Procarboxypeptidase U (TAFI) contributes to the risk of thrombosis in patients with hereditary thrombophilia

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.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

A comprehensive literature review, including unpublished data, provided greater statistical power for the analyses and decreased the likelihood of publication bias influencing the results.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

Thrombin-activatable fibrinolysis inhibitor influences disease severity in humans and mice with pneumococcal meningitis

BACKGROUND

Mortality and morbidity in patients with bacterial meningitis result from the proinflammatory response and dysregulation of coagulation and fibrinolysis. Thrombin-activatable fibrinolysis inhibitor (TAFI) is activated by free thrombin or thrombin in complex with thrombomodulin, and plays an antifibrinolytic role during fibrin clot degradation, but also has an anti-inflammatory role by inactivating proinflammatory mediators, such as complement activation products.

OBJECTIVE

To assess the role of TAFI in pneumococcal meningitis.

METHODS

We performed a prospective nationwide genetic association study in patients with bacterial meningitis, determined TAFI and complement levels in cerebrospinal fluid (CSF), and assessed the function of TAFI in a pneumococcal meningitis mouse model by using Cpb2 (TAFI) knockout mice.

RESULTS

Polymorphisms (reference sequences: rs1926447 and rs3742264) in the CPB2 gene, coding for TAFI, were related to the development of systemic complications in patients with pneumococcal meningitis. Higher protein levels of TAFI in CSF were significantly associated with CSF complement levels (C3a, iC3b, and C5b-9) and with more systemic complications in patients with bacterial meningitis. The risk allele of rs1926447 (TT) was associated with higher levels of TAFI in CSF. In the murine model, consistent with the human data, Cpb2-deficient mice had decreased disease severity, as reflected by lower mortality, and attenuated cytokine levels and bacterial outgrowth in the systemic compartment during disease, without differences in the brain compartment, as compared with wild-type mice.

CONCLUSIONS

These findings suggest that TAFI plays an important role during pneumococcal meningitis, which is likely to be mediated through inhibition of the complement system, and influences the occurrence of systemic complications and inflammation.

Effect of single nucleotide polymorphism in thrombin-activatable fibrinolysis inhibitor on the risk of diabetic macrovascular disease

Hypofibrinolysis is commonly found in patients with diabetes mellitus and is associated with the increased risk for many diabetic complications. An important inhibitor of fibrinolysis, thrombin-activatable fibrinolysis inhibitor (TAFI), participates in hypofibrinolysis in diabetes mellitus and may be involved in diabetic macrovascular disease. The present study was designed to determine whether TAFI polymorphisms (505G/A and 1040C/T) and TAFI levels are correlated with the development of type 2 diabetes mellitus (T2DM) and macrovascular diseases (MVDs). A total of 249 clinical samples were collected, including 102 healthy individuals (H group), 44 T2DM patients without MVD (T group) and 103 T2DM patients with MVD (M group). The 505G/A polymorphism was equally represented in the three groups. In contrast, analysis of the 1040C/T polymorphism revealed a statistically lower percentage of the T allele in the M group than in the H group (P = 0.014). This difference was due to decreased T/T homozygotes in the M groups compared with the H group (P = 0.029). The antigen TAFI level was 31.72 ± 13.64% in the H group, 62.56 ± 18.77% in the T group (P < 0.05, compared with the H group) and 63.70 ± 15.76% in the M group (P < 0.05, compared with the H group). As high plasma TAFI level is associated with the increasing risk of T2DM, it may thus serve as a potential marker for the diagnosis of T2DM.

TAFI gene polymorphisms in patients with cerebral venous thrombosis

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

Plasma carboxypeptidase B downregulates inflammatory responses in autoimmune arthritis

The immune and coagulation systems are both implicated in the pathogenesis of rheumatoid arthritis (RA). Plasma carboxypeptidase B (CPB), which is activated by the thrombin/thrombomodulin complex, plays a procoagulant role during fibrin clot formation. However, an antiinflammatory role for CPB is suggested by the recent observation that CPB can cleave proinflammatory mediators, such as C5a, bradykinin, and osteopontin. Here, we show that CPB plays a central role in downregulating C5a-mediated inflammatory responses in autoimmune arthritis. CPB deficiency exacerbated inflammatory arthritis in a mouse model of RA, and cleavage of C5a by CPB suppressed the ability of C5a to recruit immune cells in vivo. In human patients with RA, genotyping of nonsynonymous SNPs in the CPB-encoding gene revealed that the allele encoding a CPB variant with longer half-life was associated with a lower risk of developing radiographically severe RA. Functionally, this CPB variant was more effective at abrogating the proinflammatory properties of C5a. Additionally, expression of both CPB and C5a in synovial fluid was higher in patients with RA than in those with osteoarthritis. These findings suggest that CPB plays a critical role in dampening local, C5a-mediated inflammation and represents a molecular link between inflammation and coagulation in autoimmune arthritis.

Association between genotype and plasma levels of thrombin-activated fibrinolysis inhibitor (TAFI) in the development of preeclampsia

INTRODUCTION

The objective was to evaluate if thrombin-activated fibrinolysis inhibitor (TAFI) polymorphisms (G505A, C1040T, and G-438A), and TAFIa plasma levels are associated with preeclampsia.

MATERIALS AND METHODS

In a case-control study design, we evaluated preeclampsia patients and women with uncomplicated pregnancies. The TAFI polymorphisms were determined by real-time PCR method, and TAFIa plasma levels were established with a chromogenic assay.

