Search for New Medicines Leads to Plants of the Apes
In his UC Irvine laboratory, biochemist Eloy Rodriguez is analyzing plants, searching for new medications that might be effective against bacteria, viruses and perhaps even the AIDS virus.
Rodriguez is one of perhaps several hundred researchers around the world following a similar quest for new antibiotics and other medications from plants, but his research is unique in one aspect: The plants he is studying were selected by chimpanzees in Africa.
The plants were discovered by Harvard anthropologists who followed sick chimpanzees around in the bush and observed the plants they ate in an effort to heal themselves. Rodriguez and Harvard anthropologist Richard Wrangham believe that this is the first time animals have led researchers to potential new drugs.
So far, the researchers have identified 11 different plant species that make up what they call the “Pharmacopeia of the Apes.”
Rodriguez has not yet found anything that might have pharmaceutical companies “jumping overboard to get it on the market,” with the possible exception of a potential anti-AIDS drug. But he believes that many of the compounds and the plants themselves could prove useful for treating both humans and animals in Third World countries where parasitic and bacterial infections are endemic.
“But what really fascinates me is that this provides a lot of information about our early human diet,” Rodriguez said. “It’s a window into the past, our use of medicine from the natural world.”
The identification of the new compounds began in 1971 when Wrangham, crouched in an African rain forest at dawn, watched a chimpanzee do something that struck him as unusual. The chimp carefully selected leaves from a bush, rolled them around in its mouth, then swallowed them.
“The leaves did not seem to provide food because the chimp didn’t chew them,” said Wrangham, who was working with noted behaviorist Jane Goodall at the time. “At first I thought that the leaves were a stimulant. Then I began to observe this behavior in apes who vomited and had diarrhea. The idea finally hit me that the chimps were taking medicine.”
Dawn after dawn, Wrangham watched apparently ill chimps approach the bushes, a member of the daisy family called aspilia. They chose leaves with meticulous care, swallowed them whole, then made curious facial expressions like a child who had just taken castor oil.
Wrangham was concentrating on other aspects of the chimps’ behavior, but he eventually became so intrigued with their medicinal use of plants that, in 1985, he contacted Rodriguez, an expert in isolating unusual chemicals from plants, and asked him to see what was in the leaves. Rodriguez found a brilliant red compound that he called thiarubrin.
Researchers had previously found the chemical in roots, “but we were surprised to find it in leaves. And it is not in all the leaves, just young ones.”
Rodriguez began testing the compound and found that “it is very effective against plant and animal nematodes (parasitic worms, like hookworms). It works very nicely against fungi, like Candida albicans, which is difficult to kill.”
Rodriguez also found that thiarubrin kills retroviruses, such as the human immunodeficiency virus (HIV) that causes AIDS, but is not toxic to human cells in the laboratory.
Based on those preliminary results, researchers at the University of British Columbia are now laboratory-testing thiarubrin against HIV, and results are expected shortly.
Wrangham has since found other medicinal plants used by chimps and apes in Uganda and Tanzania.
In one case, Wrangham and his students followed a small group of apes who were very sick. “They were lethargic and had diarrhea--they obviously just felt rotten,” Rodriguez said, probably as a result of a parasite infection. “Apes are just loaded with parasites.”
The anthropologists followed the apes for three or four days and found that they were eating the stalks and leaves of a plant called vernonia. “After three days, they were feeling a lot better and their stool samples were better,” Rodriguez said. The researchers concluded that the animals were treating themselves with the plant.
Rodriguez has since isolated a chemical from vernonia that shows promise for treating intestinal parasites. From other plants, he has isolated a variety of other chemicals that may prove to be good antibiotics.
Rodriguez is not yet convinced that any of the chemicals he has found will benefit Western medicine. But, he said, “In my opinion, the more useful applications would be right there in the countries where the plants are. We’re suggesting that people mix some of these plants into the foods they give to their animals. They lose billions of dollars worth of livestock every year to parasites” and the plants could help limit those losses.
Subsequent research has shown that primitive tribes in Africa use many of the same plants that the chimpanzees use, and for much the same purposes. The new research thus suggests that the knowledge about the plants’ medicinal effects could have been passed down in both the human and animal lineages for millions of years.
