title: Quantitative analysis of circulating mitochondrial DNA in plasma.
abstract: BACKGROUND
  Recent studies have demonstrated the existence of circulating mitochondrial DNA in plasma and serum, but the concentrations and physical characteristics of circulating mitochondrial DNA are unknown. The aim of this study was to develop an assay to quantify mitochondrial DNA in the plasma of healthy individuals.
  
  
  METHODS
  We adopted a real-time quantitative PCR approach and evaluated the specificity of the assay for detecting mitochondrial DNA with a cell line (rho(0)) devoid of mitochondria. The concentrations and physical characteristics of circulating mitochondrial DNA were investigated by experiments conducted in three modules. In module 1, we evaluated the concentrations of mitochondrial DNA in plasma aliquots derived from four blood-processing protocols. In module 2, we investigated the existence of both particle-associated and free forms of mitochondrial DNA in plasma by subjecting plasma to filtration and ultracentrifugation. In module 3, we used filters with different pore sizes to investigate the size characteristics of the particle-associated fraction of circulating mitochondrial DNA.
  
  
  RESULTS
  The mitochondrial DNA-specific, real-time quantitative PCR had a dynamic range of five orders of magnitude and a sensitivity that enabled detection of one copy of mitochondrial DNA in plasma. In module 1, we found significant differences in the amounts of circulating mitochondrial DNA among plasma aliquots processed by different methods. Data from module 2 revealed that a significant fraction of mitochondrial DNA in plasma was filterable or pelletable by ultracentrifugation. Module 3 demonstrated that filters with different pore sizes removed mitochondrial DNA from plasma to different degrees.
  
  
  CONCLUSIONS
  Both particle-associated and free mitochondrial DNA are present in plasma, and their respective concentrations are affected by the process used to harvest plasma from whole blood. These results may have implications in the design of future studies on circulating mitochondrial DNA measured in different disease conditions.
authors.affiliation: Department of Chemical Pathology, The Chinese University of Hong Kong, Prince of Wales Hospital, Shatin, New Territories, Hong Kong SAR.
authors.forename: Rossa W K
authors.initials: RW
authors.lastname: Chiu
authors.forename: Lisa Y S
authors.initials: LY
authors.lastname: Chan
authors.forename: Nicole Y L
authors.initials: NY
authors.lastname: Lam
authors.forename: Nancy B Y
authors.initials: NB
authors.lastname: Tsui
authors.forename: Enders K O
authors.initials: EK
authors.lastname: Ng
authors.forename: Timothy H
authors.initials: TH
authors.lastname: Rainer
authors.forename: Y M Dennis
authors.initials: YM
authors.lastname: Lo
mesh_terms: D001775:Blood Circulation; D001800:Blood Specimen Collection; D004272:DNA, Mitochondrial / Q000097:blood*; D006801:Humans; D016014:Linear Models; D016133:Polymerase Chain Reaction; D012680:Sensitivity and Specificity
chemical_list: D004272:DNA, Mitochondrial