Ginkgo biloba Extracts and Alzheimer’s Disease Adapted from presentation by Erik Domingues, M.D. Alzheimer’s Disease (AD) • Progressive brain disorder • Accompanied by behavioral changes • Develops mostly in people 65 and over • Genetic predisposition • Certain health conditions may contribute to AD development • Incurable Biological Characteristics of AD • Neuronal cell atrophy • Amyloid- (A) precursor protein (APP) is cleaved by - and γ-secretase to A • Deposition of A plaques and neurofibrillary tangles in hippocampus and cortex • A induces apoptosis (programmed cell death) in normal neurons • Higher levels of oxidative damage • Deficiency in neurotransmitters such as acetylcholine Ginkgo biloba • Ginkgoaceae family • Also known as maidenhair tree • World’s oldest tree species • Thought to improve cerebral circulation • Dosage of 40-200 mg/day recommended • Cognitive enhancer • May be beneficial in reducing AD onset • Some side effects (GI, headache) Animal Trials ofGinkgo • Several trials used a standardized extract of Ginkgo biloba, EGb761 • EGb761 composition: – 5-7% terpene lactones (TTLs) • Ginkgolides A, B, C, J, and M and bilobalide (BB) – 22-24 % flavonols • Quercetin, kaempferol, isorhamnetin – max 5 ppm ginkgolic acid Origin? • toxic, allergenic Ginkgolides and Bilobalide in EGb716 Flavonols in EGb761 OH OH HO HO O O OH OH OH OH OH O O Kaempferol Quercetin OH HO O OMe OH OH O Isorhamnetin • Effects of Ginkgo extract from animal studies – Spatial memory deficits – A buildup (plaque formation) – Apoptosis of neuronal cells and activation of caspases – Cholesterol-lowering effect • Epidemiological study EPIDOS - France • Study used a Tg2576 mouse model and Ginkgo extract EGb761 – This mouse overexpresses APP, gets A plaque deposits and exhibits oxidative stress in its brain • Mice were treated for 6 months with EGb761 at 70 mg/kg/day A Morris water maze was used to test the effects of the extract on the mice Spatial memory impairment was reduced in the Ginkgo treated mice Blueberries have also been shown to improve performance in similar tests by Joseph, et al • Studied effects of EGb761 on A buildup, caspase-3 • • activity (enzyme controlling apoptotic cascade), and induction of apoptosis in neuroblastoma cells A proliferation was prevented Apoptosis rates and associated caspase-3 activity decreased with treatment • Effect of EGb761 on A-induced neurotoxicity in PC12 • • • • • nerve cells was tested Exposure to A for 12 or 24 hours increased ROS levels Treatment decreased ROS production in a dosedependent manner Simultaneous treatment with EGb761 and A decreased cell death compared to exposure to A alone Anti-apoptotic effects were only seen when the cells were treated simultaneously with EGb761 and A Treatment with a different extract was not neuroprotective • Free cholesterol may be involved in APP and A production • Study analyzed effects of EGb761 on free cholesterol levels and • • amyloidogenesis An increase in A and APP production is observed in presence of cholesterol As Brown Norway rats age, A levels increased – EGb761 decreased the plaques significantly – APP levels in cerebral cortex and hippocampus were decreased • EGb761 treatment – reduced free cholesterol by 16% – reduced amount of free cholesterol binding to low density proteins – decreased influx of cholesterol and increased efflux from neuronal cells • Study used a different Ginkgo extract, GbE – 26 % flavone glycosides and 6 % diterpene lactones • • • • Effects of GbE on caspase-3 and APP Rats were treated for 14 days with 100 mg/kg of GbE APP level higher in treated rats (less cleavage to A) Caspase-3 levels were higher in treated rats – Caspase-3 had been shown to convert APP to A • A case study involving 414 women in France • Women diagnosed with AD were older, had a lower financial status, and a lower educational level, and were less knowledgeable about their health – The only difference between these women and the undiagnosed was the lack of vasotherapeutic treatment • Women in the group without dementia were three • times more likely to be regularly taking treatments like Ginkgo than women in the group with dementia About 50 % of these women reported taking EGb761 In summary, Ginkgo extract • Decreased A proliferation • Decreased apoptotic activity • Increased neuronal cell viability • Decreased free cholesterol levels, linked to less amyloid formation • Improved cognitive performance in rats • Was linked to decreased incidence of AD in French women • Keeps brain cells healthier! • • • • • • • • • • • • • References  Alzheimer’s Disease. www.encarta.com, 2006.  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