Flavonoids ginkgo

SC-CO2 was reported for the extraction of sitosterol from dandelion leaves (Simandi and others 2002) flavonoids from ginkgo leaves (Chiu and others 2002) and alkaloids from mate tea leaves (Saldana and others 1999,2000, 2002a). 

Chiu K-L, Cheng Y-C, Chen J-H, Chang CJ and Yang P-W. 2002. Supercritical fluids extraction of Ginkgo ginkgoloides and flavonoids. J Supercrit Fluids 24 77—87. 

Selective Elution of Flavonoids from Terpenoids in Ginkgo biloba Leaf Extracts... 

GABA Flavonoids present in ginkgo may endow it with benzodiazepine actions but it remains in question whether they cross the blood-brain barrer (Lobstein-Guth et al. 1988 Baureithel et al. 

Oyama Y, Fuchs PA, Katayama N, Noda K. (1994). Myricetin and quercetin, the flavonoid constituents of Ginkgo biioba extract, greatiy reduce oxidative metaboiism in both resting and Ca(2+)-loaded brain neurons. Brain Res. 635(1-2) 125-29. 

Wojcicki J, Gawroska-Szkiarz B, Bieganowski W, Patalan M, Smulski HK, Samochowiec L, Zakrzewski J. (1995). Comparative pharmacokinetics and bioavailability of flavonoid glycosides of Ginkgo biloba after a single oral administration of three formulations to healthy volunteers. Materia Med Polona. 27(4) 141-46. 

Flavonoids in the diet have been widely promoted as important antioxidant contributors. Their neuroprotective properties, because of this effect, have been demonstrated by several workers. However, they have also been demonstrated to have MAOI activity and this has been proposed as part of the explanation of the use of the common herb, St Johns Wort, Hypericum perforatum L., as an antidepressant. This dual role has now been proposed for a variety of flavonoids, such as kaempferol (22) from the leaves of Ginkgo biloba L., a widely used herbal product which has been suggested as a preventative agent against neurodegeneration. Quercetin (23), similarly, has also shown to inhibit MAO-B " and reverse the effects of induced catalepsy, which mimics the bradykinesia associated with PD. Tangeretin (24) also inhibits MAO-B and crosses the blood brain barrier in a rat model. 

Within the domain of medicinal plants, preparations of Ginkgo biloba (Ginkgoaceae) are the most widely sold phytomedicines, with sales of over US 1 billion in 1998. " These principally involve special extracts of the leaves. Flavonoids are, at least in part, responsible for the beneficial effects of Ginkgo extracts. Generally, enriched ginkgo extracts for the preparation of ginkgo products are standardized to contain 24% flavonoids and 6% terpene... 

FIGURE 1.4 HPLC fingerprint of a therapeutically used dry extract of Ginkgo biloba leaves. Top chromatogram, pure reference flavonoids bottom chromatogram, leaf extract. Identified flavonoids are numbered 1 to 33. (From Hasler, A., Sticher, O., and Meier, B., J. Chromatogr., 605, 41, 1992. With permission.)... 

Pietta, P.G. et al.. Identification of flavonoid metabolites after oral administration to rats of a Ginkgo biloba extract, J. Chromatogr. B — Biomed. Appl, 673, 75, 1995. 

Animal studies In the study by Pietta et al. (39), a single dose of ginkgo leaf extract (EGb 761) was administered orally to rats. Metabolites found in the urine represented less than 40% of the flavonoids administered. The presence of phenylalkyl acids in the rat urine but not in the human urine (33,39) indicates that the flavonols were more extensively metabolized in humans than in rats. In the study by Watanabe et al. (40), mice received a diet containing ginkgo leaf extract (EGb761 36mg/kg daily) or a standard diet without the extract for four weeks. Afterwards, plasma levels of quercetin (12.0ng/mL vs. 4.8ng/mL), kaempferol (7.0ng/mL vs. 3.2 ng/ mL), and isorhamnetin (49.6ng/mL vs. Ong/mL) in both treatment groups were determined. The study indicates that these compounds can be absorbed intact into the blood stream. 

EGb761 is made up of 24% flavonoid glycosides and 6% terpenes, which are accepted as active prindples. Many undesirable constituents of Ginkgo biloba leaves (e.g., ginkgolic add due to its allergic action) are eliminated by the extraction procedures used to prepare the extract... 

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