Ginkgo biloba extract (EGb761) inhibits mitochondria-dependent caspase pathway and prevents apoptosis in hypoxia-reoxygenated cardiomyocytes

Cardiomyocytes were exposed to 24 hours of hypoxia and four hours of reoxygenation, and pretreated with EGb761, bilobalide and quertcetin. By using immunoblot, immunofluorescent, biochemical and flow cytometry techniques, we compared the effects of EGb761 and its representative constituents including quercetin and bilobalides on regulating mitochondria-dependent caspases signal pathway and apoptotic cell death in the hypoxia-reoxygenated cardiomyocytes.Pretreatment with EGb761 significantly inhibited the release of cytochrome c from mitochondria, the expression of caspase-3, cleavage activities of caspases and attenuated apoptotic cell death. The effects of quercetin on the release of cytochrome c, the cleavage activities of caspases and cell death were similar to those of EGb761 but better than those of bilobalide.The antioxidant constituents of EGb761 such as quercetin contribute to the cardioprotective effects of EGb761 and inhibit the mitochondria-dependent caspase pathway. It is possible that the mitochondria-dependent caspase pathway may be one of the molecular targets of EGb761 against myocardial ischemia-reperfusion injury.EGb761 is a standard extract from the leaves of Ginkgo biloba (Yinxing) containing 24% ginkgo-flavone glycosides (eg kaempferol, quercetin and isorhamnetin derivatives) and 6% terpenoid (eg ginkgolides A, B, C, J and bilobalide) [1]. The cardioprotective effects of EGb761 have been demonstrated in various in vivo and in vitro animal models and humans. The flavonoid components of EGb761 scavenge superoxide, hydroxyl radicals and nitric oxide (NO) and protect myocardia from ischemia-reperfusion injury [2-5]. The terpenoid constituents of EGb761 also showed their cardioprotective effects independent from the free radical-scavenging properties [6]. Therefore, it is necessary to further elucidate whether the cardioprotective mechanisms of EGb761 are attributed to its flavonoids or terpenoid conponents in the prevention of myocardial ischemia-re