Acute phase mediators modulate thrombin-activable fibrinolysis inhibitor (TAFI) gene expression in HepG2 cells

Activation of the Carboxypeptidase U (CPU, TAFIa, CPB2) System in Patients with SARS-CoV-2 Infection Could Contribute to COVID-19 Hypofibrinolytic State and Disease Severity Prognosis

Coronavirus disease 2019 (COVID-19) is a viral lower respiratory tract infection caused by the highly transmissible and pathogenic SARS-CoV-2 (severe acute respiratory-syndrome coronavirus-2). Besides respiratory failure, systemic thromboembolic complications are frequent in COVID-19 patients and suggested to be the result of a dysregulation of the hemostatic balance. Although several markers of coagulation and fibrinolysis have been studied extensively, little is known about the effect of SARS-CoV-2 infection on the potent antifibrinolytic enzyme carboxypeptidase U (CPU). Blood was collected longitudinally from 56 hospitalized COVID-19 patients and 32 healthy controls. Procarboxypeptidase U (proCPU) levels and total active and inactivated CPU (CPU+CPUi) antigen levels were measured. At study inclusion (shortly after hospital admission), proCPU levels were significantly lower and CPU+CPUi antigen levels significantly higher in COVID-19 patients compared to controls. Both proCPU and CPU+CPUi antigen levels showed a subsequent progressive increase in these patients. Hereafter, proCPU levels decreased and patients were, at discharge, comparable to the controls. CPU+CPUi antigen levels at discharge were still higher compared to controls. Baseline CPU+CPUi antigen levels (shortly after hospital admission) correlated with disease severity and the duration of hospitalization. In conclusion, CPU generation with concomitant proCPU consumption during early SARS-CoV-2 infection will (at least partly) contribute to the hypofibrinolytic state observed in COVID-19 patients, thus enlarging their risk for thrombosis. Moreover, given the association between CPU+CPUi antigen levels and both disease severity and duration of hospitalization, this parameter may be a potential biomarker with prognostic value in SARS-CoV-2 infection.

Association of TAFI gene polymorphisms with severity of coronary stenosis in stable coronary artery disease

INTRODUCTION

Coronary stenosis is a consequence of atherosclerotic plaque progression that is associated with impaired fibrinolysis. Thrombin-activatable fibrinolysis inhibitor (TAFI) and plasminogen activator inhibitor 1 (PAI-1) are fibrinolysis inhibitors whose levels are influenced by acquired conditions and by polymorphisms. This study therefore aimed to investigate the association of TAFI and PAI-1 gene polymorphisms with severity of coronary stenosis in subjects with stable coronary artery disease (CAD).

MATERIALS AND METHODS

A total of 327 subjects suspected with CAD who underwent a coronary angiogram were recruited. Gensini score was applied to stratify the severity of coronary stenosis. Based on the Gensini score, the subjects were categorized into low-medium (<20) or high (≥20) groups. The study polymorphisms included TAFI Ala147Thr (505G/A), Thr325Ile (1040C/T), +1542C/G, +1583T/A and PAI-1 -675 4G/5G. Most polymorphisms were genotyped by allele-specific polymerase chain reaction, except for TAFI Thr325Ile that was genotyped by polymerase chain reaction-restriction fragment length polymorphism.

RESULTS

A significant increase in the Gensini score was found in TAFI 505A and +1583A allele carriers. Binary regression analysis revealed the independent association of the TAFI 505G/A and +1583T/A polymorphisms with a high Gensini score [adjusted OR = 1.67 (95% CI: 1.03, 2.73) and 1.69 (95% CI: 1.04, 2.76), respectively]. Neither the homozygous PAI-1 -675 4G/4G nor the heterozygous 4G/5G was associated with a high Gensini score.

CONCLUSIONS

The results indicated the contribution of TAFI polymorphisms to atherosclerosis progression and severity of coronary stenosis in stable CAD.

Pro-inflammatory cytokines reduce human TAFI expression via tristetraprolin-mediated mRNA destabilisation and decreased binding of HuR

Thrombin activatable fibrinolysis inhibitor (TAFI) is the zymogen form of a basic carboxypeptidase (TAFIa) with both anti-fibrinolytic and anti-inflammatory properties. The role of TAFI in inflammatory disease is multifaceted and involves modulation both of specific inflammatory mediators as well as of the behaviour of inflammatory cells. Moreover, as suggested by in vitro studies, inflammatory mediators are capable of regulating the expression of CPB2, the gene encoding TAFI. In this study we addressed the hypothesis that decreased TAFI levels observed in inflammation are due to post-transcriptional mechanisms. Treatment of human HepG2 cells with pro-inflammatory cytokines TNFα, IL-6 in combination with IL-1β, or with bacterial lipopolysaccharide (LPS) decreased TAFI protein levels by approximately two-fold over 24 to 48 hours of treatment. Conversely, treatment of HepG2 cells with the anti-inflammatory cytokine IL-10 increased TAFI protein levels by two-fold at both time points. We found that the mechanistic basis for this modulation of TAFI levels involves binding of tristetraprolin (TTP) to the CPB2 3′-UTR, which mediates CPB2 mRNA destabilisation. In this report we also identified that HuR, another ARE-binding protein but one that stabilises transcripts, is capable of binding the CBP2 3’UTR. We found that pro-inflammatory mediators reduce the occupancy of HuR on the CPB2 3’-UTR and that the mutation of the TTP binding site in this context abolishes this effect, although TTP and HuR appear to contact discrete binding sites. Interestingly, all of the mediators tested appear to increase TAFI protein expression in THP-1 macrophages, likewise through effects on CPB2 mRNA stability.

