Localized delivery of the Neurturin (NTN) neurotrophic factor through focused ultrasound - Mediated blood-brain barrier opening

The blood-brain barrier (BBB) constitutes a major obstacle in drug delivery to the brain. Focused Ultrasound (FUS) in conjunction with microbubbles has been shown to open the BBB non-invasively, locally and transiently to allow the delivery of molecules to the tissue parenchyma. Neurturin (NTN), a member of the glial cell-line derived neurotrophic factor family, has been demonstrated to have neuroprotective and regenerative effects on dopaminergic neurons, suggesting its therapeutic potential for Parkinson´s disease (PD). The caudate putamen (CP) and substantia nigra (SN) are the brain structures mostly affected in PD animal models, and were selected as the target areas in this study. First, fluorescently tagged dextrans and gadolinium, were used for the optimization of the acoustic parameters and sonication locations for efficient and safe drug delivery in both CP and SN. The FUS parameters were selected as follows: 1.5 MHz (center frequency), 0.45 MPa peak-negative acoustic pressure, 10 Hz PRF, 1 min duration on each location. Polydisperse manufactured in-house lipid-coated microbubbles (8 × 105 #/g) were used. Fluorescence microscopy and Magnetic Resonance Imaging (MRI) were used to quantify and assess the BBB opening characteristics. NTN (20 mg/ kg, Invitrogen, CA, USA) diluted in saline was injected to CB57/bl wild type mice (25 g). The diffusion and the downstream signaling bioactivity were detected using immunostaining for RET, ERK1/2 and CREB, and microscopy. ELISA was performed to quantify the amount of NTN in the sonicated regions and was measured to be 210.58 ng, i.e., 0.04% of the 500 μg injected intravenously. These findings confirm the effective delivery of NTN to the murine brain parenchyma which could serve as a good therapeutic candidate for reversing the degenerative phenotype in PD animal models.