In recent years, we have discovered that certain drugs (methylxanthines, phosphodiesterase inhibitors and selective A1 adenosine receptor antagonists) will induce plasticity in the respiratory pathways which results in recovery of the diaphragm after cervical spinal cord injury. Furthermore, we discovered that after rats are exposed to 3 days of multiple systemic drug administrations (3 injections/day);the drug-induced recovery persists long after the animals are weaned from the drug. In an effort to test our basic science work at the clinical level, we conducted 3 clinical studies using the methylxanthine, theophylline. The results of these theophylline studies were mixed. Some patients showed promising results whereas others did not following the required systemic administration of the drug (either by mouth or intravenous administration). The lack of complete success at the clinical level could not be attributed to any single factor. However, it was very clear that the majority of the patients could not tolerate the theophylline doses necessary to induce recovery without experiencing significant side effects (nausea, nervousness, vomiting, etc.) which forced them to discontinue drug therapy. To directly address the problem of side effects following systemic theophylline therapy in cervical SCI patients, we recently developed a novel approach which combines nanotechnology and proven neurobiological principals to """"""""selectively target"""""""" only the respiratory motor (phrenic) and pre- motor (rVRG) neurons responsible for diaphragmatic function to induce recovery. We have shown that by using this method we can induce recovery of the diaphragm in spinal cord injured rats using 1/160th the dose of theophylline necessary to induce recovery following systemic drug administration. This approach to inducing motor recovery after SCI has never been taken by any other laboratory in the world. The purpose of this application is to optimize this technique so that it may be developed for clinical use. There will be three specific aims to address the following hypotheses: 1) that following a non-systemic administration (injection into the paralyzed hemidiaphragm) of one of three different drug-delivering conjugate nanodevices, optimal recovery will be induced. 2) that the """"""""site(s) of action"""""""" of the conjugate nanodevice in inducing recovery will be determined by using different retrograde transporters to selectively target different respiratory neurons. 3) that following the single administration of either a slow-drug release, a fast-drug release, or a combination (cocktail) of both conjugate nanodevices, long-lasting functional recovery will be achieved in the hemidiaphragm paralyzed by spinal hemisection.
The ability to induce diaphragmatic recovery in SCI rats with conjugate nanodevices using only a small fraction of the theophylline previously necessary to induce recovery, has major translational implications for the use of this drug (and others like it) in treating SCI patients with respiratory muscle weakness. The obvious advantage is the low dose of the drug should reduce (or completely eliminate) the adverse side effects normally associated with administering theophylline systemically (i.e., orally or intravenously). The purpose of this application is to optimize our newly developed technique so that it may be further developed for clinical use as soon as possible.
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