PBIO 100 Lecture Notes
Undergraduate Program in Plant Biology, University of Maryland
LECTURE 29 - MEDICINAL PLANTS
"Plants live by their chemical wits" Richard Schultes
I. Introduction
-
A. Plants are inventive chemists - more so than us animals
B. Some may be nutritious, poisonous, hallucinogenic or therapeutic.
II.
History
of Drugs from Plants [An excellent review! see also
this site for the history of medicine]
III. Novel Chemicals in Plants
-
A. Two theories account for the variety of chemicals found in plants
IV. Human Dependence on Drugs from Plants
-
A. Over 25% of our common medicines contain at least some compounds obtained
from plants.
B. In US approximately 10% of our major drugs have plant extracts as their
active ingredient.
C. In less developed countries the World Health Organization estimates that
75-80% of the people rely on plant-based medicines for primary health care.
V. Role of Synthetic Drugs
" the humblest bacterium can synthesize, in the course of its brief
existance more organic compounds than can all the world's
chemists combined. -- R. DeRopp, Drugs and the mind, 1957.
-
A. Useful plant compounds are often easy to synthesize.
B. No dependency on plant collectors or growers as a source or the long-term
survival of the plant.
C. In some instances we do not know how to synthesize the desired compound,
in other instances it is cheaper to collect from natural sources.
D. Synthetics can be patented; natural compounds can not - it is a question
of dollars.
VI. Plant-based Drugs in Use
-
A. Alkaloids: Over 5,000 alkaloids have been identified in numerous plant
families, most in the angiosperms.
-
1. Chemical
structure (ibogaine: an alkaloid from an African plant used to reduce cocaine
withdrawal symptoms; courtesy of The Ibogaine
Dossier) ---->
2. Properties
-
a. contain nitrogen
b. are alkaline or basic in reactions
c. taste bitter
d. have a physiological effect on animals, usually working on nervous
system
e. the names of most alkaloids end in "...ine" such as: morphine, quinine
3. Importance to humans
B. Representative Plants Producing Alkaloids as Drugs
-
1. Opium poppy
(Papaver somniferum): morphine and codeine
-
a. Annual, native to Turkey and Asia Minor, produces a latex-filled capsule,
and this milky sap is the source of
opium,
which contains a mixture of 26 alkaloids>
b. Morphine isolated in 1806; morphine is 10% opiate, codeine is 1%.
c. Heroin is a concentrated form extract of opium;
a major
drug in the United States.
2. Cinchona tree
or Peruvian bark (Cinchona succirubra):
quinine
-
a.
Malaria
has killed more people than all our wars put together, one of the oldest
recorded diseases
b. The alkaloid quinine is produced in the bark; native of the Andes in Peru
and Bolivia. First used by native peoples against malaria, but it wasn't
until the 1600s that news of a cure for malaria reached Europe. Knowledge
suppressed because it was used by the "heathens"; wife of Spanish official
treated with cinchona proved its effectiveness
c. Quinine gives tonic water its characteristic bitter taste - hence the
popularity of gin and tonic in tropical areas of the British Empire
d. Modern quinine comes from chemically related synthetic compounds; renewed
interest in natural quinine as some strains of plasmodium are resistant
3.
Mandrake
(Mandragora officinarum ---->): Compound: Contains several alkaloids
including atropine, scopolamine, podophyllin, mandragorin and hyoscyamine
-
a. An anesthetic alkaloid, used to deaden pain goes back to the Old
Testament
b. Used as an instrument of war - because it both deadens pain and is
sleep-inducing, it is written that Hannibal triumphed over African rebels
by staging a fake retreat leaving behind mandrake to stupefy his enemies,
after which he returned to slaughter them easily. Supposedly Caesar used
same ploy
c. Shape of mandrake: The root frequently forks with two leg-like branches
and sometimes a protuberance that suggests male genitals; hence the name
mandrake (man + dragon = potent male)
d. According to Doctrine of Signatures makes men virile; hardly a good
aphrodisiac as it puts you to sleep!
4.
