Effects Of Tempol Treatment In The Rd1 Mouse Model Of Retinal Degeneration

Abstract

Purpose: : The radical scavenger tempol and its acyl chain derivative tempol-C8 have been shown to act neuroprotectively in different retinal neuronal damage models, in particular also in a rat outer retinal light damage model. Here we present the effects of tempol and tempol-C8 treatment on photoreceptor survival in the rd1-mouse model.

Methods: : 9 rd1-mice were divided into 3 groups of 3 animals. Mice were treated with intraperitoneal injections of: (1) tempol at a dose of 150 mg/kg body weight (bw), (2) tempol-C8 at a dose of 5mg/kg bw and (3) PBS as controls. Treatment was performed for 10 consecutive days from 3rd postnatal day to 12th postnatal day. One day later, retinas were prepared, fixed and mounted in cryo blocks. Immunohistochemisty was performed using TUNEL and PAR (Poly(ADP-ribose)) staining. Relation of cones and rods was demonstrated using glycogen phosphatase and rhodopsin colocalised staining. The number of stained cells was quantified separately for the central and peripheral retina. DAPI staining was performed to visualize the absolute cell number in the outer nuclear layer (ONL). ONL thickness and the number of cell layers in the ONL were quantified.

Results: : Thickness of the ONL was not statistically different in tempol group (38.0 µm in peripheral retina and 25.3 µm in central retina) or tempol C8 group (40.4 µm and 27.7 µm) compared to PBS group (40.8 µm and 26.1 µm).The number of cell layers was similar in each group: approx. 5.5 layers in the peripheral retina and 4 layers in the central retina. No differences in the percentage of TUNEL-positive cells and PAR-positive cells were found for all groups in both peripheral and central retina. In the central retina, fewer cones were visualized by glycogen phosphatase staining in tempol (median 13.6%) and tempol-C8 (median 12.7%) groups, as compared to the PBS group (median 16.0%). No differences in the number of cones were found in the peripheral retina.

Conclusions: : Systemic application of the antioxidants tempol or tempol-C8 does not enhance photoreceptor survival in the rd1-mouse model of hereditary photoreceptor degeneration, in contrast to tempol’s effects in an acute light induced photoreceptor damage model.

Keywords: neuroprotection • retinal degenerations: hereditary • photoreceptors