Measurement of Procarboxypeptidase U (TAFI) in Human Plasma: A Laboratory Challenge

“…[6][7][8][9] Plasma concentrations of TAFI vary significantly in the human population. 10,11 The vast majority of individuals have TAFI antigen levels between 50% and 150% of the mean population value, 12,13 thereby ranging from approximately 100 to 200 nM. Importantly, these concentrations of TAFI fall below the K m for activation of TAFI by thrombin or thrombomodulin (1 M), 3 indicating that individuals with higher plasma TAFI concentrations would exhibit a higher rate of TAFIa production following a procoagulant stimulus.…”

Section: Introductionmentioning

confidence: 99%

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

Boffa

Maret

Hamill

et al. 2008

Blood

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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. IntroductionThrombin-activable fibrinolysis inhibitor (TAFI), also known as procarboxypeptidase U or R or plasma procarboxypeptidase B, is a human plasma zymogen that may play a role in mediating the balance between blood coagulation and fibrinolysis. 1 Upon cleavage of TAFI by thrombin, 2 thrombin-thrombomodulin, 3 or plasmin, 4 an enzyme is formed (TAFIa) that possesses basic carboxypeptidase activity. TAFIa has been demonstrated to attenuate plasminogen activation, and thus fibinolysis, by removing from partially degraded fibrin the carboxyl-terminal lysine residues that mediate positive feedback in the fibrinolytic cascade. 5 In addition, TAFIa has been shown to remove the carboxyl-terminal arginine residues from bradykinin and the anaphylatoxins C3a and C5a, thereby implicating the TAFI pathway as a link between coagulation and inflammation. [6][7][8][9] Plasma concentrations of TAFI vary significantly in the human population. 10,11 The vast majority of individuals have TAFI antigen levels between 50% and 150% of the mean population value, 12,13 thereby ranging from approximately 100 to 200 nM. Importantly, these concentrations of TAFI fall below the K m for activation of TAFI by thrombin or thrombomodulin (1 M), 3 indicating that individuals with higher plasma TAFI concentrations would exhibit a higher rate of TAFIa production following a procoagulant stimulus. Indeed, variation in "functional" TAFI concentrations has been observed using a clot lysis assay of plasma samples. 14 Therefore, it is reasonable to consider the gene encoding TAFI (CPB2) as a candidate gene for thrombotic disorders. Indeed, elevated concentrations of TAFI have been shown to be a mild risk factor for first venous thrombosis 15 as well as recurrent venous thrombosis, 16 and to be more common in carriers of Factor V Leiden with venous thromboembolism than in asymptomatic carriers. 17 High functional TAFI concentrations hav...

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“…5,6,14 The potential carboxypeptidase activity generated from TAFI activation is currently difficult to assess, and so the inferred role of TAFI and its correlation with pathologies are unclear. 15 New tools to measure TAFIa (reviewed in Willemse and Hendriks 15 ) will undoubtedly contribute to a better understanding of the physiologic role of TAFI. Activation of TAFI has been studied in vitro, and although TAFI is activated by thrombin it is also activated by other proteases such as trypsin, plasmin, and elastase.…”

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confidence: 99%

Thrombin-thrombomodulin connects coagulation and fibrinolysis: more than an in vitro phenomenon

Binette

Taylor

Peer

et al. 2007

Blood

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Thrombin activatable fibrinolysis inhibitor (TAFI), when activated, forms a basic carboxypeptidase that can inhibit fibrinolysis. Potential physiologic activators include both thrombin and plasmin. In vitro, thrombomodulin and glycosaminoglycans increase the catalytic efficiency of TAFI activation by thrombin and plasmin, respectively. The most relevant (patho-) physiologic activator of TAFI has not been disclosed. Our purpose was to identify the physiologic activator of TAFI in vivo. Activation of protein C (a thrombinthrombomodulin-dependent reaction), prothrombin, and plasminogen occurs during sepsis. Thus, a baboon model of Escherichia coli-induced sepsis, where multiple potential activators of TAFI are elaborated, was used to study TAFI activation. A monoclonal antibody (mAbTAFI/ TM#16) specifically inhibiting thrombinthrombomodulin-dependent activation of TAFI was used to assess the contribution of thrombin-thrombomodulin in TAFI activation in vivo. Coinfusion of mAbTAFI/TM#16 with a lethal dose of E coli prevented the complete consumption of TAFI observed without mAbTAFI/TM#16. The rate of fibrin degradation products formation is enhanced in septic baboons treated with the mAbTAFI/TM#16; therefore, TAFI activation appears to play a key role in the extent of fibrin(ogen) consumption during E coli challenge, and thrombinthrombomodulin, in a baboon model of E coli-induced sepsis, appears to be the predominant activator of TAFI. IntroductionFibrinolysis is achieved primarily through the proteolytic action of plasmin on fibrin polymers that reinforce and maintain the integrity of a thrombus. In the hemostatic response, fibrin is a critical component preventing blood loss due to injury. However, in certain circumstances inappropriate fibrin-rich thrombus formation occludes vessels required to maintain the viability of a tissue area. Degradation of fibrin by plasmin exposes basic C-terminal residues (lysines and arginines) as the fibrin strands continually truncate. 1 Generation of C-terminal basic amino acids provides positive feedback enhancing plasminogen activation. [1][2][3][4] Fibrin is a key component of the fibrinolytic cascade, not only as a substrate but as a cofactor and modulator, and is also the end product of the coagulation cascade. Therefore, fibrinolysis is regulated by all of the regulatory elements attributed to control of coagulation. Recently, another connection between coagulation and fibrinolysis has been identified and is mediated through thrombin activatable fibrinolysis inhibitor (TAFI, also known as procarboxypeptidase U and procarboxypeptidase R). 5 Activation of TAFI to TAFIa generates a carboxypeptidase capable of catalyzing the removal of C-terminal basic amino acids. [5][6][7][8][9] Therefore, by modulating the steady-state concentration of these C-terminal basic amino acids, TAFIa modulates the steady-state concentrations of various forms of bound and free plasminogen and plasmin: activated, inhibited, and inhibitable. 5,6,[10][11][12][13] TAFI, secreted by the liver, circulates...

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Measurement of Procarboxypeptidase U (TAFI) in Human Plasma: A Laboratory Challenge

Cited by 51 publications

References 44 publications

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

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

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

Thrombin-thrombomodulin connects coagulation and fibrinolysis: more than an in vitro phenomenon

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