MEDICINAL PLANTS


OUTLINE:
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 the1700's.
Many plant and fungal derivatives are important medicinally. The most important of the plant derived compounds are terpenoids (such as steroids) and alkaloids. Others such as anthraquinone glycosides and other types of glycosides are also widely used. Other compounds include those 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 (Glycyrrhizasp., 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 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.
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.

Finally, a contemporary of da Vinci, Paracelsus (1393-1451), broke publicly with the works of the Greeks and devised 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.
Today, in western culture, most of the active ingredients are isolated, purified, and standardized, or ... ironically (in the U.S.) are sold in "Health Food" stores with little assurance that the plant materials are pure, contain the active principles, or are effective.
In Europe, particularly in Germany, companies that market these products are required to establish efficacy and to provide the materials in a form that ensures that the active materials are present in a designated dosage. In many other cultures, the crude plant drugs are still used directly.
Most of the drugs used in western culture come from Europe and Asia, although a number of extremely important ones come from other sources.

Plant drugs in market in Mexico
Plant drugs in market in Madagascar

Types of compounds
The most important types of compounds are terpenoids and alkaloids. Others such as fatty acids (e.g., chaulmoogra oil) are also involved 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 Plasmodiumand is passed from one human to another by mosquitos.
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 ( Cinchonaspp., Rubiaceae) coincidentally controlled malaria.
Because the drug was discovered by Catholics, some Protestants died of malaria rather than take the drug. It was only about the end of the 17th century that the drug became an accepted treatment for malaria.
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 some is a major problem.
Quinine is also used in small amounts to make tonic water and other soft drinks such as bitter lemon etc. Although there have been extensive searches for new plant-derived antimalarials, few have surfaced. One, artemisinin from Artemisia annua, h as proven effective and is currently being used in southeast Asia.

Ephedra
Infusions of Ephedraspp. (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 compounds used are made synthetically, however.

Willows and aspirin
Even in the time of Dioscorides it was known that extracts of willow bark 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 which had similar properties to salicin.
This compound, acetylsalicylic acid, could be taken orally and was an effective analgesic, antiinflamatory, 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 20 years.

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. Although cocaine itself has been used for surgery (especially dental surgery), synthetically similar alkaloids are widely used.

Coca

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 (there are a few exceptions) and must be chemically modified before use. The most commonly used plant source of steroids is Dioscoreaspp. (Dioscoreaceae).
Diagram of plant on page 277. These are viny plants with large tuberous roots.
The steroids occur as complex glycosides (that is they have sugars attached) that give them soap-like properties and are sometimes called saponins. As it turns out, these compounds are relatively common in plants and Dioscorea species are used because they have relatively large amounts and the structure of the aglycone is particularly appropriate to conversion to steroids.
Most of the steroids from these plants are converted into hormonally active substances that simulate pregnancy and serve as antifertility or contraceptive compounds or as antiinflamatory 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 noticed that patients treated with foxglove really did improve and he standardized the dosage of the drug. Diagram of the plant on page 277. The compound became accepted and is today widely used in treatment of dropsy, a condition associated with congestive heart failure.
The compounds in this case are also saponins but have an aglycone with a special type of structure.
Other sources of cardiac glycosides are Strophanthusspp. (Apocynaceae) and squill (Urginea maritima, Liliaceae). The later is also used as a rat poison. The compound from Strophanthus is called ouabaine and is widely used.

Digitalis purpurea

The opium poppy
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.
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 goo is scraped off and made into bricks known as pure opium. The yields are about 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.
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.

Tropane alkaloids
A number of alkaloids from solanaceous plants are used as analgesics. Some of structures on page 280. The most commonly used ones are scopolamine (hyosine), hyoscyamine, and atropine. The most commonly used plants are Atropa belladonna, Hyoscyamus niger, and Duboisia species(these last native to Australia).
Belladonna has been used since the times of the Greeks. It was also used in the middle ages in Europe to enhance the appearance of women by causing them to have large pupils. What matter if they couldn't see where they were going.
Today, these alkaloids are used for antidotes for poisoning, to treat cardiac problems, for antidiarrhetic preparations, and to dilate pupils during eye examinations.

Datura stramonium
Atropa belladonna

Veratrum alkaloids
Members of the Liliaceae, especially Veratrum viride, are often used to treat certain types of heart ailments. The alkaloid have the ability to lower blood pressure.

