Release of redox-active iron by muscle crush trauma: no liberation into the circulation

After major skeletal muscle trauma, the iron-containing protein myoglobin and diverse other intracellular metabolites are liberated into the circulation from injured myocytes. Because chelatable iron should also be present in skeletal muscle cells, this redox-active, not tightly bound iron should be released from injured muscle tissue in addition to myoglobin and potentially account for oxidative tissue damage. The current study demonstrates in vitro the existence of 5 muM chelatable iron within the supernatant of a 1:10 homogenate of rat gastrocnemius muscle. This iron was almost exclusively associated with macromolecules greater than 30 kDa, most likely proteins. Presumably because of this association, only part of the chelatable iron could be scavenged by added apotransferrin. The chelatable iron was redox-active and thus responsible for the formation of thiobarbituric acid-reactive substances (TBARS) within the muscle homogenate. Correspondingly, using an in vivo model of closed trauma to the rat gastrocnemius muscle, a local TBARS formation in the damaged muscle tissue could be detected. Muscle trauma significantly increased plasma creatine kinase and myoglobin levels; however, no increase in serum non-transferrin-bound iron could be observed. Likewise, the serum parameters of iron-induced oxidative damage, TBARS, and protein carbonyls did not significantly increase after trauma. In conclusion, chelatable, redox-active iron is locally released by muscle destruction and responsible for lipid peroxidation within the damaged tissue. However, the liberation of chelatable iron into the circulation and its contribution to oxidative alterations of serum lipids and proteins could not be confirmed.