Circulating cell-free nucleic acids: characteristics and applications

Abstract

Liquid biopsy is becoming a very popular sample obtaining procedure, replacing the invasive sampling methods for the diagnostic protocols. The advantages of this method include the possibility to isolate cell-free nucleic acids (cfNAs) for diagnostic or screening purposes. A comprehensive review combining all current and perspective applications of cell-free nucleic acids is missing. Published articles are dealing with one type of cfNAs, or discuss them from the perspective of single disorder. We collected here all known types of cfNAs which are known to be present in biological fluids and could be involved in further studies to find out the exact biological role of them in normal physiological and pathological conditions. Beyond doubt, cfNAs will have a tremendous effect in future screening, diagnosis, prognosis, follow-up and treatment of cardiovascular diseases, cancer, diabetes and other diseases.

Fig. 1

Liquid biopsy scheme. Human blood contains cells, extracellular membrane vesicles (EMVS), cell-free DNA (cfDNA), cell-free RNA (cfRNA) and proteins that can be used as biomarkers for various diseases

Fig. 2

Formation of extracellular membrane vesicles (EMVs). Based on the size and origin, EMVs are divided into exosomes (40–100 nm), microvesicles (50–3000 nm) and ABs (800–5000 nm). EMVs are loaded with cellular content like nucleic acids and proteins. ABs as a product of apoptosis can also carry cellular organelles, e.g., nucleus, mitochondria and endoplasmatic reticulum (ER)