(509f) Targeted Delivery of a Theophylline Coupled Nanoconjugate Induces Recovery of the Diaphragm Following Cervical Spinal Cord Injury in Rats
Following a spinal cord hemisection, the hemidiaphragm is paralyzed due to the disruption of the rostral ventral respiratory group (rVRG) axons descending to the phrenic motoneurons. Function to the paralyzed hemidiaphragm can be regained by systemic administration of xanthine family drugs such as theophylline (THP) and 8-Cyclopentyl-1,3-dipropylxanthine (DPCPX). However, in humans, systemically administered THP cause intolerable side effects at a therapeutic dose. In addition, DPCPX is insoluble in water. In order to eliminate the side effects or to increase solubility of the drug while still maintaining the recovery of diaphragm, a tripartite nanoconjugate was synthesized in which both THP/DPCPX and a neuronal tracer are coupled with a gold nanoparticle (AuNP). The nanoconjugate was injected intradiaphragmatically, followed by endocytosis absorption and retrograde transsynaptic transportation. This talk will describe our nanoconjugate design, synthesis, and characterization. Respiratory recovery data will include electromyography (EMG) analysis, phrenic nerve recordings, and whole body plethysmography (WBP) on a validated animal model. We will discuss the key targeting mechanism of retrograde transport by a neuronal tracer. The transporter protein, wheat germ agglutinin coupled to horseradish peroxidase (WGA-HRP), is taken up by phrenic axon terminals through receptor-mediated endocytosis and transported retrogradely to the phrenic nucleus. Subsequently, the entire nanoconjugate is transsynaptically transported to the cells in the rVRG in brain medulla. A single administration of the nanoconjugate restored 75% of the respiratory drive at 0.1% of the effective systemic drug dose. This work has important translational implications.