Ingredient in vampire bat saliva may lead to new stroke drug

DALLAS -- A substance in the saliva of vampire bats could prove to be a potent new treatment for strokes, an Australian scientist says.

"When the vampire bat bites its victim, it secretes this powerful clot-dissolving substance so that the victim's blood will keep flowing, allowing the bat to feed," said Dr. Robert Medcalf of the Monash University Department of Medicine at Box Hill Hospital in Victoria, Australia.

That same substance -- Desmodus rotundus salivary plasminogen activator, or DSPA -- might someday be given to stroke victims to dissolve clots and thereby limit brain damage, he said.

The substance has yet to be tested for effectiveness and safety in humans, but it showed promise in preliminary experiments in mice. The findings were reported in Thursday's issue of the journal Stroke, published by the American Heart Association.

The research involves ischemic strokes, which are the most common kind of stroke and occur when a blood clot or narrowing of blood vessels prevents blood from getting to the brain. The other type of stroke is a hemorrhagic stroke, which occurs when a blood vessel bursts and causes bleeding in the brain.

Some ischemic stroke victims are given a clot-busting substance called tissue plasminogen activator, or TPA. But one major drawback of TPA is that it must be administered within three hours of the stroke's onset, or else the drug itself can cause bleeding and brain damage.

Medcalf's research team injected DSPA and TPA in mice and watched for brain damage. Mice that got DSPA suffered less brain damage.

Medcalf said that DSPA is not only a more potent clot-buster but can also be safely administered up to nine hours after the stroke's onset because it more precisely targets blood clots, which are held together by a string-like substance called fibrin.

"DSPA is almost inactive in the absence of fibrin and therefore much more fibrin-specific than TPA," Medcalf said.

One expert warned that the research was limited to mice that had not suffered strokes.

"This is several factors removed from a necessarily meaningful clinical effect," said Dr. Larry Goldstein, director of Duke University's Center for Cerebrovascular Disease and chairman of the American Stroke Association Advisory Committee. "Does this have potential? Yes. But whether it will prove to be safe or efficacious for humans with strokes, that's a whole different story."

And Dr. Keith A. Siller, an assistant professor of neurology at the NYU School of Medicine, said that the nine-hour window is not necessarily an advantage. He said that any drug administered after three hours is essentially pointless because the damage to the brain has already been done.

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On the Web

American Stroke Association: www.StrokeAssociation.org