Medicinal Plants 13

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Medicinal Plants


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David S. Seigler

Department of Plant Biology

University of IllinoisUrbana, Illinois 61801 USA

[email protected]://www.life.illinois.edu/seigler
mailto:[email protected]:[email protected]


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Outline: Medicinal Plants

Importance

o Primitive cultures

+ Link to religion

+ Link to psychoactive drugs

Economics

Botanical

o Many families


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Chemical

o Terpenes+ Cardiac glycosides

+ Steroids

+ Metabolically altered

triterpenes

o Alkaloids

+ Analgesic drugs

+ Antitumor drugs+ Emetics


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o Anthraquinone glycosides

+ Laxatives

o Polyketides+ Aspirin

o Mode of action

Herbal medicines


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Reading

CHAPTER 11, pp. 262 ff.


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Introduction

The use of medicinal plants is found in almostall 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.


8/90Herbal medicines in Madagascar

Courtesy Dr. Voara Randrianasolo


9/90Medicinal plants in Toluca market


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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 othertypes of glycosides are also widelyused.


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These include the active principles ofSalix(Salicaceae),Artemisia cina (Asteraceae orCompositae) (santonin used as ananthelmintic drug), quassia (used to control

lice etc.). Table of some important medicinal plants on

page 263.


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Presumably curative agents were discoveredby 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.


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The ancient Egyptians recorded muchof their knowledge of plant drugs aswell. Many of the plants used by themare still used in medicine.


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The Greeks

The Greeks made other significantcontributions to medicine.

The number of effective medicinal plantscame 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.


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Dioscorides

The most significant contribution however,was Dioscorides (ca. 40-90 A.D.) He wrote a5 volume work, De materia medica, thatbecame the standard work for 1500 years.

Because of later historical developments andthe fact that Europe went into intellectualdecline, the book was blindly followed andaccepted without question until the fifteenthcentury.


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Doctrine of Signatures

Finally, a contemporary of da Vinci, Paracelsus(1393-1451), broke publicly with the works of theGreeks and advocated the "Doctrine ofSignatures". This was soon displaced by moreobjective methods.


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In the 19th century, such compounds asquinine, strychnine, morphine, andephedrine were isolated and studied.

Later (mostly in the twentieth century) manyof the compounds were synthesized andsome became available from that source.


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Most of the drugs used in western

culture come from Europe and Asia,

although a number of extremelyimportant ones come from other

sources.


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The most important types of compounds areterpenoids and alkaloids. Others such as fattyacids (e.g., chaulmoogra oil) are also used,however.

The chemical structures of several importantdrug materials are given in this chapter.

Types of active compounds


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Historically, malaria has been one of theworst of all human diseases.

In some countries malaria is common and

millions of people suffer from the diseasethroughout the world.

Malaria is caused by a sporozoan of thegenus Plasmodium and is passed from one

human to another by mosquitoes.

Malaria and quinine


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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.


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Peru in the early 1940s

Courtesy Dr. Walter Hodge


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Quinine, Cinchona

officinalis, Rubiaceae

Calisaya type



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Harvesting cinchona

bark



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Drying and storingcinchona bark


T f Ci h b k


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Types ofCinchona bark



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The Dutch acquired seeds from a high-yielding plant near Lake Titicaca, Bolivia.

After several years of trying to grow the plantsand improve them, they were able to begin tocultivate high quality lines in the Dutch EastIndies 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. Manyare still important, but resistance to most is amajor problem.


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Quinine is also used in small amounts

to make tonic water and other softdrinks such as bitter lemon.

Although there have been extensivesearches for new plant-derivedantimalarials, few have surfaced.

One, artemisinin fromArtemisia annua,has proven effective and is currently

being used in southeast Asia.


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Artemisia annua,

Asteraceae or

Compositae


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Ephedra or ma huang, Ephedraspp.,

Ephedraceae

Infusions ofEphedra spp. (Ephedraceae, a

gymnosperm) have been used for thousandsof years in China. There it is often called "mahuang".

In the 1920's the plant was "discovered" by

western medicine and the active compoundsisolated.


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Ephedra,Ephedra sp., Ephedraceae


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Ephedrine and a series of relatedcompounds are used today asdecongestants (e.g., in Sudafed,Robitussin etc.) and to treat low blood

pressure.

Most of the active compounds are madesynthetically, however.


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Even in the time of Dioscorides it was knownthat extracts of willow bark (Salixspp.,Salicaceae) and leaves alleviated pain.

The compound that is responsible is called"salicin". Salicin is too irritating to takeinternally, however.

In the late 1800's, a German chemist made

another compound that could be taken readilyand that had similar properties to salicin.

Willows and aspirin


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Willow in flower,Salix

nigra, Salicaceae


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This compound, acetylsalicylic acid, could betaken orally and was an effective analgesic,anti-inflamatory, and antipyretic drug and isprobably the most widely used drug in the

world today. Interestingly, we only learned how aspirin

actually functions in the last 30 years. Aspirininhibits the synthesis of certain

prostaglandins.


