Ginkgolides Against Cerebral Ischemia And Its Mechanism

Ginkgolides (TG) is terpenoid constituents of Ginkgo biloba extract (EGb), which includes ginkgolides A, B, C, M, J and bilobalide. Many reports have been read about the effects of EGb on blood vessels of heart and brain. And also there were some papers about that Gin B and bolobalide have antagonistic effects on platelet activity factor (PAF). Comparing to EGb, TG is a relative pure effective fraction of Chinese traditional medicine and comparing to the mono-ginkgolides, TG is much more easily prepared. Moreover, it is known that medicines for treating ischemia and medicines having neuroprotection are more necessary in clinic. Therefore, we made attempt to study the putative cerebreprotective activity and the possible mechanism of TG in vivo and in vitro.To investigate the protective effects of TG on anoxia and acute cerebral ischemia in mice and focal cerebral ischemia in rats, anoxia was produced by close hypoxia and the surviving time and oxygen content were detected. Acute cerebral ischemia was produced by the occlusion of bilateral common carotid arteries with vague nerves of mice and the effects of TG on mortality and surviving time in mice were also detected. Ischemia of whole brain was produced by cutting out mice heads and the effect of TG on gasping time was observd. Focal cerebral ischemia was produced by permanent occlusion of the proximal of the left middle cerebral artery (MCAO). The effects of TG on neurologic deficits and content of water in the damaged brain of rats, and also the pathological examination were observed. Results showed that no significant effects of TG on the surviving time and oxygen content in mice subjected to close hypoxia. TG 32 mg-kg-1 significantly prolonged the surviving time of mice subjected to acute ischemia by occlusion of bilateral carotid arteries and decreased the death rate. TG 16 and 32 mg-kg-1 could significantly prolong the gasping time in mice subjected to being cut out heads. TG 8 and 16 mg-kg-1 markedly decreased the infarct size and ameliorated neurologic deficits score of rats subjected to MCAO. Moreover, TG could decrease the water content in the damaged brain in rats subjected to MCAO.We tried to find out whether TG could rescue cultured cortical neurons fromneurotoxicity damages. In cortical neuronal cultures from fetal rats, damage was induced by exposure to 1 mM L-glutamate (GIu) for 6-12 h in serum-free medium, by exposure to 0.2 mM hydrogen peroxide (H2O2) for 6-12 h, and by exposure to free-glucose and hypoxia medium for 4 h. Neuronal viability was confirmed by the assay of the absorbance of 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium (MTT) solution on a spectrophotometer using a test wavelength of 570 nm and a reference wavelength of 630 nm. Cell membrane damage was assessed by measuring the release of lactate dehydrogenase (LDH) using the colorimetry. TG (10-5 to 10-1 g-L-1) added to the growth medium 12h before and simultaneously protected cortical neurons from glutamate-induced damage. The cytoprotective effects of TG on the damage induced by H2O2 were observed only when it was added 12 h prior to the onset of the injury. No effect of TG was found on the insult induced by free-glucose and hypoxia.The influence of TG on the lipid peroxide product, malondialdehyde (MDA), glutathione (GSH) and catalase (CAT), glutathione peroxidase (GSH-Px), superoxide dismutase (SOD) activities in rat brain as well as lactate dehydrogenase (LDH) and creatine kinase (CK)activities in rat blood serum after occlusion of middle cerebral artery (MCAO) following reperfusion was investigated. Experimental model of the reversible middle cerebral artery occlusion without craniectomy of rat focal cerebral ischemia-reperfusion was used. Compared to sham-operated animals, rats subjected ischemia followed reperfusion exhibited severe neurologic deficits, ischemia followed reperfusion increased blood serum LDH and CK activities as well as brain GSH-Px activity and decreased SOD activity as well as GSH and MDA content. Administration of TG (4, 8, 16 mg-kg...