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Jason Carmel, M.D., Ph.D.
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Chitosan Guidance Channels Containing a Scaffold and Seeded Spinal Cord Derived Neural Stem/Progenitor Cells, and Chondroitinase-ABC for Repair of Chronic Spinal Cord Injury
Charles H. Tator, M.D., Ph.D., The Toronto Western Hospital Research Institute; 2-year Grant
Hypothesis: functional recovery after chronic spinal cord injury can be achieved by the combined action of chitosan guidance channels with scaffolds containing neural stem/progenitor cells and chondroitinase-ABC.
This project examines an innovative, four-part combination of treatments to repair the injured spinal cord in the chronic stage (in humans, more than 6-12 months after SCI; in rats, more than 4 weeks after injury). The strategy starts with a transplanted chitosan guidance channel inserted directly into the cavity in the spinal cord in the thoracic region 4 weeks after clip injury (which causes impact and compression similar to a human injury). Chitosan is a naturally occurring material that is well-tolerated by the spinal cord. The channel, 6 mm long and about 1.5 mm in diameter, allows nerve fibers to enter its ends and grow along its course without any inflammation or blockage by cells that can obstruct growth.
More Progress in Research
Dr. Tator's lab is targeting regeneration of the long fibers from the brain that are responsible for movement of the arms and legs. Combined with the channel are spinal-cord-derived neural stem cells that can generate daughter cells called progenitors; these cells should help guide fiber growth in and out of the channels. Also included are supporting cells called oligodendrocytes that make the insulation (myelin) on the nerve fibers. The channels also contain a scaffold made of a fibrin substance that can increase stem cell survival after transplantation.
Finally, chondroitinase-ABC is injected at the ends of the channels; this is an enzyme that dissolves inhibitory chemicals that accumulate at the injury site. None of these selected therapies has been thoroughly evaluated in chronic SCI, individually or collectively.
Dr. Tator says his team will be able to tell if the combo treatment is successful by counting the number of transplanted cells that survive and the number of axons that grow into the channels; they will also assess the ability of the rats to move their legs.
Ephrin Inhibition of Regeneration after Spinal Cord Injury
M. Douglas Benson, Ph.D., Baylor College of Dentistry; 2-year Grant
Hypothesis: A molecule called ephrin-B3 contributes to the inhibition of axonal regeneration in the adult spinal cord; blockage of this molecule will improve regeneration after SCI.
Surviving nerve fibers (axons) in the area of spinal cord injury retain some built-in ability to grow. Axons cannot fully regenerate, though, because they are inhibited by spinal cord myelin, disrupted and distributed in the lesion area. Several specific proteins in myelin have been identified as inhibitors of axonal growth; removing any one of them in animal models results in slight or no regeneration. Therefore, a combination of therapies against multiple inhibitors is needed to increase recovery.
Dr. Benson hopes to better understand the contributions of the individual components of myelin that restrict regeneration, and thereby target them with therapies. He was on a team that discovered that one of these proteins, ephrin-B3, is a major inhibitor of axon growth in culture. The funded project aims to 1) characterize the contribution of ephrin-B3 to myelin inhibition of axonal regeneration in SCI; and 2) establish an anti-ephrin therapy to promote axon regeneration. Dr. Benson will first examine regeneration in mice that lack one or more of the known myelin inhibitors (including ephrin-B3) to compare their relative roles in suppressing axon regrowth. He will then compare the effect of an ephrin blocking protein, EphA4/Fc, in improving regeneration to that of blockers for other inhibitors, including the anti-Nogo antibody, which has been proven to increase axon sprouting and recovery in rats and primates. This work is innovative, Dr. Benson said, because it examines multiple axon inhibitors simultaneously and combines multiple anti-inhibitor treatments to improve functional outcome. "Our results provide evidence that molecules with known repellent activity toward specific axon types during embryonic development maintain inhibitory activity in the adult mouse spinal cord," said Dr. Benson. "This implies that the regeneration of different cell populations involved in SCI may each be subject to unique combinations of inhibitory molecules."
Electrical Stimulation with and without Behavioral Training to Strengthen Spared Corticospinal Circuits and Promote Recovery after Dorsal Column Lesion
Jason Carmel, M.D., Ph.D., College of Staten Island/City University of New York; 2-year Grant
Hypothesis: Electrical stimulation boosts injury-induced sprouting in spared corticospinal axons, allowing improved behavioral recovery; this recovery can be further augmented with behavioral training.
Spinal cord injury causes paralysis when the brain loses connections to the spinal cord; most people with SCI, however, have some spared connections between the brain and spinal cord. Dr. Carmel’s intention is to restore function by strengthening those spared connections using electrical stimulation.
Previously, he showed that electrical stimulation restored movement in the impaired limbs of a rat after an injury to one side of the brain. In this experiment, he uses a rat SCI model that has lost 95 percent of its brain-to-spinal cord connections. By electrically stimulating the few remaining connections, Dr. Carmel hopes to strengthen them within the spinal cord and thereby restore movement. In addition, Dr. Carmel will combine the electrical stimulation with behavioral training to maximize recovery.
The new connections will be traced using a new viral technique: First, a virus is weakened so it can infect cells but not cause illness. Then, the virus is loaded with a marker gene that is turned on by infected neurons. As the virus and the marker move from neuron to neuron, long chains of neurons can be mapped.
Knowing which specific connections are important for restoring movement will help to optimize treatments for paralysis. Dr. Carmel notes that new techniques allow non-invasive electrical stimulation of the brain. "If our treatment proves effective," he said, "it could be brought quickly to clinical trial."
Determinants of Outcomes from Traumatic Spinal Cord Injury: Development of a Novel Classification System to Facilitate Clinical Trials and Improved Therapeutic Strategies
Jefferson R. Wilson, M.D., The University of Toronto; 2-year Grant
Hypothesis: in traumatic SCI, it is possible to predict functional and neurologic recovery at one year post-injury; the project will create a more accurate "real world" predictive scale for acute SCI. The project will also develop an improved classification system for specific subgroups of SCI patients; this will facilitate more precise protocols for clinical trials or therapies.
Dr. Wilson, a neurosurgeon, has treated many new spinal cord injuries. "In the acute period after SCI," he said, "the picture is murky - there are a lot of things going on that make it difficult to perform an accurate neurological exam or to make a reliable prediction for outcome." The picture gets more clear at 72 hours but at that point certain treatment options may no longer be appropriate.
Therefore, Dr. Wilson and his group have set out to create a new classification system, taking into account neurological status as well as demographic detail, plus imaging data (MRI, CT or X-ray). "If we look at all these factors we will be able to stratify patients into more homogenous clinical subgroups, which allows us then to look into the future and assess which patients are likely to benefit from a specific new therapy - be it medication or surgery."
Dr. Wilson hopes to arrive at a practical predictive scale, along the lines of the Glasgow Coma Scale, widely used to assess traumatic brain injury. "This would be a tool every clinician could use to make better predictions of outcome."
To create the SCI scale, Dr. Wilson's group will comb over data obtained from 650 people with SCI in the North American Clinical Trial Network (NACTN) and the Surgical Treatment of Acute Spinal Cord Injury Study (STASCIS) databases. These databases include a rigorous analysis of mechanism of injury, demographic information, clinical findings, radiologic detail and treatment history. In addition, comprehensive outcome measurements are available up to 12 months post injury; this will establish a realistic correlation between acute injury features and long-term outcome.
"Until now, we did not have access to this level of detail about acute spinal cord injury. These measures will really improve our predictive capacity," said Dr. Wilson.
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