Background and Aims Despite the presence of neutrophil extracellular traps [NETs] in inflamed colon having been confirmed, the role of NETs, especially the circulating NETs, in the progression and thrombotic tendency of inflammatory bowel disease [IBD] remains elusive. We extended our previous study to prove that NETs constitute a central component in the progression and prothrombotic state of IBD. Methods In all 48 consecutive patients with IBD were studied. Acute colitis was induced by the treatment of C57BL/6 mice with 3.5% dextran sulphate sodium [DSS] in drinking water for 6 days. Peripheral blood neutrophils and sera were collected from IBD patients and murine colitis models. Exposed phosphatidylserine [PS] was analysed with flow cytometry and confocal microscopy. Procoagulant activity was evaluated using clotting time, purified coagulation complex, and fibrin formation assays. Results We observed higher plasma NET levels and presence of NETs in colon tissue in patients with active IBD. More importantly, NETs were induced in mice with DSS colitis, and inhibition of NET release attenuated colitis as well as colitis-associated tumorigenesis. NET degradation through DNase administration decreased cytokine levels during DSS-induced colitis. In addition, DNase treatment also significantly attenuated the accelerated thrombus formation and platelet activation observed in DSS-induced colitis. NETs triggered PS-positive microparticle release and PS exposure on platelets and endothelial cells partially through TLR2 and TLR4, converting them to a procoagulant phenotype. Conclusions NETs exacerbate colon tissue damage and drive thrombotic tendency during active IBD. Strategies directed against NET formation may offer a potential therapeutic approach for the treatment of IBD.

Sepsis is invariably accompanied by altered coagulation cascade; however, the precise role of phosphatidylserine (PS) in inflammation-associated coagulopathy in sepsis has not been well elucidated. We explored the possibility of exposed PS on microparticles (MPs), blood cells, as well as on endothelium, and defined its role in procoagulant activity (PCA) in sepsis. PS-positive MPs and cells were detected by flow cytometry, while PCA was assessed with clotting time, purified coagulation complex, and fibrin formation assays. Plasma levels of PS MPs derived from platelets, leukocytes (including neutrophils, monocytes, and lymphocytes), erythrocytes, and endothelial cells were elevated by 1.49-, 1.60-, 2.93-, and 1.53-fold, respectively, in septic patients. Meanwhile, PS exposure on blood cells was markedly higher in septic patients than in controls. Additionally, we found that the endothelial cells (ECs) treated with septic serum in vitro exposed more PS than with healthy serum. Isolated MPs/blood cells from septic patients and cultured ECs treated with septic serum in vitro demonstrated significantly shortened coagulation time, greatly enhanced intrinsic/extrinsic FXa generation, and increased thrombin formation. Importantly, confocal imaging of MPs or septic serum-treated ECs identified binding sites for FVa and FXa to form prothrombinase, and further supported fibrin formation in the area where PS exposure was abundant. Pretreatment with lactadherin blocked PS on MPs/blood cells/ECs, prolonged coagulation time by at least 25%, reduced FXa/thrombin generation, and inhibited fibrin formation by approximately 85%. Our findings suggest a key role for PS exposed on MPs, blood cells, and endothelium in augmenting coagulation in sepsis. Therefore, therapies targeting PS may be of particular importance.