EDMONTON, ALBERTA--Researchers have identified a key cellular pathway by which the herbal medicine ginkgo biloba may protect brain cells. If the results are confirmed in people, ginkgo biloba might one day be used to lessen the effects of stroke.
For centuries, traditional Chinese physicians have used extracts from leaves of the maidenhair tree, Ginkgo biloba, to treat asthma, bronchitis, and brain disorders. Although many of ginkgo biloba's purported benefits remain unproven, doctors in the United States are studying the herb's potential to slow memory loss and ease confusion in patients with Alzheimer's disease. No one knows for sure how the herbal extract affects the brain.
Neuroscientist Sylvain Doré of Johns Hopkins University School of Medicine in Baltimore, Maryland, found one mechanism while studying how to combat the delayed effects of stroke. A stroke quickly decimates a small area of the brain, but surrounding brain tissue continues to die over several weeks. Doré's team had discovered that mice lacking an enzyme called heme oxygenase recovered poorly from stroke. The enzyme converts heme, a cellular compound that produces damaging oxygen radicals, to less harmful compounds, some of which neutralize oxygen radicals. Doré's team suspected that ginkgo biloba might activate heme oxygenase, thereby protecting brain cells.
To test that idea, they first cultured brain cells from embryonic mice, added a standardized ginkgo biloba extract, and tested to see how well the lab-grown neurons survived oxidative stress. The more ginkgo there was, the more enzyme the neurons produced, showing that the herb activated the protective enzyme. Higher doses of ginkgo almost completely protected cultured neurons from oxidative damage, which otherwise killed more than 60% of the cells, the researchers reported here last week at the North American Research Conference on Complementary and Integrative Medicine.
The scientists then gave mice ginkgo or an inert solution for a week, then induced stroke. In normal mice, ginkgo halved the volume of brain tissue injured after a stroke, but it had little effect on mutant mice that lacked heme oxygenase. And the ginkgo-protected mice behaved relatively normally following the stroke, whereas the unprotected mice and mice lacking heme oxygenase staggered and dragged their limbs. Together, the two experiments suggest that ginkgo exerts a protective effect by turning on heme oxygenase.
It's a "beautiful demonstration using the best tools we have to look at the molecular pathway," says molecular neurobiologist Garret Yount of the California Pacific Medical Center in San Francisco. What's more, he says, it opens the door to using ginkgo biloba to treat the aftereffects of stroke.