Human retinal pigment epithelium contains two distinct species of superoxide dismutase

Superoxide dismutase (SOD) molecules occur in all cells exposed to an oxygen-containing environment, including retinal pigment epithelial (RPE) cells. Previous studies of nonhuman RPE have either probed specifically for copper-zinc-containing SOD (CuZn-SOD) or have not distinguished between CuZn-SOD and the SOD molecule that contains manganese (Mn-SOD). The authors used specific enzymatic assays and immunologic probes, both in vivo and in vitro, to show that human RPE cells contain both CuZn-SOD and Mn-SOD. The CuZn-SOD had a diffuse cytosolic distribution, whereas the Mn form was located primarily in the mitochondria. The role of SODs in protecting the chorioretinal complex against oxidative damage and with regard to aging processes is not well understood and warrants further investigation, and the two cellular forms of SOD should be considered in future studies.