Thrombin-activatable fibrinolysis inhibitor and the risk for recurrent venous thromboembolism

Elevated plasma factor XI is associated with postthrombotic syndrome

INTRODUCTION

Postthrombotic syndrome (PTS), a common complication of deep vein thrombosis (DVT), is largely inflammatory by nature with contribution of prothrombotic mechanisms. The role of factor (F)XI in PTS has not been explored yet. We investigated whether elevated FXI is associated with PTS occurrence.

MATERIALS AND METHODS

We enrolled 180 consecutive patients (aged 43 ± 13 years) with first-ever DVT. After 3 months FXI levels were measured, along with inflammatory markers, thrombin generation, plasma clot permeability (Ks), clot lysis time (CLT), and fibrinolysis proteins. We assessed PTS using the Villalta score and recorded symptomatic venous thromboembolism (VTE) at a 1-year and venous ulcers at a median 53 months follow-up.

RESULTS

Baseline median FXI was 102 % [IQR 92-113 %] and showed positive association with Villalta score (R = 0.474, P < 0.001). Patients with PTS (n = 48, 26.7 %) had 16.1 % higher FXI (P < 0.001) and FXI ≥120 % occurred more often in PTS patients (odds ratio [OR] 5.55, 95 % confidence interval [CI] 2.28-13.47). There were associations of baseline FXI with Ks and CLT along with thrombin activatable fibrinolysis inhibitor (TAFI) activity, C-reactive protein, and interleukin-6, but not with fibrinogen, or thrombin generation. After age adjustment higher FXI was independently associated with PTS occurrence (OR per 1 % 1.06, 95 % CI 1.02-1.09) and VTE recurrence (OR 1.03, 95 % CI 1.01-1.06). At long-term follow-up, patients with venous ulcers had 13.6 % higher baseline FXI (P = 0.002).

CONCLUSIONS

Elevated FXI in association with inflammation and prothrombotic fibrin clot properties may contribute to the development of PTS following DVT.

Development of new anticoagulant in 2023: Prime time for anti-factor XI and XIa inhibitors

Thrombosis remains one of the leading causes of death in the world. The history of anticoagulation has evolved considerably from non-specific drugs (i.e., heparins and vitamin K antagonists, VKA) to agents that directly target specific coagulation factors (i.e., argatroban, fondaparinux and direct oral anticoagulants, DOAC). Since the last decade, DOAC are widely used in clinical practice because of their ease to use with favorable pharmacological profile and not requiring monitoring, particularly for venous thromboembolism treatment and prevention and stroke prevention in atrial fibrillation. However, despite having a better safety profile than VKA, their bleeding risk is not negligible. Therefore, research is underway to develop new anticoagulant therapies with a better safety profile. One of these news approaches to reduce the risk of bleeding is to target the coagulation in the intrinsic pathway, in particular the contact activation, with the ultimate goal of preventing thrombosis without impairing hemostasis. Based on epidemiological data with patients with inherited factor XI (FXI) deficiency and preclinical studies, FXI emerged as the most promising candidate target separating hemostasis from thrombosis. This review summaries the role of FXI and FXIa in hemostasis, provides evidence of initial success with FXI pathway inhibitors in clinical trials (such as IONIS-FXI_Rx, fesomersen, osocimab, abelacimab, milvexian, asundexian or xisomab 3G3) and highlights the opportunities and challenges for this next generation of anticoagulants.

Markers of Hereditary Thrombophilia with Unclear Significance

Thrombophilia leads to an increased risk of venous thromboembolism. Widely accepted risk factors for thrombophilia comprise deficiencies of protein C, protein S, and antithrombin, as well as the factor V "Leiden" mutation, the prothrombin G20210A mutation, dysfibrinogenemia, and, albeit less conclusive, increased levels of factor VIII. Besides these established markers of thrombophilia, risk factors of unclear significance have been described in the literature. These inherited risk factors include deficiencies or loss-of-activity of the activity of ADAMTS13, heparin cofactor II, plasminogen, tissue factor pathway inhibitor (TFPI), thrombomodulin, protein Z (PZ), as well as PZ-dependent protease inhibitor. On the other hand, thrombophilia has been linked to the gain-of-activity, or elevated levels, of α2-antiplasmin, angiotensin-converting enzyme, coagulation factors IX (FIX) and XI (FXI), fibrinogen, homocysteine, lipoprotein(a), plasminogen activator inhibitor-1 (PAI-1), and thrombin-activatable fibrinolysis inhibitor (TAFI). With respect to the molecular interactions that may influence the thrombotic risk, more complex mechanisms have been described for endothelial protein C receptor (EPCR) and factor XIII (FXIII) Val34Leu. With focus on the risk for venous thrombosis, the present review aims to give an overview on the current knowledge on the significance of the aforementioned markers for thrombophilia screening. According to the current knowledge, there appears to be weak evidence for a potential impact of EPCR, FIX, FXI, FXIII Val34Leu, fibrinogen, homocysteine, PAI-1, PZ, TAFI, and TFPI on the thrombotic risk.

Pathophysiological Aspects of Aging in Venous Thromboembolism: An Update

The aim of this review is to highlight all the factors that associate venous thromboembolism (VTE) with aging. Elderly people are characterized by a higher incidence of thrombosis taking into account the co-existing comorbidities, complications and fatality that arise. Based on the Virchow triad, pathophysiological aspects of venous stasis, endothelium injury and hypercoagulability in elderly people (≥65 years) are described in detail. More precisely, venous wall structure, nitric oxide (NO) and endothelin-1 expression are impaired in this age group. Furthermore, an increase in high-molecular-weight kininogen (HMWK), prekallikrein, factors V, VII, VIII, IX and XI, clot lysis time (CLT) and von Willebrand factor (vWF) is observed. Age-dependent platelet dysfunction and changes in anticoagulant factors are also illustrated. A “low-grade inflammation stage” is delineated as a possible risk factor for thrombosis in the elderly. Consequently, clinical implications for frail elderly people related to diagnosis, treatment, bleeding danger and VTE recurrence emerge. We conclude that aging is an acquired thrombotic factor closely related to pathophysiological changes.

Fibrinogen and Antifibrinolytic Proteins: Interactions and Future Therapeutics

Thrombus formation remains a major cause of morbidity and mortality worldwide. Current antiplatelet and anticoagulant therapies have been effective at reducing vascular events, but at the expense of increased bleeding risk. Targeting proteins that interact with fibrinogen and which are involved in hypofibrinolysis represents a more specific approach for the development of effective and safe therapeutic agents. The antifibrinolytic proteins alpha-2 antiplasmin (α2AP), thrombin activatable fibrinolysis inhibitor (TAFI), complement C3 and plasminogen activator inhibitor-2 (PAI-2), can be incorporated into the fibrin clot by FXIIIa and affect fibrinolysis by different mechanisms. Therefore, these antifibrinolytic proteins are attractive targets for the development of novel therapeutics, both for the modulation of thrombosis risk, but also for potentially improving clot instability in bleeding disorders. This review summarises the main properties of fibrinogen-bound antifibrinolytic proteins, their effect on clot lysis and association with thrombotic or bleeding conditions. The role of these proteins in therapeutic strategies targeting the fibrinolytic system for thrombotic diseases or bleeding disorders is also discussed.

S62798, a potent TAFIa inhibitor, accelerates endogenous fibrinolysis in a murine model of pulmonary thromboembolism

Enhancement of fibrinolysis constitutes a promising approach to treat thrombotic diseases. Venous thrombosis and thromboembolism risks are associated with increased plasma levels of TAFI (Thrombin Activatable Fibrinolysis Inhibitor) as well as its active form TAFIa. A new TAFIa inhibitor, namely S62798 has been identified. Its ability to enhance fibrinolysis was investigated both in vitro and in vivo in a mouse model of pulmonary thromboembolism, as well as its effect on bleeding. S62798 is a highly selective human, mouse and rat TAFIa inhibitor (IC₅₀ = 11; 270; 178 nmol/L, respectively). It accelerates lysis of a human clot in vitro, evaluated by thromboelastometry (EC₅₀ = 27 nmol/L). In a rat tail bleeding model, no effect of S62798 treatment was observed up to 20 mg/kg. Enhancement of endogenous fibrinolysis by S62798 was investigated in a mouse model of Tissue Factor-induced pulmonary thromboembolism. Intravenous administration of S62798 decreased pulmonary fibrin clots with a minimal effective dose of 0.03 mg/kg. Finally, effect of S62798 in combination with heparin was evaluated. When treatment of heparin was done in a curative setting, no effect was observed whereas a significantly decreased pulmonary fibrin deposition was observed in response to S62798 alone or in combination with heparin. This study demonstrates that S62798 is a potent TAFIa inhibitor with minimal risk of bleeding. In vivo, curative S62798 intravenous treatment, alone or associated with heparin, accelerated clot lysis by potentiating endogenous fibrinolysis and thus decreased pulmonary fibrin clots. S62798 is expected to be a therapeutic option for pulmonary embolism patients on top of anticoagulants.