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.

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.

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.

Mechanisms in endocrinology: The spectrum of haemostatic abnormalities in glucocorticoid excess and defect

Glucocorticoids (GCs) target several components of the integrated system that preserves vascular integrity and free blood flow. Cohort studies on Cushing's syndrome (CS) have revealed increased thromboembolism, but the pathogenesis remains unclear. Lessons from epidemiological data and post-treatment normalisation time suggest a bimodal action with a rapid and reversible effect on coagulation factors and an indirect sustained effect on the vessel wall. The redundancy of the steps that are potentially involved requires a systematic comparison of data from patients with endogenous or exogenous hypercortisolism in the context of either inflammatory or non-inflammatory disorders. A predominant alteration in the intrinsic pathway that includes a remarkable rise in factor VIII and von Willebrand factor (vWF) levels and a reduction in activated partial thromboplastin time appears in the majority of studies on endogenous CS. There may also be a rise in platelets, thromboxane B2, thrombin-antithrombin complexes and fibrinogen (FBG) levels and, above all, impaired fibrinolytic capacity. The increased activation of coagulation inhibitors seems to be compensatory in order to counteract disseminated coagulation, but there remains a net change towards an increased risk of venous thromboembolism (VTE). Conversely, GC administered in the presence of inflammation lowers vWF and FBG, but fibrinolytic activity is also reduced. As a result, the overall risk of VTE is increased in long-term users. Finally, no studies have assessed haemostatic abnormalities in patients with Addison's disease, although these may present as a consequence of bilateral adrenal haemorrhage, especially in the presence of antiphospholipid antibodies or anticoagulant treatments. The present review aimed to provide a comprehensive overview of the complex alterations produced by GCs in order to develop better screening and prevention strategies against bleeding and thrombosis.

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.

Plasma Levels of Unactivated Thrombin Activatable Fibrinolysis Inhibitor (TAFI) Are Down-Regulated in Young Adult Women: Analysis of a Normal Japanese Population

Thrombin-activatable fibrinolysis inhibitor (TAFI) is an anaphylatoxin-inactivating enzyme generated by proteolytic cleavage of its zymogen, and is the same enzyme as that first designated by our group as procarboxypeptidase R (proCPR). TAFI in plasma is presumed to influence vascular disease in its role as a fibrinolysis inhibitor. The activity of TAFI is strongly influenced by genetic polymorphism, especially at amino acids Thr/Ala-147 and Thr/Ile-325. In this study, we analyzed 202 healthy controls who were not on any medication, had no unusual medical history and whose blood data were normal. In a previous report, we established an enzyme-linked immunosorbent assay (ELISA) specific for non-activated TAFI (proCPR), and investigated levels of unactivated TAFI as an estimate of anti-fibrinolytic capacity. In this study, we determined normal Japanese TAFI levels for each age, sex, and genetic polymorphism of Thr/Ala-147 and Thr/Ile-325, and also showed that the TAFI level in young adult women is lower than in aged women.

Hypercoagulability in Cushing's syndrome: prevalence, pathogenesis and treatment

Cushing's syndrome is not only accompanied by an increased prevalence of cardiovascular disease but also by a hypercoagulable state that is reflected by an increased incidence of venous thromboembolism. Overall, patients with CS have been reported to have a more than 10-fold increased risk of developing venous thromboembolism. Moreover, the incidence of postoperative thrombosis has been shown to be comparable to the risk after major orthopaedic surgery. Hypercoagulability in CS is due to both increased production of procoagulant factors with activation of the coagulation cascade and an impaired fibrinolytic capacity, resulting in a shortened activated partial thromboplastin time and an increased clot lysis time respectively. Although these abnormalities seem to improve 1 year following successful surgery, they do not yet normalize. Therefore, sustained biochemical remission might be required to fully resolve the hypercoagulable state in CS. Considering the risk of venous thromboembolism in uncontrolled CS there may be a rationale to give patients with active CS thromboprophylaxis. So far this seems warranted following surgical interventions. However, further studies are needed to determine the optimal dosage and duration of thromboprophylaxis.

