WASHINGTON Extract from the leaves of the ginkgo tree offers promise to minimize brain damage caused by a stroke, scientists said on Thursday.
Mice given daily doses of ginkgo biloba extract before having a stroke induced in the laboratory suffered only about half the damage as animals not given it, researchers at Johns Hopkins University in Baltimore wrote in the journal Stroke.
Mice who did not get ginkgo before a stroke but were given it five minutes after a stroke sustained nearly 60 percent less damage in the day after the stroke than those not given ginkgo. And mice given ginkgo 4-1/2 hours after a stroke had about a third less damage than those not given ginkgo.
The researchers said ginkgo may offer the same benefits in people -- which would be particularly important because not much can be done to protect the brain after a stroke.
"We tested the concept of preventive medicine by giving ginkgo before stroke and we showed protection," said Sylvain Dore of Johns Hopkins, who led the study.
"And the other thing we showed is the potential therapeutic application of ginkgo. So it was given after the stroke and we also showed protection," Dore said in a telephone interview.
Some stroke patients can benefit from a clot-busting drug called tissue plasminogen activator or tPA. But it can be given to patients only within about three hours of a stroke and only when doctors feel it would not worsen bleeding in the brain.
And tPA does not protect against the brain cell damage that occurs once blood flow is restored.
Dore said ginkgo raises levels of heme oxygenase-1, or HO-1, which is an enzyme that acts as an antioxidant to protect against cell damage from "free radicals" -- toxic oxygen molecules released by cells when they are under stress.
The researchers said this idea seemed to be confirmed in experiments using genetically engineered mice that did not have the gene that produces the enzyme. When these mice were given ginkgo, they did not get any protection because its benefits come from boosting an enzyme the mice were unable to make.
So ginkgo does not act directly as an antioxidant, but raises the levels of an enzyme that does, they found.
Ginkgo has been used as a medicine for centuries and remains a very popular herbal medicine. Some findings suggest it can improve cognitive function and decrease development of Alzheimer's disease symptoms. It is generally considered safe.
Ginkgo is one of the top five highest-selling medicinal herbs in the United States, according to Katia Fowler of the American Herbal Products Association.
The ginkgo is one of the oldest types of tree living on Earth, dating back at least 270 million years.
Dore said if further work confirms the benefits, doctors could recommend that people at high risk of a stroke take daily doses of ginkgo as a preventive measure against brain damage.
It also potentially could be used to protect people from brain damage during heart bypass surgery, when the brain briefly has a lack of oxygen, Dore said.
(Editing by Julie Steenhuysen and Mohammad Zargham)