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Coca and cocaine

The Indians of Andean South America havelong used coca leaves (from Erythroxylumcoca, Erythroxylaceae) as a stimulant. TheIndians chewed the leaves mixed with lime tofree the alkaloids. The alkaloids reducedfeelings of hunger and pain.

Later when the alkaloids were isolated, it wasdiscovered that they had local anestheticproperties. Cocaine has been used forsurgery (especially dental surgery).


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Coca,Erythroxylum

coca, Erythroxylaceae


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Steroids from plants

Many types of animal hormones are steroids.Although the steroids from plants are similar,most do not have pronounced hormonalactivity 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.


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These steroids occur as complex glycosides(that is, they have sugars attached) that givethem soap-like properties and are sometimescalled saponins. These compounds are

relatively common in plants. Dioscorea species are used because they

have relatively large amounts of saponinsand the structure of the aglycone is

particularly appropriate for conversion to thedesired steroids.


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Male and femaleDioscorea plants

Disocorea root


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Disocorea root


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Steroids from these plants are convertedchemically 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.


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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 inthe folk medicine of Europe is Digitalis

purpurea (Scrophulariaceae).


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Digitalis, Digital is

purpurea(Scrophulariaceae)


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In 1775, William Withering, a British physician

documented that patients treated withfoxglove improved. He standardized thedosage of the drug.

Diagram p. 277.

Digitalis became accepted and today iswidely used in treatment of dropsy, acondition associated with congestive heartfailure.

The active compounds are saponins, buthave an aglycone with a special type ofstructure.

O i P if


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Opium poppy, Papaver somniferum

(Papaveraceae)

The alkaloids found in opium poppy, Papaver

somniferum (Papaveraceae), have long beenused to alleviate pain. See diagram of theplant on page 279.

Capsules have been found in prehistoric

deposits from the Mediterranean and from theNear East. Pictorial representations are foundin Egyptian, Greek, Roman and other art.

Opium was used to treat dysentery from at

least the first century B.C. The wild ancestorof the plant is no longer known with certainty.


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Poppy flower and capsuleCarolina Biological Supply Co.


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Opium is isolated by lightly slashing theimmature fruit capsules. The latex oozes out

and hardens after a day or so. The latex isabout 11% morphine and 1% codeine. Theexudate is scraped off and made into bricksof pure opium. The yields are 25-40 lbs. per

acre. Morphine is one of the principal alkaloids of

opium. These alkaloids are very addictive, butare potent pain killers (analgesics).

Codeine, another morphine alkaloid, is apotent antitussive agent, that is, it inhibitscoughing.

Incised poppy capsule and latex


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p ppy p

Carolina Biological Supply Co.


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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.


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Tropane alkaloids

A number of alkaloids from solanaceousplants are used as analgesics.

See p. 280.

The most commonly used alkaloids are

scopolamine (hyosine), hyoscyamine, andatropine.

The most commonly used plants areAtropabelladonna, Hyoscyamus niger, and Duboisia

species (the last species native to Australia).


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Henbane,Hyoscyamus

niger, Solanaceae


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Jimson weed,Daturastramonium, Solanaceae


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Belladonna has been used since the times ofthe Greeks. It was also used in the Middle

Ages in Europe to enhance the appearanceof women by causing them to have large

pupils. Today, these alkaloids are used as antidotes

for poisoning, to treat cardiac problems, forantidiarrhetic preparations, and to dilate

pupils during eye examinations.


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Black nightshade,

Atropa belladonna,

Solanaceae


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Rauvolfia Alkaloids

A number of plants of this group were usedmedicinally in India several centuries BC.

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 ofmental illness. Relatively large doses are

used to treat schizophrenic patients.


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Rauvol f ia serpent ina(Apocynaceae)


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Catharanthus alkaloids

Two complex alkaloids ofCatharanthus

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.

Periwinkle, Catharanthus roseus(Apocynaceae)


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, ( p y )


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Colchicine

Colchicine, an alkaloid from Colchicumautumnale (Liliaceae), is used to treat

gout. The compound is fairly specific forthe disease, but is highly toxic and itsuse must be carefully monitored.


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Autumn crocus, Colch icum autumnale(Liliaceae)

R. Bentley and H. Trimen, Medicinal Plants, London,

Churchill, 1880.


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Anthraquinone glycosides

Anthraquinone glycosides from a

number of plants [includingAloe

(Liliaceae), Rhamnus (Rhamnaceae),Cassia (Fabaceae or Leguminosae)]

are widely used as laxatives. They also

have other medicinal applications.


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Aloe,Aloe sp., Liliaceae


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Taxol

The antitumor activity of taxol (paclitaxel), aditerpene alkaloid from several Taxusspecies, was first discovered in the 1960's,

but the alkaloid didn't become widely useduntil the mid 1980's.

Taxol is useful for treating several types oftumors, but was originally developed for

ovarian tumors.


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The alkaloid occurs in highest concentrationand in the most readily purifiable form in thebark ofTaxus brevifolia, the Pacific yew.