Thrombin-activatable fibrinolysis inhibitor (TAFI) is enhanced in major trauma patients without infectious complications

BACKGROUND

Infectious complications frequently occur after major trauma, leading to increased morbidity and mortality. Thrombin-activatable fibrinolysis inhibitor (TAFI), a procarboxypeptidase in plasma, plays a dual role in regulating both coagulation and inflammation. Activated TAFI (TAFIa) has broad anti-inflammatory properties due to its inactivation of active inflammatory mediators (anaphylatoxins C3a and C5a, bradykinin, osteopontin).

OBJECTIVES

The purpose of this study was to determine if TAFI plays a role in the development of inflammatory complications after major trauma.

PATIENTS/METHODS

Upon arrival at the emergency department (ED), plasma levels of TAFI and TAFIa were measured in 26 multiple traumatized patients for 10 consecutive days. Systemic levels of inflammatory mediators, including interleukin-6 (IL-6), procalcitonin (PCT), C-reactive protein (CRP) and leukocytes were determined.

RESULTS

Fifteen patients developed pneumonia and/or sepsis (compl) and 11 had no complications (wo compl). Overall injury severity and age were comparable in both groups. Complications occurred approximately 5 days after trauma. IL-6 increased on day 5, whereas CRP, PCT and leukocytes started to increase on day 6 in the compl-group. Upon arrival at the ED and on days 1 and 4, TAFI levels were significantly lower in the compl-group compared to the wo compl-group (p=0.0215). Similarly, TAFIa was significantly lower on day 4 in the compl-group than in the wo compl-group (p=0.049).

CONCLUSIONS

This pilot study shows that TAFI levels are inversely correlated with inflammation-associated development of complications after major trauma.

C-terminal clipping of chemokine CCL1/I-309 enhances CCR8-mediated intracellular calcium release and anti-apoptotic activity

Carboxypeptidase M (CPM) targets the basic amino acids arginine and lysine present at the C-terminus of peptides or proteins. CPM is thought to be involved in inflammatory processes. This is corroborated by CPM-mediated trimming and modulation of inflammatory factors, and expression of the protease in inflammatory environments. Since the function of CPM in and beyond inflammation remains mainly undefined, the identification of natural substrates can aid in discovering the (patho)physiological role of CPM. CCL1/I-309, with its three C-terminal basic amino acids, forms a potential natural substrate for CPM. CCL1 plays a role not only in inflammation but also in apoptosis, angiogenesis and tumor biology. Enzymatic processing differently impacts the biological activity of chemokines thereby contributing to the complex regulation of the chemokine system. The aim of the present study was to investigate whether (i) CCL1/I-309 is prone to trimming by CPM, and (ii) the biological activity of CCL1 is altered after C-terminal proteolytic processing. CCL1 was identified as a novel substrate for CPM in vitro using mass spectrometry. C-terminal clipping of CCL1 augmented intracellular calcium release mediated by CCR8 but reduced the binding of CCL1 to CCR8. In line with the higher intracellular calcium release, a pronounced increase of the anti-apoptotic activity of CCL1 was observed in the BW5147 cellular model. CCR8 signaling, CCR8 binding and anti-apoptotic activity were unaffected when CPM was exposed to the carboxypeptidase inhibitor DL-2-mercaptomethyl-3-guanidino-ethylthiopropanoic acid. The results of this study suggest that CPM is a likely candidate for the regulation of biological processes relying on the CCL1-CCR8 system.

Pathogenesis of vascular complications in Cushing's syndrome

Chronic exposure to high glucocorticoid levels in Cushing's syndrome (CS) is often associated with alterations in the hemostatic system and the expression of prothrombotic phenotypes. Increased frequency of both atherothrombotic and venous thromboembolic events (VTE) has been reported in patients with CS. In general, cardiovascular complications in these patients cause a five-fold increase in mortality compared to the normal population. Although numerous abnormalities in the hemostatic system have been detected in patients with CS, the underlying mechanisms of the prothrombotic state are not fully elucidated. High levels of factor VIII and von Willebrand factor, with evidence of enhanced thrombin generation and decreased fibrinolytic activity, have been documented in several studies. However, it is not clear to what extent these changes contribute to the shift of hemostatic balance towards the hypercoagulable state and expression of thrombophilic phenotypes. Thrombosis is usually a multicausal disease, and all three components of the so-called Virchow triad, namely 1) vascular abnormalities and endothelial dysfunction, 2) hypercoagulability and 3) stasis, may play a variable role in the pathogenesis of the prothrombotic state in CS patients. Larger studies are needed to establish strategies for prevention of cardiovascular complications in patients with Cushing's syndrome.

