Direct radioimmune detection in human plasma of the association between factor VIII procoagulant protein and von Willebrand factor, and the interaction of von Willebrand factor-bound procoagulant VIII with platelets

Abstract

The predominant procoagulant factor VIII (VIII:C) form in normal human plasma containing various combinations of anticoagulants and serine/cysteine protease inhibitors is a protein with mol wt 2.6 +/- 0.2 X 10(5). This protein can be detected by 125I-anti-VIII:C Fab binding and gel electrophoresis in the presence and absence of sodium dodecylsulfate (SDS) and is distinct from the subunit of factor VIII/von Willebrand factor (VIII:vWF) multimers. No larger VIII:C form is present in plasma from patients with severe congenital deficiencies of each of the coagulation factors, other than VIII:C. The mol wt approximately 2.6 X 10(5) VIII:C form is, therefore, likely to be the in vivo procoagulant form of VIII:C, rather than a partially proteolyzed, partially activated derivative of a larger precursor. About 60% of this procoagulant mol wt approximately 2.6 X 10(5) VIII:C form in plasma is present in noncovalent complexes with larger VIII:vWF multimers, which attach reversibly to platelet surfaces in the presence of ristocetin. This VIII:vWF-bound protein of mol wt approximately 2.6 X 10(5) may be the plasma procoagulant form of VIII:C which, after proteolytic activation, accelerates the IXa-mediated cleavage and activation of X postulated to occur on platelet surfaces.

Relatively increased von Willebrand factor activity after off-pump coronary artery bypass graft surgery

“…VWF antigen (VWF:Ag), VWF collagen binding activity (VWF:CB) and VWF-propeptide antigenlevelswere measured by enzyme-linked immunosorbent assay( ELISA) as described previously (13)(14)(15). VWFr istocetin cofactor activity (VWF:Rcof)w as carried outb ya ggregometryu sing fixed human platelets (16).The resultso fVWF:Rcof,VWF-CBa nd VWF-propeptide aree xpressed in ratios of VWF:Ag. ADAMTS-13 activity wasdeterminedusing afluorescence resonancee nergy transfer( FRET) assaya sd escribed previously (17).…”