[Functionality of von Willebrand factor present in Fanhdi: adhesion to the vascular subendothelium in vitro]

To study the ability of VWF present in a plasma derived high purity factor VIII concentrate (> or = 100 UI FVIII/mg of protein, Fanhdi) to promote deposition and platelet adhesion on the injured vessel wall, as an indicator of the functionality of said VWF.

An in vitro perfusion system was employed. Adequate proportions of platelets and red cells were suspended in a human albumin solution. Aliquots of the studied product were added to obtain levels of 0.4 and 0.8 VWF:AG U/mL in the perfusates. As a comparative group, cryoprecipitate was assayed at similar VWF:Ag doses. Perfusions were performed on rabbit de-endothelialized abdominal aorta segments, placed in annular perfusion chambers, at 37 degrees C and at a flux of 140 mL/min (800 s-1) for 10 min. Results were evaluated as surface covered by platelets and as the percentage ratio between thrombus and surface covered by platelets. FVIII activity was determined by one stage clotting assay. VWF:RCo activity was determined by aggregometry and VWF:Ag by ELISA.

The VWF:Ag/FVIII:C ratio of Fanhdi is 1.57, while VWF:Roc/FVIII:C ratio is 1.15. The values of platelet deposition obtained, expressed as times of increase in the surface covered by platelets, considering the basal value (without VWF added) as 1, were: Cryoprecipitate 0.4 = 1.93; Cryoprecipitate 0.8 = 2.21; Fanhdi 0.4 = 2.99; Fanhdi 0.8 = 3.40. The ratios between thrombus and surface covered are 13.23%, 23.84%, 42.23%, 21.93% and 26.25% respectively.

These data show that VWF present in Fanhdi maintains a high degree of functionality, promoting platelet adhesion on subendothelium under flow conditions, after its incorporation into an albumin-platelet-red cell preparation and resulting in a significant increase in platelet adhesion when compared to the VWF-free basal control.