The prothrombotic tendency in metabolic syndrome: focus on the potential mechanisms involved in impaired haemostasis and fibrinolytic balance

The metabolic syndrome is a clinical disorder characterized by impairment of glucose metabolism, increased arterial blood pressure, and abdominal obesity. The presence of these clinical features exposes patients to a high risk of atherothrombotic cardiovascular events. The pathogenesis of atherothrombosis in the metabolic syndrome is multifactorial, requiring a close relationship among the main components of the metabolic syndrome, including insulin resistance, alterations of glycaemic and lipid pattern, haemodynamic impairment, and early appearance of endothelial dysfunction. Furthermore, haemostatic alterations involving coagulation balance, fibrinolysis, and platelet function play a relevant role both in the progression of the arterial wall damage and in acute vascular events. The mechanisms linking abdominal obesity with prothrombotic changes in the metabolic syndrome have been identified and partially elucidated on the basis of alterations of each haemostatic variable and defined through the evidence of peculiar dysfunctions in the endocrine activity of adipose tissue responsible of vascular impairment, prothrombotic tendency, and low-grade chronic inflammation. This paper will focus on the direct role of adipose tissue on prothrombotic tendency in patients affected by metabolic syndrome, with adipocytes being able to produce and/or release cytokines and adipokines which deeply influence haemostatic/fibrinolytic balance, platelet function, and proinflammatory state.

What has been learnt from the thrombin-activatable fibrinolysis inhibitor-deficient mouse?

SUMMARY

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a circulating zymogen that is activated physiologically by the thrombin/thrombomodulin complex to activated TAFI (TAFIa) which is a basic carboxypeptidase. Substrates include fibrin, leading to a reduction in rate of plasmin generation, and several proinflammatory mediators such as bradykinin, thrombin-cleaved osteopontin and complement factor C5a. TAFI-deficient mice have no phenotype without being challenged and TAFIa appears to play a limited role in physiological fibrinolysis in vivo. In several disease models, the TAFI-deficient mice have different outcomes from the wild type (WT), but whether the difference is beneficial or an exacerbation of the disease depends on the model. The consequences of TAFI deficiency include increased plasmin as a result of enhanced incorporation of plasminogen and tissue plasminogen activator into the fibrin clot, but also loss of its ability to degrade other substrates, with the resultant up-regulation of several proinflammatory mediators, including C5a. Criteria are recommended to demonstrate that a substrate is a physiological substrate of TAFIa.

A novel function of thrombin-activatable fibrinolysis inhibitor during rat liver regeneration and in growth-promoted hepatocytes in primary culture

Thrombin-activatable fibrinolysis inhibitor (TAFI) exhibits anti-fibrinolytic activity by removing C-terminal lysine residues from fibrin or plasminogen receptor proteins on the cellular surface, and plays an important role in the regulation of fibrinolysis. In this study, we examined the regulation of TAFI in hepatocytes during liver regeneration, and revealed its pivotal role in hepatocyte proliferation. In rat models, partial hepatectomy or carbon tetrachloride (CCl4)-induced acute liver injury suppressed the levels of plasma TAFI activity and hepatic TAFI mRNA, whereas this operation markedly increased both the hepatic plasmin activity and the level of proliferating cell nuclear antigen. In primary cultures of rat hepatocytes, the TAFI mRNA level was decreased under growth-promoting culture conditions. Treatment of the hepatocytes with TAFI siRNA increased the amount of plasmin on the hepatocytes and promoted hepatocyte proliferation. We concluded that TAFI regulates plasmin activity through its enzymatic activity whereby it reduces the plasminogen-binding capacity of the hepatocytes. The TAFI gene expression is down-regulated in hepatocyte proliferation for producing a fibrinolytic microenvironment suitable for cell growth. This is the first report on the role of TAFI in the pericellular fibrinolysis necessary for cellular proliferation.

Thrombin-activatable fibrinolysis inhibitor polymorphisms and recurrent pregnancy loss

OBJECTIVE

To investigate the possible association between selected thrombin-activatable fibrinolysis inhibitor (TAFI) single nucleotide polymorphisms (SNPs) and recurrent pregnancy loss (RPL).

DESIGN

Case-control study.

SETTING

University hospital.

PATIENT(S)

One hundred fifty-eight women (86 cases and 72 controls).

INTERVENTION(S)

Determination of TAFI SNPs -438A/G, +505A/G, +1040T/C, +1542C/G, and +1583A/T by polymerase chain reaction (PCR) reactions and sequencing analysis performed on peripheral blood samples.

MAIN OUTCOME MEASURE(S)

Analysis of the genotype and allele frequencies of TAFI SNPs -438A/G, +505A/G, +1040T/C, +1542C/G, and +1583A/T in women with and without RPL.

RESULT(S)

Genotype and allele frequencies of TAFI +505 and +1583 SNPs were significantly different in women with RPL compared with control women. The frequencies of the +505A/A and +505G/G genotypes were 1.2% and 61.6% in women with RPL and 13.9% and 43.1% in control women, respectively. The frequencies of the +1583A/A and +1583T/T genotypes were 1.2% and 61.6% in women with RPL and 13.9% and 45.8% in control women, respectively. The genotype and allele frequencies at TAFI position -438, +1040, and +1542 were not significantly different between RPL and control women.