Phosphinanes and Azaphosphinanes as Potent and Selective Inhibitors of Activated Thrombin-Activatable Fibrinolysis Inhibitor (TAFIa)

Selective and potent inhibitors of activated thrombin activatable fibrinolysis inhibitor (TAFIa) have the potential to increase endogenous and therapeutic fibrinolysis and to behave like profibrinolytic agents without the risk of major hemorrhage, since they do not interfere either with platelet activation or with coagulation during blood hemostasis. Therefore, TAFIa inhibitors could be used in at-risk patients for the treatment, prevention, and secondary prevention of stroke, venous thrombosis, and pulmonary embolisms. In this paper, we describe the design, the structure-activity relationship (SAR), and the synthesis of novel, potent, and selective phosphinanes and azaphosphinanes as TAFIa inhibitors. Several highly active azaphosphinanes display attractive properties suitable for further in vivo efficacy studies in thrombosis models.

Thrombin Activatable Fibrinolysis Inhibitor (TAFI): An Updated Narrative Review

Thrombin activatable fibrinolysis inhibitor (TAFI), a proenzyme, is converted to a potent attenuator of the fibrinolytic system upon activation by thrombin, plasmin, or the thrombin/thrombomodulin complex. Since TAFI forms a molecular link between coagulation and fibrinolysis and plays a potential role in venous and arterial thrombotic diseases, much interest has been tied to the development of molecules that antagonize its function. This review aims at providing a general overview on the biochemical properties of TAFI, its (patho)physiologic function, and various strategies to stimulate the fibrinolytic system by interfering with (activated) TAFI functionality.

Carboxypeptidase U (CPU, TAFIa, CPB2) in Thromboembolic Disease: What Do We Know Three Decades after Its Discovery?

Procarboxypeptidase U (proCPU, TAFI, proCPB2) is a basic carboxypeptidase zymogen that is converted by thrombin(-thrombomodulin) or plasmin into the active carboxypeptidase U (CPU, TAFIa, CPB2), a potent attenuator of fibrinolysis. As CPU forms a molecular link between coagulation and fibrinolysis, the development of CPU inhibitors as profibrinolytic agents constitutes an attractive new concept to improve endogenous fibrinolysis or to increase the efficacy of thrombolytic therapy in thromboembolic diseases. Furthermore, extensive research has been conducted on the in vivo role of CPU in (the acute phase of) thromboembolic disease, as well as on the hypothesis that high proCPU levels and the Thr/Ile325 polymorphism may cause a thrombotic predisposition. In this paper, an overview is given of the methods available for measuring proCPU, CPU, and inactivated CPU (CPUi), together with a summary of the clinical data generated so far, ranging from the current knowledge on proCPU concentrations and polymorphisms as potential thromboembolic risk factors to the positioning of different CPU forms (proCPU, CPU, and CPUi) as diagnostic markers for thromboembolic disease, and the potential benefit of pharmacological inhibition of the CPU pathway.

Individualised Risk Assessments for Recurrent Venous Thromboembolism: New Frontiers in the Era of Direct Oral Anticoagulants

Venous thromboembolism (VTE) is a leading cause of morbidity and mortality and is associated with high recurrence rates. The introduction of direct oral anticoagulants (DOACs) in the 2010s has changed the landscape of VTE management. DOACs have become the preferred anticoagulant therapy for their ease of use, predictable pharmacokinetics, and improved safety profile. Increasingly, guidelines have recommended long term anticoagulation for some indications such as following first unprovoked major VTE, although an objective individualised risk assessment for VTE recurrence remains elusive. The balance of preventing VTE recurrence needs to be weighed against the not insignificant bleeding risk, which is cumulative with prolonged use. Hence, there is a need for an individualised, targeted approach for assessing the risk of VTE recurrence, especially in those patients in whom the balance between benefit and risk of long-term anticoagulation is not clear. Clinical factors alone do not provide the level of discrimination required on an individual level. Laboratory data from global coagulation assays and biomarkers may provide enhanced risk assessment ability and are an active area of research. A review of the prediction models and biomarkers for assessing VTE recurrence risk is provided, with an emphasis on contemporary developments in the era of DOACs and global coagulation assays.

Identifying new clotting factor XIa inhibitors in virtual high-throughput screens using PCA-GA-SVM models and signature

Blood Clotting Factor XI is an important actor in the clotting mechanism: it activates downstream zymogen involved in the clotting process. It can be targeted for activation or inhibition depending on treatment goals to enhance or inhibit clotting. In terms of antithrombosis treatment, Factor XI has emerged as a promising target to focus on. In this work, an iterative virtual high-throughput screening pipeline was proposed that can supplement current efforts to find inhibitors. The first iteration identified 11 compounds to test with 3 active for a hit-rate of 27.3%. The second iteration of the pipeline identified another 11 compounds to test with 7 active for a hit-rate of 63.6%. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 34:1553-1565, 2018.

Fibrinolytic potential of DS-1040, a novel orally available inhibitor of activated thrombin-activatable fibrinolysis inhibitor (TAFIa)

An activated thrombin-activatable fibrinolysis inhibitor (TAFIa) attenuates fibrinolysis by removing C-terminal lysine/arginine residues from partially degraded fibrin. We have identified a novel low-molecular-weight inhibitor of TAFIa, DS-1040, to be potentially useful for treating thrombotic diseases. In this study, we investigated its in vitro pharmacological profile and in vivo effects in animal models of microthrombosis and bleeding. DS-1040 inhibited human TAFIa and carboxypeptidase N (CPN) in vitro with IC₅₀ values of 5.92 and 3.02 × 10⁶ nmol/L, respectively, suggesting that DS-1040 is highly selective for TAFIa over CPN. DS-1040 did not affect platelet aggregation and coagulation time. In a tissue factor-induced rat microthrombosis model, intravenously administered DS-1040 reduced existing fibrin clots in the lung, whereas post-treatment with enoxaparin had limited effect. Both intravenously and orally administered DS-1040 elevated plasma D-dimer levels with similar plasma exposures of DS-1040. DS-1040 significantly augmented plasma D-dimer level on top of silent dose of recombinant tissue-plasminogen activator (t-PA), suggesting DS-1040 enhances fibrinolytic activity of t-PA. In addition, DS-1040 did not prolong the tail bleeding time beyond its efficacy dose. These results indicate that DS-1040 is a potent, selective, intravenously/orally available inhibitor of TAFIa with minimum risk of bleeding. DS-1040 is a potential novel fibrinolysis enhancer useful in treating thrombotic diseases.

Thrombin-Activatable Fibrinolysis Inhibitor Polymorphisms and Cerebral Venous Thrombosis in Mexican Mestizo Patients

Thrombin-activatable fibrinolysis inhibitor (TAFI) gene polymorphisms have been proposed as a predisposing factor for cerebral venous thrombosis (CVT). We analyzed the association between CVT and TAFI single-nucleotide polymorphisms (rs3742264, rs2146881, and rs1926447) compared to healthy controls. Mexico Mestizo confirmed cases with CVT and age- and sex-matched controls with no history of venous thrombotic events were recruited from July 2006 to July 2015. Demographic, clinical, and imaging information was included in the analysis. Genotyping single-nucleotide polymorphisms were performed by allele-specific polymerase chain reaction. Allelic univariate analysis, haplotype association, and Hardy-Weinberg equilibrium were assessed. A total of 113 CVT cases (94 females [83.2%]; median age 35 years [interquartile range 27-43 years]) and 134 age- and sex-matched controls were included. The main risk factors for CVT were pregnancy/puerperium (30.9%), oral contraceptive use (19.5%), and hereditary thrombophilia (7.1%). We found no significant association for heterozygous and homozygous models for rs3742264 ( P = .30 and P = .69, respectively), rs2146881 ( P = .90 and P = .17, respectively), or rs1926447 ( P = .40 and P = .52, respectively) compared to controls; these findings were consistent in subgroup and haplotype analyses. In conclusion, TAFI rs3742264, rs2146881, and rs1926447 polymorphisms do not increase the risk of CVT in comparison to healthy controls.

