Ginkgo biloba extract has demonstrated neuroprotective effects in a variety of animal models and has improved or maintained cognitive function in AD patients.
Ginkgo biloba exerts vaso-regulatory actions that protect blood vessels and help explain its effectiveness in managing cerebral insufficiency states, neurosensory disturbances and peripheral occlusive arterial disease. Additionally, Ginkgo biloba extract has been shown to abolish Abeta-induced ROS generation and to protect, in a dose-dependent manner, against Abeta-induced apoptosis and neurotoxicity.
Ginkgo biloba extract also inhibits, in a dose-dependent manner, the formation of Abeta-derived soluble neurotoxic oligomers. These diffusible, nonfibrillar ligands derived from Abeta are potent CNS neurotoxins, which assemble when fibril formation is inhibited, and kill neurons at nonomolar concentrations. Soluble ligands of Abeta have been found in AD brains, where their levels were 12-fold higher than those present in normal brains.49
A study published in the May 2004 issue of the Journal of Neuroinflammation reported that brain cells pre-treated with nanomolar concentrations of Ginkgo biloba extract before exposure to beta-amyloid protein were resistant to its toxic effects and survived without damage.50
In vitro research conducted at Georgetown University Medical Center, Washington, D.C., confirmed that nerve cells exposed to Abeta experience increased ROS production and cellular death. If pre-treated with Ginkgo biloba extract, however, ROS production, cellular damage and death were all inhibited.52 Likewise, a study at the University of Southern Mississippi found that brain cells treated with Ginkgo biloba extract were resistant to the damaging effects of Abeta.53
In vivo research conducted at Georgetown University Medical Center suggests that the mechanism through which Gingko biloba inhibits Abeta formation and rescues neuronal cells from Abeta-induced cell death involves its ability to decrease the capacity of low density lipoproteins (LDL) to carry free cholesterol to various tissues without affecting the capacity of high-density lipoproteins (HDL) to carry cholesterol back to the liver.
High cholesterol levels affect APP generation and Abeta processing since one of the physiological functions of APP and Abeta is to control free cholesterol transport. High levels of free cholesterol induce over-production of APP mRNA expression and Abeta. Specifically, in the presence of high cholesterol levels, APP synthesis (expression) is increased, and the processing of APP for the formation of Abeta and Abeta peptide fragments is enhanced. In addition, Abeta increases the capacity of lipoprotein and apolipoprotein to carry free cholesterol, which may explain the link between the ApoE4 genotype and increased risk for cardiovascular disease as well as AD.
In additional research conducted at Georgetown, long-term treatment of aging Brown Norway rats with Gingko biloba extract lowered production of brain APP and Abeta by decreasing the capacity of LDL to carry free cholesterol, thus lowering levels of circulating free cholesterol. These in vivo results indicate a mechanism through which Gingko biloba extract inhibits the cerebral amyloidogenesis and Abeta angiopathy that characterize all forms of AD.54
Inhibition of PST
There is some concern that Ginkgo Biloba may inhibit the action of the enzyme PST (phenolsulfotransferase) which processes phenols and prevents their build up. Excess phenols are associated with symptoms such as hyperactivity.
See the page on Sulfation Deficits for tips on how to counteract the possible negative side effects of Ginkgo Biloba.
Some people become concerned when they read that ginkgo can have toxic effects but that is with the raw seeds or poor quality extracts. Good quality extracts such as Ginkgold, Nature's Way and Tebonin have had these chemicals removed.
Many parents prefer to use liquid Ginkgo extract such as that from Honeycombs Herbs and Vitamins