Generation of blood circulating DNAs: Sources, features of struction and circulation.

Extracellular nucleic acids (exNAs) were originally described in blood of healthy and sick people in 1948; however, little attention was paid to them until 1960th. exNAs are intensively studied now, especially during the last five years. The major attention is paid to exNAs as the source of a diagnostic material, whereas mechanisms of their generation, as well as mechanisms responsible for their long-term circulation in blood-stream still need better understanding. Some authors believe that the processes of apoptosis and necrosis represent the main source of blood circulating deoxyribonucleic acids (cirDNA), while others suggest nucleic acid secretion by healthy and tumor cells. Circulating DNA were found to be stable in blood for a long time, escaping from the action of DNA hydrolyzing enzymes, possibly, due to formation of various supramolecular complexes. This review summarizes literature data which support all the theories describing appearance of cirDNA; certain attention is paid to features of circulation and structure of the cirDNA and factors affecting time of DNA circulation in blood. [ABSTRACT FROM AUTHOR]