Medical Attributes of Ginkgo biloba - The Maidenhair Tree

by Desiree Carr, Rose Mary Bartoletti, and Amie D'Angelo
Wilkes University
Wilkes-Barre, PA

July, 1997

Ginkgo biloba L., the maidenhair tree (Kleijnen et al. 1992), is the sole member of the Ginkgoaceae (Tyler 1992). The species is at least 300 million years old (Anon. 1997a), and is currently native to China, though plants are cultivated worldwide as ornamentals.

The Chinese have used seeds of Ginkgo to treat various ailments including cancer, respiratory and circulatory problems, and impaired hearing. Seed extracts have also been used to promote sexual desire, and enhace longevity (Tyler 1992; Anon. 1997b). In contrast, Western medicine utilizes extracts obtained from Ginkgo biloba leaves for therapeutic purposes (Tyler 1992).

Ginkgo leaves contain two groups of active chemicals: flavoneglycosides and terpenoids. The flavoneglycosides include kaempferol, quercetin, and isorhamnetin with glucose or rhamnose. These chemicals have antioxidant abilities (Kleijnen and Knipschild 1992). The terpenoids include ginkgolides A, B, C, and bilobalide. The ginkgolides, especially ginkgolide B, are responsible for inhibiting platelet activating factor (PAF) (Anon. 1997c). PAF may cause certain conditions such as asthma, artherosclerosis, and stroke when the immune system is stressed (Anon. 1997b). These terpenoids help restore the motor nerves in bilobalide-treated animals (Bruno et al. 1993). When administered in doses of 10 mg/kg of body weight for 8 days, bilobalide may be useful in the treatment and prevention of Pneumocystis carinii. In the bilobalide-treated animals, the parasite was decreased by nearly 99% and no ill effects were experienced (Atzori et al. 1993).

The standard Ginkgo extract, EGb 761 (also called Tebofortan) (Hitzenberger 1992), used in clinical trials contains 24% flavoneglycosides and approximately 6% terpenoids (Anon. 1997c). Therefore, the therapeutic effects of Ginkgo biloba extract are attributed to a mixture of two groups of chemicals, not just a single entity (Anon. 1997b).

In Germany and France, where many general practitioners use alternative therapies (Rosslenbroich et al. 1994), Ginkgo biloba has been used as a modern phytomedicine since 1965 (Sticher 1993; Anon. 199 c). Ginkgo is presently used to treat symptoms of cerebral and vascular insufficiencies and free radical inhibition. Cerebral insufficiency, a medical term used to designate symptoms associated with poor blood circulation in the brain (Anon. 1997a), includes symptoms of confusion, memory lapse, lack of stamina, depression, tinnitus, and headaches (Anon. 1997c).

A study which focused on memory, stresses, and the patient's mood, concluded that the symptoms of cerebral insufficiency improved when treated regularly with the Ginkgo biloba extract (Vesper et al. 1994; Anon. 1997c).

A sample of 51 males and 61 females, between the ages of 55 and 94, and previously diagnosed with chronic cerebral insufficiency, received Ginkgo biloba extract daily in 120 mg doses for one year. These individuals showed significant decreases in symptoms including vertigo, headache, and tinnitus, as well as an improvement in their short-term memory and overall mood. No apparent side effects or drug interactions were noted (Vorberg 1985). A 24-week, double-blind study, involving 72 outpatients diagnosed with cerebral insufficiency concluded that EGb 761 extract improves mental performance especially in short-term memory after the sixth week of treatment with the extract (Grassel 1992).

A mechanism of Ginkgo biloba action is its ability to stimulate blood circulation to deprived areas of the body including the brain, limbs, and all of the blood vessels. This condition, vascular insufficiency, may result in visual disturbances, problems with memory, concentration, depression, vertigo, and even stroke (Anon. 1997b).

In a double-blind study, eight healthy females subjected to a Sternberg memory test showed a significant improvement in short-term memory when 600 mg of Ginkgo biloba extract was administered in comparison to a placebo (Hindmarch 1986). Thus, Ginkgo biloba implies improved blood circulation to the brain.

Daily treatment with Ginkgo biloba extract at 100 mg/kg orally or 20 mg/kg intraportioneally for three weeks showed a significant rise in the survival rates of rats with induced cerebral ischemia. In addition, more animals did not exhibit any clinical symptoms of this disorder (Larsen et al. 1979).

