Extracellular DNA in blood: an index of <i>in vivo</i> inflammatory response

Abstract

Increased concentration of cell-free DNA (cfDNA) in the circulating blood of humans and animals is a sign of inflammatory conditions and a distinctive characteristic of various pathophysiological processes in the body. The aim of the present study was to investigate the possible role of tumor necrosis factor (TNFα) in changes of cfDNA contents in peripheral blood as a response to experimentally induced systemic inflammation.We used 40 female hybrid mice (C57Bl/6xDBA/2) F1 at the age of 6-8 weeks. The concentration of cfDNA and its individual fractions was determined using a PicoGreen fluorescent dye. The dynamics of inflammatory process was evaluated after 4, 8, 11 and 24 hours following LPS injection. A significant increase in the blood plasma cfDNA levels was shown under the action of E. coli lipopolysaccharide (LPS), along with simultaneous decreased levels of cfDNA, associated with cell surface. The ratio of cell surface-bound cfDNA to the total cfDNA contents was reduced in dose-dependent manner as early as 4 hours after LPS injection to the animals, thus allowing us to consider this ratio a characteristic sign of netosis of neutrophilic granulocytes during the development of acute inflammation. The described effects are significantly suppressed with co-injection of recombinant TNFα neutralizing protein along with LPS, whereas increased intake of neutrophils in the tissues is determined by some other factors which are not directly related to the production of this cytokine.Based on the obtained data, we proposed a following hypothesis: induction of netosis by inflammatory stimuli causes an increase in the concentration of cfDNA in blood plasma not only due to de novo emerging extracellular DNA by neutrophil netosis, but also by the release of distinct cfDNA fraction that was previously firmly bound to cell membranes in multiple body tissues under the action of proteases released during netosis.