The Protective Effect Of Edaravone Against Light-induced Damage On Retina In Rat

Only the parallel rays are focused exactly on the normal retina, the vision is perfect. We are going to establish the rat model of retinal light-injury with intraperitioneal injection of Edaravone (the exogenous scavenger of oxyradical) and to investigate the protective effect of Edaravone when retina exposed to light.In this article we used one hundred and twenty-eight Sprague-Dawley (SD) rats, which were 7-10 weeks-aged. They were randomly divided into normal control group (groupⅠ), light damage group (groupⅡ) and experimental group (groupⅢandⅣ). There were thirty-two rats in each group . In groupⅣ, the SD rats were intraperitoneally injected with Edaravone three times before light damage (once a day). And in groupⅢ, the injection was replaced by 0.9% normal sodium (0.9%NS). All rats were kept in a 12-hours (8 AM to 8 PM) light-dark cycle environment for 7 days and then kept in darkness for 36 hours. Before experiment all rats were anesthetized by aether, and all pupils were turned up by mydriatic. Animals of groupⅡ,ⅢandⅣwere exposed to white fluorescent light constantly (13260±440 lux) for 2 hours after they woke up. All rats were killed at the following scheduled time point after damage. There were eight animals on phases of day 0.5, day 1, day 6, day 10 each group. All right retinas were extracted to make paraffin section and stained by HE and TUNEL(TDT-mediated dUTP nick-end labeling method) methods. Retinas were observed under light microscope and thickness of outer nuclear layer (ONL) was measured .TUNEL technique was used to evaluate positive apoptosis cells of outer nuclear layer. Using thiobarbituric acid (TBA) and xanthinoxidase (XO) methods, the content of superoxide dismutase (SOD) and malonaldehyde (MDA) of left eye retinas were detected. These were used to investigate the mechanism of light-induced damage on retinas and get the message of the relationship between oxyradical and retinal light injury.The results showed that we obtained four conclusions: (1)The retinas of groupⅠwere morphologically normal with distinct structural layers and regular arrangement of outer and inner segments. No positive marked cell was found. In groupⅡandⅢ, the arrangement of outer and inner segment was disordered. The thickness of the outer nuclear layers decreased. We could find many TUNEL-positive nuclei in the outer nuclear layers. It was obviously represented on day 1. In groupⅣ, comparing with groupⅢnot only more cell nuclei were presented but also the surviving photoreceptors had greater integrity. Only part of the mitochondrion of the inner segment were swollen. (2) The ONL of groupⅠwas the thickest. After light damage, the thickness of the ONL was thinner and thinner with the time increasing. There was significant difference among all time phases inⅡandⅢgroups(P<0.05). After light damage, the ONL of groupⅣwas thinner and thinner too, but it was obviously thicker thanⅡandⅢgroups on all phases ( P<0.05). (3) The mean apoptosis index ( AI) of groupⅠon each phase was nearly zero. The maximum AI of the other three groups was found on day 1. The AI of groupⅣwas lower than groupⅡandⅢon each phase. And there was no statistical difference between group II and groupⅢat each point (P>0.05). (4) The content of MDA reached the top on day 1 after light exposure inⅡ,ⅢandⅣgroups.Then they decreased somewhat but still higher than groupⅠon day 6 and day 10. The activity of SOD in retinas decreased to the lowest point on day 1 then it increased somewhat on day 6. In groupⅣ, the level of MDA decreased obviously on day 0.5, day 1 and day 6 compared with groupⅢ. While the activity of SOD increased significantly on all phases except day 10 ( P<0.01).The analysis shows that light-induced damage in rat retina is a kind of apoptosis. Edaravone can reduce the injury of retina and protect the photoreceptors. It resists the free radicals and lipid peroxides.