Detecting Activated Thrombin Activatable Fibrinolysis Inhibitor (TAFIa) and Inactivated TAFIa (TAFIai) in Normal and Hemophilia A Plasmas

Abstract

Thrombin activatable fibrinolysis inhibitor (TAFI) also known as plasma procarboxypeptidase B or U is a 60 kD glycoprotein, which is the major modulator of fibrinolysis in plasma. TAFI is a proenzyme, which is activated by proteolytic cleavage to an active carboxypeptidase B-like enzyme (TAFIa, 35.8 kD) by thrombin/thrombomodulin and plasmin. Modulation of fibrinolysis occurs when TAFIa enzymatically removes C-terminal lysine residues of partially degraded fibrin, thereby inhibiting the stimulation of tissue plasminogen activator (t-PA) modulated plasminogen activation. TAFIa undergoes a rapid conformational change at 37℃ to an inactive isoform called TAFIai. Potato tuber carboxypetidase inhibitor (PTCI) was shown to specifically bind to TAFIa as well as TAFIai. In this study, a novel immunoassay TAFIa/ai ELISA was used for quantitation of the two TAFI activation isoforms TAFIa and TAFIai. The ELISA utilizes PTCI as the capture agent and a double antibody sandwich technique for the detection. Low levels of TAFIa/ai antigen levels were detected in normal plasma and elevated levels were found in hemophilia A plasmas. TAFIa/ai antigen represents a novel marker to monitor fibrinolysis and TAFIa/ai ELISA may be a valuable assay for studying the role of TAFI in normal hemostasis and in pathological conditions.

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

“…Further, Aso et al showed that low-density lipoprotein cholesterol was an independent determinant of plasma proCPU levels in 105 patients with type 2 diabetes mellitus (T2DM). In addition, subgroup analysis revealed significantly higher plasma proCPU levels in two subgroups: hypercholesterolemic diabetic patients with or without metabolic syndrome [102]. In another study, proCPU levels were reported to be significantly different in dyslipidemic and normolipidemic subjects, with higher values in the dyslipidemic group [137].…”

“…A second antibody pair measures the total amount of CPU + CPUi formed (MA-T30E5/MA-T17D7-HRP) [58,59,61,62,101]. Another assay that allows combined measurement of CPU and CPUi was published by Hulme et al [102]. This assay was marketed as the Imubind ® TAFIa/ai ELISA (US20060183172A1 and US7470519B2) but has been discontinued.…”