Belladonna
(Atropa
belladonna):
atropine
and scopolamine]
-
a. In use since the Middle Ages
b. The common name, "belladonna" or "beautiful lady" refers to the ancient
practice by Italian and Spanish women of putting sap in their eyes to enlarge
the pupils - to achieve a seductive look
c. Used still by opthamologists
d. Atropine and scopolamine have many other uses - they stimulate the sympathetic
nervous system - they are used with palsy, to stimulate circulation, and
in some 50 other conditions
e. The related jimson weed (Datura spp.) is frequently used by unknowning
children; while it will cause hallucinations, it can also kill!
5.
Ipecac
(Cephaelis ipecacuana): emetine
-
a. Herbaceous perennial from Central and South America with an unusual
flower
b. The alkaloid acts as an emetic: makes you throw up "ipecac" was developed
by a pirate -- something good to do if you have been poisoned!
6.
Tobacco
(Nicotiana tabacum): nicotine
-
a. Native of the New World, first introduced for its supposed medicinal value
in 1614 by John
Rolfe, an associate of Sir Walter Raleigh. In the 17th and 18th centuries
it was recommended to
cure dozens
of illnesses - everything from cancer to the common cold
b. The botanist John Hill was the first to associate tobacco use with cancer,
reporting, in the 1791, that snuff caused nasal cancers
c. A contact poison to most insects, an important insecticide
7.
Coffee
(Coffea arabica) and tea (Camelina sinensis): caffeine
-
a. Coffee: native of northeastern Africa around Ethiopia. Alkaloids are in
the fruits
b. Used medicinally for centuries has an effect on blood pressure, pulse,
and other functions
c. Tea:
native to China and India; probably used first medically effects similar
to that of coffee
C. Glycosides: chemical compounds consist of one or more sugar molecules
(usually glucose, hence the name) attached to one or more non-sugar molecules
-
1. Properties: Often bitter; marked physiological effect on animals; important
in medicine
2. Cardiac glycoside: a medicine that stimulates the heart
3. Example:
Digitalis
or
foxglove
(Digitalis purpurea): Digitoxin ---->
-
a. Native of Europe, long in use; common garden plant; leaves are used as
a heart stimulant
b. Excessive dose
can be
fatal, extremely toxic. Don't chew the leaves!
4. Example:
plantain
(Plantago
major): aucubin
5. Example:
Colocynth
or wild gourd (Citrullus colocynthis): elaterin
-
a. North Africa to tropical Asia
b. Used as a drastic purgative; in use since biblical times
6. Example: Rose relatives (Prunus, Amygdalus): characteristic scent
of almond extract highly poisonous.
7. Special example: ginseng or ren shen (="man essence")
(Panix ginseng
or P.
quinquefolia):
ginsenosides
or panaxosides [REVIEW!] - concentrated
in roots
-
g. Wild plants are more valuable
that cultivated ones
h. Ginseng found in a variety of products
(drinks including various
soft drinks,
beer, pills, tonics,
with honey and/or bee pollen, liquid syrup(powders, chips or whole roots),
especially as a sexual
tonic for men; numerous claims
are made, but few documented.
Ginsana, a dietary supplement,
is the best known American product.
i. Minor correction: American ginseng was originally collected by John Banister
of Virginia in the 1680s; it was also noted in Maryland in the 1690s. Its
significance was not noted until the English sea captain, Cunningham, returned
from China in 1700 with information about the plant.
VII. Future Drugs in Plants
-
A. Current knowledge
-
1. About 10% of the over 250,000 species of plants have been extensively
screened in laboratories to determine their therapeutic potential
-
a. Examples:
Camptotheca
(Camptotheca acuminata), a traditional Chinese anticancer plant, the
source of
camptothecin.
This drug has just been approved for use
b. Mayapple
(Podophyllum
peltatum), a native American plant (see image ---->) and the source
of
podophyllotoxin.
