CLEARANCE OF NORMAL AND TYPE 2A VON-WILLEBRAND-FACTOR IN THE RAT

A model for the in vivo clearance of normal and mutant forms of human von Willebrand factor (VWF) has been established using catheterized ra ts, vWF clearance rates in rat plasma were determined by quantitation of reduced vWF subunits on sodium dodecyl sulfate-polyacrylamide gel e lectrophoresis (SDS-PAGE), and multimeric vWF was analyzed using nonde naturing SDS-agarose gels, Normal vWF derived from human umbilical vei n endothelial cells displayed a biphasic pattern of clearance, with ha lf times of 35 minutes (T-1/2 a; SD 15. min.) and 245 minutes (T-1/2 b ; SD 76. min.); metabolic clearance rate = 0.65%/minute. High molecula r weight multimers of vWF were cleared more rapidly than dimeric vWF, vWF containing the S1613P mutation found in some type 2A von Willebran d disease (vWD) patients was observed to undergo proteolysis in vivo r esulting in a reduction of high molecular weight vWF and concomitant a ppearance of rapidly-migrating satellite species, although the overall clearance rate of vWF antigen was similar to wild type vWF, These res ults provide direct in vivo evidence that the S1613P mutation causes t he characteristic type 2A vWD phenotype, Full-length recombinant vWF p roduced from transfected Chinese hamster ovary cells was cleared at a similar rate to endothelial cell-derived vWF, and recombinant vWF devo id of O-linked carbohydrates was cleared significantly faster, vWF dev oid of sulfate was cleared at a similar rate as wild type vWF, indicat ing the sulfate moiety of vWF does not regulate in vivo clearance, Thi s animal model should prove useful in subsequent in vivo analysis of a dditional forms of vWD and in the development of protease inhibitor th erapy for 2A vWD. (C) 1996 by The American Society of Hematology.