Medicines from the forest
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CTA. 1992. Medicines from the forest. Spore 37. CTA, Wageningen, The Netherlands.
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All over the world there is renewed interest in screening plant materials as a potential source of medical drugs. The less developed countries hope to reduce their dependence on expensive imported medicines while the industrialized countries...
All over the world there is renewed interest in screening plant materials as a potential source of medical drugs. The less developed countries hope to reduce their dependence on expensive imported medicines while the industrialized countries recognize the potential for discovering new drugs, particularly for the treatment of cancers and AIDS. Yet the forests, which are the main source of plants for immediate and possible future uses, are being destroyed and new strategies must be developed to safeguard them. Papyrus manuscripts from Ancient Egypt list some 700 plants used in medicine 3500 years ago and in many countries the folklore still abounds in natural remedies. In Ghana, for example, more than 800 woody plants and many other herbaceous species are known for their medical properties. In Asia and the Pacific it is estimated that over 4% of indigenous flora has been utilized in traditional medicine. Latin America and the Caribbean, particularly the Amazon forests, are widely recognized for their contributions to human health in the past (quinine for malaria and curare as a muscle relaxant) and their potential for future discoveries. Too often modern medicines are assumed to be products of laboratory research and synthesis. Yet, some 100 drugs in common use are derived from plants and an analysis of prescriptions for medicines in the United States showed that 38% contained one or more products of plant origin as the therapeutic agent. Not all plant-derived drugs originated in the Tropics but many did so and tropical forests are the richest potential source of new medical agents. Why the forest? Over half of all plant species are natives of tropical forests where they have had to adapt to a crowded, competitive environment and have developed a spectrum of often-complex chemicals to protect themselves against the myriad of insects and plant pathogens that thrive in the warm humid environment. These chemicals are termed secondary metabolites and include alkaloids, phenols and tannins, cyanogenic glucosides and terpenoids. The Madagascar periwinkle (Catharanthus roseus), from which the anti-cancer drug vincristine was developed, contains 90 different alkaloids. Although it came into prominence only recently, it has long been part of folk medicine in Madagascar and Jamaica as a treatment for diabetes. In Ghana, bacterial infections are treated with a preparation made from Cryptolepis sanguinolenta (a scrambling vine), while in Colombia a resinous exudate of the genus Virola is used to treat fungal skin infections. Animals may also be a source of medicines: insects, frogs and toads, spiders and snakes produce venoms which may be curative or toxic depending on the dose and form in which preparations are administered. Strategy for the future It is estimated that half of the tropical forests have been cleared already. Destruction continues at 25 to 30 million hectares per year and the majority of plant species are vanishing before they have been recorded or investigated. The fund of knowledge carried by the forest dwellers who are displaced is also being lost. The best hope for saving the remaining forests, the potential medicines that they contain and the peoples who know most about them may be in developing what has been termed 'chemical prospecting'. This permits commercial organizations to collect and identify plant materials with potential for medical uses in exchange for proper remuneration to the host country. A similar strategy is to develop 'extractive reserves' for sustainable development of forests where forest dwellers would collect rubber, nuts, coca, palm products and medicinal plants for sale. Brazil already has some such reserves and the World Wide Fund for Nature (WWF) supports a project in the Korup forest of Cameroon in collaboration with the Cameroons Centre for the Study of Medicinal Plants. In eleven villages local people helped researchers investigate the plants of the surrounding forest, leading to a collection of hundreds of herbal remedies. The US National Cancer Institute (NCI) is interested in testing plants for anti-cancer and AIDS treatments. On behalf of NCI the New York Botanical Gardens has set up a plant collecting cooperative in Belize, while the environmental group Conservation International plans to work with traditional healers in Ecuador, Guyana and Surinam. A UK company, Biotic, acts as a broker to find potential buyers for medicinal plants on behalf of tropical countries and has supplied major pharmaceutical companies with plant material from Africa and Asia. To-date the main focus of such activities appears to be in Central and South America and parts of Asia where, for example, up to 1000 tonnes of roots of the shrub Rauwolfia serpentina are exported annually for the production of the drug reserpine for the treatment of hypertension. But the potential of the African forests must not be underestimated. Policy changes to encourage commercial development on a sustainable basis would have far-reaching benefits for the environment, national incomes, and human health worldwide.
- CTA Spore (English)