CONCLUSION(S)

The SNPs leading to increased TAFI levels are associated with a reduced risk of RPL. It is possible that TAFI is involved in RPL.

AMP-activated protein kinase mediates glucocorticoid-induced metabolic changes: a novel mechanism in Cushing's syndrome

Chronic exposure to glucocorticoid hormones, resulting from either drug treatment or Cushing's syndrome, results in insulin resistance, central obesity, and symptoms similar to the metabolic syndrome. We hypothesized that the major metabolic effects of corticosteroids are mediated by changes in the key metabolic enzyme adenosine monophosphate-activated protein kinase (AMPK) activity. Activation of AMPK is known to stimulate appetite in the hypothalamus and stimulate catabolic processes in the periphery. We assessed AMPK activity and the expression of several metabolic enzymes in the hypothalamus, liver, adipose tissue, and heart of a rat glucocorticoid-excess model as well as in in vitro studies using primary human adipose and primary rat hypothalamic cell cultures, and a human hepatoma cell line treated with dexamethasone and metformin. Glucocorticoid treatment inhibited AMPK activity in rat adipose tissue and heart, while stimulating it in the liver and hypothalamus. Similar data were observed in vitro in the primary adipose and hypothalamic cells and in the liver cell line. Metformin, a known AMPK regulator, prevented the corticosteroid-induced effects on AMPK in human adipocytes and rat hypothalamic neurons. Our data suggest that glucocorticoid-induced changes in AMPK constitute a novel mechanism that could explain the increase in appetite, the deposition of lipids in visceral adipose and hepatic tissue, as well as the cardiac changes that are all characteristic of glucocorticoid excess. Our data suggest that metformin treatment could be effective in preventing the metabolic complications of chronic glucocorticoid excess.

Molecular analysis of the human thrombin-activatable fibrinolysis inhibitor gene promoter

Thrombin-activatable fibrinolysis inhibitor (TAFI) is a carboxypeptidase B-like pro-enzyme that, once activated, attenuates fibrinolysis. Little is presently known of the factors that regulate expression of CPB2, the gene encoding TAFI. This study identified 10 potential transcription factor binding sites (denoted A-J) within the proximal promoter region of CPB2, spanning nucleotides -425 to +21; two of these represent previously-described binding sites for CCAAT/enhancer binding protein and glucocorticoid receptor. We identified additional transcription factors that bind within the proximal CPB2 promoter, namely, nuclear factor-Y (NF-Y) and hepatocyte nuclear factor-1alpha (HNF-1alpha). Binding of NF-Y to the region between nucleotides -76 to -59 (Site B) is important for basal CPB2 promoter activity; NF-Y may be a key factor for the recruitment of the transcriptional machinery to the TAFI gene promoter. HNF-1alpha binds at the interface between Sites C and B. Transient transfections of CPB2 promoter-reporter constructs showed that HNF-1alpha binding is essential for the activity of this promoter in HepG2 cells, indicating that HNF-1alpha is involved in the liver-specific expression of CPB2.

Effect of single nucleotide polymorphisms on expression of the gene encoding thrombin-activatable fibrinolysis inhibitor: a functional analysis

Thrombin-activable fibrinolysis inhibitor (TAFI) is a plasma zymogen that acts as a molecular link between coagulation and fibrinolysis. Numerous single nucleotide polymorphisms (SNPs) have been identified in CPB2, the gene encoding TAFI, and are located in the 5'-flanking region, in the coding sequences, and in the 3'-untranslated region (UTR) of the CPB2 mRNA transcript. Associations between CPB2 SNPs and variation in plasma TAFI antigen concentrations have been described, but the identity of SNPs that are causally linked to this variation is not known. In the current study, we investigated the effect of the SNPs in the 5'-flanking region on CPB2 promoter activity and SNPs in the 3'-UTR on CPB2 mRNA stability. Whereas the 5'-flanking region SNPs (with 2 exceptions) did not have a significant effect on promoter activity, either alone or in haplotypic combinations seen in the human population, all of the 3'-UTR SNPs substantially affected mRNA stability. We speculate that these SNPs, in part, contribute to variation in plasma TAFI concentrations via modulation of CPB2 gene expression through an effect on mRNA stability.

Fibrinolysis, inflammation, and regulation of the plasminogen activating system

The maintenance of a given physiological process demands a coordinated and spatially regulated pattern of gene regulation. This applies to genes encoding components of enzyme cascades, including those of the plasminogen activating system. This family of proteases is vital to fibrinolysis and dysregulation of the expression pattern of one or more of these proteins in response to inflammatory events can impact on hemostasis. Gene regulation occurs on many levels, and it is apparent that the genes encoding the plasminogen activator (fibrinolytic) proteins are subject to both direct transcriptional control and significant post-transcriptional mechanisms. It is now clear that perturbation of these genes at either of these levels can dramatically alter expression levels and have a direct impact on the host's response to a variety of physiological and pharmacological challenges. Inflammatory processes are well known to impact on the fibrinolytic system and to promote thrombosis, cancer and diabetes. This review discusses how inflammatory and other signals affect the transcriptional and post-transcriptional expression patterns of this system, and how this modulates fibrinolysis in vivo.

