The antioxidant action of myricetin and quercetin, the flavonoid constituents of the extract of Ginkgo biloba (EGb), on oxidative metabolism of brain neurons dissociated from the rats was examined using 2', 7'-dichlorofluorescin (DCFH) which is retained within the neuron and then is oxidized by cellular hydrogen peroxide to be highly fluorescent. Incubation with myricetin or quercetin reduced the oxidation of DCFH in resting brain neurons, more profoundly than EGb. Myricetin decreased the oxidative metabolism at concentrations of 3 nM or more. It was 10 nM or more for the case of quercetin. Incubation with each flavonoid constituent also reduced the Ca(2+)- induced increase in the oxidative metabolism without affecting the cellular content of DCFH or the intracellular concentrations of Ca2+. Such an antioxidant action of myricetin or quercetin may be responsible for a part of the beneficial effects of EGb on brain neurons subject to ischemia.

Oyama Y Hayashi A Ueha T

Ca(2+)-induced increase in oxidative metabolism of dissociated mammalian brain neurons: effect of extract of ginkgo biloba leaves.

In: Jpn J Pharmacol (1993 Apr) 61(4):367-70

Effect of an extract of Ginkgo biloba leaves (EGb) on oxidative metabolism was studied using rat brain neurons and 2', 7'- dichlorofluorescin fluorescence. Ionomycin (100 nM to 1 microM), a Ca(2+)-ionophore, dose-dependently augmented the 2', 7'- dichlorofluorescin fluorescence in the presence of external Ca2+, but not under the external Ca(2+)-free condition. Preincubation of neurons with EGb (3 micrograms/ml) greatly reduced the ionomycin- induced increase in 2', 7'-dichlorofluorescin fluorescence. Results suggest that EGb may reduce the Ca(2+)-induced increase in the oxidative metabolism of brain neurons.

Oyama Y Ueha T Hayashi A Chikahisa L Noda K

Flow cytometric estimation of the effect of Ginkgo biloba extract on the content of hydrogen peroxide in dissociated mammalian brain neurons.

In: Jpn J Pharmacol (1992 Dec) 60(4):385-8

The effect of Ginkgo biloba extract (GBE) on the content of hydrogen peroxide was estimated in cerebellar neurons dissociated from rats, by means of a flow-cytometer and 2', 7'-dichlorofluorescein (DCF) diacetate, a fluorescent dye for intracellular hydrogen peroxide. The GBE started to reduce the DCF fluorescence of the neuron at 0.1 microgram/ml to 0.3 microgram/ml. Further increases in the GBE concentration (up to 3 micrograms/ml) produced a dose-dependent decrease in the DCF fluorescence, suggesting that GBE reduces the content of hydrogen peroxide or suppresses the reactive oxygen species (ROS) formation of cerebellar neurons. The present technique may be useful for preliminary evaluations of agents affecting the ROS formation in mammalian brain neurons.

Petkov VD Kehayov R Belcheva S Konstantinova E Petkov VV Getova D Markovska V

Memory effects of standardized extracts of Panax ginseng (G115), Ginkgo biloba (GK 501) and their combination Gincosan (PHL-00701).

In: Planta Med (1993 Apr) 59(2):106-14

In experiments on young (aged 3 months) and old (aged 26 months) rats, using some conditioned-reflex methods with punishment or positive reinforcement for active and passive avoidance (shuttle-box, step-down, step-through, and water maze), we studied the effects of the standardized extracts of Panax ginseng (G115), Ginkgo biloba (GK501) and their combination Gincosan (PHL-00701). The extracts were administered orally for 7 days before training at three increasing doses: 17, 50, and 150 mg/kg for G115; 10, 30, and 90 mg/kg for GK501; and 27, 80, and 240 mg/kg for PHL-00701. The two extracts and their combination improved the retention of learned behavior. This effect varied considerably with the extracts, with the dose and with the behavioral method used. The results suggest that the Panax ginseng G115 and the Ginkgo biloba GK501 extracts possess properties similar in every respect to those of nootropic drugs. The favorable effects on learning and memory of the combination of G115 plus GK501 and the other pharmacological activities inherent in the extracts characterize this combination, offered as Gincosan as a particularly promising drug in geriatric practice.

