Lipid Oxidation Enhances the Function of Activated Protein C

Abstract

Although lipid oxidation products are usually associated with tissue injury, it is now recognized that they can also contribute to cell activation and elicit antiinflammatory lipid mediators. In this study, we report that membrane phospholipid oxidation can modulate the hemostatic balance. Oxidation of natural phospholipids results in an increased ability of the membrane surface to support the function of the natural anticoagulant, activated protein C (APC), without significantly altering the ability to support thrombin generation. Lipid oxidation also potentiated the ability of protein S to enhance APC-mediated factor Va inactivation. Phosphatidylethanolamine, phosphatidylserine, and polyunsaturation of the fatty acids were all required for the oxidation-dependent enhancement of APC function. A subgroup of thrombotic patients with anti-phospholipid antibodies specifically blocked the oxidation-dependent enhancement of APC function. Since leukocytes are recruited and activated at the thrombus or sites of vessel injury, our findings suggest that after the initial thrombus formation, lipid oxidation can remodel the membrane surface resulting in increased anticoagulant function, thereby reducing the thrombogenicity of the thrombus or injured vessel surface. Anti-phospholipid antibodies that block this process would therefore be expected to contribute to thrombus growth and disease.

Inhibition of APC anticoagulant activity on oxidized phospholipid by anti–β2-glycoprotein I monoclonal antibodies

“…4 In the standard assay, normal pooled plasma (50 L) was mixed with X-CP, phospholipid (10 g/mL), in the presence or absence of APC (0.2 g/mL) in a total volume of 150 L. When present, IgG was at the final concentrations indicated. After 1 minute of incubation at 37°C, 50 L of 25 mM CaCl 2 was added to initiate clotting.…”

“…4 Briefly, to 1 mL of liposomes (200 g/mL) was added 1 L of 10 mM CuSO 4 in a glass tube. Suspensions were vortexed to introduce air, and the liposomes were incubated at 37°C.…”

“…We have reported that unlike the procoagulant complexes, optimal function of the APC anticoagulant complex requires the presence of phosphatidylethanolamine (PE), polyunsaturated fatty acids, 16,25 and phospholipid oxidation. 4 However, this membrane composition has little, if any, effect on the procoagulant reactions. 4 PE [26][27][28] and oxidation 29,30 increase the binding of many APAs and the ability of at least some APAs to inhibit the APC complex specifically.…”

“…4 However, this membrane composition has little, if any, effect on the procoagulant reactions. 4 PE [26][27][28] and oxidation 29,30 increase the binding of many APAs and the ability of at least some APAs to inhibit the APC complex specifically. 3,4,16,31 Indeed, immunoglobulin G (IgG) purified from several antiphospholipid syndrome patients inhibited only the lipid oxidation enhancement of APC activity, whereas IgG from nonthrombotic patients with APAs or LAs did not.…”

“…4 PE [26][27][28] and oxidation 29,30 increase the binding of many APAs and the ability of at least some APAs to inhibit the APC complex specifically. 3,4,16,31 Indeed, immunoglobulin G (IgG) purified from several antiphospholipid syndrome patients inhibited only the lipid oxidation enhancement of APC activity, whereas IgG from nonthrombotic patients with APAs or LAs did not. 31 The potential clinical relevance of enhanced inhibition of APC function is suggested by the presence of increased oxidized lipids in the antiphospholipid syndrome, 30 which we presume would normally enhance APC function.…”