Abstract
Purpose: :
Retinitis pigmentosa (RP) is a group of diseases characterized by genetic mutations leading to rod photoreceptor cell death and subsequent loss of cone photoreceptors. Previously, we had found that antioxidants such as α-tocopherol, ascorbic acid, and α-lipoic acid were effective in preserving cone photoreceptors in the heterozygous transgenic S334ter RP rat model. In this study, we established a method to automate the cone photoreceptor cell quantification by combining Confocal microscopy with Imaris 3D computer software. We then employed another antioxidant, N-acetylcysteine (NAC), and tested its effectiveness in the homozygous S334ter RP rat model, which exhibits faster onset and a more severe form of photoreceptor degeneration.
Methods: :
1m and 2m old homozygote S344ter rats were fed with drinking water containing 2mg/ml or 5mg/ml NAC. At 3m and 4m time points, retinas were isolated from NAC treated animals and age-matched S334ter control rats and stained with flourescent tagged PNA. Confocal microscopy was set up to detect and automatically image cone photoreceptors in the retina, which was flatmounted with photoreceptor side up. The cone photoreceptors were visualized and quantified using Imaris software at various regions of the retina. Additionally, retinas isolated from the contralateral eyes were processed, sectioned, H&E stained and evaluated for total photoreceptor cell loss.
Results: :
Between days 30 and 120, there was significant loss of photoreceptors in these homozygous S334ter rats. The number of photoreceptor nuclei was reduced to about 1 to 2 rows, with significant loss of photoreceptors observed in the superior retina. The degeneration of the cone photoreceptors was characterized by islands of areas lacking PNA staining with loss of cone photoreceptors observed throughout the superior retina and diffusely in the nasal and inferior regions. In animals treated with NAC, the number of cone photoreceptors was significantly higher than in the control animals at each time point. By day 120, NAC treated animals had 35% more cone photoreceptors in the superior retina than the control S334ter rats.
Conclusions: :
Antioxidant NAC administrated orally was found to significantly reduce the cone cell photoreceptor death in the homozygous transgenic S334ter rats. Combined with previous data, this strongly suggests that oxidative stress plays a major role in cone photoreceptor death in retinitis pigmentosa and that antioxidants may be a potential therapy for retinitis pigmentosa.
Keywords: photoreceptors • antioxidants • oxidation/oxidative or free radical damage