Plasma Mitochondrial DNA Concentrations after Trauma

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Both qualitative and quantitative studies on circulating DNA (1)(2)(3) and RNA(4)(5)(6) in plasma and serum have shown their usefulness in clinical diagnosis and prognosis. In addition to DNA and RNA, there is another species of nucleic acids, mitochondrial DNA (mtDNA), that is usually confined to and functions in the mitochondria. Mutations in the mitochondrial genome are associated with various diseases (7). A recent study reported the presence of a known mtDNA mutation in the serum and plasma of patients with type II diabetes mellitus (8). Mutant mtDNA has been detected in plasma of patients with hepatocellular carcinoma (9). However, unlike circulating DNA, there is a paucity of quantitative data on circulating mtDNA. The reason might be partly attributable to the presence of pseudogenes in the nuclear genome that may lead to coamplification of these nuclear copies of mtDNA (10). To overcome this problem, a mtDNA-specific real-time quantitative PCR assay has recently been developed (11). Significant increases in circulating DNA in the plasma of trauma patients have been reported and found to be useful in posttraumatic prognosis (12). One hypothesis for the increased plasma DNA concentration after trauma is that cell-free DNA is released from damaged tissues to the nearby bloodstream. We therefore proposed that mtDNA in plasma may also be increased after trauma. In this study, we aimed to investigate and compare changes in cell-free mtDNA and nuclear DNA concentration in plasma after trauma, their relationships with injury severity, and the potential prognostic value of plasma mtDNA concentrations. Thirty-eight patients who had sustained an acute blunt traumatic injury and had been admitted to the resuscitation room at the Prince of Wales Hospital between July 2000 and October 2002 were recruited. Inclusion criteria included time from injury to admission of <4 …