Pidoux B

[Effects of Ginkgo biloba extract on functional brain activity. An assessment of clinical and experimental studies]

Effets sur l'activite fonctionnelle cerebrale de l'extrait de Ginkgo biloba. Bilan d'etudes cliniques et experimentales.

In: Presse Med (1986 Sep 25) 15(31):1588-91

Electroencephalography is the only convenient method for functional exploration of the brain and recent developments allows for pharmacological studies of electoencephalograms. Using such techniques has confirmed those of clinical trials, and notably the activity of Ginkgo on alertness.

Pidoux B., Bastien C., Niddam S.:

Clinical and quantitative EEG double-blind study of GBE.

In: J. Cerebral Blood Flow Metabolism, 1983, 3, 5556-5557.

Pidoux B., Bastien C., Niddam S.:

Normalization of electroencephalographic activity in ageing brain by an extract of Ginkgo biloba;

In: Bes. A. Braquet P., Paoletti R., Siesjo B.K. Eds., Cerebral Ischemia, Amsterdam, Excerpta Medica, 1984, 385-388.

Pietta P Mauri P Rava A

Rapid liquid chromatography of terpenes in Ginkgo biloba L. extracts and products.

In: J Pharm Biomed Anal (1992 Oct-Dec) 10(10-12):1077-9

Pritz-Hohmeier S Chao TI Krenzlin J Reichenbach A

Effect of in vivo application of the ginkgo biloba extract EGb 761 (Rokan) on the susceptibility of mammalian retinal cells to proteolytic enzymes.

In: Ophthalmic Res (1994) 26(2):80-6

Lesions, inflammations, or degenerative insults of the human retina are accompanied by the release of proteolytic enzymes. Their deleterious effect may be enhanced by the release of free radicals. Ginkgo biloba extracts are known to exert protective influences against the action of free radicals, and this prompted us to ask whether the application of such extracts might protect retinal tissue against proteolytic damage. Eighteen adult rabbits were fed for 3 weeks (+/- 3 days) with 40 mg/kg of G. biloba extract (EGb 761) or a terpene-free fraction of this extract, dissolved in their drinking water. Twelve control rabbits received no G. biloba extract. The animals were then euthanatized and their retinae isolated. After appropriate enzymatic treatment, the tissue was dissociated and the number of isolated Muller cells counted as an indication of the strength of the proteolytic effects. There was a significant protective action of EGb 761: in an average control rabbit 5, 200 cells per milligram retinal tissue were isolated; application of EGb 761 markedly reduced this number to 2, 500 (terpene-free fraction; CP 205) or 3, 050 (terpene-containing fraction). It is concluded that G. biloba extracts may have a significant therapeutic value in cases of retinal damage.

Racagni G Brunello N Paoletti R

[Neuromediator changes during cerebral aging. The effect of Ginkgo biloba extract]

Variations des neuromediateurs lors du vieillissement cerebral. Effet de l'extrait de Ginkgo biloba.

In: Presse Med (1986 Sep 25) 15(31):1488-90

Ginkgo biloba extract exerts a specific effect on the noradrenergic system and on beta-receptors. No variation was found in alpha 2- receptors and serotonin uptake. These findings provide the first evidence of central effects of a drug acting on cerebral ageing, connected specifically to reactivation of the noradrenergic system in the cerebral cortex.

Ramassamy C Christen Y Clostre F Costentin J

The Ginkgo biloba extract, EGb761, increases synaptosomal uptake of 5- hydroxytryptamine: in-vitro and ex-vivo studies.

