Download Medicinal Plants

Medicinal Plants
Prehistoric times
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No one knows where or when plants first
began to be used to treat disease
Accidental discovery of some new plant food
that eased pain might have been the
beginning of folk knowledge
Early evidence: the grave of a Neanderthal
man buried 60,000 years ago. Pollen analysis
indicated that plants buried with the corpse
were all of medicinal value
Recorded history
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Earliest record 4,000 year old Sumerian
clay tablet recorded numerous plant
remedies
Ancient Egyptian civilization had a
wealth of information on medicinal
plants - Ebers Papyrus 3500 yrs ago
Ancient China
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The Pun-tsao, a pharmacopoeia
published around 1600, contained
thousands of herbal cures that are
attributed to the works of Shen-nung,
China's legendary Emperor who lived
over 4500 years ago
Ancient India
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Herbal medicine dates back several
thousand years to the Rig-Veda, the
collection of Hindu sacred verses
This is the basis of a health care system
known as Ayurvedic medicine
One useful plant that has come from
Ayurvedic tradition is snakeroot,
Rauwolfia serpentina
Foundations of western
medicine
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These ancient records indicate that in
all parts of the world native peoples
discovered and developed medicinal
uses of local plants
Herbal medicine of ancient Greece laid
the foundations of our Western
medicine
Ancient Greek and Roman
medicine
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Greek physician Hippocrates (460-377
B.C.), known as the Father of Medicine
used various herbal remedies in his
treatments
Roman physician Dioscorides (1st
century A.D.) wrote De Materia Medica
which contained an account of over 600
species of plants with medicinal value.
De Materia Medica
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Descriptions of plants, directions on the
preparation, uses, and side effects
Many still in use
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Some have been lost
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willow bark tea - precursor to aspirin
Greek and Roman women used silphium as an
effective contraceptive for 1,000 yrs - now extinct
Standard medical reference for 1500 years
Little new knowledge was added in Europe
during the Dark Ages
Age of herbals
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Beginning of Renaissance in the early
15th century saw a renewal of learning
Botanically - revival of herbalism for
medicinal plants
Coupled with the invention of the
printing press in 1440 ushered in the
Age of Herbals
Herbals
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Beautifully illustrated books that
described plants
When to collect, useful parts
Medicinal and culinary uses
Also included a lot of misinformation
and superstition
Often advocated the Doctrine of
Signatures
Doctrine of Signatures
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Medicinal use recognized by distinct
"signatures" visible on the plant which
corresponded to human anatomy
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Red juice of bloodwort to treat blood
disorders
Lobed appearance of liverworts to aid the
liver
Belief in this concept developed
independently among different cultures
18th Century
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As science progressed, a dichotomy in
medicine developed between
practitioners of herbal medicine and
regular physicians
About this same time a similar split
occurred between herbalism and
scientific botany
Path to modern medicine
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Many herbal remedies had a sound scientific
basis
Some became useful prescriptions drugs
William Withering was the first to scientifically
investigate a folk remedy
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His studies (1775-1785) of foxglove to treat
dropsy (congestive heart failure) set standard for
pharmaceutical chemistry
19th Century
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Scientists began purifying the active
extracts from medicinal plants
Breakthrough in pharmaceutical
chemistry came when Serturner isolated
morphine from opium poppy in 1806
First synthetic drugs were developed in
the middle of the 19th century based on
natural products
20th Century
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Direct use of plant extracts continued to
decrease in the late 19th and 20th centuries
Today medicinal plants still contribute
significantly to prescription drugs
25% of prescriptions written in the U.S.
