Deep in the Gombe National Park in Tanzania two famous primatologists, Richard Wrangham from Harvard University and Toshisada Nishida from Kyoto University, noticed an unusual dietary pattern among the local chimpanzees. The animals would dine on leaves of a plant from the daisy family called Aspilia. Instead of chewing on the leaves, the chimpanzees would put the leaves under their tongues for a stretch of time and then swallow the entire leaves. The chimps would frown while holding the leaves under their tongues for a good reason – Aspilia is known for its bitter taste. This means that the chimps were not eating these leaves because they tasted good but for another unknown reason that intrigued the scientists.
Fascinated by this observation, Drs. Wragham and Nishida sent samples of the Aspilia plant to a chemist, Eloy Rodriquez at the University of California in Irvine. After a thorough biochemical analysis, Dr. Rodriquez identified an abundant phytochemical in those leaves called Thiarubrine A, which acts as a potent antibacterial and antiparasitic agent. The chimpanzees consumed just enough of Thiarubrine A to kill up to 80% of parasites in their intestines.
So, how do the chimpanzees know that putting Aspilia leaves under their tongue releases Thiarubrine A to the circulation, providing protective, antibacterial effects? There is an entire field dedicated to study the behavior of animals self-medicating called zoopharmacognosy. This behavior is not only seen in nonhuman primates but also has been observed in a lot of different species such as ants, cats, dogs, and birds. Zoopharmacognosy is more common than you think – you may be familiar with the most well-known example wherein dogs eat grass to induce vomiting after eating a harmful meal.
The world-renowned primatologist Robert Sapolsky hypothesizes that “Social Learning” explains zoopharmacognosy. The Social Learning Theory simply states that animals (and humans) learn from observation and mimicking the behavior of others. In the case of the chimpanzees from Gombe National Park, perhaps one of the chimps was suffering from an unpleasant stomachache, ate some Aspilia leaves and felt better shortly afterwards. Other chimps in the group noticed that their colleague improved immediately and they started mimicking his behavior. From that point on, sublingual administration of Thiarubrine A by sucking on Aspilia leaves became a common herbal remedy used to alleviate pain of the digestive tract system among chimpanzees. Many examples of animals self-medicating is still perceived as anecdotal reports rather than experimental evidence by scientists. Drs. Rodriquez and Wragham are the pioneers in the field of zoopharmacognosy and are strongly convinced that observing animals self-medicating may provide clues aboutnew drugs to be used by humans.
In the age of supercomputers, computational drug design and high throughput drug screenings, you’d think that we have all the necessary tools to map out structures of drugs that can cure any type of cancer. But, drug discovery is currently facing some serious challenges. There are fewer new drug approvals every year and the cost of drug development has skyrocketed. The entire drug development pipeline from discovery to marketing approval takes 10-15 years and costs roughly 2.3 billion dollars. And, every year this process is getting increasingly expensive.
Searching for new and effective drugs is a fishing expedition with a low rate of success, but a savvy scientist might deduce how effective a certain plant (or one of its active ingredients) can be as an antimicrobial agent just by thoroughly observing animals medicating themselves in their natural settings. Such observational studies could help identify promising drug candidate compounds. Other creative ways pharmaceutical companies and academic researchers could discover new compounds is by investigating Ayurvedic wisdom, traditional Chinese medicine, tribal non-documented use, zoopharmacognosy and extensive literature searches. Researchers at the University of California at Berkeley, for example, have combined data-intensive computational approaches with traditional Chinese medicine to bridge the gap between Eastern and Western pharmacological practice. Applying these integrative approaches could provide us with new drugs and massively expand our medical toolbox.
In an interview on zoopharmacognosy, Dr. Rodriquez said: “Some of the compounds we’ve identified by zoopharmacognosy kill parasitic worms, and some of these chemicals may be useful against tumors. There is no question that the templates for most drugs are in the natural world.” So, who knows? Maybe somewhere in the Congo Jungle there is a chimpanzee that is eating an unknown shrub whose active ingredient has anticancer properties. If we continue to rely heavily on traditional models for drug discovery and development, we may never find out. Therefore, it’s important to keep an open mind about other ways to explore the natural world – and perhaps even a few (mildly selfish) reasons to protect it.
Authors: David Faulkner and Julia Tobacyk
Sapolsky explaining zoopharmacognosy using Social Learning Theory:
Sapolsky R. “Trouble with Testosterone.” Page 177-195.
Interview with Eloy Rodriquez:
Drug discovery from plant sources:
Katiyar C. et al. Drug discovery from plant sources: An integrated approach. AYU. 2012
Thiarubrine A, a bioactive constituent of Aspilia (Asteraceae) consumed by wild chimpanzees:
Drug cost and development (Tufts Center Report):