Thrombogenicity of β2-glycoprotein I–dependent antiphospholipid antibodies in a photochemically induced thrombosis model in the hamster

329

215

Objective. Antiphospholipid antibodies (aPL) have been shown to induce thrombosis, activate endothelial cells, and induce fetal loss. The pathogenesis of aPLinduced thrombosis, although not completely understood, may involve platelet and endothelial cell activation as well as procoagulant effects of aPL directly on clotting pathway components. Recent studies have shown that uncontrolled complement activation leads to fetal death in aPL-treated mice. In this study, we tested the hypothesis that aPL are responsible for activation of complement, thus generating split products that induce thrombosis.Methods. To study thrombus dynamics and adhesion of leukocytes we used in vivo murine models of thrombosis and microcirculation, in which injections of aPL were used.Results. Mice deficient in complement components C3 and C5 were resistant to the enhanced thrombosis and endothelial cell activation that was induced by aPL. Furthermore, inhibition of C5 activation using anti-C5 monoclonal antibodies prevented thrombophilia induced by aPL.Conclusion. These data show that complement activation mediates 2 important effectors of aPL, induction of thrombosis and activation of endothelial cells.

Section: Discussionmentioning

confidence: 99%

Requirement of activation of complement C3 and C5 for antiphospholipid antibody–mediated thrombophilia

Pierangeli¹,

Girardi²,

Vega-Ostertag³

et al. 2005

329

215

“…Monoclonal and polyclonal aPL antibodies have previously been demonstrated to have thrombogenic properties in mice (6,37,46,48). Several studies have demonstrated that aPL activate ECs in vitro, suggesting a mechanism by which these antibodies exert procoagulant properties (15,49,50).…”

Section: Discussionmentioning

confidence: 99%

“…Analysis of thrombus dynamics. The analysis of thrombus dynamics in a mouse model has been described previously (4)(5)(6)46). Briefly, mice were anesthetized at 72 hours after the first injection with IgG-APS or IgG-NHS.…”

Section: Methodsmentioning

confidence: 99%

Inhibition of the thrombogenic and inflammatory properties of antiphospholipid antibodies by fluvastatin in an in vivo animal model

Ferrara¹,

Liu²,

Espinola³

et al. 2003

137

Methods. Two groups of CD-1 male mice, each comprising ϳ18 mice, were fed either normal saline solution or 15 mg/kg fluvastatin for 15 days. Each of the 2 groups was further subdivided to receive either purified IgG from patients with the antiphospholipid syndrome (IgG-APS) or normal IgG from healthy subjects. Analysis of thrombus dynamics was performed in treated and control mice, using a standardized thrombogenic injury procedure, and the area (size) of the thrombus was measured. Adhesion of leukocytes to ECs was analyzed with a microcirculation model of exposed cremaster muscle. Baseline and posttreatment soluble intercellular adhesion molecule 1 (sICAM-1) levels were determined by enzyme-linked immunosorbent assay.Results. IgG-APS mice treated with fluvastatin showed significantly smaller thrombi, a reduced number of adherent leukocytes, and decreased levels of sICAM-1 compared with IgG-APS animals treated with placebo.Conclusion. These findings indicate that fluvastatin significantly diminishes aPL-mediated thrombosis and EC activation in vivo. These results may have important implications for the design of new treatment strategies aimed at preventing recurrent thrombosis in patients with APS.

“…Studies have shown conclusively that aPL are thrombogenic in in vivo animal models (23)(24)(25). The prothrombotic properties of aPL may be explained in part by their ability to enhance the activation of platelets.…”

Section: Discussionmentioning

confidence: 99%

Intracellular events in platelet activation induced by antiphospholipid antibodies in the presence of low doses of thrombin

Vega-Ostertag

Harris

Pierangeli

2004

118

102

Objective. Thrombosis and thrombocytopenia are features of the antiphospholipid syndrome (APS), suggesting that antiphospholipid antibodies (aPL) may bind platelets, causing activation and aggregation of platelets and thrombosis. The intracellular events involved in aPL-mediated platelet activation are not fully understood and are therefore the subject of this study.Methods. IgG fractions and their F(ab) 2 fragments were purified from the sera of 7 patients with APS and from the pooled sera of 10 healthy subjects (as controls). Phosphorylation of p38 MAPK, ERK-1/2, and [Ca 2؉ ]-dependent cytosolic phospholipase A 2 (cPLA 2 ) was determined in lysates of washed platelets pretreated with low doses of thrombin and aPL or control IgG or their F(ab) 2 fragments, by immunoblot. The effects of aPL on platelet aggregation in the presence or absence of a p38 MAPK inhibitor, SB203580, were examined. Thromboxane B 2 (TXB 2 ) production was detected by enzyme-linked immunosorbent assay on gel-filtered platelets treated with aPL and thrombin, with or without SB203580. Calcium mobilization studies were done utilizing a fluorometric assay.Results. Treatment of platelets with IgG aPL, or their F(ab) 2 fragments, in conjunction with subactivating doses of thrombin resulted in a significant increase in phosphorylation of p38 MAPK. Neither the IgG aPL nor their F(ab) 2 fragments increased significantly the phosphorylation of ERK-1/2 MAPKs. Furthermore, pretreatment of platelets with SB203580 completely abrogated the aPL-mediated enhanced aggregation of the platelets. Platelets treated with F(ab) 2 aPL and thrombin produced significantly larger amounts of TXB 2 when compared with controls, and this effect was completely abrogated by treatment with SB203580. In addition, cPLA 2 was also significantly phosphorylated in platelets treated with thrombin and F(ab) 2 aPL. There were no significant changes in intracellular [Ca 2؉ ] when platelets were treated with aPL and low doses of thrombin.Conclusion. The data strongly indicate that aPL in the presence of subactivating doses of thrombin induce the production of TXB 2 mainly through the activation of p38 MAPK and subsequent phosphorylation of cPLA 2 . The ERK-1/2 pathway does not seem to be involved in this process, at least in the early stages of aPL-mediated platelet activation.