Evaluation of von Willebrand factor concentrates by platelet adhesion to collagen using an in vitro flow assay.

BACKGROUND: Von Willebrand disease (VWD) results from quantitative or qualitative deficiency of von Willebrand factor (VWF) and is treated using VWF-containing concentrates. Several studies have compared the function of various VWF containing concentrates however this has not been performed using shear based assays. OBJECTIVES: To compare the platelet-capture potential of 10 commercially available, plasma-derived VWF concentrates under shear conditions. METHODS: VWF containing concentrates were assessed for VWF:Ag, VWF:CB, VWF:RCo, factor VIII:C ADAMTS13 content, VWF multimeric profile and glycan content using lectin binding assays. Free-thiol content of each concentrate was investigated using MPB binding assays. An in vitro flow assay was used to determine the ability of each concentrate to mediate platelet capture to collagen. RESULTS: VWF multimeric analysis revealed reduction of high molecular weight (HMW) forms in four of the concentrates (Alphante, Octanate and Haemoctin, and 8Y). The high MW multimer distribution of the remaining six concentrates (Optivate, Wilate, Fandhi, Wilfactin, Haemate P, and Voncento) was similar to the plasma control. Lectin analysis demonstrated that 8Y had increased amount of T-antigen. Although platelet capture after 5 minutes perfusion was similar for all concentrates; Alphante, Octanate, and Haemoctin, demonstrated the lowest levels of platelet capture after 60 seconds of perfusion. Free-thiol content and ADAMTS13 levels varied widely between the concentrates but was not correlated with function. CONCLUSION: Alphanate, Octanate, and Haemoctin, lacked HMW multimers and had the lowest initial platelet capture levels suggesting that the presence of VWF HMW multimers are required for initial platelet deposition.