contain plant-derived active ingredients
50% if fungal products are included
An even larger percent based on semisynthetic or wholly synthetic ingredients
originally isolated from plants
Late 20th century
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Renewed interest in investigating plants
for medically useful compounds
Recent success of taxol from the Pacific
yew tree has shown this interest is
worth pursuing
Herbal medicine today
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75%-90% of the rural population in
developing nations rely on herbal medicine as
their only health care
Medicinal herbs are sold alongside vegetables
in village markets
Practitioners of herbal medicine undergo
extensive training to learn the plants, their
uses, and preparation of remedies
People's Republic of China
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Traditional herbal medicine incorporated into
a modern health care system
Blend of herbal medicine, acupuncture, and
Western medicine
Thousands of species of medicinal herbs are
available for the Chinese herbalist
Chinese apothecaries contain an incredible
assortment of dried plant specimens
Prescriptions filled with blends of specific
herbs
India
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Traditional systems separate from Western
medicine
At universities medical students are trained in
Western medicine
Most people use traditional systems:
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Ayurvedic medicine - Hindu origin
Unani medicine - Muslim and Greek origin
Economics also a factor - manufactured
pharmaceuticals too expensive for most
Other areas
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Interest in medicinal plants has focused
on indigenous peoples in many parts of
the world
Ethnobotanists are spending time with
local tribes and learning their medical
lore before they are lost forever
Especially important among native
peoples in the tropical rain forests
Tropical rain forests
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Widespread destruction threatens to eliminate
thousands of species that have never been
scientifically investigated for medical potential
Erosion of tribal cultures is also a threat to
the knowledge of herbal practices
As younger members of native groups are
drawn away from tribal lifestyles, oral
traditions are not passed on
Active principles in plants
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Secondary plant products
Two major categories of these
compounds
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alkaloids
glycosides
Other types of compounds are also
important - essential oils
Alkaloids
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Diverse group of compounds
Over 3000 have been identified
Most occur in herbaceous dicots and fungi
Three families that are particularly known for
their alkaloids: Fabaceae (legume family), the
Solanaceae (nightshade family) and the
Rubiaceae (coffee family)
Chemistry of alkaloids
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Vary greatly in chemical structure
Alkaloids share several characteristics:
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they contain nitrogen
they are usually alkaline
they have a bitter taste
Physiological effects of
alkaloids
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Diverse effects with the most pronounced on
the nervous system
Can also have psychological effects
Some medicinally important, some
psychoactive, some poisonous
Often a fine line between a medicinal and
toxic dose
Common alkaloids: caffeine, nicotine,
cocaine, morphine, quinine, ephedrine
Psychoactive Compounds
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Affect the central nervous system often by influencing neurotransmitters
Categories of psychoactive cmpds
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Stimulants
Hallucinogens
Depressants
May also be narcotic
Narcotic Compounds
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By definition a narcotic drug induces central
nervous system depression resulting in
numbness, lethargy, sleep
In current use, a narcotic is a psychoactive
drug that is dangerously addictive
Addictive cmpds elicit: psychological
dependence, physiological dependence,
and/or tolerance
Glycosides
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Also widespread in the plant kingdom and second
in importance as medicines or toxins
Have sugar molecule (glyco-) is attached to the
active component
Active portion variable, sugar is glucose
Generally categorized by the active component:
cyanogenic glycosides, cardiac glycosides, and
saponins.
