By Lee Bowman, Scripps Howard News Service
Researchers have successfully tested injections of a liquid polymer to heal spinal injuries in dogs in an experiment that also offers hope for preventing human paralysis.
The liquid, called polyethylene glycol (PEG), if administered within 72 hours of serious spinal injury, was able to prevent three out of four dogs in a test group from suffering permanent spinal damage. Even when the spine was damaged to the point of paralysis, the PEG solution prevented nerve cells from rupturing irreversibly, allowing them to heal themselves.
“Nearly 75 percent of the dogs we treated with PEG were able to resume a normal life,” said Richard Borgens, director of the center for Paralysis Research at Purdue University’s School of Veterinary Medicine in West Lafayette, Ind., which developed the treatment. “Some healed so well that they could go on as though nothing had happened.”
The polymer has been safely ingested and injected in humans as a component of other medicines, and Borgens thinks it shows great promise as a human therapy. But he cautions: “This is very promising research, but it won’t be available in your hospital for some time.”
The research is described in the December issue of the Journal of Neurotrauma.
When nerve cells suffer trauma, their membranes weaken and rupture. Even when the cells survive, they lose their ability to produce and carry nerve impulses along the membranes from one cell to the next.
“Worse yet, chemicals seeping out of the dying spinal cord cells send a ‘suicide signal’ to other nearby cells, causing a chain reaction that kills off more cells than the initial injury did,” Borgens said. “Until now, the end result has been irreparable damage to the spinal cord, causing partial or complete paralysis.”
PEG is able to stop this cascade of injury by repairing initial membrane damage, or by fusing two damaged cells together into a larger Functional nerve cell. Significantly, the polymer is attracted only to damaged nerve cells and tissue when it’s injected into the blood stream. It doesn’t move into undamaged regions nearby.
About five years ago, Borgens and colleague Riyi Shi found that they could fuse hundreds to thousands of severed nerve fibers in a guinea pig spinal cord with just a two-minute PEG treatment. That put them on the path toward using the polymer as a repair agent to mend spinal nerve cells after traumatic injury.
In the new study, 19 Paraplegic dogs between 2 and 8 years of age were treated with a PEG injection within 72 hours of injury in addition to getting standard veterinary therapy for spinal injury.
Standard treatment includes injection of steroids, surgical removal of any potentially damaging bone chips from the spinal area and physical Rehabilitation, such as swimming. The group of 19 dogs was compared with a second group of dogs that had gotten only the standard treatment.
“This control group was taken from historical cases of dog injury that were similar to those in the 19 dogs we treated,” Borgens said. “We didn’t want to tell dog owners who walked in with injured dogs that their pets were not going to receive something that might help.”
After treatment, the improvement was measured based on criteria including desire to move.
“More than half the dogs (in the PEG group) in this study were standing or walking within two weeks of treatment,” Borgens said. “In most cases, you could notice positive signs within three to five days. These results are unprecedented in paralysis research.”
According to the Centers for Disease Control and Prevention, about 11,000 Americans sustain disabling spinal cord injuries each year, mainly from car crashes and sports mishaps, and more than half of them are younger than 30.
Researchers still are not certain how the polymer works to heal cells, but they think it has to do with removing the excess water that floods into the cell after it’s been damaged. And the polymer needs to be refined to a high level of purity before it’s effective, a manufacturing process that will have to clear tough government standards.
Borgens also noted that there are considerable differences between dog and human spinal cords that need to be addressed before the treatment can be tried in people. “In dogs, for example, some of the control of walking actually takes place in the spine, while in humans, all of this control resides in our brains.”
The researchers are working toward developing the product as an emergency drug along the lines of treatments used today for strokes and heart attacks.