von Willebrand factor contained in factor VIII concentrates of different purities supports platelet adhesion in blood samples from a heterogeneous group of patients with von Willebrand disease

BACKGROUND AND OBJECTIVE: Plasma derived FVIII-VWF concentrates in which the VWF structure is reasonably maintained are recommended as substitutive therapy in VWD. Our aim was to assess platelet deposition and binding to subendothelial structures of VWF present in FVIII concentrates. DESIGN AND METHODS: Cryoprecipitate (CRY), intermediate-purity (IPC), or high-purity (HPC) FVIII concentrates were added in vitro to citrated blood samples from 11 patients affected by different subtypes of VWD, with the aim of normalizing VWF levels. Measurements of VWF:Ag, ristocetin cofactor (RiCof) activities, FVIII coagulant activity (FVIII:C), and platelet interaction with subendothelium under flow conditions (Baumgartner's perfusion method, computer-assisted morphometry, shear rate 1000 s-1, 10 min, 37 degrees C) were determined. Binding of VWF to the luminal surface of the perfused vessels was assessed by immunofluorescence microscopy. Paired t-test statistics were performed. RESULTS: Addition of FVIII-VWF preparations raised VWF:Ag from baseline (BSL) values of 0.3 (SD 0.2) to averages of 1.4 (SD 0.5, p < 0.001), 1.2 (SD 0.6, p < 0.001), and 0.4 (SD 0.3) IU mL-1 after CRY, IPC, and HPC, respectively. A positive labeling for VWF was observed by immunofluorescence in vessels perfused with blood containing any of the concentrates. Platelet adhesion of 13.2 (SD 7.6), 22.4 (SD 10.8), 24.8 (SD 7.8, p < 0.03), or 22.5 (SD 4.8)% was measured in BSL, CRY, IPC, or HPC tests, respectively. INTERPRETATION AND CONCLUSIONS: Our observations support the hypothesis above the mechanisms involved in the beneficial effects of commercial concentrates in von Willebrand disease: the VWF in these concentrates has functional capacity to bind to subendothelium and to support platelet adhesion.