An ischemic stroke happens when at least one blood clot blocks the supply of blood to the brain. Conventional treatments are only effective when administered up to three hours after the onset of stroke. But a substance taken from the saliva of vampire bats is effective when given up to nine hours after onset, says study author Dr. Robert L. Medcalf, an associate professor at Monash University Department of Medicine at Box Hill Hospital in Victoria, Australia.

The study was done in mice, and it's not known how effective the treatment will be in humans. Moreover, some experts believe the emphasis on a longer time window obscures the necessity of treating stroke victims as quickly as possible.

"Even if this drug is better than the current one, you still need to get people treated very quickly," says Dr. Keith Sillet medical director of New York University's Comprehensive Stroke Care Center. "You have a limited time window to restore blood to the brain and that window doesn't change, no matter what you give."


Conventional clot-busting agents are beneficial, but they affect the entire circulation system, whether a clot exists or not. They pose an increased risk of cerebral hemorrhage (bleeding in the brain) and may cause brain-cell death, the study's author says. Researchers have focused on refining these agents so that they target only the clot and do not injure blood vessels.

Scientists believe they may have a candidate in the new compound extracted from vampire bat saliva. The compound takes advantage of vampire feeding principles and tries to make them work in humans. Vhen vampire bats bite their victims, they release a clot-dissolving substance that keeps the blood flowing long enough to suck a full meal. Without the clot-buster, the victim's blood would clot and dry up, leaving the bat hungry.

In this study, the compound appeared to become active only in the presence of fibrin, the "building blocks" of a clot. In fact, its clotbusting properties increase about 13,000-fold in the presence of fibrin, whereas a conventional agent increases by a factor of 72.

This is important because blood clots and, therefore fibrin, are not actually located in the brain, so the bat-saliva compound has no effect in this vulnerable region.

The next step is a test by some of the same investigators in human stroke patients.

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