Compound in bat saliva may aid stroke patients. (Nifty Spittle).

When a vampire bat bites an animal, its saliva introduces an anticlotting agent to keep the blood meal flowing. Scientists now report that this compound, which busts up blood clots as well as the leading medication for treating strokes does, avoids one of the drug's major drawbacks.

Researchers injected mice with chemicals that induce brain damage like that brought on by the most common type of human stroke--clots that block vessels and subsequently starve brain tissue. The scientists then injected some mice with the bat-saliva compound, called Desmodus rotundus salivary plasminogen activator (DSPA). They injected others with the standard clot-busting drug, tissue plasminogen activator (tPA), which shows the side effect of initiating damage to brain neurons. In the mice, DSPA caused less than 1 percent as much neuron damage as tPA did, the researchers report in the February Stroke.

Animal studies have established that tPA leads to the death of neurons, although scientists are still investigating the specific mechanism of the damage.

The new finding suggests that DSPA doesn't sabotage brain cells, says study coauthor Robert L. Medcalf, a biochemist at Monash University in Victoria, Australia.

In two current studies, scientists are assessing DSPA's effectiveness when given to people up to 9 hours after a stroke. Results could be available by the end of this year, says Mariola Sohngen, a physician and managing director of Paion, the company commercializing the drug in Aachen, Germany.

"This could be potentially very exciting, if DSPA is really better then tPA," says Stuart A. Lipton, a neurologist at the Burnham Institute and the University of California, San Diego. He and others are studying compounds that might mitigate tPA's drawbacks.

For stroke victims, tPA "is a two-edged sword," Lipton says. Doctors don't typically give the drug to someone more than 3 hours after a stroke because risks of damage, whether from neurotoxicity or bleeding in the brain, outweigh the benefits. Sohngen notes that in people, it's difficult to identify damage caused specifically by neurotoxicity.

The 3-hour window limits tPA's usefulness because a stroke's immediate symptoms can be subtle, and many people don't get to a hospital within that period. Among people who do, roughly 6 percent of those receiving tPA suffer some brain bleeding, says neurologist John R. Marler of the National Institute of Neurological Disorders and Stroke in Rockville, Md.