The average person wouldn't want to be bitten by a vampire bat. But the animal's saliva may one day give some stroke sufferers a better chance of survival. According to a report published online today by Stroke: Journal of the American Heart Association, vampire bat saliva contains a potent clot-busting substance that could help a greater number of patients than current medications do.

Scientists identified the medicinally promising bat compound, an enzyme known as desmoteplase or DSPA, more than a decade ago. The substance's true function--to thin a vampire victim's blood so that it flows freely, allowing the bat to feed--also makes it a candidate for treating strokes. During an ischemic stroke one or more clots block the supply of blood to the brain. Previous research had shown that DSPA is more active than the currently FDA-approved clog-busting drug rt-PA when exposed to fibrin (an insoluble protein that makes up the framework of blood clots). Because rt-PA can also cause brain damage, it must be administered within three hours of stroke onset and is thus only prescribed to a small percentage of patients. To test DSPA's effect on brain cells, Robert L. Medcalf of Monash University in Australia and his colleagues injected the brains of mice with both DSPA and rt-PA. They found that DSPA attacked fibrin, but did not act upon two brain receptors known to promote brain damage. The scientists therefore suggest that DSPA could be administered up to nine hours after stroke onset without adverse effects.

Although the results are encouraging, the study focused mainly on toxicity, cautions Larry Goldstein of the American Stroke Association Advisory Committee. "Whether this approach will prove either safe or efficacious in improving stroke outcomes requires further testing." According to the American Heart Association, human trials of DSPA are currently underway in Europe, Asia and Australia.