Focused ultrasound-enhanced intranasal brain delivery of brain-derived neurotrophic factor

Abstract

The objective of this study was to unveil the potential mechanism of focused ultrasound (FUS)-enhanced intranasal (IN) brain drug delivery and assess its feasibility in the delivery of therapeutic molecules. Delivery outcomes of fluorescently-labeled dextrans to mouse brains by IN administration either before or after FUS sonication were compared to evaluate whether FUS enhances IN delivery by active pumping or passive diffusion. Fluorescence imaging of brain slices found that IN administration followed by FUS sonication achieved significantly higher delivery than IN administration only, while pre-treatment by FUS sonication followed by IN administration was not significantly different from IN administration only. Brain-derived neurotrophic factor (BDNF), a promising neurotrophic factor for the treatment of many central nervous system diseases, was delivered by IN followed by FUS to demonstrate the feasibility of this technique and compared with the established FUS technique where drugs are injected intravenously. Immunohistochemistry staining of BDNF revealed that FUS-enhanced IN delivery achieved similar locally enhanced delivery as the established FUS technique. This study suggested that FUS enhances IN brain drug delivery by FUS-induced active pumping of the drug and demonstrated that FUS-enhanced IN delivery is a promising technique for noninvasive and localized delivery of therapeutic molecules to the brain.

Figure 1

Experimental timeline for (a) IN-administration followed by FUS sonication (IN + FUS) and (b) pretreatment by FUS followed by IN administration (FUS + IN).

Figure 2. Compare two protocols for focused ultrasound-enhanced intranasal brain drug delivery.

Fluorescence images of the left caudate putamen treated by (a) IN-administration followed by FUS sonication (IN + FUS) or (d) pretreatment by FUS followed by IN administration (FUS + IN). (b,e) The corresponding right caudate putamen from the same mouse was used as control for IN only. Dash lines highlight the caudate putamen regions. (c,f) quantitative fluorescence intensity analysis of the two treatment protocols. FUS significantly enhanced IN delivery efficiency when drugs were administered through IN before FUS sonication. There was no statistically significant enhancement when drugs were administered after IN; however, slightly enhanced delivery at the FUS targeted region was observed in the case shown in (d) at the FUS targeted location (the region between the two arrows).

Figure 3. Higher magnification images present the locally-enhanced delivery effect of FUS on IN drug delivery.

(a) FUS sonication enhanced dextran penetration and diffusion at the focused ultrasound targeted region. (b) Without FUS sonication, the fluorescently-labeled dextrans were confined within the perivascular space.

Figure 4. BDNF delivery by FUS-enhanced intranasal drug delivery (IN + FUS) and FUS combined with IV drug injection (IV + FUS).

(a,b) are the immunohistochemistry staining of the whole brain horizontal section from mice in the IN + FUS and IV + FUS groups, respectively. FUS was targeted at the left caudate putamen. Locally enhanced delivery was achieved for BDNF administered either through IN or IV.

Figure 5. Quantification of BDNF delivery.

No significant difference in the enhancement of BDNF delivery when comparing the increase in BDNF-stained pixel numbers of FUS treated caudate putamen and the contralateral nontreated control side.

Figure 6. Histological examinations by hematoxylin and eosin (H&E).

No tissue damage was observed in the IN + FUS and IV + FUS groups. Representative H&E stained images are shown here. (a,c) FUS sonicated left caudate putamen and (b,d) corresponding nonsonicated right caudate putamen.