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

Objective Strenuous exercise increases circulating cell free DNA (cf DNA) and stimulates blood phagocytes to generate more 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; (C) there is an association between integrity of cf DNA and LBCL. Methods Eleven average-trained men performed three treadmill exercise tests to exhaustion at speed corresponding to 70% of their individual VO2max 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) were determined with real-time PCR along with measurement of resting and fMLP-stimulated LBCL. Results 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 (p<0.05). Post-exercise cf n-DNA integrity (integrity index, I206/78) decreased after the first (0.59±0.19 vs. 0.48±0.18, p<0.05) and second (0.53±0.14 vs. 0.44±0.17, p<0.05) bout of exercise. There were negative correlations between I206/78 and rLBCL (?=–0.37, p<0.05) and I206/78 and fMLP-LBCL (?=–0.40, p<0.05) – analysis of pooled pre- and post-exercise data (n=66). Although cf-mt DNA rose by about 2-times (p<0.05) after the second and third bout, its integrity (I218/97) did not alter in response to exercise. Conclusions Repeated bouts of exhaustive exercise caused increase in cf n-DNA with decreased integrity which correlated with increased ROS production by circulating polymorphonucler leukocytes. This suggests that oxidants may be involved in the release of cf n-DNA and cf n-DNA strand breaks in response to exhaustive exercise.