Non-invasive detection of tissue-specific cell death following cardiopulmonary bypass

Cell-free circulating DNA (cfDNA) released from dying cells is emerging as a diagnostic tool for monitoring cancer dynamics and graft failure. Extending liquid biopsy potential, we used comparative methylome analysis to identify genomic loci that are unmethylated specifically in cardiomyocytes and central nervous system (CNS) cells. We further developed these as biomarkers to allow quantification of cfDNA carrying methylation patterns of the cell type of interest. The plasma of healthy individuals contained essentially no cardiomyocyte and CNS-derived cfDNA, consistent with minimal turnover of heart and brain. Proving our assay reliability, patients with myocardial infarction showed a robust cardiac cfDNA signal that correlated with levels of troponin and creatine kinase (CPK). Neuronal/glial DNA levels were identified in patients after traumatic brain injury or cardiac arrest, and in cancer patients having brain metastases. We then investigated tissue damage induced by cardiopulmonary bypass (CPB) used during heart surgery in babies, given that previous clinical tests suggested that CPB damage target organs including a neurological impairment. Serial blood sampling of 50 infants who underwent CPB showed a dramatic increase in cardiac-derived cfDNA that was sustained even 24 hours after surgery. High levels of CNS-derived cfDNA were also measured, indicative of brain damage associated with CPB. Determining tissue origins of cfDNA and thus the extent of cell type-specific death may find utility in diagnosis and monitoring of neurological disorders and cardiac pathologies, in the study of normal human brain and cardiac development and homeostasis, and in the monitoring and refinement of surgical procedures such as CPB.