Abstract A024: Clinical Significance of Neutrophil Extracellular Traps in Thrombi Retrieved with Mechanical Thrombectomy

Introduction: Neutrophil extracellular traps (NETs), which are released from neutrophils in response to local inflammation, have gained increasing attention for their critical role in vascular thrombosis. However, the role of NETs in the pathophysiology of ischemic stroke remains to be elucidated. We investigated the clinical role and significance of NETs in thrombi retrieved with mechanical thrombectomy. Hypothesis: NETs can contribute to thrombus formation in ischemic stroke and may be targeted for ischemic stroke therapy. Methods: We retrospectively analyzed 40 consecutive acute ischemic stroke patients due to large vessel occlusion with pathological specimens of retrieved thrombi at our institute between January 2023 and March 2024. In retrieved thrombi, immunohistochemical staining was performed using antibodies against citrullinated histone H3 (H3Cit) and neutrophil elastase (NE). NETs were defined as extracellular colocalization of H3Cit and NE. In addition, immunostaining for von Willebrand factor (vWF) was performed to evaluate its spatial relationship with NETs. The proportion of NETs within thrombi was quantified, and its association with pretreatment clinical information and therapeutic outcomes of thrombectomy was investigated. Results: Cardioembolic stroke was the most common subtype (31 cases, 78%). NETs were identified in all retrieved thrombi (Figure 1), and the proportion of NETs ranged from 0.2% to 35.8% (median interquartile range, 13.1% 3.6-21.2). Intracellular H3Cit-positive neutrophils were also identified in all cases, indicating early NETosis processes (Figure 2). Accumulation of vWF was noted surrounding NETs (Figures 1 and 2). The proportion of NETs within thrombi showed a positive correlation with the pretreatment platelet count (ρ=0.36, p=0.04). First pass effect (FPE), defined as 1-pass eTICI 2c-3, was achieved in 20 cases (50%), and the proportion of NETs within thrombi tended to be lower in the FPE group than in the non-FPE group (6.3% 2.4-18.3 vs. 16.1% 7.8-24.1, p=0.06). Conclusions: The presence of NETs and NETosis in retrieved thrombi surrounded by vWF, a key mediator of vascular thrombosis, suggests that NETs may contribute to thrombus formation in the pathophysiology of ischemic stroke. Furthermore, NETs in occlusive thrombi, potentially estimated by the pretreatment platelet count, may influence thrombectomy outcomes, highlighting the potential for developing more effective therapeutic approaches targeting NETs.