Tissue-type plasminogen activator transgenic rats for evaluating inhibitors of the activated form of thrombin-activatable fibrinolysis inhibitor

No rodent models are currently available for evaluating inhibitors of the activated form of thrombin-activatable fibrinolysis inhibitor (TAFIa) without exogenous supplementation of tissue-type plasminogen activator (tPA). Characterization of tPA transgenic rats as a tool for the nonclinical evaluation of TAFIa inhibitors is the objective of the current study. tPA transgenic rats were subjected to rat models of tissue-factor-induced thromboembolism, FeCl₃-induced deep vein thrombosis (DVT) and arterial thrombosis, and tail bleeding. Potato tuber carboxypeptidase inhibitor (PCI), a selective TAFIa inhibitor, was used as an experimental compound at doses of 0.1, 1, or 10 mg/kg, and its antithrombotic effects and bleeding prolongation effect were compared with nontransgenic rats. Intravenous PCI showed significant and dose-related increase in plasma d-dimer levels in the tissue-factor-induced thromboembolism model. Intravenous PCI also significantly and dose-dependently reduced thrombus weights in the two thrombosis models only in the tPA transgenic rats. These results suggest that sensitive in-vivo evaluation of TAFIa inhibitors can be achieved using tPA transgenic rats without exogenous supplementation of recombinant tPA. On the other hand, no statistically significant prolongation of bleeding times by PCI was observed in either strain, whereas increased bleeding times were observed with 10 mg/kg of intravenous recombinant tPA, suggesting that the low bleeding risk of TAFIa inhibitors is further confirmed in the tPA transgenic rats whose basal tPA levels are elevated. tPA transgenic rats may be beneficial for the pharmacological and toxicological evaluation of TAFIa inhibitors and further confirm that TAFIa is a promising target for various thrombotic disorders.

IL-10 correlates with the expression of carboxypeptidase B2 and lymphovascular invasion in inflammatory breast cancer: The potential role of tumor infiltrated macrophages

Pro-carboxypeptidase B2 (pro-CPB2) or thrombin-activatable fibrinolysis inhibitor (TAFI) is a glycoprotein encoded by the CPB2 gene and deregulated in several cancer types, including breast cancer. Thrombin binding to thrombomodulin (TM), encoded by THBD, is important for TAFI activation. CPB2 gene expression is influenced by genetic polymorphism and cytokines such as interleukin 10 (IL-10). Our previous results showed that tumor infiltrating monocytes/macrophages (CD14⁺/CD16⁺) isolated from inflammatory breast cancer (IBC) patients' secrete high levels of IL-10. The aim of the present study is to test genetic polymorphism and expression of CPB2 in healthy breast tissues and carcinoma tissues of non-IBC and IBC patients. Furthermore, to investigate whether IL-10 modulates the expression of CPB2 and THBD in vivo and in-vitro. We tested CPB2 Thr325Ile polymorphism using restriction fragment length polymorphism, (RFLP) technique in healthy and carcinoma breast tissues. The mRNA expression of CPB2, THBD and IL10 were assessed by RT-qPCR. Infiltration of CD14⁺ cells was assessed by immunohistochemistry. In addition, we investigated the correlation between infiltration of CD14⁺ cells and expression of IL10 and CPB2. Furthermore, we correlated IL10 expression with the expression of both CPB2 and THBD in breast carcinoma tissues. Finally, we validated the role of recombinant IL-10 in regulating the expression of CPB2 and THBD using different breast cancer cell lines. Our results showed that CPB2 genotypes carrying the high-risk allele [Thr/Ile (CT) and Ile/Ile (TT)] were more frequent in both IBC and non-IBC patients compared to control group. CPB2 genotypes did not show any statistical correlation with CPB2 mRNA expression levels or patients' clinical pathological properties. Interestingly, CPB2 and IL10 expression were significantly higher and positively correlated with the incidence of CD14⁺ cells in carcinoma tissues of IBC as compared to non-IBC. On the other hand, THBD expression was significantly lower in IBC carcinoma versus non-IBC tissues. Based on molecular subtypes, CPB2 and IL10 expression were significantly higher in triple negative (TN) as compared to hormonal positive (HP) carcinoma tissues of IBC. Moreover, CPB2 expression was positively correlated with presence of lymphovascular invasion and the expression of IL10 in carcinoma tissues of IBC patients. Furthermore, recombinant human IL-10 stimulated CPB2 expression in SUM-149 (IBC cell line) but not in MDA-MB-231 (non-IBC cell line), while there was no significant effect THBD expression. In conclusion, carcinoma tissues of IBC patients are characterized by higher expression of CPB2 and lower expression of THBD. Moreover, CPB2 positively correlates with IL10 mRNA expression, incidence of CD14⁺ cells and lymphovascular invasion in IBC patients. IL-10 stimulated CPB2 expression in TN-IBC cell line suggests a relevant role of CPB2 in the aggressive phenotype of IBC.

Detection of Deep Vein Thrombosis by Follow-up Indirect Computed Tomography Venography after Pulmonary Embolism

Background

Information regarding the incidence and risk factors for deep vein thrombosis (DVT) detected by follow-up computed tomographic (CT) venography after pulmonary embolism (PE) is sparse. The aim of the present study was to identify the predictors of DVT in follow-up CT images, and to elucidate their clinical significance.

Methods

Patients with PE were classified into the following three cohorts based on the time of indirect CT venography follow-up: within 1 month, 1 to 3 months, and 3 to 9 months after the initial CT scan. Each cohort was subdivided into patients with or without DVT detected by follow-up CT. Clinical variables were compared between the two groups.

Results

Follow-up CT revealed DVT in 61% of patients with PE within 1 month, in 15% of patients with PE at 1 to 3 months, and in 9% of patients with PE at 3 to 9 months after the initial CT scan. Right ventricular (RV) dilation on the initial CT (odds ratio [OR], 8.30; 95% confidence interval [CI], 1.89–36.40; p=0.005) and proximal DVT at the initial presentation (OR, 6.93; 95% CI, 1.90–25.20; p=0.003) were found to independently predict DVT in follow-up CT images within 1 month, proximal DVT at the initial presentation was found to independently predict DVT in follow-up CT images at 1 to 3 months (OR, 6.69; 95% CI, 1.53–29.23; p=0.012), and central PE was found to independently predict DVT in follow-up CT images at 3 to 9 months (OR, 4.25; 95% CI, 1.22–4.83; p=0.023) after the initial CT scan. Furthermore, the detection of DVT by follow-up CT independently predicted the recurrence of venous thromboembolism (VTE) (OR, 4.67; 95% CI, 2.24–9.74; p<0.001).

Conclusion

Three months after PE, DVT was not detected by follow-up CT in most patients with PE. RV dilation on the initial CT, central PE, and proximal DVT at the initial presentation were found to predict DVT on follow-up CT, which might predict VTE recurrence.

Predicting the risk of recurrent venous thromboembolism

Venous thromboembolism (VTE) is a disease, which often recurs. The recurrence risk is highest in patients with unprovoked proximal deep-vein thrombosis (VT) or pulmonary embolism. Men have a higher risk than women. The risk is low in patients with VTE related to a temporary risk factor such as surgery or estrogen use. Other risk factors include overweight, post-thrombotic syndrome, history of VTE, residual VT or a vena cava filter.

