Biological activity of von Willebrand factor during the manufacture of therapeutic factor VIII concentrates as determined by the collagen-binding assay.

In this study the use of collagen-binding assay, recently recommended by the European Pharmacopoeia for the characterization of Factor VIII/von Willebrand Factor (FVIII/vWF) concentrates was investigated. The collagen-binding assay was optimized to decrease reagent variability and, to allow for interlaboratory comparison, standardized against the third WHO International Plasma Standard for vWF and factor VIII, with the assumption that 1 unit of vWF antigen = 1 unit of collagen binding activity. A study of clinical samples of patients with von Willebrand's disease established that a ratio of vWF antigen; Collagen-binding activity <1.4 was associated with normal multimeric distribution and a ratio >3.7 was associated with loss of high molecular weight multimers and a decrease in biological activity. The collagen-binding assay of vWF was used to monitor changes in the biological activity of vWF during the manufacture of FVIII concentrates. Two commonly used industrial procedures using either glycine/NaCl precipitation or ion exchanges with TSK DEAE column chromatography were investigated. Samples taken at individual stages in the purification of FVIII concentrates, at the laboratory and industrial scale, were monitored using FVIII coagulant activity:vWF antigen ratio, Collagen-binding activity:vWF antigen ratio, and sodium dodecyl sulfate-agarose vWF multimeric analysis. All three parameters showed a retention of multimeric structure and biological activity during manufacture, to yield products which were clinically relevant in the treatment of von Willebrand's diseases.