Thrombin activatable fibrinolysis inhibitor (TAFI): A role in pre-eclampsia?

Pre-eclampsia (P-Ec) is a complex multisystem disorder of unknown aetiology reported to occur in about 6% to 8% of all pregnancies throughout the world. This disease is associated with fibrin deposition and occlusive lesions in placental vessels. Pro-thrombin activatable fibrinolysis inhibitor (pro-TAFI) is a relatively recently described glycoprotein that can be converted into its active form (TAFIa) by thrombin, thrombin-thrombomodulin and plasmin. TAFIa potentially inhibits fibrinolysis by removing C-terminal lysine and arginine residues from fibrin. These residues are required for adsorption of tissue-type plasminogen activator (t-PA) and plasminogen to fibrin. Therefore, TAFIa decreases plasmin formation and protects the fibrin clot against lysis. An increased of pro-TAFI/TAFIa levels has been reported in some clinical conditions associated with thrombotic tendency, as type II diabetes mellitus, deep vein thrombosis and symptomatic artery disease. Few studies have investigated pro-TAFI/TAFIa in normal or complicated pregnancy but contrasting results were reported. Understanding the role of pro-TAFI/TAFIa in the pathogenesis of P-Ec can hold great promise for improving P-Ec management. In this context, a large-scale study evaluating plasma TAFI antigen and activity, its synthesis and metabolism in pre-eclamptic women is required. Recently new selective TAFIa inhibitors have been developed. The design of a new therapy to treat and/or prevent P-Ec, based on successful use of TAFIa inhibitors, may have significant clinical ramifications.

Curiouser and curiouser: recent advances in measurement of thrombin-activatable fibrinolysis inhibitor (TAFI) and in understanding its molecular genetics, gene regulation, and biological roles

The thrombin-activatable fibrinolysis inhibitor (TAFI) pathway defines a novel molecular connection between blood coagulation and both fibrinolysis and inflammation. TAFI is a plasma zymogen that can be activated by thrombin, the thrombin-thrombomodulin complex, or plasmin. The activated form of TAFI (TAFIa) attenuates fibrinolysis by removing the carboxyl-terminal lysine residues from partially degraded fibrin that mediate positive feedback in the fibrinolytic cascade. A role for TAFIa in modulating inflammation is suggested by the ability of this enzyme to down-regulate pericellular plasminogen activation and to inactivate the inflammatory peptides bradykinin and the anaphylatoxins C3a and C5a. The focus of this review is on recent advances in the clinical measurement of the TAFI pathway in human subjects and what this has revealed in terms of the molecular genetics of TAFI, the biological variation in plasma TAFI antigen levels, potential regulators of expression of the gene encoding TAFI, and the TAFI pathway as a risk factor for the development of vascular diseases. Although this field is in its infancy, much recent progress has been made and the available data suggest that the TAFI pathway is an intriguing new player in a variety of physiological and pathophysiological contexts.

Different metabolic correlations of thrombin-activatable fibrinolysis inhibitor and plasminogen activator inhibitor-1 in non-obese type 2 diabetic patients

We investigated the plasma levels of thrombin-activatable fibrinolysis inhibitor (TAFI), plasminogen activator inhibitor-1 (PAI-1) and their relation with clinical and metabolic parameters in non-obese type 2 diabetic patients. The plasma levels of TAFI and PAI-1 were evaluated in 47 non-obese type 2 diabetic patients and 31 normal subjects. The intra-abdominal visceral and subcutaneous fat areas were measured by computed tomography (CT). The degree of insulin resistance was evaluated by the euglycemic-hyperinsulinemic clamp technique using artificial pancreas. The plasma levels of TAFI (169.0+/-108.8% versus 103.7+/-52.3%; p<0.001, mean+/-S.D.) and PAI-1 (82.7+/-54.5ng/ml versus 52.9+/-51.7ng/ml; p<0.05) were significantly higher in non-obese type 2 diabetic patients than in normal subjects. Univariate analysis showed that the plasma TAFI levels are significantly and inversely correlated with the glucose infusion rate (GIR) (r=-0.42, p<0.005) in all diabetic patients. Moreover, the plasma levels of TAFI were significantly correlated with fasting plasma glucose levels (r=0.47, p<0.001) and HbA(1c) (r=0.38, p<0.005) in all subjects. The plasma levels of PAI-1 were significantly and proportionally correlated with the visceral fat area (r=0.42, p<0.005) and body mass index (r=0.33, p<0.05). There was no significant correlation between plasma levels of TAFI and PAI-1 (r=0.04). These results show that the plasma levels of TAFI and PAI-1 differently correlate with insulin resistance and visceral fat accumulation, suggesting that different factors are implicated in the plasma elevation of TAFI and PAI-1 in non-obese type 2 diabetes mellitus.

