Association of Vitamin K–Dependent Coagulation Proteins and C4b Binding Protein With Triglyceride-Rich Lipoproteins of Human Plasma

Abstract

The triglyceride (TG) concentration in plasma is an independent risk factor for coronary heart disease. There is evidence that TG-rich lipoprotein (TGRLP), ie, chylomicrons (CMs), chylomicron remnants (CMRs), and VLDLs associate with factor VII and prothrombin and that the association enhances a platelet factor Xa-mediated prothrombin activation when the CM-prothrombin complex is exposed to platelets. In this study, we examined the association of the vitamin K-dependent coagulation factors VII, IX, X, and prothrombin, as well as the anticoagulation protein C and its cofactor protein S, in plasma lipoproteins obtained from human fasting and postprandial plasma. We also analyzed some other proteins that are related to the coagulation system but not to vitamin K-dependent proteins, including factor V, serum amyloid P component (SAP), C4b binding protein (C4BP), and thrombomodulin (TM), and as a control, Ig G. Human TGRLP (d < 1.006 kg/L), LDL (d = 1.006 to 1.063 kg/L), and HDL (d = 1.063 to 1.210 kg/L) were separated from normal subjects both in fasting and 2 to 3 hours after the ingestion of a meal containing 100 g fat. The different coagulation proteins, SAP, C4BP, TM, and Ig G were determined by SDS-polyacrylamide gel electrophoresis combined with Western blotting, using specific polyclonal or monoclonal antibodies, and were visualized by peroxidase staining. All the vitamin K-dependent proteins associate with TGRLP in both fasting and postprandial plasma, but not with LDL or HDL. Factor V, SAP, TM, and Ig G were not found in any lipoprotein classes. C4BP, which is a regulatory protein of the classic pathway of the complement system and which binds protein S in vivo to regulate blood coagulation, was present in TGRLP, especially postprandial, but not in LDL or HDL. The amounts of prothrombin, protein S, and C4BP in postprandial TGRLP were larger than those in fasting TGRLP. Vitamin K-dependent procoagulation and anticoagulation proteins, as well as C4BP, could be associated with TGRLP in vivo. If the association enhances prothrombin activation, this effect may thus be counteracted by simultaneous binding of protein S.