The effects of EGb 761 on the CNS underlie one of its major therapeutic indications; i.e., individuals suffering from deteriorating cerebral mechanisms related to age-associated impairments of memory, attention and other cognitive functions. EGb 761 is currently used as symptomatic treatment for cerebral insufficiency that occurs during normal ageing or which may be due to degenerative dementia, vascular dementia or mixed forms of both, and for neurosensory disturbances. 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" effect, EGb 761 acts via its ginkgolide constituents to decrease the expression of the peripheral benzodiazepine receptor (PBR) of the adrenal cortex.

Recent studies conducted with various molecular, cellular and whole animal models have revealed that leaf extracts of Ginkgo biloba may have anticancer (chemopreventive) properties that are related to their antioxidant, anti-angiogenic and gene-regulatory actions. The antioxidant and associated anti-lipoperoxidative effects of Ginkgo extracts appear to involve both their flavonoid and terpenoid constituents. The anti-angiogenic activity of the extracts may involve their antioxidant activity and their ability to inhibit both inducible and endothelial forms of nitric oxide synthase. With regard to gene expression, a Ginkgo extract and one of its terpenoid constituents, ginkgolide B, inhibited the proliferation of a highly aggressive human breast cancer cell line and xenografts of this cell line in nude mice. cDNA microarray analyses have shown that exposure of human breast cancer cells to a Ginkgo extract altered the expression of genes that are involved in the regulation of cell proliferation, cell differentiation or apoptosis, and that exposure of human bladder cancer cells to a Ginkgo extract produced an adaptive transcriptional response that augments antioxidant status and inhibits DNA damage. In humans, Ginkgo extracts inhibit the formation of radiation-induced (chromosome-damaging) clastogenic factors and ultraviolet light-induced oxidative stress - effects that may also be associated with anticancer activity. Flavonoid and terpenoid constituents of Ginkgo extracts may act in a complementary manner to inhibit several carcinogenesis-related processes, and therefore the total extracts may be required for producing optimal effects.

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Ginkgo biloba leaf extract (EGb 761), which contains many constituents, including flavonoid glycosides and terpenoids (ginkgolides, bilobalide), is used to treat cerebrovascular and peripheral vascular insufficiency, as well as cognitive impairment and other symptoms of dementia. Recent studies have indicated that these therapeutic effects of EGb 761 probably involve modification of the expression of many genes by actions involving several of its active constituents. As examples: EGb 761 and its ginkgolide B constituent inhibit the expression of the peripheral benzodiazepine receptor in the adrenal cortex and decrease circulating levels of corticosterone in the rat, effects that provide a mechanism for explaining the ''antistress'' action of the extract. Both the flavonoid and terpenoid constituents of EGb 761 decrease the expression of inducible nitric oxide synthase (iNOS), supporting an action of the extract of opposing the deleterious effects of excessive formation of NO. EGb 761 upregulates several genes that encode vital antioxidant enzymes, including heme oxygenase-1 and the regulatory and catalytic subunits of g-glutamyl-cysteinyl synthetase. Dietary treatment of mice with EGb 761 upregulates the expression of genes encoding neuronal tyrosine/threonine phosphatase 1 and microtubule-associated tau in the cerebral cortex, findings that are of interest since these proteins are associated with the intracellular neurofibrillary tangles found in the brain in Alzheimer's disease. Bilobalide upregulates two mitochondrial-DNA-encoded genes, subunit III of cytochrome c oxidase and subunit ND1 of NADH dehydrogenase, indicating a fundamental mechanism that may underlie EGb 761-induced neuroprotection. Collectively, such results indicate that the therapeutic effects of EGb 761 on cognitive impairment (dementia) may involve its action of altering gene expression. Drug Dev.