Changes in urinary excretion of oxidative nucleic acid modifications in the week following Copenhagen Marathon 2018, Denmark

Introduction The relationship between oxidative stress and physical activity is very complex. A single bout of exercise seems to induce oxidative stress, whereas regular exercise has been suggested to reduce oxidative stress. Here, we investigated the changes in oxidative RNA and DNA modifications in the week following a single bout of excessive exercise. Methods This observational study was conducted in relation to the Copenhagen Marathon 2018, Denmark. Male, non-professional runners (n=20) were examined before-, immediate after-, four days after-, and seven days after the marathon. Twenty-four-hour (24h) urine excretion of 8-oxo-7,8-dihydro-guanosine(8-oxoGuo) and 8-oxo-7,8-dihydro-2’-deoxyguanosine(8-oxodG) were determined using ultra performance liquid chromatography-tandem mass spectrometry as a measurement of oxidative RNA and DNA modifications, respectively. Results The runners were healthy, non-smokers with cardiorespiratory fitness level above average ((median (inter quartile range(IQR))): Age:  29.6(24.3;37.2) years, body mass index: 24.3(23.8;25.2) kg/m 2 , VO 2 max: 52.7(49.5;55.7) ml/min/kg). The baseline level of 8-oxoGuo and 8-oxodG were (median(IQR)): 33.9(29.2; 38.1) and 27.9(21.4; 30.8) nmol/24h, respectively. The level of 8-oxoGuo presented a marginal trend towards increase immediate after the marathon compared to baseline (Δmedian(IQR): 3.9 (-2.4;8.7) nmol/24h, P=0.12), no difference was found in 8-oxodG (-1.8(-4.3;2.6) nmol/24h, P=0.62). On day four, we observed a decrease in both 8-oxoGuo (-2.1(-8.4;0.1) nmol/24h, P=0.02) and 8-oxodG (-2.5(-4.0;0.1) nmol/24h, P Conclusion A single bout of strenuous exercise did not result in immediate increase in oxidative RNA and DNA modifications, however a marginal trend toward increased level of oxidative RNA modifications was observed. Both oxidative RNA and DNA modifications decreased four days after the marathon. The clinical implications of these results remain to be elucidated.