RESULTS

We included 87 women in each group. The TAFIa levels in the preeclampsia group were 20.4 μg/mL (CI 95% 17.3-23.5), while in the control group, they were significantly lower: 13.3 μg/mL (12.0-14.5, p 0.003). There were no differences in the genotype distribution or allelic frequency of TAFI polymorphisms between the two groups. In preeclampsia patients and controls heterozygous for the G505A polymorphism, the TAFIa values were 22.8 (16.7-28.9 μg/mL) and 13.2 (11.3-15.0 μg/mL, p 0.019), respectively. In G505A homozygous polymorphism the TAFIa values were 25.7 (18.7-32.6 μg/mL) and 13.5 (1.6-21.9 μg/mL, p 0.041), respectively. In the C1040T and G-438A TAFI wild type polymorphisms, the TAFIa values were 18.3 (12.5-23.9 μg/mL) and 11.5 (9.9-35.0, p 0.033), and 19.4 (10.9-27.9 μg/mL) and 12.5 (10.8-14.2 μg/mL, p 0.006), respectively, without differences in other genotypes.

CONCLUSIONS

Preeclampsia by itself may be responsible for the increase in TAFIa values rather than the presence of polymorphisms.

+1040 C/T polymorphism in coding region of thrombin-activatable fibrinolysis inhibitor gene and the risk of idiopathic recurrent fetal loss

Recurrent fetal loss (RFL) is common health problem affecting up to 5% of women of reproductive age. It has been shown that plasma thrombin-activatable fibrinolysis inhibitor (TAFI) concentrations increase during pregnancy and return to baseline levels soon after delivery. The +1040C/T single nucleotide polymorphism in coding region of TAFI gene is associated with TAFI blood levels. The aim of our study was to investigate the relationship between +1040C/T polymorphism in TAFI gene and idiopathic RFL. Study was carried out in a group of 120 women (61 controls and 59 women with idiopathic RFL). The +1040C/T polymorphism was detected by restriction fragment length polymorphism PCR. Increased frequency of +1040T/T genotype was observed in a study group, but without statistically significant difference. Carriers of T/T genotype have increased risk of fetal loss by 1.23-fold, compared with carriers of C/C (95% CI 0.462-3.277; P = 0.7) and 1.34-fold compared with carriers of C/T genotype (95% CI 0.501-3.601; P = 0.6). C allele is associated with reduced risk of recurrent fetal loss compared with T allele (OR 0.91; 95% CI 0.545-1.533; P = 0.7). In conclusion, we observed increased frequency of +1040T/T genotype in a patient group, suggesting that this genotype could be potential risk factor for idiopathic RFL. Further investigation should be carried out in order to establish the role of this polymorphism in the etiology of idiopathic recurrent miscarriages.

Thrombin activatable fibrinolysis inhibitor (TAFI): relationship to hemostatic alteration in patients with beta-thalassemia

Profound hemostatic changes have been observed among thalassemic patients. Thrombin activatable fibrinolysis inhibitor (TAFI) is a newly discovered protein that potentially attenuates fibrinolysis. The authors aimed to investigate plasma level of TAFI in beta-thalassemia patients in relation to clinical severity and hemostatic alteration. Fifty-one thalassemic patients (mean age 10.79 +/- 5.59 years) (21 splenectomized thalassemia major patients, 18 nonsplenectomized thalassemia major patients, 12 nonsplenectomized thalassemia intermedia) were recruited from Pediatric Hematology Clinic, Ain Shams University; in addition, 32 healthy age- and sex-matched controls (10.31 +/- 5.58 years) were also included. In addition to clinical assessment, laboratory investigations included complete blood count (CBC), hemoglobin electrophoresis, prothrombin time (PT), activated partial thromboplastin time (PTT), liver function tests, viral hepatitis markers, serum ferritin, and plasma TAFI levels. Nine out of 51 patients (17.5%) suffered from bleeding manifestations mainly in the form of epistaxis; none of the studied patients had thromboembolism. Significant reduction in TAFI levels was shown in thalassemic patients compared to controls (P < .0001), in splenectomized compared to nonsplenectomized thalassemia group (P < .0001), and in thalassemia major compared to thalassemia intermedia group (P < .0001). Negative correlation was present between TAFI levels and both liver enzymes and serum ferritin levels (P < .05). Thalassemic patients suffering from bleeding showed lower mean TAFI levels compared to those not suffering from bleeding (P < .001). Marked reduction in TAFI levels was observed in thalassemic patients with splenectomy, altered liver functions, and poor chelation who therefore might be at a higher risk for altered hemostasis.

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.

Development of a sensitive and selective assay for the determination of procarboxypeptidase U (thrombin-activatable fibrinolysis inhibitor) in plasma

To date, several assays for procarboxypeptidase U (proCPU) determination exist, all having their own inherent disadvantages and advantages. A drawback of activity-based assays is the interference of the constitutively active carboxypeptidase N (CPN) in plasma. Recent screening of Bz-Xaa-Arg peptides with modified aromatic amino acids at the P1 position revealed a selective CPU substrate, N-benzoyl-ortho-cyano-phenylalanyl-arginine (Bz-o-cyano-Phe-Arg), which will allow straightforward determination of proCPU in plasma. Our assay shows an excellent linearity in the concentration range of 20-2600 U/L, with within- and between-run precision values of 2.7% and 4.6%, respectively. A good correlation with our high-performance liquid chromatography (HPLC)-assisted proCPU activity assay using hippuryl-l-arginine (HipArg) as substrate was found. Besides the major improvement regarding the selectivity, the assay is much easier to perform and far less time-consuming compared with the proCPU activity assay using HipArg as substrate.