The role of cell-free DNA in fibrinolysis for intraventricular hemorrhage

OBJECTIVE Tissue plasminogen activator (tPA) fibrinolysis did not improve functional outcomes of patients with intraventricular hemorrhage (IVH), largely because of the unsatisfactory clot clearance. The presence of neutrophil extracellular traps (NETs) within the clot has been confirmed to impair tPA fibrinolysis, but the mechanism has been unclear. The authors hypothesized that cell-free DNA (cfDNA), the main framework of NETs, might be the important reason for the fibrinolysis resistance, and they validated the hypothesis, hoping to provide a new target to promote intraventricular fibrinolysis. METHODS First, cfDNA was detected in IVH clots by immunofluorescence staining in a rat model of IVH. Second, after blood (with or without exogenous cfDNA) intraventricular injection, IVH rats were given intraventricular infusion of 2 mu l of saline, tPA, or tPA + DNase1 randomly. Then, the ventricular volume, animal behavior, and reactive astrocyte proliferation were assessed. Third, the IVH clots were collected for fibrinolysis assay in vitro. Finally, the effects of exogenous cfDNA in IVH were evaluated. RESULTS The presence of cfDNA in clots was observed as early as 1 hour after IVH. Compared with the whole-blood model, blood + cfDNA caused more severe ventricular dilation (day 7: blood 32.47 +/- 2.096 mm(3) vs blood + DNA 40.09 +/- 2.787 mm(3), p < 0.05), increased fibrinolysis resistance to tPA (day 7: tPA + DNA 26.04 +/- 1.318 mm(3) vs tPA 22.15 +/- 1.706 mm(3), p < 0.05), and further deteriorated the functional defects in rats (blood vs blood + DNA, p < 0.05). Degradation of cfDNA by DNase1 further enhanced the fibrinolysis effects on relieving the ventricular dilation (day 7: tPA + DNase1 11.67 +/- 2.023 mm(3) vs tPA, p < 0.05), improving the functional outcome (tPA vs tPA + DNase1, p < 0.05) and reducing periventricular astrocyte proliferation. CONCLUSIONS cfDNA impaired tPA fibrinolysis for IVH, and degradation of cfDNA may be a new target to improve this condition.