Ginkgo biloba

Two key active ingredients in ginkgo biloba are terpene lactones (notably ginkgolides and diterpenes) and ginkgo flavone glycosides (notably ginkgetin, bilobetin, and sciadopitysin), which are present at varying concentrations. Ginkgo biloba extract EGb 761 is the standardized extract of ginkgo biloba used in studies, which contains 6% terpenoids and 24% flavonoid glycosides. Animal studies have shown that ginkgo biloba works on several neurotransmitter pathways and brain structures. Flavones were shown to inhibit lipid peroxidation; inhibit the uptake of serotonin, dopamine, and norepinephrine; and inhibit platelet aggregation. Terpene lactones may also act as potent antagonists of the platelet-activating factor and may possess anti-ischemic and fibrinolytic effects. They were also shown to downregulate adrenal peripheral benzodiazepine receptors and increase adrenocorticotropic hormone levels. Ginkgo biloba also reversibly inhibits monoamine oxidase A; and modestly inhibits anticholinesterase activity, leading to enhanced cholinergic transmission in the brain.

Several studies suggest that ginkgo biloba exerts neuroprotective effects by reducing free radical production in the prefrontal cortex, which may explain its improvement on short-term memory. Ginkgo biloba extract acts as a free radical scavenger, protecting neurons from oxidative damage and apoptosis related to aging, cerebral ischemia, and neurodegenerative disorders. Ginkgo biloba also inhibits amyloid-β neurotoxicity and protects against hypoxic challenges and increased oxidative stress. One study showed that bilobalide, a terpene lactone, delays the onset of hypoxic glycolysis. Ginkgo biloba has the potential to regulate metabolism, stabilize the membrane, and promote vasodilation. In the arterial endothelium, EGb stimulated the release of endogenous relaxing factors, such as endothelium-derived relaxing factor and prostacyclin. In the inflammatory environment that causes tissue damage, EGb promoted nitric oxide production, leading to enhanced peripheral and cerebral blood flow.