Letter to the Editor: Comments on ‘The Effect of Training Type on Oxidative DNA Damage and Antioxidant Capacity during Three-Dimensional Space Exercise’

Dear Sir, In a recent edition of Medical Principles and Practice, Kim et al. presented data about the effect of orbotron training on plasma malondialdehyde and lactate content, and erythrocyte superoxide dismutase (SOD) activity. The findings about SOD activity changes are most surprising. Results presented in table 2 and figure 1c show that erythrocyte SOD activity more than doubled (212–251% increase) when the participants in the study were subjected to intense orbotron exercise, even after 9 months of training. Those values rapidly dropped after only 30 min of recovery. Such dynamics are highly unexpected in view of the fact that SOD activity is expressed in units per gram of hemoglobin, which accounts for hematocrit changes; CuZnSOD, the only isoform present in mature erythrocytes, is not post-transcriptionally regulated, and mature erythrocytes cannot synthesize new proteins. The modest increase in erythrocyte SOD activity after 9 months of training can be explained by hemolysis of the older red blood cells (RBCs), which have lower SOD, and their replacement with younger ones containing more SOD. Investi-gations show that older RBCs are more prone to hemolysis, and lyse more during exercise.