Neutrophil Extracellular Traps in Arterial and Venous Thrombosis.

Thrombotic complications are still a major health risk worldwide. Our view on the pathophysiology of thrombosis has significantly changed since the discovery of neutrophil extracellular traps (NETs) and their prothrombotic characteristics. Generated by neutrophils that release their decondensed chromatin as a network of extracellular fibers, NETs promote thrombus formation by serving as a scaffold that activates platelets and coagulation. The thrombogenic involvement of NETs has been described in various settings of thrombosis, including stroke, myocardial infarction, and deep vein thrombosis. The aim of this review is to summarize existing evidence showing the presence of NETs in human thrombus material. Following an introduction on NETs and their role in thrombus formation, the authors address studies showing the presence of NETs in arterial or venous thrombi. In addition, they focus on potential novel therapeutic opportunities to resolve or prevent thrombosis by targeting NETs.

Neutrophil extracellular traps in ischemic stroke thrombi.

OBJECTIVE: Neutrophil extracellular traps (NETs) have been shown to promote thrombus formation. Little is known about the exact composition of thrombi that cause ischemic stroke. In particular, no information is yet available on the presence of NETs in cerebral occlusions. Such information is, however, essential to improve current thrombolytic therapy with tissue plasminogen activator (t-PA). This study aimed at investigating the presence of neutrophils and more specifically NETs in ischemic stroke thrombi. METHODS: Sixty-eight thrombi retrieved from ischemic stroke patients undergoing endovascular treatment were characterized by immunostaining using neutrophil markers (CD66b and neutrophil elastase) and NET markers (citrullinated histone H3 [H3Cit] and extracellular DNA). Neutrophils and NETs were quantified. In addition, extracellular DNA was targeted by performing ex vivo lysis of retrieved thrombi with DNase 1 and t-PA. RESULTS: Neutrophils were detected extensively throughout all thrombi. H3Cit, a hallmark of NETs, was observed in almost all thrombi. H3Cit-positive area varied up to 13.45% of total thrombus area. Colocalization of H3Cit with extracellular DNA released from neutrophils confirmed the specific presence of NETs. H3Cit was more abundant in thrombi of cardioembolic origin compared to other etiologies. Older thrombi contained significantly more neutrophils and H3Cit compared to fresh thrombi. Interestingly, ex vivo lysis of patient thrombi was more successful when adding DNase 1 to standard t-PA. INTERPRETATION: Neutrophils and NETs form important constituents of cerebral thrombi. Targeting of NETs with DNase 1 might have prothrombolytic potential in treatment of acute ischemic stroke. Ann Neurol 2017;82:223-232.