Both factor V Leiden and the prothrombin mutation confer a negligible increase in recurrence risk. High clotting factor levels, deficiency of a natural coagulation inhibitor, or hyperhomocysteinaemia are also associated with an increased risk. Reasons why routine laboratory thrombophilia screening however is no longer warranted are addressed in this article. Prediction rules combining clinical characteristics and coagulation assays have recently been developed. One such model, the Vienna Prediction Model, allows predicting recurrent VTE on the basis of VTE location, sex and D-dimer. This article describes strategies to distinguish between patients with high risk of recurrent VTE from those with a lower risk, who might not benefit from long-term antithrombotic therapy.

Peroxisome proliferator-activated receptor-alpha agonists repress expression of thrombin-activatable fibrinolysis inhibitor by decreasing transcript stability

Thrombin-activatable fibrinolysis inhibitor (TAFI) (carboxypeptidase B2) is a plasma zymogen that is biosynthesised in the liver and released into the circulation. Activated TAFI is a prothrombotic factor which inhibits fibrin clot lysis. Cultured human hepatoma HepG2 cells were treated with peroxisome proliferator-activated receptor (PPAR)α, β or γ agonists, and the levels of TAFI antigen and mRNA (here, termed CPB2 mRNA) were measured. HepG2 cells treated with the PPARα agonist WY14643, but not agonists for PPARβ or PPARγ, decreased their release of TAFI antigen into the conditioned medium. In parallel, there were decreased levels of CPB2 mRNA and TAFI antigen in the cells. The WY14643-mediated decrease in CPB2 mRNA levels was accelerated by overexpression of PPARα and abolished by RNA interference of PPARA mRNA. CPB2 gene promoter activity was not influenced by treatment of the cells with WY14643. The half-life of the CPB2 transcript was shortened by treatment with WY14643 as compared with that of the control, and the decreased half-life of mRNA returned to control levels by treatment with a PPARα antagonist MK886 or transfection of PPARΑ-specific siRNA to WY14643-treated HepG2 cells. The present results suggest that PPARα agonists not only play a hypolipidaemic role, but also decrease the expression of TAFI, a prothrombotic factor, by decreasing stability of CPB2 transcripts.

Sex-specific effect of CPB2 Ala147Thr but not Thr325Ile variants on the risk of venous thrombosis: A comprehensive meta-analysis

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI), encoded by the Carboxypeptidase B2 gene (CPB2), is an inhibitor of fibrinolysis and plays a role in the pathogenesis of venous thrombosis. Experimental findings support a functional role of genetic variants in CPB2, while epidemiological studies have been unable to confirm associations with risk of venous thrombosis. Sex-specific effects could underlie the observed inconsistent associations between CPB2 genetic variants and venous thrombosis.

METHODS

A comprehensive literature search was conducted for associations between Ala147Thr and Thr325Ile variants with venous thrombosis. Authors were contacted to provide sex-specific genotype counts from their studies. Combined and sex-specific random effects meta-analyses were used to estimate a pooled effect estimate for primary and secondary genetic models.

RESULTS

A total of 17 studies met the inclusion criteria. A sex-specific meta-analysis applying a dominant model supported a protective effect of Ala147Thr on venous thrombosis in females (OR = 0.81, 95%CI: 0.68,0.97; p = 0.018), but not in males (OR = 1.06, 95%CI:0.96-1.16; p = 0.263). The Thr325Ile did not show a sex-specific effect but showed variation in allele frequencies by geographic region. A subgroup analysis of studies in European countries showed decreased risk, with a recessive model (OR = 0.83, 95%CI:0.71-0.97, p = 0.021) for venous thrombosis.

CONCLUSIONS

A comprehensive literature review, including unpublished data, provided greater statistical power for the analyses and decreased the likelihood of publication bias influencing the results. Sex-specific analyses explained apparent discrepancies across genetic studies of Ala147Thr and venous thrombosis. While, careful selection of genetic models based on population genetics, evolutionary and biological knowledge can increase power by decreasing the need to adjust for testing multiple models.

Thrombin activatable fibrinolysis inhibitor as a bleeding predictor in liver transplantation: a pilot observational study

OBJECTIVE

To correlate the levels of thrombin activatable fibrinolysis inhibitor in the immediate postoperative period and at 24 hours postoperatively with the volume of intraoperative bleeding.

METHODS

Twenty-one patients allocated immediately before (elective or emergency) liver transplantation were analyzed. Blood samples were collected for thrombin activatable fibrinolysis inhibitor analysis at three different time points: immediately before liver transplantation (preoperative thrombin activatable fibrinolysis inhibitor), immediately after the surgical procedure (immediate postoperative thrombin activatable fibrinolysis inhibitor), and 24 hours after surgery (thrombin activatable fibrinolysis inhibitor 24 hours after surgery). The primary outcome of the study was to correlate the preoperative and immediate postoperative levels of thrombin activatable fibrinolysis inhibitor with intraoperative blood loss.

RESULTS

There was a correlation between the preoperative thrombin activatable fibrinolysis inhibitor levels and bleeding volume (ρ = -0.469; p = 0.05) but no correlation between the immediate postoperative thrombin activatable fibrinolysis inhibitor and bleeding volume (ρ = -0.062; p = 0.79). No variable included in the linear regression analysis (prehemoglobin, prefibrinogen and preoperative thrombin activatable fibrinolysis inhibitor) was a bleeding predictor. There was a similar trend in the variation between the levels of thrombin activatable fibrinolysis inhibitor at the three different time points and fibrinogen levels. Patients who died within 6 months (14.3%) showed decreased preoperative and immediate postoperative levels of thrombin activatable fibrinolysis compared with survivors (preoperative: 1.3 ± 0.15 versus 2.55 ± 0.53, p = 0.06; immediate postoperative: 1.2 ± 0.15 versus 2.5 ± 0.42, p = 0.007).

CONCLUSION

There was a moderate correlation between preoperative thrombin activatable fibrinolysis inhibitor and intraoperative bleeding in liver transplantation patients, although the predictive role of this variable independent of other variables remains uncertain. Preoperative and immediate postoperative thrombin activatable fibrinolysis inhibitor levels may have a role in the survival prognosis of this population; however, this possibility requires confirmation in further studies with larger sample sizes.

Changes to fibrinolysis in patients with systemic lupus erythematosus are associated with endothelial cell damage and inflammation, but not antiphospholipid antibodies

We investigated whether changes to fibrinolysis were associated with other manifestations of systemic lupus erythematosus (SLE), including antiphospholipid (APL) antibody status, endothelial damage, and inflammation. Ninety-four patients (36 SLE patients, 58 healthy controls) were recruited from Tasmania, Australia. Circulating levels of plasminogen, α2-antiplasmin, tissue-type plasminogen activator, plasminogen activator inhibitor-1, and thrombin-activatable fibrinolysis inhibitor (TAFI) were measured, as well as APL antibodies (including lupus anticoagulant, anticardiolipin, and antibeta-2 glycoprotein-1 antibodies), soluble E-selectin, and interleukin-6. Whereas there was a significant decrease in plasminogen (patient vs. control; median) (210 vs. 444 ng/ml; P < 0.0001) and increase in α2-antiplasmin (0.53 vs. 0.09 μg/ml; P = 0.0007), there was increased t-PA (0.65 vs. 0.40 ng/ml; P = 0.0001) and decreased TAFI (8.8 vs. 10.0 ng/ml; P = 0.002) in SLE patients compared to healthy controls. Plasminogen was significantly associated with α2-antiplasmin (rho = -0.563, P < 0.001); TAFI (rho = 0.410, P = 0.011); soluble E-selectin (rho = 0.531, P = 0.001); and interleukin-6 (rho = 0.489, P = 0.002) in SLE patients; however, APL antibody status was not associated with any of the markers measured. This study has demonstrated that fibrinolysis is significantly altered in patients with SLE compared to controls, and associated with endothelial cell damage and inflammation, but not APL antibody status.

