Characterization of monocyte tissue factor activity induced by IgG antiphospholipid antibodies and inhibition by dilazep

Abstract

Increasing evidence suggests that autoantibodies directly contribute to hypercoagulability in the antiphospholipid syndrome (APS). One proposed mechanism is the antibody-induced expression of tissue factor (TF) by blood monocytes. Dilazep, an antiplatelet agent, is an adenosine uptake inhibitor known to block induction of monocyte TF expression by bacterial lipopolysaccharide. In the current study we characterized the effects of immunoglobulin G (IgG) from patients with APS on monocyte TF activity and investigated whether dilazep is capable of blocking this effect. IgG from 13 of 16 patients with APS significantly increased monocyte TF activity, whereas normal IgG had no effect. Time-course experiments demonstrated that APS IgG-induced monocyte TF mRNA levels were maximal at 2 hours and TF activity on the cell surface was maximal at 6 hours. Dilazep inhibited antibody-induced monocyte TF activity in a dose-dependent fashion but had no effect on TF mRNA expression. The effect of dilazep was blocked by theophylline, a nonspecific adenosine receptor antagonist. In conclusion, IgG from certain patients with APS induce monocyte TF activity. Dilazep inhibits the increased expression of monocyte TF activity at a posttranscriptional level, probably by way of its effect as an adenosine uptake inhibitor. Pharmacologic agents that block monocyte TF activity may be a novel therapeutic approach in APS. IntroductionIt is widely hypothesized that autoantibodies directly contribute to hypercoagulability in patients with the antiphospholipid syndrome (APS), and numerous pathophysiologic mechanisms have been proposed. Once such mechanism is the antibody-induced expression of tissue factor (TF; CD142) on monocytes or vascular endothelial cells, or both. 1 TF is an integral membrane protein constitutively expressed in many cell types outside of the vasculature, but it is not normally expressed on cells that are in contact with flowing blood. It is a specific and high-affinity receptor for factor VII/VIIa and functions as a cofactor for factor VIIa enzymatic activity. Exposure of active TF to blood triggers physiologic blood coagulation and thrombosis in a wide variety of thrombotic diseases. 2 Blood monocytes do not constitutively express functional TF; however, they are capable of TF synthesis and expression when stimulated with lipopolysaccharide (LPS) or certain inflammatory cytokines. 3 Expression of TF on monocytes has been implicated as a mechanism of thrombosis in several conditions, including sepsis, 4 atherosclerosis, 5 the use of oral contraceptives, 6 cancer, 7 and hyperhomocysteinemia. 8 There is growing evidence that certain types of antiphospholipid antibodies, particularly those directed against ␤ 2 -glycoprotein I (␤2GPI), stimulate monocyte tissue factor expression in patients with APS. 9,10 Current treatment for the prevention of recurrent thrombosis in patients with APS is a high level of anticoagulation with warfarin. The identification of specific mechanisms of hypercoagulability in APS may allow for more spec...

Proteomic analysis in monocytes of antiphospholipid syndrome patients: Deregulation of proteins related to the development of thrombosis

“…Among these, activation of monocytic cells, with the attendant loss of anticoagulant and the gain of procoagulant functions, is likely to be important. We and others have previously demonstrated that monocytes are involved in the thrombotic state characteristic of most APS patients (4,6,9). However, no study has evaluated the changes in the proteomic patterns that could underlie the pathogenic mechanisms associated with thrombosis in this disease.…”

“…Our results showed that IgG fractions purified from the plasma of APS patients with thrombosis changed the protein expression pattern of normal monocytes in the same way that was observed in vivo for monocytes from APS patients with thrombosis ( Figures 3 and 4). These IgG fractions from APS were previously shown to activate human monocytes (4,6,17).…”

“…Many of these autoantibodies are directed against phospholipid-binding plasma proteins, such as ␤ 2 -glycoprotein I (␤ 2 GPI) and prothrombin, or phospholipid-protein complexes, located on the surface of vascular endothelial cells, platelets, or monocytes (2). Several nonexclusive mechanisms could explain the involvement of aPL in the pathogenesis of thrombosis in APS, including the induction of tissue factor (TF) expression by endothelial cells and monocytes (3,4). Intracellular mechanisms underlying aPL-induced TF gene and protein expression in endothelial cells and monocytes have also been delineated at a molecular level (5,6).…”

Involvement of annexin A2 in anti-β2GPI/β2GPI-induced tissue factor expression on monocytes

“…Their findings establish an important point that a cell surface receptor is critical in mediating the effects of autoantiphospholipid antibodies (APL) on endothelial cells. Our previous study showed that anti-β 2 GPI could induce monocyte TF activity in APS [4]. Finding the mediator for anti-β 2 GPI/β 2 GPI in monocytes would be a key step in further understanding APL associated pathology in APS.…”

The role of TLR4 in pathophysiology of antiphospholipid syndrome‐associated thrombosis and pregnancy morbidity

“…One group demonstrated that annexin A2 (ANXA2), as a high-affinity receptor for b2GPI on endothelial cells, mediates anti-b2GPI/b2GPI complex activating endothelium and increasing the levels of TF, VCAM1 and other inflammatory molecules in circulation (Ma et al, 2000;Zhang & McCrae, 2005). Similarly, our previous studies have suggested that ANXA2, rather than Fccreceptors, is the main specific receptor for b2GPI mediating anti-b2GPI antibody-induced TF activity in monocytes (Zhou et al, 2004. ANXA2, a member of the large family of annexin proteins, however, is not a transmembrane protein and lacks an intra-cellular signal transduction pathway.…”