Newswise — Scientists have known for more than 10 years that a certain extract from leaves of the ancient eastern tree, Ginkgo biloba, can somewhat ease symptoms of memory loss in Alzheimer's disease patients.
Now, researchers at the University of Maryland School of Pharmacy are learning how the popular extract actually works in Alzheimer's patients.
Understanding the biochemical workings of the ginkgo extract could help doctors expand treatment options for other medical conditions. A synergy, or the combination of separate actions by the Ginkgo extract, common in herbal remedies, may be the key to its effectiveness, says Yuan Luo, PhD, associate professor at the School of Pharmacy.
In ongoing studies, a research team led by Luo found that giving mice with the human Alzheimer's gene the ginkgo extract called Egb 761 improved the process of making new nerve cells in part of the brain much affected by the disease. The team found evidence that the protective effect of the extract also could be due to decreasing senile plaques or the clumping of beta-amyloid in the brain tissues. Amyloid is part of a protein and a central factor in the progression of Alzheimer's disease.
Currently Alzheimer's disease is causing progressive dementia and sometimes death in about four million Americans, mostly people older than 70. In the U.S., the incidence of Alzheimer's disease has steadily increased as the average life span has lengthened. Currently, there are no drugs with disease-modifying or preventive properties. However, the School of Pharmacy study and others are now suggesting that many of the symptoms can be avoided or significantly reduced.
The disease starts with loss of nerve connections and broken circuitry of nerve signals in synapses. Modern neuropathology studies beginning in the 1960's revealed that adults create new nerve cells continually in learning regions of the brain. One of the regions of neurogenesis is in the hippocampus, important to memory and cognition. Luo's study demonstrated the dual effect of Ginkgo extract in the hippocampus—enhanced making of nerve cells and decreased clumping in brain tissue.
"By finding out how it works, it might help drug discovery researchers and doctors learn how other herbal and conventional drugs work on in multiple ways," said Luo. When herbal medicines are effective, she said, it's often because of a synergy of different biological effects. "Alzheimer's disease is caused by multiple factors, not just one thing that has gone wrong." Therefore, drugs that target multiple sites would be most efficacious, she added.
Results from the School of Pharmacy experiments, slated to continue for at least another year, provide a rationale for future medicinal chemistry and for identifying other potentially efficacious compounds with desirable activity as potential therapeutic agents to prevent and/or treat Alzheimer's disease, according to Luo.
Meanwhile, to confirm or refute the theory that medicine made from Ginkgo biloba can prevent or delay changes in memory, thinking, and personality as people get older, researchers are currently analyzing data from a five-year clinical trial, The Ginkgo Evaluation of Memory, sponsored by the National Institutes of Health. About 3,000 people at four clinics, including one in Hagerstown, Md., participated.
Luo's research team is focused on aging, age-related neurodegenerative diseases, and neuroprotective mechanisms. While disease prevention theories associated with herbal medicine have the potential to both increase quality of life and reduce health care costs, ways that extracts of herbs work in the body are still poorly understood, she says.
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