Ginkgo
The best-selling
phytomedicine on the European market is derived
from the leaves of an ancient tree. The tree is ginkgo, Ginkgo biloba, a living fossil. Ginkgo is
considered the oldest tree species to survive on
earth, with a history dating back over 200 million
years. Ginkgo species were once common in North
America and Europe. Ginkgo biloba is the
only surviving member of the ginkgo family. While
its relatives became extinct in other parts of the
world Ginkgo biloba survived in China, where
it became known to Europeans in the eighteenth
century, and subsequently was introduced as a
ornamental tree throughout the Western world. Now
ginkgo trees are found in virtually every city in
the United States. It was first introduced to the
U.S. in 1784. The common name Ginkgo is a phonetic
pronunciation of a Japanese name for the tree. The
species name "biloba" refers to the two distinct
lobes, typical of the tree's leaves.
Ginkgos have survived over
millions of years because of their genetic
tenacity. They are long-lived trees, remarkably
resistance to disease, pests, and fires. They also
are extremely tolerant of air pollution, and are
often planted in harsh city environments where most
trees will not survive. The most common tree along
Manhattan sidewalks is ginkgo. The trees will get
to be over 100 feet tall. In Japan and China trees
over a thousand years old are found at ancient
temples. Its unique fan-shaped leaves with two
lobes make it one of the easiest trees to identify
once you become familiar with the unusual leaf
shape.
Despite the fact that the
tree occurs in China, the leaves are not one of the
famous classical herbal drugs of ancient China. The
first mention in Chinese herbals of use of the
leaves comes relatively late. Ginkgo leaf is first
mentioned in Lan Mao's Dian Nan Ben Cao (Pharmaceutical Natural History of Southern
Yunnan), published in 1436 during the Ming dynasty.
Lan Mao notes external use to treat skin and head
sores as well as freckles. Internal use of the
leaves is first noted in Liu Wen-Tai's Ben Cao
Pin Hui Jing Yao (Essentials of the
Pharmacopoeia Ranked According to Nature and
Efficacy), an imperial commissioned work recorded
in 1505. Liu Wen Tai notes use of the leaves in the
treatment of diarrhea. The leaves of ginkgo are
known in Chinese medicine as bai-guo-ye. Recent
clinical reports in modern China suggest that the
leaves lower serum cholesterol levels and have some
clinical value in angina pectoris.
In Traditional Chinese
Medicine the seeds (with fleshy rind removed) are
considered more important than the leaves. The
seeds are used as an astringent for the lung, to
stop asthma, enuresis, and excessive leucorrhoea. It
is thought to benefit ch'i (qi; vital energy),
cough, and regulate urinary frequency. Studies have
shown that the constituents ginkgoic acid and
ginnol inhibit certain bacteria and fungal
infections. In large doses the seeds are thought to
have some toxic effect, perhaps leading to skin
disorders or mucous membrane irritation.
Ginkgo leaves are a
Chinese herb that has been used much more in the
West than in its homeland. Over three hundred
scientific studies on the chemistry, pharmacology
and clinical effects of gingko leaf have been
conducted by European researchers over the last 20
to 30 years. Unlike most herbs, ginkgo leaf
extracts, rather than crude leaf material, are used
for clinical purposes. The majority of studies on
ginkgo leaf extract have involved a product
produced by a German/French consortium, referred to
in the scientific literature as EGb761. Ginkgo
products are standardized to contain 24% of the
bioflavonoids which occur in the leaf, as well as
ginkgolides and bilobilides, a complex group of
compounds found only in the ginkgo tree. Since
virtually all research on ginkgo has involved high
standardized extracts calibrated to specific
quantities of chemical components, it is not
possible to apply information from studies on the
standardized extracts to ginkgo leaf itself.
The complex extract
itself, rather than a single isolated component, is
believed to be responsible for Ginkgo's biological
activity. However, recently various research groups
have focused on the effects of the ginkgolides
themselves. They have been found to be very
selective antagonists of platelet aggregation
induced by platelet-activating factor (PAF), an
inflammatory autocoid. Autocoids, synthesized in
local tissue sites, mediate tissue response, such
as pain perception, blood coagulation, and smooth
muscle contraction. PAF is involved in various
inflammatory, cardiovascular, and respiratory
disorders. The ginkgolides have an anti-PAF action,
helping to modulate various enzyme systems and ion
pumps. The PAF antagonist effect of ginkgolides
helps to explain ginkgo's broad-spectrum biological
activity.
