Cognitive Function & Ginkgo
A supplemental combination of Ginkgo biloba and Panax ginseng may help to improve memory in middle-aged adults, according to this double-blind, placebo controlled study conducted on 256 healthy volunteers. Subjects received placebo, 160 mg ginseng/ginkgo twice a day, or 320 mg ginseng/ginkgo once a day for 14 weeks. The ginseng/ginkgo preparation contained 60 mg of standardized Ginkgo biloba extract and 100 mg of standardized Panax ginseng extract. Participants reported an average 7.5% improvement in memory, with improvements in long-term, working, and short-term memory. This effect lasted through the supplementation period and for two weeks after discontinuation.
Wesnes KA, Ward T, McGinty A, Petrini O: The memory enhancing effects of a Ginkgo biloba/Panax ginseng combination in healthy middle-aged volunteers, Psychopharmacology (Berl) 2000 Nov;152(4):353-61
Mechanism of Action
Mechanism of Action
Ginkgo biloba extract may increase levels of polyunsaturated fatty acids (PUFAs) and prevent oxidative damage to red blood cells, according to this study conducted in vivo on cellular lipids (fats) and function. Ginkgo extract was shown to significantly increase circulating PUFA levels, subsequently decreasing the saturated:unsaturated ratio. Red blood cell membranes also exhibited increased PUFA levels after ginkgo treatment, and experienced improved resistance to oxidative damage (induced by hydrogen peroxide).
Drieu K, et al: Effect of the extract of ginkgo biloba (EGb 761) on the circulating and cellular profiles of polyunsaturated fatty acids: correlation with the anti-oxidant properties of the extract, Prostaglandins Leukot Essent Fatty Acids 2000 Nov;63(5):293-300
Ginkgo biloba extracts may protect nerve cells against oxidative damage; however, different extracts probably differ in their effectiveness, according to this lab study. Researchers tested the effects of two different ginkgo extracts on cultured neurons exposed to oxidative stress. Neurons that did not receive ginkgo only exhibited a 50 percent survival rate. However, treatment with ginkgo dramatically increased the number of viable neurons, but each extract exhibited different hydroxyl-radical-scavenging capacities.
Guidetti C, et al: Prevention of neuronal cell damage induced by oxidative stress in-vitro: effect of different Ginkgo biloba extracts, J Pharm Pharmacol 2001 Mar;53(3):387-92
Large amounts of ginkgo may induce convulsions, according to this case report of a 36-year old woman, without past history of epilepsy/seizure. The woman consumed 70-80 ginkgo nuts, and about four hours later experienced generalized convulsions and vomiting. The authors conclude that large amounts of ginkgo notes have the potential to induce convulsions and neurotoxicity.
Miwa H, Iijima M, Tanaka S, Mizuno Y: Generalized convulsions after consuming a large amount of gingko nuts, Epilepsia 2001 Feb;42(2):280-1
Ginkgo biloba's antioxidant properties may be attributed to its action as a free radical scavenger, according to this study performed on rats. The rats were subjected to 21 days of chronic hypoxia and then given either 25 or 50 mg/kg doses of ginkgo biloba extract. Rats that received doses of the extract had decreased production of oxygenated free radicals compared to control animals, and the higher dose had a greater effect than the smaller one. In this study, the extract showed no antioxidant enzyme activity toward red blood cells.
Louajri A, Harraga S, Godot V, Toubin G, Kantelip JP, Magnin P: The effect of ginkgo biloba extract on free radical production in hypoxic rats, Biol Pharm Bull 2001 Jun;24(6):710-2
Complex with Phospholipids
Complex with Phospholipids
The complexation of ginkgo biloba with phospholipids may increase its bioavailability and therefore enhance its antioxidant activity, according to this study conducted on rats. The rats were given oral doses of either ginko biloba extract (GB) or GB embedded in phosphatidylcholine (PC) for five days, and then TRAP and FRAP assays were used to determine their total plasma antioxidant capacity. Only the GB-PC complex significantly increased the total plasma antioxidant defense. The rats' hearts were also subjected to ischemia and reperfusion to compare the cardioprotective effects of GB and GB-PC. After reperfusion, the percentage recovery of left ventricular developed pressure was measured as 35-40% in control and vehicle rats, 50.2% in GB rats, and 72.5% in GB-PC rats. Creatine kinase outflow was lower in the hearts of the GB and GB-PC treated animals than in control animals. GB and GB-PC treatment also increased the rate of prostacyclin release.
