A Transdermal Approach for Axonal Transport of Gold Nanoparticles to the Sensory Neurons of Dorsal Root Ganglion

Abstract

Delivering therapeutic cargo such as drug-loaded nanoparticles to the nervous system, even now, remains a challenging clinical scenario. More specifically, access to the peripheral nervous system (PNS) is a difficult task, mainly due to the presence of modified cellular barriers in the nerve. Therapeutic strategies that circumvent such blood-nerve barriers and allow delivery of nanoparticles to cell bodies of neurons in the PNS has significant application in conditions such as neuropathic pain, nerve injury, and nerve regeneration. Interestingly, skin may harbour an important, and a novel route to access the PNS. Axonal terminals of sensory neurons innervate layers of the skin, while remaining connected to their neuronal cell bodies in the distally located dorsal root ganglion (DRG). In this thesis we attempted to use skin dwelling axonal terminals to delivery gold nanoparticles to the DRG. Isolectin (IB4) conjugated gold nanoparticles (IB4-AuNP) were characterized using dynamic light scattering, UV-vis spectroscopy and high resolution-transmission electron microscopy. Axonal binding and transport of IB4-AuNP in DRG neurons cultured in microfluidic devices were determined using confocal microscopy with colocalization colour mapping, time-lapse imaging, and transmission electron microscopy. IB4-AuNP binding to dermal nerve fibres was demonstrated using immunohistochemical studies, while inductively coupled plasma mass spectrometer was used to detect gold content in skin, blood, DRG s and sciatic nerves harvested from rats that were topically treated (hind-paw) with IB4-AuNP. Evoked muscle action potentials were recorded to assess nerve health. Skin from rat hind-paw exposed to 22±3, 105±11, and 186±20 nm gold nanoparticle (AuNP) solution demonstrated AuNP penetration across skin layers along with accumulation in the epidermal-dermal layers. Additionally, IB4-AuNP (140.2±1.9 nm) treated DRG neurons cultured in microfluidic chambers demonstrated axonal binding and axonal transport. Further, topical application..