Neuroprotective Effect of Ginkgo Biloba Extract Against Hypoxic Retinal Ganglion Cell Degeneration <i>In Vitro</i> and <i>In Vivo</i>

Abstract

Hypoxia-induced oxidative stress and disturbed microvascular circulation are both associated with pathogenesis of glaucoma. Ginkgo biloba extract (GBE) has been reported to have positive pharmacological effects on oxidative stress and impaired vascular circulation. This study aimed to investigate the neuroprotective effect of GBE against hypoxic injury to retinal ganglion cells (RGCs) both in vitro and in vivo. The rat RGC line was used, and oxidative stress was induced by hydrogen peroxide (H2O2) in vitro. EGb 761, a standardized GBE, or vehicle was applied to RGCs. Hypoxic optic nerve injury in vivo was induced by clamping the optic nerve of rats with a "microserrefine clip" with an applicator, which was applied without crushing the optic nerve. This method is different from "optic nerve crush model" and does not involve elevation of intraocular pressure, and may serve as a possible normal tension glaucoma animal model. EGb 761 at various concentrations or vehicle was administered intraperitoneally. RGC density was measured to estimate the survival both in vitro and in vivo. The survival of RGCs was significantly (P < .001) higher upon treatment with 1 or 5 mu g/mL of EGb 761 compared with vehicle after oxidative stress in vitro. RGC density upon treatment with EGb 761 of 100 mg/kg (1465.6 +/- 175 cells/mm(2)) or 250 mg/kg (1307.6 +/- 213 cells/mm(2)) was significantly higher (P < .01, P < .05, respectively) than that obtained with vehicle (876.3 +/- 136 cells/mm(2)) in vivo. Our results suggest that GBE has neuroprotective effect on RGCs against hypoxic injury both in vitro and in vivo.