Thrombin activatable fibrinolysis inhibitor and its relationship to fibrinolysis and inflammation during the acute and convalescent phase of ischemic stroke

Inside the Thrombus: Association of Hemostatic Parameters With Outcomes in Large Vessel Stroke Patients

Background: Actual clinical management of ischemic stroke (IS) is based on restoring cerebral blood flow using tissue plasminogen activator (tPA) and/or endovascular treatment (EVT). Mechanical thrombectomy has permitted the analysis of thrombus structural and cellular classic components. Nevertheless, histological assessment of hemostatic parameters such as thrombin-activatable fibrinolysis inhibitor (TAFI) and matrix metalloproteinase 10 (MMP-10) remains unknown, although their presence could determine thrombus stability and its response to thrombolytic treatment, improving patient's outcome.

Methods: We collected thrombi (n = 45) from large vessel occlusion (LVO) stroke patients (n = 53) and performed a histological analysis of different hemostatic parameters [TAFI, MMP-10, von Willebrand factor (VWF), and fibrin] and cellular components (erythrocytes, leukocytes, macrophages, lymphocytes, and platelets). Additionally, we evaluated the association of these parameters with plasma levels of MMP-10, TAFI and VWF activity and recorded clinical variables.

Results: In this study, we report for the first time the presence of MMP-10 and TAFI in all thrombi collected from LVO patients. Both proteins were localized in regions of inflammatory cells, surrounded by erythrocyte and platelet-rich areas, and their content was significantly associated (r = 0.41, p < 0.01). Thrombus TAFI was lower in patients who died during the first 3 months after stroke onset [odds ratio (OR) (95%CI); 0.59 (0.36–0.98), p = 0.043]. Likewise, we observed that thrombus MMP-10 was inversely correlated with the amount of VWF (r = −0.30, p < 0.05). Besides, VWF was associated with the presence of leukocytes (r = 0.37, p < 0.05), platelets (r = 0.32, p < 0.05), and 3 months mortality [OR (95%CI); 4.5 (1.2–17.1), p = 0.029]. Finally, plasma levels of TAFI correlated with circulating and thrombus platelets, while plasma MMP-10 was associated with cardiovascular risk factors and functional dependence at 3 months.

Conclusions: The present study suggests that the composition and distribution of thrombus hemostatic components might have clinical impact by influencing the response to pharmacological and mechanical therapies as well as guiding the development of new therapeutic strategies.

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.

Diagnostic Accuracy in Acute Venous Thromboembolism: Comparing D-Dimer, Thrombin Generation, Overall Hemostatic Potential, and Fibrin Monomers

Introduction  For acute venous thromboembolism (VTE), a biomarker with higher specificity than D-dimer would be of great clinical use. Thrombin generation and overall hemostatic potential (OHP) reflect the hemostatic balance by globally assessing multiple coagulation factors and inhibitors. These tests discriminate between healthy controls and patients with a prothrombotic tendency but have yet to be established as clinical biomarkers of VTE.

Objective  This study compares endogenous thrombin potential (ETP) and OHP to D-dimer and fibrin monomers (FM) in outpatients with suspected VTE.

Methods  A cross-sectional diagnostic study where 954 patients with suspected pulmonary embolism or deep venous thrombosis were recruited consecutively from the medical emergency department at Karolinska University Hospital. D-dimer, FM, OHP, and ETP were analyzed in a subpopulation of 60 patients with VTE and 98 matched controls without VTE. VTE was verified either by ultrasonography or computed tomography and clinical data were collected from medical records.

Results  Compared with healthy controls, both VTE and non-VTE patients displayed prothrombotic profiles in OHP and ETP. D-dimer, FM, ETP area under the curve (AUC), and ETP T _lag were significantly different between patients with VTE and non-VTE. The largest receiver-operating characteristic AUCs for discrimination between VTE and non-VTE, were found in D-dimer with 0.94, FM 0.77, and ETP AUC 0.65. No useful cutoff could be identified for the ETP or the OHP assay.

Conclusion  Compared with D-dimer, neither ETP nor OHP were clinically viable biomarkers of acute venous thrombosis. The data indicated that a large portion of the emergency patients with suspected VTE were in a prothrombotic state.

TAFI deficiency causes maladaptive vascular remodeling after hemophilic joint bleeding

Excessive vascular remodeling is characteristic of hemophilic arthropathy (HA) and may contribute to joint bleeding and the progression of HA. Mechanisms for pathological vascular remodeling after hemophilic joint bleeding are unknown. In hemophilia, activation of thrombin-activatable fibrinolysis inhibitor (TAFI) is impaired, which contributes to joint bleeding and may also underlie the aberrant vascular remodeling. Here, hemophilia A (factor VIII-deficient; FVIII-deficient) mice or TAFI-deficient mice with transient (antibody-induced) hemophilia A were used to determine the role of FVIII and TAFI in vascular remodeling after joint bleeding. Excessive vascular remodeling and vessel enlargement persisted in FVIII-deficient and TAFI-deficient mice, but not in transient hemophilia WT mice, after similar joint bleeding. TAFI-overexpression in FVIII-deficient mice prevented abnormal vessel enlargement and vascular leakage. Age-related vascular changes were observed with FVIII or TAFI deficiency and correlated positively with bleeding severity after injury, supporting increased vascularity as a major contributor to joint bleeding. Antibody-mediated inhibition of uPA also prevented abnormal vascular remodeling, suggesting that TAFI's protective effects include inhibition of uPA-mediated plasminogen activation. In conclusion, the functional TAFI deficiency in hemophilia drives maladaptive vascular remodeling in the joints after bleeding. These mechanistic insights allow targeted development of potentially new strategies to normalize vascularity and control rebleeding in HA.

