Effects of Ginkgolide B and Ginkgo biloba extract on local cerebral glucose utilization in the awake adult rat

The effects of the extract of the leaves of Ginkgo biloba and of one of its major components, Ginkgolide B, on local cerebral glucose utilization (LCGU) have been studied in the awake adult rat. Ginkgolide B (10 mg/kg i.p.) had no significant effect on LCGU in 38 brain regions studied. In contrast, the Ginkgo biloba extract (150 mg/kg i.p. in 3 divided doses) produced significant and widespread decreases in LCGU in 21 brain regions (range 3–26% reduction). These results demonstrate that Ginkgo biloba is able to reduce brain glucose utilization, but that the substance responsible for this effect may not be Ginkgolide B.     

Ginkgolide B, a constituent of Ginkgo biloba, facilitates glutamate exocytosis from rat hippocampal nerve terminals

Although previous studies have demonstrated that Ginkgo biloba extract has modest effects in the improvement of memory and cognitive function of the Alzheimer's disease patients, the mechanism(s) underlying its beneficial effects remain(s) unclear. In this study, the effect of ginkgolide B, one of the major constituents of Ginkgo biloba extract, on the release of endogenous glutamate from rat hippocampal nerve terminals (synaptosomes) was studied. Ginkgolide B facilitated the Ca2+-dependent release of glutamate evoked by 4-aminopyridine in a concentration-dependent manner. The facilitatory action of ginkgolide B was not due to it increasing synaptosomal excitability because ginkgolide B did not alter the 4-aminopyridine-evoked depolarization of the synaptosomal plasma membrane potential. Rather, examination of the effect of ginkgolide B on cytosolic free Ca2+ concentration revealed that the facilitation of glutamate release could be attributed to an enhancement of presynaptic voltage-dependent Ca2+ influx. Consistent with this, the ginkgolide B-mediated facilitation of glutamate release was significantly prevented in synaptosomes pretreated with a wide spectrum blocker of N-, P-, and Q-type Ca2+ channels, omega-conotoxin MVIIC. Moreover, the facilitation produced by ginkgolide B was completely abolished by the protein kinase A inhibitor, but not by the protein kinase C inhibitor. These results suggest that ginkgolide B effects a increase in protein kinase A activation, which subsequently enhances the Ca2+ entry through voltage-dependent N- and P/Q-type Ca2+ channels to cause a increase in evoked glutamate release from rat hippocampal nerve terminals. In addition, glutamate release elicited by Ca2+ ionophore (ionomycin) was also facilitated by ginkgolide B, which suggests that ginkgolide B may have a direct effect on the secretory apparatus downstream of Ca2+ entry. These actions of ginkgolide B may provide some information regarding the beneficial effects of Ginkgo biloba in the central nervous system.     

Ginkgolide A contributes to the potentiation of acetaminophen toxicity by Ginkgo biloba extract in primary cultures of rat hepatocytes

The present cell culture study investigated the effect of Ginkgo biloba extract pretreatment on acetaminophen toxicity and assessed the role of ginkgolide A and cytochrome P450 3A (CYP3A) in hepatocytes isolated from adult male Long-Evans rats provided ad libitum with a standard diet. Acetaminophen (7.5-25 mM for 24 h) conferred hepatocyte toxicity, as determined by the lactate dehydrogenase (LDH) assay. G. biloba extract alone increased LDH leakage in hepatocytes at concentrations > or =75 mug/ml and > or =750 mug/ml after a 72 h and 24 h treatment period, respectively. G. biloba extract (25 or 50 mug/ml once every 24 h for 72 h) potentiated LDH leakage by acetaminophen (10 mM for 24 h; added at 48 h after initiation of extract pretreatment). The effect was confirmed by a decrease in [(14)C]-leucine incorporation. At the level present in a modulating concentration (50 mug/ml) of the extract, ginkgolide A (0.55 mug/ml), which increased CYP3A23 mRNA levels and CYP3A-mediated enzyme activity, accounted for part but not all of the potentiating effect of the extract on acetaminophen toxicity. This occurred as a result of CYP3A induction by ginkgolide A because triacetyloleandomycin (TAO), a specific inhibitor of CYP3A catalytic activity, completely blocked the effect of ginkgolide A. Ginkgolide B, ginkgolide C, ginkgolide J, quercetin, kaempferol, isorhamnetin, and isorhamnetin-3-O-rutinoside did not alter the extent of LDH leakage by acetaminophen. In summary, G. biloba pretreatment potentiated acetaminophen toxicity in cultured rat hepatocytes and ginkgolide A contributed to this novel effect of the extract by inducing CYP3A.     

