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We investigated the effects of an ultra-marathon on cell-free plasma DNA as well as on mRNA expression of pro-apoptotic (Bax, Bad), anti-apoptotic (Bcl-2) and cell-protective (Hsp70, Hsp27 and Hsp32) genes in mononuclear blood cells (MNCs). Blood samples were drawn from 14 athletes before and immediately after 6-h run. In addition, blood samples were also collected and analyzed 2 and 24 h after the end of the run. Levels of plasma DNA were significantly increased immediately after the marathon (P < 0.001) and were still higher 2 h later (P < 0.005), but significantly lower than those immediately after the race (P < 0.05). Cell-free plasma DNA returned to pre-race levels 24 h after the run. mRNA expressions of Hsp70, Hsp32 and Bax significantly increased in MNCs after the race, whereas Hsp27 and Bad mRNA expression levels showed no significant changes. Bcl-2 expressions decreased immediately after the race (P < 0.001), but increased in the 24 h later (P < 0.05). We conclude that apoptotic ladders of cell-free DNA following exhaustive exercise originate from apoptotic cells and that not only skeletal muscle cells but also leukocytes contribute to this phenomenon.

Background: We evaluated whether cell-free plasma DNA might be an appropriate marker for cell damage during hemodialysis (HD) and whether it correlated with annexin V expression and 7-amino-actinomycin D (7AAD) nuclear staining of blood leukocytes. Methods: Circulating DNA, annexin V, and 7AAD were measured in HD patients before HD, 20 min after start of HD, and after HD had ended. Healthy volunteers provided control measurements. Necrosis and apoptosis were monitored by gel electrophoresis. Results: Plasma DNA concentrations were not significantly different between controls and patients before HD. Circulating DNA increased significantly (P &lt;0.05) after 20 min of treatment with HD. Post-HD concentrations of DNA were significantly higher compared with pre-HD and controls (P &lt;0.005). Agarose gel electrophoresis showed ladders typical of apoptosis in post-HD samples. Two subpopulations of CD45+ leukocytes were defined by flow cytometry: annexin V+/7AAD+ population for apoptosis, and annexin V+/7AAD− for early apoptosis. Compared with healthy controls, mean fluorescence (MF) of 7AAD+ apoptotic cells in the annexin V+/7AAD+ subpopulation before HD was not significantly increased. HD increased MF of 7AAD+ cells in the annexin V+/7AAD+ subpopulation. In this subpopulation, MF of annexin V+ cells was significantly higher (P &lt;0.01). MF of annexin V+ cells in the annexin V+/7AAD+ subpopulation increased during HD. Conclusions: During HD, cell-free plasma DNA concentrations, annexin V expression, and 7AAD uptake in leukocytes increases. The increase in plasma DNA, appearing as ladders typical of apoptosis, and the 7AAD uptake in leukocytes demonstrate that the predominant portion of circulating DNA in HD patients originates from apoptotic leukocytes.

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