The special Ginkgo biloba extract (EGb 761®) has been shown to exert beneficial effects in the therapy of age-related neurological disorders such as Parkinson's and Alzheimer's disease [1]. Besides neuroprotective effects, EGb 761® has been demonstrated to improve cognitive functions in animal models [2] and in clinical studies [3]. Thus, it was the aim of the present study to investigate whether EGb 761® influences monoamine levels in brain areas implicated in cognitive function, motivation and mood behaviour. For this purpose, the effect of sub-chronic (14 days) daily administration of EGb 761® on basal extracellular levels of dopamine (DA), noradrenaline (NA) and serotonin (5-HT) were monitored by microdialysis in the prefrontal cortex of awake rats. Administration of EGb 761® at a dose of 100mg/kg p.o., caused a significant increase in DA levels during 40–180min, reaching a maximum level of 163% of the control group. The extracellular levels of NA increased only by about 120% and the concentrations of 5-HT were not changed from the pre-drug levels. These findings supports previous observations suggesting that Ginkgo biloba extracts could increase monoaminergic function via inhibition of MAO activity. However, the minimal effects on NA and 5-HT concentrations indicate that EGb 761® may affect brain monoaminergic system also through other mechanisms than direct inhibition of MAO activity. These results suggest that treatment with EGb 761® can lead to increased dopaminergic function in the prefrontal cortex which may be an underlying factor to clinically observed effects on improved cognitive function. References: 1. Andrieu, S. et al. (2003), J. Gerontol. A Biol. Sci. Med. Sci. 58: 372–377. 2. Muller, W.E., Chatterjee, S.S. (2003), Pharmacopsychiatry 36 (Suppl.1): S24. 3. Mix, J.A., Crews, W.D. (2002), Hum. Psychopharmacol. Cli
Depressive symptoms of patients with Alzheimer's disease (AD) and aged non-Alzheimer patients may also respond to treatment with EGb 761 since this extract has an "anti-stress" effect. Basic and clinical studies, conducted both in vitro and in vivo, support these beneficial neuroprotective effects of EGb 761. EGb 761 has several major actions; it enhances cognition, improves blood rheology and tissue metabolism, and opposes the detrimental effects of ischaemia. Several mechanisms of action are useful in explaining how EGb 761 benefits patients with AD and other age-related, neurodegenerative disorders. In animals, EGb 761 possesses antioxidant and free radical-scavenging activities, it reverses age-related losses in brain alpha 1-adrenergic, 5-HT1A and muscarinic receptors, protects against ischaemic neuronal death, preserves the function of the hippocampal mossy fiber system, increases hippocampal high-affinity choline uptake, inhibits the down-regulation of hippocampal glucocorticoid receptors, enhances neuronal plasticity, and counteracts the cognitive deficits that follow stress or traumatic brain injury. Identified chemical constituents of EGb 761 have been associated with certain actions. Both flavonoid and ginkgolide constituents are involved in the free radical-scavenging and antioxidant effects of EGb 761 which decrease tissue levels of reactive oxygen species (ROS) and inhibit membrane lipid peroxidation. Regarding EGb 761-induced regulation of cerebral glucose utilization, bilobalide increases the respiratory control ratio of mitochondria by protecting against uncoupling of oxidative phosphorylation, thereby increasing ATP levels, a result that is supported by the finding that bilobalide increases the expression of the mitochondrial DNA-encoded COX III subunit of cytochrome oxidase. With regard to its "anti-stress"
Numerous well-controlled clinical studies, realized in Europe and in USA, have revealed that EGb 761 is an effective therapy for a wide variety of disturbances of cerebral function, ranging from cerebral impairment of ischemic vascular origins (i.e. multi infarct dementia), early cognitive decline to mild-to-moderate cases of the more severe types of senile dementias (including Alzheimer's disease) or mixed origins (i.e. psychoorganic origin). Improvement of signs and symptoms have been demonstrated for cognitive functions, particularly for memory loss, attention, alertness, vigilance, arousal and mental fluidity. Some clinical studies have showed that EGb 761 treatment may improve the capacity of geriatric patients to cope with the stressful demands of daily life. The explanation is a dual stress-alleviating action of EGb 761: its facilitates behavioral adaptation to stress and may decrease the excess of cortisol release to stress. Moreover, EGb 761 shows a specific neuroprotective effects to hippocampic cells. Regarding the visual system, experimental studies have shown that EGb 761 can inhibit or reduce the functional retinal impairments resulting from ischemia-reperfusion, photo-degeneration, diabetic or proliferative retinopathy. Clinical studies have revealed that EGb 761 may be useful in treating visual activity impairments and damages to the visual field associated with chronic cerebrovascular insufficiency, senile macular degeneration and diabete mellitus. Regarding the vestibular and auditory systems, experimental and clinical studies have shown the efficacy of EGb 761 in treating hypoacusis, tinnitus, vertigo, dizziness and other symptoms of vestibulocochlear disorders. At least, adequatly controlled studies in patients with peripheral arterial occlusive disease have provided good evidence for therapeutic efficacy in intermittent claudication. The future of EGb 761 is undoubtedly in the promise in slowing the progression of Alzheimer's disease. Indeed, two recent american clinical studies have shown the efficacy and safety of EGb 761 in patients with mild to severe Alzheimer's disease and multi-infarct dementia. In clinical terms, progression of symptoms was delayed by approximately 6 months. Actually new clinical studies are undertaken in USA and Europe. At the dawn of the third millenium (the Sixth for Ginkgo biloba) we propose a state of art about it.
Ginkgo also benefits vascular microcirculation by improving blood flow in small vessels and has antioxidant activity. There has been conflicting evidence about the benefits of ginkgo, e.g. the ginkgo clinical trial published in August 2002 in JAMA concluded that a leading ginkgo supplement did not produce measurable benefits for memory in healthy adults over 60, although a month earlier, another study concluded that the same ginkgo extract is effective in helping normal healthy older adults in memory and concentration. However, in December 2002, the Cochrane Collaboration, the world's most respected scientific reviewer of clinical trials in medicine, concluded that the published literature strongly supports the safety and potential benefits of ginkgo in treating memory loss and cognitive disorders associated with age- related dementia. A phase II study of EGb 761 in combination with fluorouracil is in progress in Germany in patients with pancreatic cancer. German researchers are investigating the potential of EGb 761 for the treatment of sudden deafness and tinnitus in clinical studies. EGb 761 was undergoing preclinical development for the potential treatment of diabetes in France, diabetic neuropathies in Russia, and cancer in Brazil. However, there has been no recent development for these indications.
