Intraperitoneal Injection of Ginkgo biloba Extract Enhances Antioxidation Ability of Retina and Protects Photoreceptors After Light-Induced Retinal Damage in Rats

Purpose: To investigate the effect of Ginkgo biloba extract EGb 761, a free-radical scavenger, on the antioxidation capability of retina after light-induced retinal damage in rats in an attempt to understand the mechanism by which EGb 761 protects the photoreceptors after light-induced retinal damage. Methods: Seventy-two female Sprague-Dawley (SD) rats were evenly randomized into normal control group (NC group), light-induced retinal damage model group (M group), model + normal saline group (MN group), and model + EGb 761 group (ME group). Light-induced retinal damage model was induced via exposure to white light at 2740 ± 120 lux for 6 hr. Rats in MN group and ME group were intraperitoneally injected daily with normal saline and 0.35% EGb 761 (100 mg/kg), respectively, 1 week before and 2 weeks after light exposure. The levels of malondialdehyde (MDA), total superoxide dismutase (T-SOD), glutathione peroxidase (GSH-Px), and catalase (CAT) in the retinal tissues were determined 24 hrs after light exposure; photoreceptor apoptosis was detected 4 days after light exposure. One and 2 weeks after light exposure, histopathologic examination was carried out, and the outer nuclear layer (ONL) thickness (number of nuclei) in the superior and inferior retina was counted. Results: Twenty-four hours after exposure, the MDA levels in the other three groups were significantly higher than that in the NC group (p < 0.05); those in the M and MN groups were similar to each other (p > 0.05); and that of the ME group was significantly lower than those in the M and MN group (p < 0.05). The activities of T-SOD, GSH-Px, and CAT were similar in the M and MN groups (p > 0.05); the activities in the M and MN groups were significantly lower than those in the NC and ME groups (p < 0.05); and the activities in the ME group were significantly higher than those in the M and MN groups (p < 0.05). Four days after exposure, the apoptotic photoreceptors within the ONL in the ME group were obviously fewer than those in the M and MN groups. One week and 2 weeks after exposure, the ONL thickness (number of nuclei) in the ME group was more than that in the M and MN groups but less than that in the NC group. Conclusions: Intraperitoneal injection of EGb 761 can enhance the antioxidation ability of retina and partially inhibit the apoptosis of photoreceptors, thus exert a protective effect on photoreceptors.