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Neuroscience

Traditional African remedy provides support for alternative epilepsy treatment target

Rodent and zebrafish tests with plant-derived compounds suggest blocking a kinase enzyme could control seizures

by Carmen Drahl, special to C&EN
November 16, 2018

 

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Credit: Mark Hyde, Bart Wursten and Petra Ballings
Researchers isolated a seizure-preventing compound, indirubin, from the Indigofera arrecta plant.

For people with epilepsy, managing seizures—unpredictable electrical surges in the brain that can shut down consciousness and muscle control—is critical for protecting themselves and others. Yet up to one-third of people with epilepsy—15 to 20 million worldwide—don’t respond to medications. Now, by examining a traditional Congolese remedy for epilepsy, researchers have found support for a novel protein target for seizure-controlling medication (ACS Chem. Neurosci. 2018, DOI: 10.1021/acschemneuro.8b00281). If verified through clinical testing, it could lead to a more diversified toolkit for doctors and patients alike.

“This research shows the potential of ethnomedicinal and traditional knowledge, which is often disregarded or even resisted by mainstream science,” says study coauthor Joëlle N. Chabwine of the Salama Neuroscience Center, in the Democratic Republic of the Congo.

Established anti-epileptic drugs act on proteins involved in neurotransmission, such as ion channels, explains Najat Aourz of Vrije Universiteit Brussel, first author of the study. The new work suggests that glycogen synthase kinase-3 (GSK-3), which regulates energy storage in the body, is also a viable epilepsy drug target. Candidates for Alzheimer’s and Parkinson’s disease drugs target GSK-3, and some groups have sought a link to epilepsy, as well. Kinase inhibitors are unusual targets for anti-epileptic drugs; this study represents one of the first examples, Aourz says.

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Chabwine and her colleagues interviewed traditional Congolese healers, who shared their knowledge of a 14-plant cocktail for treating epilepsy. The researchers soon zeroed in on Indigofera arrecta, a member of the plant family that produces indigo dye. The team isolated the plant’s bioactive ingredient, a known compound called indirubin, by identifying ever-more-purified extracts that protected zebrafish larvae against chemically induced seizures. Zebrafish have become powerful screening tools; scientists can track electrical activity in the animals’ brains for epilepsy-like patterns, and their millimeter-sized larvae are small enough to fit in a 96-well plate.

The researchers then confirmed that indirubin prevented chemically and electrically induced seizures in rats and mice. However, indirubin is known to act on several kinases and other proteins in an anticancer context, so the team had to determine which one was driving the anti-seizure activity. To do so, they tested various compounds, each with different selectivities among indirubin’s protein targets, to see which ones could prevent seizures in zebrafish.

From those results, the team realized that blocking GSK-3 was likely responsible for anti-seizure activity. They further supported that conclusion in two ways. First, they demonstrated that inactivating the gene for GSK-3 in zebrafish protects against seizures. Then, they used a highly selective GSK-3 inhibitor, BIO-acetoxime, to lessen seizure severity in mice electrically induced to have recurrent seizures, a model closer to human epilepsy than the one-off seizures induced in earlier tests.

“Since this study did not explicitly determine the exact mechanism by which the enzyme directly attenuates seizures, it will be interesting to be able to establish its downstream effects,” says Priscilla Kolibea Mante, who has studied anti-seizure activity of extracts from natural sources at Kwame Nkrumah University of Science & Technology, Kumasi, in Ghana.

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Because GSK-3 is involved with many cellular processes, the team is interested in exploring how a hypothetical GSK-3 blocker would fit into the multidrug cocktails that epilepsy patients commonly take. The researchers filed a patent application on indirubin, BIO-acetoxime, and related compounds, but did not continue the process, says co-senior author Andrew D. Crawford, formerly of the University of Leuven. Crawford’s startup company, Theracule, is pursuing other families of anti-seizure drug candidates, including botanicals.

 
 

CORRECTION:

On Nov. 16, 2018, this story was updated to correct the structure of indirubin. The original structure had incorrect geometry of a double bond.

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