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A new drug has helped dogs paralyzed by spinal cord injuries walk again when given within 72 hours of the injury. As this ScienCentral News video reports, researchers at Purdue University hope it will eventually benefit people.
Going to the Dogs
Could a chemical cousin of antifreeze someday prevent the progressive damage of a spinal cord injury?
Researchers at Purdue University are studying this in dogs with paralyzed hind legs. They injected 19 injured dogs with a drug called polyethylene glycol (PEG)—a nontoxic liquid polymer related to antifreeze—on top of providing them with the standard drugs, surgery and rehab, and showed that PEG targets damaged nerve cells, protecting some of the injured cells from progressive damage and death.
"The dogs that come in that receive conventional management, that is, just surgery and rehabilitation, about 15 to 20 percent of those dogs will have some quality of life just through spontaneous repair," says Richard Borgens, director of Purdue University Center for Paralysis Research, who reported his findings in the Journal of Neurotrauma. "But most of them, about 80 percent, will remain paraplegic for the rest of their lives. What this [PEG] compound does when we inject it is it reverses those odds, it really goes from about 20-80 to 80-20; about 80 percent are leading very normal lives, good quality of life, and only about 20 percent have any kind of real problem at the end of the study time, which was, we followed them out to about a year."
In the study, 13 of the 19 dogs (about 68 percent) injected with PEG regained use of their hind legs and were able to walk within eight weeks. The dogs were injected twice—when they were brought into the veterinary emergency room (within three days of their injuries), and then after standard surgery and steroids to reduce inflammation. In a group of 24 dogs that only received the standard treatment, only about 25 percent regained a similar level of mobility and 62 percent remained paraplegic.
The researchers are not yet sure exactly how PEG works, but their study also showed that PEG accumulates only in injured nerve cells. They did this by chemically labeling, or "decorating" the PEG molecule so it can be traced using imaging techniques. When they injected the labeled PEG into dogs with no injuries, they saw no PEG accumulating in tissues. "But if we inject it into an animal that has a spinal cord injury, or as a matter of fact a brain injury, it directly labels intensely the area of damage," says Borgens, "which tells us that after injection, after getting into the bloodstream, it actually targets areas of damage but has no attachment to any other normal tissue."
Savannah is one of 19 dogs that was treated successfully with PEG.
One theory is that PEG might form a temporary seal over breaches in nerve cells in the spinal cord, helping their healing process. "If these breaches or holes are too vast or too numerous…these cells will eventually die," says Brad Duerstock, one of the researchers. "And so within hopefully hours or days after an injury if we can apply the PEG, fill these holes or these breaches, we can spare these neurons and then we can recover more function."
Might this treatment offer hope that in the future, people will be able to recover from spinal cord injuries that today end up paralyzing them for life? Wise Young, a neuroscientist at Rutgers University, discovered the standard drug treatment in people with spinal cord injuries, called methylprednisolone, which he says helps people at about the same rate as the standard treatment for dogs. "It improves recovery by about 20 percent," Young says. "But that was 20 years ago that we found this drug. It has been terribly disappointing that in the last 20 years we have not had a 2nd-generation neuroprotective drug. So this discovery of a drug, PEG, that helps spinal cord injury in dogs, is very welcome indeed. It is very exciting that there may be a therapy that could be applied during surgery that will protect the spinal cord. I think it is time to begin testing this drug in human clinical trials. I think that what is going to be very important here is to establish the dose and the safety of this drug…and there's a real question whether doses for dogs can be directly extrapolated to humans."
While the scientists don't want to offer false hope—there are big differences between human and canine spinal cords—Duerstock, himself a quadriplegic, says preserving even some function would be a win. "We can't predict what'll happen in humans, but you know, it's worth a shot," he says. "Having more use of…upper limbs [would] have a tremendous impact in my daily life," he says. "That could mean the difference between…I could feed myself, help bathe myself, instead of having to rely on attendants to do most of these daily living functions."
The researchers say they need to do further studies in dogs before the drug can be tested in people, and hope to begin testing PEG in people brought into emergency rooms with traumatic spinal cord injuries within a year.