Most of the extracts
available on the American market are made in
Europe. Supplies are also coming from Japan, China,
and elsewhere. Most of the ginkgo leaf used to
manufacture European products is produced on a farm
owned by a German company in South Carolina.
Ginkgo leaf extracts have
been shown to have a wide range of biological
activities. The most well-known use among American
is the perceived ability of the products to improve
short term memory. Other important effects include
a protective effect on the blood-brain barrier and
an anti-radical (antioxidant) effect. The leaf
extracts has also been shown to increase
vasodilation and peripheral blood flow rate in
capillary vessels and end-arteries in various
circulatory disorders. Ginkgo leaf helps to
maintain integrity and permeability of cell walls
by inhibiting lipid peroxidation of membranes.
Other studies have shown vascular-tone regulating
effects, and help in modulating cerebral energy
metabolism.
Ginkgo extracts have been
widely used in Europe for a wide variety of
clinical conditions including vertigo, tinnitus
(ringing in the ear), treatment of poor
circulation, heart disease, eye diseases, chronic
cerebral insufficiency, accidents involving brain
trauma, dementia, and various conditions associated
with senility. The standardized extract of the
leaves has been shown to be beneficial in a broad
range of conditions, including those involved with
circulation, blood conditions, metabolism, immune
function, varicose conditions, and post-thrombotic
syndrome. It has been shown to help with short-term
memory improvement (especially in older
populations), and cognitive disorders secondary to
depression, among other conditions.
New uses for Ginkgo leaf
extracts are emerging as more is learned about the
extracts usefulness in various clinical situations,
especially those involving circulatory problems.
For example, a 1991 study published in the Journal of Sex Education and Therapy evaluated the effect of Ginkgo leaf extract in the
treatment of erectile dysfunction in fifty
patients. The men, diagnosed with arterial erectile
impotence, received 240 mg of ginkgo leaf extract
daily for a period of nine months. The patients
were divided into two groups based on their
response to conventional therapies. Twenty of the
patients had previously experienced some success
with conventional drug therapy, and were placed in
the first group. The second group of thirty
patients had not experienced erection following
conventional therapies.
Following treatment with
the ginkgo leaf extract, all patients in the first
group (20 men) regained sufficient and spontaneous
erections following six months of treatment.
Rigidity at both the tip and base of the penis were
found to significantly improve after six months.
The improvement continued through the nine-month
treatment period. Nineteen of the thirty patients
in the second group responded positively to the
treatment, while eleven remained impotent. No side
effects were reported in the study. This is only
the second study published on the use of ginkgo
leaf extracts in the treatment of impotence.
A Dutch research group has
produced a retrospective analysis of ginkgo
clinical studies, assessing their quality and
reliability based on a number of objective
parameters. They look at 40 clinical trials
published since 1975 on the use of Ginkgo extracts
in cerebral insufficiency. Clinical trials
reporting results in healthy volunteers were
excluded. The dosage was 120 mg/day of the ginkgo
extract (given for at least 4-6 weeks). Of the 40
studies, eight were considered to be well-performed
using rigorous scientific standards. The authors of
the retrospective stressed the need for additional
trials, in which double-blindness is checked, a
larger number patients are involved, with better
descriptions of randomization procedures, patient
characteristics, and more effective measurement of
data.
There is no doubt that
ginkgo leaf extracts are of clinical benefit for a
number of clinical conditions. More research will
be published in the next few years that will
further confirm ginkgo's utility.
References
- Sohn, M. and R.
Sikora. 1991. Ginkgo biloba extract in
the therapy of erectile dysfunction. J. Se
Educ. Ther. 17:53-61.
- Kleijnen, J and P.
Knipschild. 1992. Ginkgo biloba for cerebral
insufficiency. Br. J. Clin. Pharmac. 34:352358.
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