David S. Seigler Department of Plant BiologyUniversity of IllinoisUrbana, Illinois 61801 USAseigler@life.illinois.eduhttp://www.life.illinois.edu/seigler
Outline: Medicinal Plants Importance o “Primitive” cultures + Link to religion + Link to psychoactive drugs Economics Botanical o Many families
Chemical o Terpenes + Cardiac glycosides + Steroids + Metabolically altered triterpenes o Alkaloids + Analgesic drugs + Antitumor drugs + Emetics
o Anthraquinone glycosides + Laxatives o Polyketides + Aspirin o Mode of action Herbal medicines
Reading • CHAPTER 11, pp. 262 ff.
Introduction • The use of medicinal plants is found in almost all cultures. In some, many types of plants are used. Some are efficacious and others are not. • The science of botany originated in the study of medicinal plants. Chemistry, botany, and medicine were all considered one field until the 1700's.
Herbal medicines in Madagascar Courtesy Dr. Voara Randrianasolo
Many plant and fungal derivatives are important medicinally. • The most important of the plant-derived compounds are terpenoids (such as steroids) and alkaloids. • Substances such as anthraquinone glycosides as well as a variety of other types of glycosides are also widely used.
These include the active principles of Salix (Salicaceae), Artemisia cina (Asteraceae or Compositae) (santonin used as an anthelmintic drug), quassia (used to control lice etc.). • Table of some important medicinal plants on page 263.
Presumably curative agents were discovered by trial and error. • Sumerian drawings of opium from 2500 B.C. suggest that they were knowledgeable about medicinal plants. • In 1770 B.C., from the Code of Hammurabi, a series of plants such as henbane (Hyoscyamus niger, Solanaceae), licorice (Glycyrrhiza sp., Fabaceae), and mints (Mentha spp., Lamiaceae) were mentioned.
The ancient Egyptians recorded much of their knowledge of plant drugs as well. Many of the plants used by them are still used in medicine.
The Greeks • The Greeks made other significant contributions to medicine. • The number of effective medicinal plants came to be about 300-400 species. • Hippocrates (460-377 B.C.), Aristotle (384-322 B.C.) and Theophrastus (372-287 B.C.) essentially started the science of botany.
Dioscorides • The most significant contribution however, was Dioscorides (ca. 40-90 A.D.) He wrote a 5 volume work, De materia medica, that became the standard work for 1500 years. • Because of later historical developments and the fact that Europe went into intellectual decline, the book was blindly followed and accepted without question until the fifteenth century.
Doctrine of Signatures • Finally, a contemporary of da Vinci, Paracelsus (1393-1451), broke publicly with the works of the Greeks and advocated the "Doctrine of Signatures". This was soon displaced by more objective methods.
In the 19th century, such compounds as quinine, strychnine, morphine, and ephedrine were isolated and studied. • Later (mostly in the twentieth century) many of the compounds were synthesized and some became available from that source.
Most of the drugs used in western culture come from Europe and Asia, although a number of extremely important ones come from other sources.
Types of active compounds • The most important types of compounds are terpenoids and alkaloids. Others such as fatty acids (e.g., chaulmoogra oil) are also used, however. • The chemical structures of several important drug materials are given in this chapter.
Malaria and quinine • Historically, malaria has been one of the worst of all human diseases. • In some countries malaria is common and millions of people suffer from the disease throughout the world. • Malaria is caused by a sporozoan of the genus Plasmodium and is passed from one human to another by mosquitoes.
In the 17th century, Jesuits in South America discovered that a native remedy for other diseases made from an infusion of the bark of cinchona (Cinchona spp., Rubiaceae) coincidentally controlled malaria.
Peru in the early 1940s Courtesy Dr. Walter Hodge
Quinine, Cinchona officinalis, RubiaceaeCalisaya type Courtesy Dr. Walter Hodge
Harvesting cinchona bark Courtesy Dr. Walter Hodge
Drying and storing cinchona bark Courtesy Dr. Walter Hodge
Types of Cinchona bark Courtesy Dr. Walter Hodge
The Dutch acquired seeds from a high-yielding plant near Lake Titicaca, Bolivia. After several years of trying to grow the plants and improve them, they were able to begin to cultivate high quality lines in the Dutch East Indies and eventually they got a monopoly on the production of quinine. • At the time of W.W. II, the allies were cut off from a supply of quinine. • During the war, a number of synthetic substitutes for quinine were developed. Many are still important, but resistance to most is a major problem.
