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. [1] 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 [2] , 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 [3, 4] . Investigations show that older RBCs are more prone to hemolysis [5, 6] , and lyse more during exercise [7] . This, however, does not explain why an exercise after 9 months of training more than doubled RBC SOD activity, and even less, why 30 min later, SOD activity drops so dramatically. Activation of erythrocyte SOD by micromolar H 2 O 2 concentrations, which could eventually explain the increase in SOD activity during exercise, has been reported earlier [8] , but this report contradicts other investigations [9] and data obtained in vivo [10–12] . Furthermore, the procedure used to prepare the erythrocyte samples for the SOD activity assay [1] rules out the presence of H 2 O 2 . Unfortunately, the ‘Subjects and Methods’ section does not describe what method was used to determine SOD activity. The ‘Discussion’ in turn does not address the surprising dynamics of the SOD activity. On the contrary, it contains statements that are completely wrong. For example, ‘However, because it is dismutated by the antioxidant defense system, SOD is present in tissue to convert O 2 – to H 2 O 2 and H 2 O 2 to H 2 O and O 2 ’. First, ‘dismutation’ is the conversion of O 2 – to H 2 O 2 and O 2 . Second, SOD does not convert H 2 O 2 to H 2 O and O 2 [9, 13] . In fact, CuZnSOD displays modest peroxidase activity [14] , but this does not mean that it decomposes H 2 O 2 to H 2 O and O 2 . Third, reference 14 in the paper by Kim et al. does not support the above-listed statements of the authors. Performing experiments in vivo and interpreting data requires knowledge and understanding of the processes at the molecular level. Lack of such knowledge and understanding leads to Received: March 24, 2010 Accepted: June 23, 2010