Abstract
Various markers are available to establish the occurrence of oxidative stress in exercise. A relatively under-investigated source of free radicals and oxidative stress involves the heme proteins hemoglobin (Hb) and myoglobin (Mb). Autoxidation of Hb and Mb is a constant source of superoxide in the body, and further reactions may produce hydrogen peroxide, protein bound radicals, and ferryl iron, which are strong oxidants. Oxidatively modified heme (OxH) is one of the products of these reactions, and might be useful as a specific marker of heme-induced oxidative stress in exercise. PURPOSE To determine the effects of two modes of exhaustive incremental exercise on blood levels of OxH. METHODS Ten untrained subjects (5 males, 5 females; 20±1 yrs, 75.2±20.0kg, 175±13cm) performed continuous incremental running test to exhaustion; eight of the subjects performed an additional cycling test one week later. Power output for the cycling test was calculated from individual running VO2-data to produce similar test durations in both tests. Venous blood samples were taken before and directly after exercise, and analyzed for OxH (as a percentage of total heme). Differences between pre- and post-exercise, values, and between cycling and running data were analyzed using paired-sample t-tests. RESULTS Average VO2peak was significantly higher for the running max-test (43.0±7.2 ml·kg −1·min −1) compared to the cycling max-test (41.4±7.5 ml·kg −1·min −1; P < 0.05). Small but significant increases in OxH levels were observed in both the running test (0.0400±0.0058% vs. 0.0431±0.0072%, P < 0.05), and the cycling test (0.0427±0.0062% vs. 0.0450±0.0058%, P < 0.05). No differences were observed between the change in OxH levels in running vs. cycling. CONCLUSION The results of the present study indicate that OxH can be used to demonstrate exercise-induced oxidative stress, and suggest a possible mechanistic role of heme proteins in oxidative stress.
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