Procarboxypeptidase U (proCPU, TAFI, proCPB2) in cerebrospinal fluid during ischemic stroke is associated with stroke progression, outcome and blood-brain barrier dysfunction

Essentials Little is known of procarboxypeptidase U (proCPU) in cerebrospinal fluid (CSF) of stroke patients. ProCPU levels were studied in CSF of controls and non-thrombolyzed acute ischemic stroke patients. ProCPU is elevated in CSF of stroke patients compared with controls. ProCPU in CSF correlates with stroke progression, outcome, and blood-brain barrier dysfunction.

SUMMARY

Background Procarboxypeptidase U (proCPU, TAFI, proCPB2), the zymogen of CPU, which is a potent antifibrinolytic enzyme and a modulator of inflammation, has previously been investigated in plasma of stroke patients, but so far, no information on the proCPU levels in cerebrospinal fluid (CSF) during acute ischemic stroke (AIS) is available. Objectives This case-control observational study investigates proCPU in CSF of AIS patients compared with controls with an intact blood-brain barrier (BBB) and evaluates the relationship of CSF/plasma proCPU ratios with stroke parameters. Methods A sensitive HPLC-based enzymatic assay was used to determine proCPU levels in CSF of non-thrombolyzed patients in the hyperacute phase (< 24 h after onset) of AIS (n = 72). Individuals (n = 32) without stroke, an intact BBB and no apparent abnormalities in biochemical and microbiological tests, served as controls. Relations between the CSF/plasma proCPU ratio and (i) stroke severity, (ii) stroke progression/recurrence, (iii) stroke outcome and (iv) BBB dysfunction (CSF/serum albumin ratio) were assessed. Results Mean (SEM) proCPU levels were elevated in the CSF of stroke patients compared with controls (4.36 (0.23) U L-1 vs. 3.50 (0.23) U L-1 ). Higher median [IQR] CSF/plasma proCPU ratios were found in patients with stroke progression ((6.0 [4.2-6.9]) × 10-3 ) and poor outcome ((6.4 [3.9-7.0]) × 10-3 ) after 3 months (modified Rankin Scale; mRS > 3) compared with patients without progression ((3.9 [2.7-5.4]) × 10-3 ) or better outcome ((4.0 [2.8-5.0]) × 10-3 ). In stroke patients with a disrupted BBB, proCPU ratios were higher compared with stroke patients with an intact BBB ((6.4 [5.8-9.0]) × 10-3 vs. (3.7 [2.8-5.0]) × 10-3 ). Conclusions ProCPU is increased in CSF during hyperacute ischemic stroke and is associated with stroke progression and outcome after 3 months, most likely due to BBB dysfunction in the hyperacute phase of ischemic stroke.

Nobiletin, a polymethoxyflavone in citrus fruits, reduces TAFI expression in HepG2 cells through transcriptional inhibition

Thrombin-activatable fibrinolysis inhibitor (TAFI, carboxypeptidase B2) is a 58-kDa plasma glycoprotein secreted by hepatocytes as an inactive form. TAFI is activated by the thrombin-thrombomodulin complex, and activated TAFI (TAFIa) plays an important role in regulating the balance between coagulation and fibrinolysis through inhibition of fibrinolysis. It has been suggested that high levels of TAFI in circulating plasma increase the risks of cardiovascular death and acute phase in ischaemic stroke. However, the mechanisms of regulating TAFI expression have been unclear. The present study investigated the effects of nobiletin (a polymethoxy flavonoid contained in the rind of citrus fruits) on TAFI gene (CPB2) and TAFI antigen expression in cultured human hepatoma HepG2 cells. Nobiletin decreased the release of TAFI antigen from HepG2 cells into conditioned medium in parallel with decreased levels of CPB2 mRNA and antigen. The half-life time of CPB2 mRNA in nobiletin-treated cells was unchanged compared to that of untreated control cells. Using nobiletin-treated cells that were transfected with a luciferase CPB2 promoter reporter plasmid, activity decreased to half of that in untreated control cells. A series of luciferase reporter constructs containing 5´-flanking region deletions of the human CPB2 gene showed that the sequences from –150 bp to –50 bp were essential for transcription of CPB2 and contained an AP-1 binding sequence at ∼ –119 bp to – 99 bp in the CPB2 promoter. The amount of complexed nuclear protein and sequences from ∼ –119 bp to –99 bp was decreased in nobiletin-treated cells. ChIP assays showed that c-Jun bound to the ∼ –119 bp to –99 bp region of the CPB2 promoter and that the amount of the immunocomplex decreased after nobiletin treatment. Therefore, nobiletin-induced repression of CPB2 transcription might involve AP-1 inhibition and/or prevention of AP-1 binding in a specific region on the CPB2 gene in HepG2 cells.

