Statins decrease thrombin generation in patients with hypercholesterolemia.

OBJECTIVE: Statins are cholesterol-lowering agents with antithrombotic effect possibly unrelated to their lipid-lowering properties. Traditional global coagulation tests failed, however, to reveal clinically relevant change after treatment. We therefore sought to investigate whether statins were able to modify thrombin generation in hypercholesterolemia. METHODS: Fifty-one patients who needed treatment with statins were enrolled in this study. Thrombin generation, assessed as endogenous thrombin potential (the amount of thrombin generated after triggering coagulation with small amount of tissue factor) was measured at pre- and two months post-treatment with statins. RESULTS: The median (inter-quartile range) level of total cholesterol that was 325 mg/dL (278-405) decreased significantly [211 mg/dL (197-247)] at post-treatment (p<0.001); the median level of HDL cholesterol that was 49 mg/dL (43-56) increased significantly [55 mg/dL (47-66)] at post-treatment (p<0.001). The median endogenous thrombin potential (inter-quartile range) before treatment was 2372 nM·min (2008-2617) and decreased to 2,048 nM·min (1764-2375) (p<0.001) after treatment. CONCLUSION: The results support the hypothesis of a direct link between statins and coagulation through their capacity to lower thrombin generation in patients with hypercholesterolemia. PRACTICE IMPLICATIONS: The antithrombotic properties of statins could be mediated (at least in part) by their endogenous thrombin potential lowering effect. This interesting hypothesis warrants evaluation by clinical trials.

Global coagulation in myeloproliferative neoplasms.

In spite of their recognized risk of thrombosis, patients with myeloproliferative neoplasms (MPN) show little or no abnormalities of traditional coagulation tests, perhaps because these are unable to represent the balance between pro- and anticoagulants nor the effect of platelets and blood cells. We investigated whether global tests such as thrombin generation in platelet-rich plasma (PRP) or thromboelastometry in whole blood were able to detect signs of procoagulant imbalance in MPN. The endogenous thrombin potential (ETP) of 111 patients and 89 controls was measured in PRP with platelet count adjusted to the original patient- or control-count. Testing was performed with and without thrombomodulin (the physiological protein C activator) and results were expressed as ETP ratios (with/without thrombomodulin). High ETP ratios reflect resistance to thrombomodulin and were taken as indexes of procoagulant imbalance. Patients were also investigated by thromboelastometry that provides such parameters as the clot formation time (CFT) and maximal clot firmness (MCF). Short CFT or high MCF were taken as indexes of procoagulant imbalance. ETP ratios were higher in patients than in controls and were directly correlated with platelet counts and inversely with the plasma levels of free protein S, protein C and antithrombin. Patients on hydroxyurea had lower ETP ratios than those on other treatments. CFT was shorter and MCF was greater in patients than controls; CFT and MCF were correlated with platelet counts. In conclusion, patients with MPN display a procoagulant imbalance detectable by thrombin generation and thromboelastometry. These tests might be useful in the frame of clinical trials to assess their association with the occurrence of thrombosis and with the effect of therapeutic strategies in MPN.

Evidence that low protein C contributes to the procoagulant imbalance in cirrhosis.

BACKGROUND & AIMS: Cirrhosis is associated with a plasmatic procoagulant imbalance, detected in vitro by thrombin generation tests performed in the presence vs. absence of such activators of protein C as thrombomodulin or Protac. This imbalance is thought to be due to decreased protein C and increased factor VIII, but this has never been directly demonstrated. To test this hypothesis we analyzed plasma from 50 patients with cirrhosis before and after in vitro addition of purified protein C meant to restore normal levels. METHODS: Results for two thrombin generation assays were expressed as ratios of endogenous thrombin potential (ETP) with-to-without thrombomodulin or as Protac-induced coagulation inhibition (PICI%). By definition, high ETP ratios or low PICI% reflect a resistance to the anticoagulant action of thrombomodulin or Protac, respectively, and can be taken as indexes of in vitro procoagulant imbalance. RESULTS: The median (range) protein C level before addition was 40% (4-101%) and increased to 156% (110-305) after addition (p<0.001). The procoagulant imbalance, which was high before protein C addition [ETP ratio=0.83 (0.44-1.00)], was reduced after addition [ETP ratio=0.60 (0.14-0.84)], p<0.001. ETP-ratios were inversely correlated with protein C activity (rho=-0.46, p<0.001). Similar results were obtained with the Protac assay. CONCLUSIONS: The results provide evidence that low protein C contributes to the procoagulant imbalance in plasma from patients with cirrhosis. The findings may have clinical implications for the treatment or prophylaxis of thrombosis in these patients.

Global hemostasis tests in patients with cirrhosis before and after prophylactic platelet transfusion.