Quinine is also used in small amounts to make tonic water and other soft drinks such as bitter lemon. • Although there have been extensive searches for new plant-derived antimalarials, few have surfaced. • One, artemisinin from Artemisia annua, has proven effective and is currently being used in southeast Asia.
Ephedra or ma huang, Ephedra spp., Ephedraceae • Infusions of Ephedra spp. (Ephedraceae, a gymnosperm) have been used for thousands of years in China. There it is often called "ma huang". • In the 1920's the plant was "discovered" by western medicine and the active compounds isolated.
Ephedrine and a series of related compounds are used today as decongestants (e.g., in Sudafed, Robitussin etc.) and to treat low blood pressure. • Most of the active compounds are made synthetically, however.
Willows and aspirin • Even in the time of Dioscorides it was known that extracts of willow bark (Salix spp., Salicaceae) and leaves alleviated pain. • The compound that is responsible is called "salicin". Salicin is too irritating to take internally, however. • In the late 1800's, a German chemist made another compound that could be taken readily and that had similar properties to salicin.
This compound, acetylsalicylic acid, could be taken orally and was an effective analgesic, anti-inflamatory, and antipyretic drug and is probably the most widely used drug in the world today. • Interestingly, we only learned how aspirin actually functions in the last 30 years. Aspirin inhibits the synthesis of certain prostaglandins.
Coca and cocaine • The Indians of Andean South America have long used coca leaves (from Erythroxylum coca, Erythroxylaceae) as a stimulant. The Indians chewed the leaves mixed with lime to free the alkaloids. The alkaloids reduced feelings of hunger and pain. • Later when the alkaloids were isolated, it was discovered that they had local anesthetic properties. Cocaine has been used for surgery (especially dental surgery).
Steroids from plants • Many types of animal hormones are steroids. Although the steroids from plants are similar, most do not have pronounced hormonal activity in animals and ordinarily must be chemically modified before use. • The most commonly used plant source of steroids is Dioscorea spp. (Dioscoreaceae). These are viny plants with large tuberous roots. • Diagram p. 277.
These steroids occur as complex glycosides (that is, they have sugars attached) that give them soap-like properties and are sometimes called saponins. These compounds are relatively common in plants. • Dioscorea species are used because they have relatively large amounts of saponins and the structure of the aglycone is particularly appropriate for conversion to the desired steroids.
Steroids from these plants are converted chemically into hormonally active substances that simulate pregnancy and serve as antifertility or contraceptive compounds or as anti-inflamatory drugs such as cortisone etc. that are used to treat a number of diseases such as arthritis etc.
Cardiac glycosides • The use of plants to treat heart disease goes back thousands of years and is found in several cultures. One of the plants found in the folk medicine of Europe is Digitalis purpurea (Scrophulariaceae).
In 1775, William Withering, a British physician documented that patients treated with foxglove improved. He standardized the dosage of the drug. • Diagram p. 277. • Digitalis became accepted and today is widely used in treatment of dropsy, a condition associated with congestive heart failure. • The active compounds are saponins, but have an aglycone with a special type of structure.
Opium poppy, Papaver somniferum (Papaveraceae) • The alkaloids found in opium poppy, Papaver somniferum (Papaveraceae), have long been used to alleviate pain. See diagram of the plant on page 279. • Capsules have been found in prehistoric deposits from the Mediterranean and from the Near East. Pictorial representations are found in Egyptian, Greek, Roman and other art. • Opium was used to treat dysentery from at least the first century B.C. The wild ancestor of the plant is no longer known with certainty.
Poppy flower and capsule Carolina Biological Supply Co.
Opium is isolated by lightly slashing the immature fruit capsules. The latex oozes out and hardens after a day or so. The latex is about 11% morphine and 1% codeine. The exudate is scraped off and made into bricks of pure opium. The yields are 25-40 lbs. per acre. • Morphine is one of the principal alkaloids of opium. These alkaloids are very addictive, but are potent pain killers (analgesics). • Codeine, another morphine alkaloid, is a potent antitussive agent, that is, it inhibits coughing.
Incised poppy capsule and latex Carolina Biological Supply Co.
Morphine is acetylated to produce heroin. • Poppies are also cultivated for the seeds which are eaten and are used as an oilseed crop in some countries. • Opium played a role in the history of China and (especially) British colonialism in the last two or three centuries.