A clot-busting drug based on the saliva of vampire bats - which is possibly more useful than existing treatments - has shown promising results in treating people who have just suffered a stroke, a small German biotechnology company reports.

Birgit Jansen of the Aachen-based company Paion GmbH told ABC Science Online the company had submitted the results of a Phase II trial to the journal Stroke.

Its developers say the new treatment causes less bleeding and can be given much later after a stroke has occured than previous treatments.

The new drug, Desmoteplase, is a recombinant form of an anti-clotting protein found in the saliva of the bat, Desmodus rotundus, which feeds on cattle, horses and donkeys in tropical areas of South and Central America. Recombinant drugs are proteins produced in vats by bacteria, which have been genetically engineered to produce large quantities.

In the 1990s, Paion's head of research, Professor Wolf-Dieter Schleuning used molecular biology techniques to isolate a protein in the bat's saliva. The protein enables the animal to dissolve blood clots, ensuring a steady flow of blood from its victim. The protein converts the pro-enzyme plasminogen into plasmin which digests fibrin, the "glue" which sticks blood together to form clots.

Paion researchers produced a recombinant form of the protein and, last week, announced positive results from a Phase II trial. According to the company, the trial, involving researchers collaborating in 44 medical centres spread over 12 countries, compared the drug to placebo in 102 patients who had just had a stroke and found it improved blood circulation in the damaged part of their brain.

According to Australian stroke expert, Dr Gabriel Liberatore of Austin Hospital in Melbourne, who collaborates with Paion on animal studies of the drug, Desmoteplase appears to provide significant advantages over existing clot-busters.

Eighty percent of strokes are "ischaemic" in that they are caused by a blood clot which lodges in the brain, depriving it of oxygen, he told ABC Science Online. He said the only drug approved world-wide for treatment of such strokes was Tissue-type Plasminogen Activator (t-PA), a drug based on a human blood protein which is related to Desmoteplase.

Bleeding
Liberatore said the limitation with t-PA is that it causes an unacceptable level of bleeding in the brain in 10 % of patients if administered more than three hours after a person has had a stroke.

"If you give t-PA to a stroke patient beyond three hours it is actually detrimental. It's worse than not giving it at all," said Liberatore.

This is a problem, he said, because by the time someone is admitted to hospital and has an CAT Scan or MRI to determine whether they should be given a clot buster, they may have passed the narrow treatment window. For this reason, t-PA is not used widely used, said Liberatore.

By comparison, reports Paion, trials showed Desmoteplase was effective up to nine hours after a stroke which means more people would be able to be treated. The drug also only brought about bleeding of the brain in less than one-tenth of the more than 100 patients in the trial, the company said.

The next step was to run a larger trial to confirm the findings found in stroke patients.

According to Paion, Desmoteplase could be available to patients in four years' time.

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