Recombinant von Willebrand factor-insight into structure and function through infusion studies in animals with severe von Willebrand disease.

We used a canine and a murine model of von Willebrand disease (vWD) to study the in vivo effects of recombinant von Willebrand factor (vWF). Two preparations were used: (1) a fully processed mature vWF; this was achieved by coexpression of furin. (2) A preparation containing unprocessed pro-vWF, the propeptide still covalently linked to mature vWF. Both preparations induced an increase in canine and murine factor VIII:C (FVIII), which was sustained even when vWF antigen had been removed from the circulation. vWF multimers were analyzed in the plasma samples after infusion using ultra high-resolution 3% agarose gels to allow the separation of homoforms and heteroforms of the vWF polymers. Administration of pro-vWF to dogs with severe vWD resulted in the removal of the propeptide and maturation of vWF in the circulation, indicating that the propeptide cleavage from unprocessed vWF can occur extracellularly. This suggests that the vWF propeptide, besides being derived from the Weibel-Palade bodies of endothelial cells after stimulation, can also be cleaved by pro-vWF in plasma. Using a murine model of vWD, the involvement of the low-density lipoprotein receptor-related protein (LRP) in the clearance of FVIII was established. The low levels of FVIII observed in the absence of vWF are due to an enhanced clearance of FVIII by binding to LRP and removal from the circulation through endocytosis. Administration of the receptor-associated protein (RAP) as a recombinant fusion protein to vWF knockout mice significantly improved the in vivo recovery of recombinant FVIII and the survival time of otherwise rapidly cleared FVIII.