PI3-Kinase Inhibitor LY294002 Repressed the Expression of Thrombin-Activatable Fibrinolysis Inhibitor in Human Hepatoma HepG2 Cells

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase B-like proenzyme biosynthesized in the liver and released into the blood circulation. Activated TAFI (TAFIa) has been implicated as an important player in maintaining the balance between blood coagulation and fibrinolysis. In the present study, regulation of TAFI (CPB2) gene expression was investigated using cultured human hepatoma HepG2 cells. HepG2 cells were treated with the phosphoinositide 3-kinase (PI3K) inhibitor LY294002, and the levels of TAFI antigen and CPB2 mRNA were measured. HepG2 cells treated with LY29400 decreased their release of TAFI antigen into the conditioned medium (CM). In parallel, there were decreased levels of CPB2 mRNA and TAFI antigen in the cells. However, CPB2 gene promoter activity was not influenced by treatment of the cells with LY294002. The half-life of the CPB2 transcript was shortened by treatment with LY294002 compared with control. The present results suggest that the PI3K inhibitor LY294002 suppresses expression of TAFI, a prothrombotic factor, by decreasing the stability of CPB2 transcripts.

Decrements in the Thrombin Activatable Fibrinolysis Inhibitor (TAFI) Levels in Association with Orlistat Treatment in Obesity

Obesity and its associated metabolic complications can impair the physiologic regulation of fibrinolysis, leading to a hyper coagulable state. We aimed to assess circulating thrombin activatable fibrinolysis inhibitor (TAFI) levels in obese female patients and to test the effects of orlistat-induced weight loss on basal TAFI concentrations. Obese female outpatients age 18 and older, with a body mass index (BMI, calculated as weight in kilograms divided by the square of height in meters) of at least 30, were included into the study. Thirteen nonobese (median BMI, 22.60 kg/m2) age-matched females were taken as controls. Plasma TAFI levels were measured before orlistat administration and after 6 months of orlistat treatment in the obese group and only one measurement was done in the control group. Twenty-seven obese patients were recruited into the study. The median TAFI level of the control group was 124.00; this value was significantly lower than the basal TAFI level of the obese group (p < 0.001). TAFI levels after orlistat therapy were statistically significantly lower than basal TAFI levels (p < 0.001) in the obese group. Hemostatic abnormalities including TAFI alterations represent a link between obesity and vascular thrombosis. Effective interventions should be considered in improving the obesity-associated prothrombotic risk profile.

Reduced plasma fibrin clot permeability and susceptibility to lysis are associated with increased risk of postthrombotic syndrome

BACKGROUND

The postthrombotic syndrome (PTS) is a severe complication of deep vein thrombosis (DVT). Reduced plasma clot permeability and lysability have been linked to DVT and residual vein obstruction. OBJECTIVES We investigated whether altered fibrin clot properties are associated with the occurrence of PTS.

PATIENTS AND METHODS

Plasma fibrin clot permeability (Ks ) and lysability were investigated in a cohort of 197 consecutive patients aged 18 to 65 years recruited 3 months following the first-ever DVT. Patients with severe thrombophilia or comorbidities known to adversely affect clot phenotype were ineligible.

RESULTS

During a 1-year follow-up PTS developed in 48 (24%) patients, who were characterized by lower Ks , prolonged fibrin clot lysis time (CLT) and slower release of D-dimer from clots (D-Drate ), together with higher plasma D-dimer, C-reactive protein and thrombin-activatable fibrinolysis inhibitor (TAFI). No PTS-associated differences in fibrinogen, thrombin generation, factor VIII, other fibrinolysis proteins and the quality of anticoagulation were observed. Ks (r = -0.71), CLT (r = 0.45), D-Drate (r = -0.30) and TAFI activity (r = 0.38) were associated with the Villalta scale (all P < 0.05). Recurrent VTE occurred also more commonly in PTS patients during follow-up and the 26 (13.2%) patients had lower Ks , longer CLT and lower D-Drate (all P < 0.05). A multivariate model adjusted for age, body mass index, fibrinogen and glucose showed that independent predictors of PTS were idiopathic DVT, plasma D-dimer, Ks , D-Drate , tissue plasminogen activator and TAFI activity.

CONCLUSIONS

This study demonstrates that formation of more compact fibrin clots displaying impaired susceptibility to lysis predisposes to PTS.

Prolonged clot lysis time increases the risk of a first but not recurrent venous thrombosis

The role of the fibrinolytic system in the development of venous thrombosis (VT) is unclear. We studied the risk of first and recurrent VT associated with reduced fibrinolysis, as measured by clot lysis time (CLT). We also studied the relationship between CLT and thrombin generation to determine if any relationship between CLT and VT was affected by thrombin generation. Analyses were performed in the Thrombophilia Hypercoagulability Environmental risk for Venous Thromboembolism Study, a two-centre population-based case-control study, including 579 patients and 338 controls, with patients followed from the event to determine incidence of recurrent VT. Hypofibrinolysis was associated with a 1·8-fold increased risk of a first VT [95% confidence interval (CI) 1·2-2·7]. Adjustment for sex, age, study location and Endogenous Thrombin Potential (ETP) did not change the result. The risk of VT was 2·9-fold increased when the 90th percentiles of prolonged CLT and high ETP were combined, with the highest risk for unprovoked first events (Odds Ratio = 4·2, 95% CI 1·3-13·5). In the follow-up study the Hazard Ratio for a recurrent VT associated with hypofibrinolysis was 1·5 (95% CI 0·9-2·6). A weak dose response effect was observed in relation to prolongation of CLT and recurrent VT. Although hypofibrinolysis constitutes a risk factor for a first VT, an association with recurrence is, at best, weak.

Assessment of Anti-Tissue Type Plasminogen Activator Antibodies in Patients With Prosthetic Heart Valve Thrombosis: The ATA Trial

BACKGROUND

Thrombolysis is an effective treatment strategy for prosthetic valve thrombosis (PVT). Recombinant tissue-type plasminogen activator (rt-PA) is widely used as a thrombolytic agent. Infusion of rt-PA may trigger the production of anti-tissue plasminogen activator (tPA) antibodies (ATAs). We aimed to evaluate the possible relationship between ATA levels and PVT formation, and the role of baseline ATA levels on outcomes of thrombolytic therapy in patients with PVT.

METHODS

This prospective, single-center cohort study included 28 patients with PVT undergoing thrombolysis and 31 controls with normal prostheses. Plasma samples were collected from patients with PVT at baseline and at 15th, 30th, 90th, and 180th days after thrombolysis and from controls at baseline only. The ATA levels were assessed in human plasma by an enzyme-linked immunosorbent assay.

RESULTS

Baseline ATA-immunoglobulin (Ig) G and IgM were significantly higher in patients with PVT than in controls. The levels of IgM and IgG peaked at 15th and 30th days after rt-PA infusion, respectively. Subtherapeutic international normalized ratio and baseline ATA-IgM were independent predictors of PVT. Thrombolysis failed in 6 patients (21%) in whom baseline IgM levels were significantly higher than successfully lysed patients. Rethrombosis occurred in 9 patients (32%) in whom baseline IgG levels were significantly higher than those without rethrombosis. There was a moderate positive correlation between baseline and 15th-day IgM levels and the dose of rt-PA needed for successful lysis.

CONCLUSION

The ATA levels tended to be higher in patients with PVT at the time of initial diagnosis compared to controls without PVT. In addition, such patients with PVT and high ATA levels may be at high risk for failed thrombolysis or rethrombosis.

Plasminogen activator inhibitor-1 4G/5G polymorphism, factor V Leiden, prothrombin mutations and the risk of VTE recurrence

Plasminogen-activator inhibitor (PAI)-1 is an important inhibitor of the plasminogen/plasmin system. PAI-1 levels are influenced by the 4G/5G polymorphism in the PAI-1 promoter. We investigated the relationship between the PAI-1 polymorphism and VTE recurrence, and its possible modification by factor V Leiden (FVL) and prothrombin (PTM) mutations. Patients (n=1,069) from the Malmö Thrombophilia Study were followed from discontinuation of anticoagulant treatment until diagnosis of VTE recurrence or the end of the study (maximum follow-up 9.8 years). One hundred twenty-seven patients (11.9 %) had VTE recurrence. PAI-1 was genotyped by TaqMan PCR. Cox regression analysis adjusted for age, sex and acquired risk factors of VTE showed no evidence of an association between PAI-1 genotype and risk of VTE recurrence in the study population as a whole. However, by including an interaction term in the analysis we showed that FVL but not PTM modified the effect of PAI-1 genotype: patients with the 4G allele plus FVL had a higher risk of VTE recurrence [hazard ratio (HR) =2.3, 95 % confidence interval (CI) =1.5-3.3] compared to patients with the 4G allele but no FVL (reference group) or FVL irrespective of PAI-1 genotype (HR=1.8, 95 % CI=1.3-2.5). Compared to reference group, 5G allele irrespective of FVL was associated with lower risk of VTE recurrence only when compared with 4G allele together with FVL. In conclusion, FVL has a modifying effect on PAI-1 polymorphism in relation to risk of VTE recurrence. The role of PAI-1 polymorphism as a risk factor of recurrent VTE may be FVL dependent.