Cyanogenic glycosides
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Release cyanide (HCN) upon breakdown
Cassava contains cyanogenic glycosides
Seeds, pits, and bark of many members
of the rose family (apples, pears,
almonds, apricots, cherries, peaches,
and plums) contain amygdalin, a
cyanogenic glycoside
Amygdalin
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Apricot pits are rich in amygdalin
Ground up for preparation of laetrile, a
controversial cancer treatment
Theoretically, laetrile releases HCN only
in the presence of tumor cells and
selectively destroys them
Not proven and laetrile not approved for
cancer therapy in the United States
Cardiac glycosides
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Steroid molecule is active component
Cardiac glycosides effect the contraction of
heart muscle
In proper doses, some are used to treat
various forms of heart failure
Best known is digitalis
Some of the deadliest plants, such as
milkweed and oleander, contain toxic levels of
cardiac glycosides
Saponins
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Steroid molecule is active component
Can be highly toxic causing severe
gastric irritation and hemolytic anemia
One useful saponin is disogenin from
yams (Dioscorea spp.) which can be
used to synthesis various hormones
such as progesterone (ingredient in
birth control pills) and cortisone
Some important medicinal
plants
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Foxglove - heart disease - digitalis
Willow bark tea - pain, fever - aspirin
Fever Bark Tree - malaria - quinine
Snakeroot - hypertension - reserpine
Aloe - burns - various glycosides
Vinca - leukemia - vincristine
Taxus - ovarian & breast cancer - taxol
Foxglove and heart disease
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Foxglove - Digitalis purpurea
Extract called digitalis
Long history as a folk remedy for
congestive heart failure (dropsy)
William Withering investigated this
remedy from 1775-1785 - first scientific
study of a medicinal plant
Digitalis purpurea
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Purple foxglove - an attractive biennial with
large purple bell-shaped flowers
Often used as a garden ornamental
Leaves contain over 30 cardiac glycosides
with digoxin and digitoxin the most
medically significant
Concentration of glycosides highest before
flowering
Leaves dried, powdered, then extracted
Foxglove
Digitalis purpurea
Physiological action
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Digitalis slows heart rate and increases
strength of each heartbeat
Results: more blood is pumped with each
contraction
Improved circulation, decreases edema, and
increases kidney output
Effective treatment - not a cure
Fine line between a therapeutic and toxic
dose of digitalis
Aspirin: willow bark to Bayer
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Most widely used synthetic drug but
origins are botanical
Bark of willow trees (Salix spp.) used by
many cultures for reducing fever and
relieving pain - in form of a tea
Path to a synthetic
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In 1828 salicin was first isolated and
over the next decade the extraction
method was refined
Salicin is a glycoside of salicylic acid
Salicylates occur widely in species of
Salix as well as many other plants
including meadowsweet (Spirea
ulmaria)
Next step
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Laboratory synthesis of salicylic acid in the
mid-19th century
Salicylic acid was an inexpensive treatment
for many ailments - rheumatic fever, gout,
arthritis
Had side effects - especially gastric
In 1898 Felix Hoffman, a chemist at Bayer
Company came across acetylsalicylic acid
Acetylsalicylic acid
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Effective and more palatable
Soon given the name aspirin
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"a" is from the acetylsalicylic acid and the
"spirin" from Spirea the plant from which
salicylic acid was first isolated
Physiological action
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Three classic properties
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anti-inflammatory
antipyretic (fever reducing)
analgesic (pain relieving)
New uses in the prevention of heart attacks,
strokes, and colon cancer
Drawbacks:
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irritates the stomach
Reye's syndrome
Malaria and fever bark tree
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Malaria known since antiquity, is still the
world's most prevalent disease
2 to 3 million people die each year from
malaria, and at least one million of these
deaths are young children
Today malaria largely confined to tropical
and subtropical countries in Asia, Africa,
South America, and Central America
Malaria
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Caused by unicellular parasites in genus
Plasmodium
Spread by bite of Anopheles mosquito
Parasite multiplies in liver and released in
blood stream
Invade red blood cells - multiply and rupture
RBC
Cycle repeats every few days -symptoms
fever, chills, anemia....death
Fever bark tree
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Native to the eastern slopes of the Andes
Mountains
Called quina-quina by the Incas
Several species of Cinchona
Small evergreen trees belong to the
Rubiaceae, the coffee family
Fever reducing powers of the tree were well
known to the Incas who shared knowledge
with Jesuit missionaries
Jesuit’s bark
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Jesuits used bark to treat people with malaria
In 1638 - Countess of Cinchon, wife of the
Viceroy of Peru - miraculous recovery spread
reputation of the bark
Years later Linnaeus named the genus
Cinchona in honor of the countess
By the end of the 17th century the powdered
