Radioprotection of Rat Eyes by a Superoxide Dismutase Mimic: a Metalloporphyrin Compound

The search for a therapeutic radioprotectant that could protect normal tissues surrounding the treated area is important in radiation therapy. The purpose of present study was to study the role of antioxidant MnTE-2-PyP in protecting the ocular tissue and retinal microvessels from radiation damage by evaluating the histology and quantifying the photoreceptor cell populations and changes in retinal capillaries. 75 rats were treated with MnTE-2-PyP at 2.5mg/injection into one eye an hour before irradiation. Proton irradiation was given to same eye at doses of 8Gy or 28Gy. Rats were sacrificed every three months. By 6 months following radiation, there was significant loss of photoreceptor outer and inner nuclear layers in the radiation-only group (28Gy) (p<0.05) compared to controls and to the metalloporphyrin-treated group. Retinal microvessel length density decreased significantly 6 months following 28Gy (p<0.05) compared to controls and MnTE-2-PyP treated rats. By 12 months following irradiation, 28Gy caused complete damage to the photoreceptor layer, whereas there was almost no morphological damage in photoreceptor layer in the 28Gy+MnTE-2-PyP group. These results demonstrated that MnTE-2-PyP has protective effects on photoreceptor and retinal capillary from radiation damage, suggesting metalloporphyrin antioxidants may play an important role regulating the oxidative damage induced by radiation.