Impact of genetic polymorphisms in thrombin activatable fibrinolysis inhibitor (TAFI) on venous thrombosis disease: A meta-analysis

BACKGROUND

Reported studies have showed that Thrombin Activatable Fibrinolysis Inhibitor (TAFI) may be associated with an increased risk of venous thromboembolism. But the relation of VT with TAFI gene SNPs could not be clearly demonstrated. Thus, we conducted a meta-analysis to analyze the associations between three TAFI variants -438G/A, 505G/A and 1040C/T and the risk of venous thrombosis.

METHODS

We carried out a systematic search to obtain all the eligible studies published before 30th October 2014. Pooled odds ratios (ORs) and 95% confidence intervals (95% CIs) were computed to assess the association.

RESULTS

13 eligible studies were enrolled including 2321 patients and 2464 controls. There was a significant association between 505G/A and the risk of VTD under all models except recessive model (G vs. A: OR=1.13, 95% CI: 1.02, 1.26; GG vs. AA:OR=1.47, 95% CI: 1.14, 1.88; GA vs. AA: OR=1.36, 95% CI: 1.06, 1.73; GG+GA vs. AA: OR=1.41, 95% CI: 1.12, 1.77). Similarly, obvious relationship was observed in subgroup analyses in light of type of disease and ethnicity. Likewise, for 1040C/T variant, significant associations were identified under homozygote, heterozygote and dominant models (CC vs. TT: OR=1.65, 95% CI: 1.06, 2.59; CT vs. TT: OR=1.55, 95% CI: 1.19, 2.03; CC+CT vs. TT: OR=1.55, 95% CI: 1.20, 2.00). Sub-analysis presented significant associations in non-CVT and non-Asian group under homozygote, heterozygote, and dominant models and CVT group in recessive model.

CONCLUSION

This meta-analysis showed that -438G/A variant was not associated with the incidence of venous thrombosis. But in non-Asian populations, G allele and GG genotype of 505G/A may increase the risk of venous thrombosis diseases. GG genotype of 505G/A and one C carrier (CC and CT) of 1040C/T gave rise to the development of venous thrombosis diseases except CVT. Additionally, the heterozygote CT may be a potential contributing factor of gene effect in venous thrombosis.

Thrombin-activatable fibrinolysis inhibitor Thr325Ile polymorphism and plasma level in breast cancer: A pilot study

This study aimed to investigate thrombin-activatable fibrinolysis inhibitor (TAFI) Thr325Ile polymorphism and TAFI antigen (Ag) levels in breast cancer (BC) in the Egyptian population to clarify their role in relation to BC. A group of 300 females was recruited in this study; of these 150 unrelated patients with different stages of BC and 150 age-matched healthy controls. Plasma TAFI Ag was measured by ELISA and TAFI Thr325Ile (rs1926447) polymorphism was genotyped using TaqMan single nucleotide polymorphism (SNP) genotyping assay. The results showed the genotypes of the minor allele; Thr/Ile (CT) and Ile/Ile (TT) were significantly more frequent in patients compared to control group (50.0% and 22.0% vs. 42.0% and 13.3%, respectively) and were also associated with BC susceptibility [OR = 1.9 and 2.6; 95% CI: (1.1–3.3) and (1.3–5.5), respectively P = 0.01]. Ile325 allele carriers were more frequent in cases than in controls (47.0% vs. 34.0%) [OR = 1.7, (95% CI = 1.2–2.4), P = 0.001]. However, TAFI Thr325Ile polymorphism was not associated with BC stage or other clincopathological characteristics. TAFI Ag levels were correlated with advanced stages of BC, poor prognosis and risk of recurrence (P = 0.02, P = 0.04 and P  < 0.001, respectively) and Thr325Ile SNP was significantly correlated with TAFI antigen levels with the C/C genotype corresponding to the highest and the T/T genotype to the lowest TAFI antigen levels (P < 0.001) in the study groups. In conclusion, this study showed for the first time that TAFI Thr325Ile polymorphism could have a contribution to BC susceptibility in our population. Furthermore, high TAFI plasma levels may serve as a predictor of poor prognosis in patients with BC.

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TAFI Thr325Ile polymorphism associated with breast cancer in studied population

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TAFI Thr325Ile polymorphism was significantly correlated with TAFI antigen levels.

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High TAFI antigen levels were correlated with advanced stages of breast cancer.

•

High TAFI plasma level could be used to recognize tumor prognosis and risk of recurrence.

Reduced fibrinogen, fibrinolytic biomarkers, and physical parameters after a weight-loss program in obese subjects

Background:

Obese subjects are at risk of multiple comorbidities including stroke and coronary heart disease (CHD), which is partly due to disturbances in the hemostatic system.

Aims:

The aims of the present study were to determine the effects of a weight-loss program on fibrinogen and fibrinolytic markers.

Materials and Methods:

Twenty-eight obese subjects were involved in a weight-loss program consisted of exercise and nutritional education for 12-weeks duration. Physical parameters were documented and blood specimen was tested at pre and post-intervention for fibrinogen, tissue plasminogen activator (t-PA), plasminogen activator inhibitor-1 (PAI-1), and thrombin activatable fibrinolysis inhibitor (TAFI). Paired t-test was used for statistical analysis.

Results:

There was a significant decline in the levels of t-PA, PAI-I, TAFI and fibrinogen following the weight-loss program (P < 0.01 for each). A significant positive correlation between tPA levels and body weight, body mass index (BMI), waist circumference, and fat-free mass were found. There was also a significant correlation betwen BMI and other blood parameters.

Conclusion:

Reduced fibrinogen, fibrinolytic, and physical parameters were demonstrated in obese subjects following the weight reduction program. These findings suggest the possible beneficial effects of this program on the hemostatic burden particularly on the fibrinolytic biomarkers.

Active PAI-1 as marker for venous thromboembolism: case-control study using a comprehensive panel of PAI-1 and TAFI assays

BACKGROUND

Both activated Thrombin Activatable Fibrinolysis Inhibitor (TAFI) and active Plasminogen Activator Inhibitor-1 (PAI-1) attenuate fibrinolysis and may therefore contribute to the pathophysiology of Venous ThromboEmbolism (VTE). Whether increased TAFI and/or PAI-1 concentrations are associated with VTE is unclear.

OBJECTIVE

To study an association of impaired fibrinolysis and VTE using a comprehensive panel of in-house developed assays measuring intact TAFI, activation peptide of TAFI (AP-TAFI), PAI-1 antigen, endogenous PAI-1:t-PA complex (PAI-1:t-PA) and active PAI-1 levels in 102 VTE patients and in 113 healthy controls (HC).

RESULTS

Active PAI-1 was significantly higher in VTE patients compared to HC (20.9 [9.6-37.8] ng/ml vs. 6.2 [3.5-9.7] ng/ml, respectively). Active PAI-1 was the best discriminator with an area under the ROC curve and 95% confidence interval (AUROC [95%CI]) of 0.84 [0.79-0.90] compared to 0.75 [0.68-0.72] for PAI-1:t-PA, 0.65 [0.58-0.73] for PAI-1 antigen, 0.62 [0.54-0.69] for AP-TAFI and 0.51 [0.44-0.59] for intact TAFI. Using ROC analysis, we defined an optimal cut-off of 12.8 ng/ml for active PAI-1, with corresponding sensitivity of 71 [61-79] % and specificity of 89 [82-94] %. A lack of association with the time between VTE event and sample collection or with the intake of anticoagulant treatment suggests that active PAI-1 levels are sustainable high in VTE patients.