The efficiency of EGb 761 was tested on rabbits subjected to 30 minutes of regional cardiac ischemia and 120 minutes of reperfusion. Subjects treated with 10 mg/kg of the extract did not show an increase in lipid peroxidation and both a decrease in tissue type plasminogen activator and an increase in plasminogen activator inhibitory caused by ischemia-reperfusion were suppressed. Thus, the ginkgo extract demonstrated antioxidant properties and its ability to adjust to fibrinolytic activity in guarding the heart (Shen et al. 1995). However, additional work needs to be done on testing this mechanism.

Free radicals created in metabolism may cause damage to the body and may cause blindness, atheroscleriosis, cancer, diabetes, and other degenerative diseases. Flavonoids in EGb 761 are responsible for its antioxidant activity and may prevent free radical damage from occurring (Anon. 1997b). EGb 761 has been found useful in the treatment of retinal impairment in diabetes (Doly et al. 1986). A significant improvement of amplitude in the electro retinograms resulted from administering 100 mg/day of the extract for two months in alloxan-induced diabetic rats (Doly 1992). The free radical scavenger, EGb 761, improves the ionic homeostasis in injured retinal cells (Droy-Lefaix et al. 1993), making it an effective antioxidant in the brain, retina, and cardiovascular system" (Anon. 1997c).

The neuroprotective effects of Ginkgo biloba extracts was tested on animals with cerebral ischemia by measuring the infarct areas of rat and mouse brains after two days. The results showed that the extract had different types of neuroprotective and cerebrovascular effects. When bilobalide was administered to the infarct areas in 10 mg/kg doses one hour prior to occlusion to the middle cerebral artery, the cortical and infarct volume decreased substantially. Ginkgolides A and B showed cerebroprotective effects in the mouse model while ginkgolides C and J did not. After ten minutes, EGb 761 showed an increase in the cerebral blood flow in the rat model. However, neuroprotection was not found (Krieglstein, et al. 1995).

Tinnitus and other hearing disorders may be caused by either free radical damage or a disturbance in the blood supply (Anon. 1997 b). Because there is no objective method in measuring tinnitus, EGb 761 needs to be tested on an individual basis. According to statistical group analysis, there is no support that Ginkgo biloba can treat tinnitus (Holgers et al. 1994). However, in an out-patient study consisting of 103 individuals suffering from this disorder, Ginkgo extract did improve their conditions (Meyer 1986). When laser therapy was combined with EGb 761, 50% of the 20 individuals tested showed a reduction in tinnitus (Olivier and Plath 1993).

EGb 761 has proven to be beneficial in treating intellectual deficiency, equilibrium disturbances (Hitzenberger 1992), and is a remedy for some symptoms of premenstrual syndrome (Tamborini et al. 1993). EGb 761 also promotes hair regrowth in C3H strain mice (Kobayashi et al. 1993). Recent studies have also shown that EGb 761 is a valid treatment for dementia and has been approved by the German BGA as an effective drug for this disesase (Itil et al. 1995). An extremely purified extract of Ginkgo biloba may also be successful in preventing organ rejection following transplants. It is less toxic than Cyclosporine, the drug used currently (Anon. 1997c).

Consuming Ginkgo biloba yields few, if any, adverse effects. When administered in large doses, it may cause nausea, diarrhea, restlessness, and other mild discomforts. Additionally, Ginkgo biloba extracts may reduce blood clotting, thus posing a danger to people taking anticoagulants (Tyler 1992).

Even though Ginkgo biloba is one of the world's most popular over-the-counter medicines (Bricklin 1995), the US Food and Drug Administration has not granted its approval as one of the nine herbs used for medicinal relevancy in the United States (Youngkin et al. 1996).

 

LITERATURE CITED

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This paper was developed as part of the BIO 368 - Medical Botany course offered at Wilkes University during the summer of 1997. Course instructor was Kenneth M. Klemow, Ph.D. (kklemow@wilkes.edu). The information contained herein is based on published sources, and is made available for academic purposes only. No warrantees, expressed or implied, are made about the medical usefulness or dangers associated with the plant species in question.

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This page posted and maintained by Kenneth M. Klemow, Ph.D., Biology Department, Wilkes University, Wilkes-Barre, PA 18766. (570) 408-4758, kklemow@wilkes.edu.