This study investigated the role of extracellular superoxide dismutase (EC-SOD), which is a major extracellular antioxidant enzyme in skeletal muscle ischemia and reperfusion (I/R) injury.

The pedicled cremaster muscle flaps from homozygous EC-SOD knockout (EC-SOD-/-), heterozygous CuZn-SOD knockout (CuZn-SOD±) and wild-type (WT) mice were subjected to 4.5 hour ischemia followed by 90 min reperfusion. The pedicled cremaster muscle flaps were examined by functional analysis during the reperfusion. The mRNA and protein expressions of each SOD after I/R were evaluated using quantitative real-time PCR and western blot.

The results showed that the EC-SOD-/- mice had a more profound I/R injury than the CuZn- SOD± or WT mice. In particular, there was a delayed and incomplete recovery of the arterial diameter and blood flow during reperfusion and as well as there being more severe inflammation. After 90 min reperfusion, the EC-SOD mRNA levels increased more in the CuZn-SOD± mice than in the WT mice. However, the CuZn-SOD and Mn-SOD mRNA levels decreased similarly in all 3 groups. The CuZn-SOD protein levels decreased in all groups. The EC-SOD protein levels decreased in the CuZn-SOD± and WT mice, but the Mn-SOD protein levels were unchanged or slightly increased in all groups. The histological results showed diffuse edema and inflammatory cell infiltration around the muscle fibers and these changes were more severe in the EC-SOD-/- mice.

EC-SOD plays an important role in protecting the skeletal muscle from I/R injury caused by the excessive generation of reactive oxygen species.