Effects of β2-Glycoprotein I and Monoclonal Anticardiolipin Antibodies on Extrinsic Fibrinolysis

Abstract

Antiphospholipid antibodies (aPLs) are associated with an increased incidence of thrombosis, but the mechanisms responsible for thrombosis are unclear. The present study investigated the effect of both beta2-glycoprotein I (beta2-GPI) and aPLs on the activity of extrinsic fibrinolysis. The remaining tissue-plasminogen activator (t-PA) of the sample consisting of beta2-GPI, two-chain recombinant t-PA, plasminogen activator inhibitor (PAI) -1 was measured by a chromogenic assay using synthetic substrate S-2251, Glu-plasminogen, and soluble fibrin monomer. Without PAI-1, beta2-GPI did not affect t-PA activity. When 14.3 ng/ml PAI-1 was added to 3.6 U/ml t-PA, the remaining t-PA activity was increased from 48.9% to 60.4% by the addition of beta2-GPI (190 microg/ml). The effect of beta2-GPI did not require phospholipids. The beta2-GPI seems to protect t-PA activity from the inhibition by PAI-1. When monoclonal anticardiolipin antibodies (aCLs), EY1C8, and EY2C9, which were established from a patient with antiphospholipid syndrome, were further added to the mixture with a diluted phospholipid (Platelin) to investigate the influence of aPL, the remaining t-PA activity decreased to 50.1 and 80.7%. Monoclonal aCLs appeared to inhibit the effect of beta2-GPI, that is, these monoclonals inhibited the fibrinolytic activity by an elevation in PAI-1 activity. These results suggest the possibility that the impairment of fibrinolytic activity by aCLs is one of reasons for the increased incidence in thrombosis in patients with aCLs.

Identification of Anti-Plasmin Antibodies in the Antiphospholipid Syndrome That Inhibit Degradation of Fibrin

“…In 1999, Ieko et al (34,35) reported that ␤ 2 GPI exerted a dose-dependent enhancement of t-PA activity in the presence of PAI-1, and that addition of EY1C8 patient-derived monoclonal aCL reduced t-PA activity by ϳ45% in a mixture of t-PA (3.6 U/ml), PAI-1 (7.1 ng/ml), and ␤2GPI (3.8 M). In 2000, Cugno et al (36) showed that of 39 patients with primary APS, three had high titers of IgG Ab against t-PA, and four had high titers of Ab against fibrin-bound t-PA, which is the physiologically active form of t-PA.…”

Antibodies to tissue-type plasminogen activator (tPA) in patients with antiphospholipid syndrome: evidence of interaction between the antibodies and the catalytic domain of tPA in 2 patients

“…These include the activation of endothelial cells, oxidant-mediated vascular endothelium lesions, interference with or modulation of the phospholipid-binding proteins regulating hemostasis, and mechanisms similar to heparin-induced thrombocytopenia. 1 Reduced fibrinolytic activity has also been described in patients with APS, and may be responsible for thrombotic events, [2][3][4][5] and antibodies directed against tissue-type plasminogen activator (tPA) might lead to a hypofibrinolytic state. Our previous studies have shown that an association between anti-tPA antibodies and thrombosis seems to be a peculiarity of APS because normal plasma anti-tPA antibody levels were found in 100 patients with a history of deep vein thrombosis (DVT) without APS, 6 but high levels in 3 of 39 patients with primary APS who had a history of thrombosis.…”

Annexin A2 is involved in antiphospholipid antibody-mediated pathogenic effects in vitro and in vivo

“…They appear to interfere with a range of normal cell surface hemostatic mechanisms by targeting coagulation factors, natural anticoagulants, oxidized low-density lipoproteins, CD36, and fibrinolytic proteins. [4][5][6][7][15][16][17][18][19] Emerging evidence suggests that plasma hypofibrinolysis is a risk factor for venous thrombosis, 20 and that fibrinolysis might be impaired in APS due to increased fibrinolytic inhibitor (plasminogen activator inhibitor type-1) activity. 21 Annexin A2 (A2) is a profibrinolytic receptor that binds both plasminogen and its activator, tissue plasminogen activator (tPA), functioning as a cofactor for plasmin generation, and localizing fibrinolytic activity to the EC surface.…”