Defibrotide inhibits antiphospholipid antibody-mediated NET formation and venous thrombosis.

Objectives Defibrotide is a heterogenous mixture of polyanionic oligonucleotides currently approved for treatment of transplant-associated veno-occlusive disease. While defibrotide has a known role in limiting endothelial cell activation, some studies have also demonstrated anti-leukocyte properties. We recently revealed a role for neutrophil extracellular traps (NETs) in the thrombotic complications of antiphospholipid syndrome (APS). Here, we hypothesized that defibrotide might act to mitigate APS-relevant NET formation in vitro and in mouse models. Methods We used in vitro assays and a mouse model to determine mechanisms by which defibrotide inhibits NET formation and venous thrombosis in APS. Results At doses ranging from 1 to 10 μg ml-1 , defibrotide significantly suppressed NET formation from control neutrophils stimulated with IgG isolated from APS patients. Defibrotide increased levels of intracellular cyclic AMP in neutrophils, and its suppressive effects on NET formation were mitigated by blocking adenosine A2A receptor or by inhibiting the cyclic AMP-dependent kinase, protein kinase A. Defibrotide at doses ranging from 15 to 150 mg/kg/day inhibited NET formation and venous thrombosis in a model of antiphospholipid antibody-accelerated thrombosis-an effect that was reduced in adenosine A2A receptor knockout mice. Conclusion This study is the first to demonstrate mechanisms by which defibrotide counteracts neutrophil-mediated thrombo-inflammation inherent to APS.