Veratrumspecies

Rauvolfia alkaloids
A number of plants of this group were used medicinally in India several centuries before the birth of Christ. One of these plants is Rauvolfia serpentina(Apocynaceae). This plant contains alkaloids that are extremely potent hypotensive agents. One of the main alkaloids, reserpine, is used to treat hypertension and certain types of mental illness. Relatively large doses are used to treat schizophrenic patients.

Rauvolfia species

Catharanthus alkaloids
Two complex alkaloids of Catharanthus roseus (Apocynaceae) are used to treat leukemia. Vinblastine and vincristine produce remissions or cures in up to 50-70% of cases in certain forms of leukemia. In lymphocytic leukemia, even higher cures are reported.

Colchicine
Colchicine, an alkaloid from Colchicum autumnale(Liliaceae), is used to treat gout. The compound is fairly specific for the disease, but is highly toxic and its use must be carefully monitored.

Ipecac
Ipecac (from Cephaelis ipecacuanha, Rubiaceae) is used as a potent emetic. See diagram of the plant on page 284. One of the alkaloids, emetine, is also used to treat amoebic dysentery. The plant is native to northern South America and to Central America.

Anthraquinone glycosides
Anthraquinone glycosides from a number of plants (including Aloe(Liliaceae), Rhamnus (Rhamnaceae), Cassia(Fabaceae or Leguminosae) are widely used as laxatives. They also have other medicinal applications.

Aloe species

Strychnine
Strychnine is isolated from Strychnos nux-vomica(Loganiaceae). This alkaloid has been used in medicine in the past, but is considered too toxic for use today. In the proper dosage, strychnine can relieve paralysis and stimulate the central nervous system. The seeds of the plant are usually collected wild in Africa and Asia. The outside portion of the fruit is eaten in some African areas. The seed have been used as a trial by ordeal plant.

Taxol
The antitumor activity of taxol, a diterpene alkaloid from several Taxusspecies, was first discovered in the 1960's, but the alkaloid didn't become widely used until the mid 1980's.
Taxol is useful for treating several types of tumors, but was originally developed for ovarian tumors. The alkaloid occurs in highest concentration and in the most readily purifiable form in the bark of Taxus brevifolia, the Pacific yew. Recently, other materials have proven useful for sources of the drug, in part alleviating the environmental problems that resulted from over harvest of the original source.

Aconite
This drug is little used today because of the extreme toxicity. The leaves of Aconitum napellus(Ranunculaceae) have been used to treat neuralgia and rheumatism. Only 6 mg is enough of the alkaloid to kill an average human. The plant is native to Europe and Asia.

Calabar bean
The seed of Physostigma venenosum(Fabaceae or Leguminosae) have also been used as a trial by ordeal plant. The active ingredient, physostigmine, is presently used to treat glaucoma.

Corynanthe yohimbe
Yohimbe is a central nervous stimulant and reputed aphrodisiac. Although the latter activity is widely accepted, there is little scientific basis for this usage.

Ergot
The alkaloids from Clavicepsspp. on cereal grains have long caused problems in human health. The compounds are vasocontrictive and, in the middle ages in Europe, caused many human poisoning problems.
People's hands and feet sometimes developed gangrene when they ate grain containing ergot. Some of the alkaloids also cause hallucinogenic effects and bizarre behavior. All together the syndrome was called "St. Anthony's fire". The basis for the syndrome was not understood until about a century ago.
Today the alkaloids are used to treat migraine headaches, control hemorrhaging after childbirth, to induce labor etc.

Quassia
The bark of Quassia amara(Simaroubaceae) is used as a febrifuge and a bitter tonic. It is also used to control lice. The active compounds are modified triterpenes.

St. John's wort
St. John's wort, Hypericum perforatum, is effective as an antidepressant drug. This plant is native to Europe and Asia, but has been introduced into North America, where it is a common weed.

Gingko
Extracts from the leaves of Gingko biloba, a gymnospermous tree from China, improve capillary blood flow and improve memory and some aspects of brain function. The active components are diterpenes.
Unfortunately, these compounds only help you to get back to where your original level of brain function was .... and won't help you do become more capable beyond that. Otherwise, this could be a panacea for students and professors alike.
Sorry guys!


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Revised October 2003

© David S. Seigler, Plant Biology 263, Plants and Their Uses, Department of Plant Biology, 265 Morrill Hall, 505 S. Goodwin Ave., University of Illinois, Urbana, Illinois 61801, USA. 217-333-7577. seigler@life.uiuc.edu.