Dose-Response Relationship Between Thrombin-Activatable Fibrinolysis Inhibitor (TAFI) and Stroke: A Chinese Case-Control Study

BACKGROUND Because TAFI (thrombin-activatable fibrinolysis inhibitor) antigen varies widely among different populations, we performed this case-control study to explore the relationship between TAFI levels and stroke in a Chinese population. MATERIAL AND METHODS Our population-based case-control study included 217 stroke patients and 218 healthy controls. The plasma TAFI level was measured by immune turbidimetry. Univariate and multivariate logistic regression analyses were used to analyze the association between different TAFI levels and stroke and its subtypes. Restricted cubic spline (RCS) combined with logistic regression analysis were used to explore the dose-response relationship between TAFI levels and stroke. RESULTS The plasma TAFI levels of cases were much higher than in the control group (p=0.038) and this difference persisted even after adjustment (OR=2.2). In the elderly (aged over 60) and female subgroups, TAFI levels in stroke patients were higher than those in controls, and the results were also noted in ischemic stroke. The dose-response curve showed that, as a whole, with the increase of TAFI levels, the relative risk of stroke first increased and then decreased (p=0.0127). Similarly, in general, with the increase of TAFI levels, the curve showed that the relative risk of ischemic stroke first increased and then decreased (p=0.0110). CONCLUSIONS There was a definite correlation between TAFI levels and stroke in this Chinese population, and with the increase of TAFI levels, the relative risk of stroke or ischemic stroke first increased and then decreased.

Global assays of fibrinolysis

Fibrinolysis is an important and integral part of the hemostatic system. Acting as a balance to blood coagulation, the fibrinolytic system protects the body from unwanted thrombus formation and occlusion of blood vessels. As long as blood coagulation and fibrinolysis remain in equilibrium, response to injury, such as vessel damage, is appropriately regulated. However, alterations in this balance may lead to thrombosis or bleeding. A variety of methods have been proposed to assess fibrinolytic activity in blood or its components, but due to the complexity of the system, the design of a "gold standard" assay that reflects overall fibrinolysis has remained an elusive goal. In this review, we describe the most commonly used methods that have been described, such as thromboelastography (TEG and ROTEM), global fibrinolytic capacity in plasma and whole blood, plasma turbidity methods, simultaneous thrombin and plasmin generation assays, euglobulin clot lysis time and fibrin plate methods. All of these assays have strengths and limitations. We suggest that some methods may be preferable for detecting hypofibrinolytic conditions, whereas others may be better for detecting hyperfibrinolytic states.

Innovative thrombolytic strategy using a heterodimer diabody against TAFI and PAI-1 in mouse models of thrombosis and stroke

Circulating thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor-1 (PAI-1) are causal factors for thrombolytic failure. Therefore, we evaluated an antibody-engineered bispecific inhibitor against TAFI and PAI-1 (heterodimer diabody, Db-TCK26D6x33H1F7) in several mouse models of thrombosis and stroke. Prophylactic administration of the diabody (0.8 mg/kg) in a thromboplastin-induced model of thromboembolism led to decreased lung fibrin deposition. In a model of cerebral ischemia and reperfusion, diabody administration (0.8 mg/kg, 1 hour postocclusion) led to a mitigated cerebral injury with a 2.3-fold reduced lesion and improved functional outcomes. In a mouse model of thrombin-induced middle cerebral artery occlusion, the efficacy of the diabody was compared to the standard thrombolytic treatment with recombinant tissue-type plasminogen activator (tPA). Early administration of diabody (0.8 mg/kg) caused a twofold decrease in brain lesion size, whereas that of tPA (10 mg/kg) had a much smaller effect. Delayed administration of diabody or tPA had no effect on lesion size, whereas the combined administration of diabody with tPA caused a 1.7-fold decrease in lesion size. In contrast to tPA, the diabody did not increase accumulative bleeding. In conclusion, administration of a bispecific inhibitor against TAFI and PAI-1 results in a prominent profibrinolytic effect in mice without increased bleeding.

Plasma thrombin-activatable fibrinolysis inhibitor as an indicator of inflammation and disease severity in acute pancreatitis

AIM

In addition to suppressing fibrinolysis, thrombin activatable fibrinolysis inhibitor (TAFI) was suggested to be involved in inflammation. To date, no study has been published that reports the role of TAFI in acute pancreatitis (AP). Therefore, the objective of the present study was to investigate the role of plasma TAFI as an indicator of inflammation in AP, and its association with disease severity.

METHODS

Plasma TAFI antigen levels quantitatively determined by using ELISA kits in 21 AP patients at onset and remission and 17 healthy controls. Associations of TAFI with inflammatory markers to determine AP and disease severity were assessed. To predict the severity of AP, modified Glasgow prognostic score (mGPS) and computerized tomography severity index (CTSI) were used for each subject.

