Commentary on "microparticle-associated tissue factor activity in patients with metastatic pancreatic cancer and its effect on fibrin clot formation"

Procoagulant extracellular vesicles in amniotic fluid

Embolization of amniotic fluid (AF) into the blood circulation leads to disseminated intravascular coagulation (DIC). Procoagulant phosphatidylserine (PS)- and tissue factor (TF)-exposing extracellular vesicles (EVs) might play an important role in AF embolism-induced DIC. It was the aim of the present study to perform analyses of the procoagulant properties of AF with a panel of functional coagulation assays and flow cytometry. We applied a prothrombinase assay (that quantifies PS exposure on EVs), an EV-associated TF activity assay, a fibrin generation assay, a thrombin generation assay, a whole blood clotting model, and flow cytometry in AF and control plasma. We found that PS exposure on EVs was 21-fold increased in AF compared with plasma. Also, EV-associated TF activity was highly increased in AF compared with plasma. AF-derived EVs activated the blood coagulation cascade via PS and TF in the fibrin and thrombin generation assays. In a whole blood clotting model, AF-derived EVs significantly shortened the clotting time from 734 ± 139 seconds in the presence to 232 ± 139 seconds in the absence of an anti-TF antibody. The contact activation pathway via factor XII (FXII) was not affected. Applying flow cytometry, a subpopulation of PS⁺ and TF⁺ EVs was identified in AF but not in control plasma. In conclusion, we investigated the effect of AF on blood coagulation and found that PS⁺ and TF⁺ EVs determine their procoagulant potential. Taken together, our data further delineate the pathomechanisms underlying AF-induced coagulopathy.

Tissue factor-bearing microparticles and CA19.9: two players in pancreatic cancer-associated thrombosis?

Background:

Cancer-related venous thromboembolism (VTE) heralds a poor prognosis, especially in pancreatic adenocarcinoma (PAC). Tissue factor (TF) is implicated as one of the main culprits in PAC-associated VTE and disease progression.

Methods:

In a prospective cohort study of 79 PAC patients, we measured plasma CA19–9 and microparticle-associated TF activity (MP-TF activity). In addition, we enumerated TF⁺MPs and MUC1⁺MPs in plasma (n=55), and studied the expression of TF, MUC1, CD31 and CD68 in tumour tissue (n=44).

Results:

Plasma MP-TF activity was markedly elevated in PAC patients with VTE compared with those without (median: 1925 vs 113 fM Xa min⁻¹; P<0.001) and correlated with the extent of thromboembolic events, metastatic disease and short survival. Similar results were found for CA19–9. Patients with massively progressing thrombosis and cerebral embolisms despite anticoagulant therapy (n=3) had the highest MP-TF activities (12 118–40 188 fM Xa min⁻¹) and CA19–9 (40 730–197 000 kU l⁻¹). All tumours expressed MUC1 and TF. MP-TF activity did not correlate with intensity of TF expression in adenocarcinoma cells, but corresponded with numbers of TF⁺ macrophages in the surrounding stroma.

Conclusions:

Circulating TF⁺MPs and mucins may concertedly aggravate coagulopathy in PAC. Understanding of underlying mechanisms may result in new treatment strategies for VTE prevention and improvement of survival.