Ginkgolides Mimic the Effects of Hypoxic Preconditioning to Protect C6 Cells Against Ischemic Injury by Up-regulation of Hypoxia-inducible Factor-1 Alpha and Erythropoietin

Hypoxic preconditioning can play a significant neuroprotective role. However, it has not been employed clinically because of safety concerns. To find a safer preconditioning stimulus that is both practical and effective, we investigated whether ginkgolides are capable of preconditioning as hypoxia to protect C6 cells against ischemic injury. We demonstrated that both ginkgolides (37.5microg/mL) and hypoxia (1% O(2) for 16h) can significantly increase cell viabilities and expression of phosphorylated glycogen synthase kinase (p-GSK), phosphorylated extracellular signal-regulated kinase (p-ERK), hypoxia-inducible factor-1 alpha (HIF-1alpha) and erythropoietin (EPO) in ischemic cells. The inhibitors of mitogen-activated protein kinase (MAPK) or phosphatidylinositol 3'-kinase (PI3K) significantly but not completely reduced the enhanced expression of these proteins and cell viabilities induced by ginkgolides and hypoxic preconditioning. These indicated that ginkgolides could mimic hypoxic preconditioning by increasing expression of HIF-1alpha as well as its target protein EPO and that the ginkgolides and hypoxic preconditioning role might be partly mediated by the activation of the p42/p44-mitogen-activated protein kinase and phosphatidylinositol 3'-kinase/AKT/glycogen synthase kinase 3beta pathways. The similar tendency in the changes of protein expression, cell viabilities and responses to MAPK or PI3K inhibitors of the cells treated with ginkgolides and hypoxia suggests that ginkgolides and hypoxic preconditioning might operate by similar mechanisms. The findings also imply that ginkgolides might have the potential for clinical use to prevent injury in high-risk conditions.