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Hyperhomocysteinemia (HHcy) is associated with thrombosis, but the mechanistic links between them are not understood. We studied effects of homocysteine (Hcy) on clot contraction in vitro and in a rat model of HHcy. Incubation of blood with exogenous Hcy for 1 min enhanced clot contraction, while 15-min incubation led to a dose-dependent suppression of contraction. These effects were likely due to direct Hcy-induced platelet activation followed by exhaustion, as revealed by an increase in fibrinogen-binding capacity and P-selectin expression determined by flow cytometry. In the blood of rats with HHcy, clot contraction was enhanced at moderately elevated Hcy levels (10–50 μM), while at higher Hcy levels (&gt, 50 μM), the onset of clot contraction was delayed. HHcy was associated with thrombocytosis combined with a reduced erythrocyte count and hypofibrinogenemia. These data suggest that in HHcy, platelets get activated directly and indirectly, leading to enhanced clot contraction that is facilitated by the reduced content and resilience of fibrin and erythrocytes in the clot. The excessive platelet activation can lead to exhaustion and impaired contractility, which makes clots larger and more obstructive. In conclusion, HHcy modulates blood clot contraction, which may comprise an underappreciated pro- or antithrombotic mechanism.

Deep vein thrombosis (DVT) is a common but unpredictable complication of surgical interventions. To reveal an association between the blood clot contraction (retraction) and the incidence of postoperative venous thrombosis, 78 patients with brain tumors that were operated on were studied, of which 23 (29%) were diagnosed with postoperative DVT. A clot contraction assay, along with other hemostatic and hematologic tests, was performed 1–3 days before the surgery and on the 1st day and 5–7th days after the surgery. On the 1st postoperative day, clot contraction was significantly suppressed in patients who subsequently developed DVT, compared to the patients without DVT. Importantly, this difference was observed at least 5 days before DVT had developed. The weakening of contraction on the 1st postoperative day was more pronounced in the DVT patients with malignant versus benign brain tumors, atherosclerosis, hypertension, as well as in patients receiving steroids before and during the operation. These results indicate that impaired clot contraction in the postoperative period is associated with imminent DVT, suggesting that it is a prothrombotic risk factor and promotional mechanism. The clot contraction assay has a predictive value in assessing the threat of postoperative thrombosis in patients with benign and malignant brain tumors.

Systemic lupus erythematosus (SLE) is an autoimmune disease with a complex and largely unclear pathogenesis. Cellular phospholipid microvesicles released upon activation and/or death of a cell have been proposed to play a role in inflammatory autoimmune pathologies, including SLE. Here, circulating microvesicles of various cellular origins were marked with fluorescently labeled cell-specific antibodies and enumerated by flow cytometry in platelet-free plasma obtained from the heparinized blood of 29 SLE patients and 19 normal subjects. Significantly higher concentrations of endothelial-, monocyte-, and erythrocyte-derived microvesicles were found in the SLE patients compared to normal subjects with prevalence of microvesicles originating from endothelial cells. No significant difference was found for platelet-derived microvesicles. A correlation analysis of microvesicle counts with laboratory parameters and clinical features of SLE suggest differential implications of various cell-derived microvesicles in the pathogenesis of SLE. These data suggest that SLE is associated with functional alterations of endotheliocytes, monocytes, and erythrocytes followed by enhanced release of microvesicles that may contribute to inflammation and hypercoagulability.

Background Congenital and acquired hemostatic disorders are among the pathogenic factors of pregnancy loss. Studying mechanistic relations between impaired hemostasis and fetal losses is important for the prognosis and prophylaxis of obstetric complications. Objective This article aims to establish latent hemostatic disorders in nonpregnant women as an important premorbid risk factor of pregnancy loss. Methods and Results Hemostasis was characterized using two relatively new in vitro assays, namely thrombodynamics (spatial clot growth) and kinetics of blood clot contraction, which together reflect the hemostatic or thrombotic potential. In addition, platelet functionality was assessed using flow cytometry. Our study included 50 women with a history of pregnancy loss and 30 parous women without previous obstetric complications. In patients with pregnancy loss, hypercoagulability was observed along with significant impairment of blood clot contraction associated with chronic platelet activation and dysfunction. Both hypercoagulability and defective clot contraction were significantly more pronounced in patients with a history of three or more miscarriages compared with patients with a history of one or two miscarriages. In addition, a significant inhibition of clot contraction was found in patients with miscarriage occurring after 10 weeks of gestation compared with those who lost a fetus earlier in pregnancy. Conclusion These results indicate that chronic hypercoagulability and impaired clot contraction constitute a premorbid status in patients with pregnancy loss. The data confirm a significant pathogenic role of hemostatic disorders in pregnancy loss and suggest the predictive value of thrombodynamics and blood clot contraction assays in evaluating the risk of pregnancy loss.