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

Abstract

Strenuous exercise increases circulating cell free DNA (cfDNA) and stimulates blood phagocytes to generate reactive oxygen species (ROS) which may induce DNA strand breaks. We tested whether: (A) elevated cfDNA 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 (r) and fMLP (n-formyl-methionyl-leucyl-phenylalanine)-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, I_229/97) 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 I_229/97 and rLBCL (ƍ = -0.37), and I_229/97 and fMLP-LBCL (ƍ = -0.40) - analysis of pooled pre- and post-exercise data (n = 66). cf mt- DNA integrity (I_218/78) 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.

Figure 1

Overview of the study design. ECG -electrocardiography, FVC – forced vital capacity, FEV1 – forced exhaled volume in the first second, VO2max – maximal oxygen consumption, fMLP –n-formyl-methionyl-leucyl-phenylalanine, cfDNA – cell free DNA, PCR – polymerase chain reaction. VO2max was measured by a continuous incremental maximal exercise test using programmable treadmill with gas exchange analysis system and 12-lead wireless ECG at day 1^st. Afterwards volunteers performed treadmill run to volitional exhaustion at speed corresponding to 70% of their personal VO2 max at days 7^th, 10^th and 13^th. Volitional exhaustion was defined as volunteer inability to maintain the required speed of running (exercise intensity) or its wish to stop the test.