bark of the quina-quina tree was the standard
treatment for malaria
Quinine
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In 1820 two French scientists isolated the
alkaloid quinine
Within a few years purified quinine was
available commercially
Demand for the bark increased even more
36 alkaloids in Cinchona bark - 4 have antimalarial properties
Quinine is the most effective
Synthetics
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During World War II synthetics were
developed
Today the most widely used drug for malaria
is chloroquine which is less toxic and more
effective than quinine
Widespread use of chloroquine has resulted
in chloroquine-resistant strains of the parasite
Quinine used for these infections in
combination with other drugs
Physiological action
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Quinine kills parasite in blood stream
Also effective as a prophylactic to
prevent initial infection of red blood
cells in travelers
"gin and tonic"
Recently scientists have been
investigating anti-malarial properties of
weed Artemesia annua, wormwood
Snakeroot, schizophrenia, and
hypertension
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Snakeroot, Rauwolfia serpentina
"doctrine of signatures"- because long coiled
roots resembled a snake, healers believed
that the root could be used for treating snake
bites
For over 4000 years, Hindu healers used the
root for the treatment of snakebites, insect
stings, and even mental illness
Rauwolfia serpentina and
reserpine
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In 1952 the alkaloid reserpine was isolated
from the roots
Later dozens of alkaloids found
The sedative effects of reserpine made it
valuable as a tranquilizers - side effect was a
reduction in blood pressure
Today, this is actually the principal application
of reserpine, as a treatment for hypertension
Burn plant - Aloe vera
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Well known folk remedy is use of Aloe
vera sap for minor burns
Used for thousands of years as
treatments for various skin ailments
Aloe vera (A. barbadensis) the best
known member of the genus but other
Aloe species also used
Aloe leaves
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Thick mucilaginous sap
Soothing effect on injured skin
Numerous compounds including several
anthraquinone glycosides collectively
referred to as aloin
Chrysophanic acid also present possibly the compound with the
greatest healing effect on skin
Action
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Sap promotes faster healing with less scaring
by stimulating cell growth
Inhibits bacterial and fungal infection
Compounds in the sap inhibit pain, itching,
and inflammation
In recent years the cosmetic industry has
capitalized on the moisturizing effects of the
sap and it can be found in a variety of skin
creams, shampoos, sun screen lotions, and
bath oils
Cancer therapy
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Cancer is a diverse group of diseases
characterized by uncontrolled growth of
abnormal cells.
Today in the United States cancer is the
leading cause of death
Search for cancer cures is relentless
Plants have figured prominently in folk
remedies for cancer
Over 3000 plant species had been used
Search for drugs
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In the late 1950's National Cancer Institute
and USDA began search for plants with anticancer properties
Thousands of plants have been scientifically
screened, and several have become standard
chemotherapy for different forms of cancers
Search is not over since only a small
percentage have been screened
Vinblastine and vincristine
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Treatments for
leukemia and lymphoma
Alkaloids from
Madagascar periwinkle,
Catharanthus roseus
(Vinca rosea)
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Used by traditional
healers as treatment for
diabetes
Screening
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Investigating this claim in the 1950's,
scientists at the University of Western Ontario
in Canada and Eli Lilly Pharmaceuticals in
Indianapolis found no evidence of usefulness
in treating diabetes
Extracts from the leaves were found to be
effective against leukemia cells and
Alkaloids responsible were identified
Use today
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Vincristine and vinblastine major
chemotherapeutic agents
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Vincristine has been especially effective for
treating acute childhood leukemia, often
with 99% remission rates
Vinblastine has been especially effective for
treating Hodgkin's disease
Both alkaloids also used for other types
of cancer
Pacific yew trees and taxol
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Taxol obtained from the bark of the Pacific
yew, Taxus brevifolia
Anti-tumor properties were first discovered in
the 1960's during the screening program of
the National Cancer Institute
Taxol - only recently approved
Clinical trials showed taxol especially
promising in treating ovarian and breast
cancer
Taxus - yew
Supply of taxol
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Original from bark of mature Pacific yew
trees, a slow-growing conifer of old-growth
forests in the Pacific NW
Concern about destruction of ancient forests
New sources
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Other species of Taxus contain taxol
Tissue cultures of bark cells promising
Recently synthesized in the laboratory
What’s in the future
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Search for medicinal plants continues
Especially in tropical rain forests
Time is critical before plants are lost
and cultural knowledge of the plants are
lost
Same is true among native peoples
everywhere includes Native Americans