RESULTS

Plasma TAFI levels was higher in AP patients at onset of the disease compared with healthy controls. The disease severity according to mGPS was significantly correlated with TAFI levels. Overall, accuracy of TAFI in determining AP was 83.3% with a sensitivity, specificity, NPV and PPV of 80.9%, 85.7%, 81.8%, and 85% respectively (AUC: 0.915).

CONCLUSIONS

The present study for the first time demonstrated that TAFI is elevated in AP. The appraisal of TAFI levels in patients with AP in conjunction with other markers of inflammation may provide additional information in estimating AP severity.

Identification of tristetraprolin as a factor that modulates the stability of the TAFI transcript through binding to the 3'-untranslated region

BACKGROUND

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a basic carboxypeptidase zymogen encoded by the human gene CPB2. TAFI constitutes a molecular link between coagulation and fibrinolysis, and between coagulation and inflammation. The 3'-untranslated region (UTR) of the human CPB2 mRNA plays a key role in regulating CPB2 mRNA abundance, but the exact mechanisms that mediate this regulation are largely unexplored.

OBJECTIVES

To pinpoint cis-acting elements in the CPB2 3'-UTR that act as stability determinants and to identify protein factors binding to these sites.

METHODS

We constructed a series of plasmids encoding mRNAs containing rabbit β-globin sequences (as a reporter) fused to sequences of the CPB2 3'-UTR (encompassing 5' and internal deletions). These plasmids were transfected into HepG2 (human hepatoma) cells and the stability of the fusion transcripts measured. We performed a series of gel mobility shift analyses using RNA probes encompassing putative (in)stability elements.

RESULTS

We identified one element conferring stability and three elements conferring instability. Supershift assays identified the protein bound to the site between the second and third polyadenylation sites as tristetraprolin (TTP). Mutation of the TTP site abolished TTP binding in gel mobility shift assays and also stabilized β-globin/CPB2 fusion transcripts. TTP knockdown stabilized the fusion transcript containing the TTP site, but not a fusion transcript in which this site was mutated.

CONCLUSIONS

Our findings are indicative of a role for TTP in constitutive, and perhaps regulated, control of CPB2 mRNA stability and hence abundance.

Activated thrombin activatable fibrinolysis inhibitor (TAFIa) is associated with inflammatory markers in inflammatory bowel diseases TAFIa level in patients with IBD

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI) has been reported to be involved in the pathogenesis and progression of inflammatory bowel disease (IBD). Activated TAFI (TAFIa) attenuates fibrinolysis by cleaving C-terminal lysine residues thus down-regulating plasminogen activation. To date, no reports on TAFIa in IBD have been published.

METHODS

Plasma levels of TAFIa were measured using a functional assay in 55 consecutive patients with ulcerative colitis (UC) and 50 with Crohn's disease (CD). Associations of TAFIa with disease activity, hemostatic variables and inflammatory markers were assessed.

RESULTS

Plasma TAFIa was higher in CD patients than in those with UC. The disease activity correlated positively with TAFIa levels in the UC group, but not in the CD group. In UC patients, there were positive correlations of TAFIa with white blood cells, C-reactive protein and fibrinogen and an inverse correlation with albumin. In the CD group, a positive correlation was shown for C-reactive protein, fibrinogen and platelet count, while a negative correlation was noted for albumin.

CONCLUSIONS

This study is the first to show that TAFIa is increased in CD patients compared with UC and its levels are associated with inflammatory markers in both forms of IBD. These findings fit in the hypothesis that TAFIa may be a marker of active IBD, and in particular of active UC.

Identification of human thrombin-activatable fibrinolysis inhibitor in vascular and inflammatory cells

TAFI (thrombin-activatable fibrinolysis inhibitor) is a carboxypeptidase zymogen originally identified in plasma. The TAFI pathway helps to regulate the balance between the coagulation and fibrinolytic cascades. Activated TAFI (TAFIa) can also inactivate certain pro-inflammatory mediators, suggesting that the TAFI pathway may also regulate communication between coagulation and inflammation. Expression in the liver is considered to be the source of plasma TAFI. TAFI has also been identified in platelets and CPB2 (the gene encoding TAFI) mRNA has been detected in megakaryocytic cell lines as well as in endothelial cells. We have undertaken a quantitative analysis of CPB2 mRNA and TAFI protein in extrahepatic cell types relevant to vascular disease. Using RT-PCR and quantitative RT-PCR, we detected CPB2 mRNA in the human megakaryoblastic cell lines MEG-01 and Dami, the human monocytoid cell line THP-1 as well as THP-1 cells differentiated into a macrophage-like phenotype, and in primary human umbilical vein and coronary artery endothelial cells. CPB2 mRNA abundance in MEG-01, Dami, and THP-1 cells was modulated by the state of differentiation of these cells. Using a recently developed TAFIa assay, we detected TAFI protein in the lysates of the human hepatocellular carcinoma cell line HepG2 as well as in MEG-01 and Dami cells and in the conditioned medium of HepG2 cells, differentiated Dami cells, and THP-1 macrophages. We have obtained clear evidence for extrahepatic expression of TAFI, which has clear implications for the physiological and pathophysiological functions of the TAFI pathway.

