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Snake venom drug may stop blood clots

Snake venom drug may stop blood clotsVenom is extracted from a Southeast Asian viper in this undated handout photo. It's one of the world's most poisonous snakes, and researchers hope the venom of a viper dubbed the hundred-pacer can provide a drug to prevent one of the world's leading killers. THE CANADIAN PRESS/HO - St. Michael's Hospital

TORONTO - It's one of the world's most poisonous snakes, and researchers hope the venom of the viper dubbed the "hundred pacer" can provide a medication to help prevent one of the world's leading killers.

A team of researchers has purified a protein from the snake's venom to develop an experimental drug aimed at preventing blood clots that can cause a heart attack or stroke.

The venom from the Southeast Asia pit viper is so potent that it is referred to by local residents as a hundred pacer — based on the belief that someone who is bitten will be able to walk no more than 100 steps before dying.

Scientifically known as Deinagkistrodon acutus, the 1.5-metre patterned snake is also called the sharp-nosed viper or Chinese moccasin and is indigenous to China, Taiwan and Vietnam.

Using venom milked from the snake, researchers filtered out all but one protein to create a drug called Anfibatide, which in human testing prevented blood clots from forming but didn't prolong bleeding as is the case with some clot-busting drugs.

"The concept that we can harness something potentially poisonous in nature and turn it into a beneficial therapy is very exciting," said Dr. Heyu Ni, a scientist at St. Michael's Hospital in Toronto involved in the drug's development.

Anfibatide is designed to target a specific receptor on the surface of platelets in the blood that is instrumental in the formation of clots.

When a blood vessel's wall is injured — typically as a result of plaque build-up — platelets clump together to stop the bleeding. However, platelets sometimes come together even after the bleeding has stopped, forming clots in blood vessels and preventing blood flow. In the coronary artery, these blockages cause heart attacks; when the clots form in the brain, they lead to strokes.

The drug works by attaching to platelets near the injured wall and controlling their response. Fewer platelets are drawn to the injury but a plug to stop bleeding is still formed.

In Ni's state-of-the-art lab in Toronto, blood from healthy volunteers was mixed with the snake venom to evaluate under a microscope how it affected the blood's properties.

"We saw that this snake venom is able to inhibit platelets from bonding one to another and to the vessel wall," Ni said in an interview.

"What's most promising is that this reaction works best when the blood is flowing very fast — exactly the conditions when there is a major blockage," said Ni, who is also a scientist with Canadian Blood Services.

The drug was tested in 94 healthy volunteers in China and was found to prevent platelets from clotting, while not prolonging bleeding. The compound appears to be safe — there were no obvious side-effects, although two volunteers withdrew from the trial because of an allergic reaction to the drug during an initial skin test.

Ni said Anfibatide is intended to act on "platelet aggregation," which can lead to a clot large enough to fully block an artery and cause a heart attack or stroke. Such clots can also form in the leg, stoppering up blood flow that can cause a potentially fatal condition known as deep-vein thrombosis.

"What we're going to target is the early stage. If a patient has chest pain, it could stop the disease becoming worse," he said, referring to the symptom that can herald an impending heart attack.

The experimental drug is now being tested in China on patients undergoing balloon angioplasty to open up narrowed coronary arteries. This phase of testing will determine how effective the compound is and the optimum dose needed.

If it's found to be effective, Anfibatide would then need to be tested in a randomized controlled trial of patients before being submitted for government approval to market the drug.

Results from the initial safety trial will be presented Monday at the American Society of Hematology annual meeting in New Orleans.

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