Vampire saliva could help treat stroke

Jan. 9, 2003 at 4:33 PM

VICTORIA, Australia, Jan. 9 (UPI) -- The saliva from vampire bats might be effective in improving the treatment for stroke, a new study released Thursday concludes.

The bats -- bloodsuckers by nature but reviled in pop culture -- have saliva that contains a blood clot-busting substance called Desmodus rotundus salivary plasminogen activator, or DSPA or desmoteplase, which can be administered to stroke patients three times longer than current drugs used to treat the condition.

Researchers led by Robert Medcalf, senior research fellow at Monash University Department of Medicine at Box Hill Hospital in Victoria, compared the effects of DSPA to the only drug approved by the Food and Drug Administration for ischemic stroke.

As reported in the January issue of the journal Stroke, they injected either DSPA or the stroke drug -- called recombinant tissue plasmingen activator or rt-PA -- into the brains of mice. The researchers then induced stroke in the animals and tracked the survival of the brain cells.

They found DSPA proved more effective in zeroing in on fibrin, a sort of structural scaffolding for blood clots. When exposed to fibrin, the clot-busting abilities of DSPA jumped 13,000-fold compared to only 72-fold from rt-PA.

Furthermore, the study showed DSPA was effective for several hours after the stroke occurred. The drug rt-PA only works if given during a very short period -- three hours with the onset of stroke symptoms.

Another advantage of DSPA, researchers note, is it focused on the blood clot without causing brain cell damage. In contrast, rt-PA can enhance brain cell death if it is administered too long after a stroke occurs.

Medcalf explained vampire bat saliva carries an anti-clotting substance called fibrinolytic to boost the victim's blood flow so the animal can continue feeding.

"It is ironic, but remember that evolution has given the vampire bat a powerful means to keep blood ... unclotted," Medcalf told United Press International. "Rather than trying to manipulate the structure of a given protein to make the protein more effective/potent, in this case, nature has already done the job for us."

DSPA has proven so promising, Medcalf added, that "human clinical trials testing DSPA in patients with ischemic stroke are currently underway in Europe, Asia, Australia and the USA." Ischemic stroke occurs when a blood clot or several clots block blood to the brain.

Another type of stroke is called hemorrhagic stroke, in which a blood clot bursts. Hemorrhagic stroke was not examined in this study.

Dr. Hal Unwin, a professor of neurology and stroke expert at the University of Texas Southwestern Medical Center in Dallas, said vampire bat saliva could mean the difference between life and death for many stroke victims.

"It may double or triple the number of people who can be treated for acute stroke," Unwin told UPI. "It may be better because it's much more specific to the actual clot, where tPA works everywhere in the body."

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(Reported by Katrina Woznicki, UPI Science News, in Washington)

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