Carini M, Aldini G, Rossoni G, Morazzoni P, Facino RM: Complexation of ginkgo biloba extract with phosphatidylcholine improves cardioprotective activity and increases the plasma antioxidant capacity in the rat, Planta Med 2001 Jun;67(4):326-30
Ginkgo biloba extract may counter-act neurological disorders by altering gene expression in the cortex and hippocampus, according to this study conducted on mice. Analysis of mRNA transcription levels using high-density oligonucleotide microarrays were performed to find those genes most affected by ginkgo biloba supplementation. The analysis revealed that ginkgo biloba extract caused an increase in neuronal tyrosine/threonine phosphatase 1 and microtubule-associated tau in the cortex. This is significant because hyperphosphorylated tau is a causal agent of Alzheimer's disease. Ginkgo also caused an up-regulation of alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid, calcium and chloride channels, prolactin, and growth hormone in the cortex. In the hippocampus, the only gene affected by ginkgo was transthyretin, which is involved in hormone transport in the brain.
Watanabe CM, Wolffram S, Ader P, Rimbach G, Packer L, Maguire JJ, Schultz PG, Gohil K: The in vivo neuromodulatory effects of the herbal medicine ginkgo biloba, Proc Natl Acad Sci USA 2001 Jun 5;98(12):6577-80
Induction of Antioxidant Response
Induction of antioxidant response
Ginkgo biloba may enhance the transcription level of mRNAs associated with intracellular transport, mitochondria, and antioxidants, according to this study conducted on a human bladder cancer cell line. After the cells were incubated in a solution with Ginkgo biloba extract, an analysis of their subsequent transcriptional response revealed that there was an overall increase in transcription. The extract's effects were associated with increases in the manufacturing of enzymes, proteins, and transcripts related to DNA repair and synthesis. Therefore the extract may be responsible for amplifying the cell's antioxidant status and inhibiting DNA damage.
Gohil K, Moy RK, Farzin S, Maguire JJ, Packer L: mRNA expression profile of a human cancer cell line in response to ginkgo biloba extract: induction of antioxidant response and the golgi system, Free Radic Res 2001 Dec;33(6):831-849
Alzheimer's disease & Ginkgo
Ginkgo biloba extract may help improve cognition in patients with mild cognitive impairment, according to this randomized, double-blind, placebo-controlled study. The participants were categorized into three groups according to their scores on the Mini-Mental State Examination score. Those who scored higher than 23 were categorized as having mild cognitive impairment, while those who scored 23 or lower were considered moderate, and those with scores lower than 15 were considered severe. To assess changes in cognitive skills, the Alzheimer's Disease Assessment Scale (ADAS-Cog) and the Geriatric Evaluation by Relative's Rating Instrument (GERRI) were used.
Participants in the mild group who received the extract showed improvement over the placebo group by increasing their ADAS-Cog score by 1.7 points and their GERRI score by 0.09 points. Patients in the moderate group that received ginkgo extract showed a 60% less decline on the ADAS-Cog than those who received placebo. In the most severely impaired group, the extract decelerated cognitive deterioration that was pronounced in those receiving placebo. Therefore, the gingko biloba extract may improve cognitive symptoms in patients with very mild to mild cognitive impairment and slow the decrease of cognitive functioning in those with severe symptoms.
Le Bars, Velasco FM, Ferguson JM, Dessain EC, Kieser M, Hoerr R: Influence of the severity of cognitive impairment on the effect of the ginkgo bikoba extract EGb 761(®) in Alzheimer's disease, Neuropsychobiology 2002 Jan;45(1):19-26