In: J Pharm Pharmacol (1992 Nov) 44(11):943-5

The Ginkgo biloba extract (EGb 761) added to a synaptosomal fraction prepared from mice cerebral cortex modified [3H]5-hydroxytryptamine ([3H]5-HT) uptake in a biphasic manner. Between 4 and 16 micrograms mL-1 EGb 761 increased significantly the [3H]5-HT uptake (maximum + 23%). A similar increase was also obtained when synaptosomes were prepared from the cortex of mice treated orally with EGb 761, either acutely (100 mg kg-1, 14 h and 2 h before death) or semi-chronically (2 x 100 mg-1 kg daily for 4 consecutive days). The in-vitro increase in [3H]5-HT uptake induced by EGb 761 was not observed in the presence of 10(-6) M clomipramine, a 5-HT-uptake inhibitor. EGb 761 did not increase [3H]dopamine uptake by synaptosomes prepared from striatum of mice. We investigated different fractions of EGb 761 in order to determine the compounds inducing the increase in [3H]5-HT uptake. The BN 52063 extract (corresponding to the EGb 761 devoid of flavonoid substances) did not increase [3H]5-HT uptake. The Cp 202 extract (corresponding to the EGb 761 devoid of terpenic substances and containing mostly flavonoid substances) increased [3H]5-HT uptake. Among the flavonoids, quercetin has been tested and had no effect on the [3H]5-HT uptake. Since at the usual therapeutic doses of EGb 761, the effective concentrations of the components responsible for this increase are likely to be reached in the brain, one may suggest that this effect could contribute to the therapeutic effect of EGb 761.

Ramassamy C Girbe F Christen Y Costentin J

Ginkgo biloba extract EGb 761 or trolox C prevent the ascorbi acid/Fe2+ induced decrease in synaptosomal membrane fluidity.

In: Free Radic Res Commun (1993) 19(5):341-50

The ability of synaptosomes, prepared from striata, to take up 3H- dopamine declined rapidly during incubation at 37 degrees C, in an oxygenated Krebs-Ringer medium with 0.1 mM ascorbic acid. Ascorbic acid was responsible for this decrease. Its effectiveness after a 60 min incubation was concentration dependent from 1 microM and virtually complete for 0.1 mM. Furthermore, a decrease of synaptosomal membrane fluidity was revealed by measurements of fluorescence polarization using 1, 6-diphenyl-1, 3, 5-hexatriene. This decrease was potentiated by Fe2+ ions (1 microM). In contrast, it was prevented by the Fe2+ ion chelator, desferrioxamine (0.1 mM), by the Ginkgo biloba extract EGb 761 [2-16 micrograms/ml], as well as by the flavonoid quercetin (0.1 microM). This preventive effect was shared by trolox C (from 0.1 mM). It is concluded that peroxidation of neuronal membrane lipids induced by ascorbic acid/Fe2+ is associated with a decrease in membrane fluidity which, in turn, reduces the ability of the dopamine transporter to take up dopamine.

Ramassamy C Naudin B Christen Y Clostre F Costentin J

Prevention by Ginkgo biloba extract (EGb 761) and trolox C of the decrease in synaptosomal dopamine or serotonin uptake following incubation.

In: Biochem Pharmacol (1992 Dec 15) 44(12):2395-401

Prolonged incubation of synaptosomes in Krebs-Ringer oxygenated medium in the presence of ascorbic acid (10(-4) M) led, after 20 min, to a decrease in [3H]dopamine (DA) (synaptosomes prepared from the striatum) and [3H]serotonin (5HT) (synaptosomes prepared from the cortex) uptake. The decrease was progressive and uptake was virtually abolished after a 60 min incubation period. A concentration-dependent (from 5 x 10(-6) M) role of ascorbic acid in the decrease of [3H]DA or [3H]5HT uptake was demonstrated. This decrease was potentiated by Fe2+ ions and prevented by the ferrous chelating agent desferrioxamine. Thus, the progressive decrease in synaptosomal uptake of either [3H]DA or [3H]5HT could depend on the generation of free radicals by the association of ascorbic acid with Fe2+ ions. The decrease in synaptosomal uptake was prevented, in a concentration- dependent manner, by the Ginkgo biloba extract EGb 761 (4-16 micrograms/mL) and the vitamin E analog trolox C (10(-4) M). The terpenic fraction of EGb 761, Bn 52063 (up to 0.5 microgram/mL), did not prevent the reduction of [3H]amine uptake. In contrast, the flavonoidic fraction, Cp 202, was effective (from 1 microgram/mL) and its efficacy was shared by the flavonoid quercetin (from 0.1 microgram/mL). The prolongation of the ability of synaptosomes to take up [3H]amine elicited by EGb 761, in particular its