Plants as a medical resource
Plants have been utilized as a medical resource for thousands of years, with their use predating recorded history. Early humans discovered various plants that had medicinal properties through a process of trial and error, leading to the identification of substances that could suppress appetite, stimulate the mind, or produce other effects. Many contemporary medicines are derived from plants, yet this connection is often overlooked, as modern pharmaceuticals are typically presented in familiar formats like pills and liquids. Medicinal compounds from plants can be categorized into various therapeutic classes, including antibacterial, anti-inflammatory, and anticancer agents. For example, penicillin, the first plant-derived antibacterial drug, was extracted from the fungus Penicillium, while salicylic acid, a precursor to aspirin, originates from willow leaves. Despite advancements in synthetic drug production, many effective treatments are still derived from natural sources. Looking ahead, ongoing exploration, especially in biodiverse areas like tropical rainforests, may yield new medicinal compounds, although threats to plant biodiversity from development pose significant challenges. Innovative approaches in biotechnology also offer promising avenues for enhancing pharmaceutical production through bioengineering plants.
Subject Terms
Plants as a medical resource
Because plants are so biochemically diverse, they produce thousands of natural products commonly referred to as secondary metabolites, and many of these secondary metabolites have medicinal properties that have proven to be beneficial to humankind.
Background
The use of plants for medicinal purposes predates the recorded history of humankind. Primitive people’s use of trial and error in the constant search for edible plants inevitably led them to the discovery of plants that contained substances that caused appetite suppression, stimulation, hallucination, or other side effects. Written records show that drugs such as opium have been in use for more than five thousand years. From antiquity until fairly recent times, most practicing physicians were also botanists or at least herbalists. In contemporary society, medicinal plants are perhaps one of the most overlooked natural resources. Because modern commercial medicines are obtained in neat packages in the form of pills, capsules, or bottled liquids, most people do not realize that many of these drugs were first extracted from plants. In some cases, chemists have learned how to duplicate synthetically the natural product that was initially identified in a plant, but in many cases, a plant may still be the only economically feasible source of the drug.
Plant-Derived Medicines
There are numerous ways to categorize medicinal compounds from plants. For this discussion, medicinal drugs will be categorized as antibacterial substances, anti-inflammatory agents, drugs affecting the reproductive system, drugs affecting the heart and circulation, drugs affecting the central nervous system, antiasthma drugs, drugs affecting the gastrointestinal tract, antiparasitic agents, and anticancer agents.
The first effective antibacterial substance was carbolic acid, but the first truly plant-derived antibacterial drug was penicillin, which was extracted from an extremely primitive plant, the fungus Penicillium, in 1928. The work with penicillin led to the discovery of other fungal and bacterial compounds that have antibacterial activity. The most notable of these are cephalosporin and griseofulvin.
Inflammation can be caused by mechanical or chemical damage, radiation, or foreign organisms. For centuries poultices of leaves from coriander (Coriandrum sativum), thornapple (Datura stramonium), wintergreen (Gaultheria procumbens), witchhazel (Hamamelis virginiana), and willow (Salix niger) were used to treat localized inflammation. In the seventeenth and eighteenth centuries, cinchona bark was used as a source of quinine, which could be taken internally. In 1876, salicylic acid was obtained from the salicin produced by the willow leaves. Today, salicylic acid, also known as aspirin, and derivatives such as ibuprofen, are the most widely used anti-inflammatory drugs in the world.
The most effective home remedy for preventing pregnancy was a tea made from the leaves of the Mexican plant zoapatle (Montana tomentosa). The drug zoapatanol and its derivatives were extracted from this plant to produce the first effective birth control substance—which has not been used in human trials, however, because of potential harmful side effects. Other plant compounds that affect the reproductive system include diosgenin, extracted from Dioscorea species and used as a precursor for the progesterone used in birth control pills; gossypol from cotton (Gossypiumspecies.), which has been shown to be an effective birth control agent for males; ergometrine, extracted from the ergot fungus (Clavicepsspecies.) and used to control postpartum bleeding; and yohimbine from the African tree (Corynanthe yohimbe), which apparently has some effect as an aphrodisiac.
Through the ages, dogbane (Apocynum cannabinum) and milkweeds (Asclepias spp) have been prized for their effects on the circulatory system because of the presence of a group of compounds called cardiac glycosides, but foxglove (Digitalis species) has produced the most useful cardiac glycosides, digitalis and digoxin. Opiate alkaloids such as opium extracted from the poppy (Papaver sonniferum) and its derivatives such as morphine, as well as cocaine from Erythroxylum coca and Erythroxylum truxillense, have long been known for their analgesic (pain-relieving) properties through their effects on the central nervous system. Both these drugs can also produce harmful side effects, however, and both have addictive properties.
The major antiasthma drugs come from ephedrine, extracted from the ma huang plant (Ephedra sinaica), and its structural derivatives. Plant-derived drugs that affect the gastrointestinal tract include castor oil, senna, and aloes as laxatives, opiate alkaloids as antidiarrheals, and ipecac from Cephaelis acuminata as an emetic. The most useful plant-derived antiparasitic agent is quinine, derived from the bark of the chinchona plant (Chinchona succirubra). Quinine has been used to control malaria, a disease that has plagued humankind for centuries. The primary plant-derived anticancer agents are vincristine and vinblastine, extracted from Catheranthus roseus, maytansinoids from Maytentus serrata, ellipticine and related compounds from Ochrosia elliptica, and taxol from the yew tree (Taxus baccata).
The Future
Many as-yet-unknown plant-derived medicinal drugs await discovery, particularly in the tropical rainforests. The threats to many plant species, and in general, from development and industrialization may compromise the ability of humankind to take advantage of the unique compounds offered by these plants.
Modern has provided the methods by which plants can be bioengineered to produce new and novel pharmaceuticals. Progress toward the production of specific proteins in transgenic plants provides opportunities to produce large quantities of complex pharmaceuticals and other valuable products in traditional farm environments rather than in laboratories. These novel strategies promise a broad array of natural or nature-based products, ranging from foodstuffs with enhanced nutritive value to the production of biopharmaceuticals.
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