BACKGROUND/AIMS: Cirrhosis presents with variable degrees of thrombocytopenia that might cause bleeding during invasive procedures. Transfusion of one standard adult platelet dose is often employed to prevent bleeding in thrombocytopenia, but the threshold platelet count that is clinically effective is not well established because clinical studies and laboratory tools to judge on efficacy are insufficient. However, in vitro studies showed that patients with cirrhosis generate as much thrombin as healthy individuals provided that their platelet count is at least 100 × 10(9) /L. METHODS: To assess the in vivo relevance of these in vitro studies, we investigated 26 thrombocytopenic patients with cirrhosis, undergoing 36 variceal ligations, to see whether transfusion of one standard adult platelet dose was able to attain the above platelet count. We also evaluated the effect of platelet transfusion on such global hemostasis tests as thrombin generation and thromboelastometry. RESULTS: Transfusion did slightly increase platelet count [pre- vs. post-infusion: 39 × 10(9) /L(16-64) vs. 52 × 10(9) /L(19-91), P < 0.001], without significant effect on thrombin generation, probably because post-transfusion platelet count was less than the target of 100 × 10(9) /L in all patients. In addition, the percentage of patients with abnormal thrombin generation (i.e. below the lower limit of normal range) was scarcely affected by transfusion (pre- vs. post-infusion: 36% vs. 42%). The small post-transfusion increase in platelet count was paralleled by some degree of improvement of thromboelastometry, but none of the patients reached normal values after transfusion. CONCLUSIONS: Infusing one standard adult platelet dose secures only a small increase in platelet count without normalizing thrombin generation and thromboelastometry tests. To obtain greater increases in platelet count and normalization of laboratory tests more intensive platelet transfusions or treatment with non-transfusional drugs are probably needed.

Detection of the imbalance of procoagulant versus anticoagulant factors in cirrhosis by a simple laboratory method.

UNLABELLED: Patients with cirrhosis possess an imbalance in procoagulant versus anticoagulant activity due to increased factor VIII and decreased protein C. This imbalance can be detected by thrombin-generation assays performed in the presence/absence of thrombomodulin (predicate assay) that are not readily available in clinical laboratories. We sought to assess this hypercoagulability with a simpler thrombin-generation assay performed in the presence/absence of Protac, a snake venom that activates protein C in a manner similar to thrombomodulin (new assay). We analyzed blood from 105 patients with cirrhosis and 105 healthy subjects (controls). Results for the predicate-assay or the new-assay were expressed as ratio (with:without thrombomodulin) or as Protac-induced coagulation inhibition (PICI%). By definition, high ratios or low PICI% translate into hypercoagulability. The median(range) PICI% was lower in patients (74% [31%-97%]) than controls (93% [72%-99%]; P < 0.001), indicating that patients with cirrhosis are resistant to the action of Protac. This resistance resulted in greater plasma hypercoagulability in patients who were Child class C than those who were A or B. The hypercoagulability of Child C cirrhosis (63% [31%-92%]) was similar to that observed for patients with factor V Leiden (69% [15%-80%]; P = 0.59). The PICI% values were correlated with the levels of protein C (rho = 0.728, P < 0.001) or factor VIII (rho = -0.517, P < 0.001). Finally, the PICI% values were correlated with the predicate assay (rho = -0.580, P < 0.001). CONCLUSION: The hypercoagulability of plasma from patients with cirrhosis can be detected with the new assay, which compares favorably with the other markers of hypercoagulability (i.e., high factor VIII and low protein C) and with the predicate-assay based on thrombin-generation with/without thrombomodulin. Advantages of the new assay over the predicate assay are easy performance and standardized results. Prospective trials are needed to ascertain whether it is useful to predict thrombosis in patients with cirrhosis.

Abnormal Protac-induced coagulation inhibition chromogenic assay results are associated with an increased risk of recurrent venous thromboembolism.

Evaluation of the risk of recurrent venous thromboembolism (VTE) is required to determine the optimal duration of secondary prophylaxis. Application of global assays reflecting the pro- versus anti-coagulant balance in vivo would be desirable. We aimed at investigating the relationship between recurrent VTE and the Protac-induced coagulation inhibition (PICI) assay, which is based on tissue factor-induced thrombin generation measured by a chromogenic substrate. One-hundred-ninety patients were followed-up after a first episode of unprovoked, objectively documented VTE for 2.7 years after stopping treatment with vitamin K antagonists (VKA). PICI was measured 1 month after stopping treatment as the percentage of the OD values recorded without or with Protac. The lower the PICI%, the greater the pro- versus anti-coagulant imbalance. The study outcome was objectively-documented symptomatic recurrent VTE. Patients with PICI% 87%. After adjustment for age, gender, type of index event, VKA duration and normal/abnormal D-Dimer, HR (95% CI) were substantially unchanged [2.91 (1.01-8.38)]. The corresponding values after further adjustment for the above variables plus the absence/presence of the most frequent thrombophilic alterations were 3.38 (1.16-9.84). These HR values compare favorably with those obtained in a previous study investigating the thrombin generation test performed in the presence of thrombomodulin. In conclusion, the measurement of PICI helps to identify patients at higher risk of VTE recurrence. Advantages of PICI over thrombin generation tests are easy performance in general clinical laboratories, easy standardization and no special equipment.