Etopiside, also isolated from Podophyllum, was worth $350 million
in 1993
c. Yew
(Taxus brevifolia and T. baccata), a Pacific Northwest native
tree, is the source of
parclitaxel,
better known by the commercial name "taxol", had sales worth $600 million
in 1995
d. Other anticancer
plants
2. Approximately 120 plant-based prescription drugs are on the market, and
these drugs come from only 95 different species of plants
3. National Cancer Institute has expanded its testing program for natural
products, and drug companies send out botanists to collect plants in the
major rain forests of Asia, Africa and the Amazon
4. Many of our drugs have come from tropical plants. 25% of the world's plants
are found in the tropical Amazon alone
5. Two major problems:
-
a. Tropical rainforests are currently being destroyed or degraded faster
than any other biome
b. Shamen and witch doctors who have knowledge of plants are disappearing.
Young Indian boys are not interested in what they perceive as old fashioned
ideas and so the knowledge is not being passed on, but dies with the medicine
men
"Every time a medicine man dies it is like a library burning
down" Mark
Plotkin, ethnobotanist
VIII. The Problem of Ownership
-
A. Intellectual Property Rights: Who owns the plants, its chemicals, its
genes - none of these questions have been solved via international
agreement
B. The rosy
periwinkle(Catharanthus
roseus) is native to Madagascar. From this plant we have isolated
two alkaloids
(vinblastine and
vincristine) - one that combats Hodgkins Disease, and another used to
treat childhood leukemia. The annual sales of these drugs is over $100 million
(and has done so for more than 30 years) - none of this goes back to Madagascar,
one of the world's poorest countries
C. Some drug companies have entered into agreements with certain countries
to survey their plants for unique compounds. Can a naturally occurring compound
be patented? Without patent protection why should a company go to the expense
of developing the compound commercially?
D. Is it worth it? Steroids, which trace their development back to wild yam,
at one time commanded some 15% of the world's pharmaceutical market, today
their annual share of that $150 billion a year market is less and most are
derived as a by-product of soybean production
IX. Herbal Medicines
"And the wages of ignorance can be death."Canterbury Tales
A recipe for abortion in a popular herbal guide for women suggests using
the herb pennyroyal (Mentha pulegium). In 1994
Kurt Cobain popularized
a song
"Pennyroyal
Tea." It is commonly found in health food stores, and most of us assume
there is nothing in a health food store would can kill us. Nevertheless,
a college student in California died a slow and painful death last year trying
to induce a "natural" abortion using pennyroyal
in spite of
numerous published warnings. BE CAREFUL, NEVER TAKE ANY PLANT COMPOUND
UNLESS YOU KNOW IT IS SAFE!
Always be
careful.
Other sites of interest:
The following sites are examples. There is no intent to endorse any site
or point of view regarding alternative medical practices or sources of
information.
Medical
Plants: A Review!
"Cancer-killing
plants" by Bryan Ness
Alternative Medicine
Sites from Yahoo
Alternative Medicine Online
Sources
Native American
traditional herbal & plant knowledge
Bibliography
of Medicinal and Useful Plants
Botanical.com: Includes a Modern
Herbal
Ethnobotanical Uses of
Plants
Herbs as Medicine: An
excellent set of links
Herb, Spice
and Medicinal Plant Digest
HerbWeb
Phytochemical and Ethnobotanical
databases: Maintained by USDA and James A. Duke
Poisonous Plant Database
(bibliography
Plants for a
future
Cyberbotanica: Plant
and Cancer Treatments - see also this
list of other
cancer-treating plants
Shamanism
Alternative
Medicines: A summary of the many treatments; a good review!
AIDS Alternative Treatment
Page
Chinese Acupuncture
Herb Research Foundation
Chinese
Herbology
Holistic
Medicine
Homeopathy Home Page
Southwest
School of Botanical Medicine
The Herbal Encyclopedia:
A valuable resource
Herbals and Early Gardening
Books
The
Cigarette Papers
History
of cigarettes in the United States
Still have a question regarding medicinal plants?
Ask Dr. James A. Duke,
noted ethnobotanist and leading authority on medicinal plants.
Last revised: Oct 16, 1998 - Straney