The interactions between inflammation and coagulation

Inflammation initiates clotting, decreases the activity of natural anticoagulant mechanisms and impairs the fibrinolytic system. Inflammatory cytokines are the major mediators involved in coagulation activation. The natural anticoagulants function to dampen elevation of cytokine levels. Furthermore, components of the natural anticoagulant cascades, like thrombomodulin, minimise endothelial cell dysfunction by rendering the cells less responsive to inflammatory mediators, facilitate the neutralisation of some inflammatory mediators and decrease loss of endothelial barrier function. Hence, downregulation of anticoagulant pathways not only promotes thrombosis but also amplifies the inflammatory process. When the inflammation-coagulation interactions overwhelm the natural defence systems, catastrophic events occur, such as manifested in severe sepsis or inflammatory bowel disease.

TAFI activity and antigen plasma levels are not increased in acute coronary artery disease patients admitted to a coronary care unit

INTRODUCTION

Hypofibrinolysis, at least in part due to high levels of plasminogen activator inhibitor-1 (PAI-1), has been reported to occur frequently in patients with coronary artery disease (CAD). A recently described carboxypeptidase, thrombin-activatable fibrinolysis inhibitor (TAFI), is involved in the regulation of the balance between coagulation and fibrinolysis. High TAFI plasma levels may therefore contribute to a hypofibrinolytic state and to an increased risk for thrombotic disorders. There are contradictory results regarding TAFI levels in CAD patients, possibly because the characteristics of patients investigated and the time of blood sampling were different among different studies.

MATERIALS AND METHODS

Fibrinolytic inhibitors (TAFI activity, TAFI antigen and PAI-1 activity plasma levels) were measured in 44 consecutive patients admitted to the Coronary Care Unit of the University of Florence and in a group of 44 healthy controls, matched for age and sex, to detect a possible association of their levels with acute CAD.

RESULTS

No differences were found in TAFI levels, either activity or antigen, between patients and controls. PAI-1 activity was significant different between patients and controls (p=0.0001). The frequencies of TAFI activity and antigen over cut-off levels were similar in patients and controls. Instead, higher PAI-1 levels were more frequent (p=0.04) in patients respect to controls. The univariate analysis confirmed the association of increased PAI-1 levels with acute CAD [OR=3.3; p=0.04]. Among the patients, TAFI and PAI-1 levels were not different according to clinical presentation of symptoms or indication to immediate percutaneous revascularization.

CONCLUSION

Our study suggests that in acute phase of CAD no increased levels of TAFI are detectable in plasma.

Measurement of procarboxypeptidase U (TAFI) in human plasma: a laboratory challenge

BACKGROUND

The importance of carboxypeptidase U (CPU) as a novel regulator of the fibrinolytic rate has attracted much interest during recent years. CPU circulates in plasma as a zymogen, proCPU, that can be activated by thrombin, thrombin-thrombomodulin (T-Tm), or plasmin. Given that the proCPU concentration in plasma is far below its K(m) for activation by the T-Tm complex, the formation of CPU will be directly proportional to the proCPU concentration. A low or high proCPU plasma concentration might therefore tip the balance between profibrinolytic and antifibrinolytic pathways and thereby cause a predisposition to bleeding or thrombosis.

CONTENT

To measure plasma proCPU concentrations, different methods have been developed based on 2 different principles: antigen determination and measurement of CPU activity after quantitative conversion of the proenzyme to its active form by addition of T-Tm. The major drawbacks that should be kept in mind when analyzing clinical samples by both principles are reviewed.

CONCLUSIONS

proCPU is a potential prothrombotic risk factor. Evaluation of its relationship with thrombosis requires accurate assays. Many assays used in different clinical settings are inadequately validated, forcing reconsideration of conclusions made in these reports.

Thrombin activatable fibrinolysis inhibitor in Behçet's disease

INTRODUCTION

Thrombin activatable fibrinolysis inhibitor (TAFI) is a procarboxypeptidase downregulating plasmin formation, thereby causing a tendency for thrombosis development. Since, Behçet's disease (BD) is a systemic vasculitis, which is commonly complicated by arterial and venous thrombosis, we aimed to find out plasma TAFI levels in BD, compared with healthy controls. We also searched whether plasma TAFI levels were significantly different between Behçet's subgroups with and without thrombosis.

MATERIALS AND METHODS

In this study, 105 BD patients (M/F: 64/41; mean age 36+/-1 years), followed up by Ege University Rheumatology Department were enrolled. The exclusion criteria were hemophilia, hyperlipidemia, diabetes mellitus, hepatic diseases renal failure, antiphospholipid positivity, oral contraceptive use and pregnancy. Age-and sex-matched healthy controls (n=53) were also included. Plasma TAFI levels were measured by ELISA. Since TAFI is also an acute-phase reactant, we also measured other inflammatory markers such as C-reactive protein (CRP).

