Decreased integrity of exercise-induced plasma cell free nuclear DNA - negative association with the increased oxidants production by circulating phagocytes

Strenuous exercise increases circulating cell free DNA (cf DNA) and stimulates blood phagocytes to generate reactive oxygen species (ROS) which may induce DNA strand breaks. We tested whether: (A) elevated cf DNA in response to three repeated bouts of exhaustive exercise has decreased integrity; (B) each bout of exercise increases luminol enhanced whole blood chemiluminescence (LBCL) as a measure of ROS production by polymorphonuclear leukocytes. Eleven men performed three treadmill exercise tests to exhaustion separated by 72 hours of resting. Pre- and post-exercise concentrations and integrity of cf nuclear and mitochondrial DNA (cf n-DNA, cf mt-DNA) and resting and fMLP-stimulated LBCL were determined. Each bout increased concentrations of cf n-DNA by more than 10-times which was accompanied by about 2-times elevated post-exercise rLBCL and fMLP-LBCL. Post-exercise cf n-DNA integrity (integrity index, I206/78) decreased after the first (0.59{+/-}0.19 vs. 0.48{+/-}0.18) and second (0.53{+/-}0.14 vs. 0.44{+/-}0.17) bout of exercise. There were negative correlations between I206/78 and rLBCL (=-0.37) and I206/78 and fMLP-LBCL (=- 0.40) - analysis of pooled pre- and post-exercise data (n=66). cf-mt DNA integrity (I218/97) did not alter in response to exercise. This suggests an involvement of phagocyte ROS in cf n-DNA strand breaks in response to exhaustive exercise.