Circulating Microparticles and Risk of Venous Thromboembolism.

Microparticles (MPs) are circulating, submicroscopic fragments (<1 μm of diameter) of membrane-bound cytoplasm that shed from the surface of an activated or apoptotic cell and play a role in coagulation, inflammation, cell remodelling and proliferation. There is increasing evidence that MPs are involved in thrombosis, but whether or not they are an independent risk factor for venous thromboembolism (VTE) is not established.

To investigate the association between high plasma levels of MPs and risk of VTE

In a case-control study, 186 patients with a first episode of VTE (deep venous thrombosis and/or pulmonary embolism) and 418 healthy controls were included. MPs were analyzed by flow cytometry with a gate defined by a 1 μm beads and using APC-Annexin V together with FITC anti-CD41 or FITC anti-CD142 antibodies in order to identify platelet MPs (MP-Plts) and MPs exposing tissue factor (MP-TF), respectively. MPs levels were expressed as number/μL.

Patients had significantly higher median plasma levels of both MPs-Plts and MPs-TF than controls [1942 vs 1519 (p<0.0001) and 579 vs 454 (p<0.0001)]. Higher median levels of MP-Plts and MP-TF were found in 41 patients who underwent blood sampling within 6 months from VTE than in those sampled later [2114 vs 1694 (p=0.086) and 652 vs 543 (p=0.120)]. Sex, age, body mass index and factor VIII plasma levels had no influence on MPs levels, as well as the use of oral contraceptives (this latter evaluated only in controls). In the whole study population, carriership of thrombophilia (antithrombin, protein C or protein S deficiency, factor V Leiden, prothrombin G20210A, antiphospholipid antibodies, hyperhomocysteinemia or combined abnormalities) had higher levels of MP-Plts and MP-TF than non-carriers [1907 vs 1565 (p=0.002) and 532 vs 468 (p=0.011)]. The odds ratio (OR) for VTE, adjusted for sex, age, body mass index and thrombophilia was 2.5-fold higher in individuals with MPs plasma levels >95^th percentile of the control group (3633/μL for MPs-Plts and 1113/μL for MPs-TF) than in those with MPs levels ≤95^th percentile [for MPs-Plts: OR=2.59 (95%CI 1.23 – 5.45); for MPs-TF: OR=2.38 (1.15 – 4.92)]. The risk increased in a dose-dependent manner for both MPs-Plts and MPs-TF, particularly above the 75^th percentile of the distribution in controls. The exclusion of patients whose MPs levels were measured within 6 months from VTE (in order to avoid the possible effect of the acute phase on MPs measurements), did not change the results [adjusted OR: 2.63 (1.18 – 5.89) for MPs-Plts and 2.36 (1.10 – 5.19) for MPs-TF]. The Table shows the relative risks of VTE associated with the presence or absence of high MPs levels and thrombophilia. Individuals with MPs >95^th percentile or thrombophilia alone had a 2 to 3-fold increased risk of VTE, whereas those with both MPs-Plts >95^th percentile and thrombophilia had a 9-fold increased risk of VTE. This synergistic effect was confirmed also for MPs-TF and remained after the exclusion of patients whose blood sample was collected within 6 months from VTE [OR 7.72 (1.68-35.4) for MP-Plts and 8.14 (2.08-31.8) for MP-TF].

Plasma levels of MPs are significantly higher in patients with VTE than in healthy controls. MPs levels >95^th percentile are associated with a 2.5-fold increased risk of VTE. There is a synergistic interaction between high levels of MPs and thrombophilia on VTE risk.

No relevant conflicts of interest to declare.