Each year in the United States, approximately 700,000 people experience the devastating effects of a stroke.  Most of those strokes, about 87% of them, are ischemic strokes, which are caused when an artery to the brain becomes blocked.  The loss of blood flow damages, even destroys, brain cells in the vicinity.  Additional damage occurs once the blockage is cleared and blood flow resumes.

Researchers at Johns Hopkins Medical Institutions have recently announced their success in minimizing some of the damage to brain cells that occurs once blood flow is resumed.  Their study was based on proving the therapeutic effects of daily doses, before the stroke occurred, of an extract from the gingko biloba tree, which seemed to prevent about half the brain damage that was expected.

The research team worked with mice so it is unknown whether the same dramatic effects would be seen in humans but the results suggest further investigation.  One group of mice, referred to as the HO-1 knockout mice, did not carry the gene that produces heme oxygenase-1(HO-1), an enzyme that breaks down an iron molecule, heme, which is a common component of blood.  Previous studies have indicated that HO-1 is a protective antioxidant agent that reduces inflammation.  A second group of mice was genetically normal.

Half the mice in each group were given a specific laboratory-grade extract of gingko biloba, EGb 761,  for each of seven days before researchers induced a stroke in them all by blocking the blood flow to one side of their brains.  Neurological function was measured one hour after the induced stroke and again two and 22 hours afterward.  Tests involved running in patterns and reaction to external stimuli.  Function was measured on a four-point scale – no functional deficiency (1), weakness in the affected forelimb (2), inability to bear weight on the side affected by the stroke (3), and no spontaneous motor activity at all (4).

The genetically normal mice that were pretreated with gingko extract experienced 50.9% less neurological impairment than the genetically normal mice that did not get daily gingko supplementation.  The areas of the brain damaged by the induced stroke were an average of 48.2% smaller in the pretreated genetically normal mice than the untreated normal  mice.

The mice in the HO-1 knockout group did not enjoy the same positive effects of the gingko extract as the normal mice did.  Neurobehavioral function proved to be about the same for these mice, whether pretreated with gingko or not.

The research team attributes the success of the gingko extract to its antioxidant properties, which, in this case, seemed to eliminate the oxygen-free radicals that accumulate at the stroke site when the flow of blood is restored.  Oxygen-free radicals, produced when a cell dies, are toxic and can trigger the death of surrounding cells.  The gingko extract is thought to be the catalyst for a series of molecular activities that neutralize oxygen-free radicals before damage can be done.

Today’s conventional treatment for ischemic stroke is to administer tissue plasminogen activator (tPA) to clear the arterial blockage causing the stroke or to remove it by some other means.  While this treatment removes the blockage and gets the blood flowing again, it does not address the damage caused when blood flow is restored.

Prescriptions for gingko biloba are frequent in Europe and Asia, where the extract is taken for memory impairment.  Sylvain Doré, PhD, and associate professor in the Johns Hopkins’ Department of Anesthesiology and Critical Care Medicine, suggests a daily dose of ginkgo may prove to be an effective preventive measure when taken by people at high risk of having a stroke.  While further work is needed to reach that goal, Doré, who was lead researcher for the study, says this study offers a possible understanding of how neurons are protected by gingko.  Full details of the study are in the current issue of the medical journal, Stroke.

Gingko biloba trees, native to China, are grown ornamentally in shaded areas in temperate regions around the world.  The US and France cultivate the trees for commercial purposes.

Source: Johns Hopkins Medical Institutions