Effect of Systemic Neuroprotective Agents on Photoreceptor Apoptosis in a Rat Model of Retinal Detachment

Abstract

Abstract: : Purpose: Photoreceptor apoptosis has been found to be a critical phenomenon limiting visual recovery following retinal detachment. The purpose of this experiment is to determine if minocycline, NG–nitro–L–arginine methylester (L–NAME) or geranylgeranylacetone (GGA) prevent photoreceptor apoptosis in a rat model of retinal detachment. Methods: Retinal detachments were created in Brown Norway rats by injecting 10% hyaluronic acid into the subretinal space using a transvitreous approach. Minocycline (45 mg/kg/day) and L–NAME (30 mg/kg/day) were injected intraperitoneally on the day of detachment induction and for the two following days (n = 10 and 8 eyes, respectively). GGA (200 mg/kg/day) was injected intraperitoneally for 3 days prior to retinal detachment induction, the day of the induction and for the two following days (n = 6 eyes). Control animals received saline intraperitoneal injections on the day of detachment induction and for the two following days (n = 6 eyes). All eyes were enucleated 72 hours after retinal detachment induction, embedded in paraffin and sectioned every 6 µm. Light microscopy and terminal dUTP–biotin nick end–labeling (TUNEL) were performed to assay for morphologic features associated with apoptosis. TUNEL–positive cells were counted by a masked observer. The mean number of TUNEL–positive cells was determined by averaging the number of TUNEL–positive cells in three sections of each eye. Results: Light microscopic analysis of detached retinas showed the presence of pyknotic nuclei in the outer nuclear layer and disruption of the normal organization of the photoreceptor outer segments. TUNEL–staining was positive in the outer nuclear layer only in the detached portions of retina. The mean number of TUNEL–positive cells was similar in control eyes (mean ± SD, 86.2 ± 34.3) vs. eyes of animals treated with minocycline (62.7 ± 26.5) or L–NAME (70.5 ± 48.2). The mean number of TUNEL–positive cells was fewer in eyes of animals treated with GGA (37.6 ± 30.0), and this difference was statistically significant by two–tailed t–test (p = 0.03). Conclusions: These data suggest that systemic administration of the neuroprotective agent GGA may decrease photoreceptor apoptosis in a rat model of retinal detachment.

Keywords: retinal detachment • apoptosis/cell death • photoreceptors