June 24, 2002 06:37 PM ET
By Maggie Fox, Health and Science Correspondent
WASHINGTON (Reuters) - A naturally produced protein can help the brain bypass the damage done by a stroke, perhaps offering a way to keep patients from losing speech and use of their limbs, researchers working on rats said on Monday.
The protein, called inosine, is still too experimental to test in humans, but the researchers hope to prove it is safe.
Experiments in rats, published in Monday's issue of the Proceedings of the National Academy of Sciences, show the protein can stimulate the growth of new nerves across the brain. They essentially bypass the damaged area, and gave the rats back limited use of their paws.
"We created stroke on one side of the brain," Dr. Larry Benowitz of Children's Hospital in Boston and Harvard Medical School, who led the work, said in a telephone interview.
"We wanted to see in a stroke model whether inosine could stimulate intact nerve cells to extend ... and compensate for the losses."
It worked, he said. The rats treated with inosine grew new axons -- the long, stringy connections between nerves -- and regained some of the ability to move that had been lost in the stroke.
"They were markedly improved over animals who had stroke but did not have inosine," Benowitz said. "Using the paw that had lost its normal input, they were better at reaching for food, they were better at using the paw for swimming."
Half of the inosine-treated rats used their stroke-affected paws to reach for food, compared to none of the untreated rats.
Some of the rats were killed and their brains examined, and Benowitz said the new axons could be seen growing from the undamaged side of the brain to the spinal cord, in effect making up for the damage on the other side of the brain.
An estimated 750,000 Americans suffer strokes every year, and it is the third most common cause of death after heart disease and cancer. Stroke occurs when a clot blocks the flow of blood to the brain, causing brain cells to die, or when a blood vessel bursts, flooding the brain and killing cells.
So far, no way has been found to regenerate these dead cells, but Benowitz's team, working with Boston Life Sciences Inc., which licenses inosine, hope to bypass the damaged area.
Benowitz said the company, which helped fund the work and which pays him fees, was negotiating with the Food and Drug Administration to begin safety trials of inosine in people.
He says more scientific study is also needed.
"We would like to understand a bit more about how inosine activates this program in nerve cells," he said. "We know it switches on a whole ensemble of genes and causes the cell to reactivate its program of axon cell growth. In doing so it returns the cell to an earlier stage of development. We would like to know a bit more about those pathways."
It is also important to know how soon inosine must be given after the
stroke occurs, and how long it must be infused into the body, he said.
The rats in his team's experiment received continuous infusions of inosine
for up to six weeks.
© 2002 Reuters Ltd