Polyphenols from Ginkgo biloba

By Sephadex LH-20 gel chromatography of an extract from Gingko biloba leaves, polymeric proanthocyanidins were eluted after the fractions of flavonol glycosides and biflavone glycosides. A purified proanthocyanidin polymer accounted for 86.6% of the total proanthocyanidins, and for 37.7% of the total antioxidant activity of this leaf extract. For structure elucidation, the polymer was submitted to acidic depolymerization in the presence of phloroglucinol. The structures of the resulting flavan-3-ols and phloroglucinol adducts were determined on the basis of 1D-and reverse 2D-NMR (HSQC, HMBC) spectra of their peracetylated derivatives, MALDI-TOF-MS and CD-spectroscopy. The observations resulting from the degradation with phloroglucinol were confirmed by (13)C-NMR spectroscopy of the polymer. The mean molecular weight of the polymeric fraction was estimated to be 9a10 flavan-3-ol-units.     

Production of ginkgolides and bilobalide by Ginkgo biloba plants and tissue cultures

The accumulation of the terpenes ginkgolides and bilobalide in Ginkgo biloba was reported in plants as well as in plant cell cultures. Several hundred plants cultivated under controlled conditions in the field have been analyzed for their terpene production over many years. Cross-pollination experiments were performed with mature trees and the terpene content of the progeny was analyzed. The age of the tree is the main factor influencing the terpene content of the leaves as the level always decreases dramatically between young and old trees. 80 cell culture strains have been established and ginkgolides analyzed by GC/MS. These cell cultures reveal very low amounts of terpenes (1 microgram g-1 D.W. or less). On the contrary, isolated in vitro root cultures accumulate terpenes at the same concentration as the young plant leaves (4 mg g-1 D.W.). Attempts to obtain rapid growing roots or even hairy-roots did not succeed but the possibility to transform Ginkgo cell strains has been demonstrated.     

银杏药理作用研究进展

银杏Ginkgo biloba为银杏科银杏属落叶乔木,是世界范围内应用最广泛的天然药物之一。银杏含多种活性成分,具有抗氧化、抗凋亡、改善脑血流、神经保护、抑制血小板活性等多种药理作用,用于心脑血管疾病、阿尔茨海默症、动脉粥样硬化、癌症、哮喘、非酒精性脂肪肝、糖尿病并发症等疾病的治疗。就银杏药理作用研究的新进展进行综述,以期为新药研发人员和临床医生提供更多的银杏药理资料,进而为新药研究提供依据。     

2,3-Dihydrobiflavone from Ginkgo biloba

From the yellow leaves of Ginkgo biloba 2,3-dihydrosciadopitysin (5,5',7'-trihydroxy-7,4',4'-trimethoxy-3',8'-flavanone/flavone) was isolated as a mixture of two diastereomers. Its structure was elucidated employing 2D NMR techniques.     