RESULTS

Plasma TAFI levels were significantly higher in Behçet's patients (91.1+/-7.4 ng/ml) compared with healthy controls (14.3+/-4.5 ng/ml) (P<0.001), but there were no significant difference between the subgroups with and without thrombosis. In BD, there was no correlation between plasma TAFI levels and CRP.

CONCLUSIONS

Regardless of manifest thrombosis, plasma TAFI levels in BD were significantly higher than in healthy controls. High TAFI levels might possibly contribute to the thrombotic tendency in BD. Future studies investigating TAFI gene polymorphism and functional activity are clearly needed, to clarify the exact role of TAFI in Behçet's thrombosis.

Comparison of effects of different heparins on thrombin activatable fibrinolysis inhibitor in hemodialyzed patients

BACKGROUND

Thrombin activatable fibrinolysis inhibitor (TAFI) is a regulator of endogenous fibrinolysis. Heparin is used routinely during dialysis sessions to prevent clot formation in the extracorporeal circuit; therefore the aim of the study was to assess whether unfractionated heparin or low-molecular-weight heparins affect TAFI concentration and activity in hemodialyzed patients.

METHODS

Dalteparin (n = 16) or enoxaparin (n = 25) were administered before the second hemodialysis session in the week in a single dose, whereas unfractionated heparin (n = 18) was given first as a bolus, then in a pump. We also evaluated thrombin activity (thrombin-antithrombin complexes, prothrombin fragments 1 + 2), TAFI activator, thrombomodulin, a catalyzer of TAFI activation and a marker of endothelial cell injury, and the degree of plasmin generation (plasmin-antiplasmin complexes).

RESULTS

TAFI concentration, activity and markers of ongoing coagulation, i.e. prothrombin fragments 1 + 2 and thrombin-antithrombin complexes, were significantly higher in patients anticoagulated with unfractionated heparin when compared to both enoxaparin and dalteparin groups. Thrombin-antithrombin complexes, plasmin-antiplasmin complexes, prothrombin fragments 1 + 2, and thrombomodulin did not differ between patients anticoagulated with dalteparin and enoxaparin.

CONCLUSIONS

Our results suggest that low-molecular-weight heparins influence TAFI and other hemostatic parameters in hemodialyzed patients to a lesser degree than unfractionated heparin. Increased TAFI is possibly due to thrombin appearance during hemodialysis with unfractionated heparin.

Role of mRNA transcript stability in modulation of expression of the gene encoding thrombin activable fibrinolysis inhibitor

Regulation of mRNA stability has emerged as a major control point in eukaryotic gene expression. The abundance of a particular mRNA can be rapidly regulated in response to a stimulus by altering the stability of existing translatable transcripts rather than by altering the rate of transcription initiation. Alternative polyadenylation of transcripts during mRNA processing can be important in determining transcript abundance if the different forms of mRNA possess different stabilities or translatability. The mRNA transcript encoding thrombin activable fibrinolysis inhibitor (TAFI) is an attractive candidate for regulation of mRNA stability because of the relatively long length of its 3'-untranslated region and because the transcript can be polyadenylated at three different sites. As well, we have previously reported that treatment of HepG2 cells with interleukins (IL) - 1beta and - 6 destabilizes the endogenous TAFI mRNA expressed in this cell line. In the current study, we report that the TAFI 3'-untranslated region contains cis-acting instability element(s) and that these elements in fact determine the intrinsic stability of the TAFI transcript. Moreover, we found that the three different polyadenylated mRNA forms have different intrinsic stabilities, with the mRNA half-life increasing from the longest to the shortest transcript. Interestingly, treatment with IL-1beta plus IL-6 not only resulted in a 2-fold decrease in stability of the transcript produced using the 3'-most polyadenylation site but also resulted in profound shifts in the relative abundances of the respective polyadenylated forms through changes in the frequency of utilization of the three polyadenylation sites. As such, in the presence of IL-1beta and IL-6, the longest transcript is over a thousand times more abundant than the two shorter transcripts whereas in the absence of the stimulus it comprises only 1% of the total TAFI transcripts.

Changes in Activity of Plasma Thrombin Activatable Fibrinolysis Inhibitor in Pregnancy

The thrombin activatable fibrinolysis inhibitor (TAFI) is a recently described inhibitor of fibrinolysis. Changes in the concentration of plasma TAFI molecules that are present and functional after activation by thrombin-thrombomodulin complex (TAFI activity) during pregnancy have not previously been studied, and we therefore conducted a present prospective study. Plasma TAFI activity was assayed in 15 healthy non-pregnant women and 176 healthy pregnant women at various stages of gestation. TAFI activity was higher in pregnant than in non-pregnant women. TAFI activity seemed to increase progressively until around 20 weeks of gestation, then maintained a moderately elevated level until delivery, and promptly decreased after delivery.