Traditional medicinal plants have been valued over the years for providing insight into an array of diseases. However isolating specific efficacious molecules from the milieu of compounds that constitute most plant species can be a daunting task. Now, researchers at the University of Toyama, Japan have developed a method to isolate and identify active compounds in plant medicines.
New data—published recently in Frontiers in Pharmacology in an article entitled, “A Systematic Strategy for Discovering a Therapeutic Drug for Alzheimer’s Disease and Its Target Molecule“, demonstrate that a new technique identifies several active compounds from Drynaria rhizome, a traditional plant medicine, that improve memory and reduce disease characteristics in a mouse model of Alzheimer's disease.
Typically, scientists will repeatedly screen crude plant medicines in lab experiments to see if any compounds show an effect on cells grown in vitro. If a compound shows a positive effect in cells or test tubes, it could potentially be used as a drug, and the scientists go on to test it in animals. However, this process is laborious and doesn't account for changes that can happen to drugs when they enter the body—enzymes in the blood and liver can metabolize drugs into various forms called metabolites. Additionally, some areas of the body, such as the brain, are difficult to access for many drugs, and only certain drugs or their metabolites will enter these tissues.
“The candidate compounds identified in traditional benchtop drug screens of plant medicines are not always true active compounds because these assays ignore biometabolism and tissue distribution,” explained senior study investigator Chihiro Tohda, Ph.D., associate professor of neuropharmacology at the University of Toyama. “So, we aimed to develop more efficient methods to identify authentic active compounds that take these factors into account.”
In the study, the Toyama team used mice with a genetic mutation as a model for Alzheimer's disease. This mutation gives the mice some characteristics of Alzheimer's disease, including reduced memory and a buildup of specific proteins in the brain, called amyloid and tau proteins.
“We report a systematic strategy for evaluating the bioactive candidates in natural medicines used for Alzheimer’s disease (AD),” the authors wrote. “We found that Drynaria rhizome could enhance memory function and ameliorate AD pathologies in 5XFAD mice. Biochemical analysis led to the identification of the bioeffective metabolites that are transferred to the brain, namely, naringenin and its glucuronides. To explore the mechanism of action, we combined the drug affinity responsive target stability with immunoprecipitation-liquid chromatography/mass spectrometry analysis, identifying the collapsin response mediator protein 2 (CRMP2) protein as a target of naringenin.”
The scientists found that the plant extract reduced memory impairments and levels of amyloid and tau proteins in mouse brains. Moreover, the team then examined the mouse brain tissue five hours after they treated the mice with the extract. They found that three compounds from the plant had made it into the brain—naringenin and two naringenin metabolites.
When the investigators treated the mice with pure naringenin, they noticed the same improvements in memory deficits and reductions in amyloid and tau proteins, implying that naringenin and its metabolites were likely the active compounds within the plant. They found a protein called CRMP2 that naringenin binds to in neurons, which causes them to grow, suggesting that this could be the mechanism by which naringenin can improve Alzheimer's disease symptoms.
The researchers are optimistic that the new technique can be used to identify other treatments. “We are applying this method to discover new drugs for other diseases such as spinal cord injury, depression, and sarcopenia,” Dr. Tohda noted.
The authors concluded that their findings indicate “that biochemical analysis coupled with pharmacological methods can be used in the search for new targets for AD intervention.”