Decreased fibrin network permeability and impaired fibrinolysis in the acute and convalescent phase of ischemic stroke

INTRODUCTION

We investigated fibrin network permeability and fibrinolysis in the acute and convalescent phase of ischemic stroke.

METHODS

20 patients with a mean age of 74 years were studied in the acute (day 1) and convalescent phase (day 60) of ischemic stroke. 23 healthy individuals (controls) were also investigated. Fibrin formation in the samples was triggered by addition of tissue factor (1 pmol/L) and washed frozen-thawed platelets obtained from a healthy donor. The permeability constant (K(s)), which reflects fibrin network permeability, was then calculated from liquid flow measurements. A global assay newly developed in our group was also employed to determine the balance between fibrin formation ("Coagulation profile"; Cp) and fibrin degradation ("Fibrinolysis profile"; Fp) in the same samples. We also measured PAI-1 antigen and fibrinogen concentrations in plasma.

RESULTS

As compared to controls, the stroke patients had lower Ks (lower fibrin network permeability) both on day 1 and on day 60 (p < 0.01 and p < 0.05, respectively). Fibrinolysis, assessed by Fp, was reduced on both day 1 and day 60 (p < 0.001, compared to controls), and PAI-1 concentrations were increased (p < 0.01 for both, compared to controls). Fibrin formation capacity in plasma (i.e. Cp) was increased in the acute phase (p < 0.05) but not in the convalescence, as compared to controls.

CONCLUSION

The combination of a proneness to form a tighter fibrin network and impaired fibrinolysis is a feature of ischemic stroke that is present in both the acute and convalescent phase of the disease.

Thrombin-activatable fibrinolysis inhibitor (TAFI) deficient mice are susceptible to intracerebral thrombosis and ischemic stroke

BACKGROUND

Thrombus formation is a key step in the pathophysiology of acute ischemic stroke and results from the activation of the coagulation cascade. Thrombin plays a central role in this coagulation system and contributes to thrombus stability via activation of thrombin-activatable fibrinolysis inhibitor (TAFIa). TAFIa counteracts endogenous fibrinolysis at different stages and elevated TAFI levels are a risk factor for thrombotic events including ischemic stroke. Although substantial in vitro data on the influence of TAFI on the coagulation-fibrinolysis-system exist, investigations on the consequences of TAFI inhibition in animal models of cerebral ischemia are still lacking. In the present study we analyzed stroke development and post stroke functional outcome in TAFI-/- mice.

METHODOLOGY/PRINCIPAL FINDINGS

TAFI-/- mice and wild-type controls were subjected to 60 min transient middle cerebral artery occlusion (tMCAO) using the intraluminal filament method. After 24 hours, functional outcome scores were assessed and infarct volumes were measured from 2,3,5-Triphenyltetrazoliumchloride (TTC)-stained brain slices. Hematoxylin and eosin (H&E) staining was used to estimate the extent of neuronal cell damage. Thrombus formation within the infarcted brain areas was analyzed by immunoblot. Infarct volumes and functional outcomes did not significantly differ between TAFI-/- mice and controls (p>0.05). Histology revealed extensive ischemic neuronal damage regularly including the cortex and the basal ganglia in both groups. TAFI deficiency also had no influence on intracerebral fibrin(ogen) formation after tMCAO.

CONCLUSION

Our study shows that TAFI does not play a major role for thrombus formation and neuronal degeneration after ischemic brain challenge.

Analysis of a new crystal form of procarboxypeptidase B: further insights into the catalytic mechanism

A new triclinic crystal structure form of porcine pancreatic procarboxypeptidase B (PCPB) was obtained at higher resolution than the previously known tetragonal crystal structure. This new crystal polymorph has allowed for a corrected, accurate assignment of residues along the polypeptide chain based on the currently available gene sequence information and crystallographic data. The present structure shows unbound PCPB in a distinct molecular packing as compared to the previous benzamidine complexed form. Its catalytically important Tyr248 residue is oriented and hydrogen-bonded to solvent water molecules, and locates the furthest away from the catalytic zinc ion as compared to previous structures. A relatively long stretch of residues flanking Tyr248 and guarding the access to the catalytic zinc ion was found to be sequentially unique to the M14 family of peptidases. Predictions from a normal mode analysis indicated that this stretch of residues belongs to a rigid subdomain in the protein structure. The specific presence of a tyrosyl residue at the most exposed position in this region would allow for a delicate balance between extreme hydrophobicity and hydrophilicity, and affect substrate binding and the kinetic efficiency of the enzyme.

The decrease in procarboxypeptidase U (TAFI) concentration in acute ischemic stroke correlates with stroke severity, evolution and outcome

BACKGROUND AND OBJECTIVES

Procarboxypeptidase U (proCPU, TAFI) concentration in plasma is potentially related to thrombotic tendency, and elevated proCPU levels have been reported in ischemic stroke patients. Improved insight into the role of proCPU in acute ischemic stroke is essential for the development of more adequate therapeutics that may include carboxypeptidase inhibitors. In this study we investigated whether the plasma concentration of proCPU and the proCPU kinetic profile in acute ischemic stroke are related to initial stroke severity, stroke evolution in the subacute phase and long-term stroke outcome.