CONCLUSIONS

This case-control study emphasizes the clinical importance of measuring active PAI-1 instead of PAI-1 antigen and identifies active PAI-1 as a potential marker of VTE. Prognostic studies will need to address the clinical significance of active PAI-1 as biomarker.

Altered plasma fibrin clot properties and fibrinolysis in patients with multiple myeloma

BACKGROUND

Multiple myeloma (MM) is associated with increased risk of venous and arterial thromboembolism. Formation of denser and poorly lysable fibrin clots is observed in patients with arterial and venous thromboembolism. We investigated fibrin clot properties and their determinants in MM patients.

MATERIALS AND METHODS

Ex vivo plasma fibrin clot permeability, turbidity and susceptibility to lysis were evaluated in 106 MM patients at the time of diagnosis vs. 100 age- and sex-matched controls. MM patients had lower clot permeability (Ks ), compaction, indicating denser fibrin clots, impaired fibrin polymerization with longer lag phase and lower final turbidity (D-Dmax ), combined with hypofibrinolysis reflected by longer lysis time and slower rate of D-dimer release from fibrin clots (D-Drate ) compared with controls (all P < 0·001).

RESULTS

Patients with IgG MM had lower Ks compared with IgA MM [5·9 (5·1-6·4) vs. 6·3 (5·9-7·2) 10(-9)  cm(2) ; P = 0·007] and longer lysis time compared with light-chain-disease patients [11·4 (10·9-12·3) vs. 10·7 (9·8-11·9) min; P = 0·022]. Of the fibrin variables, only Ks was significantly lower in patients with International Staging System (ISS) grade III than in those with ISS grade I and II [5·9 (4·9-6·6) vs. 6·2 (5·7-6·8) 10(-9)  cm(2) ; P = 0·015]. Multivariate analysis adjusted for age and fibrinogen showed that in MM patients elevated peak thrombin levels determine Ks and D-Dmax , while thrombin-activatable fibrinolysis inhibitor (TAFI) activity predicts Ks , t50% , D-Drate and lag phase.

CONCLUSIONS

Our study demonstrates prothrombotic fibrin clot phenotype in patients with MM, with a significant impact of increased thrombin formation and TAFI activity.

Association between polymorphisms in the flanking region of the TAFI gene and atherosclerotic cerebral infarction in a Chinese population

Background

Atherosclerosis is the leading etiologic factor of Atherosclerotic Cerebral Infarction (ACI). Previous studies have shown that thrombin activatable fibrinolysis inhibitor (TAFI) may play an important role in the occurrence of acute cerebral infarction, and the levels of TAFI are affected by several single nucleotide polymorphisms (SNPs) located in the regulatory and coding regions of the gene encoding TAFI. The present study aimed to determine whether polymorphisms (TAFI –2345 2G/1G, –1690 A/G, –438 A/G, +1583 A/T) of the TAFI gene were associated with ACI in a Han Chinese population.

Methods

The variant genotypes were identified by restriction fragment length polymorphism (RFLP) and allele-specific polymerase chain reactions (AS-PCR) in 225 patients with ACI and 184 age-matched healthy individuals.

Results

There was a significant difference in the genotype and allele frequencies of TAFI –2345 2G/1G and −1690 A/G polymorphisms between the ACI and control subjects. Further stratification analysis by gender revealed that the presence of the –438 AA genotype and the A allele conferred a higher risk of developing ACI in male patients (p < 0.05). Haplotype analysis demonstrated that four haplotypes of TAFI are significantly associated with ACI.

Conclusions

Our study provides preliminary evidence that the TAFI –2345 2G/1G and –1690 A/G polymorphisms are associated with ACI susceptibility in a Han Chinese population.

Residual thrombosis after a first episode of proximal deep venous thrombosis

The aim of this study was to analyse the normalization rate of compression ultrasonography after a first episode of proximal deep venous thrombosis (DVT). Patients underwent compressive ultrasound (C-US) examinations during the 3-6 months following the first proximal DVT episode. Normalization rate of compressive ultrasound (C-US) during the follow-up period was 26.4% [95% confidence interval, 16.3-37.3]. Allelic variation in factor XIII gene (Val34Leu) significantly affected the improvement of popliteal residual thrombi (P = 0.019). We also observed a significant negative correlation between D-dimer levels at 3 months and improvement of popliteal residual thrombi (P = 0.016). There was a significant positive correlation between baseline lumen diameter of the femoral thrombi and IL-8 cytokine (P = 0.015). A significant difference was also found between 1 month-tumor necrosis factor (TNF)-α levels and improvement of residual thrombi (P = 0.047). Our results show that normalization after a standard period of anticoagulation is not frequent and procoagulant and inflammatory biomarkers and also some genetic variations might be related to the resolution of thrombosis.

Factor IX-Padua enhances the fibrinolytic resistance of plasma clots

Hypercoagulable conditions may determine a hypofibrinolytic state by increasing the activation of thrombin-activatable fibrinolysis inhibitor (TAFI). Factor (F)IX-Padua is a mutated FIX with an eight-fold increased clotting activity and associates with a higher venous thrombotic risk. We evaluated the influence of FIX-Padua on TAFI-mediated regulation of fibrinolysis. A subject hemizygous for FIX-Padua, two family members (heterozygous and normal) and six healthy controls were studied. Clot lysis, TAFI activation and thrombin generation were evaluated in contact-inhibited plasma challenged with low concentrations of tissue factor. Fibrinolysis times were significantly longer in FIX-Padua carriers than controls. The difference disappeared when activated TAFI (TAFIa) was inhibited, when TAFI activation was avoided or when clotting was made independent of FIX. TAFIa generation was markedly enhanced in FIX-Padua carriers as compared to controls, and this could be explained by a greater thrombin generation in the former. Hyperactive FIX, but not wild-type FIX, enhanced fibrinolytic resistance also when the FXI-dependent positive feedback was blocked by a neutralising anti-FXI antibody. This thrombin-mediated, TAFI-dependent down-regulation of fibrinolysis provides new clues for explaining the heightened thrombotic risk in subjects carrying the FIX-Padua mutation.

Thrombin activatable fibrinolysis inhibitor : its role in slow coronary flow

BACKGROUND

The slow coronary flow (SCF) phenomenon is characterized by slow progression of angiographic contrast medium in the coronary arteries in the absence of stenosis in the epicardial vessels. The pathophysiological mechanisms of SCF phenomenon remain uncertain. Several hypotheses, however, have been suggested for SCF phenomenon, including an early form of atherosclerosis, small vessel dysfunction, dilatation of coronary vessels, imbalance between vasoconstrictor and vasodilatory factors, platelet function disorder, and inflammation. Atherosclerosis and inflammation are the most accepted mechanisms for the pathogenesis of SCF. Thrombin activatable fibrinolysis inhibitor (TAFI) was described as a new inhibitor of fibrinolysis recently and plays an important role in coagulation and fibrinolysis. In previous studies, the role of TAFI was associated with inflammation and evolution of atherosclerosis in coronary artery disease. There are no data available about TAFI levels in patients with SCF phenomenon investigated by angiography. Our goal was to evaluate TAFI antigen (Ag) levels in patients with SCF and to determine the association of the TAFI Ag level with traditional cardiovascular risk factors in our study.

METHODS

The study group constituted 41 patients with angiographically confirmed SCF and 46 patients with normal coronary flow as the control group. The TAFI Ag levels of each patient were determined.

RESULTS

Between the control and study group, a statistical difference in the levels of TAFI Ag (p < 0.05) was observed. The TAFI Ag level was significantly higher in the SCF group than the control group (132.21 ± 21.14 versus 122.15 ± 21.59).

CONCLUSION

We have demonstrated that TAFI might be a risk factor for the development of SCF independently of conventional cardiovascular risk factors. In addition, TAFI Ag levels were positively correlated with C-reactive protein (CRP) known as an acute phase reactant. Our findings support the reports of previous studies that increased TAFI levels may be associated with inflammation. Further large studies are required to evaluate the importance of TAFI antigen levels in relation to the development of SCF.

Ambivalent roles of carboxypeptidase B in the lytic susceptibility of fibrin

BACKGROUND

Removal of C-terminal lysine residues that are continuously exposed in lysing fibrin is an established anti-fibrinolytic mechanism dependent on the plasma carboxypeptidase TAFIa, which also removes arginines that are exposed at the time of fibrinogen clotting by thrombin.

