Mitochondrial Transplantation Combined with Mitochondrial-Targeted Pharmaceuticals to Treat Spinal Cord Injury

The current proposal is designed to test the hypothesis that pharmacologically reducing oxidative stress with N-acetylcysteine amide (NACA), a precursor of endogenous antioxidant glutathione (GSH), while maintaining mitochondrial homeostasis with an alternative bio-fuel, acetyl-l-carnitine (ALC), will increase the beneficial effects of concomitant mitochondrial transplantation (Mito Txp) to augment neuroprotection and functional recovery following contusion spinal cord injury (SCI). Mitochondrial dysfunction and oxidative stress are key factors in development of secondary injury cascades, and we have documented that maintaining endogenous mitochondrial bioenergetics acutely with ALC or NACA administered at 1 hr post-injury results in significantly improved long-term functional neuroprotection in rat model of contusion SCI. However, the locomotor recovery was only partial. Moreover, our recent studies demonstrate that acute penumbral intraspinal injections of mitochondria (Mito Txp) isolated from rat soleus muscle within 1-hour post-injury also significantly preserves bioenergetics function post-SCI; but this did not translate into long-term functional recovery. One reason for lack on improved function following SCI could be that direct intraspinal injections might not be an ideal route due to damage at the injection sites. Thus, we are proposing an alternative approach to deliver mitochondria intrathecally (IT) at the site of injury. At this point, the mechanisms by which transplanted exogenous mitochondria remain functional bioenergetically within hours after delivery into the destructive biochemical and pathophysiological environment of the acute SCI penumbra remains unclear. Nevertheless, the combination of mitochondrial transplantation and delivery of neuroprotective mitochondrial-targeted pharmaceuticals is hypothesized to create a less toxic host micro-environment which, in turn, can additively preserve cellular bioenergetics and tissue sparing by improving the integrity of both grafted and host mitochondria. In support of current proposal, the beneficial effects of mitochondrial transplantation have recently been reported in the heart, liver, brain, and kidney under different pathological conditions. Notably, our new preliminary data show that delayed Mito Txp in combination with ALC at 2-3 hr post-injury significantly maintains mitochondrial bioenergetics compared to either alone after 24 hrs. This data indicates synergistic effects of this novel combinatorial approach, and the potential for extending clinically relevant therapeutic time windows of administration to improve functional recovery.