METHODS

Plasma concentration of proCPU was assessed in 136 stroke patients at admission (7.5 h after stroke onset), at 24 h, at 72 h and at day 7 after stroke onset. We evaluated the relation between change in proCPU concentrations and (a) stroke severity (patients with TIA vs. stroke patients, NIHSS score at admission), (b) stroke evolution (stroke progression, infarct volume at 72 h), and (c) stroke outcome (mRS score at month 3).

RESULTS

ProCPU concentration decreased significantly in the first 72 h after stroke onset and thereafter returned to baseline. This biphasic time course, with its nadir at 72 h, was more pronounced in patients with severe stroke, unfavourable stroke evolution in the first 72 h and poor long-term outcome.

CONCLUSIONS

The decrease in proCPU concentration in the first 72 h after stroke onset correlates with more severe stroke, unfavourable stroke evolution, and poor long-term stroke outcome.

Increased thrombin-activatable fibrinolysis inhibitor and decreased tissue factor pathway inhibitor in patients with hyperthyroidism

Various abnormalities of coagulation-fibrinolytic system have been reported in patients with thyroid dysfunction. Several studies indicate that coagulation and fibrinolytic system is disturbed in the patients with hyperthyroidism. The levels of plasma thrombin-activatable fibrinolysis inhibitor (TAFI) antigen and tissue factor pathway inhibitor (TFPI) have been very rarely investigated in patients with hyperthyroidism. Therefore, the main purpose of this study was to evaluate the profile of coagulation and fibrinolytic parameters including TAFI and TFPI in patients with hyperthyroidism. We also investigated the relationships between serum thyroid hormones and hemostatic parameters in these patients. Thirty patients with untreated hyperthyroidism and 25 age- and sex-matched healthy controls were included in the study. Factor V (FV), protein C, protein S, TFPI, and TAFI were measured. The relationships between serum thyroid hormones and these hemostatic parameters were examined. Compared with the control subjects, TAFI Ag levels were increased significantly in patients with hyperthyroidism [mean ± SD (ranges)] [177.03 ± 20.37 (131-206%) versus 145.9 ± 23.0 (89-169%)] (P < 0.001), whereas FV [89.8 ± 21.02 (49-124%) versus 116.1 ± 31.4 (56.4-200%)], protein C [72.8 ± 46.22 (2-149%) versus 144.0 ± 26.3 (74-158%)] and protein S [60.06 ± 42.82 (9-156%) versus 151 ± 33 (76-231%)] activities and TFPI Ag levels [69.56 ± 17.63 (39-140 ng/ml) versus 87.5 ± 15.9 (64-121 ng/ml)] were decreased significantly (P < 0.001 for all of them). We did not find a significant difference between Graves' disease and toxic nodular goiter for hemostatic parameters. In patients with Graves' disease, serum-free T₃ levels were inversely correlated with TFPI Ag levels (r: -0.57, P < 0.05). In conclusion, we found some important differences in the hemostatic parameters between the patients with hyperthyroidism and healthy controls. Increased TAFI and decreased FV, protein C, protein S, and TFPI in these patients represent a potential hypercoagulable and hypofibrinolytic state, which might augment the risk for atherosclerotic and atherothrombotic complications. Thus, disturbances of the hemostatic system may contribute to the excess mortality due to cardiovascular disease seen in patients with hyperthyroidism.

The X-ray structure of carboxypeptidase A inhibited by a thiirane mechanism-based inhibitor

The three-dimensional X-ray crystal structure of carboxypeptidase A, a zinc-dependent hydrolase, covalently modified by a mechanism-based thiirane inactivator, 2-benzyl-3,4-epithiobutanoic acid, has been solved to 1.38 A resolution. The interaction of the thiirane moiety of the inhibitor with the active site zinc ion promotes its covalent modification of Glu-270 with the attendant opening of the thiirane ring. The crystal structure determination at high resolution allowed for the clear visualization of the covalent ester bond to the glutamate side chain. The newly generated thiol from the inhibitor binds to the catalytic zinc ion in a monodentate manner, inducing a change in the zinc ion geometry and coordination, while its benzyl group fits into the S1' specificity pocket of the enzyme. The inhibitor molecule is distorted at the position of the carbon atom that is involved in the ester bond linkage on one side and the zinc coordination on the other. This particular type of thiirane-based metalloprotease inhibitor is for the first time analyzed in complex to the target protease at high resolution and may be used as a general model for zinc-dependent proteases.

