A three-stage combination approach has been used to create a “detour” around a spinal cord injury lesion in an animal experiment.
This research, titled “Combined Delivery of Nogo-A Antibody, Neurotrophin-3 and the NMDA-NR2d Subunit Establishes a functional ‘Detour’ in the Hemisected Spinal Cord
,” was published last week in the European Journal of Neuroscience by an international collaboration of laboratories led by Victor Arvanian of the Northport Veterans Affairs Medical Center, Northport, NY.
The work is significant first because it demonstrates that a series of different interventions will likely be necessary to restore function after spinal cord trauma. In this case, Arvanian et al
activated a trio of mechanisms. First, they added an antibody called anti-Nogo-A to neutralize molecules that block axon growth in the area of injury. (This antibody has been tested, by itself, in a large scale clinical trial
in Europe, results not yet known.)
Next, the experiment delivered a growth promoting molecule called neurotrophin-3 (NT-3) using gene-engineered fibroblasts (skin cells). NT-3 helps neurons survive and remain viable. (NT-3, too, has been tested experimentally on its own, with encouraging but not always positive results.)
For the third round, a compound was added to enhance the ability of axons to grow (plasticity) and make connections (synapses), as well as to promote the effects of NT-3. This stuff doesn’t have a catchy name. Technically, it’s an “NMDA-receptor 2d (NR2d) subunit delivered via an HSV-1 amplicon vector,” which is to say, it is a complex molecule secreted by way of a gene-modified virus. It fortifies the host to handle glutamate, a type of transmitter molecule that can be poisonous to axons.
The combo approach publication was accompanied by a commentary from Jacqueline C. Bresnahan and Michael S. Beattie of the Brain and Spinal Injury Center, University of California, San Francisco. They write:
This new work and other recent studies give hope that judicious targeting of multiple aspects of axonal growth and circuit plasticity can be translated to human spinal cord injury, and that if there is any sparing of the cord at all, new connections can be formed by sprouting and rerouting without the absolute requirement for long tract regeneration.
The three-prong approach is long, difficult science that would be impossible to do in one lab; to be sure, the Arvanian work is noteworthy for its collaboration. The Reeve Foundation played a significant role in this regard. Arvanian began these experiments with Reeve funding as a post-doc in the Lorne Mendell lab at SUNY Stony Brook. Mendell is a member of the Reeve International Research Consortium on Spinal Cord Injury,
a combine of six labs addressing SCI collectively.
Arvanian, who now has his own lab at the VA, also enlisted Lisa Schnell of the Consortium lab of Martin Schwab at the Brain Research Institute, Zurich, Switzerland. Adding to the work were Phil Horner (former post-doc in the Consortium lab of Rusty Gage at the Salk Institute), now at the Institute for Stem Cell and Regenerative Medicine, University of Washington, Seattle.
Additional science was provided by the Center for Neural Development and Disease at the University of Rochester, and by the Department of Neurology, Georgetown University Medical Center, Washington, DC.
According to Arvanian’s paper, motor function was clearly improved in treated animals. The team wanted to know whether the new connections “traveled through the lesion area or around the Hx [hemisection – a type of injury model that cuts half the cord].” They carefully recut the spinal cord. The responses, recorded intracellularly by electrical signals below the lesion area, were maintained. Said the paper: “These results confirm that the novel responses recorded in Hx-lesioned rats receiving the full combination treatment were the result of the establishment of new connections around the hemisected cord rather than regeneration through the lesion area.”
So, just how does the combination treatment produce the detour? The team isn’t sure but suggest functional recovery was the result of both sprouting and axon growth. Arvanian notes that sprouting isn’t necessarily the right direction to pursue: such growth has been linked to spasticity, pain and dysreflexia. The current model is not clinically relevant, but Aravanian and his collaborators are working on new combinations.
He is lead author for a new paper, coming out soon in the Journal of Neuroscience called “Chondroitinase ABC Combined with Neurotrophin NT-3 Secretion and NR2D Expression Promotes Axonal Plasticity and Functional Recovery in Rats with Lateral Hemisection of the Spinal Cord.” This one substitutes ChABC, a drug that is getting a lot of attention lately for its apparent ability to dissolve spinal cord scar tissue and promote axon growth. For this latest experiment, Arvanian added the Reeve Consortium lab of James Fawcett, Centre for Brain Repair, University of Cambridge, UK.
Paraphrasing the unpublished paper:
Since ChABC restores plasticity in the adult CNS, it was added to the combo in adult rats with a hemisection at T8. The animals initially dragged their hindpaw and had abnormal gait. Those treated with either ChABC or NT3/HSV-NR2D recovered some locomotor function. Animals that got the combined therapy displayed the most improved body stability and interlimb coordination.
Said Arvanian, “Together, results of these two papers suggest that Nogo-A antibody and Ch-ABC have different mechanisms of action, but both are important components of a combination treatment.”
“Please note that these results we got in collaboration with the Lorne Mendell, James Fawcett and Martin Schwab laboratories. I started most of these experiments while being an associate of Lorne Mendell, and I am really proud that CRDF gave us a chance to conduct these complex experiments, which no one lab would be able to do alone."
Arvanian says his lab is continuing several promising combination approaches with an eye on regulatory and clinical application. “Although we got very encouraging preliminary results and improvements of motor function after contusion injury, new experiments are still on-going, so I would be careful describing and publicizing our new results until we are 100 percent sure that new treatment works.”