Circulating free DNA

Circulating free DNA (cfDNA) are degraded DNA fragments released to the blood plasma. cfDNA can be used to describe various forms of DNA freely circulating the bloodstream, including circulating tumor DNA (ctDNA) and cell-free fetal DNA (cffDNA). Elevated levels of cfDNA are observed in cancer, especially in advanced disease. There is evidence that cfDNA becomes increasingly frequent in circulation with the onset of age. cfDNA has been shown to be a useful biomarker for a multitude of ailments other than cancer and fetal medicine. This includes but is not limited to trauma, sepsis, aseptic inflammation, myocardial infarction, stroke, transplantation, diabetes, and sickle cell disease. cfDNA is mostly a double-stranded extracellular molecule of DNA, consisting of small fragments (70 to 200 bp) and larger fragments (21 kb). and has been recognized as an accurate marker for the diagnosis of prostate cancer and breast cancer. Circulating free DNA (cfDNA) are degraded DNA fragments released to the blood plasma. cfDNA can be used to describe various forms of DNA freely circulating the bloodstream, including circulating tumor DNA (ctDNA) and cell-free fetal DNA (cffDNA). Elevated levels of cfDNA are observed in cancer, especially in advanced disease. There is evidence that cfDNA becomes increasingly frequent in circulation with the onset of age. cfDNA has been shown to be a useful biomarker for a multitude of ailments other than cancer and fetal medicine. This includes but is not limited to trauma, sepsis, aseptic inflammation, myocardial infarction, stroke, transplantation, diabetes, and sickle cell disease. cfDNA is mostly a double-stranded extracellular molecule of DNA, consisting of small fragments (70 to 200 bp) and larger fragments (21 kb). and has been recognized as an accurate marker for the diagnosis of prostate cancer and breast cancer. Other publications confirm the origin of cfDNA from carcinomas and cfDNA occurs in patients with advanced cancer. Cell‐free DNA (cfDNA) is present in the circulating plasma, also in other body fluids. The release of cfDNA into the bloodstream appears by different reasons, including the primary tumor, tumor cells that circulate in peripheral blood, metastatic deposits present at distant sites, and normal cell types, like hematopoietic and stromal cells. Tumor cells and cfDNA circulate in the bloodstream of patients with cancer. Its rapidly increased accumulation in blood during tumor development is caused by an excessive DNA release by apoptotic cells and necrotic cells. Active secretion within exosomes has been discussed, but it is still we don't know whether this is a relevant or rather minor source of cfDNA. cfDNA circulates predominantly as nucleosomes, which are nuclear complexes of histones and DNA. They are frequently nonspecifically elevated in cancer but may be more specific for monitoring cytotoxic cancer therapy, mainly for the early estimation of therapy efficacy. Circulated cell-free DNA was first discovered by Mandel and Metais in 1948. It was later discovered that the level of cfDNA is significantly increased in the plasma of diseased patients. This discovery was first made in Lupus patients and later it was determined that the levels of cfDNA are elevated in over half of cancer patients. This increase in cfDNA in cancer patients has been shown to be due to circulating tumor cells (CTC) traveling in the peripheral blood. The ability to extract circulating tumor DNA (ctDNA) from the human plasma has led to huge advancements in noninvasive cancer detection. Most notably, it has led to what is now known as liquid biopsy. In short, liquid biopsy is using biomarkers and cancer cells in the blood as a means of diagnosing cancer type and stage. This type of biopsy is noninvasive and allows for the routine clinical screening that is important in determining cancer relapse after initial treatment. The intracellular origin of cfDNA, e.g., either from nucleus or mitochondria, can also influence the inflammatory potential of cfDNA. mtDNA is a potent inflammatory trigger. mtDNA, due to its prokaryotic origin, holds many features that are similar to bacterial DNA, including the presence of a relatively high content of unmethylated CpG motifs, which are rarely observed in nuclear DNA. The unmethylated CpG motifs are of particular importance as TLR9, the only endolysosomal DNA-sensing receptor, has a unique specificity for unmethylated CpG DNA. mtDNA was shown to activate neutrophils through TLR9 engagement unless coupled to carrier proteins, mtDNA, but not nuclear DNA, can be recognized as a danger-associated molecular pattern inducing pro-inflammation through TLR9. Collins et al. reported that intra-articular injection of mtDNA induces arthritis in vivo, proposing a direct role of mtDNA extrusion in the disease pathogenesis of RA . MtDNA, in contrast to nuclear DNA, is characterized by elevated basal levels of 8-OHdG, a marker of oxidative damage. The high content of oxidative damage in mtDNA is attributed to the close proximity of mtDNA to ROS and relatively inefficient DNA repair mechanisms that can lead to the accumulation of DNA lesions. They have shown that oxidative burst during NETosis can oxidize mtDNA and the released oxidized mtDNA by itself, or in complex with TFAM, can generate prominent induction of type I IFNs. Oxidized mtDNA generated during programmed cell death is not limited to activate TLR9, but was shown to also engage the NRLP3 inflammasome, leading to the production of pro-inflammatory cytokines, IL-1β, and IL-18. MtDNA can also be recognized by cyclic GMP-AMP synthase (cGAS), a cytosolic dsDNA sensor to initiate a STING-IRF3-dependent pathway that in turn orchestrates the production of type I IFNs. cfDNA purification is prone to contamination due to ruptured blood cells during the purification process. Because of this, different purification methods can lead to significantly different cfDNA extraction yields. At the moment, typical purification methods involve collection of blood via venipuncture, centrifugation to pellet the cells, and extraction of cfDNA from the plasma. The specific method for extraction of cfDNA from the plasma depends on the protocol desired.