Electron spin resonance and exercise-induced oxidative stress: an antitoxidant intervention study

 

Electron spin resonance (ESR) evidence concerning free radical production by exercise has been confined to animals. This thesis describes a methodology to measure free radicals using ESR in the venous circulation of healthy humans. It also describes three ESR studies of human blood to test the hypothesis that tissue damage associated with strenuous aerobic exercise is free radical-mediated due to the promotion of electron leakage from the mitochondrial electron transport chain via increased whole body oxygen flux, a mechanism known to result in free radical formation.

Study l demonstrated a significant increase in the concentration of the α-phenylbutyr-tert-nitrone (PBN) adduct (0.04 ± 0.01 vs 0.18 ± 0.04 arbitrary units, p=0.003) and ascorbyl radical (0.02 ± 0.001 vs 0.03 ± 0.002 arbitrary units, p=0.04) post-exercise. A threshold o fincrease of the PBN adduct appears to exist corresponding to approximately 70% VO2max which may prove to be clinically important. Duplicate blood samples were analysed for lipid peroxidation including malondialdhyde (MDA) and lipid hydroperoxides (LH). MDA (0.70 ± 0.05 to 0.80 ± 0.04 µmol.L-1 p=0.0125) and LH (1.15 ± 0.07 to 1.63 ± 0.29 µmol.L-1, p=0.006) significantly increased post-exercise. Study 1 also demonstrated that exhaustive aerobic exercise results in significant increases in plasma endotoxin concentration (0.16 ± 0.03 vs 0.24 ± 0.06 Eu.ml-1, p=0.001) pre vs post-exercise. This may be a free radical mediated phenomenon also of clinical significance.

Study 2 demonstrated that strenuous anaerobic exercise does not lead to increases in the concentration of the PBN adduct or the ascorbyl radical. Furthermore plasma LH did not change in this study although MDA increased significantly (0.74 ± 0.08 vs 1.73 ± 0.65 µmol.L-1, p=0.01) pre vs post-exercise. This may reflect inadequacies in clearance of MDA.

Study 3 demonstrated that ascorbic acid supplementation results in an attenuation of the ESR signal both pre and post-exercise. Supplementation with ascorbic acid resulted in attenuation of exercise-induced lipid peroxidation and enhancement of blood arch also demonstrates for the first time a complete abolition of endotoxin from the plasma of subjects who have undergone maximal aerobic exercise.

Additionally in vitro studies were performed in order to attempt to identify the origin of the radical species. These results suggest that the ESR signal of the PBN adduct is an oxygen-centred radical possibly derived from peroxidation of membrane PUFA. This work supports

The hypothesis that strenuous aerobic exercise leads to increased free radical production probably via enhancement of mitochondrial electron transport chain leakage due to increased whole body oxygen uptake which is detectable using ESR spectroscopy.