Assessing nuclear versus mitochondrial cell-free DNA (cfDNA) by qRT-PCR and droplet digital PCR using a piglet model of perinatal asphyxia

Background Since the discovery more than half a century ago, cell-free DNA (cfDNA) has become an attractive objective in multiple diagnostic, prognostic, and monitoring settings. However, despite the increasing number of cfDNA applications in liquid biopsies, we still lack a comprehensive understanding of the nature of cfDNA including optimal assessment. In the presented study, we continued testing and validation of common techniques for cfDNA extraction and quantification (qRT-PCR or droplet digital PCR) of nuclear- and mitochondrial cfDNA (ncfDNA and mtcfDNA) in blood, using a piglet model of perinatal asphyxia to determine potential temporal and quantitative changes at the levels of cfDNA. Methods and Results Newborn piglets (n = 19) were either exposed to hypoxia (n = 11) or were part of the sham-operated control group (n = 8). Blood samples were collected at baseline (= start) and at the end of hypoxia or at 40–45 min for the sham-operated control group. Applying the qRT-PCR method, ncfDNA concentrations in piglets exposed to hypoxia revealed an increasing trend from 7.1 ng/ml to 9.5 ng/ml for HK2 (hexokinase 2) and from 4.6 ng/ml to 7.9 ng/ml for β-globulin, respectively, whereas the control animals showed a more balanced profile. Furthermore, median levels of mtcfDNA were much higher in comparison to ncfDNA, but without significant differences between intervention versus the control group. Conclusions Both, qRT-PCR and the droplet digital PCR technique identified overall similar patterns for the concentration changes of cfDNA; but, the more sensitive digital PCR methodology might be required to identify minimal responses.