Natural occurring polyphenols as template for drug design. Focus on serine proteases

Several major physio-pathological processes, including cancer, inflammatory states and thrombosis, are all strongly dependent upon the fine regulation of proteolytic enzyme activities, and dramatic are the consequences of unbalanced equilibria between enzymes and their cognate inhibitors. In this perspective, the discovery of small-molecule ligands able to modulate catalytic activities has a massive therapeutic potential and is a stimulating goal. Numerous recent experimental evidences revealed that proteolytic enzymes can be opportunely targeted, reporting on small ligands capable of binding to these biological macromolecules with drug-like potencies, and primarily with comparable (or even higher) efficiency with respect to their endogenous binding partner. In particular, natural occurring polyphenols and their derivatives recently disclosed these intriguing abilities, making them promising templates for drug design and development. In this review, we compared the inhibitory capacities of a set of monomeric polyphenols toward serine proteases activity, and finally summarized the data with an emphasis on the derivation of a pharmacophore model.

Increased plasminogen activator inhibitor-1, decreased tissue factor pathway inhibitor, and unchanged thrombin-activatable fibrinolysis inhibitor levels in patients with primary hyperparathyroidism

BACKGROUND AND OBJECTIVES

Primary hyperparathyroidism (PHPT) is associated with increased cardiovascular mortality and morbidity. Little is known about hemostatic features of patients with PHPT. To our knowledge, plasma tissue factor pathway inhibitor (TFPI) and thrombin-activatable fibrinolysis inhibitor (TAFI) levels in these patints have not been investigated. Therefore, the main purpose of this study was to evaluate the markers of endogenous coagulation/fibrinolysis, including TFPI and TAFI, and to investigate the relationships between serum calcium and PTH and these hemostatic parameters in patients with PHPT.

DESIGN AND METHODS

Twenty-four patients with PHPT and 20 age-, sex-, and-weight-matched healthy controls were included in the study. Tissue plasminogen activator (t-PA), tissue plasminogen activator inhibitor-1 (PAI-1), TFPI, and TAFI were measured. The relationships between serum calcium, phosphorus, and PTH and these hemostatic parameters were examinated.

RESULTS

Compared with the control subjects, t-PA, PAI-1, and PAI-1/t-PA ratios were significantly increased in patients with PHPT (P<0.0001), whereas TFPI levels were significantly decreased (P<0.0001). Plasma TAFI Ag levels did not significantly change in patients with PHPT compared with the controls. In patients with PHPT, serum phosphorus was negatively correlated with plasma PAI-1 Ag levels and PAI-1/t-PA ratio (r: -0.453, P<0.05; r: -0.580, P<0.01 respectively). There was a positive correlation between Cl/P ratio and plasma PAI-1 levels and PAI-1/t-PA ratio (r: 0.434, P<0.05; r: 0.528, P<0.05 respectively). iPTH was positively correlated with plasma PAI-1/t-PA ratio (r: 0.429, P<0.05).

INTERPRETATION AND CONCLUSIONS

In conclusion, we found some important differences in the hemostatic parameters between the patients with PHPT and healthy controls. Increased PAI-1, PAI-1/t-PA ratios and decreased TFPI levels in these patients represent a potential hypercoagulable and hypofibrinolytic state, which might augment the risk for atherosclerotic and atherothrombotic complications. This condition may contribute to the excess mortality due to cardiovascular disease seen in patients with PHPT.

Increased thrombin-activatable fibrinolysis inhibitor and decreased tissue factor pathway inhibitor in patients with hypothyroidism

Various abnormalities of coagulation-fibrinolytic system have been reported in patients with thyroid dysfunction. Several studies indicate that coagulation and fibrinolytic system is disturbed in the patients with hypothyroidism. Also, the influence of hypothyroidism on hemostasis is controversial; both hypocoagulable and hypercoagulable states have been reported. The levels of plasma thrombin-activatable fibrinolysis inhibitor (TAFI) antigen and tissue factor pathway inhibitor (TFPI) have been investigated only once in patients with hypothyroidism. Therefore, the main purpose of this study was to evaluate the profile of coagulation and fibrinolytic parameters including TAFI and TFPI in patients with hypothyroidism. Fifteen patients with untreated hypothyroidism and 15 age-matched healthy controls were included in the study. Factors V(FV), VII (FVII), VIII (FVIII) activities, von Willebrand factor (vWF), protein C, protein S, thrombomodulin (TM), TFPI, and TAFI were measured. The relationships between serum thyroid hormones and these hemostatic parameters were examined. Compared with the control subjects, FVII activity, and TM Ag and TAFI Ag levels were significantly increased in patients with hypothyroidism, whereas FV, FVIII, vWF, protein C and protein S activities, and TFPI Ag levels were significantly decreased. We did not find any significant correlation between serum thyroid hormones and the hemostatic parameters that we measured. In conclusion, we found some important differences in the hemostatic parameters between the patients with hypothyroidism and healthy controls. Increased FVII, TM, and TAFI and decreased FV, FVIII, vWF, protein C, protein S, and TFPI in these patients represent a potential hypercoagulable and hypofibrinolytic state, possible endothelial dysfunction, which might augment the risk for atherosclerotic and atherothrombotic complications. Thus, disturbances of the hemostatic system may contribute to the excess mortality due to cardiovascular disease seen in patients with hypothyroidism.

