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 th e VWF structure is reasonably maintained are recommended as substitutive th erapy in VWD. Our aim was to assess platelet deposition and binding to sube ndothelial structures of VWF present in FVIII concentrates. Design and Methods. Cryoprecipitate (CRY), intermediate-purity (IPC), or hi gh-purity (HPC) FVIII concentrates were added in vitro to citrated blood sa mples from 11 patients affected by different subtypes of VWD, with the aim of normalizing VWF levels. Measurements of VWF:Ag, ristocetin cofactor (RiC of) activities, FVIII coagulant activity (FVIII:C), and platelet interactio n 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 v essels was assessed by immunofluorescence microscopy. Paired t-test statist ics were performed. Results. Addition of FVIII-VWF preparations raised VWF:Ag from baseline (BS L) 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, respectivel y. A positive labeling for VWF was observed by immunofluorescence in vessel s 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 sup port the hypothesis ab ove the mechanisms involved in the beneficial effects of commercial concent rates in von Willebrand disease: the VWF in these concentrates has function al capacity to bind to subendothelium and to support platelet adhesion. (C) 1998, Ferrata Storti Foundation.