Kiewert Cornelia, Kumar Vikas, Hildmann Oksana, Hartmann Joachim, Hillert Markus, Klein Jochen
Department of Pharmaceutical Sciences, School of Pharmacy, Texas Tech University Health Science Center, 1300 Coulter Dr, Amarillo, TX 79106, USA.
Brain Res. 2008 Mar 27;1201:143-50. doi: 10.1016/j.brainres.2008.01.052. Epub 2008 Jan 31.
Bilobalide, a constituent of Ginkgo biloba, has neuroprotective properties. Its mechanism of action is unknown but it was recently found to interact with neuronal transmission mediated by glutamate, gamma-aminobutyric acid (GABA) and glycine. The goal of this study was to test the interaction of bilobalide with glycine in assays of neuroprotection. In rat hippocampal slices exposed to N-methyl-D-aspartate (NMDA), release of choline indicates breakdown of membrane phospholipids. NMDA-induced choline release was almost completely blocked in the presence of bilobalide (10 microM). Glycine (10-100 microM) antagonized the inhibitory action of bilobalide in this assay. In a second assay of excitotoxicity, we measured tissue water content as an indicator of cytotoxic edema formation in hippocampal slices which were exposed to NMDA. In this assay, edema formation was suppressed by bilobalide but bilobalide's action was attenuated in the presence of glycine and of D-serine (100 microM each). To investigate bilobalide's interaction with glycine receptors directly, we determined 36chloride flux in rat cortico-hippocampal synaptoneurosomes. Glycine (100 microM) was inactive in this assay indicating an absence of functional glycine-A receptors in this preparation. [3H]Glycine was used to assess binding at the glycine binding site of the NMDA receptor but bilobalide was found to be inactive in this assay. Finally, [3H]glycine release was monitored in hippocampal slices exposed to oxygen-glucose deprivation. In this model, glycine release was induced by ischemia, an effect that was strongly reduced by bilobalide. We conclude that bilobalide does not interact with glycine receptors in neurochemical assays but it significantly reduces the release of glycine under ischemic conditions. This effect likely contributes to bilobalide's neuroprotective effects in assays of excitotoxicity and ischemia.
白果内酯是银杏叶的一种成分，具有神经保护特性。其作用机制尚不清楚，但最近发现它能与由谷氨酸、γ-氨基丁酸（GABA）和甘氨酸介导的神经传递相互作用。本研究的目的是在神经保护试验中测试白果内酯与甘氨酸的相互作用。在暴露于N-甲基-D-天冬氨酸（NMDA）的大鼠海马切片中，胆碱的释放表明膜磷脂的分解。在白果内酯（10微摩尔）存在的情况下，NMDA诱导的胆碱释放几乎被完全阻断。甘氨酸（10 - 100微摩尔）在该试验中拮抗白果内酯的抑制作用。在第二项兴奋性毒性试验中，我们测量了暴露于NMDA的海马切片中组织含水量，作为细胞毒性水肿形成的指标。在该试验中，水肿形成被白果内酯抑制，但在甘氨酸和D-丝氨酸（各100微摩尔）存在的情况下，白果内酯的作用减弱。为了直接研究白果内酯与甘氨酸受体的相互作用，我们测定了大鼠皮质-海马突触体中的氯离子通量。甘氨酸（100微摩尔）在该试验中无活性，表明该制剂中不存在功能性甘氨酸-A受体。[3H]甘氨酸用于评估在NMDA受体甘氨酸结合位点的结合情况，但发现白果内酯在该试验中无活性。最后，在暴露于氧-葡萄糖剥夺的海马切片中监测[3H]甘氨酸的释放。在该模型中，甘氨酸释放由缺血诱导，白果内酯可强烈降低这种作用。我们得出结论，在神经化学试验中，白果内酯不与甘氨酸受体相互作用，但在缺血条件下它能显著减少甘氨酸的释放。这种作用可能有助于白果内酯在兴奋性毒性和缺血试验中的神经保护作用。
