Tissue factor pathway inhibitor and thrombin-activatable carboxypeptidase B for prediction of early atherosclerosis in gouty arthritis

Background

Gouty arthritis (GA) is a chronic inflammatory arthritis in which both clinical and subclinical atherosclerosis are more frequent. The dynamic equilibrium between coagulation and fibrinolysis is impaired in inflammatory diseases. We determined TFPI and TAFI antigen levels in GA patients and evaluated their association with subclinical atherosclerosis.

Methods

We included 45 GA patients (41 males, 4 females; mean age: 51.6 years) and 25 asymptomatic hyperuricemic (AHU) subjects (19 males, 6 females; mean age: 48.1 years). Cardiovascular risk factors were determined. TAFI and TFPI levels were determined by ELISA. B-mode ultrasonography was used to detect subclinical atherosclerosis.

Results

Cardiovascular risk factors were similar in both groups. The carotid IMT was significantly higher in GA group than in AHU group (0.74 ± 0.23 mm vs. 0.61 ± 0.13 mm, p = 0.009). TFPI level was significantly higher in GA group than in AHU group (86.2 ± 48.9 ng/mL vs. 25.8 ± 21.4 ng/mL, p < 0.001); TAFI antigen was significantly higher in AHU group (22.6 ± 3.6 ng/mL vs. 25.7 ± 5.3 ng/mL, p = 0.006) than in GA patients. Atherosclerotic plaque formation was more frequent in GA group (p = 0.041). When GA patients with and without plaques were compared, the first group had significantly higher mean age (p = 0.01) and TFPI level (p = 0.028). TFPI level correlated with carotid IMT (r = 0.302; p = 0.028). Logistic regression analysis showed that age (OR: 1.236, 95%CI: 1.059-1.443, p = 0.007) and TFPI (OR: 1.031, 95%CI: 1.008-1.054, p = 0.008) were independent risk factors for the presence of plaques.

Conclusions

GA patients had more frequent subclinical atherosclerosis than subjects with AHU. Higher TFPI levels in GA patients –probably associated with enhanced endothelial damage- were related to subclinical atherosclerosis. Lower TAFI levels in GA pointed to impaired fibrinolysis.     

Target-mediated clearance and bio-distribution of a monoclonal antibody against the Kunitz–type protease inhibitor 2 domain of Tissue Factor Pathway Inhibitor

Introduction

A humanised monoclonal antibody, concizumab, that binds with high affinity to the Kunitz-type protease inhibitor (KPI) 2 domain of human tissue factor pathway inhibitor (TFPI) is in clinical development. It promotes coagulation by neutralising the inhibitory function of TFPI and may provide a subcutaneous prophylaxis option for patients with haemophilia. We aimed to study biodistribution and pharmacokinetics (PK) of concizumab.

Materials and Methods

Blockage of cellular TFPI by concizumab was measured by tissue factor/Factor VIIa-mediated Factor X activation on human EA.hy926 cells. Biodistribution of concizumab was analysed in rabbits by immunohistology, and the PK was measured in rabbits and rats.

Results and Conclusions

Concizumab bound to cell surface TFPI on EA.hy926 cells and neutralised TFPI inhibition of Factor X activation. The antibody cross-reacted with rabbit TFPI, but not with rat TFPI, allowing for comparative PK studies. PK data in rats described a log-linear profile typical for a non-binding antibody, whereas PK data in rabbits revealed a non-linear, dose-dependent profile, consistent with a target-mediated clearance mechanism. Immunohistology in rabbits during target-saturation showed localisation of the antibody on the endothelium of the microvasculature in several organs. We observed a marked co-localisation with endogenous rabbit TFPI, but a negligible sub-endothelial build-up. Concizumab binds and neutralises the inhibitory effect of cell surface-bound TFPI. The PK profile observed in rabbits is consistent with a TFPI-mediated drug disposition. Double immunofluorescence shows co-localisation of the antibody with TFPI on the endothelium of the microvasculature and points to this TFPI as a putative target involved in the clearance mechanism.