OBJECTIVE

To evaluate the impact of alterations in fibrin structure mediated by constitutive carboxypeptidase activity on the function of fibrin as a template for tissue plasminogen activator-(tPA) induced plasminogen activation and its susceptibility to digestion by plasmin.

METHODS AND RESULTS

We used the stable carboxypeptidase B (CPB), which shows the same substrate specificity as TAFIa. If 1.5 - 6μM fibrinogen was clotted in the presence of 8U/mL CPB, a denser fibrin network was formed with thinner fibers (the median fiber diameter decreased from 138 - 144nm to 89 - 109nm as established with scanning electron microscopy). If clotting was initiated in the presence of 5 - 10μM arginine, a similar decrease in fiber diameter (82 -95nm) was measured. The fine structure of arginine-treated fibrin enhanced plasminogen activation by tPA, but slowed down lysis monitored using fluorescent tPA and confocal laser microscopy. However, if lysis was initiated with plasmin in CPB-treated fibrin, the rate of dissolution increased to a degree corresponding to doubling of the plasmin concentration.

CONCLUSION

The present data evidence that CPB activity generates fine-mesh fibrin which is more difficult to lyse by tPA, but conversely, CPB and plasmin together can stimulate fibrinolysis, possibly by enhancing plasmin diffusion.

TAFI gene polymorphisms in patients with cerebral venous thrombosis

Gene polymorphisms of thrombin activatable fibrinolysis inhibition (TAFI) factor have been investigated in various studies in terms of etiology (recurrence) and treatment (fibrinolytic effect) of thrombus formation. Cerebral venous thrombosis (CVT) is a life-threatening disease observed in young persons. Fifty-nine patients with CVT and 100 healthy control subjects were enrolled in the case/control study. The association between TAFI gene polymorphisms -438G>A, +505A>G and +1040C>T and cerebral venous thrombosis was investigated. It was found that frequencies of polymorphic genotype and allele were not different in patients than in control group and that they were not significant for cerebral venous thrombosis.

Levels of thrombin activatable fibrinolysis inhibitor in gestational diabetes mellitus

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a procarboxypeptidase, which is synthesised in liver and activated by thrombin and the thrombin-thrombomodulin complex. TAFI suppresses fibrinolysis by removing carboxy-terminal lysine residues from partially degraded fibrin. In this study we aimed to assess the circulating levels of TAFI antigen, 'a fibrinolytic parameter' in women with gestational diabetes (GDM). Thirty-four pregnant women with GDM and 50 pregnant women with normal glucose tolerance were included in the study. Plasma TAFI antigen levels were significantly higher in pregnant women with GDM when compared with controls. Increased TAFI levels may contribute to the decreased fibrinolytic potency, causing a thrombophilic state. GDM is regarded as a specific form of diabetes, and it could in addition be a predictor of type 2 diabetes mellitus in the future and the risk of complications due to hypercoagulability increases in this disease. Increased TAFI levels may also have a role in increased risk of hypercoagulability.

Prediction of recurrent venous thromboembolism by clot lysis time: a prospective cohort study

Venous thromboembolism (VTE) is a chronic disease, which tends to recur. Whether an abnormal fibrinolytic system is associated with an increased risk of VTE is unclear. We assessed the relationship between fibrinolytic capacity (reflected by clot lysis time [CLT]) and risk of recurrent VTE. We followed 704 patients (378 women; mean age 48 yrs) with a first unprovoked VTE for an average of 46 months after anticoagulation withdrawal. Patients with natural coagulation inhibitor deficiency, lupus anticoagulant, cancer, homozygosity for factor V Leiden or prothrombin mutation, or requirement for indefinite anticoagulation were excluded. Study endpoint was symptomatic recurrent VTE. For measurement of CLT, a tissue factor-induced clot was lysed by adding tissue-type plasminogen activator. Time between clot formation and lysis was determined by measuring the turbidity.135 (19%) patients had recurrent VTE. For each increase in CLT of 10 minutes, the crude relative risk (RR) of recurrence was 1.13 (95% CI 1.02–1.25; p = 0.02) and was 1.08 (95% CI 0.98–1.20; p = 0.13) after adjustment for age and sex. For women only, the adjusted RR was 1.14 (95% CI, 0.91–1.42, p = 0.22) for each increase in CLT of 10 minutes. CLT values in the 4^th quartile of the female patient population, as compared to values in the 1^st quartile, conferred a risk of recurrence of 3.28 (95% CI, 1.07–10.05; p = 0.04). No association between CLT and recurrence risk was found in men. Hypofibrinolysis as assessed by CLT confers a moderate increase in the risk of recurrent VTE. A weak association between CLT and risk of recurrence was found in women only.

P1 and P2' site mutations convert protease nexin-2 from a factor XIa inhibitor to a plasmin inhibitor

The kunitz protease inhibitor domain of PN2 (PN2KPI) is a potent and specific inhibitor (K(i) 0.5-2 nM) of factor XIa (FXIa) and inhibits cerebrovascular thrombosis in mice. To determine whether the antithrombotic properties of PN2KPI arise from its FXIa-inhibitory activity, we have now prepared mutant forms of PN2KPI. Mutations at the P1 (Arg(15)) site in combination with P2' (Met(17)) mutations profoundly affect inhibition of FXIa, plasmin, kallikrein, factor Xa and thrombin. The mutant proteins PN2KPI-R(15)K, -M(17)K, -R(15)K,M(17)K and -R(15)K,M(17)R lost inhibitory activity against FXIa (K(i) 34, 94, 3081 and 707 nM, respectively) and kallikrein (no inhibition) and gained inhibitory activity against plasmin (K(i) 108, 7, 8 and 8 nM, respectively). The intravenous administration of rPN2KPI into mice dramatically decreased thrombus formation in a murine model of FeCl(3)-induced carotid injury, whereas rPN2KPI-R(15)K,M(17)K failed to inhibit thrombus formation. Molecular modelling studies showed that fine structural variations explain the observed functional differences in FXIa and plasmin inhibition. PN2KPI has potent antithrombotic activity due to its specific FXIa anticoagulant activity, whereas PN2KPI-R(15)K,M(17)K and PN2KPI-R(15)K,M(17)R have potent antifibrinolytic (antiplasmin) activity without anticoagulant or antithrombotic activity.

Increased thrombin-activatable fibrinolysis inhibitor and decreased tissue factor pathway inhibitor and thrombomodulin levels in children with hypothyroidism

OBJECTIVE

We determined the profile of coagulation/fibrinolytic and vascular endothelial cell function parameters including plasminogen activator inhibitor (PAI) and thrombin-activatable fibrinolysis inhibitor (TAFI), tissue factor pathway inhibitor (TFPI), thrombomodulin (TM), and tissue plasminogen activator (tPA) levels in children with hypothyroidism.

METHODS

Forty children with hypothyroidism aged 0-16 months who presented for the first time to our hospital and 29 age-and sex-matched healthy controls were enrolled in the study. All coagulation tests were performed with ELISA method. One year after Na-L-thyroxine treatment, the study parameters were re-evaluated in 25 euthyroid children out of the 40 patients diagnosed with hypothyroidism.

RESULTS

Although no significant effect was detected regarding PAI antigen (Ag) and tPA Ag, the levels of TAFI, TM, and TFPI were consistent with subclinical hypercoagulability and hypofibrinolysis. There was a significant increase in TAFI Ag levels and a significant decrease in TFPI Ag and TM Ag levels in hypothyroid patients compared to healthy controls. As a result of correlation tests, the largest impact of hypothyroidism on coagulation system was on TFPI. In accordance with these findings, TAFI Ag levels decreased and TFPI Ag and TM Ag levels increased with hormonal replacement therapy.

CONCLUSIONS

Increased TAFI and decreased TFPI and TM in patients with hypothyroidism may indicate a potential hypercoagulable and hypofibrinolytic state as well as possible endothelial dysfunction, which may increase the risk of atherosclerotic and atherothrombotic complications. Thyroid hormone levels should also be checked in patients with a predisposition to coagulation, and thyroid replacement therapy should be initiated.