高效液相色谱法测定银杏叶片剂中银杏黄酮含量

目的建立高效液相色谱法测定银杏叶制剂天保宁片剂中银杏黄酮的含量。方法色谱柱为YWGC18-ODS柱(250mm×4.6mm),流动相由磷酸缓冲液(pH2)-四氢呋喃-甲醇-异丙醇(60:15:10:15)组成,流速0.5mL·min-1,紫外检测波长380nm。结果槲皮素和山柰酚在2.5-50mg·L-1,异鼠李素在1.362-27.38mg·L-1的浓度范围内线性关系良好,回归方程为槲皮素:y=145642x-314528,r=0.9994;山柰酚:y=94650x-197111,r=0.9993;异鼠李素:y-62031x-20056,r=0.9997;槲皮素、山柰酚、异鼠李素平均回收率分别为99.06%,99.89%,99.06%,RSD分别为1.33%,2.21%,1.85%。检测限槲皮素和山柰酚均为0.125mg·L-1,异鼠李素0.068mg·L-1。结论本法简便,快速,灵敏,准确,重现性好,可作为控制银杏黄酮制荆质量标准的依据。     

Haemorrhage due to Ginkgo biloba?

(1) About 20 detailed reports of haemorrhage (usually cerebral, ocular, or postsurgical) in patients using Gingko biloba extracts have been published. One-third of these patients were also taking drugs that increase the risk of bleeding (anticoagulants or antiplatelet drugs). (2) Some substances contained in Gingko biloba have been shown to have an antiplatelet effect. (3) In practice, patients with risk factors for bleeding (anticoagulant or antiplatelet treatment, surgery, etc.) should avoid using Gingko biloba extracts.     

银杏叶提取物的免疫调节作用研究进展

银杏叶提取物是一种具有广泛生物学功能的活性物质。该文从免疫器官重量、单核巨噬细胞与自然杀伤细胞、体液免疫、细胞免疫、细胞因子以及红细胞免疫、粘膜免疫等方面综述了银杏叶提取物的免疫调节作用。     

Pharmaceutical quality of different Ginkgo biloba brands

Ginkgo biloba-containing brands are one of the top sellers within the growing market for herbal remedies in many European countries as well as in the USA. In the consumers' interest, these brands should feature a certain quality and should be transparent in quality claims. In this investigation, a variety of products on the USA market was studied with respect to pharmaceutical quality, such as quantity of constituents and in-vitro dissolution. In terms of the content of active substances, flavone glycosides ranged from 24% to 36% and terpene lactones from 4% to 11%. With ginkgolic acids, there was a very large range, from < 500 ppm to about 90000 ppm. Comparing the dissolution rates of terpene lactones and flavone glycosides within the single products, most were approximately the same. Thus, terpene lactones and flavone glycosides were released from these products and dissolved at the same rate in most cases. Furthermore, most of the products investigated released more than the required 75% of the content of both components within 30 min. However, several products showed clear and relevant differences in dissolution rates to the rest (e.g. < 75% within 30 min or even less than 25% after 60 min in one case, indicating much poorer pharmaceutical quality). Beside the comparability respectively standardisation of the extracts used, the in-vitro dissolution of the relevant constituents should be similar to other drugs to guarantee comparable in-vivo performance of herbal products. An important step in standardising pharmaceutical quality is the pharmacopoeial monograph for Ginkgo biloba extract in Germany, standardising the content of pharmacologically relevant substances (flavone glycosides 22-27% and terpenlactones 5-7%, 2.8-3.4% ginkgolides A, B, C and 2.6-3.2% bilobalide thereof). Many of the investigated products, which refer to the German Commission E (of the Federal Institute for Drugs and Medicinal Devices) monograph, are not in accordance with this specification. Thus, they can not be considered to be pharmaceutically equivalent.     

银杏叶提取工艺的研究

对银杏叶提取物的提取和精制工艺进行了研究，确定了提取溶剂、时间、次数及浓缩、干燥温度等提取工艺参数。比较了树脂吸附一次洗脱和二次洗脱以及超滤与树脂吸附相结合的精制工艺对产品质量及总黄酮收率的影响。结果表明，超滤与树脂吸附工艺所得产品的质量和收率最佳。