Blood coagulation and fibrinolysis in patients with Cushing's syndrome: increased plasminogen activator inhibitor-1, decreased tissue factor pathway inhibitor, and unchanged thrombin-activatable fibrinolysis inhibitor levels

BACKGROUND AND OBJECTIVES

Cushing's syndrome (CS) is associated with an increased cardiovascular mortality and morbidity. Chronic endogenous and exogenous hypercortisolism frequently induce a hypercoagulable and thrombotic condition. Little is known about hemostatic features of patients with CS. To our knowledge, plasma tissue factor pathway inhibitor (TFPI) and thrombin-activatable fibrinolysis inhibitor (TAFI) levels in these patients have not been investigated. Therefore, the main purpose of this study was to evaluate the markers of endogenous coagulation/fibrinolysis, including TFPI and TAFI, and to investigate the relationships between cortisol and these hemostatic parameters and serum lipid profile in patients with CS.

DESIGN AND METHODS

Twenty-four patients with CS and 24 age-matched healthy controls were included in the study. Prothrombin time (PT), activated partial thromboplastin time (aPTT), fibrinogen, factors V, VII, VIII, IX, and X activities, von Willebrand factor (vWF), antithrombin III (AT III), protein C, protein S, tissue plasminogen activator (t-PA), tissue plasminogen activator inhibitor-1 (PAI-1), TFPI and TAFI, as well as common lipid variables, were measured. The relationships between serum cortisol and these hemostatic parameters were examined.

RESULTS

Compared with the control subjects, platelet count, PT, fibrinogen, AT-III and PAI-1 were significantly increased in patients with CS (p<0.05, p<0.0001, p<0.01, p<0.05, and p<0.0001, respectively), whereas aPTT and TFPI levels were significantly decreased (p<0.0001 and p<0.01, respectively). Plasma TAFI Ag levels did not significantly change in patients with CS compared with the controls. In patients with CS, we showed a negative correlation between serum cortisol: 08:00 h and aPTT (r:-0.469, p<0.05). Serum cortisol: 24:00 h was positively correlated with PAI-1 Ag levels (r: 0.479, p<0.05).

INTERPRETATION AND CONCLUSIONS

In conclusion, we found some important differences in the hemostatic parameters between the patients with CS and healthy controls. Increased platelet count, fibrinogen, PAI-1, and decreased TFPI levels in these patients represent a potential hypercoagulable and hypofibrinolytic state, which might augment the risk for atherosclerotic and atherothrombotic complications. This condition may contribute to the excess of mortality due to cardiovascular disease seen in patients with CS.

Blood coagulation and fibrinolysis in patients with acromegaly: increased plasminogen activator inhibitor-1 (PAI-1), decreased tissue factor pathway inhibitor (TFPI), and an inverse correlation between growth hormone and TFPI

OBJECTIVE

Growth hormone/insulin-like growth factor-1(GH/IGF-1) hypersecretion may influence risk factors contributing to the increased cardiovascular morbidity and mortality associated with acromegaly However, so far little is known about the impact of GH/IGF-1 on coagulation and fibrinolysis in acromegalic patients as possible risk factors for cardiovascular disease (CVD). To our knowledge, plasma tissue factor pathway inhibitor (TFPI) and thrombin-activatable fibrinolysis inhibitor (TAFI) levels in these patients have not been investigated. Therefore, the main purpose of this study was to evaluate the markers of endogenous coagulation/fibrinolysis, including TFPI and TAFI, and to investigate the relationships between GH/IGF-1 and these hemostatic parameters and serum lipid profile in patients with acromegaly.

RESEARCH METHODS AND PROCEDURES

A total of 22 patients with active acromegaly and 22 age-matched healthy controls were included in the study. Fibrinogen, factors V, VII, VIII, IX, and X activities, von-Willebrand factor (vWF), antithrombin III (AT III), protein C, protein S, tissue plasminogen activator (t-PA), tissue plasminogen activator inhibitor-I (PAI-1), TFPI and TAFI, as well as common lipid variables, were measured. The relationships between serum GH/IGF-1 and these hemostatic parameters were evaluated.

RESULTS

Compared with the control subjects, fibrinogen, AT III, t-PA, and PAI-1 were increased significantly in patients with acromegaly (P < 0.0001, P < 0.05, P < 0.01, and P < 0.0001, respectively), whereas protein S activity and TFPI levels were decreased significantly (P < 0.05 and P < 0.01, respectively). Plasma TAFI Ag levels did not significantly change in patients with acromegaly compared with the controls. In patients with acromegaly, serum GH levels were inversely correlated with TFPI and apo AI levels (r: -0.514, P: 0.029 and r: -0.602, P: 0.014, respectively). There was also a negative correlation between insulin-like growth factor-1 (IGF-1) and PAI-1 (r: -0.455, P: 0.045).

DISCUSSION

We found some important differences in the hemostatic parameters between the patients with acromegaly and healthy controls. Increased fibrinogen, t-PA, PAI-1 and decreased protein S and TFPI in acromegalic patients may represent a potential hypercoagulable and hypofibrinolytic state, which might augment the risk for atherosclerotic and atherothrombotic complications. Thus, disturbances of the hemostatic system and dyslipidemia may contribute to the excess mortality due to CVD seen in patients with acromegaly.