Recently, materials from other species ofTaxus have proven useful for sources of thedrug, largely alleviating the environmentalproblems that resulted from over harvest of

the original source.


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Yew, Taxus baccata,

Taxaceae


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Calabar bean,

Physo st igma venenosum(Fabaceae or

Leguminosae)

Calabar beans have been used as a

trial-by-ordeal plant. The activeingredient, physostigmine, is presentlyused to treat glaucoma.


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Calabar bean,

Physos t igmavenenosum(Fabaceae

or Leguminosae)

R. Bentley and H. Trimen, Medicinal Plants,

London, Churchill, 1880


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Ergot, Claviceps spp., Clavicepitaceae

The alkaloids from Claviceps spp. on cereal

grains have long caused problems in humanhealth. The compounds are vasocontrictiveand in the Middle Ages in Europe causedmany human poisoning problems.


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Ergot, Claviceps spp., Clavicepitaceae

P l ' h d d f t ti


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People's hands and feet sometimesdeveloped gangrene when they ate graincontaining ergot.

Some of the alkaloids also causehallucinogenic effects and bizarre behavior.

All together the syndrome was called "St.

Anthony's fire". The basis for the syndromewas not understood until about 150 yearsago.

Today the alkaloids are used to treat migraine

headaches, control hemorrhaging afterchildbirth, and to induce labor.


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Herbal medicines


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Today, in Western Culture, most of the activeingredients are isolated, purified, andstandardized, or ... ironically (in the U.S.) aresold in "Health Food" stores with little

assurance that the plant materials are pure,contain the active principles, or are effective.Recent changes in FDA regulations promiseto improve this situation.


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In Europe, particularly in Germany,companies that market herbal medicationsare required to establish efficacy and toprovide the materials in a form that ensures

that the active materials are present in adesignated dosage. However, in manycultures, the crude plant drugs are still useddirectly.

Herbal medicines in a Mexican market


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St. John's wort, Hyper icum perforatum,

Clusiaceae

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.


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St. Johns wort,Hypericum

perforatum, Clusiaceae


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Ginkgo, Ginkgo biloba, Ginkgoaceae

Extracts from the leaves ofGinkgo

biloba, a gymnospermous tree from

China, improve capillary blood flow andimprove memory and some aspects of

brain function. The active components

are diterpenes.


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Ginkgo, Ginkgo biloba,

Ginkgoaceae


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Ginseng,Panax ginseng, Araliaceae

Ginseng has long been used by Oriental peoples as a wayof maintaining health and for treating and curing many

types of human ailments. In Japan, Korea, and China,

the most common species is Panax ginseng.

Because of the shape of the roots, based on the doctrine

of signatures, this plant was presumed to treat manyproblems.

The Eastern North American species, Panax

quinquefolia, was one of the earliest exports from theAmerican Colonies to the Orient. The active compounds

are triterpenoid glycosides; some are called

gensenosides.


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Ginseng,Panax ginseng,

Araliaceae

Takatori. Color Atlas of Medicinal Plants of

Japan.

Echinacea Echinacea purpurea Asteraceae


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Echinacea, Echinacea purpurea, Asteraceae

Echinacea was used as a medicinal plant by American

Indians. The plant was introduced into patent medicines

in the 1870s and has been used since that time to deal

with a number of problems.

Echinacea was an important plant medicine in the 1920s,

but fell into disuse as antibiotics of various types were

introduced.

Echinacea induces an immune response in humans

and has been used more recently to treat colds and other

viral diseases.This plant drug is especially popular in Europe. As the

plant is often wild harvested, there are many

conservations concerns about the continued unrestricted

use of this valuable resource.


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Echinacea, Echinacea

purpurea, Asteraceae


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Valerian, Valeriana officinalis, Valerianaceae

Valerian has long been used as a sedative. The dried roots

and rhizomes have been used as a tranquilizer and

calmative for more than 1000 years in cases of

nervousness and hysteria. The plant parts have a

somewhat disagreeable odor.

Interestingly, in this case, the active components have

never been conclusively identified. However, the plant is

documented to be an effective sleep-inducing drug.


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Valerian, Valeriana

officinalis,

Valerianaceae

Black cohosh Cimicifuga racemosa


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Black cohosh, Cimicifuga racemosa,

Ranunculaceae

The underground parts ofCimicifuga

racemosa are used to treat a number of

female problems.

This plant was used by many of the American

Indians of the Eastern United States.

Black cohosh Cimicifuga racemosa


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Black cohosh, Cimicifuga racemosa,

Ranunculaceae

An infusion of the roots and rhizomes is drunkto treat rheumatism, uterine difficulties tostimulate menstrual flow, and as anantidiarrheal, and cough suppressant.

It was the active component of LydiaPinkhams Vegetable Compound in the 1800sand early 1900s.

The plant has been shown to have estrogenic

activity and is used in Europe to treatpremenstrual syndrome (PMS).

Black cohosh, Cimicifuga


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racemosa, Ranunculaceae


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