Washington University researchers studying medicinal plants from the Peruvian rainforests have come across results that may significantly influence the direction of the fight against tuberculosis (TB) worldwide.
Walter H. Lewis, Ph.D., professor of biology in Arts & Sciences, and his colleagues examined about 1,250 plant extracts returned from Peru and found that 46 percent showed an inhibition against Mycobacterium tuberculosis, the bacterium that causes TB.
The finding is a first step toward developing potential drugs to combat the disease.
The unexpected results came after months of working with the native Aguaruna people of Peru through the International Cooperative Biodiversity Program-Peru, which seeks to identify new pharmaceutical possibilities from medicinal plants and to promote cultural and economic support to the native Indians. Lewis and his team lived among the tribe, collecting plant samples and learning about specific plants the Indians use in herbal medicinal practices.
After testing and analyzing the collected plants in St. Louis --in collaboration with Scott Franzblau at the federal Hansen Laboratory at Louisiana State University, Baton Rouge --Lewis was intrigued by the results.
"Here's the surprise: We would expect that in targeted medicinal plants --plants being used by indigenous people to treat a specific disease --we would find approximately 50 percent or higher activity. But we would never have anticipated 46 percent activity from a general survey of plants selected as medicinals not used to treat TB," Lewis explained.
Through the technique of bio-directed assaying, Lewis and his fellow researchers identified the amount of reactivity present in each of the samples against various diseases, including diarrhea, leishmania and certain strains of cancer, but the inhibitions against these paled in comparison to the effectiveness of the Peruvian plants against TB.
"The results just surprised us. We didn't realize the difference until the final results came in," Lewis said.
Lewis presented his research at the 14th Annual Meeting of the Society for Economic Botany, held this summer at the University of South Carolina, Columbia. Results of the analyses will be published in the forthcoming issue of Pharmaceutical Biology. The research is supported by the National Institutes of Health and the National Science Foundation.
Tuberculosis remains a serious health problem in the United States and worldwide. The World Health Organization (WHO) reports that TB kills up to 3 million people each year, and 18,199 new cases of the disease were reported in the United States in 1998. Additionally, the WHO estimates that one-third of the world's population is infected with M. tuberculosis.
"TB is one of the most deadly diseases of our time," Lewis said. "It has made a comeback, but 46 percent of our samples with TB inhibition is an incredibly encouraging result so early in the research."
The development of certain drug-resistant strains of tuberculosis combined with the spread of the HIV virus can account for the recent comeback of this deadly disease. For these reasons, tuberculosis possibly represents "the most threatening resurgent disease today among the immunocompromised and immunocompetent, and the need for new drugs is paramount," Lewis stated in the journal article.
Fortunately, the exposure of TB in the remote parts of the Upper Amazon has been minimal, and the native tribes, including the Aguaruna, have little experience with the disease, making the discovery of the inhibitory plant samples even more significant.
Walter Lewis and his wife, Memory Elvin-Lewis, Ph.D., professor of microbiology and ethnobotany in Arts & Sciences, have made numerous trips to the Peruvian rainforests since the early 1980s to learn about the medicinal plants used by the native tribes.
The Aguaruna, a tribe of the Jivaro Indians of the Upper Amazon Basin, still rely largely on memorization and oral transmission of their knowledge of medicinal plants to survive. However, as increasing numbers of younger Aguaruna are exposed to the outside world, many lose interest in learning the practice of herbal medicine. Thus, with fewer numbers of Aguaruna willing to learn all of the medicinal wonders and knowledge of their elders, medicinal plant knowledge could be lost forever. Recording this knowledge and documenting it thus becomes as crucial for the Washington University team as discovering new medicinal plant species.
A prime reason that tropical rainforest plants are so valuable is that they produce above-average amounts of secondary metabolites, such as alkaloids, compounds that protect them from huge numbers of pathogens and insects. Plant survival is dependent on their genetic ability to produce a wide range of these defensive compounds. Lewis believes he found such a high anti-TB reactivity across the broad range of plants because the plants have shared sensitivities that "allow secondary metabolites to inhibit the growth of M. tuberculosis at these unexpectedly high frequencies," he said.
The amount of activity against TB was surprising partly because biologists were not expecting the plants to be so specifically effective against it. "If you can find the diseases of humans that the plants are already fighting to stay alive, then we should be looking for those plants and their compounds to provide new pharmaceuticals to cure diseases and improve human health worldwide," Lewis said.
