Neurotrophic Factor Eluting Nerve Allografts for Peripheral Nerve Repair

Abstract

This dissertation is a compilation of two studies on the topic of reconstruction of traumatic peripheral nerve injuries. In the first study, I evaluate the effects of two neurotrophic factors, Nerve Growth Factor and Glial-Derived Neurotrophic Factor, as adjuvant therapeutics in nerve allograft repair. Unlike prior studies of neurotrophic factor therapy, this study evaluates their regenerative effects in gap injuries reconstructed with acellular nerve allografts. Over the last several years, acellular nerve allografts have become the preferred method to bridge large nerve gaps, because of reduced morbidity and operative timesaving. In this study, I explore the complex interaction of neurotrophic factor signaling and extracellular matrix composition in the altered microenvironment of the acellular nerve matrix. In the first half of this study, I hypothesize that Nerve Growth Factor or Glial-Derived Neurotrophic Factor may have improved regenerative effects in acellular nerve matrix due to removal of inhibitory glycosaminoglycans. Using a combination of in vitro dorsal root ganglion cell and in vivo rat sciatic nerve injury experiments, I find that adjuvant Nerve Growth Factor has significant pro-regenerative effects in both sensory and motor neurons in acellular nerve matrix. In the latter half of this study, I investigate the ability of acellular nerve allografts to deliver Nerve Growth Factor via extracellular matrix affinity. Using a combination of ex vivo Nerve Growth Factor release studies and in vitro bioactivity assays, I show that acellular nerve allografts maintain release of the neurotrophin over several weeks. I complete this study with an in-vivo evaluation of NGF-eluting acellular nerve allografts in a rat sciatic nerve gap injury, and ultimately find that these allografts are capable of enhancing early nerve regeneration.

The second study in this dissertation is on the characterization of peripheral nerve injury and repair using high-resolution diffusion tensor imaging. Diffusion tensor imaging, which is an MRI sequence that enhances anisotropy of water diffusion in axonal tracts, is a well-accepted clinical tool for evaluation of central nervous system injuries. Since prior investigations are limited to nerve crush or compression, I first evaluate the effects of different degrees of nerve severance on diffusion tensor imaging and tractography using a microsurgically-repaired rats sciatic nerve injury model. In addition to finding high sensitivity of diffusion tensor imaging to nerve severance, I find that specific measures may be useful for grading injury severity. In the last experiment, I use diffusion tensor imaging to evaluate regeneration of axons through NGF-eluting and control acellular nerve allografts. The results of these experiments support the conclusion that NGF-eluting acellular nerve allografts accelerate axon regeneration in peripheral nerve injuries.