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November 19, 2008

Ginkgo biloba Extract and Preventing Alzheimer Disease

JAMA. 2008;300(19):2306-2308. doi:10.1001/jama.2008.675

Ginkgo biloba leaves and extracts are widely used over-the-counter preparations marketed in the United States as food supplements or nutraceuticals, and as such, explicit health claims are not listed in their labeling. In other countries and in the popular press, G biloba is advocated for the treatment of a broad and seemingly ever-increasing range of medical conditions.

The extract used in the Ginkgo Evaluation of Memory (GEM) study reported in this issue of JAMA by DeKosky and colleagues1 and in many other clinical and preclinical studies is Ginkgo extract EGb 761 (Schwabe Pharmaceuticals, Karlsruhe, Germany). The extract is standardized to contain 2 major constituents: 22% to 27% flavonoids and 5% to 7% terpene lactones (ginkgolides and bilobalide).2 Unique to G biloba trees, the terpene lactones consist of several ginkgolides and bilobalide.2,3 The flavonoids and ginkgolides have protean biological activity in preclinical research. The flavonoids are active as antioxidants and appear neuroprotective.2,4 Ginkgolide B is a potent antagonist of the platelet activating factor receptor.5 Ginkgolides A and J variously inhibit hippocampal neuron dysfunction and neuronal cell death caused by amyloid beta protein-42 (Aβ42).6,7 Ginkgolides A and J decrease Aβ42-induced pathological behaviors,8 enhance neurogenesis in animal models of Alzheimer disease,9 and inhibit Aβ aggregation,10 providing considerable rationale for G biloba extracts as potential treatments for Alzheimer disease. Some of the components of G biloba extract are as active in preclinical models of neurodegeneration and Alzheimer disease as new drug candidates being developed by pharmaceutical companies and some research universities.