WEDNESDAY, August 16 (HealthSCOUT) -- Stem cell therapy begins to rebuild the damaged nerves of partly paralyzed rats, according to a new study.

The scientists who did the study had already reported that the injured rats' mobility improved somewhat following an injection of nearly 1 million stem cells apiece. But the latest research helps explain why: Axons in the damaged section of spinal cord were repaired, restoring some communication between the brain and the rest of the body. In addition, the stem cells began producing proteins that offer hope of further regeneration and growth.

"We've been trying to cure spinal cord paralysis for 3,000 years and so far haven't been successful," says Dr. Todd J. Stewart, a clinical fellow in neurosurgery at Washington University in St. Louis. He presented the findings today at the annual meeting of the American Association of Neurological Surgeons in San Francisco.

Pate Skene, a nerve expert at Duke University in Durham, N.C., says the findings are useful in providing some biology behind the behavioral changes. "Something's been done, and the animals seem to be in better shape, but we didn't have much of a clue as to what all had been done," he says. "If you don't figure this out, it's like you're fishing blindly."

An estimated 450,000 Americans have suffered spinal cord injuries, and 10,000 new cases occur each year, according to the American Association of Neurological Surgeons.

Stem cells, in this case taken from mouse embryos, are early-development cells that haven't yet committed to a specific function; they can develop into any number of different types of cells with particular jobs. The idea is that if planted in a damaged part of a body, they may assume whatever functions are necessary to repair the damage.

And that's what Stewart and the rest of his team found in the injured rats. First, stem cells helped restore the function of axons in the damaged spinal cord area. Axons, which carry messages between the brain and the rest of the body, communicate more quickly when they're "wrapped" with oligodendrocytes, specific spinal cord cells -- much like electrical cord is insulated. Damage may essentially unwrap the axons, Stewart says, but some of the stem cells turned out to have transformed themselves into oligodendrocytes, rewrapping the axons so they were fully functional once again. Unfortunately, he says, not all axons were rewrapped.

Stem cells create a glue

"We have great examples, but they're not widespread," Stewart says.

When humans, rats, and other animals suffer spinal cord injuries, often a syrinx, or hole, develops at the site of the injury, usually inflicting more damage than the original injury. Stewart's team found that the stem cells -- actually injected into the rats' syrinxes -- had begun to produce what's called extracellular matrix, or critical proteins that act like glue for cells and can provide the building blocks for new growth.

Mature animals seem to have lost the ability to regenerate the nervous system, Stewart says, whereas the extracellular matrix shows the characteristics of early development and growth. "Maybe stem cells replicate early development in the extracellular matrix they produce, which hopefully would lead to the regeneration of native cells in the spinal cord," he says.

Skene says that both aspects of the new report are critical to our understanding of nerve regeneration in spinal cord injuries. Unwrapped axons can't conduct information very far and so aren't as effective, he says. And the research showing production of extracellular matrix is "plainly important," he adds, because the proteins support further axon growth and also may trigger cell migration, so that regeneration can spread.

The original study, reported in the December 1999 issue of Nature Medicine, took 40 rats and injured their spinal cords. After nine days, scientists injected stem cells into the syrinxes of half. Scientists noted a dramatic difference in those who'd received the stem cell therapy, Stewart says.

"They were able to lift the hind portion of their bodies off the ground vs. the untreated ones, who tended to drag their bodies," Stewart says.

Current research is aimed at increasing the number of axons that are recoated, Stewart says, and at steering the stem cells into damaged areas.

What To Do

This research was conducted both in test tubes and on live animals, and that's important, but it's still just rats. As Stewart said, "With any study, you worry whether what works with rats will work with people." It's impossible to predict when and if any of this information will be used on humans, he said.