A comparative in vitro evaluation of six von Willebrand factor concentrates

The efficacy of von Willebrand factor (VWF) concentrates for treatment of von Willebrand disease (VWD) is dependent on their content of VWF and factor VIII (FVIII).

STUDY OBJECTIVES

To measure the content and quality of VWF and FVIII in six VWF concentrates: Haemate-P (Aventis Behring), Immunate (Baxter Bioscience), Koate (Bayer Corp.), 8Y (BPL), Innobrand (LFB) and Facteur Willebrand (LFB).

METHODS

The VWF antigen content (VWF:Ag), ristocetin cofactor activity (VWF:RCo), collagen-binding activity (VWF:CB), VWF multimers with electrophoresis and densitometry, FVIII activity and total protein content.

RESULTS

Specific activity (VWF:RCo/total protein) varied considerably (4.7-129.5 IU mg(-1)). Activity measures, VWF:RCo and VWF:CB, correlated well, but we found no correlation between any of these and VWF:Ag. The content of high-molecular weight multimer (HMWM) was normal or close to normal in Haemate-P, Innobrand and Facteur Willebrand, moderately reduced in Koate and 8Y, and significantly reduced in Immunate. The HMWM content correlated significantly with the VWF:RCo/VWF:Ag ratio. Only Haemate-P, Innobrand and Facteur Willebrand had VWF:RCo/VWF:Ag ratios >0.7. We found large differences in the content of FVIII and in the FVIII/VWF:RCo ratio. Facteur Willebrand had the lowest (0.02) and Immunate the highest (6.00) ratio.

CONCLUSION

Treating physicians must be aware of the large differences between different VWF concentrates and the potential clinical implications. Concentrates lacking HMWM are probably less efficient for mucosal bleedings. FVIII is most important for surgical bleedings, but concentrates with high FVIII/VWF-ratio may induce very high FVIII levels with increased risk of thrombosis. A low FVIII content may be preferable except in case of acute surgery.

Response to infusions of polyelectrolyte fractionated human factor VIII concentrate in human haemophilia A and von Willebrand's disease

Factor VIII was purified from cryoprecipitate by ion exchange chromatography on solid phase polyelectrolyte E-5 (PE-E5). The product was highly purified (3.5 u VIII:C/mg protein) compared to conventional concentrate (0.3 u VIII:C/mg protein) with low fibrinogen, low isoagglutinin titre, and a ratio of factor VIII coagulant activity (VIII:C) to factor VII related antigen (VIIIR:Ag) of 16:1. Trial infusions of this material (PE VIII) were given to three patients with severe haemophilia A and one patient with homozygous von Willebrand's disease. These patients also each received separate infusions of intermediate purity concentrate (IPC) for comparison. There were no adverse effects. The mean half life of VIII:C after PE VIII infusion in the haemophiliacs was 10.9 h and after IPC was 12.1 h, a statistically insignificant difference. The survival of factor VIII coagulant antigen (VIII:CAg) was similar to that of VIII:C. In contrast, the half life of VIII:C and of VIII:CAg was very short after infusion of PE VIII in the patient wih von Willebrand's disease (2.4 h). IPC when infused in this patient produced a typical secondary rise of VIII:C. Two bleeding episodes in severe haemophiliacs were satisfactorily treated with PE VIII. PE-E5 deserves further study as a means of preparing clinical concentrates of factor VIII.