information for the ultimate treatment of neurodegenerative diseases.